JP2010189741A - Method for depositing piezoelectric ceramic film using aerosol deposition process, and piezoelectric ceramic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film deposition process which can provide sufficient piezoelectric properties even under annealing at ≤600°C, as a method for depositing a piezoelectric ceramic using an aerosol deposition process. <P>SOLUTION: The method for depositing a piezoelectric ceramic film 4, using an aerosol deposition process, on an electrode 3 formed at the face of a substrate 2, includes: a film deposition step s3 where the powder of piezoelectric ceramic is jetted onto the electrode by an aerosol deposition process to deposit a piezoelectric ceramic film; a laser irradiation step s4 where the film face of the piezoelectric ceramic is irradiated with ultraviolet laser beam; and an annealing step s5 where, after the irradiation of the laser beam, the substrate is heat-treated at ≤600°C; wherein by the laser irradiation step and the annealing step, the piezoelectric ceramic film is crystallized. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a method for forming a piezoelectric ceramic film on a substrate by an aerosol deposition method, and a piezoelectric ceramic material. Specifically, the present invention relates to a technique for improving characteristics of a piezoelectric ceramic film formed by an aerosol deposition method.

  As an electronic ceramic material, there is a piezoelectric ceramic material in which a piezoelectric ceramic film is formed on a substrate. In addition, it is necessary to form a high-quality film having excellent characteristics in a piezoelectric ceramic material used for a microactuator or an optical device. In recent years, as an excellent technique for obtaining an electronic ceramic film having a thickness of several μm to several hundred μm, a film forming technique called an aerosol deposition (AD) method has attracted attention. This AD method is a method for forming an electronic ceramic film on a substrate by aerosolizing crystalline fine particles and placing the particles on a high-speed jet and depositing them on the substrate. And in the piezoelectric ceramic which this invention makes object, AD method is being employ | adopted as a film forming method when obtaining a film thickness of about 1-10 micrometers.

  FIG. 7 shows a conventional example of a procedure for producing a piezoelectric ceramic material by the AD method. A powder of a piezoelectric material (PZT: lead zirconate titanate, etc.) as a raw material is aerosolized using nitrogen gas or the like as a medium (s1) on the substrate (made of silicon, for example), while an electrode is formed on the substrate. It is formed (s2). Then, aerosolized powder is sprayed onto the substrate in a vacuum atmosphere to deposit piezoelectric ceramics on the substrate (AD step: s3). After the piezoelectric ceramic film having the required thickness is formed, the substrate is heat-treated (annealed) at a temperature higher than 600 ° C. (annealing step: s5), and the piezoelectric material is made to exhibit piezoelectricity. Then, a counter electrode is formed on the upper surface of the film (s6) to complete the piezoelectric ceramic material.

  Examples of the piezoelectric ceramic material as an optical device include a voltage-driven magneto-optic spatial light modulator (MOSLM) in which a piezoelectric ceramic film is formed on a substrate made of a garnet single crystal that is a magneto-optic crystal. This MOSLM is a device that spatially modulates the amplitude, phase, or polarization state of incident light, and the voltage-driven MOSLM controls the magnetization direction of the garnet single crystal that constitutes the substrate by the stress caused by the piezoelectric effect. Thus, power consumption and heat generation can be reduced as compared with a conventional current-driven MOSLM (see Patent Document 1).

JP 2003-315756 A

  The conventional piezoceramic material is a noble metal because it needs to be heat-treated at a temperature higher than 600 ° C. in the annealing step s5 shown in FIG. 7, and the electrode formed on the substrate needs to withstand this high temperature. It has been necessary to use Pt (platinum), Ti (titanium) which is a rare metal for electronic materials, or alloys thereof. Further, in optical device applications such as the above-described MOSLM, these metals have low light reflectivity, and it has been difficult to improve optical characteristics.

  For electronic materials, general Ag (silver), Al (aluminum), or alloys containing these can be expected to provide a stable supply and have high reflectivity. However, the melting point is lower than that of Pt or Ti, and the electrode may be damaged during annealing. In particular, Al has a melting point of about 660 ° C., and it was impossible to adopt the AD method.

  The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide a film forming process in which sufficient piezoelectricity can be obtained even by annealing at 600 ° C. or lower in a piezoelectric ceramic film forming method using the AD method. become. Another object of the present invention is to provide a piezoelectric ceramic material manufactured by the process.

  The present invention for achieving the above object is a method for forming a piezoelectric ceramic film on an electrode formed on a substrate surface, wherein a piezoelectric ceramic powder is applied onto the electrode by an aerosol deposition method. An AD step for forming a piezoelectric ceramic film by spraying, a laser light irradiation step for irradiating a surface of the piezoelectric ceramic with ultraviolet laser light, and an annealing step for heat-treating the substrate at 600 ° C. or lower after the laser light irradiation. A method for forming a piezoelectric ceramic film using an aerosol deposition method in which the piezoelectric ceramic film is crystallized by the laser light irradiation step and the annealing step.

In the laser beam irradiation step, it is more preferable to irradiate an excimer laser beam having an energy density of 65 mJ / cm ² or less.

  The electrode is made of aluminum, silver, or an alloy containing these metals, and may be a method for forming a piezoelectric ceramic film using an aerosol deposition method at a temperature of 500 ° C. or lower in the annealing step. The substrate may be a method for forming a piezoelectric ceramic film using an aerosol deposition method made of a garnet single crystal.

  The present invention also extends to a piezoelectric ceramic material comprising a piezoelectric ceramic film formed by any of the above methods, the piezoelectric ceramic material comprising: a substrate; an electrode formed on the substrate surface; A piezoelectric ceramic film formed on the electrode and a counter electrode formed on the upper surface of the piezoelectric ceramic film are provided.

  In the method for forming a piezoelectric ceramic film using the aerosol deposition method of the present invention, sufficient piezoelectricity can be obtained for the piezoelectric ceramic film even by annealing at 600 ° C. or lower. Thereby, for example, instead of conventional rare metals such as Pt and Ti having a high melting point, a stable electrode can be expected mainly based on Al and Ag, which are general electrode materials, and a metal having a low melting point is used as an electrode. A piezoelectric ceramic film having excellent characteristics can be formed on the electrode. Therefore, it is possible to provide an inexpensive and high-performance piezoelectric ceramic material.

  Also, since Al and Ag have a higher reflectance than conventional electrode metals, for example, if a garnet single crystal is used for the substrate, a voltage-driven magneto-optic spatial light modulator with excellent characteristics can be obtained. be able to.

It is a figure which shows an example of the procedure for producing a piezoelectric ceramic material using the aerosol deposition method of this invention. It is sectional drawing of the piezoelectric ceramic material provided with the piezoelectric ceramic film formed by the aerosol deposition method It is a figure which shows the relationship between the annealing temperature and the piezoelectric 31 coefficient in the piezoelectric ceramic material which concerns on Example 1 of this invention, and the piezoelectric ceramic material which concerns on the comparative example 1 produced in the conventional procedure. It is a figure which shows the relationship between laser irradiation energy and a dielectric constant about the piezoelectric ceramic material which concerns on the piezoelectric ceramic material which concerns on the piezoelectric ceramic material which concerns on the piezoelectric ceramic material which concerns on Example 2 of this invention, and was formed without performing annealing. is there. It is a figure which shows the relationship between the laser irradiation energy in the said Example 2, and remanent polarization. It is a figure which shows the relationship between the laser irradiation energy in the said Example 2, and piezoelectric d31 constant. It is a figure which shows the conventional procedure for producing a piezoelectric ceramic material using the aerosol deposition method.

=== Piezoelectric ceramic material ===
In order to evaluate the film forming method of the present invention, a piezoelectric ceramic film is formed by an AD method on an electrode made of an alloy of Pt and Ti (Pt / Ti alloy) formed on a gadolinium gallium garnet (GGG) substrate surface. Then, a counter electrode of Au (gold) was formed on the piezoelectric ceramic film to produce a piezoelectric ceramic material. Various piezoelectric ceramic materials with different piezoelectric ceramic film formation conditions were prepared as samples, and the characteristics of each sample were evaluated. The film thickness of the piezoelectric ceramic film of each sample was 3 μm.

  FIG. 1 shows a procedure for producing a piezoelectric ceramic material including a film forming method according to an embodiment of the present invention. In the conventional manufacturing procedure shown in FIG. 7, annealing is performed after the piezoelectric ceramic film is formed by the AD method, but in this embodiment, the piezoelectric ceramic film formed on the electrode on the substrate surface in AD step s3. The film surface is irradiated with ultraviolet laser light (laser light irradiation step: s4), and after this laser light irradiation step s4, an annealing step s5 is executed. Then, a counter electrode is formed on the surface of the piezoelectric ceramic film formed by the processes from AD step s3 to annealing step s5 (s6), thereby completing the piezoelectric ceramic material.

  FIG. 2 shows a schematic structure of the completed piezoelectric ceramic material 1 in a sectional view. On the substrate surface of the GGG substrate 2, an electrode (base electrode) 3, a piezoelectric ceramic film 4, and a counter electrode 5 made of a Pt / Ti alloy are laminated in this order.

=== Characteristic evaluation by annealing temperature ===
First, the piezoelectric characteristics with respect to the heat treatment temperature in the annealing step s5 were evaluated for the piezoelectric ceramic material produced by the procedure shown in FIG. 1 and the piezoelectric ceramic material produced by the conventional procedure shown in FIG. FIG. 3 is a graph showing the relationship between the annealing temperature and the piezoelectric d31 constant (pm / V) in the piezoelectric ceramic material 1, which is shown in FIG. The piezoelectric ceramic material (Example 1) produced by the procedure including the film forming method of the present invention is compared. In Example 1, the surface of the piezoelectric ceramic film 4 is irradiated with excimer laser light having a wavelength of 248 nm and an energy density of 50 mJ / cm ^{2 in} the laser light irradiation step s4. In the annealing step s5, both Example 1 and Comparative Example 1 were heat-treated at each temperature for 1 h in the atmosphere. The piezoelectric d31 constant was measured using a known cantilever method. Of course, Example 1 and Comparative Example 1 are all manufactured under the same conditions except for the presence or absence of the laser light irradiation step s4.

  In the graph shown in FIG. 3, the displacement in the d31 direction, that is, the substrate 2 surface direction when a voltage is applied between the base electrode 3 and the counter electrode 5 is shown. Generally, when the d31 constant is 40 (pm / V) or more, it becomes practical as a piezoelectric ceramic material. In Comparative Example 1, a temperature close to 600 ° C. was required in the annealing step s5. On the other hand, in Example 1, the characteristic which is already practical at 500 degreeC is acquired. That is, if a piezoelectric ceramic film is formed by the method of the present invention, practically sufficient characteristics can be obtained at 500 ° C. or lower. This indicates that Ag or Al that could not be conventionally used as the base electrode 5 can be used. Further, if annealing is performed at a temperature of 600 ° C. as in the conventional case, a piezoelectric ceramic material having extremely excellent piezoelectric characteristics can be obtained. However, when the temperature is higher than 600 ° C., the effect of irradiating the excimer laser light is reduced.

  Note that the piezoelectric d31 constant increases sharply at about 550 ° C. or more while changing from the crystallization temperature at which the piezoelectricity appears in the piezoelectric ceramic film on the low temperature side, almost leveling off as the temperature increases. And the value falls rapidly about 600 degreeC. This is presumed to be caused by degradation of the base electrode 3 such as peeling, but this degradation does not always occur, and may not occur depending on the production conditions of the piezoelectric ceramic material as a sample. By the way, the crystallization temperature and the deterioration temperature of each part differ depending on the process conditions before the annealing step s5. For example, it varies depending on conditions such as the aerosol injection speed in AD step s3 and conditions for aerosolization s2 (powder concentration, powder particle size, etc.). In the first embodiment, it naturally depends on conditions such as the wavelength and energy density of the laser beam. Therefore, it is difficult to specify the temperature in the annealing step s5, particularly the lower limit value of the temperature. In any case, in specifying the invention, it is a requirement that the piezoelectric body in the piezoelectric ceramic film is crystallized after the annealing step s5.

=== Characteristic evaluation under laser light irradiation conditions ==
In the previous characteristic evaluation by the annealing temperature, it was found that the characteristics of the piezoelectric ceramic film 4 are improved by inserting the laser irradiation step s4 between the AD step s3 and the annealing step s5. Next, the conditions in the laser light irradiation step s3 will be examined. FIG. 4 is a diagram illustrating the relationship between the irradiation energy density of laser light and the dielectric constant. The piezoelectric ceramic material (Comparative Example 2) manufactured without performing the annealing step s5 after the laser light irradiation step s4, and the piezoelectric ceramic. The characteristic about each of the piezoelectric ceramic material (Example 2) which formed the film | membrane with the method of this invention is shown. In the laser beam irradiation step s4, the excimer laser beam having the wavelength of 248 nm described above was used. Moreover, in Example 2, it annealed on the conditions of 500 degreeC / 1h in air | atmosphere.

From FIG. 4, it was confirmed that the dielectric constant was increased by annealing after irradiation with ultraviolet laser light. This means that the piezoelectric ceramic film 4 is sufficiently crystallized by the laser light irradiation step s4 and the annealing step s5. In addition, since the irradiation energy density exceeded 130 mJ / cm ² , the dielectric constant improvement by the laser beam irradiation step s4 was not recognized. It is presumed that this is because the piezoelectric ceramic film 4 is evaporated by irradiating the laser beam with a high energy density. The energy density of the laser light that causes this transpiration changes depending on the conditions in the AD step s3 and the aerosolization step s1 and the heat treatment conditions (temperature, time) in the annealing step s5. There may be cases. In any case, the piezoelectric ceramic film 4 formed by the AD method can be sufficiently crystallized by irradiating laser light before the annealing step s5.

Here, with respect to Example 2 above, the residual polarization and the piezoelectric d31 constant were measured when the irradiation condition of the ultraviolet laser beam in the laser beam irradiation step s4 was changed. Regarding the remanent polarization, the CV characteristic of the piezoelectric ceramic material 1 was measured and obtained from the hysteresis in the measured value. 4 and 5 show the remanent polarization characteristic and the piezoelectric d31 constant characteristic with respect to the irradiation energy density of the laser beam, respectively. Residual polarization and the piezoelectric d31 constant, when irradiated with a laser beam, both the irradiation energy up to about 50 mJ / cm ² has been at a high number, then is slowly value to around 20 mJ / cm ² decreases, the The value when the laser beam is not irradiated with the vicinity of 65 mJ / cm ² as the inflection point is attenuated as an asymptotic line (10, 11). Therefore, from these characteristics, it can be said that in the laser light irradiation step s4, if the ultraviolet laser light is irradiated with energy of 65 mJ / cm ² or less, the piezoelectric ceramic film 4 having more excellent characteristics can be formed.

  Even if infrared laser light is used as the laser light, the same effect can be expected for the piezoelectric ceramic film 4 itself, but laser light having a long wavelength including the infrared laser is transmitted through the piezoelectric ceramic film 4. Therefore, in the piezoelectric ceramic material 1 with the base electrode 3, the base electrode 3 may be damaged by the transmitted laser light, and the function as a device may be impaired.

1 Piezoelectric Ceramic Material 2 Substrate 3 Base Electrode 4 Piezoelectric Ceramic Film 5 Counter Electrode

Claims (5)

A method for forming a piezoelectric ceramic film on an electrode formed on a substrate surface,
An AD step of forming a piezoelectric ceramic film by injecting a piezoelectric ceramic powder onto the electrode by an aerosol deposition method;
A laser beam irradiation step of irradiating the piezoelectric ceramic film surface with an ultraviolet laser beam;
An annealing step of heat-treating the substrate at 600 ° C. or less after the laser light irradiation;
Including
A method for producing a piezoelectric ceramic film using an aerosol deposition method, wherein the piezoelectric ceramic film is crystallized by the laser light irradiation step and the annealing step. ^{2. The method of} forming a piezoelectric ceramic film using an aerosol deposition method according to claim 1, wherein in the laser light irradiation step, excimer laser light having an energy density of 65 mJ / cm ² or less is irradiated.   3. The aerosol deposition method according to claim 1, wherein the electrode is made of aluminum, silver, or an alloy containing these metals, and the annealing step is performed at a temperature of 500 ° C. or lower. A method for forming a piezoelectric ceramic film.   4. The method for forming a piezoelectric ceramic film using an aerosol deposition method according to claim 1, wherein the substrate is made of a garnet single crystal.   A piezoelectric ceramic material comprising a substrate, an electrode formed on the substrate surface, a piezoelectric ceramic film formed on the electrode, and a counter electrode formed on an upper surface of the piezoelectric ceramic film, A ceramic film is formed by the film forming method according to claim 1.

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