JPS626597A - Manufacture of piezoelectric element - Google Patents

Abstract

PURPOSE:To obtain a monocrystal lead titanate thin film having an excellent crystallizing/property by forming an electrode material having an opening on a monocrystal substrate such as SrTiO3 and forming a PbTiO3 monocrystal thin film by a lateral epitaxy method through the opening part. CONSTITUTION:On a surface (100) of strontium titanate monocrystal 1, a platinum of an electrode is vapor deposited to a thickness of about 50nm and a resist pattern having a line off 1mu width and a space of 1mum width is formed by a photolithography method. At first, by using CF4 gas, a platinum film is etched by a reactive ion etching, then, the resist is removed in an oxygen plasma to form a pattern 2 of the platinum film. Then, through an opening 3, a thin film having a main component of lead titanate of 150nm is formed by a high frequency magnetron spattering method. This is thermally processed and crystallized, thereafter, on this thin film, further a lead titanate thin film 4 is formed to about 3mum by the high frequency spattering method. Then, by using a mask of 5mmphi, Cr and Au are vapor deposited to form an upper electrode 5.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for manufacturing a thin film piezoelectric element using a ferroelectric material lead titanate PbTi0□.

[Background of the invention]

Lead titanate PbTi0. has a ferroelectric phase (tetragonal system) with large crystal lattice anisotropy and spontaneous polarization Ps.

Piezoelectricity and pyroelectricity in the polarization axis (C-axis) direction are extremely large.

However, this lead titanate PbTi0. When it is formed as a thin film by sputtering or the like, it becomes a polycrystalline film with random crystal axes, and the characteristic of lead titanate PbTiO3, which has high piezoelectricity in the C-axis direction, cannot be fully utilized.

On the other hand, it is known that a lead titanate thin film is epitaxially grown on a single crystal substrate such as MgO.

However, in order to use the lead titanate PbTiO3 thin film as a piezoelectric element or a pyroelectric element, it is necessary to provide an electrode on the base. Therefore, attempts have been made to first orient an electrode film using a single crystal substrate, and then to orient a piezoelectric thin film thereon. For example, it is discussed in the document titled "Dielectric properties of C-axis oriented PbTiO3 thin film" in the Proceedings of the 31st Japan Society of Applied Physics related lectures, Spring 1984, p. 240 (lecture number IP-H-6). Platinum (Pt) on a magnesium oxide MgO single crystal substrate as shown in
The film is (100) oriented, and lead titanate Pb is deposited on this electrode.
The TiO3 thin film is C-axis oriented. In this method, lead titanate PbTi0. Although a C-axis oriented film has been obtained, since a Pt film is interposed in between, the characteristics inevitably deteriorate compared to a film formed directly on a single crystal substrate.

[Purpose of the invention]

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a piezoelectric element having a structure in which a single-crystal lead titanate thin film having excellent crystallinity can be obtained.

[Summary of the invention]

The piezoelectric element of the present invention is made of strontium titanate SrTiO
The method is characterized in that an electrode material having an opening is formed on a single crystal substrate such as No. 3, and a lead titanate PbTiO3 single crystal thin film is formed through the opening by a lateral epitaxy method. The lateral epitaxy method is a method used when forming an element made of silicon Si on an insulator. [For example, J, C, C, Fan, M, W, Ga1
s and B, Y.

Tsaur, Appl, Phys, Lett.
38 (5), 365 (1981)) According to this method, a lead titanate thin film epitaxially grown on a single crystal of strontium titanate 5rTiO, etc. in the opening of the electrode material is further grown laterally on the electrode material. can be made into a single-crystal thin film that envelops the electrode material.

As a result, a lead titanate thin film with excellent crystallinity can be formed on the base electrode material, and by further providing an upper electrode by vapor deposition, an excellent piezoelectric element that takes advantage of the original characteristics of lead titanate can be obtained. be able to.

As a method for forming a lead titanate thin film, the sputtering method is widely used because it is relatively simple and the film formation speed is fast. There are two methods for forming a sputtering method depending on the person. One is to maintain the substrate temperature at about 600°C and obtain a directly crystallized thin film, and the other is to form an amorphous film. This method is followed by heat treatment using laser light or an electric furnace. In lateral epitaxy, it is desirable that nucleation occurs preferentially from the single crystal substrate and grows laterally onto the electrode film.From this point of view, the latter method is preferred, that is, crystallization of an amorphous film by heat treatment. The preferred method is to However, as the film thickness increases, random nucleation occurs on the surface of the film and polycrystallization occurs, making it difficult to form a thick film.On the contrary, when the former method is used, it is difficult to form a thick film. It is relatively thick at the top (several μ
m) Although a single crystal film can be obtained, there is a problem in that polycrystalline grains are likely to be formed on the platinum electrode film.

Therefore, in the piezoelectric element using the lead titanate thin film according to the present invention, first, an amorphous film that covers the electrode film is crystallized by heat treatment to become a single crystal, and then the desired thickness is achieved! It is characterized by forming.

[Embodiments of the invention]

Hereinafter, embodiments of the present invention will be described in detail using the drawings.

FIG. 1 shows the external structure of the piezoelectric element according to the present invention, and FIG. 2 shows the cross-sectional structure of the element. In the figure, 1 is a single crystal substrate made of strontium titanate, etc., 2 is a lower electrode, 3 is an opening, and 4
5 indicates a thin film whose main component is lead titanate, and 5 indicates an upper electrode.

Platinum as an electrode was evaporated to a thickness of about 50 nm on the (Zoo) plane of a strontium titanate single crystal l.

Furthermore, a resist pattern of 1 μm wide lines and 1 μm wide spaces was formed by photolithography. First, the platinum film was etched by reactive ion etching using Freon CF gas, and then the resist was removed in oxygen plasma to form pattern 2 of the platinum film. The platinum film pattern can also be formed by depositing a Pt film on a previously formed resist pattern and then removing the resist, or by a lift-off method. Next, a 150 nm thin film mainly composed of lead titanate was formed by high frequency magnetron sputtering.
0℃, pressure of introduced gas (Ar90%-〇, 10%) 4P
It was set as a. When this film was evaluated by X-ray diffraction, no diffraction peak appeared and it was found to be an amorphous film. After being heat-treated to crystallize it, it was evaluated again by XS diffraction.

A strong peak of (001) and peaks of (002) and (003) appeared, indicating C-axis orientation. On this thin film, a lead titanate thin film was further formed to a thickness of approximately 3 μm by high frequency sputtering.The manufacturing conditions were: substrate temperature 550°C;
The gas pressure is 4 Pa as before. When evaluated again by X-ray diffraction, it was found to be (001).

The intensity of (002) and (003) increased, and no other diffraction lines appeared. Further evaluation by reflection electron beam diffraction revealed spot-like patterns, confirming that a uniform alignment film was obtained.

Next, chromium Cr and gold Au were deposited using a 5 .phi. mask to form an upper electrode. Keeping the temperature of the sample at 200°C, a DC voltage of 1 OOKV/cm was applied between both electrodes for 20 minutes to generate ultrasonic waves, and the intensity of the echo reflected from the other end of the cylindrical strontium titanate was measured. Measurements were made in the frequency range of 0.1 to 1.2G7, and the electromechanical coupling coefficient was calculated from this frequency characteristic, and a value of 0.65 was obtained. This exceeds the coupling coefficient of lead titanate ceramics, which is 0.5, and is thought to be due to the effect of forming a C-axis oriented film also on the platinum electrode by lateral epitaxy.

Incidentally, after forming a lead titanate thin film to cover the electrode, a process of forming an amorphous film of an appropriate thickness and heat treatment may be repeated to form a thin film of a desired thickness.

〔Effect of the invention〕

As explained above, an amorphous film is first formed on a platinum electrode film having an opening to a thickness that covers the electrode film, and then heat-treated to crystallize it, and then sputtered to a desired thickness. By forming a thin film of C on the platinum electrode,
A lead titanate thin film with axial orientation and excellent crystallinity can be formed. By further forming an upper electrode on the lead titanate thin film created by this method, a highly sensitive piezoelectric element can be obtained.

[Brief explanation of drawings]

FIG. 1 is a three-dimensional view showing an example of the structure of a piezoelectric element according to the present invention, and FIG. 2 is a partial sectional view thereof. 1...Single crystal substrate of strontium titanate, etc., 2.
... lower electrode, 3 ... opening, 4 ... thin film mainly composed of lead titanate, 5 ... upper electrode.

Claims (1)

[Claims] 1. An electrode having an opening is formed on a single crystal substrate of strontium titanate SrTiO_3 and magnesium oxide MgO, and a thin film mainly composed of lead titanate PbTiO_3 is formed thereon, and an upper electrode is formed on the substrate. In the piezoelectric element provided with the lead titanate, the lead titanate thin film is first formed as an amorphous film to a thickness that covers the electrode, then heat-treated to crystallize it, and then a thin film is formed on top of it to the desired thickness. A method of manufacturing a piezoelectric element, characterized by: 2. The method of manufacturing a piezoelectric element according to claim 1, wherein the thin film containing lead titanate as a main component is formed by high-frequency sputtering.