Method of thermal treatment of monocrystals of lanthanum-gallium silicate

FIELD: electronic industry; methods of production of the crystals with the triclinic crystal system.

SUBSTANCE: the invention is pertaining to the method of production of the crystals with the triclinic crystal system. Substance of the invention: the monocrystals of lanthanum-gallium silicate grown in compliance with Czochralski method from the iridium crusible are subjected to the two-stage thermal treatment. The monocrystals are preliminary subjected to the vacuum annealing at the pressure of 1·10-2 -1·10-4Pa and the temperature of 600-1200°C within 0.5-10 hours, and then conduct their isothermal air aging at the temperature of 300-350°C within 0.5-48 hours. The invention allows reproducibly produce the discolored monocrystals of lanthanum-gallium silicate and also to speed up propagation of the surface-acoustic waves (SAW) by 1-1.5 m\s at the simultaneous decrease of dispersion of the waves propagation velocity by 20-30 ppm.

EFFECT: the invention ensures production of the discolored monocrystals of lanthanum-gallium silicate and allows to increase the speed of propagation of the surface-acoustic waves at simultaneous reduction of the waves propagation dispersion by 20-30 ppm.

 

The invention relates to methods of obtaining crystals of the triclinic crystal system, in particular for entangling silicate having a piezoelectric effect and is suitable for manufacturing devices on bulk and surface acoustic wave (saw).

The analysis of literature data shows that the single crystals entangling silicate (langasite) La3Ga5SiO14are a promising material in order to meet the needs of electronic industry. One of the main requirements for single crystals entangling silicate, are along with the electrophysical properties large enough single crystals, which conserves crystals when they cut and as a consequence reduces the cost of manufactured on the basis of their devices. The size of the ingots entangling silicate must be at least 60 mm, with langasite crystals should be free from crystal defects, such as scattering centers, controlled beam of He-Ne laser.

Have been made various attempts in the art to improve the structural properties of langasite, but most of them brought only a minor improvement of quality (see, for example, S.Uda, .Buzanov. J. of Crystal Growth, 2000, v.211, pp.318-324).

One of the ways to improve the quality of pyramisaisishotel is their heat treatment. From the document M.F.Dubovik et.al. "On some electrophysical parameters of langasite crystals", 1996 IEEE International frequency control symposium, p.84-89) there is a method of heat treatment of single crystals entangling silicate, including exposure langasite plate thickness of 2-3 mm at a temperature of C in a period of time not less than 6 hours. In the known method, the heat treatment is subjected to plate, cut out of langasite crystals grown by the Czochralski method. There is a method of heat treatment is not possible to sufficiently reduce the mechanical stresses in the langasite crystal diameter > 50 mm

In the patent RU, 2143015 disclosed technology pokerstove annealing of langasite crystals grown by the Czochralski method from the iridium crucible. In the known method the annealing of single crystals is carried out in the process of cooling speeds of 15 deg/HR for 40 hours and 25 deg/h for 24 hours. Known technology pokerstove annealing avoids the curvature form of the crystal.

For a long time uses the method of heat treatment, including the shutter plates at temperatures above 1000 K (.Shimamura et.al. "Growth and characterization of lanthanum and should be gallium silicate La3Ga5SiO14single crystals for piezoelectric applications", J. of Crystal Growth, 1996, v.163, p.388-392). Disclosed in the above document, the method provides for the heat treatment of langasite wafers with a thickness of 1-3 mm, cut from bulk Crist is low, grown by the Czochralski method from a platinum crucible. The heat treatment is conducted in air at a temperature of 1673 K for 12 hours. Unfortunately, langasite crystals subjected to heat treatment according to known technology, there is the presence of scattering centers that are visible in the beam of He-Ne laser. In addition, with the increase of the diameter of the monocrystal ingot number of scattering centers is also increasing.

In the patent RU, 2126853 disclosed a method of heat treatment of single crystals entangling silicate, including shutter speed bulk crystal at a temperature in the range 1300-1673 To within 20-36 hours in argon at a pressure of 1.1 to 1.8 ATM. There is a method of heat treatment reduces the magnitude of the mechanical stresses in the langasite crystals, however it does not provide reproducible quality of the crystals associated with the magnitude of the velocity of propagation of surface acoustic waves and the degree of dispersion of this velocity.

In the framework of this proposal solves the problem of the development of industrial methods of heat treatment of langasite single crystals grown by the Czochralski method, allowing to reproducibly obtain discolored langasite crystals, as well as to increase the velocity of propagation of surface acoustic waves in these crystals. There is a need in the reproduced obtaining odnorodnyh langasite crystal by reducing the dispersion of the velocity of propagation of surfactant waves.

The problem is solved in that in the method of heat treatment of single crystals entangling silicate grown by the Czochralski method from the iridium crucible, conduct preliminary vacuum annealing of single crystals entangling silicate at a pressure of 1·10-2-1·10-4PA and a temperature of 600-1200°C for 0.5 to 10 hours, and then carry out isothermal annealing by keeping the crystals in air at a temperature in the range 300-350°C for 0.5 to 48 hours.

In the absence of established patterns between the structural properties of langasite crystal and thermodynamic regimes of their processing, the authors have experimentally determined parameters of the two-stage heat treatment, the volume of langasite single crystals grown by the Czochralski method.

The essence of this invention is illustrated non-limiting example of its implementation.

Example

Conduct two-stage heat treatment of the crystal entangling silicate grown by the Czochralski method from the iridium crucible. The crystal is grown from a mixture obtained by the so-called method of self-propagating high temperature synthesis, at the same time as the original ingredients used lanthanum oxide 99.99%purity; silica purity 99,999%; oxide of gallium 99.99% purity and gallium use the th purity of 99,999%. The original mixture obtained by the method of self-propagating high temperature synthesis, corresponds to the congruent composition in the diagram condition of these ingredients. The grown crystal has a diameter of 85 mm inscribed circle on the cylindrical part of the bulk crystal. After completion of the process of growing the single crystal is cooled in the growth chamber to the ambient temperature of not less than 20 hours. Grown in iridium crucible Czochralski single crystal entangling silicate is subjected to a preliminary vacuum annealing at a pressure of 2·10-3PA and a temperature of 1000°C for 8 hours. After vacuum annealing is conducted isothermal annealing in air, for which the langasite single crystal is maintained at a constant temperature of 320°C for 28 hours.

This method of treatment allows us to reproducibly obtain discolored langasite crystals. In this two-stage method of heat treatment of the saw velocity of the waves increases by 1-1,5 m/s, and the dispersion of the velocity of propagation of waves is reduced by 20-30 ppm.

The method of heat treatment of single crystals entangling silicate grown by Czochralski method, including pre-vacuum annealing of single crystals entangling silicate at a pressure of 1·10-2-1·10-4the a and a temperature of 600-1200° C for 0.5 to 10 hours, and subsequent isothermal aging of single crystals in air at a temperature in the range 300-350°C for 0.5 to 48 hours



 

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