JPH01172299A - Polling method for lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:To enable polling at the temp. higher than a conventional method and to improve uniformity and reproducibility of polling by utilizing single crystal powder of lithium niobate or the sintered body of this powder as a medium and pinching lithium tantalate single crystal between a pair of platinum electrodes and subjecting this single crystal to polling treatment. CONSTITUTION:Lithium tantalate single crystal (1) is pinched between a pair of platinum electrodes 3, 3 while utilizing single crystal powder of lithium niobate or a sintered body of this powder as a medium (6) and polling voltage is impressed on the platinum electrodes 3, 3. In the above-mentioned method, it is utilized that lithium tantalate is made stable for lithium niobate and also lithium niobate is made electroconductive at the temp. not lower than about 650 deg.C.

Description

[Detailed Description of the Invention] [Summary] Regarding the poling method of lithium tantalate single crystal for collecting element substrates such as piezoelectric elements and surface acoustic wave filters, the present invention improves the uniformity and reproducibility of poling and eliminates cracks that occur during poling. For the purpose of reduction, the lithium tantalate single crystal is sandwiched between a pair of platinum electrodes using a lithium niobate single crystal powder or a sintered body of the powder as a medium, and a poling voltage is applied to the platinum electrodes. do.

[Industrial application field]

The present invention relates to an improvement in a method of poling a lithium tantalate (LiTaOs) single crystal, particularly a lithium tantalate single crystal for collecting element substrates such as piezoelectric elements and surface acoustic wave filters.

A single crystal of lithium tantalate, for example, a single crystal (ingot) grown by the Czochralski method, is annealed to remove the internal strain created during the growth before being cut into thin pieces to create a wafer. Polling processing is performed to unify the domain.

[Conventional technology]

FIG. 4 is a side view for explaining the conventional poling method of a grown lithium tantalate single crystal, in which a single crystal 1 grown in a cylindrical shape is coated with conductive paste on opposing cylindrical surfaces in the Z-axis direction of the crystal. 2 is applied and sandwiched between a pair of platinum electrodes 3 having an arc-shaped cross section through the conductor paste 2.
Connect to DC power supply 4.

Such a single crystal 1, for example, a single crystal 1 having a diameter of 3 inches, is polled by applying a predetermined DC voltage to the electrode 3 for about 4 hours in an atmosphere heated to 650°C to 700°C.

Note that the reference numeral 5 in the figure is a porcelain stand that supports the single crystal 1;
Reference numeral 6 is a magnetic lid that holds down the electrode 3 mounted on the single crystal 1, and the conductive paste 2 is generally made by kneading platinum palladium powder with a solvent.

[Problem that the invention seeks to solve]

In the conventional poling method, the solvent of the conventional conductive paste 2, which is the connection medium for the platinum electrode 3, is heated at 650°C.
As a result, the organic matter contained in the solvent undergoes deterioration such as carbonization, and as a result, the distribution of the poling voltage becomes uneven, resulting in uneven poling, and the carbonization products cause microcracks to occur. In addition, there was a problem that the reproducibility of the polling characteristics was poor.

In addition, when performing the temperature-dependent polling, 65
A temperature of 0°C is a processing condition with insufficient reproducibility, especially in the case of a single crystal 1 with a diameter of about 3 inches, it becomes difficult to perform poling at the center. When the deterioration of the solvent becomes noticeable and the poling voltage is increased in order to make the poling uniform, fine racks are generated in the single crystal 1, and the yield at which the desired element substrates can be obtained is reduced.

[Means for solving problems]

The present invention, which aims to eliminate the above problems, takes advantage of the fact that lithium tantalate is stable with respect to lithium niobate and that lithium niobate becomes conductive at temperatures above about 650'C. FIG. 1 is a basic diagram for explaining the method of the present invention.

In FIG. 1, the method of the present invention uses a lithium niobate single crystal powder or a sintered body of the powder as a medium 6, and a lithium tantalate single crystal 1 is sandwiched between a pair of platinum electrodes 3, and a DC power source 4 connects the pair of electrodes. This is a poling method for a lithium tantalate single crystal, which is characterized by applying a poling voltage to the lithium tantalate single crystal.

[Effect]

Using a lithium niobate single crystal powder or a sintered body of the powder that becomes conductive at about 650°C or higher as a medium, a lithium tantalate single crystal is sandwiched between a pair of platinum electrodes, and the single crystal is subjected to a poling treatment. This enables poling at higher temperatures than conventional methods, improving uniformity and reproducibility, and eliminating the occurrence of micro-cranks in the single crystal.
The yield of required element substrates is improved.

〔Example〕

Examples of the method of the present invention will be described below with reference to the drawings.

FIG. 2 is a sectional view for explaining one embodiment of the present invention, and FIG. 3 is a side view for explaining another embodiment of the present invention.

In FIG. 2, which utilizes an alumina crucible and lithium niobate single crystal powder, and uses the same reference numerals for the same parts as in FIG. For example, it is spread to a thickness of 2c+++, and on top of that is lithium tantalate single crystal 1 and single crystal 1.
A pair of platinum electrodes 3 facing each other in the Z-axis direction of the single crystal 1 are stood upright by an appropriate distance from the lithium niobate single crystal powder 13 between the single crystal 1 and the platinum electrode 3. , lithium niobate single crystal powder (medium) 1 between the single crystal 1 and the crucible 11 and between the platinum electrode 3 and the crucible 11
Fill 4.

Therefore, a pair of platinum electrodes 3 are connected to a DC power source 4, heated to 850°C at a rate of, for example, 100'C per hour, and held for 1 hour while applying the same poling voltage as before to the single crystal 1. , the single crystal 1 is slowly cooled at a rate of about 75° C. per hour, and the poling of the single crystal 1 is completed.

In this poling process, lithium niobate single crystal powder 12°13,1 which becomes conductive at 650°C or higher is used.
4 is compositionally stable even at a high temperature of 850'C, so no cracks occur in the single crystal 1, and poling is performed more uniformly over the entire single crystal 1 than in the past.

In addition, in FIG. 2, the powder 14 through which the poling current flows
In order to improve the current flow, it is preferable to pound and harden the powder to make it denser than the powder 13. Instead of the lithium niobate single crystal powder 14, ideally, a highly conductive material with a high melting point, such as platinum powder, is used. However, such materials are extremely expensive and impractical.

In Fig. 3, which utilizes a sintered body of lithium niobate single crystal powder and uses the same reference numerals for parts common to the previous figure, the lithium tantalate single crystal 1 is orient flat 1a.
In the orient flat 1a which forms and faces upward,
A sintered body 21 formed by sintering lithium niobate single crystal powder and formed into a plate shape of uniform thickness is mounted, and a flat platinum electrode 31 corresponding to one of the platinum electrodes 3 described above is attached to the sintered body 21. A plate-shaped porcelain lid 23 is mounted on the platinum electrode 3.

A plate-shaped porcelain base 24 for supporting the single crystal 1 has a plate-shaped platinum electrode 31 corresponding to the other platinum electrode 3 described above.
A sintered body 22 of sintered lithium niobate single crystal powder is mounted on the sintered body 22, the upper surface of which is formed into a cylindrical surface in contact with the cylindrical surface of the single crystal L. Load crystal l.

Therefore, the pair of platinum electrodes 31 are connected to the DC power supply 4, heated to 850°C at a rate of, for example, 100''C per hour, and kept in the holding chamber for 1 hour while applying the same poling voltage as before to the single crystal 1. Thereafter, it is slowly cooled at a rate of about 75° C. per hour, and the poling of the single crystal I is completed.

In this poling process, the sintered bodies 21 and 22 obtained by sintering the lithium niobate single crystal powder that becomes conductive at 650°C or higher are compositionally stable even at a high temperature of 850°C, so the single crystal 1 is No cracks, single crystal 1
Polling will now be performed more uniformly across the entire area than before.

〔Effect of the invention〕

As explained above, the present invention utilizes a lithium niobate single crystal powder or a sintered body of the powder that becomes conductive at temperatures above about 650'C as a medium, and polls a lithium tantalate single crystal. , it is possible to perform poling at a higher temperature than the conventional method, improving uniformity and reproducibility, and eliminating the occurrence of microcracks, resulting in an improvement in the yield of substrates such as piezoelectric elements collected from the single crystal, and This has the effect of stabilizing the performance of the element, etc.

[Brief explanation of the drawing]

Figure 1 is a basic diagram for explaining the method of the present invention, Figure 2 is a sectional view for explaining one embodiment of the present invention, and Figure 3 is a diagram for explaining another embodiment of the present invention. Side View FIG. 4 is a side view for explaining the conventional poling method of lithium tantalate single crystal. In the figure, 1 is a lithium tantalate single crystal, 1a is an orient flat, 3.31 is a platinum electrode, 4 is a DC power supply, 6 is a medium, 11 is an alumina crucible, 12 and 13 are lithium niobate single crystal powder , 14 is a lithium niobate single crystal powder (medium), 21.22 is a sintered body of lithium niobate single crystal powder (
medium), indicates. f′ Complete・纺～Shi 1 Neru r: Ah (7)′ Seizu Haya
Z (8)

Claims (1)

[Claims] (1) A single crystal of lithium tantalate (1) is sandwiched between a pair of platinum electrodes (3, 31) using a lithium niobate single crystal powder or a sintered body of the powder as a medium (6). A method for poling a lithium tantalate single crystal, comprising applying a poling voltage to the platinum electrodes (3, 31). (2) Spread the first powder (12) of lithium niobate single crystal on the bottom of the crucible (11) made of alumina, and place the first powder (12) of the lithium tantalate single crystal (12) on top of the powder (12).
) and the pair of platinum electrodes (3) facing the single crystal (1).
) are made to stand upright, and the single crystal (1) and the platinum electrode (3)
The medium (6) made of lithium niobate single crystal powder (14) is filled between the crucible (11), the single crystal (1) and the platinum electrode (3). 2. The method of poling a lithium tantalate single crystal according to claim 1, wherein the poling voltage is applied after filling the second powder (13) of the lithium tantalate single crystal. (3) The powder (14) of the lithium niobate single crystal filled between the lithium niobate single crystal (1) and the platinum electrode (3) is pounded and solidified to form the medium (6).
) A method for poling a lithium tantalate single crystal according to claim 2. (4) The medium (6) is a pair of sintered bodies (21, 22) obtained by sintering lithium niobate single crystal powder, and the orient flat (1a) is attached to the lithium tantalate single crystal (1). One of the sintered bodies (21) in contact with the orient flat (1a) is formed into a plate shape having a substantially constant thickness, and the lithium tantalate single crystal (1) facing the orient flat (1a) is ) is formed into a plate shape having a cylindrical surface along the cylindrical surface, and the pair of sintered bodies (21, 22) are in contact with Lithium tantalate according to claim 1, characterized in that platinum electrodes (31) sandwich the single crystal (1) of lithium tantalate, and the poling voltage is applied to the platinum electrodes (31). Single crystal polling method.