CN102823007A - Piezoelectric thin film device, manufacturing method thereof, and piezoelectric thin film device - Google Patents

Abstract

Disclosed is a piezoelectric thin-film element which comprises a substrate and, disposed thereon, at least a lower electrode, a piezoelectric thin film represented by the general formula (NaxKyLiz)NbO3 (0=x=1, 0=y=1, 0=z=0.2, and x+y+z=1), and an upper electrode, characterized in that the piezoelectric thin film has a crystal structure constituted of a quasi-cubic, tetragonal, or orthorhombic system or has a state in which at least one of those crystal systems is coexistent, that the crystal grains have been oriented preferentially along up to two specific crystallographic axes among those axes, and that with respect to the ratio between (001) components and (111) components, as the oriented crystallographic components, the proportion by volume of the (001) components is 60-100% and the proportion by volume of the (111) components is 0-40%, when the sum of both is taken as 100%.

Description

Piezoelectric thin film device, manufacturing method thereof, and piezoelectric thin film device

technical field

The present invention relates to a piezoelectric thin film device and a piezoelectric thin film device using lithium potassium sodium niobate film or the like.

Background technique

Piezoelectric bodies are processed into various piezoelectric devices for various purposes, and are especially widely used as functional electronic components such as actuators that generate strain by applying a voltage, sensors that generate voltage from the strain of the device, and the like. Lead-based dielectrics with excellent piezoelectric characteristics have been widely used as piezoelectric materials used in actuators and sensors, especially Pb(Zr _1-x Ti _x )O ₃ -based dielectrics called PZT. Perovskite-type ferroelectrics, piezoelectrics are generally formed by sintering oxides containing various elements. In addition, due to concerns about the environment in recent years, it is hoped to develop lead-free piezoelectric bodies, and lithium potassium sodium niobate (general formula: (Na _{x Ky} Li _z )NbO ₃ (0<x<1, 0<y<1,0<z<1, x+y+z=1) (hereinafter referred to as LKNN), etc. Since this LKNN has piezoelectric properties comparable to PZT, it is expected to be a strong candidate for non-lead piezoelectric materials .In addition, LKNN includes potassium sodium niobate (KNN) film.

On the other hand, currently, with the development of miniaturization and high performance of various electronic components, there is also a strong demand for miniaturization and high performance of piezoelectric devices. However, the piezoelectric material produced by the production method centered on the sintering method of the conventional production method, especially when the thickness is 10 μm or less, is close to the size of the crystal grains constituting the material, and the influence of the size cannot be ignored. Thus, there arises a problem that deviation or deterioration of characteristics becomes conspicuous. In order to avoid this problem, in recent years, a method of forming a piezoelectric thin film using thin film technology or the like instead of the sintering method has been studied.

Recently, PZT thin films formed by RF sputtering are actually used as drivers for high-definition, high-speed inkjet printheads and small and low-cost gyro sensors (see, for example, Patent Document 1 and Non-Patent Document 1). In addition, a piezoelectric thin film device using a lead-free LKNN piezoelectric thin film has also been proposed (for example, refer to Patent Document 2).

prior art literature

patent documents

Patent Document 1: Japanese Patent Application Laid-Open No. H10-286953

Patent Document 2: Japanese Patent Laid-Open No. 2007-19302

non-patent literature

Non-Patent Document 1: High Performance and Advanced Application Technology of Piezoelectric Materials (High Performance and Advanced Application Technology of Piezoelectric Materials) edited by Nakamura Nakamura (Science & technology (サイエンス & Technology) published in 2007)

Contents of the invention

The problem to be solved by the invention

By forming a lead-free piezoelectric thin film as a piezoelectric thin film, it is possible to manufacture a head for a high-definition high-speed inkjet printer or a small and low-cost gyro sensor with a small environmental burden. As a specific candidate, basic research on the thinning of LKNN is underway.

However, in the prior art (for example, Patent Document 2), the orientation and the like of the piezoelectric thin film have not been studied in detail, and a piezoelectric thin film device capable of exhibiting a piezoelectric constant cannot be realized stably.

An object of the present invention is to provide a piezoelectric thin-film device and a piezoelectric thin-film device in which piezoelectric characteristics are improved.

solutions to problems

According to one aspect of the present invention, a piezoelectric thin film device is provided, which is provided with at least a lower electrode on a substrate, and the general formula (Na _{x Ky} Li _z ) NbO ₃ (0≤x≤1, 0≤y ≤1, 0≤z≤0.2, x+y+z=1) and the piezoelectric film laminate of the upper electrode, wherein the piezoelectric film has quasi-cubic, tetragonal or orthorhombic Crystal structure of crystal, or at least one of these said crystal structures coexists in a state where some specific axes below 2 axes are preferentially oriented among their crystal axes, and as a component of said oriented crystal axes, in In the ratio of (001) component and (111) component, when the total of the two is 100%, the volume fraction of (001) component is in the range of 60% or more and 100% or less, and the volume fraction of (111) component In the range of 0% or more and 40% or less.

In this case, it is particularly preferable that the volume fraction of the (001) component is in the range of 70% to 100% with high crystallinity, and the volume fraction of the (111) component is in the range of 0% to 30%.

In addition, the piezoelectric film is preferably in a state where the (001) component and the (111) component coexist, and the volume fraction of the (111) component is more preferably greater than 1%.

In addition, it is preferable that the piezoelectric thin film has an aggregate structure composed of particles of a columnar structure.

In addition, a part of the piezoelectric thin film may contain any of a crystalline layer of ABO ₃ , an amorphous layer of ABO ₃ , or a mixed layer of crystalline and amorphous ABO ₃ .

Among them, A is one or more elements selected from Li, Na, K, La, Sr, Nd, Ba and Bi, and B is selected from Zr, Ti, Mn, Mg, Nb, Sn, Sb, Ta and In One or more elements in , O is oxygen.

In addition, the piezoelectric thin film may be strained in a direction parallel to the substrate surface.

In addition, the strain may be a strain in a state of tensile stress or a strain in a state of compressive stress in a direction parallel to the substrate surface. In addition, the piezoelectric thin film may be in an unstrained state with no internal stress.

In addition, the piezoelectric thin film may have non-uniform strain in a direction perpendicular to the substrate surface, in a direction parallel to it, or in both directions.

In addition, the lower electrode layer is preferably Pt or an alloy mainly composed of Pt, or an electrode layer of a laminated structure including these electrode layers mainly composed of Pt.

In addition, the lower electrode layer may be an electrode layer of a stacked structure including layers of Ru, Ir, Sn, In, oxides thereof, and compounds formed with elements contained in the piezoelectric thin film.

In addition, the upper electrode layer is Pt or an alloy mainly composed of Pt, or an electrode layer of a laminated structure including these electrode layers mainly composed of Pt.

In addition, the upper electrode layer may be an electrode layer having a stacked structure of electrode layers including Ru, Ir, Sn, In, oxides thereof, and compounds formed with elements contained in the piezoelectric thin film.

In addition, the lower electrode layer is preferably a single layer or a stacked electrode layer that is preferentially oriented in a direction perpendicular to the surface of the substrate in relation to its crystal orientation.

In addition, the substrate may be one selected from Si substrates, MgO substrates, ZnO substrates, SrTiO substrates, SrRuO substrates, glass substrates, quartz glass substrates, GaAs substrates, _GaN substrates _, sapphire substrates, Ge substrates and stainless steel substrates. kind of substrate. Particularly preferably, the substrate is a Si substrate.

According to another aspect of the present invention, there is provided a piezoelectric thin film device in which the general formula (Na _x K _y Li _z ) NbO ₃ (0≤x≤1, 0≤y≤1, 0≤z ≤0.2, x+y+z=1) Piezoelectric film laminates of piezoelectric films,

Wherein, the piezoelectric thin film has a crystal structure of quasi-cubic crystal, tetragonal crystal or orthorhombic crystal, or is in a state where at least one of these crystal structures coexists, and some of their crystal axes below the 2-axis The specific axis is preferentially oriented, and the (001) component and the (111) component that are the components of the crystal axis of the preferential orientation coexist in a state, and in the ratio of the (001) component and the (111) component, the total of the two When it is 100%, the volume fraction of the (001) component is in the range of more than 60% and less than 100%, and the volume fraction of the (111) component is in the range of less than 40%.

In addition, a base layer may be provided between the substrate and the piezoelectric thin film. The base layer can use LaNiO ₃ , NaNbO ₃ , or a Pt thin film preferentially oriented in (111).

In addition, according to another aspect of the present invention, there is provided a piezoelectric thin film device including the above-described piezoelectric thin film device, and voltage applying means or voltage detecting means.

The effect of the invention

According to the present invention, a piezoelectric thin film device and a piezoelectric thin film device having excellent piezoelectric characteristics can be provided.

Description of drawings

FIG. 1 is a cross-sectional view of a piezoelectric thin film device using a piezoelectric thin film according to Example 1 of the present invention.

FIG. 2 is a graph showing an example of an X-ray diffraction pattern of a 2θ/θ scan of the piezoelectric thin film device according to Example 1 of the present invention.

FIG. 3 is a diagram showing the crystal structure of the KNN piezoelectric thin film of Example 1 of the present invention.

Fig. 4 is a diagram of an experiment arrangement for measuring a pole figure of a KNN piezoelectric thin film according to Example 1 of the present invention.

5 is a characteristic diagram of the KNN piezoelectric thin film according to Example 1 of the present invention, (a) is an example of measurement results of wide-angle reciprocal lattice mapping, and (b) is a simulation example of wide-angle reciprocal lattice mapping.

Fig. 6 is a characteristic diagram of the KNN piezoelectric thin film (KNN-1) according to Example 1 of the present invention, (a) is an example of a measurement result using a two-dimensional X-ray detector, (b) is an edge in (110) diffraction X-ray reflection curves caused by (111) and (001) obtained by integral calculation in the x-axis direction.

Fig. 7 is a characteristic diagram of the KNN piezoelectric thin film (KNN-2) according to Example 1 of the present invention, (a) is an example of measurement results using a two-dimensional X-ray detector, and (b) is an edge in (110) diffraction X-ray reflection curves caused by (111) and (001) obtained by integral calculation in the x-axis direction.

8 is a characteristic diagram of Example 1 of the present invention, (a) is a stereographic diagram of a pole figure, and (b) is a diagram converted from the stereographic diagram of a pole diagram into orthogonal coordinates.

Figure 9 is the pole figure of Example 2 of the present invention, (a) a model of a (110) pole figure with a (001) orientation as a pole, and (b) a (110) pole figure with a (111) orientation as a pole model.

Fig. 10 is a graph showing the characteristics of the X-ray diffraction curve of Example 2 of the present invention, (a) is an example of fitting analysis of the measurement results of the X-ray diffraction curve shown in Fig. 6 and Fig. 7, (b) is An example of the analysis results of the volume fractions of (001) and (111) after considering the correction coefficient for the integrated intensity obtained by the fitting analysis of FIG. 10( a ).

Figure 11 is a cross-sectional view of the KNN piezoelectric thin film device of Example 3 of the present invention, (a) is a schematic diagram of a highly oriented film forming a KNN piezoelectric thin film, and (b) shows that the crystal grains of the highly oriented KNN piezoelectric thin film are relatively Schematic diagram of tilting on the substrate surface.

12 is a graph showing the relationship between the film-forming temperature of the KNN piezoelectric thin film formed by sputtering and the integrated intensity derived from (111) and (001) preferential orientations according to Example 4 of the present invention.

13 is a diagram showing changes in (001) orientation components and (111) orientation components with respect to film formation temperature in the sputtering film formation of the KNN piezoelectric thin film according to Example 4 of the present invention.

FIG. 14 is a diagram showing changes in internal stress with respect to film formation temperature during sputtering film formation of the KNN piezoelectric thin film according to Example 4 of the present invention.

15 shows a cross-sectional view of crystal grains of each preferred orientation with a certain tilt angle relative to the substrate surface of the KNN piezoelectric thin film in which (001) and (111) preferred orientations coexist in Example 4 of the present invention.

FIG. 16 is a graph showing the relationship between the integral intensity derived from the (111) preferential orientation of the piezoelectric film and the piezoelectric constant in the piezoelectric film device using the piezoelectric film of Example 5 of the present invention.

17 is a graph showing the relationship between the volume fraction of the (111) orientation component of the piezoelectric film and the piezoelectric constant in a piezoelectric film device using the piezoelectric film of Example 5 of the present invention.

18 is a graph showing the relationship between the volume fraction of the (001) orientation component of the piezoelectric film and the piezoelectric constant in a piezoelectric film device using the piezoelectric film of the present invention formed in Example 5 of the present invention.

Fig. 19 is a schematic configuration diagram of an RF sputtering apparatus for fabricating a piezoelectric thin film device using the piezoelectric thin film according to Example 3 of the present invention.

Fig. 20 shows the deviation of the volume fraction of the (111) orientation component of the piezoelectric film and the piezoelectric constant in the wafer plane ( %) relationship diagram.

Fig. 21 is a schematic configuration diagram of a piezoelectric thin film device according to an embodiment of the present invention.

Fig. 22 is a schematic cross-sectional view of a filter device using the piezoelectric thin film of the present invention.

Detailed ways

Embodiments of the piezoelectric thin film device according to the present invention will be described below.

[summary of embodiment]

The inventors of the present invention realized that a piezoelectric film exhibiting a piezoelectric constant can be realized by quantitatively and precisely controlling crystal orientation, which has not been studied in the prior art, for a non-lead-based piezoelectric thin film located at the backbone of a piezoelectric device. Thin film devices and piezoelectric devices.

If the crystal orientation of the piezoelectric thin film is not managed and controlled, the piezoelectric constant cannot be obtained, and since the crystal orientation varies depending on the film-forming position, the piezoelectric constant is not uniform within the device.

According to the embodiment of the present invention, the (001) crystal axis of the preferential orientation of the piezoelectric film is adjusted to The volume fractions of the and (111) components (component ratios of crystal orientation) are respectively set within predetermined ranges, whereby a piezoelectric thin-film device with high piezoelectric characteristics and a method for manufacturing the same can be realized.

[A Basic Structure of Piezoelectric Thin Film Devices]

The piezoelectric thin film device of this embodiment has a laminated structure consisting of: a substrate; an oxide film formed on the surface of the substrate; a lower electrode layer formed on the oxide film; and a lower electrode layer formed on the lower electrode layer. A piezoelectric film; an upper electrode layer formed on the piezoelectric film.

The piezoelectric film is an ABO ₃ -type oxide with a perovskite structure, and its composition is: A position is one or more elements selected from Li, Na, K, La, Sr, Nd, Ba and Bi, and B The position is one or more elements selected from Zr, Ti, Mn, Mg, Nb, Sn, Sb, Ta, and In, and O is oxygen.

The substrate can be any one selected from Si substrates, MgO substrates, ZnO substrates, SrTiO substrates, SrRuO substrates, glass substrates, quartz glass substrates, GaAs substrates, _GaN substrates _, sapphire substrates, Ge substrates, stainless steel substrates, etc. 1 substrate. In particular, an Si substrate that is inexpensive and industrially practical is desired.

The oxide film formed on the surface of the substrate includes a thermal oxide film formed by thermal oxidation, a Si oxide film formed by CVD (Chemical Vapor Deposition), and the like. In addition, without forming the oxide film, a lower electrode layer such as a Pt electrode may be directly formed on an oxide substrate such as a quartz glass (SiO ₂ ), MgO, SrTiO ₃ , or SrRuO ₃ substrate.

The lower electrode layer is preferably an electrode layer composed of Pt or an alloy containing Pt as a main component, or an electrode layer including an electrode layer formed by laminating them. In addition, it is preferable that the lower electrode layer is formed in the (111) plane orientation, and between the substrate and the electrode layer composed of Pt or an alloy containing Pt as the main component, an electrode for improving the adhesion with the substrate may be provided. the adhesive layer. The (111) plane-oriented Pt thin film functions as a base layer for the piezoelectric thin film.

It can also be that the ABO ₃ -type oxide used as the piezoelectric film is potassium sodium niobate, lithium potassium sodium niobate (hereinafter referred to as LKNN), and the general formula (Na _x K _y Li _z )NbO ₃ (0≤x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 0.2, x + y + z = 1) represented by the perovskite-type oxide as the main phase of the piezoelectric film. The LKNN film can also be doped with a predetermined amount of Ta or V, etc. The piezoelectric thin film can be formed using RF sputtering, ion beam sputtering, CVD, or the like. In this embodiment, the RF sputtering method is used.

[Crystal Orientation Control According to Embodiment]

Regarding the crystal orientation of the LKNN film, it has not been analyzed in detail and accurately controlled based on it. That is, the crystal orientation of the piezoelectric thin film is still unclear: whether it is a random orientation state; or whether only a certain 1-axis is preferentially oriented in the direction perpendicular to the Si substrate surface; or whether a specific 2-axis Or at what ratio are the two or more axes preferentially oriented? In other words, regarding the crystal orientation, which is one of the factors determining the characteristics of the piezoelectric film, it is impossible to produce the piezoelectric film based on only qualitative evaluation results without accurate quantification for finding small changes. Good reproduction of the desired piezoelectric constant.

Actually, the piezoelectric characteristics of the LKNN film exhibiting this (001) preferential orientation state vary depending on the film-forming position or each production batch. The reason for this is that the (110) orientation, (111) orientation, and (210) orientation including the (001) orientation were not analyzed in detail because the subtle changes in the (001) orientation of the piezoelectric film could not be found. , so it is difficult to strictly control the orientation of the above-mentioned individual crystal planes to grow the crystal.

For example, by increasing the input power (Power) during sputtering film formation, due to the impact of energy particles such as Ar ions, a large number of sputtered particles are forced to penetrate into the substrate along a certain direction, resulting in the formation of a gap with the substrate surface. A piezoelectric thin film of polycrystalline grains with a large inclination in the normal direction. At this time, by using the known simple X-ray diffraction method called 2θ/θ scanning, it can be confirmed that the crystal orientation is approximately (001) preferential orientation. Since all other positions are fixed, the actual crystal orientation cannot be evaluated. As a result, since the coexistence state of other crystal orientation components was not clear or the measurement results showing the orientation were not obtained, the deterioration of the piezoelectric properties caused by the structure could not be grasped. Stable production of piezoelectric films.

Controlling the crystal orientation of Pt thin films and piezoelectric thin films based on the above insights.

[Crystal Orientation of Lower Electrode Layer]

(Crystal orientation of Pt thin film)

Therefore, first, in order to strictly manage and control the crystal orientation of the LKNN film, the film-forming temperature, film-forming gas and Optimization of vacuum degree, etc. As the film-forming conditions, the film-forming temperature was first studied, and as the condition for forming (111) preferential orientation, it was found that the film-forming range of 100-500°C was the most suitable temperature range. As the film-forming gas, Ar gas, a mixed gas of Ar and O ₂ , or a gas mixed with at least one inert gas such as He, Ne, Kr, and N ₂ can be used.

In addition, in order to improve the smoothness of the Pt surface, a Ti layer with a smooth surface of 0.1 nm to several nm is formed to improve the uniformity of the Ti layer as an adhesive layer with the substrate. By forming a Pt electrode on the top of the Ti layer, it is possible to The surface roughness of the Pt lower electrode is reduced and controlled to a size of a few nm.

Furthermore, the film thickness of the Pt lower electrode layer can be precisely controlled, the surface unevenness of the Pt lower electrode layer can be reduced, and a polycrystalline Pt lower electrode layer can also be formed by controlling the crystal particle size of the Pt lower electrode layer to be uniform.

The lower electrode layer is related to its crystal orientation, and is a single layer or a stacked electrode layer that is preferentially oriented in a direction perpendicular to the substrate surface. The lower electrode layer may be made of not only Pt but also an alloy mainly composed of Pt, or a thin film (Pt thin film) of Pt or mainly composed of Pt. In addition, a layer of Au, Ru, Ir, Sn, In, oxides thereof, and compounds of elements contained in the piezoelectric thin film may be included. In these cases, by optimizing the film-forming temperature and film-forming gas similarly to the case of the Pt thin film, the crystallinity of the lower electrode thin film located under the LKNN thin film can be stably realized. The fabrication conditions cause the state of crystal orientation of the piezoelectric thin film to change. In addition, the internal stress (strain) of the piezoelectric film changes to compressive stress or tensile stress. Sometimes it is a stress-free state, that is, a state without strain.

In addition, as candidates for substrates for forming these lower electrode thin films, crystalline or amorphous materials such as Si, MgO, ZnO, SrTiO ₃ , SrRuO ₃ , glass, quartz glass, GaAs, GaN, sapphire, Ge, stainless steel, or For their composites, etc., for devices in which an adhesive layer and a lower electrode layer are formed on these substrates, and an LKNN film is formed on the upper part of the adhesive layer and the lower electrode layer, the crystal orientation of the LKNN film is compared in detail. It is recommended to select a substrate that can strictly control the preferential orientation.

[Crystal Orientation of Piezoelectric Film]

In addition, in order to more reliably realize the preferential orientation of the LKNN film, in the above-mentioned embodiment, by seeking the film-forming temperature of the LKNN film itself, the type of the sputtering operating gas, the operating gas pressure, the degree of vacuum, the input power, and By optimizing the heat treatment after film formation, the conditions for producing the piezoelectric thin film having crystal orientation to improve the piezoelectric characteristics were found, and the objective was achieved. By adapting these conditions to each device or each environment, and carefully and rigorously studying production conditions, evaluation, and management methods, etc., it is possible to reproduce the preferred orientation of (001) preference, (111) preference, or both coexistence. Oriented quasi-cubic LKNN films.

In order to strictly control the preferred orientation of the polycrystalline or epitaxially grown single crystal LKNN film itself, for example, it is precisely set to keep the film formation temperature constant, so that the (001) orientation component or (111) orientation component falls into a certain within the ratio range. As the heating means at the time of actual film formation, heat radiation by an infrared lamp or heat conduction by heating with a heater via a heat conduction plate is used, and the setting falls within a temperature range for forming an optimum crystal orientation component ratio.

In addition, in accordance with the above conditions, by determining the sputtering input power, the pressure or the flow rate of the gas introduced into the film forming device to the most appropriate value, and selecting an appropriate gas type, the following effect can be expected: it is possible to obtain a strict Various orientation components including (001) orientation and (111) orientation as the crystal structure are controlled to obtain a stable and reproducible LKNN film exhibiting a piezoelectric constant.

Specifically, sputtering film formation is performed using a gas mixture of Ar and O ₂ or a gas mixed with at least one inert gas such as Ar gas, He, Ne, Kr, and N ₂ . For forming the LKNN piezoelectric thin film, a (Na _{x Ky} Li _z )NbO ₃ (0≤x≤1.0, 0≤y≤1.0, 0≤z≤0.2) ceramic target can be used.

In addition, the same effects can be expected by changing the density of the sputtering target material from the above-mentioned situation.

In addition, after film formation, heat treatment may be performed in oxygen or inert gas or a mixed gas of the two, or in air or vacuum to control the internal stress of the piezoelectric thin film.

The LKNN film thus obtained has an aggregated structure composed of columnar structured crystal grains. In addition, when the lower electrode layer is formed with (111) plane orientation, the piezoelectric thin film layer is formed by preferentially oriented in a predetermined direction with respect to the lower electrode layer.

In addition, preferably, the piezoelectric film layer is in a state where at least one of (001) preferentially oriented crystal grains, (110) preferentially oriented crystal grains and (111) preferentially oriented crystal grains coexists. By realizing such a state of crystal orientation, internal stress can be controlled to improve piezoelectric characteristics.

The piezoelectric thin film constituting the piezoelectric thin film device of Example 1 has a quasi-cubic, tetragonal, or orthorhombic crystal structure, or is in a state where at least one of these crystal structures coexists. In addition, piezoelectric thin films are preferentially oriented to some specific axes below 2 axes among their crystal axes. In addition, the piezoelectric thin film is formed such that the volume fraction of the (001) component is the ratio of the (001) component to the (111) component when the total of the two is 100% as a component of the crystal axis of the orientation. In the range of 60 to 100%, the volume fraction of the (111) component is in the range of 0 to 40%. By forming such a configuration, it is possible to prevent the piezoelectric constant from being lowered due to random crystal orientation or increased internal strain. (Figure 16 to Figure 18 of Example 5)

For the above-mentioned piezoelectric film in which the volume fraction of the (001) component is in the range of 60 to 100%, or the volume fraction of the (111) component is in the range of 0 to 40%, it is possible to control the piezoelectric film The film-forming conditions of the thin film are realized, for example, controlling the film-forming temperature. (Figure 13 of Example 4)

[Strain of Piezoelectric Film]

By controlling the composition ratio (volume fraction) of the crystal orientation of the piezoelectric thin film, it is possible to have a strain in a state of tensile stress in a direction parallel to the substrate surface, or to have a compressive state in a direction parallel to the substrate surface. The strain of the stress state. In addition, by controlling the volume fraction, the piezoelectric thin film can be brought into an unstrained state with no internal stress. In addition, by controlling the volume fraction, the piezoelectric thin film can have non-uniform strain in the direction perpendicular to or parallel to the substrate surface, or in both directions. By controlling the volume fraction of the piezoelectric film in this way, the internal stress of the piezoelectric film can be controlled, and a piezoelectric film having a desired internal stress can be obtained. (Figure 13 and Figure 14 of Example 4)

[Piezoelectric film device]

For the substrate with the piezoelectric thin film of the above-mentioned embodiment, by forming the upper electrode layer 15 on the top of the piezoelectric thin film layer, a piezoelectric thin film device exhibiting a high piezoelectric constant can be produced, and then by making the piezoelectric thin film device By processing it into a predetermined shape and installing a voltage applying unit (voltage detecting unit) 16, piezoelectric thin film devices such as various actuators and sensors can be fabricated. (Figure 21)

In addition, in the substrate with the piezoelectric thin film of the above-mentioned embodiment, by forming the pattern electrode 51 having a predetermined pattern on the upper portion of the piezoelectric thin film, a filter device utilizing surface acoustic waves can be produced. (Figure 22)

In addition, in the filter device using surface acoustic waves, the lower electrode (Pt thin film) mainly functions as a base layer.

The upper electrode layer formed on the above-mentioned piezoelectric thin film, or the pattern electrode having a predetermined pattern, is preferably Pt or an alloy containing Pt as a main component, or an electrode containing these Pt-based electrodes, similarly to the lower electrode layer. The electrode layer of the laminated structure of the layer. Alternatively, the electrode layer may have a stacked structure of electrode layers including Ru, Ir, Sn, In, oxides thereof, and compounds formed with elements contained in the piezoelectric thin film.

[Effect of Embodiment]

The present invention has one or more effects listed below.

(1) If one or more embodiments of the present invention are adopted, the LKNN piezoelectric thin film has a quasi-cubic, tetragonal or orthorhombic crystal structure, or a state in which at least one of these crystal structures coexists, and in their Among the crystal axes, some specific axes below the 2 axes are preferentially oriented, and as the components of the oriented crystal axes, in the ratio of (001) component and (111) component, when the total of the two is 100% , by making the volume fraction of the (001) component in the range of 60 to 100%, and the volume fraction of the (111) component in the range of 0 to 40%, it is possible to prevent the decrease in piezoelectric constant.

(2) In addition, if one or more embodiments of the present invention are adopted, it is possible to accurately The degree of crystal orientation of the piezoelectric thin film thus obtained is accurately quantified, and the atomic-level structure of the piezoelectric thin film is strictly controlled to improve piezoelectric characteristics. As a result, a high-performance piezoelectric thin-film device can be realized, and the manufacturing yield of the device can be improved.

(3) In addition, according to one or more embodiments of the present invention, internal stress can be controlled to improve piezoelectric characteristics by co-existing (001) preferentially oriented crystal grains and (111) preferentially oriented crystal grains. Furthermore, by relieving the stress, film peeling can be suppressed, so that a piezoelectric thin film having improved mechanical strength and excellent processability can be provided.

(4) In addition, if one or more embodiments of the present invention are adopted, as the lower electrode of the above-mentioned piezoelectric thin film device, by using a Pt electrode whose crystal orientation is controlled, or a Pt alloy, or Ru, Ir and its oxide Pt, a compound formed of elements contained in the piezoelectric thin film, can control the crystal orientation of the piezoelectric thin film formed on the upper part with high precision, and improve the environmental resistance of the device.

(5) In addition, if one or more embodiments of the present invention are adopted, as the substrate, Si and MgO substrates, ZnO substrates, SrTiO ₃ substrates, SrRuO ₃ substrates, glass substrates, quartz glass substrates, GaAs substrates, and GaN substrates are used. , sapphire substrate, Ge substrate, stainless steel substrate, etc., can control the crystal orientation of the piezoelectric thin film formed on it.

(6) In addition, according to one or more embodiments of the present invention, according to this embodiment, a piezoelectric thin film with good piezoelectric characteristics can be realized, and a high-quality piezoelectric thin-film device can be obtained with a high yield.

(7) In addition, according to one or more embodiments of the present invention, since the piezoelectric thin film device is equipped with a thin film that does not use lead, by mounting the piezoelectric thin film device, it is possible to realize a small motor with reduced environmental load and high performance. , sensors, and drivers and other small system devices, such as MEMS (Micro Electro Mechanical System, MicroElectro Mechanical System) and so on. A filter device utilizing surface elastic waves and having good filter characteristics can be realized.

(8) In addition, if one or more embodiments of the present invention are adopted, when using a Si substrate to make a driver or a sensor, for the non-lead-based piezoelectric film located at the backbone of the piezoelectric device, due to the quantitative and precise control and manage its crystal orientation, so it is possible to stably produce non-lead-based devices that have a long life and exhibit a high piezoelectric constant. In addition, in the device, since the crystal orientation does not vary depending on the location, the piezoelectric constant of the piezoelectric thin film formed on the substrate is uniform, thereby improving the yield in manufacturing.

(9) In addition, according to one or more embodiments of the present invention, it is possible to control the orientation using LKNN or the like to improve the piezoelectric characteristics.

(10) In addition, if one or more embodiments of the present invention are adopted, by stably controlling the crystal orientation of these piezoelectric thin films, the piezoelectric properties of piezoelectric thin film devices and piezoelectric thin film devices can be improved or stabilized, Therefore, a high-performance microdevice can be provided at low cost.

(11) In addition, if one or more embodiments of the present invention are adopted, according to the present invention, it is possible to obtain a piezoelectric thin-film device or a piezoelectric thin-film device having excellent piezoelectric characteristics in which the atomic-level structure of a piezoelectric thin film such as LKNN is controlled with high precision. thin film device.

Example 1

Embodiments of the present invention are described below.

(Example 1)

Use Figure 1 to Figure 8 to explain.

FIG. 1 is a cross-sectional view showing the outline of a substrate with a piezoelectric thin film. In this embodiment, an adhesive layer 2 is formed on a Si substrate 1 having an oxide film, and a lower electrode layer 3 and a piezoelectric thin film layer 4 of KNN with a perovskite structure are sequentially formed on the upper portion of the adhesive layer 2. Piezoelectric thin film devices.

At this time, the crystal system of the piezoelectric film layer 4 is quasi-cubic, tetragonal or orthorhombic, and at least a part of the piezoelectric film layer 4 may be ABO ₃ crystal or amorphous or a mixture of both. Here, A is one or more elements selected from Li, Na, K, La, Sr, Nd, Ba, and Bi, and B is an element selected from Zr, Ti, Mn, Mg, Nb, Sn, Sb, Ta, and One or more elements in In, O is oxygen. Pb-containing piezoelectric material may be used as the A-site piezoelectric material, but a Pb-free piezoelectric thin film is required from an environmental point of view.

As the lower electrode layer 3, a Pt thin film or an Au thin film can be used. Alternatively, it may be a Pt alloy, an alloy containing Ir or Ru, or a laminated structure thereof.

The manufacturing method of the piezoelectric thin film device will be described below. First, a thermally oxidized film was formed on the surface of a 4-inch circular Si substrate 1, and the lower electrode layer 3 was formed on the thermally oxidized film. Among them, the thermal oxide film is provided with a thickness of 150 nm.

The lower electrode layer 3 is composed of a Ti film with a thickness of 2 nm formed as the adhesive layer 2 and a Pt thin film with a thickness of 100 nm formed on the Ti film as an electrode layer. This electrode layer is formed using a sputtering method. A metal target was used as the sputtering target 12 shown in FIG. 19 , the sputtering input power during film formation was 100 W, and 100% Ar gas was used as the sputtering gas. In addition, film formation was performed at a substrate temperature of 350° C. to form a thin film made of Pt as a polycrystalline thin film.

Next, a KNN thin film was formed as the piezoelectric thin film layer 4 on the lower electrode layer. The KNN thin film was also formed using the sputtering method. The substrate temperature is 700 ℃ ~ 730 ℃, and the plasma condition generated by the 5:5 mixed gas of Ar and O ₂ is carried out by sputtering to form a KNN thin film. In addition, as the target, a (Na _{x Ky} Li _z )NbO ₃ (x=0.5, y=0.5, z=0) ceramic target was used. Film formation was performed until the film thickness became 3 μm. In addition, heat treatment is performed in air after film formation. However, a self-revolving furnace was used for sputtering, and the distance between the substrate and the target during sputtering (hereinafter, distance between TS) was set to 50 mm.

The cross-sectional shape of the KNN film produced in this way was observed using a scanning electron microscope or the like, and its structure was composed of a columnar structure. As a result of investigating the crystal structure using a conventional X-ray diffraction apparatus, it was confirmed that the Pt thin film of Example 1 formed by heating the substrate was formed perpendicular to the substrate surface, as shown in the X-ray diffraction pattern (2θ/θ scanning measurement) in FIG. 2 . The (111) plane oriented film.

A KNN film was formed on the (111) preferentially oriented Pt film. As a result, it was confirmed that the fabricated KNN film was a polycrystalline film having a quasi-cubic perovskite crystal structure as shown in FIG. 3 . In addition, as can be seen from the X-ray diffraction pattern in Figure 2, since only (001), (002), and (003) diffraction peaks can be confirmed, it can be predicted that the KNN piezoelectric film is basically (001) preferentially oriented.

In Example 1, the pole figure (Pole figure) measurement was performed for the KNN piezoelectric thin film in which the crystal orientation was intentionally controlled, in order to evaluate the orientation of the KNN thin film in detail and accurately. A pole figure is a diagram of the extension of the pole of a specific crystal lattice plane projected three-dimensionally, and is an analysis method capable of evaluating the orientation state of a polycrystal in detail. For details, please refer to Citation 1 (Edited by Rigaku Denki Co., Ltd., Introduction to X-ray Diffraction (X-ray Diffraction の手引き), Revised 4th Edition, (Rigaku Denki Co., Ltd., 1986)), Citation 2 (Karity Denki, New Edition X Ray Diffraction Essentials, (Agne, 1980)).

The determination of the polar figures allows for a clear definition of the preferred orientations. For substances (including thin films) composed of polycrystals, when each crystal particle is in a state of "preferential orientation" in a certain direction, in the determination of the pole figure of the substance, it is certain to be able to find a spot or ring at a specific angular position The local distribution of X-ray reflections like Debye rings.

On the other hand, when each crystal grain of the substance is in an arbitrary direction, in other words, when it is "randomly oriented", it is impossible to find spot-shaped or ring-shaped X-ray reflections in the pole figure. According to the presence or absence of these X-ray reflections, it can be judged whether the piezoelectric thin film is preferentially oriented, and it is defined as the existence of the preferential orientation.

In the structural analysis of the piezoelectric thin-film device in Example 1, a high-output X-ray diffraction device equipped with a two-dimensional detector with a large-area X-ray detection range was used. "D8 DISCOVER with HiStar, VANTEC2000" manufactured by Bruker AXS (Trademark)". In this example, the pole figure with (110) of the KNN thin film as the pole was measured.

（β）轴，随之需要长时间测定。然而，由于本实施例中使用了大面积的二维检测器（D8 DISCOVER withHi Star,VANTEC2000（注册商标）），因而几乎不需要伴随所述2轴的扫描的零维检测器的动作，所以能够短时间地测定。因此，可大量且迅速地取得在各种条件下制作的KNN薄膜的晶体取向性的分析结果，从而实现本实施例的具有晶体结构的KNN压电薄膜。FIG. 4 shows a schematic diagram of a measurement arrangement of pole figures performed in this example. This is a method known as the Schultz reflex method. In the previous pole figure measurement, since most of the X-ray detectors used are zero-dimensional, it is necessary to scan the χ(α) axis and

(β) axis, and it takes a long time to measure accordingly. However, since a large-area two-dimensional detector (D8 DISCOVER with Hi Star, VANTEC2000 (registered trademark)) is used in this embodiment, the operation of the zero-dimensional detector accompanying the scanning of the two axes is hardly required, so it is possible to measured in a short time. Therefore, a large number of analysis results of the crystal orientation of KNN thin films produced under various conditions can be quickly obtained, and the KNN piezoelectric thin film having a crystal structure of this embodiment can be realized.

FIG. 5 shows the analysis results of the wide-angle reciprocal lattice point diagram in the piezoelectric film of Example 1. FIG. The horizontal axis is the X-ray diffraction angle of 2θ/θ, and the vertical axis is the x-axis in the direction perpendicular to the diffraction angle axis (2θ/θ) shown in FIG. 4 . In addition, the bar graph on the right reflects the intensity of X-ray reflection in black and white grayscale, which serves as a reference for the intensity of X-ray reflection on the same graph.

Figure 5(a) shows the actual analysis results of KNN, and Figure 5(b) shows the results of the reciprocal lattice point simulation in (001)/(111)-oriented KNN films for comparison. ○ indicates diffracted X-rays from (001)-oriented KNN, ● indicates diffracted X-rays from (111)-oriented KNN. The simulation program used at this time is SMAP/for Cross Sectional XRD-RSM provided by Bruker AXS.

Comparing the two figures, it can be seen that the (001) orientation and (111) orientation can be confirmed in the range of 15° to 75° centered on χ=45° under the 2θ/θ equivalent to 110 diffraction of about 32° of two 110 diffractions. This analysis result suggests that (001) orientation and (111) orientation coexist in this piezoelectric thin film. Since the X-ray diffraction curve in the x-axis direction cannot be measured only by the conventional 2θ/θ scanning X-ray diffraction measurement, the analysis result of this embodiment is an example of a new structural parameter related to improving the properties of the piezoelectric film.

FIG. 6 shows the results of X-ray diffraction measurement of the actual piezoelectric thin film in Example 1. FIG. Figure 6(a) shows the diffracted X-rays from the sample KNN-1 recorded with an X-ray two-dimensional detector, with black spot-like patterns drawn in arcs corresponding to the reflection of the diffracted X-rays. In addition, the direction in which the arc is drawn corresponds to the aforementioned x-axis direction, and the arrow in the normal direction to the arc corresponds to the 2θ/θ direction. When focusing on diffracted X-rays at a 2θ/θ of approximately 32°, it is observed that two X-ray reflected spots overlap. At this time, it can be seen that the inversion on the left is the X-ray reflection caused by the KNN (111) orientation, and the spot on the right is the X-ray reflection caused by the KNN (001) orientation.

Based on these results, by setting the integration range in a sector shape, the respective intensities of the reflected X-ray spectra caused by the (001) orientation and the (111) orientation can be displayed. The integration in this embodiment is performed within the range of 17.5° to 72.5° on the x-axis, and the integration along the 2θ/θ axis is performed within the range of 31.4° to 32.4°.

Figure 6(b) shows the integration results. The horizontal axis is the x-axis, and the vertical axis is the X-ray diffraction intensity obtained based on the integration conditions described above. The respective intensities of the reflected X-ray spectra caused by (001) orientation and (111) orientation can be seen.

FIG. 7 shows the results of X-ray diffraction measurement of the actual piezoelectric thin film in Example 1 with respect to another sample KNN-2 thin film. Similar to FIG. 6 , it can be seen that two spectra due to orientation are found. However, it can be seen that the X-ray intensity caused by the (001) orientation and the X-ray intensity caused by the (111) orientation are different from the results shown in Figure 6, especially the X-ray intensity caused by the (001) orientation is different from that caused by The intensity ratio of the X-ray intensity caused by (111) orientation is obviously different.

In this example, the curves of FIG. 6( b ) and FIG. 7( b ) are calculated using a fitting function, and the X-ray reflection intensity and its ratio are quantified.

（β）轴。在极径方向的χ轴上，在距离中心的角度为45°附近观察到相当于（001）的衍射面的环（德拜环）。另一方面，在35.3°附近观察到相当于（111）的衍射面的德拜环。尤其可知，每个德拜环偏离同心圆的配置，而是距中心略微偏心。结果确认在圆周方向的

轴上，在0°至约80°以及约330°至360°的范围内，由（001）取向引起的反射X射线与由（111）取向引起的反射X射线重叠。此时，准确计算各个取向成分的强度非常困难。FIG. 8 shows an example of measurement results of the (110) pole figure of the piezoelectric thin film in Example 1. FIG. Here, as shown in Figure 8(a), the polar radial direction is set as the χ(α) axis, and the circumferential direction is set as

(β) axis. On the χ-axis in the polar radial direction, a ring (Debye ring) corresponding to a diffraction surface of (001) was observed at an angle of 45° from the center. On the other hand, a Debye ring corresponding to a diffraction plane of (111) was observed around 35.3°. In particular, it can be seen that each Debye ring deviates from the configuration of concentric circles, but is slightly eccentric from the center. The results confirm that in the circumferential direction the

On-axis, in the range of 0° to about 80° and about 330° to 360°, the reflected X-rays caused by the (001) orientation overlap with the reflected X-rays caused by the (111) orientation. In this case, it is very difficult to accurately calculate the intensity of each orientation component.

轴）。另外，最合适的轴不明确时，需要基于极图的测定结果，确定由（001）取向引起的反射谱与由（111）取向引起的反射谱明确分离的

轴。为此，重要的是准确把握各个德拜环的偏心状态，找到相当于（001）取向方向与（111）取向方向之间的角度δ为最大时的

轴的角度。Therefore, in order to solve this problem, it is necessary to consider the position of the sample in the in-plane rotation direction (here, equivalent to

axis). Additionally, the most appropriate When the axis is not clear, it is necessary to determine the clear separation of the reflection spectrum caused by the (001) orientation and the reflection spectrum caused by the (111) orientation based on the measurement results of the pole figure.

axis. For this reason, it is important to accurately grasp the eccentric state of each Debye ring, and find the angle δ corresponding to the maximum angle δ between the (001) orientation direction and the (111) orientation direction.

The angle of the axis.

（β）轴的极座标系的图转换为横轴设为χ轴、纵轴设为

轴的正交坐标系的图。图8（b）显示转换为正交坐标系后的

的图。基于图8（b），对于δ的角度为最大时的

轴位置（图8（b）中的虚线）上的X射线反射曲线进行各取向成分的积分强度计算。另外，此处得到的积分强度通过使用高斯（Gauss）函数、洛伦兹（Lorentz）函数及作为它们的卷积函数的Pesudo Voight函数、皮尔生（Pearson）函数和Split Pesudo Voight函数等分布函数的谱拟合分析而求出。In this embodiment, in order to obtain this δ accurately, the polar radial direction shown in FIG.

(β) The graph of the polar coordinate system of the axis is converted to the horizontal axis as the χ axis and the vertical axis as

A plot of an orthogonal coordinate system for the axes. Figure 8(b) shows the transformed into an orthogonal coordinate system

diagram. Based on Figure 8(b), the angle for δ is maximum when the

The integrated intensity calculation of each orientation component is performed on the X-ray reflectance curve at the axial position (dashed line in Fig. 8(b)). In addition, the integrated intensity obtained here is calculated by using distribution functions such as the Gauss function, the Lorentz function, and the Pesudo Voight function, Pearson function, and Split Pesudo Voight function as their convolution functions. obtained by spectral fitting analysis.

轴位置上的X射线反射曲线进行各取向成分的积分强度计算即可。According to the above-mentioned Example 1, it can be seen that the accurate calculation of the strength of the orientation component only needs to be the maximum angle corresponding to the angle δ between the (001) orientation direction and the (111) orientation direction.

The X-ray reflection curve at the axial position can be used to calculate the integrated intensity of each orientation component.

(Example 2)

Use Figure 9~Figure 10 to illustrate.

Next, when accurately calculating the diffraction intensity ratio of the (001) orientation component and the (111) orientation component, it is necessary to discuss the correction values of the respective X-ray diffraction intensities. For this purpose, the pole figures of (001) and (111) are investigated.

Figure 9 shows the simulation results of the pole figures. Figure 9(a) is the simulation result of the pole figure with (001) as the pole. As shown in this figure, it can be seen that the (110) diffraction of the (001) oriented KNN contributes 4 equivalent diffractions. At this time, the correction factor is considered to be 4. On the other hand, from the simulation results of the pole figure with (111) as the pole in Figure 9(b), it can be seen that the (110) diffraction of the (111)-oriented KNN contributes 3 equivalent diffractions, so the correction factor is 3 . Therefore, when the volume fraction of (001) orientation and (111) orientation calculated from the integrated intensity described in Example 1 is 1:1, the actual diffraction intensity ratio is (001):(111)=4: 3.

Next, Figure 10 shows the analysis of the (001) and (111) orientation component ratios using the measurement results shown in Figure 6 and Figure 7 shown in Example 1 for KNN-1 and KNN-2 piezoelectric films with different fabrication conditions the result of. FIG. 10( a ) is obtained by applying a fitting function to the X-ray diffraction curve shown in FIG. 6( b ). The smooth curve is the Pesudo Voight function used as the fitting function in this example. It can be seen that it is consistent with the diffraction curves caused by (111) and (100). At this time, the peak position (x-axis in this example), integrated intensity, and half-peak width of each curve were obtained. Here, since the purpose is to calculate the diffraction intensity ratio, attention is paid to the integrated intensity. Figure 10(b) shows a table summarizing the analysis results. The integrated intensity listed in Example 1 is 298 for the (111) orientation and 2282 for the (001) orientation in KNN-1.

On the other hand, as far as KNN-2 is concerned, the former is 241 and the latter is 2386. These integral calculation results are divided by the above-mentioned correction coefficient to obtain the integral intensity correction value shown in FIG. 10( b ), so as to obtain the exact diffraction intensity of each orientation component. If the sum of the (001) orientation component and (111) orientation component is set to 100% for analysis, the result is that the volume fraction of KNN-1 is (001): (111) = 85%: 15%, the volume of KNN-2 The fraction is (001): (111) = 88%: 12%, which shows that the ratio of orientation components between samples is different.

(Example 3)

Use Fig. 11, Fig. 19 to explain.

An attempt was made to fabricate the preferentially oriented KNN film involved in Example 1. As Example 3, FIG. 11 shows a schematic cross-sectional view thereof. In addition, FIG. 19 shows a schematic diagram of an RF sputtering apparatus for forming a KNN thin film. In the piezoelectric thin film device, an adhesive layer 2 is formed on a Si substrate 1 having an oxide film, and a lower electrode layer 3 and a piezoelectric thin film layer 4 of KNN having a perovskite structure are formed on the upper portion of the adhesive layer 2 . Here, the polycrystalline piezoelectric thin film has an aggregate structure in which crystal grains of each columnar structure (columnar crystal grains) are arranged approximately in a certain fixed direction.

轴转变为x-y轴呈正交轴的图时，没有看到波形曲线，而为直线状。In Example 3, when the input power is set to 100W and the center of the sputtering target 12 shown in FIG. 19 coincides with the center of the substrate 1 to form a KNN piezoelectric thin film 4, the A polycrystalline piezoelectric thin film in which the normal to the (001) crystal plane shown in 11(a) is almost in the same direction as the normal to the substrate surface. Here, columnar crystal grains 5 crystallize in a direction perpendicular to the substrate. At this time, in the measurement using the stereographic projection diagram of the polar figure, the drawn Debye rings of (001) and (111) were not found to be eccentric, and were arranged concentrically. In addition, the x-axis and

When the axis is converted to a graph in which the xy axis is perpendicular to the axis, the waveform curve is not seen, but a straight line.

Next, in this example, when the input power is set to 100W, and the center of the substrate 1 shown in FIG. The normal direction to the crystal plane of the preferentially oriented crystal grains is slightly deviated from the normal direction of the substrate surface and inclined. At this time, the columnar crystal grains 6 are crystal-grown obliquely with respect to the normal direction of the substrate surface ( FIG. 11( b )). In addition, the offset amount is appropriately determined according to the size of the substrate used and the desired inclination angle. In this embodiment using a 4-inch Si substrate, the offset is set to 10 mm.

In the stereographic projection diagram of the pole figure of this example with the offset of 10mm, two Debye rings (001) and (111) are observed in the same manner as in Figure 8(a), and they are similar to Figure 8(b) ) can also be seen to have different magnitudes. That is, each crystal plane representing (001) and (111) has a different off angle from the substrate plane. At this time, the analytical value of the amplitude of (001) is 9.9°. On the other hand, the analytical value of the magnitude of (111) is 0.52°. As a result, in the piezoelectric thin film of the present invention, the angle of the (001) crystal orientation direction is inclined by about 5° and the angle of the (111) crystal orientation direction is inclined by about 0.3° with respect to the normal direction of the substrate surface.

(Example 4)

Use Figure 12 to Figure 15 to illustrate.

This example shows the result of intentionally changing the volume fraction of (001) orientation component and (111) orientation component.

FIG. 12 shows changes in integrated intensity of diffraction due to (111) and due to (001) with respect to film-forming temperature in the sputtering film-forming method. It can be seen that the diffraction intensity caused by (001) decreases with the increase of film forming temperature. On the other hand, it can be seen that the diffraction intensity due to (111) increases as the film formation temperature increases. Next, using these results, the film-forming temperature dependence of the volume fraction in consideration of the correction coefficient shown in Example 2 is discussed.

FIG. 13 shows the change in the volume fraction of (111) and (001) orientation components with respect to the film-forming temperature of the KNN piezoelectric thin film in the sputtering film-forming method. As shown in this figure, it can be seen that within the film-forming temperature range of 550°C to 650°C, the volume fraction of (111) orientation components is basically 0, and when the temperature exceeds 650°C, the volume fraction of (111) orientation components increases with the increase of the film-forming temperature. increase with increasing temperature.

On the other hand, regarding the change of the volume fraction of the (001) orientation component with respect to the film formation temperature, it can be seen that in the range of 550°C to 650°C, the (001) orientation component is almost 100%, and almost only the (001) plane individual orientation status. In addition, it can be seen that when the temperature exceeds 650°C, the volume fraction of the (001) orientation component gradually decreases as the film-forming temperature increases. In this example, it is shown that the ratio of the (111) orientation component to the (001) orientation component can be controlled by changing the film forming temperature.

In addition, FIG. 14 shows the change of internal stress (strain) with respect to the film-forming temperature of the KNN piezoelectric thin film in the sputtering film-forming method. It can be seen that as the film forming temperature increases, the compressive stress decreases, and the state transitions to a stress-free and strain-free state. It can be seen that when the film forming temperature is raised to 700°C~750°C, the state changes from basically no strain to a slight tensile stress state. In addition, Pa is mentioned as an example of the unit of internal stress in this Example.

As long as it is compared with FIG. 13 , it can be seen that the decrease in compressive stress appears due to the increase in the volume fraction of (111). That is, it was shown that internal stress relaxation of the piezoelectric thin film can be achieved by increasing the (111) orientation component ratio of the KNN piezoelectric thin film. As a result, the internal stress of the piezoelectric thin film can be controlled by precisely controlling the composition ratio (volume fraction) of crystal orientation.

Since the piezoelectric thin film has a volume fraction of the (111) component, the stress of the piezoelectric thin film can be relaxed, and film peeling can be suppressed. As a result, a piezoelectric film having improved mechanical strength and excellent processability can be provided.

As one of the above embodiments, Fig. 15 shows a schematic cross-sectional view. It is a state where (001) preferentially oriented crystal grains ([001] axis orientation) 9 and (111) preferentially oriented crystal grains ([111] axis orientation) 10 coexist. By realizing the state of crystal orientation as shown in FIG. 15 , it is possible to control the internal stress and improve the piezoelectric characteristics. Furthermore, by relieving stress, film peeling can be suppressed, so that a piezoelectric thin film having improved mechanical strength and excellent processability can be provided.

By confirming the yield of devices that can be obtained from multiple 4-inch substrates, it was found that the yield of devices obtained from substrates with piezoelectric thin films with a (111) composition of less than 1% was less than 70%, while that obtained from substrates with Substrates with piezoelectric films with a (111) composition greater than 1% yielded devices with yields in excess of 90%.

According to the research results of the inventors, it is considered that this is caused by the variation in the piezoelectric constant within the wafer plane. The results of checking the relationship between the volume fraction of the (111) orientation component and the variation (%) of the piezoelectric constant in the wafer plane are shown in Table 1 and FIG. 20 . As shown in FIG. 20 , it can be seen that the variation in the piezoelectric constant in the wafer plane does not increase but is substantially constant even when the volume fraction of the (111) orientation component is approximately 1%. The piezoelectric constant deviation shown here is a relative standard deviation obtained by dividing the standard deviation of the piezoelectric constant measured in the 4-inch wafer plane by the average value thereof. At this time its value is about 23%. However, when the volume fraction of (111) is about 0.2%, the deviation fluctuates from 15.3% to 27.1%. Even if the volume fraction of (111) is the same, the difference in the deviation value of the piezoelectric constant between wafers is large, which causes the yield to decrease. .

[Table 1]

sample (111) volume fraction (%) Deviation of piezoelectric constant (%) Sample 1 3.6 21.4 Sample 2 3.3 24.5 Sample 3 9.9 9.3 Sample 4 12.6 9.4 Sample 5 0.1 27.1 Sample 6 0.1 25.6 Sample 7 0.1 23.9 Sample 8 0.2 15.3 Sample 9 0.2 22.7 Sample 10 9.8 16.3

(Example 5)

Use Figure 16 to Figure 18 to illustrate.

As a present example, FIG. 16 shows the variation of the piezoelectric characteristics of the KNN piezoelectric film with respect to the (111) integral intensity. The horizontal axis is the (111) integral intensity, and the vertical axis is the piezoelectric constant. Here, the piezoelectric constant when an electric field of 6.7 MV/m or 0.67 MV/m is applied is shown as an example. Wherein, the unit of the piezoelectric constant is an arbitrary unit, and as a specific example of the actual piezoelectric constant, it is the stretching change amount d ₃₃ perpendicular to the electrode surface (thickness direction), or the stretching change amount d ₃₁ along the electrode surface direction .

The piezoelectric constant is set to an arbitrary unit for the following reason. In order to obtain the piezoelectric constant, values such as the Young's modulus and Poisson's ratio of the piezoelectric layer are required, but it is not easy to obtain the values of the Young's modulus and Poisson's ratio of the piezoelectric layer (piezoelectric film) . Especially in the case of a thin film, unlike a bulk body, it is not easy to obtain the Young's modulus and Poisson's ratio (constant) of the thin film itself in principle due to the influence (constraint, etc.) from the substrate used for film formation. Absolute value (truth value). Therefore, the piezoelectric constant was calculated using estimated values of Young's modulus and Poisson's ratio of the KNN film known so far. Since the obtained piezoelectric constants are estimated values, they are set to relative arbitrary units in order to reflect objectivity. However, although the values of Young's modulus and Poisson's ratio of the KNN film used to calculate the piezoelectric constant are estimated values, they are also reliable values to some extent. About 80 [arbitrary units] of the piezoelectric constant can be roughly said The electrical constant d ₃₁ is 80 [-pm/V]. The same applies to FIGS. 17 and 18 .

As shown in Fig. 16, when the X-ray intensity caused by the (111) orientation is slightly increased, a tendency to increase the piezoelectric constant can be observed. However, when the integrated intensity due to (111) analyzed in this example exceeds 100, it can be confirmed that the piezoelectric constant decreases monotonously as the integrated intensity increases.

Next, for comparison with the (001) orientation component, Table 2 and FIG. 17 plotting Table 2 show the dependence of the piezoelectric characteristics of the KNN piezoelectric thin film on the (111) orientation component ratio. The horizontal axis is the volume fraction of (111) orientation components, and the vertical axis is the piezoelectric constant. In this example, it can be known that the (111) orientation composition is in the range of 0 to 20%, and the piezoelectric constant increases with the increase of the (111) volume fraction, regardless of the magnitude of the applied electric field.

However, when the volume fraction of (111) exceeds 20%, it is known that the piezoelectric constant decreases as the volume fraction increases. In particular, when it exceeds 40%, it can be seen that the piezoelectric constant is approximately half of the maximum value obtained in this example. In other words, in order to secure 50% or more of the maximum piezoelectric constant of the piezoelectric thin film of this example, it is desirable that the volume fraction of (111) be 40% or more. In addition, in general, in order to improve the piezoelectric characteristics of piezoelectric materials, it is also important to increase the crystallinity, and it has been confirmed that the integrated intensity of X-ray diffraction increases. In this example, when the volume fraction of (111) is less than 30%, the degree of crystallinity is high. If the most suitable volume fraction is specified on the basis of achieving high crystallinity, a piezoelectric film with higher performance can be realized.

[Table 2]

Next, Table 3 and FIG. 18 plotting Table 3 show the dependence of the piezoelectric characteristics of the KNN piezoelectric thin film on the (001) orientation component ratio. It can be seen that the dependence of the piezoelectric constant on the (001) volume fraction and the dependence on the (111) volume fraction have a negative relationship. That is, it can be seen that the piezoelectric constant increases as the (001) orientation component increases. However, when the volume fraction of (001) is 80% or more, it can be seen that the piezoelectric constant tends to decrease. In addition, in order to realize a value of 50% or more of the maximum piezoelectric constant of the piezoelectric thin film of this example, it is indicated that the volume fraction of (001) is preferably 60% or more. In addition, in this example, the total of (001) and (111) volume fractions is assumed to be 100%.

[table 3]

As can be seen from the above, in a piezoelectric thin film device having at least a lower electrode, a piezoelectric thin film, and an upper electrode disposed on a substrate, the piezoelectric thin film has a quasi-cubic, tetragonal, or orthorhombic crystal structure, or is one of these crystal structures. In at least one coexisting state of their crystal axes, some specific axes below 2 axes are preferentially oriented, and as the composition of the oriented crystal axes, in the ratio of (001) component and (111) component, When the total of the two is taken as 100%, the volume fraction of the (001) component is in the range of 60 to 100%, or the volume fraction of the (111) component is in the range of 0 to 40% to accurately By controlling the crystal orientation, new high-performance piezoelectric thin film devices can be manufactured.

As shown in Figures 17 and 18, a voltage of 6.7MV/ m, the piezoelectric constant is 87. The deviation angles between the (001) and (111) crystal planes of the obtained piezoelectric thin film device and the substrate surface are: relative to the normal direction of the substrate, the angle of the crystal orientation direction of (001) is inclined by 3.0°, (111) The angle of the crystal orientation direction is tilted by 0.5°.

The production conditions at this time were as follows: a Si substrate with a thickness of 0.525 mm was prepared as a substrate, and a 200 nm oxide film was formed on the surface of the Si substrate by subjecting the surface to thermal oxidation treatment. Next, under the conditions of substrate temperature 350°C, input power 100W, Ar gas 100% atmosphere, pressure 2.5Pa, film formation time 1-3 minutes (Ti adhesive layer), 10 minutes (Pt lower electrode), a 2nm A Ti adhesion layer was formed on the thermally oxidized film, and a 100 nm Pt lower electrode formed with (111) preferential orientation was formed on the Ti adhesion layer.

The target uses (Na _x K _y Li _z ) NbO ₃ (x=0.5, y=0.5, z=0), a ceramic target with a target density of 4.6g/cm ³ , and the film thickness is 3μm on the Pt lower electrode. Film formation of KNN piezoelectric film. The substrate temperature during film formation was 700° C., the input power was 100 W, a 5:5 mixed gas of Ar and O ₂ was used, and the pressure was set to 1.3 Pa. In addition, the amount of deviation between the center of the target and the center of the substrate was set to 10 mm. In addition, an annealing treatment at 700° C. for 2.0 hr was performed in an air atmosphere after the film formation. Among them, the sputtering device used a self-revolving furnace, and the distance between TS was set to 50 mm.

In this way, by appropriately selecting electrodes and piezoelectric films as constituent materials, controlling the film-forming conditions such as the film-forming temperature of the piezoelectric film, and controlling the volumes of the (001) and (111) components of the preferential orientation of the piezoelectric film Fractions, good piezoelectric properties can be achieved. In addition, a sufficiently good result of 96% yield of devices obtained from the substrate with the piezoelectric thin film was also obtained.

As above, although the present invention has been described based on a limited number of embodiments, the scope of the present invention is not limited to these embodiments. For example, as a factor other than the film formation temperature, by changing the composition of the sputtering target, the input power during its film formation, the type of operating gas, the flow rate and pressure of the gas, or the type or structure of the substrate or base, etc., it is possible to control Crystal orientation to obtain a piezoelectric film with desired internal stress. The scope of the present invention should be defined by the claims, and various changes within the scope of the claims and their equivalents are included.

Explanation of reference signs

1 Si substrate

2 Adhesive layer

3 lower electrode layer

4 piezoelectric film

5 Preferentially oriented crystal grains

6 Crystal grains preferentially oriented in the same direction as the normal direction of the substrate surface

7 (001) preferentially oriented crystal grains

8 (111) preferentially oriented crystal grains

9 Angle between (001) orientation orientation and substrate surface normal

10 Angle between (111) orientation orientation and substrate surface normal

Claims (11)

1. piezoelectric thin film device, its on substrate, dispose lower electrode at least, with general formula (Na _xK _yLi _z) NbO ₃The piezoelectric membrane of expression and the range upon range of body of piezoelectric membrane of upper electrode, wherein, 0≤x≤1,0≤y≤1,0≤z≤0.2, x+y+z=1,

Said piezoelectric membrane has accurate cube of crystalline substance, regular crystal or orthorhombic crystal structure; It perhaps is the state of at least a coexistence in these said crystal structures; Some specific axis preferred orientation in their crystallographic axis below 2; And as the composition of the crystallographic axis of said orientation, in the ratio of (001) composition and (111) composition, with the two add up to 100% o'clock; (001) volume fraction of composition is in the scope more than 60% and below 100%, and the volume fraction of (111) composition is in the scope below 40%.

2. piezoelectric thin film device according to claim 1, it is the structure of said (001) composition and the coexistence of said (111) composition.

3. piezoelectric thin film device according to claim 2, wherein, the volume fraction of said (111) composition is in greater than 1% scope.

4. piezoelectric thin film device, it is for to dispose on substrate with general formula (Na _xK _yLi _z) NbO ₃The range upon range of body of piezoelectric membrane of the piezoelectric membrane of expression, wherein, 0≤x≤1,0≤y≤1,0≤z≤0.2, x+y+z=1,

Said piezoelectric membrane has accurate cube of crystalline substance, regular crystal or orthorhombic crystal structure; It perhaps is the state of at least a coexistence in these said crystal structures; Some specific axis preferred orientation in their crystallographic axis below 2; (001) composition as the composition of the crystallographic axis of said preferred orientation is a coexisting state with (111) composition, and in the ratio of (001) composition and (111) composition, with the two add up to 100% o'clock; (001) volume fraction of composition greater than 60% and less than 100% scope in, the volume fraction of (111) composition is in less than 40% scope.

5. piezoelectric thin film device according to claim 4, it has basalis between said substrate and said piezoelectric membrane.

6. piezoelectric thin film device according to claim 5, wherein, said basalis be the Pt film or be the alloy firm of main component with Pt, or for comprising the electrode layer of stepped construction that these are the electrode layer of main component with Pt.

7. according to each described piezoelectric thin film device in the claim 1 to 6, wherein, said piezoelectric membrane has the aggregate structure that the particle by column structure constitutes.

8. according to each described piezoelectric thin film device in the claim 1 to 7, wherein, said piezoelectric membrane has strain in the direction parallel with real estate.

9. piezoelectric thin film device according to claim 8, wherein, said strain has the strain of tensile stress state or the strain of compressing stress state.

10. according to each described piezoelectric thin film device in the claim 1 to 9, wherein, said substrate is the Si substrate.

11. a piezoelectric membrane device, it possesses each described piezoelectric thin film device and voltage applying unit or voltage detection unit in the claim 1 to 10.

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