Method for manufacturing piezoelectric oxide single crystal substrate

Abstract

To provide a method for manufacturing a piezoelectric oxide single crystal substrate having a single-sided mirror polishing specification, replaced with surface grinding without using conventional wrapping and capable of suppressing a spurious influence due to reflection caused when irregularly reflecting a bulk wave on the rear surface of the substrate when using the piezoelectric oxide single crystal substrate as a SAW filter.SOLUTION: A method for manufacturing a piezoelectric oxide single crystal substrate comprises: a slicing step of slicing a piezoelectric oxide single crystal ingot to form a single crystal thin plate; a surface grinding step of surface-grinding the front and rear surfaces of the single crystal thin plate generated in the slicing step; and a blasting step of blasting the rear surface on the side opposite to the main surface of the single-crystal thin plate subjected to the surface-grinding; and a polishing step of mirror-polishing the main surface of the single-crystal thin plate subjected to the surface-grinding.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a piezoelectric oxide single crystal substrate.

Background Art

[0002] Lithium tantalate (LT) single crystal and lithium niobate (LN) single crystal are ferroelectrics with melting points of about 1650°C and about 1250°C, respectively, and Curie temperatures of about 600°C and about 1140°C, respectively, and have piezoelectricity. The piezoelectric oxide single crystal substrate (sometimes simply referred to as a single crystal substrate) manufactured using this LT single crystal or LN single crystal is mainly used as a device material for surface acoustic wave (SAW) filters for signal noise removal of mobile phones, optical elements, and the like.

[0003] Next, an example of the manufacturing process of a piezoelectric single crystal substrate will be described. Since the LT single crystal or LN single crystal is treated in the same way both crystallographically and in the manufacturing process, the manufacturing method of the LT single crystal substrate will be mainly described.

[0004] The LT single crystal is grown by a single crystal growth method such as the Czochralski method (Cz method). After cutting the end of the grown crystal with insufficient diameter, the LT single crystal is subjected to a single polarization treatment (poling). This poling polarizes the crystal by applying a voltage in the <001> axis direction of the LT single crystal at a temperature above the Curie point.

[0005] Next, when creating a surface acoustic wave element or the like, an orientation flat (OF) that is a reference plane, that is, a plane indicating the crystal orientation and the propagation direction of the surface acoustic wave, is processed, and a circumferential grinding process for adjusting the outer diameter is performed to obtain an LT single crystal ingot.

[0006] Next, a method for manufacturing a single crystal substrate from this LT single crystal ingot will be described. First, the LT single crystal ingot is sliced into a disk-shaped thin plate with a predetermined thickness along a desired crystal orientation by a cutting device such as a wire saw.

[0007] Next, both sides of the obtained thin plate are subjected to lapping using a slurry composed of abrasive grains of, for example, #800 to #2000 mesh and water to remove damage on both sides of the thin plate, and while obtaining flatness and parallelism, the thin plate is made to have a predetermined thickness.

[0008] After lapping, the main surface side of the thin plate is subjected to surface grinding, and as a finish, the main surface side of the thin plate is mirror-polished by, for example, mechanical chemical polishing (CMP) using a slurry such as colloidal silica. Thereby, an LT single crystal substrate is obtained.

Prior Art Documents

Patent Documents

[0009]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0010] Among the manufacturing processes for manufacturing a single crystal substrate from the above-described LT single crystal ingot, lapping is a process in which a single crystal substrate is mounted on a carrier sandwiched between an upper platen and a lower platen using a lapping device, and is polished by free abrasive grains between the upper platen and the lower platen by rotation and pressurization of the upper platen and the lower platen. Lapping can process a plurality of single crystal substrates simultaneously on both sides, and has good productivity. However, since lapping is basically a batch-type process, it is a process that requires a lot of personnel for attaching and detaching the single crystal substrate. Also, in terms of quality, since the single crystal substrate is a thin plate and lapping is performed under pressure, the load on the single crystal substrate is large, and there is a problem that the single crystal substrate cracks during lapping. Furthermore, since the processed surface during lapping can only be a matte surface, the subsequent polishing amount increases, resulting in poor work efficiency. When surface grinding is performed after lapping, since grinding is performed twice, there is a problem that the cost of wafer processing increases significantly.

[0011] Therefore, Patent Document 1 describes a method of grinding a GaAs wafer, in which, instead of the lapping process, grinding using a surface grinding apparatus is performed on both sides one by one.

[0012] In addition, as described above, such a single crystal substrate has two specifications depending on the specifications: a double-sided mirror-finished product (double-sided mirror-finishing specification) in which both sides of the single crystal substrate are mirror-finished, and a single-sided mirror-polished product (single-sided mirror-finishing specification) in which only one of the main surfaces is mirror-finished. The single-sided mirror-polished product is generally used in a SAW filter. By setting the surface roughness of the back surface of the single crystal substrate to, for example, Ra0.1 μm to 0.5 μm, bulk waves can be diffusely reflected by the back surface of the substrate, and the influence of spurious due to reflection can be suppressed.

[0013] Conventionally, in a single-sided mirror-polished product, one side (main surface side) is mirror-finished, and the other side is a lapped surface (a surface with a larger surface roughness than the mirror-finished surface). Since the processed surface (lapped surface) of the substrate subjected to the lapping process is lapped using a slurry containing free abrasive grains, it becomes a matte processed surface with a surface roughness adjusted to about Ra0.1 μm to 0.5 μm.

[0014] However, in a single-sided mirror-polished product, when the lapping process is replaced with a surface grinding process, the surface grinding processed surface becomes a processed surface with regularity, and it has been difficult to suppress the influence of spurious.

[0015] Therefore, the present invention provides a method for manufacturing a piezoelectric oxide single crystal substrate having a single-sided mirror-polishing specification, which can replace the conventional lapping process with a surface grinding process and can suppress the influence of spurious due to reflection that occurs when bulk waves are diffusely reflected by the back surface of the piezoelectric oxide single crystal substrate used as a SAW filter.

Means for Solving the Problems

[0016] According to an aspect of the present invention, there is provided a method for manufacturing a piezoelectric oxide single crystal substrate, including: a slicing step of slicing an ingot of a piezoelectric oxide single crystal into a thin plate-like single crystal thin plate; a surface grinding step of planar grinding the front and back surfaces of the single crystal thin plate produced in the slicing step; a blasting step of blasting the back surface on the side opposite to the main surface of the single crystal thin plate subjected to the planar grinding; and a polishing step of mirror-polishing the main surface of the single crystal thin plate subjected to the planar grinding.

[0017] Also, in the above aspect, the blasting may be wet blasting. The piezoelectric oxide single crystal may be a lithium tantalate single crystal or a lithium niobate single crystal.

Advantages of the Invention

[0018] According to the present invention, in a method for manufacturing a piezoelectric oxide single crystal substrate with a single-sided mirror polishing specification, it is possible to replace the conventional lapping process with a surface grinding process, and it is possible to manufacture a piezoelectric oxide single crystal substrate that can suppress the influence of spurious caused by reflection when bulk waves are diffusely reflected from the back surface of the substrate when the piezoelectric oxide single crystal substrate is used as a SAW filter.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Embodiments for Carrying Out the Invention

[0020] Hereinafter, specific embodiments of the present invention will be described in detail. Note that the present invention is not limited to the following embodiments, and can be appropriately changed without changing the gist of the present invention. In each drawing, part or all of the drawing is schematically shown, and the scale is changed. Also, in the following description, the description "A to B" means "A or more and B or less".

[0021] Hereinafter, this embodiment will be described. FIG. 1 is a flowchart showing an example of a method for manufacturing a piezoelectric oxide single crystal substrate according to this embodiment. FIG. 2 is a flowchart showing an example of a conventional method for manufacturing a piezoelectric oxide single crystal substrate for comparison with this embodiment.

[0022] The method for manufacturing a piezoelectric oxide single crystal substrate according to this embodiment (the manufacturing method of this embodiment, which may also be abbreviated as this manufacturing method) is a method for manufacturing a piezoelectric oxide single crystal substrate, and includes a surface grinding step of performing surface grinding on the front and back surfaces of a single crystal thin plate obtained by slicing a piezoelectric oxide single crystal instead of the conventional lapping process. This will be described in detail below.

[0023] Note that the method for manufacturing a piezoelectric single crystal substrate according to this embodiment is a method for manufacturing a single crystal substrate with a single-sided mirror polishing specification in which only one of the main surfaces of the front and back surfaces is mirror-polished.

[0024] The method for manufacturing a piezoelectric single crystal substrate according to this embodiment includes a slicing step (S1) of slicing an ingot of a piezoelectric oxide single crystal into a thin plate-shaped single crystal thin plate, a surface grinding step (S2) of performing surface grinding on the front and back surfaces of the single crystal thin plate produced in the slicing step, a blasting step (S3) of blasting the back surface on the side opposite to the main surface of the single crystal thin plate subjected to the surface grinding, and a polishing step (S4) of mirror-polishing the main surface of the single crystal thin plate subjected to the surface grinding.

[0025] <Piezoelectric oxide single crystal> In this embodiment, the piezoelectric oxide single crystal (which may be abbreviated as oxide single crystal) is a piezoelectric oxide single crystal such as lithium niobate LiNbO3 (LN) single crystal, lithium tantalate LiTaO3 (LT) single crystal, and lithium tetraborate single crystal. The manufacturing method of the piezoelectric oxide single crystal substrate of this embodiment can be suitably used for a lithium tantalate single crystal or a lithium niobate single crystal, which is a brittle material. In this manufacturing method, the piezoelectric oxide single crystal is not limited to the above single crystals as long as it is a single crystal of a piezoelectric oxide. Hereinafter, the LT single crystal will be described as a representative example of the oxide single crystal.

[0026] The LT single crystal is grown by a single crystal growth method such as the Czochralski method (CZ method). The Czochralski method is a growth method in which a single crystal is grown by dipping and pulling up a seed crystal into a melt obtained by melting raw material powder. For example, by using a high-frequency induction heating device or the like, a large single crystal can be stably manufactured. In the grown LT single crystal ingot, heat treatment is performed under soaking near the melting point to remove the residual strain due to the thermal stress of the crystal, and then a single polarization treatment (poling) is performed. This poling treatment polarizes the single crystal over about 0.5 to 2 hours by heating the grown LT single crystal to a temperature above the Curie point, for example, 600 to 700 °C, and applying a voltage of, for example, 200 to 500 V in the Z-axis direction. In this manufacturing method, the conditions such as the above growth method and poling treatment are not particularly limited.

[0027] Subsequently, the upper and lower ends of the LT single crystal with insufficient diameter are cut, and cylindrical grinding for adjusting the outer diameter is performed on the LT single crystal (ingot). In addition, orientation flat processing is performed on the reference plane when manufacturing an elastic surface wave element or the like, that is, the plane indicating the crystal orientation and the propagation direction of the elastic surface wave.

[0028] <Slicing step (S1)> The slicing step (S1) slices the LT single crystal ingot into a thin plate-like single crystal thin sheet. In the slicing step (S1), the LT single crystal ingot is sliced, for example, along a desired crystal orientation, into a thin plate-like, disk-shaped single crystal thin sheet having a predetermined thickness. In the present embodiment, the single crystal ingot used in the slicing step (S1) is not limited to the above example, and any piezoelectric oxide single crystal ingot can be used. The slicing process presses the workpiece against a plurality of ultra-fine wire rows arranged in parallel at a constant pitch, and while feeding the wire in the linear direction, supplies a processing liquid (also called slurry) containing abrasive grains between the workpiece and the wire to perform polishing and cutting. Or it is performed by a wire saw (cutting device) or the like using a method of polishing and cutting the workpiece while feeding a wire with diamond fixed by electrodeposition or an adhesive in the linear direction. In the present manufacturing method, the method, conditions, etc. of the slicing process are not particularly limited.

[0029] <Surface grinding step (S2)> In this manufacturing method, after the slicing step (S1), instead of the conventional lapping step, a surface grinding step (S2) is performed. The surface grinding step (S2) performs surface grinding on the front and back surfaces of the single crystal thin sheet produced in the slicing step (S1). The surface grinding is performed by a surface grinding device. By the surface grinding, a single crystal thin sheet having a surface grinding processed surface on the front and back surfaces is obtained. In the surface grinding step (S2), the thickness variation of each single crystal thin sheet generated in the slicing process is made uniform to a predetermined thickness, and the warp is reduced. The surface grinding is, for example, a surface processing method in which a rotating grindstone is pressed against the surface of a single crystal thin sheet supported on a processing table to grind the surface of the single crystal thin sheet. This surface grinding is a work in which the grindstone rotating at high speed scrapes the surface of the single crystal thin sheet little by little with the abrasive grains as cutting edges and finishes it precisely, and has the advantage that the cutting speed is very fast. Also, since the pressure applied to the workpiece in the surface grinding is smaller than that in the lapping process, cracking of the workpiece can be suppressed more than when performing the lapping process. Also, the surface grinding can be carried out by automation.

[0030] In the surface grinding process (S2), for example, using a single-sided surface grinding apparatus with a grinding wheel containing diamond abrasive grains such as #600 to #10,000, surface grinding is performed using a grinding fluid. As a result, the flatness of the front and back surfaces of the single-crystal thin plate can be increased, and the polishing accuracy can also be improved.

[0031] Note that since the surface roughness of the back surface of the single-crystal substrate to be manufactured can be adjusted and determined in the subsequent blasting process, there is no specification or limitation on the surface roughness of the back surface of the single-crystal thin plate in the surface grinding process (S2). Also, since the surface roughness of the main surface of the single-crystal substrate to be manufactured can be adjusted and determined in the subsequent polishing process, there is no specification or limitation on the surface roughness of the main surface of the single-crystal thin plate in the surface grinding process (S2). Therefore, in the surface grinding process (S2), for example, the grit size of the grinding wheel can be appropriately selected in consideration of the quality of the single-crystal thin plate, particularly the warpage of the single-crystal thin plate, and the production efficiency of the surface grinding process. For example, the surface roughness of the main surface can be set to Sa0.01 μm to 0.04 μm.

[0032] <Blasting Process (S3)> Next is the blasting process (S3). In the blasting process (S3), the back surface on the side opposite to the main surface of the single-crystal thin plate subjected to surface grinding is blasted. Blasting is a method of spraying an abrasive onto the back surface side of the single-crystal thin plate to roughen the surface. By blasting, the surface ground surface of the back surface is blasted, and a single-crystal thin plate having a blasted surface on the back surface is obtained. The blasted surface becomes an irregular uneven surface (a surface having random unevenness without directionality), and similar to the satin-like processed surface of the lapping processed surface, it can suppress the influence of spurious caused by reflection when the bulk wave generated when using the piezoelectric single-crystal substrate as a SAW filter is diffusely reflected from the back surface of the substrate. In this specification, the main surface of the single-crystal thin plate means the surface on the side where mirror finishing is performed, and the back surface of the single-crystal thin plate means the surface on the side opposite to the main surface.

[0033] The method of blasting can use methods such as the dry blasting method (dry blasting), the wet blasting method (wet blasting), etc. The dry blasting method is a method of directly spraying abrasive onto the workpiece with compressed air. Dry blasting can be carried out by a dry blasting device. The wet blasting method is, for example, a method of spraying a slurry in which abrasive is dispersed in water with compressed air. Wet blasting can be carried out by a wet blasting device. In this manufacturing method, it is preferable that the blasting is the wet blasting method (wet blasting). In the dry blasting method, since the abrasive is directly sprayed onto a single-crystal thin plate with a thin thickness, there may be a problem of substrate cracking. Therefore, a protective film may be attached to the surface of the single-crystal thin plate where blasting is not performed on the main surface for reinforcement. Also, in the dry blasting method, since dust is generated, the entire device or the processing chamber may be made airtight. The wet blasting method uses water as a buffer material, eliminating strong impacts and making it possible to suppress cracking of the single-crystal thin plate. Also, the above-mentioned protective film is not required. Also, in the wet blasting method, dust is not generated by using water, and the generation of static electricity and heat can also be suppressed.

[0034] The surface roughness of the blasted surface can be set, for example, to be about the same as that of a conventional lapped surface. The surface roughness of the blasted surface can be, for example, Sa 0.22 μm to 0.25 μm of the surface roughness of a lapped surface as shown in Reference Example 1 described later. For example, in wet blasting, the surface roughness can be adjusted by adjusting abrasive grains and the like. For example, in wet blasting, when the abrasive grains are #1000 and the spraying pressure is 0.12 to 0.25 MPa, it is possible to adjust the surface roughness to Sa 0.12 μm to 0.3 μm, and the target surface roughness can be set by appropriately adjusting the spraying amount, pressure, time, etc. Also, in the case of the dry blasting method, the surface roughness and the like can be appropriately adjusted by appropriately setting processing conditions such as the material and particle diameter of the abrasive, and the spraying amount, pressure, and time of the abrasive.

[0035] <Polishing process (S4)> The polishing process (S4) mirrors the main surface of the single-crystalline thin plate that has been subjected to surface grinding. The single-crystalline thin plate has its front and back surfaces surface-ground in the surface grinding process (S2). After the back surface side is blasted, the front surface (main surface) is mirror-finished (polished, mirror-polished). By performing the polishing process (S3), a piezoelectric single-crystalline substrate is manufactured.

[0036] The polishing process (S4) is carried out, for example, by polishing the single-crystalline thin plate with a polishing device. By polishing, the surface roughness of the processed surface (polished surface) can be made Sa0.1 nm to 0.3 nm. Note that a known device can be used as the polishing device. For example, the polishing device attaches or adsorbs and fixes the back surface of the single-crystalline thin plate to the block of the upper platen, presses the block against the lower platen with an abrasive cloth attached, supplies abrasive liquid from the abrasive liquid supply part between the surface of the single-crystalline thin plate and the abrasive cloth, and rotates the single-crystalline thin plate and the abrasive cloth with a rotating shaft to mirror-finish the single-crystalline thin plate.

[0037] When mirror-finishing only one side of the single-crystalline thin plate, for example, a plurality of single-crystalline thin plates are fixed with wax or the like to a block such as ceramic. As a means for fixing and holding the single-crystalline thin plate on the surface not to be polished, in addition to the method of water adsorption and bonding the single-crystalline thin plate to a block such as ceramic, a method of providing suction holes in the substrate holding part of the ceramic block and vacuum-adsorbing the single-crystalline thin plate may also be used.

[0038] In this manufacturing method, between the steps of the above steps, steps of well-known techniques, for example, a beveling step, a reduction treatment step, an etching step, an edge polishing step, etc. of well-known techniques may be added as necessary. For example, a disk-shaped single-crystalline thin plate manufactured by slicing has corners at the upper and lower ends of the outer peripheral edge, so it is prone to cracking and chipping. Therefore, bevel processing (bevelling processing) may be performed on the outer peripheral edge of the single-crystalline thin plate in the bevel step to chamfer the outer peripheral edge of the single-crystalline thin plate.

[0039] As described above, the method for manufacturing a piezoelectric oxide single crystal substrate according to the present embodiment is a method for manufacturing a piezoelectric oxide single crystal substrate, including a slicing step of slicing an ingot of a piezoelectric oxide single crystal into a thin plate-shaped single crystal thin plate, a surface grinding step of planar grinding the front and back surfaces of the single crystal thin plate produced in the slicing step, a blasting step of blasting the back surface on the side opposite to the main surface of the single crystal thin plate subjected to the planar grinding, and a polishing step of mirror-finishing the main surface of the single crystal thin plate subjected to the planar grinding. In the method for manufacturing a piezoelectric oxide single crystal substrate of the present embodiment, the configuration other than the above is an arbitrary configuration.

[0040] According to the method for manufacturing a piezoelectric oxide single crystal substrate according to the present embodiment, in the method for manufacturing a piezoelectric oxide single crystal substrate with a single-sided mirror polishing specification, it is possible to replace the conventional lapping process with a surface grinding process, and it is possible to suppress the influence of spurious caused by reflection when the bulk wave generated when the piezoelectric oxide single crystal substrate is used as a SAW filter is diffusely reflected on the back surface of the substrate, and a piezoelectric oxide single crystal substrate can be manufactured.

[0041] In addition, the method for manufacturing a piezoelectric oxide single crystal substrate of the present embodiment can be suitably used for a lithium tantalate single crystal or a lithium niobate single crystal, which is a brittle material. Further, since the method for manufacturing a piezoelectric oxide single crystal substrate advances the processing of the substrate by surface grinding without performing lapping, the problems caused by the above-described lapping can be solved. For example, in this manufacturing method, it is possible to suppress the number of personnel required for attaching and detaching the single crystal substrate in the lapping process. In addition, the method for manufacturing a piezoelectric oxide single crystal substrate can prevent the substrate from cracking due to lapping. This manufacturing method can be suitably used for a lithium tantalate single crystal or a lithium niobate single crystal, which is a brittle material and is prone to cracking. Furthermore, although lapping is a batch process and automation is difficult, the surface grinding process is easy to automate with a loading device or the like, and unmanned operation can be promoted.

Example

[0042] Hereinafter, the present invention will be specifically described using examples of the present invention, but the present invention is not limited to these examples at all.

[0043] (Example 1) An LT single crystal grown by the Czochralski method was annealed and polished, and a 6-inch diameter LT single crystal ingot subjected to end cutting and cylindrical grinding was prepared.

[0044] After using this LT single crystal ingot, an LT single crystal substrate was fabricated. First, it was sliced to a thickness of 0.43 mm using a wire saw to produce a single crystal thin plate.

[0045] Next, double-sided surface grinding was performed on both sides using a #2000 grinding wheel in a surface grinding apparatus (manufactured by DISCO Corporation) until the thickness reached approximately 0.365 mm.

[0046] Thereafter, using a wet blasting apparatus, only the back surface was subjected to wet blasting treatment with a slurry of WA#1000 abrasive grains at an air pressure of 0.2 MPa to roughen the back surface.

[0047] Thereafter, while discharging colloidal silica using a polishing apparatus, only one side (main surface) opposite to the surface roughened by blasting was mirror-polished to obtain a single crystal substrate.

[0048] Thereafter, using a laser microscope (manufactured by Olympus Corporation), the surface roughness at five points in the plane shown in FIG. 3 was measured for the back surface of the single crystal substrate. Two single crystal substrates were measured, and the measurement results are shown in Table 1 as Example 1-1 and Example 1-2.

[0049] In addition, a SAW filter was fabricated using the obtained single crystal substrate, and bulk waves were diffusely reflected from the back surface of the substrate to confirm the influence of spurious due to reflection. As a result, the single crystal substrate of Example 1 was able to suppress spurious as well as a SAW filter using a conventional single crystal substrate subjected to lapping processing of Reference Example 1 described below.

[0050] (Reference Example 1) Similar to Example 1, an LT single crystal ingot was sliced to obtain a single crystal thin plate. After chamfering the obtained single crystal thin plate by beveling the outer circumference and the orifice portion, it was processed with a #1000 abrasive grain using a lapping and polishing apparatus. The obtained substrate was evaluated in the same manner as in Example 1. The measurement results are shown in Table 1 respectively.

[0051] [Table 1]

[0052] From the results of the above Examples and Reference Examples, according to the manufacturing method of the present embodiment, in the manufacturing method of a piezoelectric oxide single crystal substrate with a single-sided mirror finish specification, it is possible to replace the conventional lapping process with a surface grinding process, and when the piezoelectric oxide single crystal substrate is used as a SAW filter, it is possible to suppress the influence of spurious caused by reflection when the bulk wave is diffusely reflected from the back surface of the substrate. It is confirmed that a piezoelectric oxide single crystal substrate can be manufactured.

[0053] Note that the technical scope of the present invention is not limited to the aspects described in the above embodiments and the like. One or more of the requirements described in the above embodiments and the like may be omitted. Also, the requirements described in the above embodiments and the like can be combined as appropriate. Further, to the extent permitted by law, the disclosures of all the documents cited in the above embodiments and the like are incorporated by reference and made part of the description of the present text.

Claims

1. A method for manufacturing a piezoelectric oxide single crystal substrate, a slicing step of slicing an ingot of a piezoelectric oxide single crystal into a thin single crystal sheet, a surface grinding step of surface grinding the front and back surfaces of the single crystal sheet produced in the slicing step, a blasting step of blasting the back surface on the side opposite to the main surface of the single crystal sheet subjected to the surface grinding, and a polishing step of mirror polishing the main surface of the single crystal sheet subjected to the surface grinding, the method for manufacturing a piezoelectric oxide single crystal substrate.

2. The method for manufacturing a piezoelectric oxide single crystal substrate according to claim 1, wherein the blasting is wet blasting.

3. The method for manufacturing a piezoelectric single crystal according to claim 1, wherein the piezoelectric oxide single crystal is a lithium tantalate single crystal or a lithium niobate single crystal.

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