JPWO2015125520A1 - Ferroelectric thin film, substrate with piezoelectric thin film, piezoelectric actuator, ink jet head, ink jet printer, and method for manufacturing ferroelectric thin film - Google Patents

Abstract

The ferroelectric thin film is made of lead lanthanum zirconate titanate. In the ferroelectric thin film, the ratio a of lanthanum to the sum of lead and lanthanum is 6% to 8% in terms of molar ratio, and the ratio b of zirconium to the sum of zirconium and titanium is 54% in terms of mole ratio. It is 59% or less.

Description

  The present invention relates to a ferroelectric thin film made of lead lanthanum zirconate titanate (PLZT), a substrate with a piezoelectric thin film provided with the ferroelectric thin film, a piezoelectric actuator, an inkjet head, an inkjet printer, and a method of manufacturing a ferroelectric thin film. Is.

  Conventionally, piezoelectric materials such as lead zirconate titanate (PZT) have been used as electromechanical conversion elements such as drive elements and sensors. In recent years, MEMS (Micro Electro Mechanical Systems) elements using a silicon (Si) substrate are increasing in response to demands for downsizing, high density, and low cost of devices. In order to apply a piezoelectric body to a MEMS element, it is desirable to make the piezoelectric body thin. By reducing the thickness of the piezoelectric body, high-precision processing using semiconductor process technology such as film formation and photolithography can be performed, and miniaturization and high density can be realized. Further, since the elements can be collectively processed on a large-area wafer, the cost can be reduced. Furthermore, there is an advantage that the conversion efficiency of mechanical electricity is improved and the characteristics of the drive element and the sensitivity of the sensor are improved.

  As an application example of a device using such a MEMS element, an ink jet printer is known. In an inkjet printer, a two-dimensional image is recorded on a recording medium by controlling the ejection of ink while moving an inkjet head having a plurality of channels for ejecting liquid ink relative to the recording medium such as paper or cloth. Formed.

  Ink can be ejected using a pressure actuator (piezoelectric, electrostatic, thermal deformation, etc.) or by generating bubbles in the ink in the tube by heat. Among them, the piezoelectric actuator has advantages such as high output, modulation, high responsiveness, and choice of ink, and has been frequently used in recent years. In particular, in order to realize a small-sized and low-cost printer with high resolution (small droplets may be used), it is suitable to use an inkjet head using a thin film piezoelectric body.

In recent years, inkjet printers are required to form high-definition images at higher speeds. For this purpose, the ink jet head is required to be capable of ejecting ink having a high viscosity of 10 cp (0.01 Pa · s) or more. In order to realize high-viscosity ink ejection, the piezoelectric thin film (ferroelectric thin film) requires high piezoelectric characteristics (piezoelectric constant d ₃₁ ) and displacement generation force (film thickness of 1 μm or more).

  On the other hand, as a method of forming a piezoelectric material such as PZT on a substrate such as Si, a chemical film forming method such as a CVD (Chemical Vapor Deposition) method, a physical method such as a sputtering method or an ion plating method, a sol gel The growth method in the liquid phase such as the method is known. The upper limit of the thickness of the thin film obtained by these manufacturing methods is about 10 μm. If the film thickness exceeds that, cracks and film peeling occur, and desired characteristics cannot be obtained.

The deposited PZT exhibits a good piezoelectric effect when the crystal has the perovskite structure shown in FIG. The perovskite structure ideally has a cubic unit cell, and is arranged at each vertex of the cubic A, metal B arranged at the body center, and arranged at each face center of the cubic crystal. It is an ABO ₃ type crystal structure composed of oxygen O. Crystals having a perovskite structure include tetragonal crystals, orthorhombic crystals, rhombohedral crystals and the like in which cubic crystals are distorted.

  The PZT thin film formed on the electrode on the Si substrate becomes a polycrystal composed of an aggregate of a plurality of crystals due to the difference in lattice constant from the crystal of the electrode. Depending on the production method, this polycrystal is composed of granular crystals (granular crystals) with a particle size of several hundreds of nanometers, or a width of several hundreds of nanometers and one elongated crystal grain in the film thickness direction. A certain columnar crystal is gathered together. As for columnar crystals, it is known that the more the crystals grown on the same crystal plane in the film thickness direction (the higher the orientation), the higher the piezoelectric properties of the film.

One method of improving the piezoelectric characteristics is to improve the relative dielectric constant and the piezoelectric characteristics by adding impurities to the piezoelectric body so that non-180 ° domain rotation of the domain can easily occur. In particular, in the ABO ₃ type perovskite structure piezoelectric body shown in FIG. 11, lead (Pb) located at the A site is replaced with lanthanum (La), which is an element having a valence higher than that of Pb by one. It is known that the substance called PLZT has a high relative dielectric constant and a piezoelectric constant by setting the La addition amount in a desired range and a composition ratio of zirconium (Zr) / titanium (Ti). Yes.

  For example, Non-Patent Document 1 describes that in PLZT of bulk ceramics, La, Zr, and Ti have a predetermined composition ratio (for example, molar ratio, La / Zr / Ti = 7/60/40), thereby achieving high piezoelectric characteristics. Is disclosed. Patent Document 1 discloses that the composition of PLZT of bulk ceramics for actuators is set to a Zr / Ti composition ratio corresponding to the amount of La added when the amount of La added is in the range of 7.5 to 21% in terms of molar ratio. Discloses that high characteristics can be obtained.

  On the other hand, Patent Document 2 discloses a technique in which a layer of lead lanthanum titanate (PLT) that does not contain Zr is formed on a substrate, and a PLZT layer is formed on the PLT layer. In this technique, it is possible to improve the crystallinity of PLZT by using a PLT layer having good crystallinity as an undercoat layer.

  Patent Document 3 discloses a technique for increasing the La ratio of PLZT substantially in the vicinity of the substrate to 0% in the thickness direction of the thin film. In this technique, a relatively high crystallinity is obtained by forming a low La ratio PLZT near the substrate, and the entire PLZT crystallinity is increased by continuously increasing the La ratio in the film thickness direction. I try to improve.

JP 61-44764 A (see FIG. 1) Japanese Patent Laid-Open No. 6-290983 (see claim 1, paragraph [0028], FIG. 1 etc.) Japanese Patent No. 4998652 (refer to claim 1, paragraph [0015], FIG. 1 etc.)

Gene H. Heartling “Ferroelectric Ceramics: History and Technology”, Journal of American Ceramic Society, 82 [4] 797-818 (1999)

  By the way, PLZT of bulk ceramics is obtained as a single substance by firing or the like, but a thin film of PLZT cannot be obtained as a single substance, and is formed on a substrate by film formation such as sputtering. Thus, since the formation method differs between the bulk and the thin film, the composition of the bulk ceramic PLZT defined in Non-Patent Document 1 and Patent Document 1 is applied straight to the PLZT thin film as it is to obtain high piezoelectric characteristics. Even if applied, high piezoelectric properties cannot be obtained. That is, when trying to obtain PLZT having a composition with a large amount of La as a thin film, only a thin film having poor crystallinity as compared with PZT has been obtained so far, and high piezoelectric characteristics as obtained in bulk are obtained. It has not been realized.

  Further, Patent Document 2 focuses only on a PLZT thin film for memory use, and therefore only describes a thin film with a film thickness of 100 nm or less, and a composition for realizing high piezoelectric characteristics with a film with a film thickness of 1 μm or more. There is no description about.

  Further, in the configuration in which the La composition ratio continuously changes in the film thickness direction as in Patent Document 3, the characteristic value (for example, piezoelectric constant) indicating the piezoelectric characteristics changes in the film thickness direction. For this reason, when compared with a homogeneous composition film having a constant La / Zr / Ti ratio, there is a concern that high piezoelectric characteristics cannot be obtained throughout the film thickness direction.

  The present invention has been made to solve the above-described problems, and its purpose is to achieve high piezoelectric characteristics over the entire film thickness direction with a thin film of PLZT by appropriately defining the composition ratio of PLZT. An object of the present invention is to provide a ferroelectric thin film that can be manufactured, a substrate with a piezoelectric thin film provided with the ferroelectric thin film, a piezoelectric actuator, an ink jet head, an ink jet printer, and a method of manufacturing a ferroelectric thin film.

  A ferroelectric thin film according to one aspect of the present invention is a ferroelectric thin film made of lead lanthanum zirconate titanate, and the ratio a of lanthanum to the sum of lead and lanthanum is 6% or more and 8% in molar ratio. The ratio b of zirconium to the sum of zirconium and titanium is 54% or more and 59% or less in terms of molar ratio.

  According to the above configuration, by appropriately defining the composition ratio (ratio a, ratio b) of the PLZT thin film, it is possible to obtain high piezoelectric characteristics throughout the film thickness direction with the PLZT thin film.

1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention. FIG. FIG. 2 is a plan view showing a schematic configuration of an actuator of an ink jet head provided in the ink jet printer, and a cross-sectional view taken along line A-A ′ in the plan view. It is sectional drawing of the said inkjet head. It is sectional drawing which shows the manufacturing process of the said inkjet head. It is sectional drawing which shows the other structure of the said inkjet head. It is sectional drawing which shows the manufacturing process of the board | substrate with a piezoelectric thin film which formed the piezoelectric thin film on the board | substrate. It is sectional drawing of the said board | substrate with a piezoelectric thin film which has a seed layer. It is a perspective view which shows the schematic structure of a piezoelectric displacement measuring meter. The ratio of Zr to the sum of Zr and Ti in the PLZT, is a graph showing the relationship between the piezoelectric constant d _31. And the PLZT film thickness is a graph showing the relationship between the piezoelectric constant d _31. It is explanatory drawing which shows typically the crystal structure of a piezoelectric material.

  An embodiment of the present invention will be described below with reference to the drawings. In the present specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B.

[Configuration of inkjet printer]
FIG. 1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer 1 according to the present embodiment. The ink jet printer 1 is a so-called line head type ink jet recording apparatus in which an ink jet head 21 is provided in a line shape in the width direction of a recording medium in the ink jet head unit 2.

  The ink jet printer 1 includes an ink jet head unit 2, a feed roll 3, a take-up roll 4, two back rolls 5 and 5, an intermediate tank 6, a liquid feed pump 7, a storage tank 8, and a fixing tank. And a mechanism 9.

  The ink jet head unit 2 ejects ink from the ink jet head 21 toward the recording medium P to perform image formation (drawing) based on image data, and is disposed in the vicinity of one back roll 5. Details of the inkjet head 21 will be described later.

  The feed roll 3, the take-up roll 4 and the back rolls 5 are members each having a cylindrical shape that can rotate about its axis. The feeding roll 3 is a roll that feeds the long recording medium P wound around the circumferential surface toward the position facing the inkjet head unit 2. The feeding roll 3 is rotated by driving means (not shown) such as a motor, thereby feeding the recording medium P in the X direction in FIG.

  The take-up roll 4 is taken out from the take-out roll 3 and takes up the recording medium P on which the ink is ejected by the inkjet head unit 2 around the circumferential surface.

  Each back roll 5 is disposed between the feed roll 3 and the take-up roll 4. One back roll 5 located on the upstream side in the conveyance direction of the recording medium P is opposed to the inkjet head unit 2 while winding the recording medium P fed by the feeding roll 3 around and supporting the recording medium P. Transport toward The other back roll 5 conveys the recording medium P from a position facing the inkjet head unit 2 toward the take-up roll 4 while being wound around and supported by a part of the peripheral surface.

  The intermediate tank 6 temporarily stores the ink supplied from the storage tank 8. The intermediate tank 6 is connected to a plurality of ink tubes 10, adjusts the back pressure of ink in each inkjet head 21, and supplies ink to each inkjet head 21.

  The liquid feed pump 7 supplies the ink stored in the storage tank 8 to the intermediate tank 6 and is disposed in the middle of the supply pipe 11. The ink stored in the storage tank 8 is pumped up by the liquid feed pump 7 and supplied to the intermediate tank 6 through the supply pipe 11.

  The fixing mechanism 9 fixes the ink ejected to the recording medium P by the inkjet head unit 2 on the recording medium P. The fixing mechanism 9 includes a heater for heat-fixing the discharged ink on the recording medium P, a UV lamp for curing the ink by irradiating the discharged ink with UV (ultraviolet light), and the like. Yes.

  In the above configuration, the recording medium P fed from the feeding roll 3 is transported to a position facing the inkjet head unit 2 by the back roll 5, and ink is ejected from the inkjet head unit 2 to the recording medium P. Thereafter, the ink ejected onto the recording medium P is fixed by the fixing mechanism 9, and the recording medium P after ink fixing is taken up by the take-up roll 4. As described above, in the line head type inkjet printer 1, ink is ejected while the recording medium P is conveyed while the inkjet head unit 2 is stationary, and an image is formed on the recording medium P.

  The ink jet printer 1 may be configured to form an image on a recording medium by a serial head method. The serial head method is a method of forming an image by ejecting ink by moving an inkjet head in a direction orthogonal to the transport direction while transporting a recording medium. Further, as the recording medium P, in addition to the long one, a sheet-like one that has been cut into a predetermined size (shape) in advance may be used.

[Configuration of inkjet head]
Next, the configuration of the inkjet head 21 will be described. FIG. 2 is a plan view showing a schematic configuration of an actuator 21a (substrate with piezoelectric thin film, piezoelectric actuator) of the inkjet head 21, and a cross-sectional view taken along line AA ′ in the plan view. is there. FIG. 3 is a cross-sectional view of the inkjet head 21 in which the nozzle substrate 31 is joined to the actuator 21a of FIG.

  The inkjet head 21 has a thermal oxide film 23, a lower electrode 24, a piezoelectric thin film 25, and an upper electrode 26 in this order on a substrate 22 having a plurality of pressure chambers 22a (openings).

  The substrate 22 is composed of a semiconductor substrate made of a single crystal Si (silicon) simple substance having a thickness of about 300 to 500 μm, for example, or an SOI (Silicon on Insulator) substrate. Note that FIG. 2 shows a case where the substrate 22 is configured by an SOI substrate. The SOI substrate is obtained by bonding two Si substrates through an oxide film. The upper wall of the pressure chamber 22a in the substrate 22 constitutes a diaphragm 22b serving as a driven film, which is displaced (vibrated) as the piezoelectric thin film 25 is driven (expanded / contracted), and applies pressure to the ink in the pressure chamber 22a. Give.

The thermal oxide film 23 is made of, for example, SiO ₂ (silicon oxide) having a thickness of about 0.1 μm, and is formed for the purpose of protecting and insulating the substrate 22.

  The lower electrode 24 is a common electrode provided in common to the plurality of pressure chambers 22a, and is configured by laminating a Ti (titanium) layer and a Pt (platinum) layer. The Ti layer is formed in order to improve the adhesion between the thermal oxide film 23 and the Pt layer. The thickness of the Ti layer is, for example, about 0.02 μm, and the thickness of the Pt layer is, for example, about 0.1 μm.

  The piezoelectric thin film 25 is composed of, for example, a ferroelectric thin film made of PLZT (lead lanthanum zirconate titanate) obtained by adding La to PZT, and is provided corresponding to each pressure chamber 22a. The thickness of the piezoelectric thin film 25 is, for example, 1 μm or more and 10 μm or less.

  In this embodiment, the additive amount of La in PLZT constituting the piezoelectric thin film 25 is 6 to 8% in terms of molar ratio, and the composition ratio of Zr / (Zr + Ti) is in the range of 54 to 59% in terms of molar ratio. . That is, the ratio a of La to the sum of Pb and La in PLZT is 6% or more and 8% or less in terms of molar ratio, and the ratio b of Zr to the sum of Zr and Ti is 54% or more and 59% in terms of mole ratio. It is as follows. By defining the composition ratio of PLZT in this way, it is possible to realize PLZT having high piezoelectric characteristics over the entire film thickness direction, and details thereof will be described in the examples described later.

  The upper electrode 26 is an individual electrode provided corresponding to each pressure chamber 22a, and is configured by laminating a Ti layer and a Pt layer. The Ti layer is formed in order to improve the adhesion between the piezoelectric thin film 25 and the Pt layer. The thickness of the Ti layer is about 0.02 μm, for example, and the thickness of the Pt layer is about 0.1 to 0.2 μm, for example. The upper electrode 26 is provided so as to sandwich the piezoelectric thin film 25 from the film thickness direction with the lower electrode 24. Note that a layer made of gold (Au) may be formed instead of the Pt layer.

  The lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 constitute a thin film piezoelectric element 27 for discharging ink in the pressure chamber 22a to the outside. The thin film piezoelectric element 27 is driven based on a voltage (drive signal) applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26. The ink jet head 21 is formed by arranging the thin film piezoelectric element 27 and the pressure chamber 22a vertically and horizontally.

  A nozzle substrate 31 is bonded to the opposite side of the pressure chamber 22a from the diaphragm 22b. The nozzle substrate 31 is formed with ejection holes (nozzle holes) 31a for ejecting ink stored in the pressure chambers 22a to the outside as ink droplets. Ink supplied from the intermediate tank 6 is stored in the pressure chamber 22a.

  In the above configuration, when a voltage is applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is in a direction perpendicular to the thickness direction (substrate) according to the potential difference between the lower electrode 24 and the upper electrode 26. (Direction parallel to the surface of 22). Then, due to the difference in length between the piezoelectric thin film 25 and the diaphragm 22b, a curvature is generated in the diaphragm 22b, and the diaphragm 22b is displaced (curved or vibrated) in the thickness direction.

  Therefore, if ink is accommodated in the pressure chamber 22a, a pressure wave is propagated to the ink in the pressure chamber 22a by the vibration of the vibration plate 22b described above, and the ink in the pressure chamber 22a is ejected from the ejection hole 31a. Is discharged to the outside.

  In the inkjet head 21a of the present embodiment, as will be described later, since the piezoelectric characteristics of the piezoelectric thin film 25 of the piezoelectric actuator 21a are high, ink ejection using high-viscosity ink is possible, which is advantageous for high-speed and high-definition drawing. Ink jet printer 1 can be realized.

  Further, in the above-described piezoelectric actuator 21a (substrate with a piezoelectric thin film), another upper electrode 26 is formed on the opposite side of the piezoelectric thin film 25 from the lower electrode 24. Therefore, the piezoelectric thin film 25 is applied according to the applied voltage. Can be expanded and contracted reliably.

[Inkjet head manufacturing method]
Next, the manufacturing method of the inkjet head 21 of this embodiment is demonstrated below. FIG. 4 is a cross-sectional view showing the manufacturing process of the inkjet head 21.

  First, the substrate 22 is prepared. As the substrate 22, crystalline silicon (Si) often used in MEMS (Micro Electro Mechanical Systems) can be used. Here, two Si substrates 22 c and 22 d are bonded via an oxide film 22 e. An SOI structure is used.

The substrate 22 is put in a heating furnace and held at about 1500 ° C. for a predetermined time, and thermal oxide films 23a and 23b made of SiO ₂ are formed on the surfaces of the Si substrates 22c and 22d, respectively. Next, on the one thermal oxide film 23a, each layer of titanium and platinum is sequentially formed by sputtering to form the lower electrode 24.

  Subsequently, the substrate 22 is reheated to about 600 ° C., and a PLZT layer 25a serving as a displacement film is formed by sputtering. Next, a photosensitive resin 35 is applied to the substrate 22 by a spin coating method, and unnecessary portions of the photosensitive resin 35 are removed by exposure and etching through a mask, and the shape of the piezoelectric thin film 25 to be formed is transferred. . Thereafter, using the photosensitive resin 35 as a mask, the shape of the layer 25 a is processed using a reactive ion etching method to form the piezoelectric thin film 25.

  Next, a titanium layer and a platinum layer are sequentially formed by sputtering on the lower electrode 24 so as to cover the piezoelectric thin film 25, thereby forming a layer 26a. Subsequently, a photosensitive resin 36 is applied onto the layer 26a by a spin coating method, and unnecessary portions of the photosensitive resin 36 are removed by exposure and etching through a mask, and the shape of the upper electrode 26 to be formed is transferred. To do. Thereafter, using the photosensitive resin 36 as a mask, the shape of the layer 26a is processed using a reactive ion etching method to form the upper electrode 26.

  Next, a photosensitive resin 37 is applied to the back surface (thermal oxide film 23b side) of the substrate 22 by a spin coat method, and unnecessary portions of the photosensitive resin 37 are removed by exposure and etching through a mask. The shape of the pressure chamber 22a to be formed is transferred. Then, using the photosensitive resin 37 as a mask, the substrate 22 is removed using a reactive ion etching method to form a pressure chamber 22a to be an actuator 21a.

  Thereafter, the substrate 22 of the actuator 21a and the nozzle substrate 31 having the discharge holes 31a are bonded using an adhesive or the like. Thereby, the inkjet head 21 is completed. It should be noted that an intermediate glass having a through hole at a position corresponding to the discharge hole 31a is used, the thermal oxide film 23b is removed, and the substrate 22 and the intermediate glass, and the intermediate glass and the nozzle substrate 31 are anodic bonded to each other. Also good. In this case, the three parties (substrate 22, intermediate glass, nozzle substrate 31) can be joined without using an adhesive.

The electrode material constituting the lower electrode 24 is not limited to the above-described Pt, and for example, Au (gold), Ir (iridium), IrO ₂ (iridium oxide), RuO ₂ (ruthenium oxide). ), LaNiO ₃ (lanthanum nickelate), SrRuO ₃ (strontium ruthenate) or a metal, or a combination thereof.

[Other configurations of inkjet head]
FIG. 5 is a cross-sectional view showing another configuration of the inkjet head 21. As shown in the figure, a seed layer 29 may be provided between the lower electrode 24 and the piezoelectric thin film 25. The seed layer 29 is an orientation control layer for controlling the crystal orientation of the piezoelectric thin film 25. Such seed layer 29 is made of, for example, PLT (lead lanthanum titanate), but may be made of LaNiO ₃ or SrRuO ₃ .

〔Example〕
Next, a specific example of the composition ratio of PLZT constituting the piezoelectric thin film will be described as an example including the manufacturing method of the piezoelectric thin film. Moreover, a comparative example is also demonstrated for the comparison with an Example. FIG. 6 is a cross-sectional view showing a manufacturing process of a substrate with a piezoelectric thin film in which a piezoelectric thin film is formed on the substrate.

Example 1
First, a thermal oxide film 42 of about 100 nm was formed on a substrate 41 made of a single crystal Si wafer having a thickness of about 400 μm. The wafer thickness may be a standard value such as 300 μm to 725 μm and a diameter of 3 inches to 8 inches. The thermal oxide film 42 can be formed by exposing the Si wafer to a high temperature of about 1200 ° C. in an oxygen atmosphere using a wet oxidation furnace. The substrate 41 and the thermal oxide film 42 correspond to the substrate 22 and the thermal oxide film 23 in FIG.

  Next, on the Si substrate with a thermal oxide film, a Ti layer having a thickness of about 10 nm was formed as an adhesion layer by sputtering, and a Pt layer was further formed to have a thickness of about 150 nm to form the lower electrode 43. The sputtering conditions of Ti at this time were Ar flow rate: 20 sccm, pressure: 0.9 Pa, RF power applied to the target: 100 W, and substrate temperature: 400 ° C. The sputtering conditions for Pt were Ar flow rate: 20 sccm, pressure: 0.8 Pa, RF power applied to the target: 150 W, and substrate temperature: 400 ° C. The lower electrode 43 corresponds to the lower electrode 24 in FIG.

  The Ti and Pt films were formed using a binary sputtering apparatus having two targets of Ti and Pt in the chamber. Thereby, the laminated structure of the Pt / Ti / Si substrate can be continuously formed without taking vacuum.

Subsequently, using a sputtering apparatus, a PLZT film having a thickness of about 4 μm was formed on Pt to form a piezoelectric thin film 44 made of PLZT. Thereby, the substrate 40 with the piezoelectric thin film in which the piezoelectric thin film 44 is formed on the substrate 41 is formed. The piezoelectric thin film 44 corresponds to the piezoelectric thin film 25 of FIG. The sputtering conditions for PLZT were Ar flow rate: 20 sccm, O ₂ flow rate: 0.6 sccm, pressure: 0.5 Pa, substrate temperature: 600 ° C., and RF power applied to the target: 500 W.

  A sputtering target having a La / Zr / Ti ratio of 8/57/43 in molar ratio was used. Note that Pb contained in the target is likely to be re-evaporated at the time of high-temperature film formation, and the formed thin film tends to be Pb deficient. Therefore, it is necessary to add Pb more than the stoichiometric ratio of the perovskite crystal. Although the target Pb amount depends on the film formation temperature, it is desirable to increase it by 10 to 30% from the stoichiometric ratio.

  As a result of measuring the formed PLZT film by X-ray diffraction (XRD), the (100) orientation degree of the film was 90%. The (100) orientation refers to the crystal orientation of the perovskite, which includes not only the <100> direction in which the polarization direction is parallel to the surface of the substrate, but also an equivalent direction (for example, < (001> direction) is also included. Since the degree of (100) orientation of the film is 90% as described above, the remaining 10% can be considered to be (111) orientation.

  Further, when the cross-sectional shape of the formed PLZT film was confirmed with a scanning electron microscope (SEM), it was found that a columnar crystal having a film thickness of 4 μm was obtained. Furthermore, as a result of analyzing the composition of the PLZT film by energy dispersive X-ray analysis (EDX), the La / Zr / Ti ratio is 7.5 / 56.8 / 43. It was found that a film having a composition close to the target composition was obtained. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 150 MPa.

Next, Au is vapor-deposited on the piezoelectric thin film 44 to form an upper electrode, and the piezoelectric element 50 (see FIG. 8) is completed. Then, the piezoelectric element 50 is cut into a strip shape from the wafer, and the piezoelectric element shown in FIG. The piezoelectric constant d ₃₁ was determined by a cantilever method using a displacement meter. As a result, it was found that d ₃₁ = −195.6 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

In the piezoelectric displacement measuring instrument described above, the end of the piezoelectric element 50 is clamped by the fixed portion 51 so that the movable length of the cantilever is 10 mm, and the cantilever structure is used. A maximum voltage of 0 V was applied to the lower electrode, and a minimum voltage of −20 V was applied to the lower electrode at a frequency of 500 Hz. Then, the piezoelectric constant d ₃₁ was obtained from the obtained piezoelectric displacement by a known method.

  Since the crystal structure of the formed PLZT film is a columnar crystal, a film composed of a single crystal grain is obtained in the film thickness direction, and the volume of the crystal grain is larger than that of the granular crystal. For this reason, more polarization domains are present in the single crystal, which can improve the piezoelectric characteristics due to polarization rotation.

(Example 2)
A 2 μm film of PLZT was formed on a Pt / Ti / Si substrate produced in the same manner as in Example 1 by the sol-gel method to form a piezoelectric thin film 44. More details are as follows.

  Using a PLZT precursor solution whose molar ratio was adjusted so that the La / Zr / Ti ratio was 6/54/46, the number of revolutions was about 3 seconds at about 500 rpm with a spin coater on the lower electrode 43. Was coated at about 3000 rpm for about 20 seconds. Thereafter, the organic solvent was volatilized by placing it on a hot plate set at 110 ° C. for 5 minutes (drying step). Subsequently, by using a RTA (rapid thermal annealing) furnace, a preliminary baking at 450 ° C. for 5 minutes and a main baking at 700 ° C. for 2 minutes are continuously performed to form a PLZT film having a thickness of about 100 nm. Was repeated a predetermined number of times to form a 2 μm thick PLZT film.

  As a result of measuring the formed PLZT film by XRD, it was multi-oriented. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a granular crystal having a thickness of 2 μm was obtained. Further, as a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio is 6.2 / 54.1 / 55.9 in terms of molar ratio, which is close to the composition of the precursor solution. It was found that a film was obtained. Moreover, as a result of measuring the film stress by measuring the warpage of the wafer before and after film formation, the film stress of PLZT was 100 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −188.3 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

(Example 3)
On a Pt / Ti / Si substrate produced in the same manner as in Example 1, a PLT as the seed layer 45 shown in FIG. The seed layer 45 corresponds to the seed layer 29 in FIG. The sputtering conditions for PLT were Ar flow rate: 30 sccm, O ₂ flow rate: 0.6 sccm, pressure: 0.5 Pa, substrate temperature: 700 ° C., and RF power applied to the target: 300 W.

Subsequently, a PLZT film having a thickness of about 5 μm was formed on the PLT with a sputtering apparatus, and the piezoelectric thin film 44 was formed. The sputtering conditions for PLZT were Ar flow rate: 20 sccm, O ₂ flow rate: 0.5 sccm, pressure: 0.4 Pa, substrate temperature: 650 ° C., and RF power applied to the target: 600 W. A sputtering target having a La / Zr / Ti ratio of 8/55/45 in terms of molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 99%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 5 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 7.8 / 55.4 / 44.6 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film stress by measuring the warpage of the wafer before and after the film formation, the film stress of PLZT was 250 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −204.2 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

Example 4
On the PLT / Pt / Ti / Si substrate produced in the same manner as in Example 3, about 6 μm of PLZT was formed by sputtering to form the piezoelectric thin film 44. The sputtering conditions for PLZT were the same as in Example 3, and a sputtering target having a La / Zr / Ti ratio of 7/58/42 in terms of molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 98%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 6 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 7.1 / 58.9 / 41.1 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 200 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −202.9 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

(Example 5)
On a Pt / Ti / Si substrate produced in the same manner as in Example 1, about 5 μm of PLZT was formed by sputtering to form a piezoelectric thin film 44. The sputtering conditions of PLZT at this time were Ar flow rate: 20 sccm, O ₂ flow rate: 0.6 sccm, pressure: 0.5 Pa, substrate temperature: 700 ° C., and RF power applied to the target: 500 W. That is, in order to increase the film stress, the film formation temperature of PLZT was set high. A sputtering target having a La / Zr / Ti ratio of 8/57/43 in molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 5 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 7.9 / 57.2 / 42.8 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 260 MPa. For this reason, a part of the PLZT film cracked, and there was a portion where the piezoelectric characteristics could not be evaluated.

Next, in the same manner as in Example 1, the upper electrode is formed on the piezoelectric thin film 44 (only the portion where no crack is generated here) to complete the piezoelectric element 50, and then the piezoelectric element 50 is formed from the wafer. Was cut into strips and the piezoelectric constant d ₃₁ was determined by the cantilever method. As a result, it was found that d ₃₁ = −190.2 pm / V, and a piezoelectric characteristic higher than the target value of −180 pm / V was obtained.

(Comparative Example 1)
On a Pt / Ti / Si substrate produced in the same manner as in Example 1, about 4 μm of PLZT was formed by sputtering to form a piezoelectric thin film. The sputtering conditions for PLZT were the same as in Example 1, and a sputtering target having a La / Zr / Ti ratio of 7/52/48 in molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 4 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.8 / 51.8 / 48.2 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 90 MPa.

Next, in the same manner as in Example 1, an upper electrode was formed on the piezoelectric thin film to complete the piezoelectric element, and then the piezoelectric element was cut into a strip shape from the wafer, and the piezoelectric constant d ₃₁ was obtained by a cantilever method. As a result, d ₃₁ = −173.0 pm / V, which did not reach the target value of −180 pm / V.

(Comparative Example 2)
On a Pt / Ti / Si substrate produced in the same manner as in Example 1, about 5 μm of PLZT was formed by sputtering to form a piezoelectric thin film. The sputtering conditions for PLZT were the same as in Example 1, and a sputtering target having a La / Zr / Ti ratio of 7/60/40 in terms of molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 5 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio is 7.2 / 60.1 / 39.9 in terms of molar ratio, and a film having a composition close to the target composition is obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 190 MPa.

Next, in the same manner as in Example 1, an upper electrode was formed on the piezoelectric thin film to complete the piezoelectric element, and then the piezoelectric element was cut into a strip shape from the wafer, and the piezoelectric constant d ₃₁ was obtained by a cantilever method. As a result, d ₃₁ = −168.7 pm / V, which did not reach the target value of −180 pm / V.

(Comparative Example 3)
A PZT film having a thickness of about 4 μm was formed on a Pt / Ti / Si substrate produced in the same manner as in Example 1 by sputtering to form a piezoelectric thin film. The sputtering conditions for PZT were the same as in Example 1. The sputtering target used was a La / Zr / Ti ratio of 0/52/48 in molar ratio.

  As a result of measuring the formed PZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 4 μm was obtained. Further, as a result of analyzing the composition of the PZT film by EDX, the La / Zr / Ti ratio is 0 / 52.2 / 47.8 in molar ratio, and a film having a composition close to the target composition is obtained. I understood it. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PZT was 90 MPa.

Next, in the same manner as in Example 1, an upper electrode was formed on the piezoelectric thin film to complete the piezoelectric element, and then the piezoelectric element was cut into a strip shape from the wafer, and the piezoelectric constant d ₃₁ was obtained by a cantilever method. As a result, d ₃₁ = −166.0 pm / V, which did not reach −180 pm / V, which was achieved with PLZT.

(Comparative Example 4)
A PZT film having a thickness of about 4 μm was formed on a Pt / Ti / Si substrate produced in the same manner as in Example 1 by sputtering to form a piezoelectric thin film. The sputtering conditions for PZT were the same as in Example 1, and the sputtering target used had a La / Zr / Ti ratio of 0/55/45 in molar ratio.

  As a result of measuring the formed PZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 4 μm was obtained. As a result of analyzing the composition of the PZT film by EDX, the La / Zr / Ti ratio is 0 / 54.5 / 45.5 in terms of molar ratio, and a film having a composition close to the target composition is obtained. I understood it. Further, as a result of measuring the film stress by measuring the warpage of the wafer before and after the film formation, the film stress of PZT was 110 MPa.

Next, in the same manner as in Example 1, an upper electrode was formed on the piezoelectric thin film to complete the piezoelectric element, and then the piezoelectric element was cut into a strip shape from the wafer, and the piezoelectric constant d ₃₁ was obtained by a cantilever method. As a result, d ₃₁ = −144.3 pm / V, which did not reach −180 pm / V, which was achieved with PLZT.

(Comparative Example 5)
A PZT film having a thickness of about 4 μm was formed on a Pt / Ti / Si substrate produced in the same manner as in Example 1 by sputtering to form a piezoelectric thin film. The sputtering conditions for PZT were the same as in Example 1, and the sputtering target used had a La / Zr / Ti ratio of 0/60/40 in molar ratio.

  As a result of measuring the formed PZT film by XRD, the (100) orientation degree of the film was 90%. Further, when the cross-sectional shape of the PZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 4 μm was obtained. Further, as a result of analyzing the composition of the PZT film by EDX, the La / Zr / Ti ratio is 0 / 60.3 / 39.7 in molar ratio, and a film having a composition close to the target composition is obtained. I understood it. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PZT was 100 MPa.

Next, in the same manner as in Example 1, an upper electrode was formed on the piezoelectric thin film to complete the piezoelectric element, and then the piezoelectric element was cut into a strip shape from the wafer, and the piezoelectric constant d ₃₁ was obtained by a cantilever method. As a result, d ₃₁ = −137.1 pm / V, which did not reach −180 pm / V, which was achieved with PLZT.

Table 1 summarizes the results of Examples 1-5 and Comparative Examples 1-5. 9 is a graph plotting the relationship between the ratio of Zr to the sum of Zr and Ti and the piezoelectric constant d ₃₁ based on the results of Examples 1 to 5 and Comparative Examples 1 to 5.

From Table 1 and FIG. 9, in a PLZT film (piezoelectric thin film, ferroelectric thin film) in which the ratio of La to the sum of Pb and La is 6 to 8 mol%, the Zr ratio is 54 to 59 mol%. It can be said that high piezoelectric characteristics with d ₃₁ exceeding −180 pm / V can be obtained. In particular, as in Examples 1 and 3 to 5, if the Zr ratio is 55 mol% or more, it can be said that higher piezoelectric characteristics where d ₃₁ exceeds −190 pm / V can be obtained.

Therefore, the above, the composition of the PLZT, when expressed _{(Pb 1-x, La x} ) (Zr y, Ti 1-y) in _{1-x /} 4 O _3, is in obtaining high piezoelectric properties,
0.06 ≦ x ≦ 0.08
0.54 ≦ y ≦ 0.59
At the same time, more preferably,
0.55 ≦ y
It can be said that it is sufficient to satisfy.

  Moreover, in the PLZT thin films of Examples 1 to 5, since the addition amount of La is constant in the film thickness direction, the piezoelectric characteristics do not change in the film thickness direction, and high piezoelectric characteristics can be realized over the entire film thickness direction. It can be said.

  In order to further improve the piezoelectric characteristics by making the PLZT thin film a uniform composition, the variation of the value of x (La ratio in terms of molar ratio) in the film thickness direction is within 0.01 (within 1%). Is desirable. Further, the variation in the value of y (molar ratio Zr ratio) in the film thickness direction is also preferably within 0.01 (within 1%). The above-mentioned variation refers to the difference between the maximum value and the minimum value of x (or y) in the film thickness direction.

Further, in Example 5 where the film stress of PLZT is 260 MPa, the piezoelectric characteristics are lower (| d ₃₁ | is lower) than in Example 3 where the film stress of PLZT is 250 MPa. This is considered to be due to the fact that in Example 5, the film stress is higher as the film is cracked. For this reason, it can be said that the film stress of PLZT is desirably 250 MPa or less. In addition, when the film stress of PLZT is smaller than 100 MPa in Example 2, the optimum composition is close to that of a bulk without stress, and it is difficult to obtain high piezoelectric characteristics with a thin film-specific composition. ing. Therefore, by setting the film stress in the range of 100 to 250 MPa, it is possible to reliably realize high piezoelectric characteristics with a thin film-specific composition (La ratio and Zr ratio).

  In Examples 1 to 5, the (100) orientation degree of the PLZT film is 90% or more, and the crystal orientation (main orientation) can be said to be (100) orientation. In the case of (100) orientation, the piezoelectric characteristics are improved by utilizing the polarization rotation of the domain (for example, the change in the polarization direction from the <100> direction parallel to the substrate surface to the <001> direction perpendicular to the substrate surface). Can be made. Therefore, higher piezoelectric characteristics can be realized as compared with the (111) orientation in which such domain rotation does not occur.

Further, in the substrate 40 with the piezoelectric thin film in which the piezoelectric thin film 44 is formed on the substrate 41, the above-described high film stress (thermal) is applied to the piezoelectric thin film 44 due to the difference in thermal expansion coefficient between the piezoelectric thin film 44 and the substrate 41 which are different materials. Stress). Thus, it is possible to d ₃₁ to obtain the piezoelectric properties exceeding -180pm / V.

  In particular, since the thermal expansion coefficient of Si is 2.6 ppm / K and the thermal expansion coefficient of PLZT is about 8 ppm / K, when the substrate 41 is made of Si and the piezoelectric thin film is made of PLZT, It is considered that a high film stress is surely applied to the piezoelectric thin film 44 by the high temperature film formation due to the difference in thermal expansion coefficient with the substrate 41. Thereby, high piezoelectric characteristics can be reliably realized in the piezoelectric thin film 44. The substrate 41 may be a single silicon substrate or the aforementioned SOI substrate as long as it contains Si.

Further, as in the third and fourth embodiments, the seed layer 45 is formed between the substrate 41 and the piezoelectric thin film 44, so that the seed layer 45 is used as an undercoat layer, and a piezoelectric material having high crystallinity thereon. A thin film 44 can be formed. Thereby, it is considered that a piezoelectric characteristic in which d ₃₁ exceeds −180 pm / V can be easily realized.

  In particular, since the seed layer is PLT having a perovskite structure, it is easy to form the piezoelectric thin film 44 as a single perovskite layer on the PLT, and it is considered that it is easier to realize high piezoelectric characteristics.

  Further, since the electrode (lower electrode 43) is formed between the substrate 41 and the piezoelectric thin film 44, a piezoelectric actuator (piezoelectric) configured by sandwiching the piezoelectric thin film 44 between a pair of electrodes (lower electrode 43 and upper electrode). A substrate 40 with a piezoelectric thin film suitable for the element 50) can be realized.

  Next, the results of examining the relationship between the film thickness of the PLZT thin film and the piezoelectric characteristics are shown below.

(Example 6)
On the PLT / Pt / Ti / Si substrate produced in the same manner as in Example 3, about 3 μm of PLZT was formed by sputtering to form the piezoelectric thin film 44. The sputtering conditions for PLZT were Ar flow rate: 20 sccm, O ₂ flow rate: 0.6 sccm, pressure: 0.5 Pa, substrate temperature: 500 ° C., and RF power applied to the target: 500 W. A sputtering target having a La / Zr / Ti ratio of 6/55/45 in terms of molar ratio was used.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 95%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 4.0 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.3 / 56.3 / 43.7 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 200 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −201.6 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

(Example 7)
On the PLT / Pt / Ti / Si substrate manufactured in the same manner as in Example 3, a PLZT film having a thickness of about 6 μm was formed by sputtering using the same target as in Example 6 under the same conditions as in Example 6. A thin film 44 was formed.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 98%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 6.2 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.2 / 55.3 / 44.7 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 220 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −205.2 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

(Example 8)
On the PLT / Pt / Ti / Si substrate manufactured in the same manner as in Example 3, a PLZT film having a thickness of about 10 μm was formed by sputtering using the same target as in Example 6 under the same conditions as in Example 6. A thin film 44 was formed.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 99%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 10.0 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.2 / 55.3 / 44.7 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film stress by measuring the warpage of the wafer before and after the film formation, the film stress of PLZT was 250 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −204.8 pm / V, and piezoelectric characteristics higher than the target value of −180 pm / V were obtained.

(Comparative Example 6)
On the PLT / Pt / Ti / Si substrate produced in the same manner as in Example 3, using the same target as in Example 6 and using the same conditions as in Example 6, a PLZT film having a thickness of about 11 μm was formed by sputtering. A thin film was formed.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 99%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 11.2 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.2 / 55.3 / 44.7 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 260 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Asked. As a result, it was found that d ₃₁ = −163.0 pm / V, which did not reach the target value of −180 pm / V.

(Comparative Example 7)
On the PLT / Pt / Ti / Si substrate manufactured in the same manner as in Example 3, a PLZT film having a thickness of about 13 μm was formed by sputtering using the same target as in Example 6 under the same conditions as in Example 6. A thin film was formed.

  As a result of measuring the formed PLZT film by XRD, the (100) orientation degree of the film was 99%. Further, when the cross-sectional shape of the PLZT film was confirmed by SEM, it was found that a columnar crystal having a film thickness of 13.2 μm was obtained. As a result of analyzing the composition of the PLZT film by EDX, the La / Zr / Ti ratio was 6.2 / 55.3 / 44.7 in terms of molar ratio, and a film having a composition close to the target composition was obtained. I found out. Moreover, as a result of measuring the film | membrane stress by measuring the curvature of the wafer before and behind film-forming, the film | membrane stress of PLZT was 300 MPa.

Next, in the same manner as in Example 1, after completing the piezoelectric element 50 to form the upper electrode on the piezoelectric thin film 44, cut out piezoelectric element 50 from the wafer into strips, the piezoelectric constant d ₃₁ by cantilever method Although an attempt was made to find it, the film had cracks, and the piezoelectric properties could not be evaluated.

Table 2 summarizes the results of Examples 6-8 and Comparative Examples 6-7. Further, from the results of Examples 6-8 and Comparative Example 6-7 shows the PLZT film thickness, a graph plotting the relationship between the piezoelectric constant d ₃₁ in FIG. 10.

From Table 2 and FIG. 10, when the film thickness of the PLZT film exceeds 10 μm, d ₃₁ does not reach −180 pm / V, and as a result, the film cracks. Therefore, the film thickness of the PLZT film is preferably 10 μm or less. It can be said. Further, it has been found that when the film thickness of the PLZT film is less than 1 μm, it is difficult to obtain a desired displacement generation force with the thin film, and it is difficult to apply it to a device such as a piezoelectric actuator. Therefore, considering the application to the device and the piezoelectric characteristics, it can be said that the film thickness of the PLZT film is desirably in the range of 1 to 10 μm.

[Others]
In the above embodiment, the sputtering method or the sol-gel method is used for forming the piezoelectric thin film (ferroelectric thin film), but the film manufacturing method is not limited thereto. If the composition ratio of PLZT shown in the present embodiment can be realized, for example, a physical film forming method such as a pulse laser deposition (PLD) method or an ion plating method, a MOCVD (Metal Organic Chemical Vapor Deposition) method, etc. A piezoelectric thin film may be formed using a chemical film forming method.

  The ferroelectric thin film, the substrate with the piezoelectric thin film, the piezoelectric actuator, the ink jet head, the ink jet printer, and the manufacturing method of the ferroelectric thin film of the present embodiment described above can be expressed as follows. Has an effect.

  The ferroelectric thin film of this embodiment is a ferroelectric thin film made of lead lanthanum zirconate titanate, and the ratio a of lanthanum to the sum of lead and lanthanum is 6% to 8% in molar ratio. The ratio b of zirconium to the total of zirconium and titanium is 54% or more and 59% or less in terms of molar ratio.

By defining the Zr composition ratio (ratio b) in the case where the La addition amount (ratio a) is in a predetermined range in the ferroelectric thin film (PLZT thin film) made of PLZT in the above range different from the optimum range in bulk. High piezoelectric characteristics (for example, | d ₃₁ | ≧ 180 pm / V) that cannot be realized with a PZT thin film can be realized with the PLZT thin film over the entire film thickness direction.

The ratio b is desirably 55% or more in terms of molar ratio. In this case, higher piezoelectric characteristics (for example, | d ₃₁ | ≧ 190 pm / V) can be realized with a PLZT thin film.

  In the above ferroelectric thin film, the film stress is preferably 100 MPa or more and 250 MPa or less. When the film stress is smaller than 100 MPa, the optimum composition is close to that of an unstressed bulk, and it is difficult to obtain high piezoelectric characteristics with a composition unique to the thin film. On the other hand, when the film stress is larger than 250 MPa, the film is cracked, or when the film is formed on the substrate, the film is easily peeled off and it is difficult to obtain high piezoelectric characteristics. Therefore, by setting the film stress within the above range, it is possible to realize high piezoelectric characteristics without causing cracks or the like with the composition (ratio a and ratio b) unique to the thin film described above.

  In addition, it is preferable that the film stress is large, but if it exceeds 190 MPa, the piezoelectric characteristics increase, and film peeling tends to occur when a film is formed on the substrate. Therefore, reinforcement for preventing film peeling is performed by a known method. It is desirable.

  In the above ferroelectric thin film, the crystal orientation of the film is preferably (100) orientation. In this case, since the piezoelectric characteristics can be improved by utilizing the non-180 ° polarization rotation of the domain, higher piezoelectric characteristics can be realized as compared with the case where the crystal orientation of the film is the (111) orientation.

  In the above ferroelectric thin film, the crystal structure of the film is preferably a columnar crystal. In this case, more polarization domains are present in the single crystal than in the case where the crystal structure of the film is a granular crystal, and an improvement in piezoelectric characteristics due to polarization rotation can be expected.

  In the above ferroelectric thin film, the film thickness is desirably 1 μm or more and 10 μm or less. When the film thickness of the PLZT thin film is less than 1 μm, it is difficult to obtain a desired displacement generation force with the thin film, and it is difficult to apply to a device such as a piezoelectric actuator. On the other hand, if the film thickness exceeds 10 μm, cracks tend to occur in the film, making it difficult to obtain high piezoelectric characteristics. Therefore, by defining the film thickness of the PLZT thin film within the above range, it is possible to obtain a desired displacement generating force with the thin film and easily apply it to the device, and obtain high piezoelectric characteristics.

  The variation in the film thickness direction of the ratio a is preferably within 1% (in terms of the molar ratio), and the variation in the film thickness direction of the ratio b is also within 1% (in terms of the molar ratio). It is desirable. In this case, the piezoelectric characteristics can be further improved by using a PLZT thin film with a uniform composition in the film thickness direction.

  The substrate with a piezoelectric thin film of this embodiment is a substrate with a piezoelectric thin film in which a piezoelectric thin film is formed on the substrate, and the piezoelectric thin film is composed of the above-described ferroelectric thin film. In this case, high piezoelectric characteristics can be realized by applying high film stress to the piezoelectric thin film (ferroelectric thin film) due to the difference in thermal expansion coefficient from the substrate.

  The substrate is preferably a silicon substrate or an SOI substrate. Note that an SOI (Silicon on Insulator) substrate is a substrate in which two silicon substrates are bonded together through an oxide film. Since Si and PLZT of the substrate have different thermal expansion coefficients, high film stress can be reliably applied to the piezoelectric thin film made of PLZT, and high piezoelectric characteristics can be reliably realized.

  It is desirable that a seed layer for controlling the crystal orientation of the piezoelectric thin film is formed between the substrate and the piezoelectric thin film. In this case, it becomes easy to realize a high piezoelectric characteristic by forming a piezoelectric thin film having high crystallinity on the seed layer.

  The seed layer is preferably made of lead lanthanum titanate. Since PLT has a perovskite structure, it is easy to form a piezoelectric thin film on the PLT as a single perovskite layer, and it is easier to realize high piezoelectric characteristics.

  It is desirable that an electrode is formed between the substrate and the piezoelectric thin film. In this case, a substrate with a piezoelectric thin film suitable for a piezoelectric actuator configured by sandwiching a piezoelectric thin film between a pair of electrodes can be realized.

  The piezoelectric actuator of the present embodiment has a configuration in which another electrode is formed on the opposite side of the substrate with the piezoelectric thin film and the piezoelectric thin film of the substrate with the piezoelectric thin film from the electrode. In this case, it is possible to reliably realize a configuration in which the piezoelectric thin film is expanded and contracted according to the applied voltage.

  The ink jet head of this embodiment includes the above-described piezoelectric actuator and a nozzle substrate having nozzle holes for ejecting ink accommodated in openings formed in the substrate of the piezoelectric actuator to the outside. In this configuration, since the piezoelectric characteristics of the piezoelectric actuator are high, it is possible to eject ink using high-viscosity ink.

  The ink jet printer of this embodiment includes the above ink jet head, and ejects ink from the ink jet head toward a recording medium. By including the above-described inkjet head, an inkjet printer advantageous for high-speed and high-definition drawing can be realized.

  The ferroelectric thin film described above can be formed by sputtering or sol-gel method. By using such a film forming method, the above-described PLZT thin film having high piezoelectric characteristics over the entire film thickness direction can be easily realized.

  The ferroelectric thin film of the present invention can be used for a substrate with a piezoelectric thin film in which a piezoelectric thin film is formed on a substrate, a piezoelectric actuator having the substrate with a piezoelectric thin film, an ink jet head, and an ink jet printer.

1 Inkjet printer 21 Inkjet head 21a Actuator (substrate with piezoelectric thin film, piezoelectric actuator)
22 Substrate 22a Pressure chamber (opening)
24 Lower electrode 25 Piezoelectric thin film (ferroelectric thin film)
26 Upper electrode 29 Seed layer 31 Nozzle substrate 31a Discharge hole (nozzle hole)
40 Substrate with piezoelectric thin film 41 Substrate 43 Lower electrode 44 Piezoelectric thin film (ferroelectric thin film)
45 Seed layer

Claims (17)

A ferroelectric thin film made of lead lanthanum zirconate titanate,
The ratio a of lanthanum to the sum of lead and lanthanum is 6% to 8% in molar ratio,
A ferroelectric thin film in which a ratio b of zirconium to a sum of zirconium and titanium is 54% or more and 59% or less by molar ratio.   The ferroelectric thin film according to claim 1, wherein the ratio b is 55% or more in terms of molar ratio.   The ferroelectric thin film according to claim 1 or 2, wherein the film stress is 100 MPa or more and 250 MPa or less.   The ferroelectric thin film according to any one of claims 1 to 3, wherein the crystal orientation of the film is a (100) orientation.   The ferroelectric thin film according to claim 1, wherein the crystal structure of the film is a columnar crystal.   The ferroelectric thin film according to claim 1, wherein the film thickness is 1 μm or more and 10 μm or less.   The ferroelectric thin film according to any one of claims 1 to 6, wherein variation in the film thickness direction of the ratio a is within 1%.   The ferroelectric thin film according to any one of claims 1 to 7, wherein variation in the film thickness direction of the ratio b is within 1%. A substrate with a piezoelectric thin film in which a piezoelectric thin film is formed on a substrate,
The said piezoelectric thin film is a board | substrate with a piezoelectric thin film comprised with the ferroelectric thin film in any one of Claim 1-8.   The substrate with a piezoelectric thin film according to claim 9, wherein the substrate is made of a silicon substrate or an SOI substrate.   The substrate with a piezoelectric thin film according to claim 9 or 10, wherein a seed layer for controlling crystal orientation of the piezoelectric thin film is formed between the substrate and the piezoelectric thin film.   The substrate with a piezoelectric thin film according to claim 11, wherein the seed layer is made of lead lanthanum titanate.   The substrate with a piezoelectric thin film according to claim 9, wherein an electrode is formed between the substrate and the piezoelectric thin film. A substrate with a piezoelectric thin film according to claim 13,
A piezoelectric actuator, wherein another electrode is formed on the opposite side of the piezoelectric thin film of the substrate with the piezoelectric thin film from the electrode. A piezoelectric actuator according to claim 14,
An inkjet head comprising: a nozzle substrate having a nozzle hole for discharging ink accommodated in an opening formed in the substrate of the piezoelectric actuator.   An ink jet printer comprising the ink jet head according to claim 15, wherein ink is ejected from the ink jet head toward a recording medium.   A method for producing a ferroelectric thin film, wherein the ferroelectric thin film according to claim 1 is formed by a sputtering method or a sol-gel method.

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