JPS595560B2 - LiNb↓1-xTaxo↓3 single crystal film manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides LiNb1-xTaxO3 (0≦X≦1
) relates to a method for producing single crystal thin films.

LiNb1-xTaxO3 is a ferroelectric material with a high Curie point, and has excellent properties in terms of electromechanical coupling coefficient, electro-optic effect, nonlinear optical effect, etc., and is the most suitable for a wide range of application fields. It is an interesting dielectric material.

In recent years, the development of new devices by thinning various materials has attracted attention, and dielectric materials are also expected to be used as surface acoustic wave devices or optical thin film devices with various functions. Due to its excellent properties, LiNb1-xTaxO3 is a material that attracts the most attention as a dielectric thin film element, and efforts are being made to create a thin film.

In particular, recently L1Nb0-xTaxO3 has been regarded as one of the important core materials for optical integrated circuits, and LiNb1
Optical waveguides using -xTaxO3 are expected to be used as various functional elements such as mode converters, optical switches, optical modulators, and optical harmonic generation elements.

Therefore, a technique for accurately forming a thin film of LiNb7-xTaxO3 having a thickness of several hundred angstroms to several tens of microns is very important. L1Nb1-XTaXO
In order to effectively utilize the various physical properties of LiNb1-xTaxO3, it is necessary to create it as a single crystal or a thin film with strong orientation. It is an oxide with an anisotropic structure, and it is difficult to grow it heteroepitaxially due to the selection of substrate materials and film manufacturing methods.

The following examples have been reported regarding the conventional method of forming a LiNbO3 film and the substrate material used at that time.

There are examples of growing twinned LiNbO3 films by sputtering, liquid phase epitaxy (LPE), etc. using sapphire Z planes, crystal Z planes, LiTaO3 single crystals, etc. as substrates. These substrates have advantages and disadvantages; for example, although sapphire Z-plane and quartz Z-plane are easily available at a price, they have a large mismatch in lattice constant with the grown film, making it difficult to obtain a high-quality LiNbO3 film, and
Even if it is obtained, the piezoelectric properties are not necessarily the best due to Z-plane growth.

In addition, the LiTaO3 substrate is crystallographically very compatible and enables planar growth of LiNbO3 with good piezoelectric properties.
Due to its high price, it is not practical in terms of price. The present invention greatly alleviates the above-mentioned drawbacks of the prior art.

In other words, the periodicity of oxygen ions in the (10V2) plane (commonly known as the R plane) of easily available sapphire is LiNb1-xTaxO.
3 (however, 0≦X≦1), the (1010) plane (commonly known as the Y plane) matches very well with the periodicity of oxygen ions. We have discovered the possibility that the Y-plane of LiNb, -XTaxO3, which is good and highly useful, can be epitaxially grown on the R-plane of sapphire. A fabrication method using the sputtering method will be described below as one of the embodiments. The sputtering device used was a normal two-pole high frequency sputtering device.

Li,O (5Nb,0, 5.5:4 as target)
．． The mixture was mixed in a ratio of 5 parts, pressure-molded into a size of 140 mm x 5 pieces, and then sintered. The atmosphere in the sputter is a mixed gas of 60% argon and 40% oxygen at a gas pressure of 2 x 10-2.
It was used as mmHJ. Substrate temperature is room temperature to 800°C,
We conducted experiments at film growth rates ranging from 100 to 2000 layers/hour.As a result, when the substrate temperature was 300°C or higher, the Y-plane of twinned LiNbO was formed on the R-plane of sapphire. Growth was confirmed by electron diffraction. Here, the twin crystals are those in a positional relationship rotated by 60 degrees around the Z axis of I, iNbO3.

In addition, from the back Laue photograph, the Y plane of LiNbO, the R plane of Saphire, the direction of LiNbO, 0001〉 (Z axis), and the <10th direction> of Saphire are in a parallel relationship (
I found out that there is this. Since the grown film was formed by sputtering in a high electric field, the ferroelectric LlNbO film was polarized. In addition, the propagation loss of light within the film, which indicates the quality of the film, is 5 to 8 d with a He-Ne laser (wavelength 6328 input).
B1 drift is small and piezoelectric constant D33 is about 100d-
It was found that it was a good LiNbO3 film with y close to D,3 (=107dK1rp) of the bulk crystal. Generally, the higher the substrate temperature and the slower the growth rate, the better the crystallinity of the grown film, and the higher the amount of oxygen in the atmospheric gas in the sputtering, the better the crystallinity tended to be. That is, as a sputtering atmosphere, a mixed system of argon and oxygen with an oxygen concentration of 25% to 90% is suitable for epitaxial growth, but an oxygen concentration of 40% to 80% is particularly desirable. Further, an epitaxially grown film can be obtained at a substrate temperature of 3008C to 1000'C, but a temperature of 500T to 800T is particularly desirable. In place of the LlNbO3 sintered body in the above example, LiNb
,,xTaxO, (0$Xll) is generally L
It has been found that a good single crystal film of LiNbl-XTaxO can be obtained even when the i,O(7)E ratio is increased and used as a sputter target.

In addition, not only the sputtering method of the above embodiment, but also general methods such as LPE method, vapor phase growth method, melt solidification method, etc. are used to form LiNb on the R-plane of the sapphire single crystal as a substrate.
Of course, it is possible to epitaxially grow a single crystal film of l-XTaxO. However, these methods require very difficult polarization operations after film formation, and the optical propagation loss is 10 to 30 dB/C.
m is not necessarily good.

As described above, according to the present invention, an easily available and inexpensive sapphire single crystal substrate can be used, and a good LiNb, -XTaxO, single crystal film excellent as a dielectric material can be easily obtained at a low cost.

Claims (1)

[Claims] 1 Sapphire single crystal a-Al_2O_3 {1012
} surface of LiNb_1_−_XTa_XO_3 {10
10} plane epitaxially grown by sputtering, the substrate temperature is 500°C to 800°C, and the oxygen concentration in the sputtering atmosphere is 40% to 80%. Method.