JPH0311487B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ferroelectric thin film element having a ferroelectric thin film.

In general, ferroelectric compounds are widely used in electrical components such as piezoelectric filters and vibrators due to their piezoelectric properties. It is also applied to laser modulation elements and optical shutters that utilize the electro-optic effect.
Ferroelectric compounds have a wide range of practical applications.

It is generally difficult to produce a single crystal as the element of a ferroelectric compound, and even if it is possible, it is often expensive, as seen in barium titanate piezoelectric ceramics, PZT porcelain, and PLZT porcelain. It is often used as porcelain. However, in porcelain, the crystal orientation of the particles is disordered, which reduces the usefulness of the ferroelectric properties originally possessed by single crystals.
When used as a light modulator or a light shutter, the element body must be transparent. Even if the material itself is transparent, when made into porcelain,
Since ferroelectric compounds other than PLZT porcelain and a very small number of compositions are opaque, a single crystal is desired as an electro-optic effect element.

More than 100 types of ferroelectric compounds have been discovered, and although they have good electrical and optical properties in single crystal form, it is difficult to produce single crystals, and single crystals tend to be deliquescent. Only a few of them are used as optical modulation elements because of their unstable durability.

On the other hand, from the perspective of the structure of ferroelectric elements, with recent advances in optical communication technology, thin films of ferroelectric compounds are being used to make optical modulators and optical switches for optical integrated circuits (ICs). What you have is desired. Ferroelectric compounds are essentially optically anisotropic, and when polycrystallineized, light scatters at the interface between particles. Therefore, in order to use it as an optical waveguide circuit, it is necessary to form a thin film into a single crystal. desirable. Lead titanate is a material that has excellent ferroelectric properties from a practical standpoint, and is actually widely used as a ferroelectric ceramic in high-frequency filters and pyroelectric effect elements.

However, lead titanate has not been applied to optical surfaces because it is difficult to produce a good single crystal due to its large crystallographic anisotropy and the high vapor pressure of lead. Even in the production of porcelain, it is difficult to obtain a sintered body of a pure substance due to its large crystallographic anisotropy.

As can be seen from the above, single-crystal ferroelectric compounds are desired from both the viewpoint of piezoelectric properties and optical applications, and the single crystals can be easily produced from an industrial perspective. is necessary. Furthermore, considering the application in combination with recent optical ICs and semiconductor ICs, it is desirable that the film can be made thin.

As a result of studying ferroelectric elements that meet these requirements, the inventors found that an element made by epitaxially growing lead titanate on a single crystal of magnesium oxide is easy to fabricate, has good crystallinity, and has good translucency. This is what I discovered to be excellent.

The lead titanate single crystal thin film of the present invention was produced by high frequency sputtering.

A magnesium oxide single crystal plate cleaved along the (100) plane was used as the substrate and fixed on a heater. Lightly sintered lead titanate powder was used as the target. The atmospheric gas was a mixture of argon and oxygen, the total pressure was approximately 5 Pa, and the mixture ratio of argon and oxygen was 90% argon and 10% oxygen, and a thin film was formed on a magnesium oxide single crystal plate by magnetron high frequency sputtering method.

The substrate temperature is 575°C. The composition ratio of the thin film prepared as described above was analyzed using an X-ray microanalyzer, and the crystals were identified using X-ray diffraction and electron beam diffraction.
The direction was determined. The figure shows the X-ray diffraction pattern of this thin film.

From the figure, it can be seen that the growth occurs in the <100> direction and the <001> direction.

On the other hand, electron beam diffraction revealed a dotted diffraction pattern, confirming epitaxial growth. Even if the substrate temperature is varied between 550°C and 700°C, a single crystal thin film of lead titanate epitaxially grown in the <100> direction or <001> direction is formed. In addition, titanic acid epitaxially grown in the <100> direction or <001> direction was prepared with a composition ratio of argon gas and oxygen gas of 100% argon, 50% argon - 50% oxygen in an atmosphere with a total pressure of 2 Pa to 20 Pa. A single crystal of lead is obtained. In either case, a colorless and transparent film with good light transmittance can be obtained.

From the above results, single crystal films grown in the <100> direction or <001> direction on the (100) plane of magnesium oxide single crystal can be fabricated over a wide range of sputtering conditions, and are industrially advantageous. be.

When considering its application as an electro-optic effect element,
Magnesium oxide single crystal is colorless and transparent in the visible light region and has no optical anisotropy, so it is also advantageous when performing light modulation using the electro-optic effect of lead titanate. The directions in which lead titanate can be polarized are the <001> direction and the <100> direction, and both when passing light perpendicularly to the thin film surface of lead titanate and when using the in-plane as an optical waveguide. Also, since the polarization direction can be selected perpendicular to the light transmission direction, it is also advantageous for light modulation.

[Brief explanation of the drawing]

The figure is an X-ray diffraction diagram of a ferroelectric thin film element in an example of the present invention.

Claims (1)

[Claims] 1 On the (100) plane of a magnesium oxide single crystal
A ferroelectric thin film element comprising a lead titanate thin film whose crystals are grown in the 100> direction or the <001> direction.