JP3903474B2 - Actuator, ink jet recording head, and method of manufacturing piezoelectric thin film element - Google Patents

Description

[0001]
[Technical field to which the invention belongs]
The present invention relates to a piezoelectric thin film element, an actuator using the piezoelectric thin film element, and the piezoelectric thin film element.
[0002]
[Prior art]
This actuator converts electrical energy into mechanical energy or vice versa, and is used in pressure sensors, temperature sensors, ink jet recording heads, and the like. In this ink jet recording head, a piezoelectric thin film element is used as a vibrator serving as an ink discharge drive source.
[0003]
The piezoelectric thin film element generally has a structure including a piezoelectric thin film made of a polycrystalline body, and an upper electrode and a lower electrode arranged with the piezoelectric thin film interposed therebetween.
[0004]
The composition of this piezoelectric thin film is generally a two-component system mainly composed of lead zirconate titanate (hereinafter referred to as “PZT”), or a three-component system in which a third component is added to this two-component system PZT. Ingredient system. Piezoelectric thin films having these compositions can be formed, for example, by sputtering, sol-gel, MOD process (Metalo organic decomposition process), laser ablation, CVD, or the like.
[0005]
As these examples, a ferroelectric using a binary PZT is described in "Applied Physics Letters, 1991, Vol. 58, No. 11, pages 1161-1163". Japanese Laid-Open Patent Publication No. 6-40035 and “Journal of The American Ceramic Society, 1973, Vol. 56, No. 2, pages 91-96” disclose a piezoelectric body using a two-component PZT. Yes.
When the piezoelectric thin film element is applied to, for example, an ink jet recording head, a piezoelectric thin film (PZT film) having a film thickness of about 0.4 μm to 20 μm is desired. Since this piezoelectric thin film is required to have a high piezoelectric strain constant, it is usually necessary to perform heat treatment at a temperature of 700 ° C. or higher to grow crystal grains of this piezoelectric thin film.
[0006]
[Problems to be solved by the invention]
However, when a piezoelectric thin film (PZT film) having a film thickness of 0.5 μm or more is formed, there is a problem that cracks occur in the film when heat treatment is performed to obtain a high piezoelectric strain constant.
[0007]
In addition, a method of increasing the film thickness of the piezoelectric thin film by applying a sol or gel composition and firing it at a high temperature to crystallize the piezoelectric thin film and repeating this is described in "Philips J. Res. 47 ( 1993 ') pages 263-285 ".
[0008]
However, the piezoelectric thin film obtained by this method has a problem that it has a layered laminated interface and cannot obtain good piezoelectric characteristics and has poor workability. Moreover, if heat treatment is performed many times, it leads to deterioration of piezoelectric characteristics such as non-orientation of crystals.
[0009]
Here, the piezoelectric thin film is usually formed on the lower electrode formed on the substrate, but there is a problem that the substrate is warped or distorted by the heat treatment performed when the piezoelectric thin film is formed. is there. It is also necessary to obtain good adhesion between the lower electrode and the piezoelectric thin film.
[0010]
As a result of various studies conducted by the present inventor to increase the piezoelectric strain constant of the piezoelectric thin film, as proposed in Japanese Patent Application No. 8-245353, the piezoelectric thin film has a columnar structure oriented in the 100 plane, and It has been found that it is effective to have a crystal structure with a particle size of 0.1 μm to 0.5 μm.
[0011]
In particular, since the crystallization of the piezoelectric thin film by the sol-gel method or the MOD process occurs from the lower electrode side, the interface between the lower electrode and PZT is important. Furthermore, it is effective that the piezoelectric thin film has an orientation of (100), but the lower electrode is strongly (111) oriented, so the orientation when forming the piezoelectric thin film is taken into consideration. There must be.
[0012]
An object of the present invention is to provide a piezoelectric element capable of reliably achieving such crystal orientation and crystal grain size and a method for manufacturing the same. Furthermore, an object of the present invention is to provide an actuator, particularly an ink jet recording head, provided with this piezoelectric element.
[0013]
Furthermore, the present invention aims to solve the above-mentioned problems, and there is no generation of cracks in the film during production, it has a high piezoelectric strain constant, and good adhesion to the lower electrode. Another object of the present invention is to provide a piezoelectric thin film element. Still another object of the present invention is to provide a piezoelectric element in which the crystal of the piezoelectric thin film has a (100) orientation.
[0014]
[Means for Solving the Problems]
In order to achieve this object, the present invention provides a piezoelectric thin film element comprising a piezoelectric thin film made of a polycrystal, and an upper electrode and a lower electrode arranged with the piezoelectric thin film interposed therebetween, A crystal source serving as a nucleus of the crystal of the piezoelectric body is formed in an island shape on the surface of the lower electrode on the piezoelectric body side.
[0015]
The crystal source is composed of a constituent element of the lower electrode, preferably titanium, and is formed on a crystal grain such as platinum or a grain boundary between crystal grains constituting the lower electrode. In order to make the crystal source into an island shape, a thin layer (40 to 60 angstroms) made of constituent elements is formed on the lower electrode.
[0016]
The piezoelectric thin film has a crystal structure with a columnar grain size of 0.1 μm to 0.5 μm having a crystal orientation of a plane orientation (100). Preferably, a piezoelectric thin film crystal grown using a crystal source formed on the lower electrode as a nucleus is formed across a plurality of crystal grains of the lower electrode. By doing so, the adhesion between the piezoelectric thin film and the lower electrode is improved.
[0017]
In the piezoelectric thin film element of the present invention, the particle size of the lower electrode is set to a preferable particle size for the piezoelectric material to exhibit piezoelectric characteristics, and the crystal particle size of the piezoelectric material grows using the crystal source as a nucleus. By doing so, the particle size of the lower electrode is approximately equal to or larger than that.
[0018]
The actuator of the present invention uses the piezoelectric thin film element as a mechanical energy source. Furthermore, the method for manufacturing a piezoelectric thin film according to the present invention includes a step of arranging an upper electrode and a lower electrode with a polycrystalline thin film interposed therebetween, and the piezoelectric crystal is formed on the piezoelectric body side of the lower electrode. The method includes a step of forming a crystal source serving as a nucleus into an island shape.
[0019]
Furthermore, an ink jet recording head according to the present invention is characterized in that the piezoelectric thin film element described above is provided as a vibrator. In one embodiment, the ink jet recording head includes a substrate on which an ink chamber is formed, a diaphragm that seals one of the ink chambers, and a piezoelectric thin film element in a flexural vibration mode is fixed to the surface. A nozzle plate for sealing the other surface of the ink chamber and having a nozzle port for discharging ink, wherein the piezoelectric thin film element is composed of the piezoelectric thin film element described above. Features.
[0020]
According to the piezoelectric thin film according to the present invention, an island-like crystal seed (crystal source) is formed between platinum crystal grains constituting the lower electrode or on the crystal grains, and this seed crystal is used as a nucleus. The grown piezoelectric thin film can have a columnar crystal structure oriented in the plane orientation 100.
[0021]
Furthermore, by setting the crystal of the lower electrode to a grain size preferable for the piezoelectric body to exhibit piezoelectric characteristics, and the crystal of the piezoelectric body grows with the crystal source as a nucleus, the crystal grain size of the piezoelectric body Can be greater than or equal to a value approximately equal to the particle size of the lower electrode. That is, since the crystal of the piezoelectric thin film can have a structure straddling a plurality of lower electrodes, it is possible to have a particle size exceeding the particle size of the lower electrode.
[0022]
In addition, by forming a crystal source at a grain boundary that is not easily affected by the orientation of the lower electrode crystal, the crystal of the piezoelectric thin film grows with this crystal source as a nucleus, and thus the orientation of the piezoelectric thin film crystal is targeted. Can be a thing.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments according to the present invention will be described with reference to the drawings. In the present embodiment, a case where a PZT film is formed as a piezoelectric thin film will be described.
[0024]
(Embodiment 1)
FIG. 1 is a schematic diagram showing a configuration of a piezoelectric element according to the present invention. As shown in FIG. 1, this piezoelectric thin film element includes a silicon substrate 11, a silicon oxide film 12 formed on the silicon substrate 11, a titanium oxide film 13 formed on the silicon oxide film 12, and a titanium oxide film. 13, a lower electrode 14 formed on the upper electrode 13, a PZT film 15 formed on the lower electrode 14, and an upper electrode 16 formed on the PZT film 15.
[0025]
The lower electrode 14 is made of platinum. Although not shown in the drawing, in order to improve the adhesion of the PZT film 15, a titanium film (Ti / TiO 2) is formed between the silicon oxide film 12 and the titanium oxide film 13.₂/ Ti etc.) is preferably formed.
[0026]
The PZT film 15 is made of a polycrystalline body, and grain boundaries of the crystalline body exist in a direction substantially perpendicular to the planes of the upper and lower electrodes 14 and 16 as shown in FIGS. That is, the crystal grains of PZT have a columnar structure as will be described later. In this crystal body, the width of the crystal grain in the film thickness direction is longer than the width of the crystal grain in the grain size direction, and there is a relationship between the width of the crystal grain in the film thickness direction and the width of the crystal grain in the grain size direction. The width in the grain size direction / the width in the film thickness direction = 1/3 to 1/10.
[0027]
Further, the crystal structure of the PZT film 15 is a columnar crystal that is strongly oriented in the crystal plane of the plane orientation (100) and extends in the film thickness direction of the piezoelectric thin film. Further preferably, one columnar crystal of the piezoelectric thin film is formed with a width of 0.1 to 0.3 μm.
[0028]
Here, the “degree of orientation” is, for example, when the reflection intensity of the plane orientation (XYZ) plane of the PZT film is expressed by I (XYZ) by the wide angle XRD method.
I (XYZ) / {I (100) + I (110) + I (111)}
It is defined that In the present invention, when the plane orientation (100) of the piezoelectric thin film is 0.15 or more, the piezoelectric thin film has a substantially columnar structure extending in the film thickness direction.
[0029]
The piezoelectric strain constant is proportional to the product of the relative permittivity and the voltage output coefficient. The relative dielectric constant increases as the size of the crystal grain in the direction of electric field application increases, and the piezoelectric output coefficient increases in the width direction (vertical direction in FIG. 1) of the piezoelectric thin film. For the reason that the narrower the width, the larger the piezoelectric strain constant of the PZT film 15 can be improved by providing the columnar structure as described above in the present invention.
[0030]
As the PZT film 15, a film mainly composed of a two-component system and a film composed mainly of a three-component system obtained by adding a third component to the two-component system are preferably used. Preferred specific examples of the binary PZT include
Pb (Zr_xTi_1-x) O_Three+ YPbO
(Where 0.40 ≦ X ≦ 0.6, 0 ≦ Y ≦ 0.3)
Those having a composition represented by the chemical formula:
[0031]
Further, preferred specific examples of the ternary PZT include those having a composition represented by the following chemical formula in which, for example, a third component is added to the two-component PZT.
[0032]
PbTi_aZr_b(A_gB_hcO_Three+ EPbO + (fMgO)_n
(Here, A is selected from a divalent metal selected from the group consisting of Mg, Co, Zn, Cd, Mn and Ni or a group consisting of Sb, Y, Fe, Sc, Yb, Lu, In and Cr. B represents a pentavalent metal selected from the group consisting of Nb, Ta and Sb, or a hexavalent metal selected from the group consisting of W and Te. A + b + c = 1, 0.35 ≦ a ≦ 0.55, 0.25 ≦ b ≦ 0.55, 0.1 ≦ c ≦ 0.4, 0 ≦ e ≦ 0.3, 0 ≦ f ≦ 0.15c , G = f = 1/2, n = 0, provided that A is a trivalent metal, B is not a hexavalent metal, A is a divalent metal, and B Is a pentavalent metal, g is 1/3, h is 2/3, and A represents Mg only when A is Mg and B is Nb.
More preferable specific examples of the ternary system include lead magnesium niobate, that is, A is Mg, B is Nb, g is 1/3, and h is 2/3.
[0033]
Further, in any of these two-component PZT and three-component PZT, in order to improve the piezoelectric characteristics, a small amount of Ba, Sr, La, Nd, Nb, Ta, Sb, Bi, W, Mo and Ca etc. may be added. In particular, in a ternary system, addition of 0.10 mol% or less of Sr, Ba is more preferable for improving piezoelectric characteristics. Further, in the case of a ternary system, addition of 0.10 mol% or less of Mn and Ni is preferable because the sinterability is improved.
[0034]
Next, a method for manufacturing a piezoelectric thin film element having this structure will be described with reference to the drawings. 4 (a) to 4 (c) are cross-sectional views showing the manufacturing process of the piezoelectric thin film element described above. In the step shown in FIG. 4A, thermal oxidation is performed on the silicon substrate 11 to form a silicon oxide film 12 having a thickness of about 0.3 to 1.2 μm on the silicon substrate 11. Next, a titanium oxide film 13 having a thickness of about 0.01 μm to 0.04 μm is formed on the silicon oxide film 12 by sputtering. Next, a lower electrode 14 made of platinum is formed on the titanium oxide film 13 by sputtering so as to have a crystal grain size of 0.01 to 0.3 μm and a thickness of about 0.2 to 0.8 μm.
[0035]
Next, in the step shown in FIG. 4B, titanium is formed in an island shape by sputtering on the lower electrode 14 formed in the step shown in FIG. For example, island titanium can be formed by making this titanium into a film thickness of 40 to 60 angstroms.
[0036]
The crystal structure of the piezoelectric thin film grown using titanium as a crystal source has an orientation to 100 planes, and the crystal grains are 0.1 μm to 0.5 μm. Details of this will be described later.
[0037]
A case where the PZT film 15 is manufactured by a sol-gel method will be described. Here, PZT is manufactured by multilayer coating using a sol-gel method. This sol-gel method is as follows.
[0038]
This manufacturing method is a method in which a hydrated complex of a metal component hydroxide capable of forming the PZT film 15, that is, a sol is dehydrated to form a gel, and the gel is heated and fired to adjust the inorganic oxide. This manufacturing method includes the following steps.
[0039]
a. Film formation process of sol composition
In the present embodiment, the metal component sol constituting the PZT film can be prepared by hydrolyzing a metal alkoxide or acetate capable of forming the PZT film with an acid, for example. In the present invention, the composition of the PZT film described above can be obtained by preparing the composition of the metal in the sol. That is, titanium, zirconium, lead, and alkoxides or acetates of other metal components are used as starting materials.
[0040]
Here, there is an advantage that the composition of the metal component constituting the PZT film is substantially maintained until the PZT film (piezoelectric thin film) is finally formed. That is, there is very little variation due to evaporation of the metal component, particularly the lead component, during firing and annealing treatment, and therefore the composition of the metal component in these starting materials matches the metal composition in the finally obtained PZT film. It will be. That is, the composition of the sol is determined according to the piezoelectric thin film to be generated (PZT film in the present embodiment).
[0041]
Further, in the present embodiment, in order to obtain a PZT film free of the lead component by evaporation of the lead component described above, the lead component in the sol is preferably up to 15 mol% from the amount required from the stoichiometry. It is preferable to make it excessive to%.
[0042]
In the present embodiment, this sol is preferably used as a composition mixed with an organic polymer compound. This organic polymer compound absorbs the residual stress of the thin film during drying and baking, and effectively prevents the thin film from cracking. Specifically, when a gel containing this organic polymer is used, pores are generated in the gelled thin film described later. These pores are considered to absorb the residual stress of the thin film in the pre-annealing and annealing processes described later.
[0043]
Here, as the organic polymer compound preferably used, polyvinyl acetate, hydroxypropyl cellulose, polyethylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol, polyvinyl alcohol, polyacrylic acid, polyamide, polyamic acid, acetyl cellulose and derivatives thereof, As well as their copolymers.
[0044]
In the present embodiment, by adding polyvinyl acetate, a porous gel thin film having a large number of pores of about 0.05 μm is added to hydroxypropicellulose, and the size is 1 μm or less. A porous gel thin film having a wide distribution can be formed.
[0045]
In this embodiment, polyethylene glycol having an average molecular weight of about 285 to 420 is preferably used. Further, as the polypropylene glycol, those having an average molecular weight of about 300 to 800 are preferably used.
[0046]
In the manufacturing method according to the present embodiment, first, this sol composition is applied onto the lower electrode 14 (see FIG. 4B) on which the PZT film 15 is to be formed. The coating method at this time is not particularly limited, and can be performed by a commonly performed method such as spin coating, dip coating, roll coating, bar coating, or the like. Moreover, it can also apply | coat by flexographic printing, screen printing, offset printing, etc.
[0047]
In addition, the thickness of the film formed by the above-described coating is 0.1 to 0.3 μm in thickness of the porous gel thin film formed in the gelation step described later in consideration of the subsequent steps. It is desirable to control so as to be, more preferably about 0.15 μm.
[0048]
Next, the applied sol composition is naturally dried or heated at a temperature of 200 ° C. or lower. Here, the sol composition may be further applied on the dried (heated) film to increase the film thickness. In this case, the underlying film is desirably dried at a temperature of 80 ° C. or higher.
[0049]
b. Gelation process of film made of sol composition
Next, the film obtained in the above-described sol composition film forming step is baked to form a porous gel thin film made of an amorphous metal oxide substantially free of residual organic matter.
[0050]
Firing is performed by heating the sol composition film at a temperature sufficient to gel the sol composition film and remove organic substances from the film for a sufficient time. In the present embodiment, the firing temperature is preferably 300 to 500 ° C, and more preferably 350 to 400 ° C. The firing time varies depending on the temperature and the type of furnace used. For example, when a degreasing furnace is used, it is preferably about 10 to 120 minutes, more preferably about 15 to 60 minutes. When a hot plate is used, it is preferably about 1 to 60 minutes, and more preferably about 5 to 30 minutes. Through the above steps, a porous gel thin film was formed on the lower electrode 14.
[0051]
c. Pre-annealing process
Next, the porous gel thin film obtained in step b described above is heated and fired, and this film is converted into a film made of a crystalline metal oxide film. Firing is performed at a temperature necessary to convert the porous gel thin film into a film made of a crystalline metal oxide, but it is not necessary to perform perovskite crystals in the crystal, and the gel thin film is uniform. It may be terminated when it is crystallized.
[0052]
In the present embodiment, the firing temperature is preferably in the range of 500 to 800 ° C, and more preferably in the range of 550 to 750 ° C. The firing time varies depending on the firing temperature and the type of furnace used. For example, when an annealing furnace is used, it is preferably about 0.1 to 5 hours, more preferably about 0.5 to 2 hours. When an RTA (Rapid Thermal Annealing) furnace is used, it is preferably about 0.1 to 10 minutes, more preferably about 1 to 5 minutes.
[0053]
In the present embodiment, this pre-annealing step can be performed in two stages. Specifically, first, annealing can be performed at a temperature in the range of 500 to 600 ° C. as the first stage, and then annealing can be performed at a temperature in the range of 600 to 800 ° C. as the second stage. More preferably, annealing can be performed at a temperature in the range of 500 to 550 ° C. as the first stage, and then annealing can be performed at a temperature in the range of 600 to 750 ° C. as the second stage. By this step, the porous gel thin film was converted into a film made of a crystalline metal oxide film.
[0054]
d. Repeat process
Next, the above-described steps a and b are further repeated three times to laminate four layers of polycrystalline gel thin films, and then converted into a film made of a metal oxide film by the pre-annealing step of step C.
[0055]
Next, island-shaped titanium is formed in an island shape on the PZT by the above-described method, and the above-described steps a, b, and c are further repeated four times.
[0056]
The number of laminated films obtained as a result of this repeating process may be appropriately determined in consideration of the final film thickness of the PZT film 15. Here, 0.15 μm per layer is preferable. In addition, it cannot be overemphasized that it is preferable that it is the film thickness which a crack etc. do not generate | occur | produce in the following process (process e) mentioned later.
[0057]
In this repeating process, a new porous gel thin film is formed on the previously formed film, and as a result of the subsequent pre-annealing, the newly formed porous gel thin film is substantially integrated with the previously formed film. It becomes the film made into.
[0058]
Here, the substantially integrated film is not only the case where there is no discontinuous layer between the laminated layers, but is different from the case of the finally obtained PZT film 15 according to the present embodiment. There may be discontinuous layers between the layers. When steps a and b are further repeated, a new porous gel thin film is further formed. As a result of the subsequent pre-annealing, this new porous gel thin film is substantially the same as the crystalline laminated film obtained above. Integrated film.
[0059]
e. Perovskite crystal growth process
Next, the film obtained in the step d is annealed at a firing temperature of 600 to 1200 ° C., more preferably 800 to 1000 ° C. The firing time varies depending on the firing temperature and the type of furnace used. For example, when an annealing furnace is used, about 0.1 to 5 hours is preferable, and about 0.5 to 2 hours is more preferable. Moreover, when using an RTA furnace, about 0.1 to 10 minutes are preferable and about 0.5 to 3 minutes are more preferable.
[0060]
In this embodiment, the perovskite crystal growth process, that is, annealing can be performed in two stages. Specifically, annealing is performed at a temperature of about 600 to 800 ° C. in the first stage, and annealing is performed at a temperature of 800 to 1000 ° C. in the second stage. More preferably, annealing can be performed at a temperature of about 600 to 750 ° C. in the first stage, and annealing can be performed at a temperature of 800 to 950 ° C. in the second stage.
[0061]
By the above operation, PZT having a grain size of 0.1 μm to 0.5 μm and a film thickness of 1.2 μm is formed on the lower electrode 14 and made of a columnar polycrystal grown with titanium as a nucleus. Here, the effect of titanium on crystallization of PZT will be described. This effect has been confirmed by the present inventor using an electron microscope.
[0062]
In FIG. 1, island-like titanium is formed on the grain boundaries of the lower electrode 14 by sputtering. The crystal grain size of the lower electrode is 0.01 to 0.3 μm. It is possible to make the lower electrode into a columnar crystal having such a crystal grain size because platinum has an FCC structure, so that it tends to be a columnar crystal, and the crystal grain size can be controlled by the deposition rate during sputtering. is there.
[0063]
When an island-shaped titanium crystal is formed on the surface of the lower electrode, titanium island-shaped crystals tend to be formed at grain boundaries between platinum crystals having a low platinum surface energy. At this time, the PZT crystal grains grown using titanium as a nucleus are formed across a plurality of titanium crystals.
[0064]
FIG. 6 is a schematic diagram showing the formation process of a PZT crystal confirmed by an electron microscope, (1) is a diagram along the height direction of the PZT crystal, and (2) is the diameter (width) of the PZT crystal. It is a figure along a direction. FIG. 7 is an actual electron micrograph, in which columnar PZT crystals are formed on a Pt electrode. The titanium crystal 15 in FIG. 6 is formed at the grain boundary 14 A of the lower electrode crystal 14.
[0065]
When PZT is grown using titanium crystals as nuclei, the crystal grains of PZT grow across a plurality of platinum crystals of adjacent lower electrodes. Usually, Pt has a stable 111 orientation and is easy to produce, but when a titanium seed crystal is formed at a grain boundary that is less affected by the orientation of platinum, the PZT crystal is affected by the crystal plane orientation of platinum. It is easy to form a columnar crystal in 100 directions that is not received. Furthermore, since the PZT crystal grains are formed across the crystal grains of the plurality of lower electrodes, it is expected that the adhesion with the lower electrodes is further improved.
[0066]
FIG. 8 is a chart of X-ray diffraction analysis (XRD) when a piezoelectric thin film PZT is formed on a lower electrode on which island-shaped titanium is formed, and FIG. 9 is a chart when no island-shaped titanium is formed. is there. Comparing FIG. 8 and FIG. 9 with each other, when island-like titanium is not formed, the orientation of the PZT film is only the (111) orientation, and the piezoelectric constant is as low as 90 pC / N. On the other hand, when island-like titanium is formed, the (100) orientation of PZT appears, and the ratio increases with respect to the (111) orientation, so that the piezoelectric constant increases to 133 pC / N.
[0067]
Furthermore, when another PZT layer is sequentially formed on PZT in which titanium is formed in an island shape, further titanium is formed in an island shape, and further, four layers of PZT are sequentially formed, and then crystallized. PZT is crystallized as described above with nuclei as the nucleus, and other PZTs are also crystallized in accordance with the crystal grain size and crystal structure of the adjacent PZT. The island titanium between the PZT layer and the PZT layer also controls the crystallization of PZT on the titanium as described above. When there is no island-like titanium, the PZT crystal is oriented in the 111 plane under the influence of platinum, so that it does not have the columnar structure with the orientation in the 100 plane as described above, and is excellent in piezoelectricity. Does not show properties.
[0068]
FIG. 10 is an explanatory diagram when a crystal source made of titanium is formed on the crystal grains of the lower electrode. On the crystal grains 14 of the lower electrode, island-like titanium is formed by sputtering. The crystal grain size of the lower electrode is 0.1 to 0.3 μm.
[0069]
PZT formed on the lower electrode by the above-described sol-gel method is crystallized using this titanium as a nucleus. Reference numeral 14B in FIG. 5B is an alloy of crystallized PZT and titanium. Each PZT crystal grown with each titanium as a nucleus stops growing at the grain boundary 14C of the lower electrode, and further grows in the film thickness direction of the piezoelectric thin film. Columnar crystals with higher strength grow in the thickness direction of PZT. At this time, since the grain size of each crystal of PZT is controlled by the grain size of the lower electrode of the lower layer, by adjusting the grain size of the lower electrode, as shown in (3), the PZT layer is columnar (PZT Columnar crystal heading in the thickness direction) and having a crystal grain size of 0.1 to 0.5 μm.
[0070]
FIG. 11 is a characteristic diagram showing the relationship between island-like titanium and the piezoelectric strain constant. It was confirmed that a high piezoelectric strain constant was obtained when the film thickness of titanium was in the range of 40 to 60 angstroms, and the degree of orientation on the 100 plane at this time was high. The degree of orientation of the 100 plane relative to the 111 plane of the present invention is 20 to 30, and preferably 20 or more, whereby the columnar crystal structure described above can be obtained.
[0071]
Within the range of the titanium film thickness, it was confirmed that the crystal grain size of PZT was also in a suitable range. The film thickness of titanium was set by keeping the sputtering power constant and proportionally distributing the sputtering time. The degree of orientation on the 100 plane is the intensity ratio between the 100 plane and the 111 plane in the wide-angle X-ray analysis, and the intensity on the 111 plane is calculated as 100. Here, when the film thickness by sputtering is set to 40 to 60 angstroms, titanium is formed into an island shape instead of a continuous film. When the film thickness by sputtering is in this range, it is well known from, for example, pages 25 to 27 of the NTS thin film production application handbook, that the film does not become a continuous film but becomes an island shape. .
[0072]
When the thickness of titanium is 20 angstroms or less, the PZT crystal grows by using the crystalline platinum of the lower electrode as a seed, so that the degree of 111-plane orientation becomes high. At 80 angstroms or more, the titanium film is a continuous film and the film thickness is small, so that PZT is amorphous and the crystal size of PZT is increased.
[0073]
FIG. 12 is a characteristic diagram showing the relationship between the thickness of titanium on the lower electrode and the piezoelectric strain constant, and suitable piezoelectric characteristics can be obtained when the titanium has a thickness of 20 to 80 angstroms. The piezoelectric characteristic has a maximum value when the thickness of titanium is around 50 angstroms. On the other hand, as described above, the degree of orientation in 100 plane is that the film thickness of titanium is 40 to 60 angstroms, and the film thickness of titanium is 20 to 80 angstroms, and preferably 40 to 60 angstroms. In addition, the PZT crystal in the vicinity of 50 Å of titanium has a strong orientation of 100 planes.
[0074]
The piezoelectric strain constant is measured using a 2 mmφ PZT dot pattern impedance analyzer, and the voltage output coefficient obtained from the voltage generated in the dot pattern when the free end of the cantilever is weighted. It was calculated by the product of
[0075]
Thus, the process of FIG. 4B is completed, and then the process proceeds to the process shown in FIG. In this step, the upper electrode 16 made of platinum having a thickness of about 0.05 to 0.2 μm is formed on the PZT film 15 obtained in the step shown in FIG.
[0076]
In this way, a piezoelectric thin film element as shown in FIG. 1 was obtained. In addition, it was confirmed that the obtained PZT film 15 was free from cracks, and the cross-section did not have the layered discontinuous surface due to the above-described lamination.
[0077]
FIG. 5 is a cross-sectional view showing one ink reservoir of an ink jet recording head using the piezoelectric thin film element according to the present invention as a vibrator.
[0078]
As shown in FIG. 5, the ink jet recording head according to the third embodiment includes a silicon substrate 21 on which an ink reservoir 27 is formed, a diaphragm 22 formed on the silicon substrate 21, and a desired on the diaphragm 22. A lower electrode 23 formed at a position, a piezoelectric thin film 24 formed on the lower electrode 23 at a position corresponding to the ink reservoir 27, an upper electrode 25 formed on the piezoelectric thin film 24, silicon And a second substrate 26 bonded to the lower surface of the substrate 21. The lower electrode 23 has the same configuration as the lower electrode described in the above-described embodiment. The piezoelectric thin film 24 has the same configuration as the PZT film described in the first embodiment.
[0079]
In the ink jet recording head, ink is supplied to the ink reservoir 27 via an ink flow path (not shown). Here, when a voltage is applied to the piezoelectric thin film 24 through the lower electrode 23 and the upper electrode 25, the piezoelectric thin film 24 is deformed and pressurized in the ink reservoir 27 to apply pressure to the ink. With this pressure, ink is ejected from a nozzle (not shown), and ink jet recording is performed.
[0080]
Here, since the ink jet recording head uses the piezoelectric thin film element having excellent piezoelectric characteristics described above as a vibrator, ink can be ejected with a large pressure.
[0081]
In addition, although titanium was demonstrated as a crystal source, it is not restricted to this, If it is a constituent element of a piezoelectric thin film and becomes a seed crystal and can be alloyed with a piezoelectric thin film, it can be used. Moreover, although the lower electrode is platinum, iridium having the same FCC structure can obtain the same effect.
[0082]
Further, a MOD process can be used instead of the sol-gel method. This process is the same as the sol-gel method, except that the sol preparation means is different from that of the sol-gel method. The preparation of the sol in the MOD process is characterized in that the dispersion sol does not undergo a sol-gel reaction beyond the formation of a gel network after hydrolysis and dehydration polycondensation in the prepared sol liquid.
[0083]
Specifically, one of the alkanolamines and monoethanolamine is selected as one of the starting materials for the sol solution as a hydrolysis inhibitor for metal alkoxides and metal acetates. By the action of monoethanolamine, the metal alkoxide and metal acetate maintain a uniform dispersion state in the sol solution. Therefore, since a gel network found in the sol-gel method is not formed, a more uniform crystal can be obtained as compared with the sol-gel method. Everything from the sol coating process to the sintering process for obtaining crystals is the same as the sol-gel method. In addition to the aforementioned monoethanolamine, diethanolamine, triethanolamine, acetylacetone, acetic acid, and the like can be used as a sol hydrolysis inhibitor.
[0084]
【The invention's effect】
As described above, the piezoelectric thin film element according to the present invention includes a piezoelectric thin film made of a polycrystalline body, and an upper electrode and a lower electrode that are arranged with the piezoelectric thin film interposed therebetween, and is provided on the lower electrode surface. Since the crystal source serving as the nucleus of the crystal of the piezoelectric body is formed in an island shape, the crystal of the piezoelectric body can be formed into a columnar shape oriented in the 100 plane, and the piezoelectric characteristics can be improved.
[0085]
Furthermore, in the piezoelectric thin film element according to the present invention, the crystal of the lower electrode is set to a preferable grain size for the piezoelectric body to exhibit piezoelectric characteristics, and the crystal grain size of the piezoelectric body is the nucleus of the crystal source. As a result, it is possible to prevent the grain size of the piezoelectric thin film from fluctuating due to the grain size of the lower electrode, and to set the crystal grain size of the piezoelectric thin film to a value that is suitable for exhibiting piezoelectric characteristics. It becomes possible.
[0086]
By configuring the crystal source from titanium having a predetermined film thickness, the piezoelectric characteristics can be made to be more suitable values.
[0087]
The piezoelectric thin film is made of a crystal grown with the crystal source as a nucleus, and this crystal has a crystal orientation with a plane orientation (100) and a crystal structure with a columnar grain size of 0.1 μm to 0.5 μm. By doing so, it becomes possible to make the piezoelectric characteristics more suitable values.
[0088]
Since the actuator of the present invention, particularly the ink jet recording head, uses such a piezoelectric thin film element as a pressure generation source, the amount of mechanical deformation is large and the ink discharge pressure can be increased.
[0089]
Furthermore, according to the method for manufacturing a piezoelectric thin film element of the present invention, a piezoelectric thin film having excellent piezoelectric characteristics can be manufactured.
[0090]
Further, according to the piezoelectric thin film element of the present invention, cracks are not generated in the film during production, and the piezoelectric thin film element has a high piezoelectric strain constant and good adhesion to the lower electrode.
[0091]
Furthermore, since the crystal of the piezoelectric thin film grows using the crystal source between the crystal grains of the lower electrode as a nucleus, the crystal structure of the piezoelectric thin film element can be set to a suitable plane orientation.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a piezoelectric thin film element according to a first embodiment of the present invention.
2 is a scanning electron microscope (SEM) photograph showing a cross section of a PZT film constituting the piezoelectric thin film element according to Embodiment 1. FIG.
3 is a scanning electron micrograph showing the plane of the PZT film shown in FIG. 2. FIG.
FIGS. 4A to 4C are cross-sectional views showing manufacturing processes of the piezoelectric thin film element described above. FIGS.
FIG. 5 is a cross-sectional view showing one ink reservoir portion of an ink jet recording head using the piezoelectric thin film element according to the present invention as a vibrator.
FIG. 6 is a schematic view showing that a piezoelectric thin film crystal is grown by forming an island crystal of titanium at a grain boundary of a lower electrode crystal.
FIG. 7 is a structure diagram photograph of a piezoelectric thin film element taken by a scanning electron microscope, and shows a structure image corresponding to FIG. 6 (1).
FIG. 8 is a chart of X-ray diffraction analysis (XRD) when a piezoelectric thin film PZT is formed on a lower electrode on which island-shaped titanium is formed.
FIG. 9 is a chart in the case where island-like titanium is not formed.
FIG. 10 is a conceptual diagram showing a second example in which a piezoelectric body is grown with a titanium seed crystal as a nucleus.
FIG. 11 is a table showing the relationship between the film thickness of titanium and the piezoelectric characteristics.
FIG. 12 is a characteristic graph of this.
[Explanation of symbols]
11, 21 Silicon substrate
12 Silicon oxide film
13 Titanium oxide film
14, 23 Lower electrode
14A Titanium seed crystal
15 PZT film
16, 25 Upper electrode
22 Diaphragm
24 Piezoelectric thin film
26 substrates
27 Ink reservoir

Claims (17)

An actuator that mechanically uses a piezoelectric thin film element as an energy source,
The piezoelectric thin-film element comprises a piezoelectric thin film made of a polycrystalline substance, and the upper and lower electrodes that sandwich the piezoelectric thin film, comprising a crystal of the piezoelectric the piezoelectric body side of the lower electrode The core crystal source is formed in an island shape ,
The crystal grains of the piezoelectric thin film have a columnar structure, and the width of the crystal grains in the film thickness direction is longer than the width of the crystal grains in the grain size direction. The relationship between the width in the grain size direction and the width in the grain size direction / width in the film thickness direction is 1/3 to 1/10. 2. The actuator according to claim 1, wherein the piezoelectric thin film is made of PZT having a crystal orientation of 100, and the lower electrode is made of platinum having a crystal orientation of 111. By setting the crystal of the lower electrode to a grain size suitable for the piezoelectric thin film to exhibit piezoelectric characteristics, the crystal grain size of the piezoelectric thin film grows using the crystal source as a nucleus, thereby the lower electrode The actuator according to claim 1, wherein the actuator has a value substantially equal to or greater than the particle diameter of the above. The actuator according to claim 1, wherein the crystal source is formed on a crystal grain of the lower electrode. The actuator according to claim 1, wherein the crystal source is formed at a grain boundary of the lower electrode. The actuator according to claim 4 or 5, wherein crystal grains of the piezoelectric thin film are formed across a plurality of crystal grains of the lower electrode. The actuator according to claim 1, wherein the crystal source is a constituent element of a piezoelectric thin film. The actuator according to claim 7, wherein the crystal source is made of titanium. 6. The actuator according to claim 4, wherein the crystal source is formed on the lower electrode so as to have a film thickness of 40 to 60 angstroms. The piezoelectric thin film is composed of crystal grains grown using the crystal source as a nucleus. The crystal grains have a crystal orientation of a plane orientation (100) and a columnar crystal size of 0.1 μm to 0.5 μm. The actuator according to any one of claims 1 to 9. A method of manufacturing a piezoelectric thin film element comprising a step of arranging an upper electrode and a lower electrode across a piezoelectric thin film made of a polycrystalline body,
Forming a crystal source serving as a nucleus of the crystal of the piezoelectric body in an island shape on the piezoelectric body side of the lower electrode ;
With the crystal source as a nucleus, the crystal grains have a columnar structure, and the width in the film thickness direction of the crystal grains is longer than the width in the grain size direction of the crystal grains, and the width in the film thickness direction of the crystal grains and the crystal Forming a piezoelectric thin film having a relationship between the width in the particle size direction of the grains and the width in the particle size direction / the width in the film thickness direction = 1/3 to 1/10. Device manufacturing method. The method for manufacturing a piezoelectric thin film element according to claim 11, wherein the piezoelectric thin film is manufactured by a sol-gel method. 12. The method of manufacturing a piezoelectric thin film element according to claim 11 , wherein the piezoelectric thin film is manufactured by a MOD process. 12. The method for manufacturing a piezoelectric thin film element according to claim 11, wherein the piezoelectric thin film element is formed of a plurality of layers, and a crystal source is formed between the layers. The manufacturing method according to claim 11 , wherein the crystal source is a constituent element of a piezoelectric thin film. The manufacturing method according to claim 11 , wherein the crystal source is a constituent element of a piezoelectric thin film. A substrate on which an ink chamber is formed, one of the ink chambers is sealed, a vibration plate having a piezoelectric vibration element in a flexural vibration mode fixed to the surface, and the other surface of the ink chamber is sealed An ink jet recording head comprising a nozzle plate having an ink ejection nozzle opening formed thereon,
The piezoelectric thin film element includes a piezoelectric thin film made of a polycrystalline body, and an upper electrode and a lower electrode arranged with the piezoelectric thin film interposed therebetween, and the piezoelectric crystal is disposed on the piezoelectric body side of the lower electrode. The core crystal source is formed in an island shape,
The crystal grains of the piezoelectric thin film have a columnar structure, and the width of the crystal grains in the film thickness direction is longer than the width of the crystal grains in the grain size direction. An ink jet recording head in which the relationship between the width in the particle size direction and the width in the particle size direction / the width in the film thickness direction is 1/3 to 1/10 .

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