JP5370346B2 - Piezoelectric element and ink jet recording head - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric thin film element which dose not generate a crack in a film during manufacturing, has a high piezoelectric strain constant, and has good close contactness with a lower electrode; and to further provide an inkjet recording head using such piezoelectric thin film element, the inkjet recording head being capable of high resolution printing. <P>SOLUTION: The piezoelectric thin film element includes a piezoelectric film made of a polycrystal body, and an upper electrode and a lower electrode that are arranged by sandwiching the piezoelectric film. A crystal body of the piezoelectric film is formed in a direction substantially perpendicular to the electrode surfaces. <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a thin film piezoelectric element that converts electrical energy into mechanical energy or vice versa. This piezoelectric element is used in actuators such as pressure sensors, temperature sensors, and ink jet recording heads. The present invention relates to this ink jet recording head. Furthermore, the present invention relates to a method for manufacturing this piezoelectric thin film element.

  In a conventional ink jet recording head, a vibrator serving as a driving source for ejecting ink is composed of a piezoelectric thin film element. This 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 disposed with the piezoelectric thin film interposed therebetween.

  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. It consists of a system. The piezoelectric thin film having these compositions is formed by, for example, a sputtering method, a sol-gel method, a laser ablation method, a CVD method, or the like.

  Ferroelectrics using binary PZT are described in “Aied Physics Letters, 1991, Vol. 58, No. 11, pages 1161-1163”.

  In addition, Japanese Patent Laid-Open No. 6-40035 and “Jornal 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 an ink jet recording head, it is desirable to use a piezoelectric thin film (PZT film) having a film thickness of about 0.5 μm to 25 μm. A piezoelectric strain constant is required.

  In order to obtain a piezoelectric thin film having such a high piezoelectric strain constant, it is usually necessary to heat-treat the PZT film at a temperature of 700 ° C. or higher and grow crystal grains of the piezoelectric thin film. Has been. As a material constituting the lower electrode of the piezoelectric thin film element, a conductor such as platinum, titanium, platinum, gold, or nickel is used.

  Japanese Patent Application Laid-Open No. 6-116095 describes crystal grains of a piezoelectric body. This publication discloses a method of forming a ferroelectric thin film by applying a precursor solution of lead zirconate titanate or lanthanum-containing lead zirconate titanate on a platinum substrate whose substrate surface is oriented in the (111) plane and heating it. In this method, after the precursor solution is applied onto the substrate, first, heat treatment is performed in a temperature range of 150 to 550 ° C. which brings about a desired crystal orientation, and then the substrate surface is baked and crystallized at 550 to 800 ° C. It is disclosed that a specific crystal plane of a thin film is preferentially oriented in a direction according to a heat treatment temperature.

  In addition, as a prior art relating to the present invention, there is a method for manufacturing a bulk piezoelectric ceramic described in, for example, Japanese Patent Application Laid-Open No. 3-232755. As shown in this conventional example, in the case of a piezoelectric ceramic, it is considered that the higher the density (the higher the density), the higher the piezoelectric characteristics.

Japanese Patent Application Laid-Open No. 50-145899 discloses an example in which a bulk piezoelectric ceramic is used for generating a high voltage such as a gas appliance. In this publication, holes having a diameter of 4 to 10 μm are uniformly dispersed in a piezoelectric porcelain 4 × 10 ⁵ to 8 × 10 ⁵ holes / cm ² , and the specific gravity is 90 to 93% of the true specific gravity. It is described that the discharge rate has a good characteristic of 100%.

  As a conventional example of an ink jet recording head using a thin film piezoelectric element, there is, for example, US Pat. No. 5,265,315.

JP-A-6-40035 JP-A-6-116095 JP-A-3-232755 JP 50-145899 A US Pat. No. 5,265,315

"Aied Physics Letters, 1991, Vol. 58, No. 11, pages 1161-1163" "Jornal of The American Ceramic Society, 1973, Vol. 56, No. 2, pages 91-96" "Philips J. Res. 47 (1993 ') pages 263-285"

  When a piezoelectric thin film (PZT film) having a film thickness of 1 μm or more is formed, there is a problem that cracks are generated in the film when the above-described heat treatment is performed in order to obtain the above-described high piezoelectric strain constant. As described in JP-A-3-232755, in bulk ceramics, the higher the density, the better the piezoelectric characteristics. However, a very dense film is suitable as an actuator for an ink jet recording head or the like. Therefore, when the piezoelectric film having such a thickness is about to be manufactured in one manufacturing process, the film usually has cracks. I will enter. In the case of laminating with a thin film thickness so as not to cause cracks, the manufacturing process becomes long, which is industrially incompatible.

  A method for increasing the film thickness of a piezoelectric thin film by applying a sol or gel composition to a substrate, baking it at a high temperature for crystallization, and repeating this is described in “Philips J. Res. 47 (1993). ') Pages 263-285 ". However, the piezoelectric thin film obtained by this method has a layered laminated interface, and there are problems that good piezoelectric characteristics cannot be obtained and workability is deteriorated.

  A piezoelectric thin film is usually formed on a metal film, which is a lower electrode formed on a substrate. However, there is a problem that the substrate is warped or distorted by 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.

  Japanese Laid-Open Patent Publication No. 50-145899 is a piezoelectric element using a bulk porcelain suitable for high voltage generation, and is a thin film piezoelectric element and applied to an ink jet recording head. Use is different from the case.

  US Pat. No. 5,265,315 describes an ink jet recording head as in the present invention, but does not describe the pores of PZT as a piezoelectric film or the density thereof, and the method for producing the piezoelectric film is also sol-gel. Since this method is used, deposition of a plurality of layers and a heat treatment step are required, which is not suitable industrially.

  In the above-mentioned Japanese Patent Laid-Open No. 6-116095, the orientation by the X-ray diffraction wide angle method, that is, the degree of orientation of the crystal plane with respect to the substrate parallel direction is discussed, but the discussion by the X-ray diffraction thin film method is not made.

  In addition, when the piezoelectric element is used as an actuator for an ink jet recording apparatus or the like, high piezoelectric characteristics are required, but the relationship between the piezoelectric characteristics with respect to crystal orientation is not disclosed in Japanese Patent Laid-Open No. 6-116095.

  An object of the present invention is to solve such a conventional problem, and an object of the present invention is to provide a piezoelectric thin film element having improved piezoelectric characteristics as compared with the conventional one, and a method for manufacturing the same.

  Another object of the present invention is to provide a method of manufacturing a piezoelectric thin film element having a high piezoelectric strain constant. Another object of the present invention is to provide a piezoelectric thin film element including a piezoelectric thin film having a required film thickness without causing cracks.

  Furthermore, another object of the present invention is to provide a method for manufacturing a piezoelectric thin film element that can provide a piezoelectric thin film element including a piezoelectric thin film having a required film thickness without causing cracks in a single process. There is to do.

  Furthermore, another object of the present invention is to provide a piezoelectric element provided with a piezoelectric thin film having good adhesion to a lower electrode. Furthermore, another object of the present invention is to provide an ink jet recording head capable of high-definition printing using such a piezoelectric thin film element.

  The present invention that achieves this object relates to a novel improved piezoelectric thin film element. That is, in order to improve the piezoelectric characteristics of the piezoelectric thin film element, a metal film formed on the substrate, and a PZT thin film formed on the metal film by adding a third component to lead zirconate titanate; The PZT thin film has a rhombohedral crystal structure, and the degree of (100) orientation of the crystal structure measured by the X-ray diffraction thin film method is 30% or more. It is characterized by.

  In order to make the orientation degree in this way, the annealing temperature of the PZT thin film is higher than 750 ° C. and lower than 1000 ° C., preferably 800 ° C. or higher and 1000 ° C. or lower, more preferably, Zr / Ti is a molar ratio, 35/45 ≦ (Zr / Ti) ≦ 45/35.

  Further, preferably, the crystal structure of the piezoelectric thin film is further improved, and a piezoelectric body comprising a piezoelectric film made of a polycrystalline body, and an upper electrode and a lower electrode arranged with the piezoelectric film interposed therebetween. In the thin film element, the crystal of the piezoelectric film is formed in a direction substantially perpendicular to the electrode surface. That is, the grain boundaries of the piezoelectric crystal are formed in a direction substantially perpendicular to the electrode surface.

  In a preferred embodiment of the piezoelectric thin film element, the piezoelectric film has a rhombohedral crystal structure, a crystal plane with a plane orientation (111), a crystal plane with a plane orientation (100), or It is strongly oriented to either the crystal orientation of the plane orientation (111) or the plane orientation (100).

  The piezoelectric film has a tetragonal crystal structure and is strongly oriented to a crystal plane having a plane orientation (001).

  An even higher piezoelectric strain constant can be obtained by making the width of the crystal grains in the film thickness direction longer than the width of the crystal grains in the film surface direction. Preferably, the relationship between the width of the crystal grains in the film thickness direction and the width of the crystal grains in the film surface direction is expressed as follows: width in the film surface direction / width in the film thickness direction = 1/10 or more 1/3 It is made below.

  Preferably, the lower electrode is made of a compound of platinum and an oxide of a metal element that is a constituent element of the piezoelectric film. By doing so, the adhesion between the piezoelectric film and the lower electrode is improved. This oxide is composed of, for example, at least one selected from the group consisting of titanium oxide, lead oxide, zirconium oxide, magnesium oxide, and niobium oxide.

  More preferably, the grain boundaries of the crystal constituting the lower electrode are present in a direction substantially perpendicular to the film surface of the piezoelectric film. Further, the width in the film thickness direction of the crystal grains of the crystal constituting the lower electrode is made longer than the width in the film surface direction of the crystal grains. Further, the relationship between the width in the film thickness direction of the crystal grains of the crystal constituting the lower electrode and the width in the film surface direction of the crystal grains is as follows: width in the film surface direction / width in the film thickness direction = 1/10 or more 1/3 or less. By doing so, the substrate is prevented from being warped or distorted by the heat treatment performed when the piezoelectric film is formed.

The PZT thin film is formed by a sol-gel method or a sputtering method. The piezoelectric film is composed of two-component PZT or three-component PZT obtained by adding a third component to this two-component PZT. In the case of the sol-gel method, the third component of the PZT thin film is, for example, lead magnesium niobate. In the PZT thin film to which lead magnesium niobate is added as the third component, _{x of} Pb (Mg _1/3 Nb _2/3 ) _0.2 Zr _x Ti _0.8-x O ₃ is preferably 0.35 to 0.45. It is.

  In a thin film piezoelectric element including a piezoelectric film made of a polycrystalline body having a film thickness of 0.5 to 25 μm and two electrodes sandwiching the piezoelectric film so as not to cause cracks in the piezoelectric thin film, There are pores in the body membrane, the average pore diameter of the pores is 0.01 μm or more, and the surface density is adjusted to 0.3% or more. Preferably, the average pore diameter of the pores is 0.1 μm or less, and the area density is 5% or less. Such pores are formed, for example, when the organic substance in the sol composition is evaporated and removed when the sol composition for producing the PZT film is gelled and heat-treated. When the PZT film is formed by sputtering, it is formed, for example, by controlling the heating conditions described later.

  Preferably, in the manufacturing method for forming the PZT thin film on the substrate on which the metal film is formed, the heat treatment temperature of the PZT thin film is 800 to 1000 ° C. in the case of the sol-gel method. In that case, the PZT thin film obtained by adding a third component to lead zirconate titanate may be used.

As described above, in order to make the crystal of the piezoelectric thin film into a columnar shape, a PZT precursor film is preferably sputtered on the metal film on the substrate in an atmosphere containing no oxygen. In this case, the composition range of the PZT target is PbZrO ₃ : PbTiO ₃ : Pb (A _g B _h ) O ₃ = a: b: c, and a, b, and c are in molar ratios,
a + b + c = 1,
0.10 ≦ a ≦ 0.55,
0.25 ≦ b ≦ 0.55,
0 ≦ c ≦ 0.5,
It is characterized by being.

  Where A is a divalent metal selected from the group consisting of Mg, Co, Zn, Cd, Mn and Ni, or a trivalent selected from the group consisting of 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. When A is a trivalent metal and 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. Preferably, A is Mg and B is Nb.

Preferably, (a, b, c) is A ′, B ′, C, where a: b: c is mol%, respectively.
It is in the area surrounded by ', D', E ', F'.

A ': (45, 55, 0)
B ': (50, 50, 0)
C ': (25, 25, 50)
D ′: (10, 40, 50)
E ': (10, 45, 40)
F ': (35, 45, 20)
That is, the PZT film constituting the piezoelectric film is composed of the components.

  The present invention further includes a substrate on which an ink chamber is formed, a vibration plate that seals one of the ink chambers and has a piezoelectric thin film element in a flexural vibration mode fixed to the surface, and the other of the ink chambers. In an ink jet recording head comprising a nozzle plate having a surface sealed and an ink ejection nozzle opening, the piezoelectric thin film element is composed of the above-described novel and useful piezoelectric thin film element It is characterized by that.

It is a schematic perspective view at the time of applying the piezoelectric thin film element by this invention to an actuator (inkjet recording head). FIG. 2 is a detailed cross-sectional view of the piezoelectric thin film element of FIG. 1. It is a characteristic view which shows the X-ray-diffraction pattern by the thin film method of the PZT thin film annealed at 900 degreeC. It is a characteristic view which shows the X-ray-diffraction pattern by the thin film method of the PZT thin film annealed at 750 degreeC. (A) is a scanning electron microscope (SEM) photograph showing a cross section of a PZT film of columnar crystals constituting a piezoelectric thin film element according to the present invention, and (B) is a scanning electron microscope photograph showing the plane. is there. (A) thru | or (c) is sectional drawing of each process which shows the manufacturing process of the piezoelectric material thin film element of FIG. It is a characteristic view which shows the composition range of the piezoelectric material thin film of FIG. 3 is a scanning electron micrograph showing a cross section of a PZT film constituting Comparative Product 1. FIG. It is a scanning electron micrograph which shows the plane of the PZT film | membrane shown in FIG. It is a scanning electron micrograph which shows the cross section of the lower electrode of the columnar crystal which comprises a piezoelectric material thin film element. It is a scanning electron micrograph which shows the cross section of the lower electrode which comprises a comparative product. It is an expanded sectional view of the dotted line part of FIG. It is a perspective view at the time of applying the thin film piezoelectric element by this invention to a bimorph type actuator. It is sectional drawing which used the piezoelectric material thin film element of this invention for the inkjet recording device. The composition range represented by the formula (I) in the detailed description of the invention is shown in FIG.

  Next, embodiments and drawings according to the present invention will be described below with reference to the drawings as necessary. In the present embodiment, a case where a PZT film is formed as a piezoelectric film will be described.

  I. First, a specific structure of a thin film piezoelectric element will be described with reference to the drawings. In FIG. 1, a thin film piezoelectric element includes a silicon (Si) substrate 10, a lower electrode (for example, made of Pt) 12, a piezoelectric film (for example, two-component PZT) 14, and an upper electrode 16 (for example, Pt).

  FIG. 2 is a cross-sectional view showing the structure of the piezoelectric thin film element in more detail. The silicon substrate 10, the silicon oxide film 11 formed on the silicon substrate, and the titanium oxide film formed on the silicon oxide film. 11A, a lower electrode 12 formed on the titanium oxide film, a PZT film (piezoelectric film) 14 formed on the lower electrode, and an upper electrode 16 formed on the PZT film. ing.

  By forming the lower electrode from, for example, platinum, the lattice constant of the lower electrode can be brought close to the lattice constant of the PZT film, and the adhesion between the lower electrode and the PZT film to be formed later can be improved.

(Reference Example 1)
In Reference Example 1, first, platinum was formed as the lower electrode 12 on the silicon substrate 10 by sputtering. Next, the piezoelectric thin film 14 was formed by a sol-gel method. The sol was prepared as follows. 0.105 mol of lead acetate, 0.045 mol of zirconium acetylacetonate, 0.005 mol of magnesium acetate and 30 ml of acetic acid were heated to 100 ° C. and dissolved.

  The sol was cooled to room temperature, and 0.040 mol of titanium tetraisopropoxide and 0.010 mol of pentaethoxyniobium were dissolved in 50 ml of ethyl cerasolve and added. After stabilizing by adding 30 ml of acetylacetone, 30% by weight of polyethylene glycol was added to the metal oxide in the sol, and stirred well to obtain a homogeneous sol.

  The sol prepared on the substrate on which the lower electrode is formed is applied by spin coating, and calcined at 400 ° C. to form an amorphous porous gel thin film. Repeatedly, a porous gel thin film was formed. During this heating, the polyethylene glycol in the sol evaporates to form a porous material.

  Next, in order to obtain a perovskite crystal, an RTA (Raid Thermal Anneaing) furnace was used, heated to 650 ° C. for 5 seconds in an oxygen atmosphere, held for 1 minute, and pre-annealed to obtain a dense PZT thin film.

  The process of applying this sol again by spin coating and pre-baking at 400 ° C. was repeated three times to laminate an amorphous porous gel thin film. Next, it was pre-annealed at 650 ° C. using RTA and held for 1 minute to obtain a dense crystalline thin film. By setting the temperature during this pre-annealing to 400 to 800 ° C., preferably 450 to 750 ° C., and more preferably 550 to 750 ° C., it is possible to integrate the porous thin film laminated interface described above.

  Furthermore, using an RTA furnace, annealing was performed by heating to each temperature of 750, 800, 850, 900, 950, 1000, and 1050 ° C. in an oxygen atmosphere for 1 minute. As a result, a piezoelectric thin film 14 having a thickness of 1.0 μm was obtained.

  The PZT thin film thus obtained was analyzed by the X-ray diffraction thin film method. The measurement was performed using RINT-1400 manufactured by Rigaku Corporation with a copper tube at an X-ray incident angle of 1 °.

  FIG. 3 shows an X-ray diffraction pattern of a PZT thin film annealed at 900 ° C. by a thin film method. FIG. 4 shows an X-ray diffraction pattern of a PZT thin film annealed at 750 ° C. by a thin film method.

  All peaks in the X-ray diffraction patterns shown in FIGS. 3 and 4 are reflection peaks of PZT having a perovskite structure. Furthermore, although this PZT thin film adopts rhombohedral or tetragonal crystals as the crystal system, the peaks of (100), (110), etc. are not separated but become one sharp peak. It is a crystal.

  In addition, an aluminum electrode was formed on the piezoelectric thin film by vapor deposition, and the piezoelectric constant d31 was measured. Table 1 shows the relationship between the annealing temperature, the (100) orientation degree, and the piezoelectric constant d31.

  Here, the degree of orientation P (100) of (100) is represented by P (100) = I (100) / ΣI (hkl). ΣI (hkl) is the X-ray diffraction thin film method and represents the sum of the total diffraction intensities of PZT with 2θ of 20 ° to 60 ° when CuKα rays are used for the wavelength.

  However, since the (200) plane is a crystal plane equivalent to the (100) plane, it is not included in ΣI (hkl). Specifically, (100), (110), (111), (210), (211), and the total sum of crystal plane reflection intensities. I (100) similarly represents the (100) crystal plane reflection intensity of PZT.

  As the orientation degree P (100) of (100) increases, the piezoelectric constant d31 increases and the characteristics of the actuator are improved.

Example 1
Gold was formed by sputtering on the silicon substrate as the lower electrode. Next, a piezoelectric thin film was formed by a sol-gel method. The sol was prepared as follows. 0.105 mol of lead acetate, 0.030 mol of zirconium acetylacetonate, 0.007 mol of magnesium acetate and 30 ml of acetic acid were dissolved by heating to 100 ° C.

  The sol was cooled to room temperature, and 0.050 mol of titanium tetraisopropoxide and 0.013 mol of pentaethoxyniobium were dissolved in 50 ml of ethyl cerasolve and added. After stabilization by adding 30 ml of acetylacetone, 30% by weight of polyethylene glycol was added to the metal oxide in the sol and stirred well to obtain a homogeneous sol (Zr / Ti = 30/50).

  Similarly, 0.035 mol of zirconium acetylacetonate, 0.045 mol of titanium tetraisopropoxide (Zr / Ti = 35/45), 0.040 mol of zirconium acetylacetonate, 0.040 mol of titanium tetraisopropoxide ( Zr / Ti = 40/40), zirconium acetylacetonate 0.045 mol, titanium tetraisopropoxide 0.035 mol (Zr / Ti = 45/35), four types of sols having different compositions of zirconium and titanium A liquid was prepared.

  Thereafter, in the same manner as in Reference Example 1, a piezoelectric thin film element was prepared by laminating with each sol solution and evaluated. Table 2 shows the relationship between Zr / Ti, (100) orientation, and piezoelectric constant d31.

  As in Reference Example 1, the higher the (100) orientation degree P (100), the greater the piezoelectric constant d31, and the better the characteristics as an actuator.

  In Reference Example 1 and Example 1 described above, Pt and Au are used as the lower electrode. However, the (100) orientation degree of the PZT thin film only needs to be 30% or more. Au, Pt—Ir Other metal films such as Pt—Pd, Pt—Ni, and Pt—Ti may be used.

  Furthermore, although the description has been made using lead magnesium niobate as the third component, it is sufficient that the (100) orientation degree of the PZT thin film is 30% or more, and other things such as lead nickel niobate, lead cobalt niobate, etc. It does not prevent that Nb, La, Mo, W, Ba, Sr, Bi, etc. are contained as impurities.

  II. Next, a piezoelectric element including a piezoelectric thin film in which crystal grains are formed in a direction substantially perpendicular to the electrode surface will be described. 5A is a scanning electron microscope (SEM) photograph showing a cross section of the PZT film constituting the piezoelectric thin film element, and FIG. 5B is a scanning type showing the plane of the PZT film shown in FIG. It is an electron micrograph.

The PZT film 14 shown in FIGS. 1 and 2 is made of a polycrystal, and grain boundaries of the crystal exist in a direction substantially perpendicular to the planes of the upper and lower electrodes as shown in FIG. In FIG. 5, it is confirmed that the intermediate white is the PZT film, and the crystal grains are formed in a column shape extending vertically in FIG. A layer displayed in white below the PZT film is a lower electrode, and SiO ₂ is disposed further below the lower electrode. The grain boundary of a crystal is a boundary between adjacent crystal grains. The crystal grain is a crystal having a perovskite structure, whereas the crystal grain boundary is composed of an amorphous material.

  This crystal body has a width in the film thickness direction (indicated by Y in FIG. 5) larger than the width in the film surface direction (indicated by X in FIG. 5) of the crystal grain, and the film thickness direction of the crystal grain. And the width of the crystal grain in the film surface direction are within the range of the width in the film surface direction / the width in the film thickness direction = 1/10 or more and 1/3 or less.

  Furthermore, the crystal structure of this PZT film is rhombohedral and is strongly oriented to the crystal plane of the plane orientation (111). The “degree of orientation” shown here is defined as follows when, for example, 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)}
The relationship between the orientation degree of the plane orientation (111) and the piezoelectric strain constant is as follows.

Orientation degree of (111) plane Voltage distortion constant 50% 80 pC / N
70% 120pC / N
90% 150pC / N
In the above-described Reference Example 1 and Example 1, it has been described that the degree of orientation of (100) is preferably 30%. As can be seen, by setting the degree of orientation of (111) to 50% or more, the same voltage distortion constant as in Reference Example 1 and Example 1 can be obtained to obtain piezoelectric characteristics.

  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 (Y direction in FIG. 5) increases, and the piezoelectric output coefficient increases in the lateral direction (X direction in FIG. 5). The PZT film 15 having such a structure has an improved piezoelectric strain constant because the width is larger as the width is smaller.

  For this reason, as described above, the value of the width in the film surface direction / the width in the film thickness direction of the crystal of the piezoelectric thin film is in the range of 1/10 to 1/3. Preferably they are 1/8 or more and 3/10 or less, More preferably, they are 1/6 or more and 3/11 or less.

  Here, a PZT film having a two-component system as a main component and a ternary system obtained by adding a third component to the two-component system as a main component is preferably used. As a preferred specific example of the two-component PZT, when a PZT film is formed by sol-gel, for example, it has a composition of the following chemical formula.

Pb (Zr _x Ti _1-x ) O ₃ + YPbO
(Where 0.40 ≦ X ≦ 0.6, 0 ≦ Y ≦ 0.1)
In addition, a binary PZT film in the case of forming a PZT film by sputtering has, for example, a composition represented by the following chemical formula.

Pb (Zr _x Ti _1-x ) O ₃ + YPbO
(Where 0.40 ≦ X ≦ 0.6, 0 ≦ Y ≦ 0.3)
As a preferred specific example of the ternary PZT, in the sputtering method, for example, a third component (preferably lead magnesium niobate) is added to the two-component PZT. What has a composition represented by these is mentioned.

PbTi _b Zr _a (A _g B _h ) _c O ₃ + ePbO + (fMgO) _n (formula I)
(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 Y, Fe, Sc, Yb, Lu, In and Cr. B represents a trivalent metal, and 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. , B, and c, respectively, a + b + c = 1, 0.10 ≦ a ≦ 0.55, 0.25 ≦ b ≦ 0.55, 0 ≦ c ≦ 0.5, 0 ≦ e ≦ 0. 3, 0 ≦ f ≦ 0.15c, g = h = 1/2, n = 0, provided that A is a trivalent metal, B is not a hexavalent metal, and A is When divalent metal and B is pentavalent metal, g is 1/3, h is 2/3, A is Mg, and B is Nb. Only, n represents represents 1.)
More preferable specific examples of the ternary system include lead magnesium niobate, wherein A is Mg, B is Nb, g is 1/3, and h is 2/3.

The PZT film to which lead magnesium niobate is added as the third component when using the sol-gel method is, for example, Pb (Mg _1/3 Nb _2/3 ) _0.2 Zr _x Ti _0.8-x O ₃ (x is 0.35). ~ 0.45).

  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. A part of the third component may be replaced with the fourth component. In that case, one of the third components is used as the fourth component.

  In addition to the above-described orientation, the PZT film may be strongly oriented in either the crystal plane of the plane orientation (100) or the crystal plane of the plane orientation (111) and the plane orientation (100). Further, the crystal structure of the PZT film may be tetragonal and may be strongly oriented on the crystal plane with the plane orientation (001).

(Reference Example 2)
Next, a method for manufacturing a piezoelectric thin film element having this structure will be described with reference to the drawings.
6A to 6C are cross-sectional views in each manufacturing process of the piezoelectric thin film element described above.

  In the step shown in FIG. 6A, thermal oxidation is performed on the silicon substrate 10 to form a silicon oxide film 11 having a thickness of about 0.3 to 1.2 μm on the silicon substrate. Next, a titanium oxide film 11A having a thickness of about 0.005 to 0.04 μm is formed on the silicon oxide film by sputtering.

  Next, the lower electrode 12 made of platinum is formed on the titanium oxide film with a film thickness of about 0.2 to 0.8 μm. Next, in the step shown in FIG. 6B, the PZT film 14 is formed to a thickness of about 0.5 to 3.0 μm on the lower electrode formed in the step shown in FIG. Further, the case where the PZT film is manufactured by the sputtering method and the case of the sol-gel method will be described.

Reference Example 2-1: Method for Producing PZT Film by Sputtering Method First, a PZT sintered body having a specific component is used as a sputtering target, the substrate temperature is set to 200 ° C. or less, and RF magnetron sputtering is performed in an Ar gas 100% atmosphere. A precursor film of a PZT film made of an amorphous or pyrochlore phase is formed on a substrate.

  Next, this precursor film is heated, crystallized and sintered. This heating is preferably performed in two stages in an oxygen atmosphere (for example, in oxygen or a mixed gas of oxygen and an inert gas such as argon).

  That is, in the first heating step, the amorphous precursor film is heated at a temperature of about 500 to 700 ° C. in an oxygen atmosphere, thereby crystallizing the precursor film. This first heating step may be terminated when the precursor film is uniformly crystallized.

  Next, in the second heating step, the generated crystal grains are grown and further the sintering of the crystal grains is promoted. Specifically, the precursor film crystallized in the first heating step is heated at a temperature of about 750 to 1200 ° C. In this heating, the grain boundary of the crystal exists in a direction substantially perpendicular to the surface of the lower electrode 14, and the relationship between the width in the film thickness direction of the crystal grain and the width in the film surface direction of the crystal grain is The process is performed until the width in the plane direction / the width in the film thickness direction is within a range of 1/3 to 1/10.

  In this way, the lower electrode is made of a polycrystal and the grain boundary exists in a direction substantially perpendicular to the lower electrode surface (Y direction in FIG. 5), and the film thickness direction of the crystal grains of the crystal The width of the crystal grain in the film surface direction (X direction) is longer than the width of the crystal grain (X direction), and the relationship between the width of the crystal grain in the film thickness direction and the width of the crystal grain in the film surface direction is A PZT film having a width in the plane direction / width in the film thickness direction = 1/3 to 1/10 was formed.

  Here, the first heating step and the second heating step may be performed continuously, and after the first heating step, the first heating step is cooled to room temperature, and then the second heating step is performed. May be.

  In the first and second heating steps, various heating furnaces are used as long as the precursor film can form the PZT film 15 having the structure described above. However, it is preferable to use a heating furnace with a high heating rate. . For example, it is preferable to use a lamp annealing furnace. In addition, the preferable temperature increase rate in a 1st and 2nd heating process is 50 degreeC / second or more, More preferably, it is 100 degreeC / second or more.

FIG. 7 shows a preferable composition range of the PZT film (or PZT target) when the PZT precursor film is formed by sputtering. Here, Pb (Mg _1/3 Nb _2/3 ) O ₃ is used as the third component from the Pb (A _g B _h ) O ₃ of the above-described (formula I). A region surrounded by A, B, C, D, E, and F in FIG. 7 corresponds to this composition range.

When PbZrO ₃ : PbTiO ₃ : Pb (Mg _1/3 Nb _2/3 ) O ₃ = a: b: c, (a, b, c) is expressed in mol%, the following results.

A: (45, 55, 0)
B: (50, 50, 0)
C: (25, 25, 50)
D: (10, 40, 50)
E: (10, 45, 40)
F: (35, 45, 20)
That is, 10 ≦ a ≦ 50, 20 ≦ b ≦ 55, and 0 ≦ c ≦ 50. This range is a preferable range of the range described in the formula (I).

  The significance of defining the right boundary (C-B) in FIG. 7 is as follows.

It has been found that when PbTiO ₃ is increased from PbZrO ₃ , a columnar film is suitably formed by the sputter film formation method.

  Further, the left boundary (D-E-F-A) in FIG. 7 was determined in order to obtain a high voltage distortion constant (100 pC / N or more). Further, since the Curie temperature approaches room temperature, the upper boundary (D-C) in FIG. 7 may be deteriorated in stability as a device. In addition, above the Curie temperature, the piezoelectric characteristics of the piezoelectric element are not sufficiently exhibited. The composition range represented by the formula (I) is shown in FIG.

Reference Example 2-2: Manufacturing Method by Sol-Gel Method In this manufacturing method, a hydroxide hydrate complex of a metal component capable of forming a PZT film, that is, a sol is dehydrated into a gel, and the gel is heated and fired. Two methods for adjusting the inorganic oxide will be described. These sol-gel methods are substantially the same as those in Reference Example 1 and Example 1 described above, but will be described in detail here.

(Part 1)
a. In the present reference example, 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, for example, an acid. In the present invention, the composition of the PZT film described above can be obtained by controlling 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.

  In this reference example, 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 gel is determined according to the piezoelectric film to be generated (PZT film in this reference example).

  Further, in this reference example, in order to obtain a PZT film in which the above-described lead component is excessive, the lead component is excessively increased to 20 mol%, preferably 15 mol%, from the amount required from the stoichiometry. It is preferable.

  In this reference example, 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.

  Examples of the organic polymer compound preferably used include polyvinyl acetate, hydroxypropyl cellulose, polyethylene glycol, polyethylene glycol monomethyl ether, polypropylene glycol, polyvinyl alcohol, polyacrylic acid, polyamide, polyamic acid, acetylcellulose, and derivatives thereof, and There are copolymers.

  In addition, in this reference example, by adding polyvinyl acetate, a porous gel thin film having a large number of pores of about 0.05 μmφ is added to a size of 0.1 μm or less by adding hydroxypropylcellulose. In addition, a porous gel thin film having a wide distribution of pores can be formed.

  In this reference example, 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.

  In the manufacturing method according to this reference example, first, this sol composition is applied on the lower electrode (see FIG. 6B) on which a PZT film 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.

  In addition, the thickness of the film formed by coating can be controlled so that the thickness of the porous gel thin film formed in the gelation step described later becomes 0.01 μm or more in consideration of the subsequent steps. Desirably, more preferably about 0.1 to 1 μm.

  Next, the applied sol composition is naturally dried or heated at a temperature of 200 ° C. or lower. Here, the sol composition can 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.

b. Next, the film obtained in the above-described sol composition film-forming step is fired to form a porous gel made of an amorphous metal oxide substantially free of residual organic substances. A thin film is formed.

  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 this reference example, the firing temperature is preferably 300 to 450 ° C, 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.

c. Pre-annealing step Next, the porous gel thin film obtained in the above-described step b 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.

  In this embodiment, the firing temperature is preferably in the range of 400 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. Further, when an RTA (Rapid Thermal Annealing) furnace is used, it is preferably about 0.1 to 10 minutes, and more preferably about 1 to 5 minutes.

  In this reference example, the pre-annealing process is performed in two stages. Specifically, first, pre-annealing is performed at a temperature in the range of 400 to 600 ° C. as the first stage, and then pre-annealing is performed at a temperature in the range of 600 to 800 ° C. as the second stage. More preferably, pre-annealing is performed at a temperature in the range of 450 to 550 ° C. as the first stage, and then pre-annealing is 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.

d. Repeating Steps Next, steps a, b and c described above are repeated at least once to deposit a crystalline metal oxide film. Here, the film thickness, baking temperature, and pre-annealing conditions of the film obtained in this repeating process are the same as those in the case where the first film is formed on the lower electrode.

  The film thickness of the laminated film obtained as a result of this repeating process may be appropriately determined in consideration of the final film thickness of the PZT film, but an appropriate film that does not generate cracks or the like in the subsequent process (process e) described later. Thickness is preferred.

  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.

  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 this reference example. There may be discontinuous layers between the layers. When the steps a, b and c 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 obtained from the previously obtained crystalline laminated film. And a film that is substantially integrated.

  The patterning for forming the piezoelectric thin film element and the formation of the upper electrode are preferably performed at this stage.

e. Perovskite-type crystal growth step Next, the film obtained in 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.

  This 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.

  By the above operation, the lower electrode 14 is made of a polycrystal, the grain boundary exists in a direction substantially perpendicular to the surface of the lower electrode 14, and the width of the crystal grain in the film thickness direction is It is longer than the width of the crystal grain in the film surface direction, and the relationship between the width of the crystal grain in the film thickness direction and the width of the crystal grain in the film surface direction is: width in the film surface direction / width in the film thickness direction = 1/10. A PZT film 15 in a range of ˜1 / 3 was formed.

(Part 2)
Next, another method for manufacturing a piezoelectric thin film element using the sol-gel method will be described.

f. Step of forming porous gel thin film First, steps a and b described above are repeated at least once to form a laminated film of porous gel thin films. In addition, the film thickness formed in processes a and b and the firing temperature are in accordance with the manufacturing process (part 1) described above.

  In this reference example, the thickness of the laminated film is preferably set to 1 μm or less, and more preferably 0.5 μm or less. By setting the thickness of the laminated film to this level, it is possible to prevent the film from cracking during the pre-annealing in the next step (step c ′). By this step, a laminated film in which a plurality of porous gel thin films were laminated was obtained.

c '. Pre-annealing step Next, the laminated film obtained in the step f is baked to convert the laminated film into a film made of a crystalline metal oxide. This firing is performed at a temperature necessary to convert the laminated 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 uniformly formed. What is necessary is just to complete | finish when it crystallizes. The firing temperature and time may be substantially the same as in step c. In addition, this firing may be performed in two steps as in the step c. By this step, a laminated film in which a plurality of polycrystalline gel thin films were laminated was converted into a crystalline thin film.

d '. Repeat Steps Next, steps f and c ′ are repeated at least once. That is, in this step, the steps a and b are repeated at least once more to form a laminated film of a porous gel thin film, which is further baked to convert it into a film made of crystalline metal oxide. Repeat more than once. In this manner, a laminated film in which a plurality of films made of a crystalline metal oxide film are laminated is formed. Various conditions in the repeated steps a, b and c ′ were the same as those described above.

  The film thickness of the laminated film obtained in this step d ′ is appropriately determined in consideration of the film thickness of the finally obtained PZT film 15, but in the next step (step e ′) described later, the film is cracked. It is preferable to set the film thickness so that no such phenomenon occurs.

  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. Here, the definition of the substantially integrated film is as described above.

  The patterning for forming the piezoelectric thin film element and the formation of the upper electrode 16 are preferably performed at this stage.

  Thereafter, the step e is performed, and the lower electrode 14 is made of a polycrystal, the grain boundary is present in a direction substantially perpendicular to the surface of the lower electrode 14, and the width of the crystal grain in the film thickness direction is The width of the crystal grain in the film surface direction is longer than the width of the crystal grain in the film surface direction, and the relationship between the width of the crystal grain in the film surface direction is as follows. A PZT film having a range of / 10 to 1/3 was formed.

  Next, in the step shown in FIG. 6 (c), the PZT film obtained in the step shown in FIG. 6 (b) is made of aluminum having a thickness of about 0.2 to 1.0 μm by sputtering. The electrode 16 is formed.

  In this way, the piezoelectric thin film element shown in FIG. 2 was obtained. In addition, it was confirmed that the obtained PZT film 14 had no cracks, and the cross-section had no layered discontinuous surface due to the above-described lamination.

(Reference Example 3)
Next, the piezoelectric thin film element (invention product 1) according to Reference Example 3 and the crystal product constituting the PZT film were invented except that the grain boundaries did not exist in a direction substantially perpendicular to the surface of the lower electrode. When the piezoelectric strain constant (pC / N) of the piezoelectric thin film element (comparative product 1) having the same structure as in FIG. 1 was measured, the piezoelectric strain constant of invention product 1 was 150 pC / N. The piezoelectric strain constant of was 100 pC / N.

  As a result, it was confirmed that the inventive product 1 exhibits a higher piezoelectric strain constant than the comparative product 1. The piezoelectric strain constant is measured by measuring the dielectric constant using an impedance analyzer with a PZT dot pattern of 2 mmφ and the voltage output coefficient obtained from the voltage generated in the dot pattern when the free end of the cantilever is applied. It was calculated by the product of Further, FIG. 8 shows an SEM photograph showing a cross section of the PZT film of Comparative Product 1, and FIG. 9 shows an SEM photograph showing a plane of the PZT film shown in FIG. Invention 1 had a good appearance with little warpage and distortion.

  In Reference Example 3, the case where the PZT film is manufactured by the sputtering method or the sol-gel method has been described. However, the present invention is not limited to this, and a structure in which the grain boundary of the crystal exists in a direction substantially perpendicular to the surface of the lower electrode. Of course, other methods may be used as long as a PZT film having the above can be formed.

  In Reference Example 3, the grain boundary of the crystal exists in a direction substantially perpendicular to the plane of the electrode, and the width of the crystal grain in the film thickness direction is larger than the width of the crystal grain in the film surface direction. The relationship between the width in the film thickness direction of the crystal grain and the width in the film surface direction of the crystal grain is configured in the range of the width in the film surface direction / the width in the film thickness direction = 1/10 to 1/3. Although the PZT film has been described, it is sufficient that at least the grain boundary of the crystal body exists in a direction substantially perpendicular to the plane of the electrode.

(Reference Example 4)
FIG. 10 is a scanning electron microscope (SEM) photograph showing a cross section of a lower electrode constituting another piezoelectric thin film element. In Reference Example 4, differences from Reference Example 3 described above will be described, and the same configurations and processes as in Reference Example 2 will be denoted by the same reference numerals, and detailed description thereof will be omitted.

  The difference between the piezoelectric thin film element according to the reference example and the piezoelectric thin film element according to the reference example 2 is the structure and manufacturing method of the lower electrode. That is, the lower electrode of the piezoelectric thin film element according to this reference example is composed of a compound of platinum and titanium oxide (platinum 99 wt%, titanium oxide 1 wt%), and the grain boundary of the crystal of this compound is As shown in FIG. 10, it has a structure that exists in a direction substantially perpendicular to the surface of the substrate.

  Further, the crystal body constituting the lower electrode has a grain boundary substantially perpendicular to the film surface of the PZT film, and the relationship between the width in the film thickness direction of the crystal grain and the width in the film surface direction. However, the width in the film surface direction / the width in the film thickness direction = 1/10 to 1/3.

  The lower electrode having such a structure suppresses the substrate from being warped or distorted by the heat treatment performed when forming the PZT film because titanium oxide suppresses the shrinkage of platinum. Can do. In addition, the adhesion between the PZT film and the titanium oxide film can be improved.

  Next, the manufacturing method of the lower electrode provided with this structure is demonstrated.

  First, a silicon oxide film 11 and a titanium oxide film 11A are formed on a silicon substrate 10 by a method similar to the process shown in FIG. Next, the lower electrode 12 is formed on the titanium oxide film by a multi-sputtering method in which a platinum target and a titanium oxide target are simultaneously discharged to form a film. By doing so, it is composed of a compound of platinum and titanium oxide (platinum 99 wt%, titanium oxide 1 wt%), and the grain boundary of the crystal of this compound is substantially perpendicular to the surface of the substrate 10. The relationship between the width in the film thickness direction of the crystal grain and the width in the film surface direction is as follows: width in the film surface direction / width in the film thickness direction = 1/10 to 1/3 The lower electrode 12 configured in such a range can be obtained.

  Thereafter, the PZT film 14 and the upper electrode 16 were formed on the lower electrode 12 by the same method as in Reference Example 3 described above, and a piezoelectric thin film element was obtained. It was confirmed that the piezoelectric thin film element according to Reference Example 4 also showed a high piezoelectric strain constant.

  Next, a piezoelectric thin film element (Invention product 2) according to Reference Example 4 and a piezoelectric thin film element (Comparative product 2) having the same structure as that of Invention product 2 except that the lower electrode is made of only platinum. The occurrence of warpage and distortion was investigated. FIG. 11 is a scanning electron micrograph showing a cross section of the lower electrode constituting the comparative product 2. FIG. 11 is a comparative example with respect to FIG. 10 and shows a structure in which PZT is not columnar. This investigation was performed by measuring the warpage of the substrate on which the piezoelectric thin film element was formed.

  As a result, it was confirmed that the inventive product 2 hardly warped or distorted, but the comparative product 2 produced more warp or distorted than the inventive product 2.

  In addition, regarding the inventive product 2 and the comparative product 2, the adhesion between the lower electrode 12 and the PZT film 14 and the adhesion between the lower electrode 12 and the titanium oxide film 11A were investigated. This investigation was conducted with a scratch testing machine. As a result, it was confirmed that the inventive product 2 was better in both the adhesion between the lower electrode and the PZT film and the adhesion between the lower electrode and the titanium oxide film than the comparative product 2.

  In this reference example, the lower electrode has the composition described above. However, the present invention is not limited to this, and the platinum and titanium oxide content is 90 to 99.5 wt% for platinum and 0.5 to 10 for titanium oxide. % By weight.

  In this reference example, the grain boundary of the crystal body of the lower electrode exists in a direction substantially perpendicular to the surface of the substrate 10, and the relationship between the width in the film thickness direction of the crystal grain and the width in the film surface direction However, the lower electrode 14 configured in a range of width in the film surface direction / width in the film thickness direction = 1/10 to 1/3 has been described. However, the lower electrode is not limited thereto, and at least the crystal grains are formed. The field only needs to exist in a direction substantially perpendicular to the surface of the substrate 10.

  In this reference example, the case where the lower electrode is composed of a compound of platinum and titanium oxide has been described. However, the present invention is not limited thereto, and the lower electrode is made of platinum and other metal elements that are constituent elements of the PZT film. You may comprise from a compound with an oxide. Examples of the oxide include lead oxide, zirconium oxide, magnesium oxide, niobium oxide and the like in addition to titanium oxide.

(Reference Example 5)
Next, a description will be given of a reference example of the present invention in which cracks in the piezoelectric thin film are prevented by controlling the diameter of closed pores (pores). FIG. 12 shows an enlarged cross-sectional view of the dotted line portion in FIG. As shown in FIG. 12, pores 20 are present in the piezoelectric film 10, and the pores are rounded and confined within crystal grains or between crystal grains. Closed pores (individual crystal grains are not shown in the figure), the average pore diameter is 0.01 to 0.1 μm, and the area density is 0.3 to 5%.

  The film thickness of the piezoelectric film is preferably about 0.5 to 25 μm, and more preferably about 1 to 5 μm. Furthermore, the thicknesses of the other films may be appropriately determined. For example, the Si substrate has a thickness of about 10 to 1000 μm, the Si thermal oxide film has a thickness of about 0.05 to 3 μm, and the upper electrode and the lower electrode have a thickness of 0.05. About ~ 2 μm is preferable.

  Hereinafter, a method for manufacturing a piezoelectric element using the piezoelectric film will be described in detail, but the manufacturing method is not limited to the manufacturing method of these reference examples.

  A Si substrate having a thickness of 400 μm and a diameter of 3 inches is washed with sulfuric acid and then heated in an oxygen atmosphere containing water vapor at 1000 ° C. for 4 hours to form wet thermal oxidation to form a 1 μm thick Si thermal oxide film. did. Next, a Ti film having a film thickness of 200 angstroms and a Pt film having a film thickness of 2000 angstroms were successively formed by direct current magnetron sputtering. Further, a PZT sintered body having a controlled composition was used as a sputtering target, and a 1 μm-thick piezoelectric film precursor film was formed on the Pt film by RF magnetron sputtering. This precursor film was in an amorphous state because it was sputtered without heating.

  The Si substrate on which the precursor film was formed was heated in an oxygen atmosphere in a diffusion furnace to crystallize and sinter the precursor film to obtain a piezoelectric film. The temperature condition at that time was heating until crystallization at 600 ° C. as the first heating step, and then sintering was performed at 750 ° C. as the second heating step. Adjustment of the average pore diameter and area density of the pores in the piezoelectric film mainly takes effect of the Pb composition ratio in the film in the amorphous state, the first heating step temperature, and the second heating step time. When the amount of Pb in the amorphous film is large, both the pore diameter and the area density tend to increase. If the temperature of the second heating step is high or the heating time is long, the pore diameter tends to increase.

  A Pt film having a film thickness of 2000 angstroms was further formed on the piezoelectric film by direct current magnetron sputtering, and finally processed as shown in FIG. 1 to obtain the shape of the piezoelectric element.

  When the piezoelectric element was prepared by changing the average pore diameter of the pores by changing the manufacturing conditions as described above, the occurrence of cracks in the piezoelectric film and the electric leakage between the upper and lower electrodes are as shown in Table 3. Became.

  The pores were observed by breaking the sample and observing the fractured surface with a scanning electron microscope (SEM).

  However, the area density of the pores of the samples shown in Table 3 was in the range of 1 to 2%. The electric leakage was measured by using a sample in which a circular upper electrode having a diameter of 2 mm was formed and applying a voltage of 100 V between the upper and lower electrodes. The sample with cracks seems to have leaked at the cracks.

  From this result, it was found that an actuator having an average pore diameter of 0.01 to 0.1 μm, no cracks, and no electric leakage can be obtained.

  The reason is considered as follows. A piezoelectric body undergoes a phase transition where the crystal structure changes at the boundary of the Curie temperature, but since the heat treatment temperature for crystallization is higher than the Curie temperature, the piezoelectric film becomes dense when the temperature drops to room temperature. If it is too much, the strain at that time cannot be absorbed and a crack is generated.

  Further, since the thermal expansion coefficient is larger than that of the silicon substrate, cracks may occur when the piezoelectric film cannot absorb the thermal stress.

  That is, if there are some pores, strain and stress can be absorbed, so that a film without cracks can be obtained.

  On the other hand, when the pore diameter is larger than the above range, the electric field strength applied to the piezoelectric film is effectively increased, and there is a risk of breakage.

  In addition, a durability acceleration test as a piezoelectric element was performed. As conditions, a pulse voltage having a duty of 10%, a frequency of 10 KHz, and 30 V was applied between the upper and lower electrodes, and the change in the displacement amount at the tip of the piezoelectric element was examined.

As a result, when the average pore diameter was 0.05 μm or less, repeated durability of 2 × 10 ⁹ times or more was shown, but when the average pore diameter was more than 0.05 μm and 0.1 μm or less. Will be reduced by 2 × 10 ⁹ times.

(Reference Example 6)
When actuators were prepared by changing the area density of the pores in the same manner as in Reference Example 5, the occurrence of cracks in the piezoelectric film and the electric leakage between the upper and lower electrodes were as shown in Table 4.

  However, the average pore diameter of the samples shown in Table 4 was set in the range of 0.03 to 0.07 μm. From this result, it was found that an actuator having a pore area density of 0.3 to 3%, no cracks, and no electric leakage can be obtained. When the area density of the pores is larger than the above range, the electric field strength that is practically applied to the piezoelectric film is increased, and there is a risk of leak destruction.

In addition, a durability acceleration test as a piezoelectric element was performed. The conditions were the same as in Reference Example 1. As a result, when the area density of the pores was 1% or less, the durability was 2 × 10 ⁹ times or more. However, when the area density of the pores was more than 1% and 5% or less, The displacement amount decreases by 2 × 10 ⁹ times.

  In Reference Examples 5 and 6, although the Si substrate was used as the substrate, a ceramic substrate such as magnesia, alumina, zirconia, etc. may be used, and the description has been made using the two-component PZT as the piezoelectric film. Of course, it is desirable to change the material of the piezoelectric film depending on the application. For example, in the case of an ink jet recording head described later, a three-component that can obtain a high piezoelectric strain constant d31 at a Curie point of 200 ° C. or higher. A PZT system is desirable, and a 3-component system PZT using lead magnesium niobate as the third component is more desirable.

  Although FIG. 1 illustrates an example of a unimorph type actuator, as shown in FIG. 13, the present invention can also be applied to a bimorph type actuator. This has a symmetrical structure with respect to 12 lower electrodes, 101 and 201 are both piezoelectric films, and 103 and 203 are both upper electrodes.

Other Embodiments III. Next, an ink jet recording apparatus provided with the piezoelectric thin film element described above will be described. A sectional view schematically showing this ink jet recording head is shown. FIG. 14 shows one ink reservoir portion of an ink jet recording head using the piezoelectric thin film element according to the present invention as a vibrator.

  The ink jet recording head includes a silicon substrate 21 on which an ink reservoir 27 is formed, a diaphragm 22 formed on the silicon substrate 21, a lower electrode 23 formed at a desired position on the diaphragm 22, and a lower electrode. 23, a piezoelectric thin film 24 formed at a position corresponding to the ink reservoir 27, an upper electrode 25 formed on the piezoelectric thin film 24, and a second substrate bonded to the lower surface of the silicon substrate 21 26. The substrate 26 is provided with an ink discharge nozzle 26 </ b> A communicating with the ink reservoir 27.

  The lower electrode 23 has the configuration described in the above-described reference examples and examples. The same applies to the piezoelectric thin film 24.

  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 film 24 via the lower electrode 23 and the upper electrode 25, the piezoelectric film 24 is deformed to create a negative pressure in the ink reservoir 27 and apply pressure to the ink. With this pressure, ink is ejected from a nozzle (not shown), and ink jet recording is performed.

  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.

  More specifically, it is as follows. The piezoelectric thin film was patterned to a width of 0.2 mm and a length of 4 mm by photoetching, and a groove having a width of 0.3 mm was formed on the silicon substrate by anisotropic etching. After forming the upper electrode, it was bonded to a second glass substrate to form an ink flow path. When the entire substrate was cut to assemble the inkjet head and the ink was ejected, a sufficient ejection force was obtained. When printing was carried out by incorporating it in an ink jet recording apparatus, good printing quality was obtained.

The recording head has, for example, a silicon thermal oxide film as a diaphragm, and a thin film piezoelectric element composed of a lower electrode, a piezoelectric film, and an upper electrode is integrally formed thereon by a thin film process, and a cavity A chip made of a single crystal silicon substrate on which (ink reservoir) is formed and a nozzle plate (second substrate) made of stainless steel provided with a nozzle for discharging ink are bonded together with an adhesive. Here, as a piezoelectric film, for example, a ternary PZT to which lead magnesium niobate is added as a third component is used as the piezoelectric film so that a larger displacement amount can be obtained, and the thickness is 2 μm. did. When the piezoelectric film has pores in its cross section, the average pore diameter is 0.01 to 0.1 μm, and the area density is in the range of 0.3 to 5%, actual ink jet recording is performed. When a durability test corresponding to a head reliability of 5 years was performed, ink was ejected, and printing was performed, there was no problem in printing 4 × 10 ⁹ times.

  When photoetching is used, high-definition printing can be achieved, and a large number of elements can be obtained from a single substrate, thereby reducing the cost. In addition, the production stability and reproducibility of the characteristics were also excellent. That is, by using the thin film piezoelectric element according to the present invention, it is possible to manufacture a high-density ink jet recording head with a high yield with a simple manufacturing process.

  The thin film piezoelectric element according to the present invention may be used for various applications by utilizing its good characteristics. For example, as described above, it is used as a vibrator of an ink jet recording head.

  As described above, the piezoelectric thin film element of the present invention can improve the piezoelectric characteristics by using the PZT thin film having the optimum crystal orientation.

  In the piezoelectric thin film element according to the present invention, the grain boundary of the crystal of the piezoelectric film as the constituent element exists in a direction substantially perpendicular to the electrode surface. The constant can be improved. As a result, a highly reliable and high performance piezoelectric thin film element can be provided.

  Moreover, this effect can be improved by making the width of the crystal grains in the film thickness direction longer than the width of the crystal grains in the film surface direction. This effect can be further improved by specifically defining the relationship between the width of the crystal grains in the film thickness direction and the width of the crystal grains in the film surface direction within the range described above.

  And, by constructing the lower electrode from a compound of platinum and an oxide of a metal element that is a component of the piezoelectric film, the substrate is warped by heat treatment performed when the piezoelectric film is formed, Distortion can be suppressed. In addition, the adhesion to the piezoelectric film and the substrate can be improved.

  Further, this effect can be improved by causing the grain boundary of the crystal constituting the lower electrode to exist in a direction substantially perpendicular to the film surface of the piezoelectric film. Furthermore, this effect can be further improved by making the width of the crystal grains of the crystal constituting the lower electrode in the film thickness direction longer than the width of the crystal grains in the film surface direction.

  In addition, the thin film piezoelectric element of the present invention can be easily manufactured without cracking even with a relatively thin film having a film thickness of 0.5 μm or more. High density recording heads can be manufactured with good yield. Further, when the thin film piezoelectric element of the present invention is used as an actuator, it shows good reproducibility even in repeated durability tests when it is displaced.

  In addition, since the ink jet recording head according to the present invention includes the above-described piezoelectric thin film element as a vibrator, the ink can be ejected with a large pressure.

  DESCRIPTION OF SYMBOLS 10 ... Silicon substrate, 12 ... Lower electrode, 14 ... Piezoelectric film, 16 ... Upper electrode.

Claims (9)

A piezoelectric element having a lower electrode, a piezoelectric film, and an upper electrode, wherein the lower electrode includes platinum and titanium oxide, and lead oxide or zirconium oxide, and the platinum is 0.2 to 0 in the lower electrode. The titanium oxide is formed from a film thickness of 0.005 to 0.04 μm, and the titanium oxide content is 0.5 wt% to 10 wt%. Piezoelectric element.   The piezoelectric element according to claim 1, wherein the piezoelectric film includes Pb, Zr, and Ti as constituent elements. 3. The piezoelectric element according to claim 1, wherein grain boundaries of crystal grains of the lower electrode extend in a film thickness direction. The crystal grain of the lower electrode is such that the relationship between the width in the film surface direction and the width in the film thickness direction (width in the film surface direction / width in the film thickness direction) is in the range of 1/10 to 1/3. 4. The piezoelectric element according to claim 3 , wherein The piezoelectric film includes lead zirconate titanate, has a rhombohedral crystal structure, and is measured by an X-ray diffraction thin film method (100), (110), (111), (210), and (211). ) degree of orientation of (100) to the total crystal surface reflection intensity, the piezoelectric element according to any one of claims 1 to 4, characterized in that 30% or more. The piezoelectric crystal grains in the film, a piezoelectric element according to any one of claims 1 to 5, characterized in that a columnar extending on said electrode direction from the lower electrode. The relationship (width in the film surface direction / width in the film thickness direction) between the width in the film surface direction and the width in the film thickness direction of the crystal grains of the piezoelectric film is in the range of 1/10 to 1/3. The piezoelectric element according to claim 6 . The piezoelectric film has pores, and the average pore diameter of the pores is 0.03 μm or more and 0.07 μm.
The piezoelectric element according to any one of claims 1 to 7 , wherein the area density of the pores is 0.3% or more and 3% or less. Ink-jet recording head, characterized in that it comprises a piezoelectric device according to any one of claims 1 to 8.