JPS5829280B2 - LINB1-XTAX03 - Google Patents

Description

Detailed Description of the Invention The present invention relates to LiNb1-XTaX03 (where 0≦X≦1
) relates to a method for producing single crystal thin films.

LiNb1-XTaX03 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. Dielectric materials are of interest In recent years, the development of new devices by making various materials into thin films has attracted attention, and dielectric materials are also being used as surface acoustic wave devices or optical thin film devices with various functions. It is expected.

Due to its excellent properties, LiNb1-XTaXO3 is a material that is attracting the most attention as a dielectric thin film element, and efforts are being made to create a thin film.

In particular, recently, LiNb11TaxO3 has been regarded as an important core material for optical integrated circuits, and optical waveguides using LiNb1-XTaXO3 can be used for various functions such as mode converters, optical switches, optical converters, and high-frequency generating elements. Elements are expected.

Therefore, a technique for accurately forming a thin film of L iN b 1 x T a x 03 with a thickness of several hundred angstroms to several microns is extremely important.

In order to effectively utilize the various physical properties of LiNb and XTaX03, it is necessary to create them as single crystals or thin films with strong orientation.
x T a x 03 is an oxide with an anisotropic structure whose crystallographic point group is described by R3C, and growing it heteropitaxially is difficult in terms of substrate material selection and film manufacturing method. It's not easy.

The currently reported LiNbO3 film production methods and substrate materials will be briefly described.

Sapphire Z-plane substrate, crystal Z-plane substrate, L t T
Example of creation by sputtering method using a Oa substrate,
LPE and melt solidification (EG) using LiTa0a substrate
M) There is an example of preparation by law.

The LPE method and the EGM method have drawbacks in that a very thin film must be formed with high precision in thickness and that surface polishing is required after growth.

In addition to these methods, using bulk LiNbOs or LiTaO3, LiNb can be produced by external diffusion of Li ions or internal diffusion of various metal ions.
Although there is a technique in which the surface layer of Os or Li Tag3 crystal has a slightly high refractive index to form an optical waveguide, it has the drawback that a sufficient difference in refractive index cannot be obtained.

The present invention is characterized in that three planes of LiNb1-XTaX03 are epitaxially grown using a (111) plane of a magnesium oxide single crystal as a substrate by a sputtering method, but in general, the method is not limited to the sputtering method, but also the LPE method, the EGM method, etc. Magnesium oxide single crystal (11
1) It goes without saying that it is possible to epitaxially grow a LiNb11Taxo3 film on a plane substrate.

For epitaxial growth, substrate selection is important.

In particular, matching of the lattice constant of the grown film and the lattice constant of the substrate material is important.

The periodicity of oxygen ions on the (111) plane of MgO of the present invention and the periodicity of oxygen ions on the Z plane of LiN b 1-x T a x O3 show a very good matching of 0.2070 or less. By paying attention to this, we discovered the possibility that the Z plane of LiNb1-xTaxO3 grows epitaxially in a twin crystal shape.

Sapphire (Z
plane) and crystal (Z plane), the lattice constant mismatch is 5
．． 0% and 8.2%, which has an adverse effect on the grown film.

In addition, although LiTaO3 as a substrate has only a few differences in refractive index with respect to normal light compared to LiNbO3,
MgO has a low refractive index of about 1.75 and exhibits only small dispersion, making it an excellent substrate for LiNb1-xTaXO3 optical thin film elements.

A manufacturing method using a sputtering method will be described below as one of the embodiments.

The sputtering device used was a normal two-pole high frequency sputtering device.

As a target, Li2O and Nb2O were mixed at a ratio of 55:45 and 140. (A sintered body press-molded into X5 was used.

A mixed gas of 60% argon and 40% oxygen was used as the atmosphere at a gas pressure of 2×10 −2 myrtHg.

Substrate temperature is room temperature to 700℃, film growth rate is 100 people/
Experiments were conducted in the range of hr to 2000 people/hr.

As a result, twinned L i N
It was confirmed by electron beam diffraction that the Z plane of b03 had grown.

The twin crystal here has an orientation relationship that is rotated by 60 degrees around the Z axis.

This is essentially due to the fact that the <111> axis of MgO has a 6-fold symmetry, whereas the Z-axis of LiNbO3 has only a 3-fold symmetry.

That is, the orientation relationship between the MgO substrate and the L i NbO3 growth film is MgO:<111n/...NbO3<001>,
MgO: <211≧91NbO3: <110> and <
100>.

LiNbO3 is a uniaxial crystal centered on the Z axis, and even the above-mentioned twin crystal structure does not limit the application.

The crystallinity of the grown film was better as the substrate temperature was higher and the growth rate was slower.

In addition, using a rutile prism, a He-Me laser (6
328A) It was found that light can be introduced into the grown film and used as an optical waveguide.

In addition, it is possible to excite surface acoustic waves by attaching comb-shaped electrodes on a film of approximately 1 μm of LiNbO3 grown.
The insertion loss was 50 MHz and about 20 dB.

As described above, it was found that the L t NbO3 single crystal film according to the present invention can be used as an optical waveguide device or a surface acoustic wave device.

Even when a liquid crystal of LiNb1-xTax03 (0≦X≦1) is used as a sputtering target instead of the LiNbo3 sintered body in the above example, LiNb
It was found that a good single crystal film of 1-xTaXO3 could be obtained.

As described above, according to the present invention, an inexpensive MgO single crystal substrate can be used, and a good L iN b that is excellent as a dielectric material can be used.
A 1-x T a xo 3 single crystal film is easily obtained.

This proves that the present invention is industrially valuable.

Claims (1)

[Claims] I LiNb4, TaXOs (O≦X≦1)
In a method for creating a single crystal thin film, LiNb is formed using a (111) plane of a magnesium oxide (MgO) single crystal as a substrate.
A method for producing a LiNb1-XTaXO3 single crystal thin film, which comprises epitaxially growing the C-plane of I-XTaXO3.