JPS61137000A - Method for forming single domain in lithium tantalate single crystal - Google Patents

Abstract

PURPOSE:To form a uniform single domain by turning a single crystal lifted in the X-axis direction sideways, keeping the Z-axis in the horizontal direction, providing a positive and a negative strip electrode both of which are long in the X-axis direction to the side surface of the crystal, and impressing a voltage on the crystal. CONSTITUTION:Lithium tantalate single crystal lifted in the X-axis direction is turned sideways, the Z-axis is kept in the horizontal direction, and a positive and a negative electrode both of which are long in the X-axis direction are provided to the side surface of the crystal. Besides, the relation of the angle alphabetween the lines connecting the central point O and the respective upper edges of the positive and the negative electrode which are provided to the side surfaces of the single crystal to the angle beta between the lines connecting the central point O and the respective lower edges of the electrodes is regulated as shown by equation I. The ratio of strip widths l1 of the positive and negative electrodes to the diameter l2 of the single crystal is regulated as shown by equation II. A voltage is impressed on the single crystal by the positive and negative electrodes to form a single domain.

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to an improved method for single-segmenting lithium tantalate single crystals, and in particular, to improve the method of single-segmenting lithium tantalate single crystals, and in particular, to eliminate the uneven single-sectoring caused by the self-weight of the single crystal. The aim is to eliminate this problem by improving the condition and electrode installation shape. (Prior art) Conventionally, as a method for forming a ferroelectric crystal such as lithium tantalate into a single domain, long strip-shaped positive and negative electrodes are formed in plane symmetry on the side surfaces of a single crystal grown by a pulling method in the pulling direction. ,
In the method of dividing a crystal into a single region by applying a voltage, the center point of the plane when the band widths of both positive and negative band-shaped electrodes formed on the side of the crystal are cut perpendicular to the direction in which the crystal is pulled. A single segmentation method has been proposed in which the angle between the electrode and both widthwise edges of the electrode is in the range of 5 degrees to 100 degrees (see Japanese Patent Publication No. 57-41161). However, in recent years, efforts have been made to gradually increase the diameter of lithium tantalate single crystals in order to improve their productivity, and currently the diameter is 3 inches, 4 inches, and even 5 inches.
Large-diameter single crystals of inch size have now been produced. In this way, as the diameter of the crystal increases, the weight of the crystal itself increases, and the piezoelectric effect due to its own weight inside the crystal cannot be ignored. It has become difficult to maintain a uniform distribution of crystals, and as a result, a new problem has arisen in which single domain distribution becomes non-uniform within the crystal. (Structure of the Invention) In order to solve this problem, the present inventors first placed a single crystal pulled in the X-axis direction on its side and maintained the two axes in the vertical direction, and attached strip-shaped positive and negative electrodes. We attempted to achieve a single domain by applying a voltage to the upper and lower sides of a horizontal crystal.However, in this case, a piezoelectric effect due to its own weight was generated in the lower part of the crystal in its two axes. (This piezoelectric effect becomes more pronounced as the diameter of the crystal increases), the distribution of the applied electric field becomes significantly uneven between the stress concentration area due to its own weight and the upper part, resulting in non-singularization. It was not possible to homogeneously divide the entire crystal into a single domain due to the formation of small areas.Therefore, we further examined in detail the installation conditions of the single crystal, the width of the positive and negative electrodes, and the installation conditions of the electrodes. As a result, when the single crystal pulled in the X-axis direction is kept horizontally so that the Z-axis is substantially horizontal, band-shaped strips are formed on both left and right sides when viewed from a plane cut perpendicular to the X-axis direction. Excellent results can be obtained by performing single segmentation by arranging positive and negative electrodes and applying voltage, and more preferably, by biasing the band-shaped positive and negative electrodes arranged on the sides of the crystal toward the top. and install it,
We also discovered that by making the band width of the positive and negative electrodes sufficiently large, the piezoelectric effect in the lower stress concentration part within the crystal can be well corrected, and as a result, the entire crystal can be uniformly divided into a single domain. The invention has been completed. The present invention will be explained in detail below based on the drawings. The first reason shows a state in which the single crystal is kept horizontally so that its two axes are in the horizontal direction, and a band-shaped electrode is disposed on the upper side of the side surface. In the single crystal cross section in the same figure,
The angle α is the angle between the center point 0 and the upper edges of the positive and negative strip electrodes, the angle β is the angle between the center point O and the lower edges of the electrodes, and the angle θ is the angle between the center point and the electrodes. It is the angle formed with the band width. Im indicates the diameter of the single crystal. Figure 1 (+2 shows the plane ■ of the strip electrode,
The frame indicates the band width. By maintaining the single crystal as shown in the first factor, the direction of the piezoelectric effect (horizontal direction) generated within the crystal due to its own weight is equal to the direction of the electric field applied by the strip-shaped electrodes arranged on the side. Become. In this state, the inventors
The unevenness of the electric field distribution within the crystal caused by the piezoelectric effect caused by its own weight being large in the lower part of the crystal can be easily corrected by biasing the strip electrodes installed on the sides upwards, resulting in a uniform electric field. It was determined that the distribution was formed throughout the crystal. As a result of a detailed study of the degree of upward bias, the angles α and β in the cross section shown in Figure 1A were found to be in the range β - α = 2 to 35 degrees (more preferably 10 to 30 degrees). On the other hand, as a result of studying the band width of the band-shaped electrode above, it was found that in the present invention, the direction of the piezoelectric effect due to the weight of the crystal is the same as the direction of the electric field applied by the electrode. Therefore, the band width of the electrode can be made sufficiently large so that a uniform and sufficient electric field is applied to the entire crystal, and the desired size is such that the band width j1 is equal to the diameter Is of the single crystal.
It was found that the ratio was in the range of 0.8 to 1.2. When a large-diameter single crystal is a target as in the present invention, the band width is determined according to the configuration of the present invention as M/Is =
It is desirable to set the angle of θ to a value of 0.8 to 1.2 (which corresponds to approximately 92 to 138'), thereby effectively achieving uniform single domainization. Ru. Next, specific examples will be given and explained. Example: Approximately 3 inches in diameter and approximately 15 cm in length, grown by X-axis pulling
A zero-length lithium tantalate single crystal is placed so that its two axes are in the horizontal direction as shown in Fig. A single area processing was performed. [Strip electrodes used] The length is approximately 150 m, and the diameter of the band width stone and single crystal! ! The ratio II/Im is 0.7.0.8.0.
9.1.0, 1.1.1.2 or 1.3 made of platinum were used. [Installation shape of strip electrode] In the cross-sectional view of Fig. 1 (a), the value of β-α is 00.2.
The strip electrodes were arranged so as to have an angle of 20°, 300°, or 40°. [Heating temperature conditions] The temperature was raised from room temperature to about 630°C over about 4 hours, and the temperature was 0.5
After maintaining the temperature at 630°C for an hour, it is gradually cooled. [Voltage application conditions] After holding at 630°C for 0.5 hours, 120V was applied.
When the temperature dropped to about 500° C. or lower during slow cooling, about 2.5 hours after the voltage was applied, the applied voltage was set to Ov. The heating and voltage application conditions described above are illustrated in FIG. 2. The crystal is single-segmented under each of the above conditions, and the inside of the crystal is investigated using strain inspection using polarized light and light scattering inspection using He-Ha laser light, resulting in good single-segmentation. It was determined whether this was done. The result is first!
It was as shown in I. IJt table (judgment criteria) O mark: 100% single segmentation, very good Bad xb mark: left and right side of crystal

[Central part of the electrode part] has an unconsolidated part, which is extremely bad! From the results of l, the ratio of 11/nobu is 0.8 to 1.2.
Excellent results are obtained when the value of β-α is in the range of 2 to 35.

[Brief explanation of the drawing]

Figure 1A shows a state in which a single crystal is installed so that its Z axis is horizontal, and a strip electrode is placed near the side surface, and Figure 11 is a plan view of the strip electrode. This is what is shown. . Figure 2 shows the heating and ↑h
The pressure application conditions are illustrated.

Claims (1)

[Claims] 1. Lithium tantalate single crystal pulled in the X-axis direction,
The Z-axis is maintained in the horizontal direction in a horizontal position, and long strip-shaped positive and negative electrodes are arranged in the X-axis direction on this side, and a voltage is applied to create a single domain. Features a single domainization method for lithium tantalate single crystals. 2. In the cut plane perpendicular to the X-axis direction of the single crystal,
The angle α between the center point and the upper edge of the strip-shaped positive and negative electrodes arranged on the side surface of the single crystal, and the angle β between the center point and the lower edge of the positive and negative electrodes are β − α = 2 ~ 35°. A single segmentation method according to claim 1. 3. The band width l_1 of the positive and negative electrodes disposed on the side surfaces of the single crystal is such that the ratio of l_1/l_2=0.8 to 1.2 is obtained with respect to the diameter j_2 of the single crystal. 1. Single segmentation method according to item 1.