JPS59223230A - Manufacture of oriented thin lead titanate film - Google Patents

Abstract

PURPOSE:To form a thin lead titanate film having the direction of its C-axis in the direction of polarization in general and an increased degree of orientation by cooling a thin lead titanate film formed on a substrate at a low cooling rate. CONSTITUTION:A thin lead titanate film formed on a substrate of magnesium oxide or the like having a positive coefft. of thermal expansion is cooled from a temp. above the Curie temp. at <=200 deg.C/hr low cooling rate. By selecting the material of the substrate and the cooling rate, a thin lead titanate film having a high degree of orientation and little strain in the (001) direction, that is, the direction of its C-axis is formed. The film can be utilized as a piezoelectric element, a pyroelectric element or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a manufacturing method for improving the degree of orientation of a lead titanate thin film.

Conventional configuration and its problems In recent years, ferroelectric thin films have been used as surface acoustic wave filters.

Among these ferroelectric thin films, lead titanate thin films have come to be widely applied to light modulation elements, optical shutters, optical waveguides, and pyroelectric devices. It has the characteristics of being small in comparison, having a large residual polarization, and having excellent piezoelectric properties, so it has high utility value as a high-frequency piezoelectric element or a pyroelectric heat detection element.

When a ferroelectric material is used as a piezoelectric element or a pyroelectric element, polarization treatment is required. Lead titanate is tetragonal at room temperature, with lattice constants 14a = 3.899, c = 4
, 15328, and is characterized by a large ratio of the lattice constants of the C-axis and the a-axis. Therefore, when polarizing in the direction perpendicular to the surface of the thin film, if there are many parts with the a-axis direction perpendicular to the thin film surface before polarization, the distortion before and after polarization will be large and the polarization process will be difficult. Even if polarization is possible, internal stress is generated, which is a practical problem. therefore,
In order to use a lead titanate thin film as a piezoelectric element or a pyroelectric element, it is necessary to align the direction perpendicular to the thin film surface, that is, the polarization direction, along the C axis.

When cooling from a temperature above the point (approximately 490″C).

By keeping the cooling rate below 200°C/hour.

(001) is characterized by improving the degree of orientation.

DESCRIPTION OF THE EMBODIMENTS Thin films are prepared by conventional high frequency sputtering methods. The substrates are a (1oo) plane of a magnesium oxide single crystal and a (10o) plane of a strontium titanate single crystal.

Platinum was sputtered as a base electrode using Blumina porcelain, an R surface of sapphire, a platinum plate, and a gold plate, and then lead titanate was sputtered. The substrate temperature is from 550°C to eoo'c,
The film thickness is 2 to 3 μm. The degree of orientation A was estimated from the X-ray diffraction pattern. That is, in the X-ray diffraction pattern (100
, ) surface and (Ool) surface are respectively calculated as 100j.
When IO01 is defined by the following formula, Al<001
) The cooling rate of 1800 is shown in Figure 1 as a guide for the orientation of the direction.
°C/hour, 2oO"C/hour, 50"C/hour, 10"C/hour
The following table shows the cooling temperature dependence of the (001) orientation A when the substrate is changed. 001) Cooling rate dependence of orientation degree A As shown in FIG.
1) It can be seen that the degree of orientation increases. When cooled, lead titanate has a cubic crystal system with equal lattice constants for the a-axis and the a-axis at temperatures above one Curie temperature, but below one Curie temperature, the coefficient of linear expansion in the C-axis direction is negative. It has a unique property that the coefficient of linear expansion in the C-axis direction is positive, so if a material with a positive coefficient of thermal expansion is used for the substrate, the a-axis will be oriented parallel to the surface of the substrate when it is cooled ( C-axis orientation) has less distortion. By reducing the cooling rate,
This is because this state of less distortion is achieved. Note that the C-axis direction here refers to the (ool) direction,
The axial direction refers to the (100) direction. Then (Ool
) As an example of the industrial utility of orientation, the effect of the degree of (ool) orientation on the pyroelectric effect is shown. In FIG. 2, the horizontal axis shows the degree of orientation, and the vertical axis shows the pyroelectric coefficient. In addition, magnesium oxide is used for the substrate, and its polarization is determined by applying an electric field of 100 kv/cm at 200°C.
The test was carried out by applying a It can be seen from FIG. 2 that the pyroelectric coefficient is large when the degree of orientation A is large.

Effects of the Invention As described above, the present invention is effective in improving the degree of (001) orientation of lead titanate, and has great industrial value.

[Brief explanation of drawings]

Figure 1 shows the degree of orientation A when magnesium oxide is used as the substrate.
FIG. 2 is a diagram showing the dependence of the pyroelectric coefficient on the degree of orientation.

Claims (1)

[Claims] (1) When cooling a lead titanate thin film fabricated on a substrate with a positive coefficient of thermal expansion from a temperature higher than the Curie temperature, the degree of orientation is improved by setting the cooling rate to 200'C/hour or less (ool). A method for producing an oriented lead titanate thin film, characterized in that: (Rumor) The method for producing a lead titanate oriented thin film according to claim 1, wherein the material of the substrate is magnesium oxide, strontium titanate, alumina porcelain, sapphire, platinum, or gold.