JPH09130199A - Piezoelectric thin film element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength of the film element itself and to reduce the disturbance of piezoelectric vibrations despite the high mechanical strength of the support of a piezoelectric thin film by providing a 2nd support which holds a vibration part and a 1st support which holds the 2nd support. SOLUTION: A 1st piezoelectric thin film driving electrode 4, a piezoelectric thin film 5 and a 2nd piezoelectric thin film driving electrode 6 are formed on a 2nd support 3. The support 3 covers a 1st support 2 and a substrate 1 and is held by the support 2. The support 3 has plural etching holes 7 formed along the outer edge of the film 5 in a slit shapes, and the parts forming no holes 7 are used as the connection parts. The substrate 1 placed under the support 2 has a cavity part 8 where the support 2 is connected to the substrate 1 in a bridge shape. Then the part of the support 2 that is corresponding to to the lower part of a vibration part is removed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device structure to which a piezoelectric thin film capable of high performance, small size and high integration is applied. More specifically, in order to avoid that the piezoelectric vibration generated by applying an electric field to the piezoelectric thin film is restrained by the substrate and the support, the substrate part under the vibrating part is hollowed and the support is thinned, The present invention relates to a piezoelectric element structure having an element structure that strongly supports these structures by supports made of different materials, that is, a piezoelectric element structure having a thin film structure that is mechanically strong but does not hinder piezoelectric vibration.

[0002]

2. Description of the Related Art Miniaturization of communication-related equipment and electronic equipment,
With the increase in frequency, filters, oscillators and the like used in these devices are also required to have higher frequencies, and are required to be small and have high performance. Conventionally, in such components, a SAW (surface acoustic wave) device using a single crystal substrate such as lithium niobate or lithium tantalate or a zinc oxide single crystal film is widely used. However, in the SAW device, the upper limit of the frequency is about 1 GHz or more in view of the surface wave propagation velocity and the IDT (inter digital transducer) formation processing accuracy.

In recent years, a device using bulk vibration of a piezoelectric body has been proposed as an element that can be applied at frequencies above the above-mentioned frequency (hereinafter, simply referred to as bulk wave filter). The resonance frequency of the bulk vibration of the piezoelectric body depends on the speed of sound in the piezoelectric body and the thickness of the piezoelectric body, and when a piezoelectric thin film having a film thickness of about 1 μm is formed, it has a resonance frequency of about 2 GHz. In the current thin film forming technology, the above-mentioned 1 μm
It is possible to easily obtain a piezoelectric thin film having a film thickness of a level, and it is possible to increase the frequency by reducing the film thickness.
In addition, such an element has a planar size of several tens.
Since the filter is formed with a size of 0 μm square or less, if a filter is configured with such an element, the chip size per filter can be formed to be about 1 mm square.
It can be made smaller than a filter.

Conventionally, as such a device, D. Cus has been used.
hman et al. Proc. Ultrasonics Symposium (199
0) and those described on page 519. D.
Cushman et al. Formed aluminum nitride, an upper piezoelectric thin film drive electrode and a lower piezoelectric thin film drive electrode on a gallium arsenide substrate, and then removed the gallium arsenide substrate under the vibrating part by etching from the back surface to remove the piezoelectric film. A structure is created in which vibration is not restrained. A filter having a resonance frequency of 1023 MHz is produced by a 400 μm square vibrating section made of an aluminum nitride piezoelectric film having a film thickness of 1.8 μm and having such a structure.

[0005]

If the piezoelectric thin film is formed on the substrate as it is, the piezoelectric vibration of the thin film is restrained by the substrate and is significantly attenuated. Therefore, in such a device, the piezoelectric thin film and the piezoelectric thin film drive electrode are held by themselves or by a support, and the portion under the vibrating portion is removed by a method such as etching to reduce the constraint on piezoelectric vibration. The structure is taken.

In the device by D. Cushman et al., A gallium arsenide substrate is mechanically polished to have a thickness of about 100 μm, and then the substrate under the vibrating portion is removed by etching from the side opposite to the surface on which the piezoelectric thin film is formed and the back side. doing. When such a structure is adopted, the substrate is thin, and since a part of it is removed, the mechanical strength is weakened, and care must be taken in handling. Further, since the vibrating portion forms a structure on the diaphragm, noise due to vibration of air is easily picked up, and the vibrating portion may be destroyed if a pressure difference occurs between the inside and outside of the substrate removing portion. .

In order to solve these drawbacks, the substrate portion may be removed not from the back surface of the substrate but from the side where the piezoelectric thin film is formed. With this manufacturing method, the substrate strength is high because it is not necessary to process the substrate thinly. Further, since the etching hole for etching the substrate portion is formed from the upper surface, air can be released through this hole, and it is possible to reduce vibration and pressure difference of air. However, in this case, the support for holding the vibrating portion has etching holes for removing the portion under the vibrating portion, and therefore has only a few connecting points with the substrate. Therefore, generally, the strength of this connecting point becomes weak, and it becomes the starting point of the destruction of the element. When this connecting point is strengthened, the entire support, especially the part holding the vibrating part, has mechanically high strength. As a result, the vibrating portion is constrained by the support, and the performance cannot be fully exhibited.

The present invention solves these problems, and the strength of the element itself is high, and the mechanical strength of the support for supporting the piezoelectric thin film is strong, but the composite support structure does not hinder the piezoelectric vibration. The purpose of the present invention is to obtain a piezoelectric element having a thin film structure.

[0009]

A piezoelectric thin film element according to the present invention comprises a vibrating portion composed of a first piezoelectric thin film driving electrode, a piezoelectric thin film, and a second piezoelectric thin film driving electrode, and a vibrating portion supporting the vibrating portion. A piezoelectric thin film element comprising first and second supports, and a substrate holding the two supports, comprising: (1) a first piezoelectric thin film drive electrode, a piezoelectric thin film and a second piezoelectric thin film drive. An electrode is formed on the second support, and (2) the second support is formed to cover the first support and the substrate and is held by the first support, and the second support A plurality of slit-like opening holes are provided along the outer edge of the piezoelectric thin film so as to surround the outer edge of the piezoelectric thin film, and the portion not provided with the opening holes is a connecting portion. A cavity is formed in the substrate below the first support member, and the first support member has a cross-shaped substrate shape. Formed are connected, characterized in that (4) the first support of the first support portion corresponding to the lower portion of the vibrating portion is removed.

It is preferable that the mechanical strength of the first support is stronger than the mechanical strength of the second support.

It is preferable that the piezoelectric thin film drive electrodes are formed on both surfaces of the piezoelectric thin film.

It is preferable that the first and second piezoelectric thin film drive electrodes are formed on the same surface of the piezoelectric thin film.

It is preferable that a part of the substrate is used as the first support.

The substrate is a silicon <100> single crystal, the first support is a part of the substrate doped with boron of 10 ²⁰ / cm ³ or more, and the second support is a silicon dioxide film. The piezoelectric thin film driving electrode is platinum and titanium, and the piezoelectric thin film is a piezoelectric body containing (A) lead titanate and (B) lead zirconate titanate as main components, and the second piezoelectric thin film driving electrode is It is preferably composed of platinum and titanium.

It is preferable that the second piezoelectric thin film driving electrode is made of aluminum, and that a protective film made of silicon nitride is formed on the entire surface of the piezoelectric thin film element.

It is preferable that the second support is a silicon nitride film.

The second support is a silicon nitride film, the piezoelectric thin film is a piezoelectric body containing lead titanate or lead zirconate titanate as a main component, and the surface of the piezoelectric thin film element. It is preferable that a protective film made of silicon nitride is formed on the entire surface.

The second support is preferably a tantalum oxide film.

The second support is a tantalum oxide film, the second piezoelectric thin film driving electrode is aluminum, and a protective film made of silicon nitride is formed on the entire surface of the piezoelectric thin film element. It is preferable that

In the method for manufacturing a piezoelectric thin film element of the present invention, (1) after forming the first support, a portion corresponding to a lower portion of the vibrating portion is removed, and the removed portion is removed by the first portion.
Filling with a low corrosion resistant material having a lower corrosion resistance than that of the support, and (2) after the second support and the vibrating portion are formed on the first support, the low corrosion resistant material is removed by etching. And leaving only the first support.

Further, according to the method of manufacturing the piezoelectric thin film element of the present invention, boron is formed on the surface of the substrate made of silicon single crystal in an amount of 10 ²⁰
/ Cm ³ or more to form a boron-doped portion to improve the etching resistance of the boron-doped portion, and the boron-doped portion is left in the substrate etching step to form the first support. And

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, a piezoelectric thin film support is made thin and does not interfere with piezoelectric vibration, and all of these are held by different supports having sufficient mechanical strength and connected to a substrate. . This piezoelectric thin film element is characterized in that it hardly interferes with piezoelectric vibration, has high mechanical strength of the element itself, and is easy to handle.

Since the piezoelectric thin film element of the present invention is held by the two supports, the second support for holding the vibrating portion and the first support for further holding these, the characteristics of the support are different from each other. It becomes possible to individually adapt to the optimum characteristics, and the above-mentioned object can be achieved. Further, in the present invention, the strength of the first support can be configured to be higher than the strength of the second support, the second support does not interfere with the piezoelectric vibration, and The support can hold the vibrating section and the second support.

The structure of the vibrating portion is not particularly limited as long as it is a structure in which piezoelectric vibration is generated, and a pair of piezoelectric thin film driving electrodes formed on both surfaces in a manner sandwiching the piezoelectric thin film,
Plural pairs of piezoelectric thin film driving electrodes formed on both sides by sandwiching the piezoelectric thin film and the piezoelectric thin film, common piezoelectric thin film driving electrodes are formed on one side by sandwiching the piezoelectric thin film and the piezoelectric thin film, and multiple electrodes are formed on the other surface. For forming the piezoelectric thin film drive electrode of
Alternatively, there is a configuration such as a piezoelectric thin film and a pair of piezoelectric thin film driving electrodes formed on one surface of the piezoelectric thin film. In any of the piezoelectric thin film driving electrode configurations, it is possible to select and use a piezoelectric vibration mode according to the purpose of use and the frequency of use.

The piezoelectric material that can be used for these piezoelectric thin film elements is not particularly limited as long as it is a material that can be manufactured as a thin film, and lead titanate (PbTiO ₃ , hereinafter simply referred to as PT), lead zirconate titanate (Pb). (Zr, Ti) O
₃ , hereinafter simply referred to as PZT), zinc oxide, aluminum nitride, lithium tantalate, lithium niobate, barium titanate (Bi ₃ Ti ₄ O ₁₂ ), and the like.
Zinc oxide and aluminum nitride are relatively easy to form as a thin film, and lead titanate and lead zirconate titanate can be mentioned as those having a large piezoelectric constant.

Since the piezoelectric thin film drive electrode constitutes a vibrating portion, it is preferable that the material has a small mass so as not to interfere with vibration. Examples of the electrode material for driving the piezoelectric thin film include aluminum, gold, platinum and the like. Further, for gold and platinum, it is preferable to form titanium and chromium between these and the base because the adhesion to the base is enhanced.
Aluminum is a preferable material because it is lightweight and has excellent workability, but the melting point of aluminum itself is 600 ° C.
Since it is so low, it easily deteriorates if there is a high temperature process and a high temperature oxidizing process at a temperature close to the melting point of aluminum after forming aluminum, and it cannot be used as a piezoelectric thin film drive electrode. On the other hand, since platinum and gold are noble metals, they are difficult to oxidize even in a high temperature and oxidizing environment, and in most cases, they can be effective piezoelectric thin film drive electrode materials.

Therefore, since zinc oxide and aluminum nitride, which are piezoelectric materials, can be formed even at a relatively low temperature, regarding aluminum, which is an electrode material,
It is also possible to form it on the support, that is, before the piezoelectric thin film forming process. Further, it can be used in all cases when it is formed on the surface after forming the piezoelectric thin film.
Among the above-mentioned piezoelectric materials, PT and PZT generally require a high temperature of 500 ° C. or higher for fabrication, and therefore aluminum cannot be formed before forming a piezoelectric thin film. Therefore, when PT and PZT are used, the piezoelectric thin film drive electrodes that can be formed on the support and below the piezoelectric thin film are limited to gold and platinum. In addition, gold and platinum may be formed on the surface of the piezoelectric thin film. In this case, the piezoelectric thin film driving electrode itself has high chemical stability, so that the reliability of the piezoelectric thin film element and the applied device of the piezoelectric thin film element is high. Is improved.

The second supporting body for holding the vibrating portion composed of the piezoelectric thin film and the piezoelectric thin film driving electrode is preferably made of a material having a small mass so as not to hinder the piezoelectric vibration. Since it is exposed to the chemical etching solution in the forming process, it must be resistant to the etching solution that corrodes the easy-to-etch portion and the substrate portion of the first support. Examples of such an etching solution include potassium hydroxide aqueous solution, sodium hydroxide aqueous solution, an aqueous solution containing ethylenediamine and pyrocatechol (there may be the case where pyridine is added), and an inorganic or organic strong alkaline aqueous solution such as a hydrazine aqueous solution. Often used, potassium hydroxide aqueous solution is preferable in terms of safety during work, toxicity, and stability of etching solution.

Preferred examples of the second support having resistance to the above-mentioned etching solution include silicon oxide, silicon nitride, and tantalum pentoxide. Among them, a thin film of silicon nitride or tantalum pentoxide is preferable because it can give a compressive stress to the film depending on the film forming conditions, and therefore does not cause slack when the underlayer is removed. Since the portion of the second supporting body that holds the vibrating portion and the portion that connects the first supporting body are in contact with each other over a wide area, the vibrating portion will not be affected even if the thickness of the second supporting body is reduced to 2000 Å or less. Since a hole such as an etching hole that causes stress concentration is not necessarily required on the second support to be held, the risk of mechanical destruction is small.

The first support holds the vibrating section and the second support, and connects these to the substrate. In the first support, the portion corresponding to the lower portion of the vibrating portion and the portion forming the etching hole of the first support need to be removed. Therefore, the lower portion of the vibrating portion and the etching hole are required. It is necessary that the portion forming the film has a higher etching rate with respect to the etching solution than the other portions. There are roughly two types of methods for forming such a first support.

The first method is a method of forming a layer of a uniform material as a first support on a substrate and then doping a specific element for reducing the etching rate into a portion to be left finally. The second method may be a method in which the portion to be etched is made of a material having a high etching rate and the remaining portion is made of a material having a low etching rate. Silicon is a typical material that realizes the first method, and after the support is formed of a silicon film,
There is a method of doping boron in the remaining portion. In this method, the boron doping amount for doping boron is 10
It is necessary to set it to ²⁰ / cm ³ or more.

In the second method, first, a material for the first support is formed into a film, and then the material is patterned into a shape that finally remains as the first support. To form a material that is removed by etching. These surfaces are flattened by etching back, and then a second support, a piezoelectric thin film drive electrode, etc. are sequentially formed. In this case, the layer corresponding to the first support is composed of a plurality of materials before etching. Finally, as the material forming the first support,
Many materials, such as silicon, silicon dioxide, silicon nitride, tantalum oxide, alumina, and magnesia, which can provide greater mechanical strength than the second support, are possible. Further, examples of the material of the part to be finally removed by etching include glasses such as phosphosilicate glass, zinc oxide, vanadium oxide and the like.

[0033]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. However, the present invention is not limited to the following examples.

[Embodiment 1] FIG. 1 is a plan view and a sectional view taken along the line AA of a piezoelectric thin film element according to an embodiment of the present invention. In this example, the silicon <100> single crystal substrate 1 is formed on the portion where the first support 2 is to be formed, by using silicon dioxide as a mask and doping with boron trichloride as a raw material by boron vapor deposition. went. A boron concentration of 10 ²⁰ / cm ³ was achieved to a depth of greater than about 6000 Å in the substrate by diffusion for 60 minutes at a flow rate of 10 sccm and a temperature of 900-1000 ° C.
After removing the mask, the film thickness of the second support 3 is 2000
An angstrom silicon dioxide film was formed by the RF magnetron sputtering method using an oxide target. At this time, the film forming condition is that the film forming atmosphere is argon 10
0%, gas pressure 1 Pa, substrate temperature was room temperature, and deposition rate (hereinafter simply referred to as deposition rate) was about 100 Å / min. Further, titanium and platinum are formed on the second support by the electron beam evaporation method, and the first piezoelectric thin film drive electrode (hereinafter simply referred to as the first electrode) 4 and the first electrode pad are formed by the lift-off method. Patterned as 15. Next, 0.2 (PbO)
A piezoelectric thin film 5 made of lead titanate was formed by RF magnetron sputtering using an oxide target having a composition of 1.0 (PbTiO ₃ ) so as to have a film thickness of about 1 μm. The film forming conditions at this time are as follows: the film forming atmosphere is a mixed atmosphere of argon and oxygen, and the gas pressure ratio is argon: oxygen = 9:
1, the gas pressure was 1 Pa, the substrate temperature was 550 ° C., and the deposition rate was about 70 Å / min. This piezoelectric thin film
110 ° C. nitric acid: hydrochloric acid: hydrogen peroxide water = 4: 12: 84
Patterning was performed by wet etching with a mixed solution (volume ratio). Further, on this piezoelectric thin film, a second piezoelectric thin film drive electrode (hereinafter, simply referred to as a second electrode) 6 made of titanium and platinum and a second electrode for titanium and platinum are formed in the same manner as the above-described method for forming titanium and platinum. The pad 9 was formed by the lift-off method. Next, an etching hole 7 was formed in the silicon dioxide film as the second support by using a 10 vol% hydrogen fluoride aqueous solution. Finally, using an aqueous solution composed of 750 ml of ethylenediamine, 120 g of pyrocatechol, and 240 g of water, from the etching hole,
By removing the substrate portion not doped with boron by anisotropic etching at a temperature of 115 ° C. for about 4 to 5 hours, a cavity portion 8 is formed in the substrate portion below the vibrating portion of about 100 μm square, and boron doping is performed. The first support was formed by the remaining parts. Through the steps described above, a piezoelectric thin film element (FIG. 1) having a composite support structure was obtained.

[Embodiment 2] In this embodiment, the piezoelectric thin film in Embodiment 1 is formed by using lead zirconate titanate in place of lead titanate.
Since it is the same as, the description will be made with reference to FIG. Also in this example, the first piezoelectric thin film drive electrode 4 and the first electrode pad 15 were formed by the same process as in Example 1. Next, 0.5 (PbO)
A piezoelectric thin film 5 made of lead zirconate titanate was formed by RF magnetron sputtering using an oxide target having a composition of 0.48 (PbTiO ₃ ) · 0.52 (PbZrO ₃ ) to a film thickness of about 1 μm. Filmed In this case, the film forming conditions are as follows: the film forming atmosphere is a mixed atmosphere of argon and oxygen, the gas pressure ratio is argon: oxygen = 9: 1, and the gas pressure is 1
Pa, the substrate temperature was 630 ° C., and the deposition rate was about 90 Å / min. After that, by the same process as in the case of Example 1, patterning of the piezoelectric thin film, formation of the second electrode 6 and the pad 9 for the second electrode, formation of etching holes, and anisotropic etching of the substrate were carried out to obtain a composite support. A piezoelectric thin film element having a structure (Fig. 1) was obtained.

[Embodiment 3] In this embodiment, a piezoelectric thin film element having the same structure as in Embodiment 1 is provided with an electrode pad and a protective film. FIG. 2 is a plan explanatory view and an AA line sectional explanatory view showing an example of a piezoelectric thin film element including an electrode pad and a protective film according to the present embodiment.

Also in this embodiment, the patterning of the first piezoelectric thin film drive electrode 4 and the first electrode pad 15 was performed by the same process as in the first embodiment. At this time, the second electrode pad 9 made of platinum and titanium is simultaneously formed. Further, patterning of the piezoelectric thin film 5 was performed by the same process as in Example 1. Next, aluminum was vapor-deposited on the piezoelectric thin film by an electron beam vapor deposition method, and then patterned by a lift-off method to form a second piezoelectric thin film drive electrode 6. At this time, the second electrode 6 and the second electrode pad 9 are connected.
After that, a silicon nitride film 2000Å is formed on the entire surface as the protective film 10 by the plasma CVD method, an etching hole is formed by the ion beam etching method, and the protective film on the electrode pad portion is removed. After that, the substrate was anisotropically etched by the same process as in Example 1 to obtain a piezoelectric thin film element having a composite support structure (FIG. 2).

[Embodiment 4] In this embodiment, a second support is formed by using tantalum oxide, an etching hole is formed by ion beam etching, and a cavity is anisotropically etched by a potassium hydroxide aqueous solution. Example of formation (Fig. 1
See).

In this embodiment, silicon <100>
The portion of the single crystal substrate 1 where the first support 2 is to be formed was doped with boron trichloride as a raw material by the vapor phase thermal diffusion method using silicon dioxide as a mask.
A boron concentration of 10 ²⁰ / cm ³ was achieved to a depth of greater than about 6000 Å in the substrate by diffusion for 60 minutes at a flow rate of 10 sccm and a temperature of 900-1000 ° C. After removing the mask, the film thickness of the second support 3 is 20
A 00 angstrom tantalum oxide film was formed by an RF magnetron sputtering method using an oxide target. In this case, the film forming conditions were that the film forming atmosphere was 100% argon, the gas pressure was 1 Pa, the substrate temperature was room temperature, and the deposition rate was about 100 angstrom / min. further,
Titanium and platinum were formed on the second support by the electron beam evaporation method, and patterned by the lift-off method as the first piezoelectric thin film drive electrode 4 and the first electrode pad 15. Next, 0.2 (PbO) 1.0 (PbT
A piezoelectric thin film 5 made of lead titanate was formed by RF magnetron sputtering using an oxide target having a composition of (iO ₃ ) so as to have a film thickness of about 1 μm. In this case, the film forming conditions are a mixed atmosphere of argon and oxygen, a gas pressure ratio of argon: oxygen = 9: 1, and a gas pressure of 1 P.
a, the substrate temperature was 550 ° C., and the deposition rate was about 70 Å / min. This piezoelectric thin film was wet-etched with a mixed liquid of nitric acid: hydrochloric acid: hydrogen peroxide solution = 4: 12: 84 (volume ratio) at 110 ° C. to perform patterning. Further, on the piezoelectric thin film, the second piezoelectric thin film drive electrode 6 and the second electrode pad 9 made of titanium and platinum were formed by the lift-off method in the same manner as the above-described method for forming titanium and platinum. Next, the etching hole 7 was formed in the tantalum oxide film which is the second support by the ion beam etching method. Finally, 70 ℃,
By using a 30 wt% potassium hydroxide aqueous solution, the substrate portion not doped with boron is removed from the etching hole by anisotropic etching for about 2 to 3 hours, so that the substrate below the vibrating portion of about 100 μm square. A cavity 8 was formed in the portion, and the boron-doped portion remained to form a first support. By the steps described above, a piezoelectric thin film element (FIG. 1) having a composite support structure was obtained.

[Embodiment 5] In this embodiment, the piezoelectric thin film in Embodiment 4 is formed by using lead zirconate titanate instead of lead titanate, and other parts are the same as in Embodiment 4. Therefore, it will be described with reference to FIG. 1 similarly to the fourth embodiment. Also in this example, the first piezoelectric thin film drive electrode 4 and the first electrode pad 15 were formed by the same process as in Example 4. Next, 0.5 (Pb
O) ・ 0.48 (PbTiO ₃ ) ・ 0.52 (PbZr
The piezoelectric thin film 5 made of lead zirconate titanate was formed to a thickness of about 1 μm by the RF magnetron sputtering method using an oxide target having a composition of O ₃ ). The film forming conditions at this time were a mixed atmosphere of argon and oxygen, a gas pressure ratio of argon: oxygen = 9: 1, a gas pressure of 1 Pa, a substrate temperature of 630 ° C., and a deposition rate of about 90 Å / min. After that, the composite support structure is formed by patterning the piezoelectric thin film, forming the second electrode 6 and the electrode pad 9, forming etching holes, and anisotropically etching the substrate by the same process as in the first embodiment. A piezoelectric thin film element (Fig. 1) was obtained.

[Embodiment 6] In this embodiment, a piezoelectric thin film element having the same structure as that of Embodiment 4 is provided with an electrode pad and a protective film (see FIG. 2). Also in this embodiment, the fourth embodiment
Patterning of the first piezoelectric thin film drive electrode was performed by the same process as in the above case. At this time, the second electrode pad 9 made of platinum and titanium is simultaneously formed. Further, patterning of the piezoelectric thin film 5 was performed by the same process as in Example 1. Next, after evaporating aluminum on the piezoelectric thin film by the electron beam evaporation method,
The second piezoelectric thin film drive electrode 6 was patterned by the lift-off method. At this time, the second electrode 6 and the second electrode pad 9 are connected. After that, the protective film 10
As a result, after forming a silicon nitride film of about 2000 liters on the entire surface by plasma CVD, etching holes are formed by ion beam etching and the protective film on the electrode pad portion is removed. After that, the substrate was anisotropically etched by the same process as in Example 1. By the steps described above, a piezoelectric thin film element (FIG. 2) having a composite support structure was obtained.

[Embodiment 7] In this embodiment, the second support in Embodiment 1 is formed by the plasma CVD method using silicon nitride. This will be described using 1. Also in the present embodiment, silicon dioxide is used as a mask in the portion where the first support 2 is formed on the silicon <100> single crystal substrate 1.
Boron was doped with boron trichloride as a raw material by a vapor phase thermal diffusion method. Flow rate 10 sccm, temperature 900
Boron concentration 1 to a depth of about 6000 angstroms or more in the substrate by diffusion for 60 minutes at ˜1000 ° C.
0 ²⁰ / cm ³ was achieved. After removing the mask, a silicon nitride film having a film thickness of 2000 angstrom and forming the second support 3 was formed by the plasma CVD method. At this time, the film forming condition is that the film forming atmosphere is a flow rate of SiH ₄ of 30 m.
The flow rate was 1 / min, the flow rate of NH ₃ was 60 ml / min, the flow rate of N ₂ was 200 ml / min, the gas pressure was 0.55 Torr, the substrate temperature was 300 ° C., and the RF power was 300 W. Furthermore, the second
Titanium and platinum were formed on the support by electron beam evaporation, and patterned by the lift-off method as the first piezoelectric thin film drive electrode 4 and the first electrode pad 15. Next, 0.2 (PbO) 1.0 (PbTiO
_The piezoelectric thin film 5 made of lead titanate was formed to have a film thickness of about 1 μm by the RF magnestron sputtering method using the oxide target having the composition ₃ ). At this time, the film forming conditions were as follows: the film forming atmosphere was a mixed atmosphere of argon and oxygen, the gas pressure ratio was argon: oxygen = 9: 1, and the gas pressure was 1
Pa, the substrate temperature was 550 ° C., and the deposition rate was about 70 Å / min. This piezoelectric thin film was wet-etched with a mixed liquid of nitric acid: hydrochloric acid: hydrogen peroxide solution = 4: 12: 84 (volume ratio) at 110 ° C. to perform patterning. Further, the second piezoelectric thin film driving electrode 6 and the second electrode pad 9 made of titanium and platinum were formed on the piezoelectric thin film by the lift-off method in the same manner as the above-described titanium and platinum forming method. Next, the etching hole 7 was formed in the silicon nitride film which is the second support by the ion beam etching method. Finally, 70 ℃, 30w
By using a t% KOH aqueous solution, the substrate portion not doped with boron is removed from the etching hole by anisotropic etching for about 2 to 3 hours to obtain about 10
The cavity 8 was formed in the substrate portion below the 0 μm square vibrating portion, and the boron-doped portion remained to form the first support. By the steps described above, a piezoelectric thin film element (FIG. 1) having a composite support structure was obtained.

[Embodiment 8] In this embodiment, the piezoelectric thin film of Embodiment 7 is formed by using lead zirconate titanate instead of lead titanate, and other parts are the same as in Embodiment 7. (See FIG. 1). Also in this example, the first piezoelectric thin film drive electrode 4 and the first electrode pad 15 were formed by the same process as in Example 4. Next, 0.5 (PbO) 0.48 (Pb
A piezoelectric thin film 5 made of lead zirconate titanate was formed by RF magnetron sputtering using an oxide target having a composition of TiO ₃ ) .0.52 (PbZrO ₃ ), to a film thickness of about 1 μm. The deposition conditions at this time are as follows:
The deposition atmosphere was a mixed atmosphere of argon and oxygen, the gas pressure ratio was argon: oxygen = 9: 1, the gas pressure was 1 Pa, the substrate temperature was 630 ° C., and the deposition rate was about 90 Å / min. After that, by the same process as in the case of Example 1, patterning of the piezoelectric thin film, second electrode 6 and second
The piezoelectric thin film element (FIG. 1) having a composite support structure was obtained by forming the electrode pad 9 of 1. above, forming an etching hole, and anisotropically etching the substrate.

[Embodiment 9] In this embodiment, a piezoelectric thin film element having the same structure as that of Embodiment 8 is provided with an electrode pad and a protective film (see FIG. 2). Also in this embodiment, the fourth embodiment
Patterning of the first piezoelectric thin film drive electrode 4 and the first electrode pad 15 was performed by the same process as in the above case. At this time, the second electrode pad 9 made of platinum and titanium is simultaneously formed. Furthermore, Example 1
The piezoelectric thin film 5 was patterned by the same process as described above. Next, aluminum was vapor-deposited on the piezoelectric thin film by an electron beam vapor deposition method, and then patterned by a lift-off method to form a second piezoelectric thin film drive electrode 6.
At this time, the second electrode 6 and the second electrode pad 9 are connected. After that, a silicon nitride film of about 2000 Å is formed on the entire surface as the protective film 10, an etching hole is formed by the ion beam etching method, and the protective film on the electrode pad portion is removed. After that, the substrate was anisotropically etched by the same process as in Example 1 to obtain a piezoelectric thin film element having a composite support structure (FIG. 2).

[Embodiment 10] In this embodiment, the first support and the second support in Embodiment 1 are formed by RF sputtering using tantalum oxide. FIG. 3 is a plan explanatory view and an AA line cross-sectional explanatory view showing an example of the piezoelectric thin film element according to the present embodiment. Also in this embodiment, a tantalum oxide film having a film thickness of 5000 angstrom was formed as a film for forming the first support on the entire surface of the silicon <100> single crystal substrate 1 by the RF magnestron sputtering method using an oxide target. Formed. Next, the tantalum oxide film is subjected to an ion beam etching method to remove the etching hole 11 and a portion of the first supporting body which finally becomes a lower portion of the vibrating portion, thereby removing a removed portion 12 of the first supporting body. And formed. RF on this
The silicon dioxide film 60 is formed by the magnetron sputtering method.
00Å is formed and the removed portion 12 of the first support is filled with silicon dioxide as a material having low corrosion resistance. Further, the surface was flattened by etching back about 1000Å. After that, the film thickness of the second support 2
A 000 Å tantalum oxide film was formed by an RF magnetron sputtering method using an oxide target. In this case, the film forming conditions were that the film forming atmosphere was 100% argon, the gas pressure was 1 Pa, the substrate temperature was room temperature, and the deposition rate was about 100 angstrom / min. Further, titanium and platinum were formed on the second support by the electron beam evaporation method, and patterned by the lift-off method as the first piezoelectric thin film drive electrode 4 and the first electrode pad 15. Next, 0.2 (PbO) 1.0 (P
RF using an oxide target having a composition of bTiO ₃ ).
A piezoelectric thin film 5 made of lead titanate was formed by magnetron sputtering so as to have a film thickness of about 1 μm. In this case, the film forming conditions were a mixed atmosphere of argon and oxygen, a gas pressure ratio of argon: oxygen = 9: 1, a gas pressure of 1 Pa, a substrate temperature of 550 ° C., and a deposition rate of about 70 Å / min. This piezoelectric thin film was wet-etched with a mixture of nitric acid: hydrochloric acid: hydrogen peroxide solution = 4: 12: 84 (volume ratio) at 110 ° C. to perform patterning. Further, on the piezoelectric thin film, the second piezoelectric thin film drive electrode 6 and the second electrode pad 9 made of titanium and platinum were formed by the lift-off method in the same manner as the above-described method for forming titanium and platinum. Next, the etching hole 7 was formed in the tantalum oxide film which is the second support by the ion beam etching method. Finally, 70 ℃,
Using a 30 wt% potassium hydroxide aqueous solution, the substrate portion was removed from the etching hole by anisotropic etching for about 2 to 3 hours. At the same time, the silicon dioxide below the second support below the vibrating section was also removed by etching, and a cavity 8 was formed in the substrate section below the vibrating section of about 100 μm square. Through the above steps, a piezoelectric thin film element (FIG. 3) having a composite support structure was obtained.

[Embodiment 11] In this embodiment, a cross electrode is provided on the upper surface of a piezoelectric thin film, and FIG. 4 is a plan explanatory view and a sectional view taken along the line AA of the piezoelectric thin film element of this embodiment. Is. Also in the present embodiment, boron doping is performed on the portion where the first support 2 is formed on the silicon <100> single crystal substrate 1 using silicon dioxide as a mask by a vapor phase thermal diffusion method using boron trichloride as a raw material. It was Flow rate 10
A boron concentration of 10 ²⁰ / cm ³ was achieved to a depth of greater than about 6000 angstroms in the substrate by diffusion for 60 minutes at a sccm temperature of 900-1000 ° C. After removing the mask, a silicon dioxide film having a film thickness of 2000 angstroms which constitutes the second support 3 was formed by an RF magnetron sputtering method using an oxide target. In this case, the film forming condition is that the film forming atmosphere is argon 100.
%, The gas pressure was 1 Pa, the substrate temperature was room temperature, and the deposition rate was about 100 Å / min. Further, platinum and titanium were formed on the second support by the electron beam evaporation method, and the first and second pair of cross electrodes 13 and 14 were formed by lift-off. Next, the piezoelectric thin film 5 made of zinc oxide was formed to a thickness of about 7 μm by the RF magnetron sputtering method using an oxide target. The film forming conditions at this time are as follows: the film forming atmosphere is a mixed atmosphere of argon and oxygen, the gas pressure ratio is argon: and oxygen = 5: 5, the gas pressure is 1 Pa, the substrate temperature is 500 ° C., the deposition rate is about 100 angstrom / min. did. This piezoelectric thin film was wet-etched with a 10% nitric acid aqueous solution using a resist as a mask to perform patterning. After that, as a protective film 10, a silicon nitride film of about 2000 Å is formed on the entire surface by a plasma CVD method, an etching hole is formed by an ion beam etching method, and the protective film on the electrode pad portion is removed. After that, the substrate was anisotropically etched by the same process as in Example 1 to obtain a piezoelectric thin film element (FIG. 4) having a composite support structure.

[0047]

According to the present invention, since the support of the piezoelectric thin film is thin and does not hinder the piezoelectric vibration, it is held by different supports having sufficient mechanical strength and connected to the substrate. A piezoelectric thin film element capable of efficiently utilizing piezoelectric vibration can be put to practical use. In addition, since the element itself has high mechanical strength and is easy to handle,
It is also advantageous in terms of device manufacturing yield and excellent in mass productivity.

In the piezoelectric thin film element of the present invention, the mechanical strength of the first support is made stronger than the mechanical strength of the second support, so that the second support does not interfere with piezoelectric vibration, and The first support has an effect of being able to hold the vibrating portion and the second support.

Further, in the piezoelectric thin film element of the present invention, the first and second piezoelectric thin film driving electrodes can be formed on both sides of the piezoelectric thin film or on both sides of the piezoelectric thin film. There is an effect that the piezoelectric vibration mode can be selected.

Further, in the piezoelectric thin film element of the present invention, since a part of the substrate can be used as the first support, it is easy to manufacture a bar-shaped structure, and a strong mechanical strength of the bar is obtained. be able to.

In the piezoelectric thin film element of the present invention, the substrate is a silicon <100> single crystal and the first support is boron.
A part of the substrate doped with ²⁰ / cm ³ or more, the second
Is a silicon dioxide film, the first piezoelectric thin film drive electrode is platinum and titanium, and the piezoelectric thin film is a piezoelectric body containing (A) lead titanate and (B) lead zirconate titanate as main components. Since the second piezoelectric thin film driving electrode can be made of platinum and titanium, the chemical stability of the electrode is high, and the reliability and efficiency of the piezoelectric thin film element are improved.

Further, in the piezoelectric thin film element of the present invention, the second piezoelectric thin film driving electrode is made of aluminum, and a protective film made of silicon nitride can be formed on the entire surface of the piezoelectric thin film element. As a result, the efficiency is improved, the chemical stability of the electrode is further improved even in a high temperature and oxidizing environment, and the mechanical strength of the entire piezoelectric thin film element is improved.

Further, in the piezoelectric thin film element of the present invention, since the second support can be made of a silicon nitride film, silicon nitride is light in weight and excellent in mechanical strength and chemical stability. At the same time, it is possible to reduce the occurrence of damage during etching. Therefore, improvement in reliability and yield of the piezoelectric thin film element can be expected.

In the piezoelectric thin film element of the present invention, the second support is a silicon nitride film, and the piezoelectric thin film is a piezoelectric body containing lead titanate or lead zirconate titanate as a main component. Furthermore, since a protective film made of silicon nitride can be formed on the entire surface of the piezoelectric thin film element, a piezoelectric body having a large piezoelectric constant can be obtained.

Further, in the piezoelectric thin film element of the present invention, since the second support can be a tantalum oxide film, it is possible to obtain the effect of giving a compressive stress in the film.

In the piezoelectric thin film element of the present invention, the second support is a tantalum oxide film, the second piezoelectric thin film driving electrode is aluminum, and silicon nitride is formed on the entire surface of the piezoelectric thin film element. Since the protective film made of a substance can be formed, the above-described effect of giving a compressive stress to the film can be stably maintained.

According to the method of manufacturing a piezoelectric thin film element of the present invention, (1) after forming the first support, a portion corresponding to a lower portion of the vibrating portion is removed, and the removed portion is removed by the first portion. Filling with a low corrosion resistant material having a lower corrosion resistance than that of the support, and (2) after the second support and the vibrating portion are formed on the first support, the low corrosion resistant material is removed by etching. Then, the piezoelectric thin film element of the present invention can be obtained by a simple process since it includes a step of leaving only the first support.

In the piezoelectric thin film element of the present invention, the surface of the substrate made of silicon single crystal is doped with boron of 10 ²⁰ / cm 3.
³ or more is doped to form a boron-doped portion to increase the etching resistance of the boron-doped portion, and the boron-doped portion is left in the substrate etching step to form the boron-doped portion as the first support. The piezoelectric thin film element of the present invention can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view and a cross-sectional view showing the structure of a piezoelectric thin film element according to an embodiment of the present invention.

FIG. 2 is a plan view and a cross-sectional view showing the structure of a piezoelectric thin film element according to another embodiment of the present invention.

FIG. 3 is a plan view and a cross-sectional view showing the structure of a piezoelectric thin film element according to another embodiment of the present invention.

FIG. 4 is a plan view and a cross-sectional view showing the structure of a piezoelectric thin film element according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Silicon substrate, 2 1st support body, 3 2nd support body, 1st piezoelectric thin film drive electrode, 5 piezoelectric thin film, 6
Second piezoelectric thin film drive electrode, 7 etching holes,
8 cavity, 9 second electrode pad, 10 protective film,
11 etching hole, 12 first support removed portion, 13 first crossing electrode, 14 second crossing electrode, 1
5 First electrode pad.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Eiko Uchikawa 2-3-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd. (72) Toshihisa Honda 2-3-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Electric Co., Ltd.

Claims (13)

[Claims] 1. A first piezoelectric thin film driving electrode, a piezoelectric thin film,
A piezoelectric thin film element comprising: a vibrating section including a second piezoelectric thin film driving electrode; first and second supporting bodies that support the vibrating section; and a substrate that holds the two supporting bodies, (1) A first piezoelectric thin film drive electrode, a piezoelectric thin film and a second piezoelectric thin film drive electrode are formed on a second support, and (2) a second support is a first support and a substrate. A second support formed over and over and held by the first support and a second support.
The support is provided with a plurality of opening holes in a slit shape along the outer edge of the piezoelectric thin film so as to surround the outer edge of the piezoelectric thin film, and the portion not provided with the opening holes is a connecting portion. 3) A cavity is formed in the substrate below the first support, and the first support is formed by connecting the substrate in the shape of a bar, and (4) the first support is the first support. Of the piezoelectric thin film element, wherein a portion corresponding to the lower portion of the vibrating portion is removed. 2. The piezoelectric thin film element according to claim 1, wherein the mechanical strength of the first support is higher than the mechanical strength of the second support. 3. The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film driving electrodes are formed on both surfaces of the piezoelectric thin film. 4. The piezoelectric thin film element according to claim 1, wherein the first and second piezoelectric thin film driving electrodes are formed on the same surface of the piezoelectric thin film. 5. The piezoelectric thin film element according to claim 1, wherein a part of a substrate is used as the first support. 6. The substrate is a silicon <100> single crystal,
The first support is a part of the substrate doped with boron of 10 ²⁰ / cm ³ or more, the second support is a silicon dioxide film, the first piezoelectric thin film drive electrode is platinum and titanium,
The piezoelectric thin film is any one of (A) lead titanate and (B) lead zirconate titanate as a main component.
The piezoelectric thin film element according to claim 1, wherein the piezoelectric thin film driving electrode is made of platinum and titanium. 7. The second piezoelectric thin film driving electrode is made of aluminum, and a protective film made of silicon nitride is formed on the entire surface of the piezoelectric thin film element.
The piezoelectric thin film element described. 8. The piezoelectric thin film element according to claim 6, wherein the second support is a silicon nitride film. 9. The second support is a silicon nitride film, the piezoelectric thin film is a piezoelectric body containing lead titanate or lead zirconate titanate as a main component, and the piezoelectric thin film element. 7. The piezoelectric thin film element according to claim 6, wherein a protective film made of silicon nitride is formed on the entire surface of the piezoelectric thin film element. 10. The piezoelectric thin film element according to claim 6, wherein the second support is a tantalum oxide film. 11. The second support is a tantalum oxide film, the second piezoelectric thin film drive electrode is aluminum, and a protective film made of silicon nitride is formed on the entire surface of the piezoelectric thin film element. The piezoelectric thin film element according to claim 6, which is formed. 12. The method of manufacturing a piezoelectric thin film element according to claim 1, wherein (1) after forming the first support, a portion corresponding to a lower portion of the vibrating portion is removed, and the portion is removed. Filling the portion with a low corrosion resistant material having a lower corrosion resistance than the first support, and (2) forming the second support and the vibrating portion on the first support, and And a step of leaving only the first support by etching away the corrosion resistant material, and manufacturing the piezoelectric thin film element. 13. The method for manufacturing a piezoelectric thin film element according to claim 5, wherein the surface of the substrate made of silicon single crystal is doped with boron at a concentration of 10 ²⁰ / cm ³ or more to form a boron-doped portion, and the boron-doped portion is formed. Increased etching resistance,
A method of manufacturing a piezoelectric thin film element, comprising the step of forming the first support by leaving the boron-doped portion in a substrate etching step.