Method for manufacturing piezoelectric single crystal substrate

Abstract

To provide a method for manufacturing a piezoelectric single crystal substrate, capable of controlling the piezoelectric single crystal substrate to a predetermined volume resistivity for improving a fault due to pyroelectricity and continuously preventing poor color unevenness from occurring even while reducing a plurality of lots.SOLUTION: A method for manufacturing a piezoelectric single crystal substrate comprises: the previous heating step of heating aluminum powder and aluminum oxide powder to reduce a water content included in the powders and the amount of impurities adhering to the powders; and the reduction step of embedding a substrate-like piezoelectric single crystal into the mixture of the aluminum powder and aluminum oxide powder subjected to the previous heating and performing reduction heated at a temperature less than the curie temperature.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a piezoelectric single crystal substrate such as a lithium tantalate substrate or a lithium niobate substrate. [Background technology]

[0002] Lithium tantalate (hereinafter sometimes abbreviated as LT) single crystals and lithium niobate (hereinafter sometimes abbreviated as LT) single crystals are ferroelectric and have piezoelectric properties, and lithium tantalate substrates and lithium niobate substrates manufactured using these single crystals are mainly used as materials for surface acoustic wave (SAW) filters used in transmitting and receiving devices for mobile phones.

[0003] The above-mentioned LT single crystals and LN single crystals are mainly grown industrially by the Czochralski method. The method for growing LT single crystals will be explained below as an example. LT single crystals are grown by the Czochralski method in an electric furnace in a nitrogen-oxygen mixed gas atmosphere with an oxygen concentration of about several percent to 20%, usually using a high-melting-point iridium crucible. After growth, the crystals are cooled in the electric furnace at a predetermined cooling rate and then removed from the electric furnace.

[0004] The grown LT single crystal is colorless and transparent or has a highly transparent pale yellow color. After growth, to remove residual strain due to thermal stress in the crystal, it is heat-treated under soaking at a temperature close to the melting point, and then a poling process is carried out to achieve a single polarization. This involves a series of processes: heating the LT single crystal from room temperature to a predetermined temperature above the Curie temperature, applying a voltage to the crystal, cooling it to a predetermined temperature below the Curie temperature while still applying the voltage, then stopping the voltage application and cooling it to room temperature. After the poling process, the LT single crystal (called an ingot) is ground to adjust its outer diameter, and then machined to become a substrate through processes such as slicing, lapping, and polishing. The final substrate is nearly colorless and transparent, and its volume resistivity is approximately 10 14 ~10 15 It is about Ω·cm.

[0005] In the surface acoustic wave element (SAW filter) manufacturing process, substrates obtained by such conventional methods exhibit a pronounced pyroelectric effect, which is a characteristic of piezoelectric single crystals. As a result, electric charges build up on the substrate surface due to temperature changes experienced during the process. This causes discharges that destroy the comb-shaped electrodes formed on the substrate surface and even cause cracks in the substrate, resulting in a decrease in yield in the element manufacturing process.

[0006] To address the pyroelectric drawbacks of piezoelectric single crystals, several techniques for increasing their electrical conductivity have been proposed. For example, Patent Document 1 proposes a method of embedding a substrate in a mixture of aluminum powder (Al powder) and aluminum oxide powder (Al2O3 powder) and then reducing it. This reduction process is generally performed after the single crystal has been sliced and processed into a disk-shaped substrate. Furthermore, LT substrates with increased electrical conductivity absorb light due to the introduction of oxygen vacancies. The observed color appears reddish-brown in transmitted light and black in reflected light; therefore, the reduction process that increases electrical conductivity is also called a blackening process. This color change phenomenon is also called blackening. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4063191 [Patent Document 2] Japanese Patent Publication No. 2020-040840 Summary of the Invention [Problem to be solved by the invention]

[0008] In the method of Patent Document 1, in which the substrate is embedded in a mixed powder of Al powder and Al2O3 powder and then reduced, lithium niobate substrates with a melting point of approximately 1250°C and lithium tantalate substrates with a high melting point of approximately 1650°C can have varying volume resistivities depending on the production lot of the Al2O3 powder. For this reason, the Al powder ratio in the mixed powder is adjusted to match the production lot of the Al2O3 powder to achieve a predetermined volume resistivity, which reduces productivity. Furthermore, when the Al powder ratio in the mixed powder is set higher than 20%, black dots (color unevenness defects) with a diameter of approximately 1 to 5 mm occur, further reducing productivity. The color unevenness (color unevenness defects) is due to uneven reduction (reduction unevenness).

[0009] Patent Document 2 describes a method in which a substrate is embedded in a mixed powder of Al powder and Al2O3 powder and then reduced, in which the Al2O3 powder is dried and then humidified before the reduction process to control the moisture content of the Al2O3 powder to a predetermined amount, and then reduced. It was found that by drying the Al2O3 powder before the reduction process, it is possible to reduce variation between production lots of Al2O3 powder and to some extent the occurrence of color unevenness.

[0010] However, even if the Al2O3 powder is dried before the reduction treatment and then reduced, localized color unevenness may occur during the production of multiple lots.

[0011] The present invention has been made in view of the above problems, and aims to provide a method for manufacturing a piezoelectric single crystal substrate that can control the volume resistivity to a predetermined value to improve the above-mentioned defects due to pyroelectricity, and can continuously suppress the occurrence of color unevenness defects even when multiple lots are subjected to reduction treatment. [Means for solving the problem]

[0012] According to an aspect of the present invention, there is provided a method for producing a piezoelectric single crystal substrate, comprising: a pre-heat treatment step of heat-treating aluminum powder and aluminum oxide powder to reduce the amount of moisture contained in the powder and impurities adhering to the powder; and a reduction treatment step of embedding a substrate-shaped piezoelectric single crystal in a mixed powder of the pre-heat-treated aluminum powder and aluminum oxide powder, and then performing a reduction treatment by heat-treating the substrate at a temperature below the Curie temperature.

[0013] In the method for producing a piezoelectric single crystal substrate according to the present invention, the preliminary heat treatment is preferably performed on a mixed powder of aluminum powder and aluminum oxide powder. The temperature of the preliminary heat treatment is preferably 500°C or higher and 600°C or lower. The heating holding time of the preliminary heat treatment is preferably 12 hours or higher and 30 hours or lower. The volume resistivity of the piezoelectric single crystal substrate obtained by the reduction treatment is preferably 10 8 Ω cm or more 10 10 It is preferable that the resistivity is Ω·cm or less. [Effects of the Invention]

[0014] The method for manufacturing a piezoelectric single crystal substrate according to an embodiment of the present invention can control the volume resistivity to a predetermined value to improve defects caused by pyroelectricity, and can continuously suppress the occurrence of color unevenness defects even when multiple lots are subjected to reduction treatment. [Brief explanation of the drawings]

[0015] [Figure 1] 10 is a graph showing the results of comparing the transition of the pressure inside the furnace depending on whether or not a mixed powder of Al powder and Al2O3 powder is subjected to a pre-heat treatment. DETAILED DESCRIPTION OF THE INVENTION

[0016] Specific embodiments of the present invention will be described in detail below. The present invention is not limited to the following embodiments, and can be modified as appropriate without departing from the spirit of the present invention. In the drawings, some or all of the drawings are shown schematically and scales are changed as appropriate. In the following description, the expression "A to B" means "A or more and B or less."

[0017] In the present invention, it has been discovered that in a method of embedding a single crystal substrate in a mixed powder of aluminum powder (Al powder) and aluminum oxide powder (Al2O3 powder) and performing a reduction treatment, the mixed powder used in this method is pre-heat-treated, thereby enabling the reduction treatment to be carried out stably. The method for producing a piezoelectric single crystal substrate of this embodiment (hereinafter sometimes abbreviated as "this production method") will be described in detail below.

[0018] The single crystal substrate that can be used in this manufacturing method is a single crystal substrate (piezoelectric single crystal substrate) that uses a piezoelectric single crystal having piezoelectric properties, such as a lithium tantalate single crystal (LT single crystal), a lithium niobate single crystal (LN single crystal), etc. Below, an example of a lithium tantalate substrate will be explained.

[0019] This manufacturing method comprises the following three steps (A) to (C). (A) Mixing process of aluminum powder and aluminum oxide powder (B) Pre-heat treatment process of mixed powder (C) Reduction treatment process of piezoelectric single crystal substrate using pre-heat-treated mixed powder Each step will be described below.

[0020] (A) Mixing process of aluminum powder (Al powder) and aluminum oxide powder (Al2O3 powder) The mixing step involves mixing aluminum powder and aluminum oxide powder in a predetermined ratio to obtain a mixed powder. The mixing ratio of aluminum powder and aluminum oxide powder (hereinafter sometimes abbreviated as "mixing ratio") is such that, when the total mass of the mixed powder is converted to 100 mass%, the proportion of Al powder (hereinafter sometimes abbreviated as "Al powder proportion") is preferably less than 25 mass%, more preferably 20 mass% or less, and even more preferably in the range of 5 to 20 mass%. When the Al powder proportion is 25 mass% or more, sufficient conductivity (volume resistivity) can be obtained, but as the Al powder proportion increases, the incidence of black dots (color unevenness defects) about 1 to 5 mm in diameter tends to increase.

[0021] It should be noted that the volume resistivity of the substrate after reduction treatment may vary even under the same conditions due to variations in the Al2O3 powder and Al powder between lots, storage conditions, variations in the LT substrates used for reduction treatment, etc. Therefore, it is preferable to first carry out reduction treatment on a small amount of single crystal substrates, check the volume resistivity of the substrate after reduction treatment, and then adjust the Al powder ratio in the mixed powder so that the predetermined volume resistivity is achieved. The volume resistivity of the substrate after reduction treatment can be, for example, 10 8 ~10 10 When the volume resistivity is within the above range, the properties of the piezoelectric material are maintained and the above-mentioned problems caused by pyroelectricity can be eliminated.

[0022] The mixed powder is then pre-heat-treated in the next step. As will be described in detail later, pre-heat-treatment reduces the moisture and organic components in the mixed powder. For this reason, it has been found that the reduction ability of pre-heat-treated mixed powder is reduced compared to mixed powder that has not been pre-heat-treated. Therefore, when pre-heat-treating the mixed powder, it is preferable to increase the Al powder concentration compared to when pre-heat-treatment is not performed. For example, the Al powder concentration may be increased by 2 to 5% by weight compared to when pre-heat-treatment is not performed.

[0023] The Al powder and Al2O3 powder used in the mixing step can be the same as those used in conventional methods. Furthermore, there are no particular limitations on the method for mixing the Al powder and Al2O3 powder. Existing techniques and devices can be used. In the manufacturing method of this embodiment, as will be described later, the Al powder and the Al2O3 powder may be pre-heat-treated separately without being mixed.

[0024] (B) Pre-heat treatment process of mixed powder This step is a step of heat-treating a mixed powder obtained by mixing Al powder and Al2O3 powder in a predetermined ratio in the previous step. In this step, the mixed powder obtained by mixing Al powder and Al2O3 powder is placed in a container or the like and heat-treated in an electric furnace. Since the melting point of Al powder is 660°C, the heat treatment is carried out at a temperature at which the Al powder does not melt. The heat treatment temperature is less than 660°C, preferably 500°C to 600°C.

[0025] The moisture in the mixed powder can be removed if the treatment temperature is 300°C or higher, but it is more preferable to carry out the treatment at a temperature of 500°C to 600°C, as this makes it possible to remove impurities adhering to the Al powder and Al2O3 powder.

[0026] When Al powder or Al2O3 powder is heat treated, impurities are generated as gas. Therefore, to confirm what kind of gas is being generated, TG-MS (thermobalance-mass spectrometry) was used, and small amounts of organic matter-derived gas and hydrogen-derived gas were detected from the Al powder, while organic matter-derived gas was detected from the Al2O3 powder. The organic matter-derived gas is thought to be due to organic components adhering to the powder surface. Hydrogen gas is thought to be generated by the reaction of Al with water (Equation 1). Furthermore, when Al(OH)3 exceeds 200°C, it decomposes by dehydration into Al2O3 and water (Equation 2). 2Al+6H2O → 2Al(OH)3+3H2...(Formula 1) 2Al(OH)3→ Al2O3+3H2O (Formula 2)

[0027] It is believed that organic gases and hydrogen gases derived from these powders contribute to reduction and are the cause of color unevenness within the LT substrate surface. Therefore, this manufacturing method performs a heat treatment (pre-heat treatment) on the Al powder and Al2O3 powder before using them in the reduction process, thereby removing organic and hydrogen-derived gases generated from the Al powder and organic gases generated from the Al2O3 powder, thereby reducing color unevenness defects caused by these gases. In this manufacturing method, the pre-heat treatment reduces the amount of moisture contained in the powder and the amount of impurities attached to the powder, thereby reducing color unevenness defects caused by gases.

[0028] In this manufacturing method, it is also possible to pre-heat treat the Al powder and Al2O3 powder separately, rather than mixing them as a powder mixture. However, if pre-heat treatment is performed on the Al powder alone, the Al powder particles tend to bond together. This is particularly noticeable at temperatures above 500°C, which is close to the melting point of Al (approximately 660°C). For this reason, by mixing the Al powder and Al2O3 powder and dispersing the Al powder within the Al2O3 powder before heat treatment, bonding of the Al powder particles to each other can be prevented, and heat treatment can be performed at a temperature close to the melting point of Al.

[0029] The heating and holding time (holding time) depends on the amount of Al powder and Al2O3 powder to be pre-heat-treated, but is set appropriately so that the gases can be removed uniformly. The holding time is preferably 12 to 30 hours, and more preferably 12 to 24 hours.

[0030] As noted in Patent Document 2, impurities adhering to Al2O3 powder can be completely removed by heat-treating the powder at around 1000°C. However, the preferred heating temperature range for both Al and Al2O3 powders in this manufacturing method is 500°C to 600°C. This heat treatment leaves some impurities in the mixed powder. Therefore, to confirm the amount of gas generated by this heat treatment, we investigated the change in pressure inside the heat treatment furnace. Figure 1 shows the results of comparing the changes in furnace pressure between pre-heat-treated and non-pre-heat-treated mixed powders of Al and Al2O3 powders. In the investigation shown in Figure 1, the pre-heat-treated mixed powders were pre-heat-treated at 580°C for 24 hours. These powders were then placed in a heat treatment furnace, where they were heated to 560°C over three hours and then to 580°C over one hour. The changes in furnace pressure are shown. As shown in Figure 1, the pressure gradually increases when the furnace temperature is above 500 °C. The peak pressure is 320 Pa without pre-heat treatment, but is reduced to 170 Pa with the pre-heat-treated mixed powder. This indicates that the amount of gas generated is reduced by the pre-heat treatment. However, it is also clear that a certain amount of gas is generated even with the pre-heat-treated mixed powder of this embodiment. Because organic gases and hydrogen gas derived from these powders contribute to the reduction, in this manufacturing method, it is preferable to adjust the pre-heat treatment so that a certain amount of gas is generated from the pre-heat-treated mixed powder during the reduction treatment. That is, in this manufacturing method, it is preferable to reduce the moisture contained in the powder and impurities attached to the powder during the pre-heat treatment, and adjust the pre-heat treatment so that some of the impurities remain. This allows the gas derived from the pre-heat-treated powder to be effectively used in the reduction reaction during the reduction treatment. This simplifies the process, eliminating the need for heat treatment of Al2O3 powder at around 1000 °C and humidification to achieve a predetermined moisture content after complete impurity removal, as described in Patent Document 2.

[0031] As a result of conducting several tests, the inventors have confirmed that, as an example of the conditions for the pre-heat treatment of a mixed powder of Al powder and Al2O3 powder, if the treatment temperature is 500°C to 600°C and the holding time is 12 to 30 hours, the occurrence of local color unevenness can be suppressed without humidification treatment. In the manufacturing method of this embodiment, when the treatment temperature and holding time are set as described above, the effects of this embodiment can be stably exhibited.

[0032] The pre-heat treatment is preferably carried out in a vacuum or in an inert gas atmosphere, since Al powder is prone to oxidation. Argon gas or nitrogen gas can be used as the inert gas.

[0033] Furthermore, from the viewpoint of maintaining a predetermined reducing power, the pre-heat-treated mixed powder is preferably subjected to the subsequent reduction treatment within two days, more preferably within one day. Care must be taken when storing the pre-heat-treated mixed powder for a long period of time, as it may absorb moisture from the surrounding environment. If the pre-heat-treated mixed powder is stored for more than two days, it must be stored in a low-humidity environment or pre-heat-treated again before use.

[0034] (C) Reduction treatment process of piezoelectric single crystal substrate using pre-heat-treated mixed powder The reduction treatment process involves embedding the LT substrate in a mixture of preheat-treated Al powder and Al2O3 powder, and then heat-treating it at a temperature below the Curie temperature to perform reduction. The ratio of Al powder to Al2O3 powder in the mixture is as described above. The heat treatment temperature is set below the Curie temperature. For example, in the case of an LT substrate, the Curie temperature is approximately 600°C, and the heat treatment temperature is set below 600°C. The heat treatment atmosphere may be a vacuum or an inert gas atmosphere, or an atmospheric pressure atmosphere in which an inert gas is continuously supplied and exhausted. When a vacuum or an inert gas atmosphere is used, heat inside the heating furnace tends to accumulate in one place, causing uneven reduction. Therefore, it is preferable to continuously supply and exhaust an inert gas into the heating furnace under an atmospheric pressure atmosphere. Continuous supply of an inert gas can ensure uniform heat distribution inside the furnace. The inert gas can be argon gas, nitrogen gas, or the like. When the inert gas is argon gas, the flow rate of the inert gas continuously supplied and exhausted into the heating furnace is preferably 0.5 to 5 L / min. In this manufacturing method, the volume resistivity of the substrate obtained by the reduction treatment step can be controlled within a predetermined range. For example, 8 Ω cm or more 10 10 It can be controlled to Ω·cm or less.

[0035] As described above, the method for producing a piezoelectric single crystal substrate according to this embodiment is a method for producing a piezoelectric single crystal substrate, and includes a pre-heat treatment step of heat-treating aluminum powder and aluminum oxide powder to reduce the amount of moisture contained in the powder and impurities adhering to the powder, and a reduction treatment step of embedding a substrate-shaped piezoelectric single crystal in a mixed powder of aluminum powder and aluminum oxide powder that has been pre-heat-treated, and then performing a reduction treatment by heat-treating the substrate at a temperature below the Curie temperature. Note that in the method for producing a piezoelectric single crystal substrate according to this embodiment, configurations other than those described above are optional.

[0036] In the manufacturing method of this embodiment, aluminum powder and aluminum oxide powder are pre-heat-treated to reduce the amount of moisture contained in the powder and the amount of impurities adhering to the powder, while maintaining a certain level of impurities. By performing a reduction process using the pre-heat-treated aluminum powder and aluminum oxide powder, the volume resistivity after the reduction process of the single crystal substrate can be stabilized and controlled to a predetermined volume resistivity to improve defects due to pyroelectricity, and the occurrence of localized color unevenness defects can be continuously suppressed even when multiple lots are subjected to the reduction process. [Example]

[0037] The present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples in any way.

[0038] [Example 1] Using raw materials with a congruent composition, LT single crystals with a diameter of 4 inches were grown by the Czochralski method. The growth atmosphere was a nitrogen-oxygen mixed gas with an oxygen concentration of approximately 3%. The resulting LT crystal ingot was transparent and pale yellow in color.

[0039] This LT crystal ingot was subjected to heat treatment to remove thermal distortion and poling to obtain a single polarization, after which the outer periphery was ground, sliced, and polished to obtain a 42°RY (Rotated Y axis) LT substrate. The obtained 42°RY LT substrate was colorless and transparent, with a volume resistivity of 10 15 The surface roughness was Ω·cm and the Curie temperature was 603°C. This substrate was then subjected to a reduction treatment.

[0040] First, Al powder and Al2O3 powder were mixed. Aluminum powder with an average particle size of 100 μm and Al2O3 powder with an average particle size of 52 μm were prepared. The average particle size was measured using a laser diffraction particle size distribution analyzer.

[0041] The Al powder and Al2O3 powder were weighed and mixed so that the ratio of Al powder was 5% by weight to 25% by weight. The ratio of Al powder and Al2O3 powder was determined by reducing a small amount of single crystal substrate to a volume resistivity of 10 8 ~1010 The volume resistivity was adjusted to Ω·cm. The volume resistivity was measured using the three-terminal method in accordance with JIS K-6911.

[0042] Next, the mixed powder, mixed at a predetermined ratio, was pre-heat-treated. The mixed powder was placed in a container, placed in a heat treatment furnace, and treated at a treatment temperature of 580°C for 24 hours in an argon gas atmosphere.

[0043] The pre-heat-treated mixed powder was used and subjected to a reduction treatment within one day of the pre-heat treatment. A disk-shaped substrate was placed in a stainless steel container and embedded in the pre-heat-treated mixed powder, and the container was placed in a heating furnace equipped with an air inlet and an exhaust port. Commercially available argon gas was continuously supplied into the heating furnace through the air inlet, and the argon gas was continuously exhausted out of the heating furnace through the exhaust port, maintaining the interior of the heating furnace at atmospheric pressure. The flow rate of argon gas supplied to and exhausted from the heating furnace was set to 2 L / min.

[0044] In the reduction treatment, the temperature of the heating furnace was set to 580°C, and argon gas was supplied for 24 hours. 200 substrates were treated in the same way at one time, and the occurrence rate of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots. As a result, the treated substrates had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0045] [Comparative Example 1] In the pre-heat treatment of Example 1, only Al2O3 powder was placed in a container and placed in a heat treatment furnace, and treated at a treatment temperature of 580 °C for 24 hours. After that, it was mixed with Al powder in a predetermined ratio, and then a reduction treatment was performed without pre-heat treatment. The rest was the same as Example 1.

[0046] The same method was used to process 200 substrates at a time, and the incidence of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots.

[0047] As a result, the treated substrate had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0048] Comparative Example 2 In Example 1, Al powder and Al2O3 powder were mixed in a predetermined ratio, and then a reduction treatment was carried out without carrying out a preliminary heat treatment.

[0049] The same method was used to process 200 substrates at a time, and the incidence of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots.

[0050] As a result, the treated substrate had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0051] [Example 2] In Example 1, the size of the LT single crystal was changed from 4 inches to 6 inches. The rest was the same as in Example 1.

[0052] The same method was used to process 200 substrates at a time, and the incidence of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots.

[0053] As a result, the treated substrate had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0054] Comparative Example 3 In the pre-heat treatment of Example 2, only the Al2O3 powder was placed in a container and placed in a heat treatment furnace, and treated at a treatment temperature of 580°C for 24 hours. After that, it was mixed with Al powder in a predetermined ratio, and then a reduction treatment was performed without pre-heat treatment. The rest was the same as Example 2.

[0055] The same method was used to process 200 substrates at a time, and the incidence of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots.

[0056] As a result, the treated substrate had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0057] Comparative Example 4 In Example 2, Al powder and Al2O3 powder were mixed in a predetermined ratio, and then a reduction treatment was carried out without a preliminary heat treatment. The other conditions were the same as in Example 2.

[0058] The same method was used to process 200 substrates at a time, and the incidence of color unevenness was investigated. This was done five times using Al powder and Al2O3 powder from different production lots.

[0059] As a result, the treated substrate had a volume resistivity of 10 8 ~10 10 The incidence of localized color unevenness is shown in Table 1.

[0060] [Table 1]

[0061] As shown in Table 1, by pre-heat-treating the Al powder and Al2O3 powder, the volume resistivity after the reduction treatment of the single crystal substrate can be stabilized and the occurrence of the above-mentioned local color unevenness defect can be continuously suppressed.

[0062] The technical scope of the present invention is not limited to the aspects described in the above-mentioned embodiments. One or more of the requirements described in the above-mentioned embodiments may be omitted. The requirements described in the above-mentioned embodiments may be combined as appropriate. Furthermore, to the extent permitted by law, the disclosures of all documents cited in the above-mentioned embodiments are incorporated by reference into this specification.

Claims

1. A method for manufacturing a piezoelectric single crystal substrate, comprising: a preliminary heat treatment step of heat treating the aluminum powder and aluminum oxide powder to generate and remove the moisture contained in the powder and the impurities adhering to the powder as gas, thereby reducing the amount of moisture contained in the powder and the impurities adhering to the powder; a reduction treatment step of embedding a substrate-shaped piezoelectric single crystal in a mixed powder of aluminum powder and aluminum oxide powder that has been subjected to the pre-heat treatment, and performing a reduction treatment by heat treatment at a temperature below the Curie temperature.

2. 2. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the preliminary heat treatment is performed on a mixed powder obtained by mixing aluminum powder and aluminum oxide powder in a predetermined ratio.

3. 3. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the temperature of the preliminary heat treatment is 500° C. or higher and 600° C. or lower.

4. 4. The method for producing a piezoelectric single crystal substrate according to claim 1, wherein the heating and holding time of the preliminary heat treatment is 12 hours or more and 30 hours or less.

5. The volume resistivity of the piezoelectric single crystal substrate obtained by the reduction treatment is 10 ８ Ω・cm or more 10 １０ The method for producing a piezoelectric single crystal substrate according to claim 1 , wherein the resistivity is Ω·cm or less.

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