JP2664508B2 - Method for producing lithium niobate single crystal - Google Patents

Description

The present invention relates to an improved method for producing a lithium niobate single crystal used for a surface acoustic wave filter.

[Prior Art] Large single crystals of lithium niobate are used for surface acoustic wave filters. The lithium niobate single crystal is usually made of lithium niobate obtained by mixing lithium carbonate and niobium pentoxide in a congruent composition ratio and firing at a high temperature. This raw material is melted in a platinum crucible in a high-frequency induction heating furnace and pulled up to form a large crystal (referred to as a boule). After cooling the whole, it is kept in another resistance heating furnace at 1000 ° C. or higher for several tens of hours, annealed, and further subjected to a single domaining treatment. As a single-domain treatment, a boule is placed on a lead plate using a lithium niobate sintered ceramic plate as an electrode, and a DC voltage is applied while heating above the Curie temperature in a resistance heating furnace, followed by cooling. It passes through the Curie temperature and is polarized.

However, as mentioned above, annealing the Boolean,
In addition, when single-domain processing is performed, cracks are likely to occur at the interface with the lithium niobate ceramic plate on which the boule is placed during annealing, and in the single-domain processing, the cleavage surface of the boule is likely to produce cracks. There was a problem that the sex was extremely inconvenient.

[Problems to be Solved by the Invention] An object of the present invention is to solve the above-mentioned problems and to prevent the occurrence of cracks at the time of annealing of a boule and at the time of a single domaining process, and a single crystal of lithium niobate. It is to provide a manufacturing method of.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a method in which a lithium niobate single crystal (a boule) obtained by a pulling method is placed on a plate on which lithium lithium niobate single crystal ground products are spread. It is characterized in that it is installed and the boule is subjected to a single domaining process and annealing.

[Action] The lithium niobate single crystal pulverized product that can be used in the method of the present invention may be of any production method as long as it is a single crystal, but is preferably qualitatively equivalent to the boule. Therefore, a product obtained by the pulling method is preferable, and a defective product or a residual product after cutting may be used. As a pulverizing method, the single crystal is made into a wafer having a thickness of 0.5 to 1 mm with a slicer or the like, washed with water, an organic solvent, or the like, and then mortar, a ball mill, or the like, 5 mm or less, preferably 3 to 5 mm square. It is preferred that the material be granular.

The size of the pulverized product does not necessarily need to be equal,
3 to 5 mm is desirable, and any shape may be used, but a pellet is desirable. The dish is preferably made of a material that can withstand high temperatures and oxidation, and platinum is particularly preferred.
Upon spreading the crushed product on the dish,
It is important to pack without gaps. The spread thickness of the crushed product is desirably 1 cm or less, and the width thereof may be larger than the bottom surface of the boule provided thereon. In order to set the boule on the dish on which the crushed products are spread, the boule may be set upright, and annealing may be performed in a furnace as it is. In addition, by applying a lead wire to the upper part of the boule and the lower part of the dish and applying a current, the boule can be heated in an electric furnace to perform a single domaining process.

[Example-1] A lithium niobate single crystal obtained by the pulling method was cut into wafers having a thickness of 0.5 mm to 1 mm with an inner peripheral slicer, and surface dirt was washed with water and ethanol, and then an alumina mortar. To form pellets of 3 mm to 5 mm square. Next, make a 10 cm × 10 cm dish with a platinum plate, and place the pellet in this
m m. The dish was placed on a firebrick and the leads were wired between the dish and the firebrick. An 80 mm _φ × 150 mm boule was set upright on the pellet, a ceramic plate was placed on top of the boule, and a platinum plate with lead wires was placed on this ceramic plate. Thus, it was placed in an electric furnace and maintained at 1190 ° C. for 1 hour while passing a current, then cooled and passed through the Curie temperature to perform a single domaining treatment. As a result, no crack was observed.

[Example 2] A sample consisting of a platinum dish, pellets, and a boule exactly as in Example 1 except that no lead wire was wired was annealed at about 1200 ° C for 2 days in a resistance heating furnace.

 As a result, no crack was observed.

[Effects of the Invention] By performing the method of the present invention, annealing and single-domain processing can be performed on the boule obtained by the pulling method without generating cracks.

Claims (1)

(57) [Claims] 1. A lithium niobate single crystal obtained by the pulling method is placed on a plate on which a lithium niobate single crystal ground product of 3 to 5 mm square is spread and a single domain of the lithium niobate single crystal is placed. A method for producing a lithium niobate single crystal, which comprises performing a crystallization treatment and an annealing.