JP2017065951A - Lithium tantalate single crystal and manufacturing method of same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium tantalate single crystal used for a substrate of a surface acoustic wave (SAW) device and capable of improving a thermal property, and a manufacturing method of the same.SOLUTION: A lithium tantalate single crystal is provided, the Li site or Ta site of which is partly substituted by a Ga element, and Ga content in the single crystal is 0.01 wt% or more and 0.3 wt% or less. A saw filter using the lithium tantalate single crystal is provided.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a lithium tantalate single crystal and a method for manufacturing the same, and more particularly, to a lithium tantalate single crystal that can be used for a surface acoustic wave (SAW) device substrate and the like and can improve temperature characteristics. It relates to a manufacturing method.

  Lithium tantalate single crystals are known as substrate materials for SAW filters, vibrators, and transmitters. In recent years, with the enhancement of the performance of mobile phones, the demand for higher performance of SAW filters used in transmission / reception devices has become stricter. For example, in applications where high power is applied to a device such as an antenna duplexer, improvement in temperature characteristics is required in addition to low loss and high suppression in order to improve the performance of SAW filters.

  A lithium tantalate (hereinafter, abbreviated as LT) substrate has a large electromechanical coupling coefficient indicating the conversion efficiency between vibration energy and electrical energy of SAW, which is advantageous in device design. This is because the temperature dependency is large and the frequency characteristics of the device are likely to change with temperature.

  The center frequency f of the SAW filter is expressed by f = v / λ where the sound velocity (propagation velocity) of the surface acoustic wave is v and the period of the IDT (Inter Digital Transducer) electrode is λ. Due to the thermal expansion of the LT substrate, the electrode period changes and the center frequency f shifts. Due to the frequency shift due to this temperature, it has been pointed out that a problem of greatly reducing the S / N occurs, for example, the transmission frequency band of the transmission wave filter is in the wavelength range of the reception wave. There is a need for improved properties.

Therefore, in order to improve the temperature characteristics of the LT single crystal, a method has been proposed in which a material having a smaller thermal expansion coefficient than that of the LT single crystal is bonded to the LT single crystal to suppress the thermal expansion of the single crystal (Patent Documents 1 to 3). 3).
For example, in Patent Document 1, two substrates having a difference in linear thermal expansion coefficient within a specific value are used, and a cut is formed on either substrate to relieve stress. In Patent Document 2, an LT substrate and a sapphire substrate are provided. Are bonded to each other, and an amorphous bonding region is provided at the interface, and in Patent Document 3, it is proposed that the piezoelectric substrate and the Si support substrate whose surface is oxidized with a specific thickness are bonded together via an adhesive layer. ing.

  However, since the substrates manufactured by these methods are bonded with materials having different thermal expansion coefficients, cracks are generally generated in the SAW device manufacturing process that undergoes a thermal history of about 300 ° C., which only deteriorates the yield. In addition, the substrate becomes thick and it is difficult to achieve a low device height. Furthermore, there is a problem that the low thermal expansion material to be bonded to the LT substrate, the cost of the bonding process, and the yield are reduced in the bonding process.

  Therefore, the present applicant has proposed to add a specific amount of Ni to the LT substrate (see Patent Document 4), and was able to improve the sonic temperature dependency of the crystal at low cost. However, the addition of nickel, which is an iron-based metal, has a problem that the thermal conductivity is lowered and the heat dissipation of the LT substrate is deteriorated.

  Under such circumstances, there is a need for a lithium tantalate single crystal for an LT substrate that not only can improve the sonic temperature dependency of the crystal but also does not lower the thermal conductivity like iron or nickel. ing.

JP 2003-124767 A JP 2005-252550 A JP 2005-347295 A JP 2010-280525 A

  In view of the above-described problems, an object of the present invention is to provide a lithium tantalate single crystal that can be used for a surface acoustic wave (SAW) device substrate and the like and can improve temperature characteristics, and a method for manufacturing the same.

  As a result of intensive studies to solve the above-mentioned problems, the present inventor searched for an element that replaces the Li site or Ta site without changing the crystal structure of the LT single crystal, and improved the temperature characteristics of the LT single crystal. When the effect was investigated, it was found that the thermal conductivity of the grown crystal is increased by adding a specific amount of gallium (Ga) for substituting the Li site to the raw material melt for growing the LT single crystal. By using Ga-doped crystal as the substrate of the SAW device, Joule heat generated in the IDT electrode of the device is efficiently exhausted and the temperature characteristics of the SAW device are improved, thereby completing the present invention. It was.

  That is, according to the first invention of the present invention, a part of the Li site or Ta site of the lithium tantalate single crystal is substituted with the gallium (Ga) element, and the gallium (Ga) content in the single crystal Is in the range of 0.01 wt% or more and 0.3 wt% or less. A lithium tantalate single crystal is provided.

  According to the second invention of the present invention, the tantalum acid according to the first invention of the present invention is characterized in that the thermal conductivity of the single crystal is 4.0 to 4.5 W / m · K. A lithium single crystal is provided.

  According to the third invention of the present invention, in the first or second invention of the present invention, a gallium raw material powder as a dopant is added to a raw material powder of a lithium tantalate single crystal, and the Czochralski method is used. A method for producing a lithium tantalate single crystal for growing crystals, wherein the gallium raw material powder is added so that the Ga concentration in the raw material melt is 0.05 wt% or more and 1.5 wt% or less. A method for producing a featured lithium tantalate single crystal is provided.

According to a fourth aspect of the present invention, there is provided the method for producing a lithium tantalate single crystal according to the third aspect of the present invention, wherein the gallium raw material powder is a Ga ₂ O ₃ powder. Is done.

  The fifth aspect of the present invention provides a SAW filter using the lithium tantalate single crystal of the first or second aspect of the present invention as a substrate.

  According to the present invention, a lithium tantalate single crystal having a high thermal conductivity can be produced relatively easily. In addition, the temperature characteristics can be improved as compared with the conventional lithium tantalate substrate, and the cost of the SAW device can be reduced.

It is the schematic of the SAW device produced on the board | substrate for the sound speed measurement. It is the graph which showed the relationship between Ga addition amount to a LT single crystal, and thermal conductivity. It is the schematic which showed the SAW filter typically.

  Hereinafter, specific embodiments of the lithium tantalate single crystal of the present invention, a manufacturing method thereof, and a SAW filter will be described.

1. Lithium tantalate single crystal That is, the lithium tantalate single crystal of the present invention contains gallium (Ga) as a dopant in the range of 0.01 wt% to 0.3 wt%.

  In the present invention, gallium (Ga) is added as an element to replace the Li site or Ta site without changing the crystal structure of the LT crystal, and the SAW characteristics such as the electromechanical coupling coefficient and the sound speed in the LT substrate are maintained. However, the thermal conductivity of the crystal is increased, and the temperature characteristics of the crystal can be improved.

  The crystal structure of the LT crystal has a deformed ilmenite structure, and Ga, which is a substitution element, has an intermediate ionic radius between Li and Ta, so that distortion of the crystal structure due to substitution can be reduced. Further, Ga is easy to grow as a doping material for the LT raw material, and is effective for improving the sonic temperature coefficient. In addition to Ga, in the periodic table where similar effects can be expected, Al and In of the same group can be contained within a range that does not impair the object of the present invention.

  As shown in the graph of FIG. 2, the relationship between the Ga concentration in the grown crystal and the thermal conductivity shows that the temperature coefficient of the crystal is significantly different from that of the undoped crystal when the Ga concentration is less than 0.01% by weight. Therefore, a sufficient improvement effect does not appear. Further, the thermal conductivity increases until the Ga concentration in the crystal is near 0.1% by weight, and is maintained at a high level near 0.3% by weight. If it exceeds 4% by weight, there is a concern that cracking may occur even if the thermal conductivity is maintained at a higher level than before. Therefore, in order to improve the thermal conductivity, the Ga concentration in the crystal needs to be 0.01 wt% or more and 0.4 wt% or less. A preferable Ga concentration is 0.04 to 0.3% by weight, and a more preferable Ga concentration is 0.1 to 0.3% by weight.

The LT single crystal of the present invention preferably has a thermal conductivity of 4.0 to 4.5 W / m · K. The thermal conductivity is thinly cut out from a single crystal to about 500 μm and measured by a laser flash method.
If the thermal conductivity is less than 4.0 W / m · K, the heat dissipation is poor and a SAW device with good characteristics cannot be obtained. On the other hand, it is difficult and expensive to produce an LT single crystal having a thermal conductivity exceeding 4.5 W / m · K.

2. Manufacturing method of lithium tantalate single crystal The present invention relates to a lithium tantalate single crystal in which a gallium raw material powder as a dopant is added to a raw material powder of a lithium tantalate single crystal and a crystal is grown by the Czochralski method. In the production method, the gallium raw material powder is added so that the Ga concentration in the raw material melt is 0.05 wt% or more and 1.5 wt% or less.

  Here, the growth of the single crystal is not particularly limited, but is preferably performed by the Czochralski method. The Czochralski method is a growth method in which a single crystal is grown by immersing a seed crystal in a melt obtained by melting raw material powder and pulling it up. For example, the method is performed using a high-frequency induction heating device or the like. Can do. According to the Czochralski method, a large crystal can be stably produced.

Specifically, first, the single crystal raw material weighed so as to have a predetermined melt composition is put into a crucible of a growth apparatus.
The crucible to be used is not particularly limited, and for example, a crucible made of platinum, molybdenum, tungsten, iridium, rhodium, rhenium, or an alloy thereof can be used. Among these, since lithium tantalate has a relatively high melting point, it is preferable to use a material made of a material having excellent heat resistance such as iridium.

Specifically, in the production method of the present invention, Ta ₂ O ₅ and Li ₂ O oxide powders are used, and each raw material is weighed so that the melt obtained by heating has a predetermined composition. In addition, although the raw material oxide powder to be used is not specifically limited, It is preferable that the purity is 4N or more.

In addition, as a form of the dopant to be added, metal Ga and Ga ₂ O ₃ which is an oxide are conceivable. However, it is desirable to select Ga ₂ O ₃ as a raw material because it is dissolved in the LT melt which is an oxide. . Ga ₂ O ₃ is easy to use because it is difficult to escape to the moderate vapor pressure of since the outside of the system when dissolved.

  The Ga raw material powder may be mixed with each raw material powder of lithium tantalate from the beginning, or an LT calcined powder of lithium tantalate may be prepared in advance, and a Ga elemental compound may be added thereto. In addition to Ga, when the same group of Al and In are included in the periodic table, a small amount is added as a substance whose vapor pressure does not become too small so as not to impair the object of the present invention.

Further, in the method for producing a lithium tantalate single crystal of the present invention, the raw material melt used for crystal growth is preferably adjusted so that the Ga concentration is 0.05 wt% or more and 2.0 wt% or less. .
Here, Ga ₂ O ₃ is added to the raw material melt used for crystal growth so that the Ga concentration in the raw material melt is 0.05 wt% or more and 2.0 wt% or less. This is because the segregation coefficient of Ga in LT single crystal growth (that is, Ga concentration in the crystal / Ga concentration in the melt) is approximately 0.2. The content may be from 01% by weight to 0.4% by weight.

Note that the Ga concentration in the crystal is measured by mixing Ga ₂ O ₃ powder in a crucible so that the Ga concentration in the LT raw material becomes a predetermined amount, mixing by high frequency induction heating, cooling, and then cooling the raw material in the crucible. Sampling is performed, and Ga concentration analysis is performed by the ICP-AES method.

  As for the Ga concentration in the grown crystal, the crystal whose thermal conductivity is less than 0.01% by weight shows no significant difference in thermal conductivity from that of the undoped crystal. Further, if the difference in Ga concentration between the seed crystal and the grown crystal is too large, a crack is generated at the interface between the seed crystal and the grown crystal, making it difficult to grow a single crystal. Therefore, it is preferable that the Ga concentration in the raw material melt is 2.0% by weight or less.

  Subsequently, the raw material powder charged in the crucible is heated and melted. At that time, the atmosphere in the furnace is preferably a mixed gas atmosphere of oxygen and an inert gas such as nitrogen or argon.

Next, a single crystal is grown from the melt obtained by melting the raw material powder. When growing a single crystal by the Czochralski method (pull-up method), keep the inside of the chamber in the above-mentioned mixed gas atmosphere, immerse the seed crystal in the melt with the desired composition, and adjust the rotation speed and pull-up speed. While forming the neck and shoulder, continue to form the straight body.
The crystal shape can be adjusted, for example, by measuring the crystal weight during growth, deriving the diameter, growth speed, and the like by calculation, and adjusting the rotation speed and pulling speed. Alternatively, the melt temperature may be controlled by feeding back the change in crystal weight to the input power to the heater.

In addition, since the lithium tantalate single crystal has a relatively high melting point, an excessive Li ₂ O component suitable for evaporation may be added to the melt in consideration of evaporation of Li during the growth process.

In this production method, a lithium tantalate single crystal having a uniform composition and excellent characteristics can be produced by an extremely easy method of growing crystals using a melt having a predetermined composition as described above. . If necessary, annealing can be performed.
The obtained single crystal (ingot) can be sliced and polished to a predetermined thickness to form a substrate such as the following SAW filter.

3. SAW filter The SAW filter of the present invention is an element using the above-mentioned lithium tantalate single crystal. A high frequency power is input to a comb-shaped electrode formed on the piezoelectric substrate to generate a surface acoustic wave on the surface of the piezoelectric substrate. This is a device that generates and returns this surface acoustic wave to a high frequency electric signal again by another comb electrode.

  As shown in FIG. 3, the SAW filter 10 is manufactured using a piezoelectric substrate 10 made of a lithium tantalate (LT) single crystal 1, and the SAW propagation direction is in the X direction on the main surface of the piezoelectric substrate 10. The SAW resonator 11 is provided so that

SAW filters can be downsized because the surface acoustic wave wavelength is about 10 ⁻⁵ smaller than electromagnetic waves, have high efficiency because of low propagation loss, and semiconductor process technology can be applied to their production. Therefore, the device is excellent in mass productivity and can be reduced in price, and is widely used as a band-pass filter in communication equipment such as a mobile phone.

  With the recent improvement in performance of mobile phones and the like, SAW filters are also required to have higher performance. However, in the present invention, lithium tantalate (LT) contains gallium (Ga) and has broadband filter characteristics. It is a piezoelectric material with a large electromechanical coupling coefficient that is advantageous for realizing high thermal conductivity, and has improved thermal stability and improved temperature stability. It can be manufactured at low cost.

  EXAMPLES Hereinafter, although this invention is demonstrated using an Example and contrasting with a comparative example, this invention is not limited to these Examples.

  In addition, the obtained single crystal was cut out to a thickness of 500 μm, and the thermal conductivity of the sample was measured by a laser flash method. In addition, the sound velocity was obtained by fabricating a 1-port SAW device in which a comb electrode 2 having an electrode period of 4 μm, that is, an electrode width of 1 μm and an interval of 1 μm, was formed on a substrate of the LT single crystal 1 as shown in FIG. The resonance frequency was measured with a network analyzer (electrode material: Cu) and reflectors 3 arranged on both sides.

[Example 1]
An LT single crystal containing Ga was grown by a Czochralski method using a high frequency induction heating furnace.
First, an iridium (Ir) crucible having a diameter of 170 mm is installed in the furnace, and a congruent composition in the crucible, that is, harmonic melting (coincidence melting) in which a crystal having a uniform composition can be easily obtained without composition deviation (composition fluctuation) The LT calcined powder and Ga ₂ O ₃ powder prepared in the above were filled and melted at about 1750 ° C.
The amount of Ga ₂ O ₃ powder added was weighed so that the Ga concentration in the raw material melt (hereinafter referred to as the charged Ga concentration) was 0.05% by weight.

Thereafter, the melt temperature was adjusted to the vicinity of the melting point (1650 ° C.) of LT, and the seed crystal was brought into contact with the melt surface while rotating at 10 rpm.
After the growth, the inside of the furnace was cooled to near room temperature and the crystal was taken out to obtain a φ4 inch crack-free Ga-doped LT single crystal.
Then, after annealing and poling the obtained single crystal, the sample for thermal conductivity measurement was cut out from the crystal, and the crystal was sliced and polished to prepare a sound speed measurement sample (substrate).

When Ga concentration analysis in the LT single crystal was conducted by ICP-AES method, it was 0.01% by weight. Further, the thermal conductivity of the obtained sample for measuring thermal conductivity was measured by a laser flash method and found to be 4.29 W / m · K. An improvement of about 11% was seen compared to the thermal conductivity of the undoped crystal.
Also, a 1-port SAW device with an electrode period of 4 μm as shown in FIG. 1 is fabricated on the LT substrate fabricated for sound velocity measurement (electrode material: Cu), and the resonance frequency is measured with a network analyzer to obtain the sound velocity. The calculated value was 3850 m / sec. Furthermore, when the Ga concentration analysis in the obtained LT single crystal was conducted by ICP-AES method, it was 0.01% by weight. The results are shown in Table 1.

[Example 2]
In Example 2, crystal growth was performed in the same manner as in Example 1 except that Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 1.5 wt%, and crack-free Ga-doped LT was obtained. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.40 W / m · K, which was an improvement of about 14% compared to the thermal conductivity of the undoped crystal. Also, the sound velocity was 3840 m / sec, and no change was seen compared to undoped. Furthermore, when the Ga concentration analysis in the obtained LT single crystal was conducted by ICP-AES method, it was 0.29% by weight.

[Example 3]
In Example 3, crystal growth was performed in the same manner as in Example 1 except that Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 0.5 wt%, and crack-free Ga-doped LT was obtained. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.45 W / m · K, which was an improvement of about 14% compared to the thermal conductivity of the undoped crystal. Also, the sound velocity was 3840 m / sec, and no change was seen compared to undoped. Furthermore, when Ga concentration analysis in the obtained LT single crystal was performed by ICP-AES method, it was 0.11% by weight.

[Example 4]
In Example 4, crystal growth was performed in the same manner as in Example 1 except that the Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 0.9 wt%, and crack-free Ga-doped LT was performed. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.43 W / m · K, which was an improvement of about 14% compared to the thermal conductivity of the undoped crystal. Also, the sound velocity was 3840 m / sec, and no change was seen compared to undoped. Furthermore, Ga concentration analysis in the obtained LT single crystal was performed by ICP-AES method, and it was 0.18% by weight.

[Example 5]
In Example 5, crystal growth was performed in the same manner as in Example 1 except that Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 0.2 wt%, and crack-free Ga-doped LT was obtained. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.32 W / m · K, which was an improvement of about 12% compared to the thermal conductivity of the undoped crystal. Also, the sound velocity was 3840 m / sec, and no change was seen compared to undoped. Furthermore, when the Ga concentration analysis in the obtained LT single crystal was conducted by ICP-AES method, it was 0.04% by weight.

[Example 6]
In Example 6, crystal growth was performed in the same manner as in Example 1 except that the Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 0.4 wt%, and crack-free Ga-doped LT was obtained. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.35 W / m · K, an improvement of about 13% compared to the thermal conductivity of the undoped crystal. The speed of sound was determined to be 3850 m / sec. Furthermore, when the Ga concentration analysis in the obtained LT single crystal was conducted by ICP-AES method, it was 0.08% by weight.

[Example 7]
In Example 7, crystal growth was performed in the same manner as in Example 1 except that Ga ₂ O ₃ powder was charged in the crucible so that the charged Ga concentration was 1.7% by weight, and crack-free Ga-doped LT was obtained. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.16 W / m · K, which was an improvement of about 8% compared to the thermal conductivity of the undoped crystal. Also, the sound velocity was 3840 m / sec, and no change was seen compared to undoped. Furthermore, Ga concentration analysis in the obtained LT single crystal was performed by ICP-AES method, and it was 0.34% by weight.

[Example 8]
In Example 8, crystal growth was performed in the same manner as in Example 1 except that the crucible was charged with Ga ₂ O ₃ powder so that the charged Ga concentration was 1.9 wt%, and crack-free Ga-doped LT was performed. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 4.08 W / m · K, which was an improvement of about 6% compared to the thermal conductivity of the undoped crystal. The speed of sound was determined to be 3850 m / sec. Furthermore, Ga concentration analysis in the obtained LT single crystal was performed by ICP-AES method, and it was 0.38% by weight.

[Conventional example]
An undoped LT single crystal was grown using the Czochralski method. For the growth, a high-frequency induction heating furnace was used as in Example 1. An iridium (Ir) crucible having a diameter of 170 mm was placed in the furnace, and the LT calcined powder prepared with a congruent composition was filled in the crucible and melted at about 1700 ° C.
Thereafter, the melt temperature was adjusted to the vicinity of the melting point (1650 ° C.) of LT, and the seed crystal was brought into contact with the melt surface while rotating at 10 rpm.

  After the growth, the inside of the furnace was cooled to near room temperature and the crystal was taken out to obtain a φ4 inch undoped LT single crystal. Then, after annealing and poling the obtained single crystal, the sample for thermal conductivity measurement was cut out from the crystal, and the crystal was sliced and polished to prepare a sound speed measurement sample (substrate).

It was 3.85 W / m * K when the heat conductivity of the obtained sample for thermal conductivity measurement was measured by the laser flash method.
Also, a 1-port SAW device with an electrode period of 4 μm as shown in FIG. 1 is fabricated on the LT substrate fabricated for sound velocity measurement (electrode material: Cu), and the resonance frequency is measured with a network analyzer to obtain the sound velocity. The calculated value was 3840 m / sec.

[Comparative Example 1]
In Comparative Example 1, crystal growth was performed in the same manner as in Example 1 except that the crucible was charged with Ga ₂ O ₃ powder so that the charged Ga concentration was 0.03% by weight, and crack-free Ga-doped LT was performed. A single crystal was obtained.
When the thermal conductivity of the obtained crystal was measured, it was 3.89 W / m · K, and almost no change was observed with respect to the thermal conductivity of the undoped crystal. The speed of sound was 3840 m / sec and no change was seen compared to undoped. Furthermore, Ga concentration analysis in the obtained LT single crystal was performed by ICP-AES method, and it was 0.006% by weight.

[Comparative Example 2]
In Comparative Example 2, crystals were grown in the same manner as in Example 1 except that the crucible was charged with Ga ₂ O ₃ powder so that the charged Ga concentration was 2.0 wt%. The crystal taken out from the furnace after cooling had cracks, and a single crystal could not be obtained. The Ga concentration in the crystal obtained at this time was 0.42% by weight.

"Evaluation"
As is apparent from Table 1 showing the experimental results, the Ga concentration in the LT single crystals obtained in Examples 1 to 8 was 0.01 to 0.38% by weight, and the thermal conductivity was 4.08. It was ˜4.43 W / m · K, and an improvement of about 6 to 15% was seen compared to the thermal conductivity of the undoped crystal of the conventional example. In addition, the speed of sound obtained with a SAW device produced on a substrate using the obtained crystal was 3840 to 3850 m / sec, and almost no change in the speed of sound was observed.
On the other hand, in Comparative Example 1, since the Ga concentration in the obtained LT single crystal was as low as 0.006% by weight, the thermal conductivity was 3.89 W / m · K. Not much improvement was seen compared to the thermal conductivity. In Comparative Example 2, since the Ga concentration in the obtained LT single crystal was as high as 0.42% by weight, cracks occurred.

  From the results of the above Examples and Comparative Examples, it can be seen that according to the present invention, a lithium tantalate crystal having a high thermal conductivity can be produced, and a low-cost substrate with improved temperature characteristics can be provided. .

  The lithium tantalate single crystal of the present invention can be used as a substrate material for SAW filters, vibrators and transmitters.

Claims (5)

  A part of the Li site or Ta site of the lithium tantalate single crystal is substituted with a gallium (Ga) element, and the gallium (Ga) content in the single crystal is 0.01% by weight or more and 0.3% by weight. A lithium tantalate single crystal having the following range.   2. The lithium tantalate single crystal according to claim 1, wherein the single crystal has a thermal conductivity of 4.0 to 4.5 W / m · K. A method for producing a lithium tantalate single crystal in which a gallium raw material powder as a dopant is added to a raw material powder of a lithium tantalate single crystal and a crystal is grown by the Czochralski method,
The lithium tantalate single crystal according to claim 1 or 2, wherein the gallium raw material powder is added so that a Ga concentration in the raw material melt is 0.05 wt% or more and 1.5 wt% or less. Manufacturing method. The gallium raw material powder, the manufacturing method of the lithium tantalate single crystal according to claim 3, characterized in that the Ga ₂ O ₃ powder. A SAW filter using the lithium tantalate single crystal according to claim 1 or 2 as a substrate.

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