JP7557454B2 - Sputtering target material - Google Patents

Description

This disclosure relates to a piezoelectric laminate, a method for manufacturing a piezoelectric laminate, a sputtering target material, and a method for manufacturing a sputtering target material.

Piezoelectric materials are widely used in functional electronic components such as sensors and actuators. Piezoelectric materials containing potassium, sodium, niobium, and oxygen have been proposed, and a laminate (hereinafter, piezoelectric laminate) has been proposed that has a piezoelectric film (KNN film) formed by sputtering using such a piezoelectric material (see, for example, Patent Document 1).

JP 2011-146623 A

Patent Document 1 discloses that by controlling the strength of the magnetic field on the surface exposed to the plasma of the target material used when depositing a KNN film on a substrate using a sputtering method and the crystal orientation of the film that serves as the base of the KNN film, the half-width of the X-ray rocking curve of the (001) plane when performing X-ray diffraction measurement on the KNN film is set within the range of 0.5° to 2.5°. Patent Document 1 also discloses that the KNN film is deposited by sputtering while the substrate is rotated and revolved in order to improve the in-plane uniformity of the film quality of the KNN film.

However, with the technology described in Patent Document 1, it has been found that when a KNN film is formed on a large-diameter substrate having a diameter of 3 inches or more by sputtering using a large-diameter target material having a diameter of 3 inches or more, as is used in mass production, regions (defective regions) in which the half-width falls outside the above range appear locally within the main surface of the KNN film. In other words, it has been found that with the technology described in Patent Document 1, regions in which the film quality (film characteristics) is locally deteriorated appear within the main surface of the KNN film. This is a new problem that has become clear for the first time through the inventors' diligent research.

The present disclosure aims to provide a piezoelectric laminate having a large-diameter piezoelectric film with uniform film quality and no localized defective areas on the entire main surface except for the peripheral edge, and to provide related technologies.

According to one aspect of the present disclosure,
A substrate having a major surface with a diameter of 3 inches or more;
a piezoelectric film formed on the substrate, the piezoelectric film containing potassium, sodium, niobium, and oxygen and made of an alkali niobium oxide having a perovskite structure;
The present invention provides a piezoelectric laminate and related technology, in which the half-width of the X-ray rocking curve for the (001) plane, when subjected to X-ray diffraction measurement of the piezoelectric film, is within a range of 0.5° to 2.5° over the entire inner area excluding the peripheral portion of the main surface of the piezoelectric film.

According to the present disclosure, it is possible to obtain a piezoelectric laminate having a large-diameter piezoelectric film with uniform film quality, without any localized defective areas appearing on the entire main surface except for the peripheral portion.

FIG. 2 is a diagram showing an example of a cross-sectional structure of a piezoelectric laminate according to an embodiment of the present disclosure. 1A and 1B are diagrams illustrating modified examples of the cross-sectional structure of the piezoelectric laminate according to an embodiment of the present disclosure. FIG. 2 is a plan view of a principal surface of a piezoelectric film showing measurement points of X-ray diffraction. 1 is a diagram illustrating an example of a schematic configuration of a piezoelectric device module according to an embodiment of the present disclosure. FIG. 1 is a diagram showing an example of a schematic configuration of a sputtering target material according to one embodiment of the present disclosure. FIG. 2 is a schematic diagram of a molding device used when producing a sputtering target material, and a graph showing the temperature distribution in a processing chamber. 11A and 11B are diagrams illustrating a modified example of the cross-sectional structure of the piezoelectric device module according to an embodiment of the present disclosure.

<Knowledge gained by the inventors>
It has been found that the quality of the KNN film formed on a substrate by sputtering is strongly influenced by the strength of the electromagnetic field on the surface of the target material used in sputtering that is exposed to plasma (hereinafter also referred to as the "sputtering surface") and the crystal orientation (crystal orientation) of the film (underlying film) that serves as the underlayer of the KNN film. In order to improve the in-plane uniformity of the quality of the KNN film, the KNN film is sputtered while the substrate is rotated and revolved. However, even if the strength of the electromagnetic field on the sputtering surface and the crystal orientation of the underlayer are adjusted (controlled) or the sputtering is performed while the substrate is rotated and revolved, when the KNN film is formed on a large-diameter substrate with a diameter of 3 inches or more using a target material with a sputtering surface with a diameter of 3 inches or more, as used in mass production, the inventors have discovered a new problem that a defective region, whose film quality is locally inferior to the surroundings, inevitably appears on the main surface of the KNN film. The defective region referred to here means, for example, a localized region in which the full width at half maximum (hereinafter, FWHM(001)) value of the X-ray rocking curve of the (001) plane when X-ray diffraction measurement is performed on the KNN film does not fall within the range of 0.5° to 2.5°.

The inventors have conducted extensive research into the above problem. As a result, they have discovered that in a target material having a large-diameter sputtering surface, there are areas in the sputtering surface where the crystal orientation is not random, and that abnormal discharge occurs in such areas during sputtering deposition, which is the cause of the above-mentioned defective areas appearing in the main surface of the KNN film deposited on the substrate. The "area where the crystal orientation is not random" can also be referred to as an area where the crystal orientation is reduced, and specifically, when X-ray diffraction measurements are performed on the sputtering surface, it refers to an area where the ratio R of the X-ray diffraction peak intensity from the (110) plane to the X-ray diffraction peak intensity from the (001) plane is not within the range of 0.3 to 5.

The inventors have conducted intensive research into the mechanism by which "regions in which the crystal orientation is not random" appear locally on the sputtering surface of a target material. The KNN target material can be produced by compressing a mixture of a powder of a potassium (K) compound, a powder of a sodium (Na) compound, and a powder of a niobium (Nb) compound in a predetermined ratio to produce a molded body, and then firing the resulting molded body. However, when firing the molded body, even if an attempt is made to adjust the temperature so that the temperature within the surface of the molded body (the surface that will become the sputtering surface) is uniform, it is difficult to make the temperature within the surface of the molded body completely uniform. In particular, when producing a target material having a sputtering surface with a diameter of 3 inches or more, it is practically very difficult to make the temperature within the surface of the molded body completely uniform. If there is a temperature gradient (temperature unevenness) exceeding a certain critical value on the surface of the molded body during firing, that is, if the temperature on the surface of the molded body is not completely uniform, in areas where the temperature gradient is large, crystals (crystal grains) tend to grow along the temperature gradient in the creeping direction on the surface of the molded body, compared to areas where the temperature gradient is small. As a result, when the surface (sputter surface) of the molded body after firing is viewed from above in the vertical direction, there will be areas where crystals (e.g., crystal grains with a diameter of more than 30 μm) that have grown large in the creeping direction are locally present, and in these areas, the orientation of the crystals will not be random (they will be greatly influenced by the exposed surface of the large crystals) compared to other areas (areas where many crystals with a diameter of less than 30 μm are gathered). In this way, the non-orientation of the crystals on the sputter surface of the target material will be locally reduced.

The inventors conducted extensive research into methods for avoiding the phenomenon of localized deterioration of the non-orientation of crystals on the sputtering surface of a target material. As a result, they discovered that by intentionally creating a temperature gradient in the thickness direction of a molded body when firing the molded body, it is possible to suppress crystal growth in the creeping direction on the surface of the molded body even when there are temperature unevenness within the surface of the molded body, thereby avoiding localized deterioration of the non-orientation of crystals on the sputtering surface.

This disclosure has been made based on the above-mentioned findings and problems that the inventors have encountered.

<One aspect of the present disclosure>
Hereinafter, one embodiment of the present disclosure will be described with reference to the drawings.

1, a laminate 10 having a piezoelectric film according to this embodiment (hereinafter also referred to as piezoelectric laminate 10) includes a substrate 1, a lower electrode film 2 provided on the substrate 1, a piezoelectric film (piezoelectric thin film) 3 provided on the lower electrode film 2, and an upper electrode film 4 provided on the piezoelectric film 3. Note that in this embodiment, a case will be described taking as an example a case where one laminate structure (a structure formed by laminating at least the lower electrode film 2, the piezoelectric film 3, and the upper electrode film 4) is provided on one substrate 1.

The substrate 1 has a main surface with a diameter of 3 inches or more. The substrate 1 has a circular outer shape in a plan view. The outer shape of the substrate 1 (the planar shape of the main surface of the substrate 1) can be various shapes such as a circle, an ellipse, a rectangle, or a polygon. In this case, the substrate 1 preferably has a main surface with an inscribed circle having a diameter of 3 inches or more. As the substrate 1, a single crystal silicon (Si) substrate 1a on which a surface oxide film (SiO ₂ film) 1b such as a thermal oxide film or a CVD (Chemical Vapor Deposition) oxide film is formed, that is, a Si substrate having a surface oxide film, can be suitably used. As the substrate 1, as shown in FIG. 2, a Si substrate 1a having an insulating film 1d formed on its surface from an insulating material other than SiO ₂ can also be used. As the substrate 1, a Si substrate 1a on which a Si(100) surface or a Si(111) surface is exposed on the surface, that is, a Si substrate having no surface oxide film 1b or insulating film 1d can also be used. Also, a metal substrate made of a metal material such as an SOI (Silicon On Insulator) substrate, a quartz glass (SiO ₂ ) substrate, a gallium arsenide (GaAs) substrate, a sapphire (Al ₂ O ₃ ) substrate, stainless steel (SUS), etc. may be used as the substrate 1. The thickness of the single crystal Si substrate 1a may be, for example, 300 μm or more and 1000 μm or less, and the thickness of the surface oxide film 1b may be, for example, 1 nm or more and 4000 nm or less.

The lower electrode film 2 can be formed using, for example, platinum (Pt). The lower electrode film 2 is a polycrystalline film. Hereinafter, the polycrystalline film formed using Pt is also referred to as a Pt film. It is preferable that the (111) plane of the Pt film is parallel to the main surface of the substrate 1 (including the case where the (111) plane is inclined at an angle of ±5° or less with respect to the main surface of the substrate 1), that is, the Pt film is oriented in the (111) plane direction. The Pt film being oriented in the (111) plane direction means that no peaks other than the peaks due to the (111) plane are observed in the X-ray diffraction pattern obtained by X-ray diffraction (XRD) measurement. In this way, it is preferable that the main surface of the lower electrode film 2 (the surface that serves as the base of the piezoelectric film 3) is composed of a Pt (111) plane. The lower electrode film 2 can be formed using a sputtering method, a vapor deposition method, or the like. The lower electrode film 2 can be formed using various metals such as gold (Au), ruthenium (Ru), or iridium (Ir), alloys mainly composed of these metals, or metal oxides such as strontium ruthenate (SrRuO ₃ , abbreviated as SRO) or lanthanum nickelate (LaNiO ₃ , abbreviated as LNO), in addition to Pt. The lower electrode film 2 can be a single layer film formed using the above-mentioned various metals or metal oxides. The lower electrode film 2 may be a laminate of a Pt film and a film made of SRO provided on the Pt film, or a laminate of a Pt film and a film made of LNO provided on the Pt film. In addition, between the substrate 1 and the lower electrode film 2, an adhesion layer 6 mainly composed of, for example, titanium (Ti), tantalum (Ta), titanium oxide (TiO ₂ ), nickel (Ni), ruthenium oxide (RuO ₂ ), iridium oxide (IrO ₂ ), zinc oxide (ZnO), etc. may be provided in order to enhance the adhesion between them. The adhesion layer 6 can be formed by a method such as a sputtering method or a vapor deposition method. The thickness of the lower electrode film 2 (when the lower electrode film 2 is a laminate, the total thickness of each layer) can be, for example, 100 nm or more and 400 nm or less, and the thickness of the adhesion layer 6 can be, for example, 1 nm or more and 200 nm or less.

The piezoelectric film 3 is, for example, a film made of an alkali niobium oxide containing potassium (K), sodium (Na), niobium (Nb), and oxygen (O). The piezoelectric film 3 can be formed using an alkali niobium oxide represented by the composition formula (K _1-x Na _x ) NbO ₃ , that is, potassium sodium niobate (KNN). The coefficient x [= Na/(K+Na)] in the above composition formula can be set within the range of 0<x<1, preferably 0.4≦x≦0.7. The piezoelectric film 3 is a KNN polycrystalline film (hereinafter also referred to as the KNN film 3). The crystal structure of KNN is a perovskite structure. That is, the KNN film 3 has a perovskite structure. In addition, it is preferable that more than half of the crystals in the crystal group constituting the KNN film 3 have a columnar structure. In this specification, the crystal system of KNN is regarded as a tetragonal system. The KNN film 3 can be formed using a method such as a sputtering method. The thickness of the KNN film 3 can be set to, for example, 0.5 μm or more and 5 μm or less.

The KNN film 3 is made of lithium (Li), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), bismuth (Bi), antimony (Sb), vanadium (V), indium (In), Ta, molybdenum (Mo), tungsten (W), chromium (Cr), Ti, zirconium (Zr), hafnium (Hf), scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium (Nd), samarium ( The KNN film 3 may contain one or more elements (dopants) selected from the group consisting of Cr, Cu, Eu, Gd, Tb, Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium (Tm), Ytterbium (Yb), Lutetium (Lu), Copper (Cu), Zinc (Zn), Silver (Ag), Manganese (Mn), Iron (Fe), Cobalt (Co), Ni, Aluminum (Al), Si, Germanium (Ge), Tin (Sn), and Gallium (Ga). The concentration of these elements in the KNN film 3 may be, for example, 5 at% or less (if a plurality of the above elements are contained, the total concentration is 5 at% or less).

The crystals constituting the KNN film 3 are preferably preferentially oriented in the (001) plane direction with respect to the main surface of the substrate 1 (Si substrate 1a when the substrate 1 is, for example, a Si substrate 1a having a surface oxide film 1b or an insulating film 1d, etc.). In other words, the main surface of the KNN film 3 (the surface that serves as the base for the upper electrode film 4) is preferably composed mainly of the KNN (001) plane. For example, by directly depositing the KNN film 3 on a Pt film (lower electrode film 2) whose main surface is mainly composed of a Pt (111) plane, a KNN film 3 whose main surface is mainly composed of a KNN (001) plane can be easily obtained.

In this specification, the crystals constituting the KNN film 3 being oriented in the (001) plane direction means that the (001) plane of the crystals constituting the KNN film 3 is parallel or approximately parallel to the main surface of the substrate 1. In addition, the crystals constituting the KNN film 3 being preferentially oriented in the (001) plane direction means that there are many crystals whose (001) plane is parallel or approximately parallel to the main surface of the substrate 1. For example, it is preferable that 80% or more of the crystals constituting the KNN film 3 are oriented in the (001) plane direction with respect to the main surface of the substrate 1. In other words, the orientation rate of the crystals constituting the KNN film 3 in the (001) plane direction is, for example, preferably 80% or more, and more preferably 90% or more. In addition, the "orientation rate" in this specification is a value calculated by the following (Equation 1) based on the peak intensity of the X-ray diffraction pattern (2θ/θ) obtained by performing XRD measurement on the KNN film 3.

(Equation 1)
Orientation rate (%)={(001) peak intensity/((001) peak intensity+(110) peak intensity)}×100

In addition, the "(001) peak intensity" in the above (Equation 1) refers to the intensity of a diffraction peak due to crystals oriented in the (001) plane direction (i.e., crystals whose (001) plane is parallel to the main surface of the substrate 1) among the crystals constituting the KNN film 3 in the X-ray diffraction pattern obtained by performing XRD measurement on the KNN film 3, and is the intensity of a peak that appears within a range of 2θ of 20° to 23°. In addition, when multiple peaks appear within a range of 2θ of 20° to 23°, it is the intensity of the highest peak. In addition, the "(110) peak intensity" in the above (Equation 1) refers to the intensity of a diffraction peak due to crystals oriented in the (110) plane direction (i.e., crystals whose (110) plane is parallel to the main surface of the substrate 1) among the crystals constituting the KNN film 3 in the X-ray diffraction pattern obtained by performing XRD measurement on the KNN film 3, and is the intensity of a peak that appears within a range of 2θ of 30° to 33°. If multiple peaks appear within the 2θ range of 30° to 33°, the intensity is that of the highest peak.

The KNN film 3 has a major surface (upper surface) with a diameter of 3 inches or more, i.e., a major surface with a large diameter. In the KNN film 3, no localized defective areas appear in the entire inner area except for the peripheral area of the major surface of the KNN film 3, and the film quality is uniform. Specifically, when XRD measurement is performed on the KNN film 3, the value of the half-width (FWHM(001)) of the X-ray rocking curve of the (001) plane when the XRD measurement is performed on the KNN film 3 is within the range of 0.5° to 2.5° inclusive in the entire inner area except for the peripheral area of the major surface of the KNN film 3. Here, "the FWHM(001) value is within the range of 0.5° to 2.5° in the entire inner area excluding the peripheral area on the main surface of the KNN film 3" means that, as shown in FIG. 3, the FWHM(001) value is within the range of 0.5° to 2.5° in all points when XRD measurements are performed at 1 cm intervals in a grid pattern on the main surface of the KNN film 3 in the area 3b inside the outer peripheral area 3a 5 mm from the edge (area excluding the outer peripheral area 3a 5 mm from the edge). In FIG. 3, the measurement points of FWHM(001) are indicated by ● marks. In the following, "the entire inner area excluding the peripheral area on the main surface of the KNN film 3" is also referred to as "the entire main surface of the KNN film 3".

By having the FWHM(001) value fall within the range of 0.5° to 2.5° across the entire main surface of the KNN film 3, the film characteristics of the KNN film 3 can be made uniform (in-plane uniform) across the entire main surface of the KNN film 3. This makes it possible to avoid variations in characteristics between multiple piezoelectric elements 20 (piezoelectric device modules 30) (described below) obtained from a single piezoelectric laminate 10. As a result, the yield and reliability of the piezoelectric elements 20 (piezoelectric device modules 30) can be improved.

The upper electrode film 4 can be formed using various metals such as Pt, Au, Al, Cu, or alloys thereof. The upper electrode film 4 can be formed using a method such as a sputtering method, a vapor deposition method, a plating method, or a metal paste method. The upper electrode film 4 does not have a large effect on the crystal structure of the KNN film 3, unlike the lower electrode film 2. Therefore, the material, crystal structure, and film formation method of the upper electrode film 4 are not particularly limited. In addition, an adhesion layer mainly composed of, for example, Ti, Ta, TiO ₂ , Ni, RuO ₂ , IrO _2, or the like may be provided between the KNN film 3 and the upper electrode film 4 in order to increase the adhesion between them. The thickness of the upper electrode film 4 can be, for example, 100 nm to 5000 nm, and when an adhesion layer is provided, the thickness of the adhesion layer can be, for example, 1 nm to 200 nm.

(2) Configuration of Piezoelectric Device Module FIG. 4 shows a schematic configuration diagram of a device module 30 having a KNN film 3 (hereinafter also referred to as a piezoelectric device module 30). By forming the above-mentioned piezoelectric laminate 10 into a predetermined shape, an element (device) 20 (element 20 having a KNN film 3, hereinafter also referred to as a piezoelectric element 20) as shown in FIG. 4 is obtained. The piezoelectric device module 30 includes at least a piezoelectric element 20 and a voltage application means 11a or a voltage detection means 11b connected to the piezoelectric element 20. The voltage application means 11a is a means for applying a voltage between the lower electrode film 2 and the upper electrode film 4, and the voltage detection means 11b is a means for detecting a voltage generated between the lower electrode film 2 and the upper electrode film 4. As the voltage application means 11a and the voltage detection means 11b, various known means can be used.

By connecting the voltage application means 11a between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device module 30 can function as an actuator. By applying a voltage between the lower electrode film 2 and the upper electrode film 4 by the voltage application means 11a, the KNN film 3 can be deformed. This deformation action can operate various members connected to the piezoelectric device module 30. In this case, examples of applications of the piezoelectric device module 30 include heads for inkjet printers, MEMS mirrors for scanners, and vibrators for ultrasonic generators.

By connecting the voltage detection means 11b between the lower electrode film 2 and the upper electrode film 4 of the piezoelectric element 20, the piezoelectric device module 30 can function as a sensor. When the KNN film 3 deforms in response to a change in some physical quantity, a voltage is generated between the lower electrode film 2 and the upper electrode film 4 due to the deformation. By detecting this voltage with the voltage detection means 11b, the magnitude of the physical quantity applied to the KNN film 3 can be measured. In this case, applications of the piezoelectric device module 30 include, for example, an angular velocity sensor, an ultrasonic sensor, a pressure sensor, an acceleration sensor, etc.

The piezoelectric device module 30 (piezoelectric element 20) is made from a piezoelectric stack 10 having a KNN film 3 whose FWHM(001) value is within the range of 0.5° to 2.5° across the entire main surface. This makes it possible to avoid variations in characteristics between multiple piezoelectric elements 20 (piezoelectric device modules 30) obtained from one piezoelectric stack 10. In other words, multiple piezoelectric elements 20 (piezoelectric device modules 30) with uniform characteristics can be obtained from one piezoelectric stack 10.

For example, in a plurality of piezoelectric device modules 30 obtained by processing one piezoelectric laminate 10 in which a Ti layer (thickness: 2 nm) as an adhesion layer 6, a Pt film (thickness: 200 nm) as a lower electrode film 2, a KNN film 3 (thickness: 2 μm), a RuO ₂ layer (thickness: 30 nm) as an adhesion layer for enhancing adhesion between the KNN film 3 and the upper electrode film 4, and a Pt film (thickness: 100 nm) as an upper electrode film 4 are sequentially provided on a large-diameter substrate 1, when an electric field of −100 kV/cm is applied between the lower electrode film 2 and the upper electrode film 4, the piezoelectric constant −e ₃₁ of all the piezoelectric device modules 30 can be 10 C/m ² or more. Also, for example, in the plurality of piezoelectric device modules 30, when an electric field of −150 kV/cm is applied between the lower electrode film 2 and the upper electrode film 4, the leakage current density of all the piezoelectric device modules 30 can be 1×10 ⁻⁵ A/cm ² or less. Here, in this specification, "applying an electric field of -100 kV/cm or -150 kV/cm between the lower electrode film 2 and the upper electrode film 4" means that with the upper electrode film 4 side being negative and the lower electrode film 2 side being earthed, a negative voltage is applied to the upper electrode film 4 so that an electric field of 100 kV/cm or 150 kV/cm is generated between the upper electrode film 4 and the lower electrode film 2 in the upward thickness direction of the KNN film 3 (in the direction from the lower electrode film 2 to the upper electrode film 4).

In this way, the characteristics of multiple piezoelectric elements 20 (piezoelectric device modules 30) are made uniform, thereby improving the yield and reliability of the piezoelectric elements 20 (piezoelectric device modules 30).

(3) Methods of Manufacturing the Piezoelectric Laminate, Piezoelectric Element, and Piezoelectric Device Module Methods of manufacturing the above-mentioned piezoelectric laminate 10, piezoelectric element 20, and piezoelectric device module 30 will now be described.

(Deposition of adhesion layer and lower electrode film)
First, a large-diameter substrate 1 with a main surface having a diameter of 3 inches or more is prepared, and an adhesion layer 6 (e.g., a Ti layer) and a lower electrode film 2 (e.g., a Pt film) are formed in this order on either of the main surfaces of the substrate 1 by, for example, a sputtering method. Note that a substrate 1 on which the adhesion layer 6 and the lower electrode film 2 have been formed in advance on either of the main surfaces may be prepared.

The conditions for providing the adhesive layer 6 are exemplified as follows.
Temperature (substrate temperature): 100° C. or higher and 500° C. or lower, preferably 200° C. or higher and 400° C. or lower Discharge power: 1000 W or higher and 1500 W or lower, preferably 1100 W or higher and 1300 W or lower Atmosphere: Argon (Ar) gas atmosphere Atmosphere pressure: 0.1 Pa or higher and 0.5 Pa or lower, preferably 0.2 Pa or higher and 0.4 Pa or lower Time: 30 seconds or higher and 3 minutes or lower, preferably 45 seconds or higher and 2 minutes or lower

The conditions for forming the lower electrode film 2 are exemplified as follows.
Temperature (substrate temperature): 100° C. or higher and 500° C. or lower, preferably 200° C. or higher and 400° C. or lower Discharge power: 1000 W or higher and 1500 W or lower, preferably 1100 W or higher and 1300 W or lower Atmosphere: Ar gas atmosphere Atmosphere pressure: 0.1 Pa or higher and 0.5 Pa or lower, preferably 0.2 Pa or higher and 0.4 Pa or lower Time: 3 minutes or higher and 10 minutes or lower, preferably 4 minutes or higher and 8 minutes or lower, more preferably 5 minutes or higher and 6 minutes or lower

(KNN membrane production)
After the deposition of the adhesion layer 6 and the lower electrode film 2 is completed, the KNN film 3 is deposited on the lower electrode film 2 by a sputtering method such as RF magnetron sputtering. At this time, a target material 100, which will be described later, is used, which contains K, Na, Nb, and O and is made of a sintered body of an alkali niobium oxide having a perovskite structure. The target material 100 has a sputtering surface 101 having a diameter of 3 inches or more and having random crystal orientations over the entire inner area except for the peripheral portion. The target material 100 will be described in detail later. The composition ratio of the KNN film 3 can be adjusted, for example, by controlling the composition of the target material 100.

The following conditions are exemplified as conditions for forming the KNN film 3. The film forming time can be appropriately set depending on the thickness of the KNN film 3.
Discharge power: 2000 W or more and 2400 W or less, preferably 2100 W or more and 2300 W or less. Atmosphere: Ar gas + oxygen (O ₂ ) gas mixed gas atmosphere. Atmosphere pressure: 0.2 Pa or more and 0.5 Pa or less, preferably 0.2 Pa or more and 0.4 Pa or less. Partial pressure of Ar gas to O ₂ gas (Ar/O ₂ partial pressure ratio): 30/1 to 20/1, preferably 27/1 to 22/1.
Film-forming temperature: 500° C. to 700° C., preferably 550° C. to 650° C. Film-forming speed: 0.5 μm/hr to 2 μm/hr, preferably 0.5 μm/hr to 1.5 μm/hr

By using the target material 100 described below, which has a sputtering surface 101 with random crystal orientation over the entire inner area except for the peripheral portion, and depositing the KNN film 3 under the above-mentioned conditions, it is possible to avoid abnormal discharges over the entire sputtering surface during sputtering deposition. This makes it possible to avoid localized defective areas appearing on the main surface of the KNN film 3, even when depositing a large-diameter KNN film 3 on a large-diameter substrate 1 (on a large-diameter lower electrode film 2 deposited on a large-diameter substrate 1). In other words, it is possible to obtain a large-diameter KNN film 3 having uniform film quality over the entire main surface. Specifically, it is possible to obtain a large-diameter KNN film 3 whose FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface.

(Deposition of upper electrode film)
After the deposition of the KNN film 3 is completed, the upper electrode film 4 is deposited on the KNN film 3 by, for example, a sputtering method. The conditions for depositing the upper electrode film 4 can be the same as those for depositing the above-mentioned lower electrode film 2. As a result, a piezoelectric laminate 10 as shown in FIG. 1 is obtained.

(Fabrication of Piezoelectric Elements and Piezoelectric Device Modules)
The obtained piezoelectric laminate 10 is then shaped into a predetermined shape by etching or the like (micromachining is performed into a predetermined pattern). This results in a piezoelectric element 20 as shown in Fig. 4, and a piezoelectric device module 30 is obtained by connecting a voltage application means 11a or a voltage detection means 11b to the piezoelectric element 20. As the etching method, for example, a dry etching method such as reactive ion etching, or a wet etching method using a predetermined etching solution can be used.

When the piezoelectric laminate 10 is formed by dry etching, a photoresist pattern serving as an etching mask for dry etching is formed on the piezoelectric laminate 10 (for example, the upper electrode film 4) by a photolithography process or the like. As an etching mask, a noble metal film (metal mask) such as a Cr film, a Ni film, a Pt film, or a Ti film may be formed by a sputtering method. Then, dry etching is performed on the piezoelectric laminate 10 (the upper electrode film 4, the KNN film 3, etc.) using a gas containing a halogen element as an etching gas. The halogen element includes chlorine (Cl), fluorine (F), etc. As the gas containing a halogen element, BCl ₃ gas, SiCl ₄ gas, Cl ₂ gas, CF ₄ gas, C ₄ F ₈ gas, etc. can be used.

When forming the piezoelectric stack 10 by wet etching, a silicon oxide (SiO _x ) film or the like is formed on the piezoelectric stack 10 (e.g., the upper electrode film 4) as an etching mask for wet etching. Then, the piezoelectric stack 10 is immersed in an etching solution that contains an alkaline aqueous solution of a chelating agent and does not contain hydrofluoric acid, and wet etching is performed on the piezoelectric stack 10 (the upper electrode film 4, the KNN film 3, etc.). Note that an etching solution that contains an alkaline aqueous solution of a chelating agent and does not contain hydrofluoric acid can be an etching solution that is a mixture of ethylenediaminetetraacetic acid as a chelating agent, ammonia water, and hydrogen peroxide water.

(4) Configuration of the target material The configuration of the sputtering target material 100 used in sputtering the KNN film 3 will be described in detail below with reference to Fig. 5. The target material 100 is fixed to a backing plate via an adhesive such as In, and then mounted in a sputtering device so that the sputtering surface 101 is irradiated with plasma. As described above, the "sputtering surface" refers to the surface of the target material 100 that is exposed to plasma during sputtering (the surface that ions collide with during sputtering).

Figure 5 is a schematic diagram showing an example of a target material 100 according to this embodiment. In Figure 5, the target material 100 is shown with the sputtering surface 101 facing upward.

The target material 100 contains K, Na, Nb, and O, and is composed of a sintered body of alkali niobium oxide with a perovskite structure, i.e., a KNN sintered body. The target material 100 has a composition within the range of 0<Na/(K+Na)<1, preferably 0.4≦Na/(K+Na)≦0.7. The target material 100 is composed of multiple KNN crystal grains.

The target material 100 may contain one or more of the following elements as a dopant: Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga. The concentration of the above elements in the target material 100 may be, for example, 5 at% or less (if multiple elements are contained, the total concentration is 5 at% or less).

The target material 100 has a circular outer shape. That is, the target material 100 has a sputtering surface 101 that is circular in plan view. The diameter of the sputtering surface 101 can be, for example, 3 inches or more. The outer shape of the target material 100 (planar shape of the sputtering surface 101) can be various shapes such as an ellipse, a rectangle, or a polygon in addition to a circle. In this case, the diameter of the inscribed circle of the sputtering surface 101 can be, for example, 3 inches or more. In this way, the target material 100 has a sputtering surface 101 with a diameter of 3 inches or more, i.e., a large-diameter sputtering surface 101.

The target material 100 is configured so that the ratio R of the (110) peak intensity to the (001) peak intensity (=(110) peak intensity/(001) peak intensity) during XRD measurement of the sputtering surface 101 is within the range of 0.3 to 5, preferably 1.2 to 5, more preferably 1.2 to 3, throughout the entire inner area of the sputtering surface 101 excluding the periphery.

Note that the "(001) peak intensity" referred to here is the X-ray diffraction peak intensity from the (001) plane when XRD measurement is performed on the sputtering surface 101, i.e., the intensity of the diffraction peak due to the crystals oriented in the (001) plane orientation among the crystals constituting the target material 100 in the X-ray diffraction pattern obtained by performing XRD measurement on the sputtering surface 101, and is the intensity of the peak that appears when 2θ is in the range of 20° to 23°. Note that when multiple peaks appear in the range of 2θ is in the range of 20° to 23°, it is the intensity of the highest peak. In addition, the "(110) peak intensity" referred to here is the X-ray diffraction peak intensity from the (110) plane when XRD measurement is performed on the sputtering surface 101, that is, the intensity of the diffraction peak due to the crystals oriented in the (110) plane orientation among the crystals constituting the target material 100 in the X-ray diffraction pattern obtained by performing XRD measurement on the sputtering surface 101, and is the intensity of the peak that appears within the range of 2θ of 30° to 33°. Note that, when multiple peaks appear within the range of 2θ of 30° to 33°, it is the intensity of the highest peak.

Furthermore, "the ratio R is within the range of 0.3 to 5 in the entire inner area of the sputtering surface 101 excluding the peripheral portion" means that the value of the ratio R is 0.3 to 5 in all points (37 points in the case of a sputtering surface 101 with a diameter of 3 inches) when XRD measurements are performed in a grid pattern at 1 cm intervals on the area of the sputtering surface 101 excluding the area 5 mm from the edge (periphery) (area inside the area 5 mm from the edge). Hereinafter, "the entire inner area of the sputtering surface 101 excluding the peripheral portion" is also referred to as "the entire sputtering surface".

Thus, in the target material 100, even in the large-diameter sputtering surface 101, there are no regions where the crystal orientation is not random locally, i.e., there are no regions where the crystal orientation is locally reduced, and the crystal orientation is random throughout the entire sputtering surface. Preferably, in the target material 100, no regions where crystal grains with a grain size exceeding 30 μm are locally concentrated are observed throughout the entire sputtering surface and the entire surface parallel to the sputtering surface 101, except for the peripheral portion (hereinafter also referred to as "the entire surface parallel to the sputtering surface 101"). More preferably, in the target material 100, no crystal grains with a grain size exceeding 30 μm are observed throughout the entire sputtering surface and the entire surface parallel to the sputtering surface 101. That is, the target material 100 is composed of crystal grains having a grain size of, for example, 0.1 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.1 μm to 10 μm, over the entire sputtering surface and the entire surface parallel to the sputtering surface 101.

By using such a target material 100 to sputter a KNN film 3 on a substrate 1 having a diameter of 3 inches or more, it is possible to avoid abnormal discharge occurring over the entire sputtering surface during sputtering. As a result, it is possible to obtain a large-diameter KNN film 3 whose FWHM (001) value is within the range of 0.5° to 2.5° over the entire main surface.

The relative density of the target material 100 is 60% or more, preferably 70% or more, more preferably 80% or more over the entire sputtering surface. The relative density (%) here is a value calculated by (actual density/KNN theoretical density) x 100. The theoretical density of KNN is 4.51 g/cm ^3. The flexural strength of the target material 100 is 10 MPa or more, preferably 30 MPa or more, more preferably 40 MPa or more, and even more preferably 50 MPa or more over the entire sputtering surface. The flexural strength here is a value measured by a three-point bending test (in accordance with JIS R1601:2008). In this way, by having a relative density of 60% or more or a flexural strength of 10 MPa or more over the entire sputtering surface, it is possible to reliably avoid abnormal discharge occurring over the entire sputtering surface during sputtering film formation using the target material 100.

It is also preferable that the target material 100 has a high resistance. For example, it is preferable that the volume resistivity of the target material 100 is 1000 kΩcm or more. This makes it possible to obtain a KNN film 3 with good insulating properties. The upper limit of the volume resistivity is not particularly limited, but can be, for example, 100 MΩcm or less.

(5) Manufacturing Method of Target Material Hereinafter, a manufacturing method of the target material 100 in which the ratio R falls within the range of 0.3 to 5 over the entire sputtering surface will be described in detail with reference to FIG.

In the production sequence of the target material 100 in this embodiment,
A process (mixing process) of mixing a powder of a K compound, a powder of a Na compound, and a powder of a Nb compound in a predetermined ratio to obtain a mixture;
A process of applying a predetermined pressure (load) to the mixture to mold it into a molded body having a diameter of 3 inches or more (compression molding process);
A treatment (sintering treatment) of heating and sintering the molded body for 1 hour or more and 5 hours or less under conditions in which the temperature within the surface of the molded body is 800° C. or more and 1150° C. or less over the entire surface and has a temperature gradient that increases at 10° C./mm or more in the direction from the front surface to the back surface; and
In this embodiment, the case where the compression molding process and the firing process are carried out simultaneously (all at once) will be described.

In addition, after the mixing process and before the compression molding process,
A process of pre-firing the mixture at a temperature lower than the heating temperature in the firing process (pre-firing process);
A process of crushing the mixture after the calcination (crushing process);
In this case, in the compression molding process, a predetermined pressure is applied to the mixture that has been pulverized after the preliminary firing.

After the firing process, the sintered body may be further heated at a predetermined temperature (heat treatment).

(Mixing process)
A powder made of a K compound, a powder made of a Na compound, and a powder made of a Nb compound are mixed in a predetermined ratio to obtain a mixture.

Specifically, first, a powder made of a K compound, a powder made of a Na compound, and a powder made of a Nb compound are prepared.

The K compound is at least one selected from the group consisting of K oxides, K composite oxides, and K compounds that become oxides when heated (e.g., carbonates, _oxalates ). As the powder consisting of a K compound, for example, potassium carbonate ( _K2CO3 ) powder can be used.

The Na compound is at least one selected from the group consisting of Na oxides, Na composite oxides, and Na compounds that become oxides by heating (e.g., carbonates, _oxalates ). As the powder consisting of a Na compound, for example, sodium carbonate ( _Na2CO3 ) powder can be used.

The Nb compound is at least one selected from the group consisting of an oxide of Nb, a composite oxide of Nb, and a compound of Nb that becomes an oxide by heating. As the powder consisting of a Nb compound, for example, niobium oxide (Nb ₂ O ₅ ) powder can be used.

When preparing a target material 100 containing a predetermined dopant, a powder consisting of a compound of one or more elements of Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga is prepared. The powder of the compound of each of the above elements is at least one selected from the group consisting of oxide powder of each of the above elements, composite oxide powder of each of the above elements, and powder of a compound of each of the above elements that becomes an oxide when heated (e.g., carbonate, oxalate).

Then, the mixing ratio of each of the powders is adjusted and each powder is weighed so that the composition of the target material 100 becomes a predetermined composition. The weighing may be performed in the air, but it is preferable to perform the weighing in an inert gas atmosphere such as Ar gas or nitrogen (N ₂ ) gas in order to avoid the occurrence of deviation in the composition ratio of the target material 100. Furthermore, in order to reliably avoid the occurrence of deviation in the composition ratio of the target material 100, it is preferable to weigh each powder after sufficiently drying (dehydrating).

Next, the powders are mixed (wet mixed) using a mixer such as a ball mill, a bead mill, etc. The mixing conditions are exemplified as follows.
Solvent: organic solvent such as ethanol or water Mixing time: 5 hours or more and 30 hours or less, preferably 10 hours or more and 26 hours or less Mixing atmosphere: air

By mixing under the above conditions, it is possible to prevent the powder from agglomerating. As a result, the composition of the target material 100 can be made uniform over the entire sputtering surface and over the entire surface parallel to the sputtering surface 101.

(Pre-calcination and crushing)
After the mixing process is completed, the mixture obtained by the mixing process is pre-calcined by heating at a temperature lower than the heating temperature in the calcination process described below (pre-calcination process).

The conditions for the calcination are exemplified as follows.
Heating temperature: 650° C. or more and 1100° C. or less, preferably 700° C. or more and 900° C. or less, more preferably 700° C. or more and less than 800° C., and a temperature lower than the heating temperature in the firing treatment described below. Heating time: 1 hour or more and 50 hours or less, preferably 5 hours or more and 40 hours or less, more preferably 10 hours or more and 35 hours or less.

After the pre-firing process is completed, the pre-firing mixture is mixed while being pulverized using a ball mill or the like (pulverization process).

The conditions for pulverization are exemplified as follows.
Grinding (mixing) time: 3 hours or more and 10 hours or less, preferably 5 hours or more and 9 hours or less. Other conditions can be the same as those in the above-mentioned mixing treatment.

(Compression molding process/firing process)
After the preliminary firing and crushing processes are completed, a molding apparatus 200 shown in Fig. 6 is used to simultaneously perform a process of applying a predetermined pressure to the mixture obtained by crushing and mixing after the preliminary firing to form a molded body (compression molding process) and a process of heating and firing the molded body under predetermined conditions to form a sintered body (sintering process). That is, hot press sintering is performed in which firing is performed while compression molding is performed.

The molding device 200 shown in FIG. 6 is made of SUS or the like and has a chamber 203 with a processing chamber 201 inside. A jig (mold) 208 is provided in the processing chamber 201, in which the mixture 210 is filled (contained). The jig 208 is made of a material such as graphite and is configured to be able to form a molded body (sintered body) with a diameter of 3 inches or more. A pressing means 217 (e.g., a hydraulic press pressing means 217) is provided in the processing chamber 201, which is configured to be able to apply a predetermined pressure to the mixture 210 filled in the jig 208. A heater 207 is provided inside the processing chamber 201 to heat the mixture 210 in the jig 208 to a desired temperature. The heater 207 is configured such that an upper heater 207a, a central heater 207b, and a lower heater 207c are arranged in order from the top to the bottom of the processing chamber 201, and an inner heater 207d for heating the inner zone of the jig 208 and an outer heater 207e for heating the outer zone of the jig 208 are arranged in separate parts. Each of the upper heater 207a, the central heater 207b, and the lower heater 207c is cylindrical, and each of the inner heater 207d and the outer heater 207e is donut-shaped, and is configured so that the temperature can be controlled individually. In addition, a temperature sensor 209 for measuring the temperature inside the processing chamber 201 is provided inside the processing chamber 201. Each member of the molding device 200 is connected to a controller 280 configured as a computer, and is configured so that the procedures and conditions described below are controlled by a program executed on the controller 280.

The compression molding process and the firing process can be carried out using the above-mentioned molding device 200, for example, according to the following procedure.

First, the mixture 210 obtained by crushing and mixing after the preliminary firing is filled into the jig 208. Then, a predetermined pressure is applied to the mixture 210 in the jig 208 in the direction perpendicular to the pressing surface by the pressing means 217 as shown by the white arrow in FIG. 6 to form a molded body.

Examples of conditions for carrying out the compression molding include the following conditions.
Applied pressure (load): 100 kgf/cm2 or ^more and 500 kgf/cm2 or ^less Pressurization time: 1 hour or more and 5 hours or less, preferably 2 hours or more and 4 hours or less Atmosphere: inert gas atmosphere or vacuum atmosphere

By setting the load during compression molding to 100 kgf/cm ² or more and 500 kgf/cm ² or less, it is possible to obtain a target material 100 having a predetermined mechanical strength while avoiding damage to the jig 208. If the load is less than 100 kgf/cm ² , compression may be insufficient, resulting in a sintered body with low mechanical strength. If the mechanical strength is low, cracks may easily occur during the production of the target material 100, and the yield may decrease. In addition, when the target material 100 made of such a sintered body is used, cracks may occur in the target material 100 even during the formation of the KNN film 3, and as a result, various physical properties such as the crystal quality and film thickness of the KNN film 3 may locally decrease. In addition, if the load exceeds 500 kgf/cm ² , the jig 208 is more likely to be damaged.

In addition, while the compression molding process is being carried out under the above-mentioned conditions, the molded body is heated and fired under specified conditions.

The firing process is performed by heating the molded body (mixture 210) for 1 hour to 5 hours under conditions where the temperature (firing temperature) within the surface of the molded body (mixture 210 in jig 208) is 800°C or higher and 1150°C or lower over the entire surface, and the temperature gradient increases at 10°C/mm or higher in the direction from the front to the back of the molded body. At this time, the molded body (mixture 210) is heated while controlling the temperatures of heaters 207a to 207c based on the temperature detected by temperature sensor 209 so that the temperature within the processing chamber 201 (molded body, mixture 210) has a desired temperature distribution (for example, so that the temperature distribution within the processing chamber 201 is as shown in the graph in FIG. 6), and controlling the temperatures of heaters 207d and 207e based on the temperature detected by temperature sensor 209 so that the temperature within the surface of the molded body is uniform. In this specification, the surface of the molded body refers to the surface of the target material 100 that will become the sputtering surface 101, and the back surface of the molded body refers to the surface opposite to the surface of the molded body.

The firing conditions are exemplified as follows.
Firing temperature: 800° C. or higher and 1150° C. or lower, preferably 900° C. or higher and 1150° C. or lower, more preferably 1000° C. or higher and 1150° C. or lower Temperature gradient: a gradient that rises at 10° C./mm or higher, preferably 10° C./mm or higher and 15° C./mm or lower in the direction from the front surface to the back surface of the molded body Firing time (heating time): 1 hour or higher and 5 hours or lower, preferably 2 hours or higher and 3 hours or lower

The timing of starting and ending the heating (firing) is not particularly limited. Heating may start simultaneously with the start of pressurization, may start before the start of pressurization, or may start after the start of pressurization. Heating may end simultaneously with the end of pressurization, may end before the end of pressurization, or may end after the end of pressurization.

By carrying out compression molding and sintering under the above conditions, it is possible to obtain a large-diameter target material 100 in which the crystal orientation is random across the entire sputtering surface. Specifically, it is possible to obtain a large-diameter sintered body in which the ratio R is within the range of 0.3 to 5 across the entire surface that will become the sputtering surface 101. As a result, it is possible to obtain a large-diameter target material 100 in which the ratio R is within the range of 0.3 to 5 across the entire sputtering surface.

In particular, by intentionally applying a temperature gradient that rises at 10°C/mm or more in the direction from the front surface to the back surface of the molded body during firing, a large-diameter target material 100 can be obtained in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface. This is because, by intentionally applying the above-mentioned temperature gradient during firing, even if a temperature gradient (temperature unevenness) that exceeds a predetermined critical value occurs in the surface of the molded body during firing, it is possible to suppress crystal growth (solid-phase growth) in the creeping direction (hereinafter also simply referred to as the "creeping direction") on the surface of the molded body along the temperature gradient in the surface of the molded body. This makes it possible to avoid, for example, the appearance of a region in which crystal grains with a grain size exceeding 30 μm are locally concentrated. It is also possible to avoid the appearance of crystal grains with a grain size exceeding 30 μm. As a result, even with a large-diameter sputtering surface 101, it is possible to avoid the local appearance of a region in which the ratio R is not within the range of 0.3 to 5. In other words, it is possible to avoid a local decrease in the non-orientation of the crystals on the sputtering surface 101.

In addition, by intentionally applying the above-mentioned temperature gradient during firing, it is possible to obtain the effect of suppressing crystal growth in the surface direction, and therefore it is also possible to obtain a target material 100 in which no crystals with a grain size exceeding 30 μm are observed over the entire sputtering surface and the entire surface parallel to the sputtering surface 101. In other words, it is also possible to obtain a target material 100 in which the entire sputtering surface and the entire surface parallel to the sputtering surface 101 are composed of crystals with a grain size of 0.1 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.1 μm to 10 μm.

If the temperature gradient is less than 10°C/mm, it becomes difficult to obtain the effect of suppressing crystal growth along the surface during firing.

The above-mentioned temperature gradient can be, for example, 15°C/mm or less. This makes it possible to obtain a target material 100 in which the crystal orientation does not differ significantly between the front and back surfaces, i.e., the crystal orientation is almost the same. As a result, it is possible to make the various physical properties and characteristics, such as the crystal quality, of the KNN film 3 uniform among multiple piezoelectric stacks 10 fabricated using one target material 100. In other words, it is possible to prevent the various physical properties and characteristics of the KNN film 3 from changing run-to-run during the fabrication of the piezoelectric stack 10. As a result, it is possible to further improve the yield and reliability of the piezoelectric elements 20 and the piezoelectric device modules 30.

In addition, by heating the molded body (mixture 210) while controlling the temperature of heaters 207d and 207e based on the temperature detected by temperature sensor 209 so that the temperature within the surface of the molded body is uniform (uniform within the surface), that is, so that a temperature gradient is minimized within the surface of the molded body, the effect of suppressing crystal growth in the lateral direction can be reliably obtained. As a result, a large-diameter target material 100 in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface can be reliably obtained.

By setting the firing temperature to 800°C or more and 1150°C or less over the entire surface of the molded body and setting the firing time to 1 hour or more and 5 hours or less, sufficient firing (sintering) can be performed while suppressing crystal growth in the lateral direction. As a result, a target material 100 can be obtained in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface and which has sufficient mechanical strength.

If the firing temperature is less than 800°C (including cases where the firing temperature is not 800°C or higher over the entire surface of the molded body) or if the firing time is less than one hour, firing may be insufficient, resulting in a sintered body with low mechanical strength. For this reason, cracks are likely to occur in the target material 100 during the preparation of the target material 100 or during the deposition of the KNN film 3.

In addition, if the firing temperature exceeds 1150°C or the firing time exceeds 5 hours, even if a specified temperature gradient is applied in the thickness direction of the molded body, crystal growth in the lateral direction cannot be suppressed, and the crystals may grow large. As a result, areas in the sputtering surface 101 where the crystal orientation is not random may appear locally.

In addition, by carrying out compression molding and firing under the above-mentioned conditions, and in particular by intentionally creating the above-mentioned temperature gradient during firing, it is possible to obtain a target material 100 with a relative density of 60% or more and a flexural strength of 10 MPa or more over the entire sputtering surface.

(Heat Treatment)
After the compression molding process and the firing process are completed, the obtained sintered body is subjected to a predetermined heat treatment using the above-mentioned molding device 200. The heat treatment is preferably performed while controlling the temperatures of the heaters 207a to 207e based on the temperature detected by the temperature sensor 209 so that the temperature in the surface of the sintered body (the surface that becomes the sputtering surface 101) is uniform (uniform in-plane).

The heat treatment conditions are exemplified as follows.
Temperature: 600° C. or higher and 900° C. or lower, preferably 700° C. or higher and 800° C. or lower Atmosphere: air or oxygen-containing atmosphere Time: 1 hour or higher and 20 hours or lower, preferably 5 hours or higher and 15 hours or lower

Even if the carbon (C) contained in the jig 208 reacts with the O in the mixture 210 during the firing process, causing oxygen deficiencies in the sintered body, the oxygen deficiencies in the sintered body can be replenished by performing heat treatment under the above-mentioned conditions. As a result, it is possible to obtain a target material 100 with a higher resistance. For example, it is possible to obtain a target material 100 with a volume resistivity of 1000 kΩcm or more.

(Finishing process)
After the heat treatment is completed, the outer shape and thickness of the molded body after the heat treatment are adjusted as necessary, and the surface is polished to improve the surface condition, thereby obtaining a target material 100 as shown in FIG.

(6) Effects According to the present disclosure, one or more of the following effects can be obtained.

(a) In the KNN film 3 according to this embodiment, even if the diameter is large (diameter 3 inches or more), no localized defective areas appear over the entire main surface. In other words, the FWHM (001) value of the KNN film 3 is within the range of 0.5° to 2.5° over the entire main surface. Therefore, the KNN film 3 has uniform film quality over the entire main surface, and the film characteristics of the KNN film 3 are uniform over the entire main surface of the KNN film 3. As a result, it is possible to avoid variations in characteristics between multiple piezoelectric elements 20 and piezoelectric device modules 30 obtained by processing one piezoelectric laminate 10. This makes it possible to improve the yield and reliability of the piezoelectric elements 20 and piezoelectric device modules 30.

(b) By sputtering the KNN film 3 using a target material 100 in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface, it is possible to avoid abnormal discharges occurring over the entire sputtering surface during sputtering. As a result, even when a large-diameter KNN film 3 is sputtered on a large-diameter substrate 1, it is possible to avoid the appearance of localized defective areas over the entire main surface of the KNN film 3. In other words, by depositing the KNN film 3 using the above-mentioned target material 100, it is possible to obtain a large-diameter KNN film 3 in which the FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface.

Here, as a method for evaluating the crystal orientation (crystal orientation) of the sputtering surface, for example, a method is conceivable in which the ratio R is calculated and evaluated at a total of nine points, including one point at the center of the sputtering surface, four points at 1/2 the radius at 90° intervals, and four points at 90° intervals inside a certain distance from the outer periphery. However, this evaluation method has fewer evaluation points than the present embodiment, so it may not be possible to accurately evaluate the crystal orientation over the entire sputtering surface. In particular, in the case of a large-diameter target material with a sputtering surface of 3 inches or more, it may be difficult to find areas where the ratio R is not within the range of 0.3 to 5 (areas where the crystal orientation is not random), even though these areas appear locally.

In contrast, in the target material 100 according to the present embodiment, the ratio R is within the range of 0.3 to 5 at all points (e.g., 37 points on a sputtering surface 101 with a diameter of 3 inches) when XRD measurements are performed in a grid pattern at 1 cm intervals on the area excluding the peripheral portion, which is a region 5 mm from the edge of the sputtering surface 101. By sputtering a KNN film 3 on a large-diameter substrate 1 using such a target material 100, it is possible to obtain a large-diameter KNN film 3 whose FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface.

(c) In the above-mentioned firing process, by heating the molded body under conditions with a temperature gradient that increases from the front surface to the back surface of the molded body at a rate of 10°C/mm or more, crystal growth in the lateral direction can be suppressed. As a result, a large-diameter target material 100 can be obtained in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface.

(d) In the above-mentioned firing process, the firing temperature is 800°C or more and 1150°C or less over the entire surface of the molded body, and the molded body is heated for 1 hour or more and 5 hours or less under the conditions of the above-mentioned temperature gradient, whereby a large-diameter target material 100 can be obtained in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface and which has sufficient mechanical strength.

(7) Modifications This embodiment can be modified as follows. In the following description of the modifications, the same components as those in the above embodiment are denoted by the same reference numerals, and the description thereof will be omitted. The above embodiment and the following modifications can be combined in any combination.

(Variation 1)
The piezoelectric stack 10 may not include the lower electrode film 2. In other words, the piezoelectric stack 10 may include a large-diameter substrate 1, a large-diameter KNN film 3 formed on the substrate 1, and an upper electrode film 4 (electrode film) formed on the KNN film 3.

7 shows a schematic diagram of a piezoelectric device module 30 produced using the piezoelectric laminate 10 according to this modification. The piezoelectric device module 30 is configured to include at least a piezoelectric element 20 obtained by forming the piezoelectric laminate 10 into a predetermined shape, and a voltage application means 11a and a voltage detection means 11b connected to the piezoelectric element 20. In this modification, the piezoelectric element 20 has pattern electrodes formed by forming an electrode film into a predetermined pattern. For example, the piezoelectric element 20 has a pair of positive and negative pattern electrodes 4p ₁ on the input side and a pair of positive and negative pattern electrodes 4p ₂ on the output side. An example of the pattern electrodes 4p ₁ and 4p ₂ is an interdigital transducer (abbreviated as IDT).

By connecting the voltage application means 11a between the pattern electrodes _4p1 and the voltage detection means 11b between the pattern electrodes _4p2 , the piezoelectric device module 30 can function as a filter device such as a surface acoustic wave (SAW) filter. By applying a voltage between the pattern electrodes _4p1 by the voltage application means 11a, a SAW can be excited in the KNN film 3. The frequency of the SAW to be excited can be adjusted, for example, by adjusting the pitch of the pattern electrodes _4p1 . For example, the shorter the pitch of the IDT as the pattern electrode _4p1 , the higher the frequency of the SAW, and the longer the pitch, the lower the frequency of the SAW. Of the SAW excited by the voltage application means 11a and propagating through the KNN film 3 to reach the pattern electrodes _4p2 , a SAW having a predetermined frequency (frequency component) determined according to the pitch of the IDT as the pattern electrode _4p2 generates a voltage between the pattern electrodes _4p2 . By detecting this voltage with the voltage detection means 11b, it is possible to extract a SAW having a predetermined frequency from among the excited SAWs. Note that the term "predetermined frequency" used here may include not only a predetermined frequency but also a predetermined frequency band whose center frequency is a predetermined frequency.

In this modified example, by sputtering the KNN film 3 using a target material 100 in which the ratio R is within the range of 0.3 to 5 across the entire sputtering surface, it is possible to obtain a large-diameter KNN film 3 in which the FWHM(001) value is within the range of 0.5° to 2.5° across the entire main surface.

Also, in this modified example, the FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface of the large-diameter KNN film 3. This allows the film characteristics of the KNN film 3 to be uniform over the entire main surface of the KNN film 3. As a result, in this modified example, it is possible to avoid variations in characteristics between multiple piezoelectric elements 20 (piezoelectric device modules 30) obtained from a single piezoelectric stack 10. As a result, it is possible to improve the yield and reliability of the piezoelectric elements 20 (piezoelectric device modules 30).

(Variation 2)
In the above-mentioned embodiment, a case where a powder made of a compound of K (e.g., _{K2CO3 powder} ), a powder made of a compound of Na (e.g., _Na2CO3 powder), and a powder made of a compound of _Nb (e.g., _{Nb2O5 powder} ) are mixed in a predetermined ratio in the mixing process when producing the target material 100 has been described as an example, but is not limited thereto. For example, in the mixing process, a powder made of a compound containing K and Nb and a powder made of a compound containing Na and Nb may be mixed in a predetermined ratio to obtain a mixture.

The compound containing K and Nb is at least one selected from the group consisting of an oxide (composite oxide) containing K and Nb, and a compound containing K and Nb that becomes an oxide by heating (e.g., carbonate, oxalate). As the powder of the compound containing K and Nb, for example, _{KNbO3 powder can be used. KNbO3 powder} can be obtained by, for example, mixing a compound of K (e.g., _{K2CO3 powder} ) and a compound of Nb ( _e.g. , _Nb2O5 powder), calcining the mixture, and pulverizing and mixing the mixture after calcination using a ball mill or the like.

The compound containing Na and Nb is at least one selected from the group consisting of an oxide (composite oxide) containing Na and Nb, and a compound containing Na and Nb that becomes an oxide by heating (e.g., carbonate, oxalate). As the powder of the compound containing Na and Nb, for example, _NaNbO3 powder can be used. _NaNbO3 powder can be obtained by, for example, mixing a compound of Na (e.g., _{Na2CO3 powder} ) and a compound of Nb (e.g. _{, Nb2O5} powder), calcining the mixture, and pulverizing and mixing the mixture after calcination using a ball mill or the like.

In this case, the composition of the target material 100 can be controlled by adjusting the mixing ratio of the _KNbO3 powder and the _NaNbO3 powder, the mixing ratio of the K compound and the Nb compound when producing the _KNbO3 powder, and the mixing ratio of the Na compound and the Nb compound when producing the _NaNbO3 powder.

In this modified example, the conditions for calcination when producing the _KNbO3 powder and the _NaNbO3 powder can be the same as the conditions for the calcination treatment in the above-mentioned embodiment, and the conditions for mixing can be the same as the conditions for the mixing treatment in the above-mentioned embodiment.

In this modified example, the molded body is heated for 1 hour to 5 hours in the firing process under conditions in which the temperature within the surface of the molded body is 800°C or more and 1150°C or less over the entire surface, and the temperature gradient increases at 10°C/mm or more in the direction from the surface to the back surface of the molded body. This makes it possible to obtain a large-diameter target material 100 in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface. In addition, by sputtering the KNN film 3 using this target material 100, it is possible to obtain a large-diameter KNN film 3 in which the FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface.

(Variation 3)
In the above-mentioned embodiment and modified example, the mixing method of each powder in the mixing process and the pulverization process is a wet mixing method, but this is not limited to this. The mixing method in the mixing process may be a dry mixing method. In other words, in the mixing process, each powder may be mixed using a mixer such as an attritor.

(Variation 4)
In the above embodiment, an example in which the compression molding process and the sintering process are performed simultaneously, i.e., an example in which hot press sintering is performed, has been described, but the present invention is not limited to this. For example, the sintering process may be performed after the compression molding process. That is, for example, using a molding device 200 shown in FIG. 6, a predetermined pressure may be applied to the mixture 210 in the jig 208 to perform compression molding to obtain a molded body, and then the molded body may be heated and sintered under predetermined conditions to obtain a sintered body.

The conditions for the compression molding process in this modified example are, for example, as follows:
Temperature: room temperature (25° C.) or higher, preferably 25° C. or higher and 50° C. or lower. Other conditions can be the same as those for the compression molding treatment of the above-mentioned embodiment.

In this modified example, the firing process involves heating the molded body for 1 hour to 5 hours under conditions in which the temperature within the surface of the molded body is 800°C or higher and 1150°C or lower over the entire surface, and the temperature gradient increases from the surface to the back of the molded body at a rate of 10°C/mm or higher. Other conditions for the firing process in this modified example can be the same as those for the firing process in the above-mentioned embodiment.

Even with this modified example, by carrying out the firing process under the above-mentioned conditions, it is possible to obtain a large-diameter target material 100 in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface. In addition, by sputtering the KNN film 3 using this target material 100, it is possible to obtain a large-diameter KNN film 3 in which the FWHM(001) value is within the range of 0.5° to 2.5° over the entire main surface.

(Variation 5)
In the above-mentioned embodiment and modified example, a series of processes from compression molding to heat treatment are performed in one molding device 200, but the present invention is not limited to this. The compression molding, firing, and heat treatment may each be performed in a different device, or two of these processes may be performed in the same device and the other processes may be performed in a different device.

(Variation 6)
In the above embodiment, the example of carrying out the pre-baking process, the crushing process, and the heat treatment has been described, but the present invention is not limited thereto. These processes may be carried out as necessary. That is, as long as it is possible to obtain a large-diameter target material 100 in which the ratio R is within a range of 0.3 to 5 over the entire sputtering surface, these processes may not be carried out.

(Variation 7)
In the above embodiment, an example has been described in which the heater 207 includes the upper heater 207a, the central heater 207b, and the lower heater 207c, as well as the inner heater 207d and the outer heater 207e, but the present invention is not limited to this. As long as the temperature inside the surface of the molded body can be set to 800° C. or higher and 1150° C. or lower over the entire surface, and the baking process can be performed under conditions in which the temperature gradient increases at 10° C./mm or higher in the direction from the surface to the back surface of the molded body, the configuration of the heater 207 is not particularly limited.

(Variation 8)
For example, the heating in each of the pre-baking treatment, the baking treatment, and the heat treatment may be performed in a plurality of separate steps. This modification also makes it possible to obtain a large-diameter target material 100 in which the ratio R is within the range of 0.3 to 5 over the entire sputtering surface.

(Variation 9)
For example, the jig 208 may be connected to a rotating mechanism via a rotating shaft and configured to be freely rotatable. Then, the heat treatment of the above-mentioned embodiment and modified example, the firing treatment of modified example 4, etc. may be performed while rotating the jig 208 by the rotating mechanism via the rotating shaft. This makes it easier to heat the molded body or sintered body uniformly within the surface, and makes it easier to make the physical properties of the target material 100 uniform across the entire sputtering surface.

(Variation 10)
For example, an orientation control layer for controlling the orientation of the crystals constituting the KNN film 3 may be provided between the lower electrode film 2 and the KNN film 3, i.e., directly under the KNN film 3. When the lower electrode film 2 is not provided, an orientation control layer may be provided between the substrate 1 and the KNN film 3. The orientation control layer may be formed using a metal oxide such as SRO, LNO, or strontium titanate (SrTiO ₃ , abbreviated as STO), which is different from the material constituting the lower electrode film 2. It is preferable that the crystals constituting the orientation control layer are preferentially oriented in the (100) plane with respect to the main surface of the substrate 1. This allows the orientation rate of the KNN film 3 to be easily and reliably set to, for example, 80% or more, preferably 90% or more.

(Modification 11)
In the above embodiment, an example in which one laminated structure is formed on one substrate 1 has been described, but the present invention is not limited to this. For example, a plurality of laminated structures may be formed on one substrate 1. In this case, it is preferable that each of the plurality of laminated structures has a lower electrode film 2, a KNN film 3, and an upper electrode film 4. In the embodiment according to the first modification, it is preferable that each of the plurality of laminated structures has a KNN film 3 and an electrode film 4. The substrate 1 on which one or more laminated structures are formed is also referred to as a piezoelectric laminated substrate.

(Variation 12)
For example, when the above-mentioned piezoelectric stack 10 is molded into the piezoelectric element 20, the substrate 1 may be removed from the piezoelectric stack 10 as long as the piezoelectric device module 30 produced using the piezoelectric stack 10 (piezoelectric element 20) can be applied to a desired application such as a sensor or actuator.

Below, we will explain the experimental results that support the effects of the above-mentioned aspect.

(Samples 1 and 2)
As samples 1 and 2, a molding apparatus 200 shown in FIG. 6 was used to fabricate a target material having a diameter of 3 inches and made of a (K _1-x Na _x )NbO ₃ sintered body containing Mn at a predetermined concentration.

Samples 1 and 2 were prepared by performing a mixing process, a preliminary calcination/pulverization process, a compression molding process, a calcination process, and a heat treatment. In addition, the compression molding process and the calcination process were performed simultaneously (all at once). In the mixing process, _K2CO3 powder, _Na2CO3 powder, and _Nb2O5 powder were mixed so that the value of Na/(K+Na ₎ was _0.55 , and MnO powder was mixed so that Mn was contained at a predetermined concentration to prepare a mixture. In the compression molding process, a molded body was prepared with a load of ₃₀₀ kgf/ ^cm2 . In the calcination process, the molded body was heated for 3 hours under conditions in which the temperature (calcination temperature) in the surface of the molded body was 900°C over the entire surface and had a temperature gradient rising at 10°C/mm in the direction from the surface to the back surface. Other conditions in each process were set to predetermined conditions within the range of processing conditions described in the above-mentioned embodiment.

(Samples 3 to 8)
In Samples 3 to 8, the temperature gradient increasing in the direction from the front surface to the back surface of the molded body during the firing treatment was changed from that of Sample 1. Specifically, the temperature gradient was set to 12° C./mm in Samples 3 and 4, 15° C./mm in Samples 5 and 6, 5° C./mm in Sample 7, and 7° C./mm in Sample 8. The rest of the temperature gradient was the same as that used in producing Sample 1.

(Samples 9 to 13)
In Samples 9 to 13, the firing temperature in the firing treatment was changed from that of Sample 1. Specifically, in Sample 9, the firing temperature was 750° C. over the entire surface of the molded body, in Sample 10, the firing temperature was 800° C. over the entire surface of the molded body, in Sample 11, the firing temperature was 1000° C. over the entire surface of the molded body, in Sample 12, the firing temperature was 1150° C. over the entire surface of the molded body, and in Sample 13, the firing temperature was 1200° C. over the entire surface of the molded body. The rest were the same as those in the preparation of Sample 1.

(Samples 14 to 17)
In Samples 14 to 17, the load in the compression molding process was changed from that of Sample 1. Specifically, the load was 100 kgf/ ^cm2 in Sample 14, 200 kgf/cm2 in Sample ¹⁵ , 400 kgf/ ^cm2 in Sample 16, and 500 kgf/ ^cm2 in Sample 17. The rest of the loads were the same as those used in producing Sample 1.

(Samples 18-23)
In Samples 18 to 23, the time for heating the molded body in the firing treatment (firing time) was changed from Sample 1. Specifically, the firing time was 0.5 hours in Sample 18, 1 hour in Sample 19, 2 hours in Sample 20, 4 hours in Sample 21, 5 hours in Sample 22, and 5.5 hours in Sample 23. The rest were the same as those in the preparation of Sample 1.

(Sample 24)
In sample 24, a target material with a diameter of 3 inches was prepared, which was made of a ( _{K1-xNax ) NbO3} sintered body that did not contain dopants such as Mn. Specifically, in the mixing process, _{K2CO3 powder} , _{Na2CO3 powder} , and _Nb2O5 powder were mixed so that the value of Na/(K+ _Na ) was 0.55, and a mixture was prepared without mixing MnO powder. The other steps were the same as those used when preparing sample 1.

(Sample 25)
In the case of Sample 25, the compression molding process was performed, and then the firing process was performed. In other words, the compression molding process and the heat treatment were performed separately. The other steps were the same as those in the case of producing Sample 1.

(Sample 26)
In the case of Sample 26, the compression molding process and the sintering process were separately performed, and the other steps were the same as those in the case of Sample 24.

(Samples 27 and 28)
In samples 27 and 28, the composition of the (K1 _{-xNax ) NbO3} sintered body, i.e., the composition of the target material, was changed from sample 1. Specifically, in sample 27, _K2CO3 powder, _Na2CO3 powder, and _Nb2O5 powder were mixed in the mixing process so that the value of Na/(K+Na) was 0.40. In sample 28, _K2CO3 powder, _{Na2CO3 powder} , _{and Nb2O5 powder} were mixed to prepare a mixture so that the value of Na/(K+ _Na ) was 0.70. The rest was _the same as those used when preparing sample ₁ .

(Samples 29-32)
For samples 29 to 32, a target material having a diameter of 4 inches was prepared, which was made of a ( _{K1-xNax ) NbO3} sintered body containing a predetermined concentration of Cu as a dopant. Specifically, for samples 29 to 32, a mixture was prepared by mixing CuO powder in a predetermined ratio instead of MnO powder in the mixing process. Also, for sample 30, the temperature gradient in the firing process was set to 12°C/mm, for sample 31, the temperature gradient was set to 3°C/mm, and for sample 32, the temperature gradient was set to 8°C/mm. The rest of the process was the same as that for sample 1.

(Samples 33 to 36)
In samples 33 to 26, a target material having a diameter of 6 inches was prepared, which was made of a ( _{K1-xNax ) NbO3} sintered body containing a predetermined concentration of Cu and a predetermined concentration of Mn. Specifically, in samples 33 to 36, a mixture was prepared by mixing CuO powder and MnO powder in a predetermined ratio in the mixing process. In addition, in sample 34, the above-mentioned temperature gradient in the firing process was set to 14°C/mm, in sample 35, the above-mentioned temperature gradient was set to 4°C/mm, and in sample 36, the above-mentioned temperature gradient was set to 9°C/mm. The rest of the process was the same as that in sample 1.

<Evaluation>
The target materials of Samples 1 to 36 were evaluated for cracking and the ratio R, and the KNN films formed by sputtering using each sample were also evaluated.

(Crack evaluation)
Each sample was visually evaluated for the presence or absence of cracks. As a result, it was confirmed that cracks were generated in Sample 9 and Sample 18, and that no cracks were generated in the other samples except for Samples 9 and 18. From this, it can be confirmed that if the firing temperature is less than 800° C. or the firing time is less than 1 hour, firing is insufficient, resulting in a sintered body with low mechanical strength.

(Evaluation of ratio R)
For each of the samples other than Samples 9 and 18 in which cracks were generated, XRD measurement was performed on the sputtered surface of the target material, and the ratio R of the (110) peak intensity to the (001) peak intensity was calculated. The XRD measurement was performed on the area excluding the area 5 mm from the edge of the sputtered surface in a lattice pattern with 1 cm intervals. That is, XRD measurement was performed at 37 points for samples with a diameter of 3 inches (Samples 1 to 28), XRD measurement was performed at 69 points for samples with a diameter of 4 inches (Samples 29 to 32), and XRD measurement was performed at 147 points for samples with a diameter of 6 inches (Samples 33 to 36). The ratio R was calculated at all points of the XRD measurement points. The calculation results are shown in Table 1 below. In addition, in the evaluation of the ratio R in Table 1, the "passed measurement points" is the number of measurement points where the ratio R is in the range of 0.3 to 5, and the "pass rate" is the ratio of the number of passed measurement points to the number of all measurement points (= number of passed measurement points/total number of measurement points).

(Evaluation of KNN membrane)
KNN films were formed by the following procedure using the samples other than Samples 9 and 18 in which cracks had occurred.

In the sputtering deposition using Samples 1, 3, 5, 7, 8, 10-17, and 19-28, a Si substrate having a diameter of 4 inches, a thickness of 510 μm, a surface oriented in the (100) plane, and a thermal oxide film (SiO ₂ film) having a thickness of 200 nm formed on the surface was prepared as a substrate. Then, on this substrate (on the thermal oxide film), a Ti layer (thickness: 2 nm) as an adhesion layer, a Pt film (oriented in the (111) plane direction relative to the main surface of the substrate, thickness: 200 nm) as a lower electrode film, and a KNN film (preferentially oriented in the (001) plane direction relative to the surface of the substrate, thickness: 2 μm) having a diameter of 4 inches as a piezoelectric film were deposited in this order by RF magnetron sputtering.

In the sputtering deposition using Samples 2, 4, 6, and 29 to 36, a Si substrate having a diameter of 6 inches, a thickness of 610 μm, a surface oriented in the (100) plane, and a thermal oxide film (SiO ₂ film) having a thickness of 200 nm formed on the surface was prepared as a substrate. Then, on this substrate (on the thermal oxide film), a Ti layer (thickness: 2 nm) as an adhesion layer, a Pt film (oriented in the (111) plane with respect to the main surface of the substrate, thickness: 200 nm) as a lower electrode film, and a KNN film having a diameter of 6 inches (preferentially oriented in the (001) plane with respect to the surface of the substrate, thickness: 2 μm) as a piezoelectric film were deposited in this order by RF magnetron sputtering.

The conditions for forming the Ti layer were as follows:
Temperature (substrate temperature): 300℃
Discharge power: 1200W
Atmosphere: Ar gas atmosphere Atmosphere pressure: 0.3 Pa
Film formation speed: The speed at which a Ti layer of 2.5 nm thickness is formed in 30 seconds

The conditions for forming the Pt film were as follows:
Temperature (substrate temperature): 300℃
Discharge power: 1200W
Atmosphere: Ar gas atmosphere Atmosphere pressure: 0.3 Pa
Time: 5 minutes

The target materials used in forming the KNN film were the samples other than Samples 9 and 18. The conditions in forming the KNN film were as follows.
Discharge power: 2200W
Atmosphere: Ar gas + _O2 gas mixed gas atmosphere Atmosphere pressure: 0.3 Pa
Ar/O2 _partial pressure ratio: 25/1
Temperature (substrate temperature): 600℃
Film forming speed: 1μm/hr

Then, XRD measurement was performed on the sputtered KNN film to obtain the FWHM (001) value. The XRD measurement was performed on the area excluding a 5 mm area from the edge of the main surface (upper surface) of the KNN film, in a grid pattern with 1 cm intervals. That is, XRD measurement was performed at 69 points for the KNN film with a diameter of 4 inches, and at 147 points for the KNN film with a diameter of 6 inches. The measurement results are shown in Table 1 below. In addition, in the evaluation of the KNN film in Table 1, "passing measurement points" refers to the number of measurement points whose FWHM (001) value is within the range of 0.5° to 2.5°, and "pass rate" refers to the ratio of the number of passing measurement points to the number of all measurement points (= number of passing measurement points/total number of measurement points).

From Table 1, it can be seen that for both target materials containing at least one of Mn and Cu as dopants and target materials not containing dopants, by performing a firing process (hereinafter also referred to as "firing process under predetermined conditions") by heating the molded body for 1 hour to 5 hours under conditions in which the temperature within the surface of the molded body is 800°C to 1150°C over the entire surface and there is a temperature gradient that increases from the front surface to the back surface of the molded body at a rate of 10°C/mm or more, it is possible to obtain target materials in which the ratio R is within a range of 0.3 to 5 over the entire sputtering surface (see Samples 1 to 6, 10 to 12, 19 to 22, 24, 29, 30, 33, and 34). In other words, it can be seen that by performing a firing process under the above conditions, it is possible to obtain target materials in which the crystal orientation is random over the entire sputtering surface.

The inventors also confirmed that if the temperature gradient during the firing process is 15°C/mm or less, the crystal orientation can be made approximately the same between the sputtering surface of the target material and the surface opposite the sputtering surface while keeping the ratio R within the range of 0.3 to 5 over the entire sputtering surface.

Also, from Table 1, it can be seen that when the temperature gradient in the firing process is less than 10°C/mm, the pass rate for the ratio R is less than 1, i.e., there are cases where a target material with a ratio R within the range of 0.3 to 5 over the entire sputtering surface cannot be obtained (see Samples 7, 8, 31, 32, 35, and 36). This is thought to be because it becomes difficult to obtain the effect of suppressing crystal growth in the creeping direction of the molded body surface during firing.

It can also be seen from Table 1 that when the firing temperature exceeds 1150°C or the firing time exceeds 5 hours, the pass rate of the ratio R is less than 1 over the entire sputtering surface, i.e., there are cases where a target material with a ratio R within the range of 0.3 to 5 cannot be obtained (see Samples 13 and 23). This is thought to be because when the firing temperature exceeds 1150°C or the firing time exceeds 5 hours, crystal growth along the surface cannot be suppressed even when firing is performed under conditions with the above-mentioned temperature gradient, and therefore areas where the crystal orientation is not random are generated locally within the sputtering surface.

Also, from Table 1, it can be confirmed that if the load in the compression molding process is within the range of 100 kgf/cm2 or ^more and 500 kgf/ ^cm2 or less, it is possible to obtain a target material with random crystal orientation over the entire sputtering surface while avoiding the occurrence of cracks (see Samples 14 to 17). The inventors also confirmed that if the load in the compression molding process is within the above range, the jig used during compression molding was not damaged.

Also, from Table 1, it can be seen that even if the firing process is performed after the compression molding process, by performing the specified firing process, it is possible to obtain a target material with random crystal orientation over the entire sputtering surface (see samples 25 and 26).

Furthermore, Table 1 confirms that by performing a specified firing process, it is possible to obtain a target material with random crystal orientation across the entire sputtering surface, regardless of the KNN composition of the target material (see samples 27 and 28).

Also, from Table 1, it can be seen that by sputtering a KNN film on a large-diameter substrate using a target material whose ratio R is in the range of 0.3 to 5 over the entire sputtering surface, a large-diameter KNN film whose FWHM(001) value is in the range of 0.5° to 2.5° over the entire main surface can be obtained. Furthermore, from Table 1, it can be seen that when a KNN film is sputtered on a large-diameter substrate using a target material whose ratio R is in the range of 0.3 to 5 over the entire sputtering surface, the pass rate is less than 1, that is, a large-diameter KNN film whose FWHM(001) value is in the range of 0.5° to 2.5° over the entire main surface cannot be obtained. In other words, it can be seen that a localized defective area appears in the main surface of the KNN film.

<Preferred embodiment of the present disclosure>
Preferred aspects of the present disclosure will be described below.

(Appendix 1)
According to one aspect of the present disclosure,
A substrate having a major surface with a diameter of 3 inches or more;
a piezoelectric film formed on the substrate, the piezoelectric film containing potassium, sodium, niobium, and oxygen and made of an alkali niobium oxide having a perovskite structure;
The piezoelectric laminate has an X-ray rocking curve half-width for the (001) plane, which is measured by X-ray diffraction, within a range of 0.5° to 2.5° over the entire inner area, excluding the peripheral portion, of the main surface of the piezoelectric film.

(Appendix 2)
The laminate according to claim 1, preferably
The piezoelectric film contains one or more of the following dopants: Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga.

(Appendix 3)
The laminate according to claim 1 or 2, preferably
A lower electrode film is formed between the substrate and the piezoelectric film.

(Appendix 4)
The laminate according to any one of appendices 1 to 3, preferably
An upper electrode film is formed on the piezoelectric film.

(Appendix 5)
According to another aspect of the present disclosure,
A step of preparing a sputtering target material made of a sintered body of an alkali niobium oxide having a perovskite structure, the alkali niobium oxide containing potassium, sodium, niobium, and oxygen;
providing a substrate having a major surface with a diameter of 3 inches or more;
and forming a piezoelectric film on the substrate using the sputtering target material, the piezoelectric film being made of the alkali niobium oxide, the full width at half maximum of an X-ray rocking curve of a (001) plane being within a range of 0.5° to 2.5° over the entire inner area excluding the peripheral portion of the main surface when measured by X-ray diffraction.

(Appendix 6)
According to yet another aspect of the present disclosure,
A substrate having a major surface with a diameter of 3 inches or more;
A lower electrode film formed on the substrate;
a piezoelectric film formed on the lower electrode film, the piezoelectric film containing potassium, sodium, niobium, and oxygen and made of an alkali niobium oxide having a perovskite structure;
an upper electrode film formed on the piezoelectric film;
The piezoelectric element (piezoelectric device module) is provided in which, when X-ray diffraction measurement is performed on the piezoelectric film, the half-width of the X-ray rocking curve for the (001) plane is within a range of 0.5° or more and 2.5° or less over the entire inner area excluding the peripheral portion of the main surface of the piezoelectric film.

(Appendix 7)
According to yet another aspect of the present disclosure,
A substrate having a major surface with a diameter of 3 inches or more;
a piezoelectric film formed on the substrate, the piezoelectric film containing potassium, sodium, niobium, and oxygen and made of an alkali niobium oxide having a perovskite structure;
An electrode film formed on the piezoelectric film,
The piezoelectric element (piezoelectric device module) is provided in which, when X-ray diffraction measurement is performed on the piezoelectric film, the half-width of the X-ray rocking curve for the (001) plane is within a range of 0.5° or more and 2.5° or less over the entire inner area excluding the peripheral portion of the main surface of the piezoelectric film.

(Appendix 8)
According to yet another aspect of the present disclosure,
A sputtering target material comprising a sintered body of an alkali niobium oxide having a perovskite structure, the sputtering target material comprising:
The diameter of the surface (sputtering surface) that is exposed to plasma during the film formation process by the sputtering method is 3 inches or more;
The sputtering target material has a ratio of the intensity of the X-ray diffraction peak from the (110) plane to the intensity of the X-ray diffraction peak from the (001) plane, when X-ray diffraction measurement is performed on the surface to be exposed to the plasma, within a range of 0.3 to 5 over the entire inner area, excluding the peripheral portion, of the surface to be exposed to the plasma.

(Appendix 9)
According to yet another aspect of the present disclosure,
A sputtering target material comprising a sintered body of an alkali niobium oxide having a perovskite structure, the sputtering target material comprising:
When used as a target material for film formation by sputtering to form a piezoelectric film on a substrate with a diameter of 3 inches or more,
A sputtering target material is provided which, when X-ray diffraction measurement is performed on the piezoelectric film, gives a piezoelectric film in which the half-width of the X-ray rocking curve for the (001) plane is within a range of 0.5° or more and 2.5° or less over the entire inner area excluding the peripheral portion of the main surface of the piezoelectric film.

(Appendix 10)
The target material according to claim 8 or 9, preferably
The dopant contains one or more of Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga.

(Appendix 11)
The target material according to any one of appendices 8 to 10, preferably
In the entire area of the surface exposed to plasma during the film formation process by sputtering and in the entire area of any surface parallel to this surface, no region in which crystal grains having a grain size exceeding 30 μm are densely concentrated is observed. That is, the entire area of the surface exposed to plasma during the film formation process by sputtering and in the entire area of any surface parallel to this surface are composed of crystal grains having a grain size of 0.1 μm to 30 μm, preferably 0.1 μm to 20 μm, and more preferably 0.1 μm to 10 μm.

(Appendix 12)
The target material according to any one of appendices 8 to 11, preferably
The relative density is 60% or more over the entire surface that is exposed to plasma during the film formation process by sputtering.

(Appendix 13)
The target material according to any one of appendices 8 to 12, preferably
The flexural strength is 10 MPa or more over the entire surface that is exposed to plasma during the film formation process by sputtering.

(Appendix 14)
The target material according to any one of appendices 8 to 13, preferably
The volume resistivity is 1000 kΩcm or more.

(Appendix 15)
According to yet another aspect of the present disclosure,
A method for producing a sputtering target material made of a sintered body of an alkali niobium oxide having a perovskite structure, the method comprising the steps of:
(a) mixing a powder of a potassium compound, a powder of a sodium compound, and a powder of a niobium compound in a predetermined ratio to obtain a mixture;
(b) applying a predetermined pressure to the mixture to form a molded body having a diameter of 3 inches or more;
(c) heating and firing the molded body for 1 hour to 5 hours under conditions in which the temperature within the front surface, which is the surface that will be exposed to plasma when performing a film formation process by sputtering (the surface that will be the sputtered surface), is 800° C. or more and 1150° C. or less over the entire surface, and the temperature gradient increases at 10° C./mm or more in the direction from the front surface to the back surface, which is the surface opposite to the front surface, to obtain a sintered body;
and thereby obtain a sputtering target material having a surface (sputtering surface) exposed to the plasma with a diameter of 3 inches or more.

(Appendix 16)
According to yet another aspect of the present disclosure,
A method for producing a sputtering target material made of a sintered body of an alkali niobium oxide having a perovskite structure, the method comprising the steps of:
(a) mixing a powder made of a compound containing potassium and niobium with a powder made of a compound containing sodium and niobium in a predetermined ratio to obtain a mixture;
(b) applying a predetermined pressure to the mixture to form a molded body having a diameter of 3 inches or more;
(c) heating and firing the molded body for 1 hour to 5 hours under conditions in which the temperature within the front surface, which is the surface that will be exposed to plasma when performing a film formation process by sputtering (the surface that will be the sputtered surface), is 800° C. or more and 1150° C. or less over the entire surface, and the temperature gradient increases at 10° C./mm or more in the direction from the front surface to the back surface, which is the surface opposite to the front surface, to obtain a sintered body;
and thereby obtain a sputtering target material having a surface (sputtering surface) exposed to the plasma with a diameter of 3 inches or more.

(Appendix 17)
The method according to claim 15 or 16, preferably comprising:
(b) and (c) are carried out simultaneously, i.e. (c) is carried out while (b) is being carried out.

(Appendix 18)
The method according to any one of appendices 15 to 17, preferably comprising:
After (a) and before (b),
(d) heating the mixture at a temperature lower than the heating temperature of the molded body in (c) to calcinate it;
(e) pulverizing the mixture after the calcination;
In step (b), a predetermined pressure is applied to the mixture that has been calcined and then pulverized, and the mixture is molded to obtain the molded body.

(Appendix 19)
The method according to any one of appendixes 15 to 18, preferably comprising:
(c), followed by
(f) A step of heating the sintered body at a predetermined temperature is further carried out.

1 Substrate 3 Piezoelectric film (KNN film)
10 Piezoelectric laminate 100 Target material 101 Sputtering surface

Claims (5)

A sputtering target material comprising a sintered body of an alkali niobium oxide having a perovskite structure, the sputtering target material comprising:
The diameter of the surface that will be exposed to plasma during the film formation process by sputtering is 3 inches or more;
when X-ray diffraction measurement is performed on the surface to be exposed to the plasma, a ratio of the intensity of the X-ray diffraction peak from the (110) plane to the intensity of the X-ray diffraction peak from the (001) plane is within a range of 0.3 to 5 inclusive over the entire inner area of the surface to be exposed to the plasma, excluding a peripheral portion within a region 5 mm from the edge;
A sputtering target material, wherein the entire inner area, excluding the peripheral portion, of a surface to be exposed to the plasma, and the entire inner area , excluding the peripheral portion of a region 5 mm from the edge, of any surface parallel to the surface to be exposed to the plasma, are composed of crystal grains having a grain size of 0.1 μm or more and 30 μm or less. 2. The sputtering target material according to claim 1, wherein the surface exposed to the plasma has a relative density of 60% or more over the entire inner area excluding the peripheral edge portion. 3. The sputtering target material according to claim 1, wherein the surface exposed to the plasma has a flexural strength of 10 MPa or more over the entire inner area excluding the peripheral edge portion. 4. The sputtering target material according to claim 1, wherein the surface to be exposed to the plasma has a volume resistivity of 1000 kΩcm or more over the entire inner area excluding the peripheral edge portion. The sputtering target material according to any one of claims 1 to 4, containing at least one of the following dopants: Li, Mg, Ca, Sr, Ba, Bi, Sb, V, In, Ta, Mo, W, Cr, Ti, Zr, Hf, Sc, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Cu, Zn, Ag, Mn, Fe, Co, Ni, Al, Si, Ge, Sn, and Ga.

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