JPH0690035A - Piezoelectric and its manufacture - Google Patents

Abstract

PURPOSE:To obtain an electric conductivity which can be used for an acoustoelectric effect device by doping a single crystal made mainly of ZnO with a specified amount of Li. CONSTITUTION:A growth container 10 is filled with a ZnO sintered body 1, where a baffle plate 3 is installed to partition its inside into a material filled zone 14 and a crystal growth zone 16. ZnO seed crystals 7 are hang on an Ag frame 5, and the frame 5 is arranged in the crystal growth zone 16. The growth container 10 is injected with a solvent made of 3mol/l KOH and 1.5mol/l LiOH. The growth container 10 is installed in an autoclave, which is then injected with distilled water and sealed with water. After heating with the autoclave installed in an electric furnace, ZnO single crystals are taken out. The ZnO single crystals are dipped in an LiOH solution and subjected to diffusion treatment at high temperature in an oxygen stream to dope them with Li. The electric conductivities and Li doping amounts of obtained ZnO single crystals are 10<-3>-10<-6>1/OMEGAcm and 15-120ppm, respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric semiconductor composed of a single crystal containing zinc oxide (ZnO) as a main component, and more specifically, a piezoelectric semiconductor preferably used as an acoustoelectric effect element and The manufacturing method is related.

[0002]

2. Description of the Related Art Zinc oxide (ZnO) has a chemical composition of Zn.
It is an excess n-type semiconductor, and is a substance that has attracted attention as a piezoelectric body due to its crystal structure. Currently Zn
Although the use of O is carried out by a thin film, there is a problem that it cannot be used because the film is polycrystalline and is affected by the grain boundaries and the propagation loss becomes large. Therefore, high-purity ZnO is used.
Single crystallization is an important issue.

Regarding the single crystallization of ZnO, "high-purity Z
Hydrothermal growth of nO single crystal and evaluation of stoichiometry ”
(Noboru Sakagami, February 1988, Bulletin of the Akita National College of Technology No. 2
No. 3) has been reported. In this document, hydrothermal method Z
The growth of an nO single crystal is described. According to this growth method, a ZnO sintered body is placed in the lower part of the crystal growth apparatus, while Z
The nO seed crystals are respectively placed on the upper part of the growing apparatus, and then a solvent of an alkaline aqueous solution composed of KOH and LiOH (hereinafter, referred to as “alkali solvent”) is filled. In this state, the inside of the crystal growing apparatus is operated at a growing temperature of 370 to 400 ° C. and a pressure of 700 to 1000 kg / cm ² , where the upper and lower parts of the crystal growing apparatus are at the lower temperature. A ZnO single crystal is grown by operating at 10 to 15 ° C. higher than the temperature.

In the ZnO single crystal grown and formed as described above, when only an alkaline solvent is used as a growth solution, the growth environment becomes a reducing atmosphere, and the excess amount of Zn atoms is more than 10 ppm. The electric conductivity is 10 ⁰ to 10 ⁻² 1 / Ω · cm, which is more than 10 ppm. Therefore, this Z
The nO single crystal is not suitable for use as an acoustoelectric effect element because of its large electrical conductivity. Therefore, hydrogen peroxide (H ₂ O ₂ ) is added to make the growth system an oxygen atmosphere, and Z is added.
We are trying to improve the purity of nO single crystal.

[0005]

However, the above-mentioned H
The electrical conductivity of ZnO single crystal grown by the action of ₂ O ₂ is 10 ⁻⁸ to 10 ⁻¹⁰ 1 / Ω · cm,
There is a problem that the electrical conductivity is small and not suitable for use as an acoustoelectric effect element. Further, since H ₂ O ₂ is a strong oxidizing agent, it is necessary to coat the inside of the growth container with platinum or to make the growth container itself with platinum, which is disadvantageous in terms of cost. The present invention has been made in view of the above problems of the prior art, and the object thereof is to have characteristics such as electric conductivity suitable for use as an acoustoelectric effect element, and to reduce the manufacturing cost. An object of the present invention is to provide a reduced piezoelectric semiconductor and a method for manufacturing the same.

[0006]

Means for Solving the Problems As a result of earnest studies for achieving the above object, the present inventor has found that the above object can be achieved by doping Li into a ZnO single crystal, and the present invention has been completed. It was Therefore, the piezoelectric semiconductor of the present invention is a piezoelectric semiconductor composed of a single crystal containing ZnO as a main component, and this semiconductor contains Li of 15 to 120 pp.
It is m-doped and has an electric conductivity of 10 ^-3 to 10 ^-6 1 /
Ω · cm, preferably 10 ⁻⁴ to 10 ⁻⁵ 1 / Ω · cm. Further, in the method for manufacturing a piezoelectric semiconductor of the present invention, the ZnO sintered body raw material is placed in the raw material filling portion in the lower portion of the container, the ZnO seed crystal is placed in the crystal growing portion in the upper portion of the container, and the alkaline solvent is placed in the container. A method for manufacturing a piezoelectric semiconductor in which a ZnO single crystal is grown under hydrothermal conditions by adjusting a temperature in a container so that a temperature of a raw material filling portion is higher than a temperature of a crystal growing portion, the grown ZnO single crystal In addition, Li was doped to control electric conductivity.

Further, this piezoelectric semiconductor generates both an acoustoelectric effect voltage and a piezo effect voltage. Therefore, in order to use this piezoelectric semiconductor as an acoustoelectric effect element, it is necessary to remove the piezoelectric effect voltage with a filter. In order to separate both effect voltages with a filter, it is necessary that the voltage ratio of acoustoelectric effect voltage: piezoelectric effect voltage is 3: 1 or more, and for that purpose, mobility (mobility of carrier) is 30 cm ^2. / V · sec or more is preferable. In order to provide a better function as an acoustoelectric effect element, it is preferable that the above voltage ratio is 9: 1 or more.
It is preferably cm ² / V · sec or more. Moreover, the piezoelectric semiconductor, in order to achieve uniform acoustoelectric characteristics, in order to stabilize the power output value, variation of the electrical conductivity in the ZnO single crystal 10 ² 1 / Ω · c
It is preferably within m, and even more preferably within 10 ¹ 1 / Ω · cm.

[0008]

In the piezoelectric semiconductor of the present invention, by doping with Li, the electrical conductivity is controlled to a value suitable for use as an acoustoelectric effect element. Therefore, the piezoelectric semiconductor of the present invention has excellent acoustoelectric effect characteristics. Further, in manufacturing this piezoelectric semiconductor, it is not necessary to use H ₂ O ₂ as in the conventional case. Therefore, the inside of the single crystal growth container should be coated with expensive Pt, or the growth container itself should be Pt.
Since it is not necessary to manufacture it in, the manufacturing cost can be reduced.

Next, a method of manufacturing the piezoelectric semiconductor of the present invention will be described. First, a ZnO sintered body used as a raw material for growing a ZnO single crystal is manufactured by an ordinary method. It is preferable to select one having a diameter of about 1 to 2 mm from the obtained sintered bodies. Next, in a growth container with Ag coated inside or A
The above-mentioned ZnO sintered body is filled in the growth container manufactured by g. Then, if necessary, a baffle plate is installed in the container to divide into a raw material filling portion filled with a ZnO sintered body and a crystal growth portion in which a ZnO seed crystal is arranged. Then Zn
The O seed crystal is placed above the inside of the container (in the case of using a baffle plate, the crystal growth part), and KOH of 2 to 6 mol / l is placed.
An alkaline solvent consisting of 1 to 3 mol / l LiOH is poured into the container. The injection rate is preferably about 60 to 85% of the free volume of the container, that is, the volume remaining when the ZnO sintered body, the baffle plate and the like are installed in the container.

Next, the growing container is placed in another container, for example, an autoclave, a pressure medium is filled in the autoclave, and the container is immersed. The pressure medium may be any substance that is weakly corrosive under high temperature and high pressure, and distilled water is preferable. The pressure medium generates pressure at the growth temperature according to the filling rate with respect to the internal volume (hereinafter, referred to as "free internal volume") remaining when the growth container is installed in the autoclave. Adjusts the filling rate of the pressure medium so that the pressure becomes equal to or slightly higher than the pressure in the growth container, thereby fulfilling the function of protecting the growth container. When distilled water is used as the pressure medium in the above solvent and solvent concentration, its filling rate is preferably about 60 to 85% of the free internal volume of the autoclave. Next, the autoclave is installed in a heating furnace, the temperature of the growth container is raised, and the crystal growth part and the raw material charging part are heated to a predetermined temperature. At this time, it is preferable that the temperature of the crystal growth part is lower by about 5 to 25 ° C. than the temperature of the raw material filling part. That is, it is preferable that the temperature of the crystal growth part is 360 to 400 ° C. and the temperature of the raw material filling part is 380 to 420 ° C.
Then, in this state, a steady operation is performed for 10 to 30 days to grow a crystal, and then the heating furnace is stopped and the temperature is lowered to room temperature.
The nO single crystal is taken out.

In the firing of the ZnO sintered body of the above-mentioned manufacturing method, by removing the heavy metal impurities in advance, the mobility of the obtained ZnO single crystal can be improved. When a ZnO single crystal is used as an acoustoelectric effect element, the mobility is a predetermined value or more, that is, 30 cm ² / V ·
It is preferably not less than sec, but in the conventional method, a heavy metal as an impurity such as Pb is mixed in the ZnO single crystal, which may reduce the mobility. Pb is about 50 in ZnO powder.
Although it is contained in ppm, for example, Zn can be manufactured to produce high-purity ZnO after repeating high-purity Zn by repeating distillation of Zn. Furthermore, ZnO variation in electrical conductivity in the single crystal, the crystal growth part and the temperature difference △ T between the material filling portion, 10 ² 1 / Ω · cm by reducing in the second half than the first half of the breeding process
Can be suppressed within. For example, ΔT is 10 to 25 ° C in the first half of the growing period and 5 to 10 ° C in the second half.
It can suppress by setting. Also, ΔT
As described above, it is possible to suppress variations in electric conductivity not only in two stages, but also in multiple stages and continuously in accordance with the crystal growth state.

Next, Li doping, which is a feature of the present invention, will be described. This Li-doped has a Li concentration of 15 to 120 ppm in the ZnO single crystal obtained as described above,
It is preferable to carry out the treatment so that the concentration is 30 to 90 ppm. The doping method is not particularly limited, and Li
Examples include dipping using an OH solution, coating and spraying. In this case, the concentration of the LiOH solution can be appropriately changed depending on the size of the single crystal to be treated, and for example, when using a ZnO single crystal of 5 × 5 × 5 mm,
5m LiOH solution containing 50-200ppm Li
The single crystal may be dipped in l. Then, this single crystal is heated to 100 ° C. at 800 to 1000 ° C. in the air or an O ₂ stream.
Li doping can be performed by performing a diffusion process for up to 300 hours. The LiOH solution is used because it is an alkaline solution and thus does not impair the crystallinity of the crystal surface during the diffusion treatment. Also, it is because only Li enters the crystal and control is easy. The reason why the diffusion treatment is performed under the above conditions is to uniformly diffuse not only the crystal surface but also the inside.

[0013]

The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. (Examples 1 to 6) (Growth of single crystal) 500 g of high-purity ZnO powder obtained through Zn distillation and 500 g of distilled water were mixed, and the obtained mixture was molded into a spherical shape having a diameter of 2 to 3 mm. It was dried at 100 ° C. for 2 hours. The obtained dried body,
Sintering was carried out in an alumina container at 1100 ° C. for 24 hours in an oxygen atmosphere, and ZnO sintered bodies having a particle size of 1 to 2 mm were sieved and selected. 200g of ZnO sintered body 1
Was filled in the growth container 10 shown in FIG. This growth container 10 is provided with thermocouple insertion portions 12 and 12 'and has an inner diameter of 30 m.
m × height is 300 mm, and it has a cylindrical shape with an internal volume of 2
The amount is 50 ml, and the inside is coated with Ag.

Next, the baffle plate 3 having a porosity of 5% is installed in the growth container 10 and the inside of the container 10 is filled with the raw material filling section 14.
And the crystal growth part 16. Then, the ZnO seed crystal 7 was hung on the Ag frame 5, and the frame 5 was placed in the crystal growth section 16. At this time, the seed crystal 7 was fixed to the frame 5 by penetrating the Ag wire 9 which is an example of a noble metal wire and fastening both ends of the Ag wire 9 to the frame 5. 3 mol / l K in the growth container 10
An alkaline solvent consisting of OH and 1.5 mol / l LiOH was injected. The injection amount was 80% of the free volume of the growth container 10.

Next, as shown in FIG. 2, the growth container 10
Is installed in the autoclave 20 and the thermocouple 18, 18 '
After the placement, distilled water 22 was injected into the autoclave 20. The injection amount is 7 of the free internal volume of the autoclave 20.
It was set to 0%. Next, cap the autoclave 20
Then, the autoclave 20 was installed in an electric furnace 30. The electric furnace 30 has an upper and lower two-stage structure so that the growth temperature can be finely adjusted, and further includes thermocouples 32 and 34.

Next, the temperature of the crystal growing portion 16 was raised so that it was always lower than the temperature of the raw material filling portion 14, and the temperature of the crystal growing portion was raised to 380 ° C. and the raw material filling portion was raised to 395 ° C. In this state, steady operation was performed for 20 days, after which the electric furnace was cooled to room temperature, and then the ZnO single crystal was taken out.
In addition, in order to suppress the variation in electrical conductivity,
In Table 4, as shown in Table 1, the temperature difference ΔT between the crystal growth portion and the raw material filling portion was reduced from 10 days (first half) to 10 days (second half) after the start of growth. In Examples 5 and 6, ΔT was constant.

(Li Doping) The ZnO single crystal obtained as described above was dipped in a LiOH solution having a predetermined concentration, and then subjected to a diffusion treatment in an O ₂ gas stream at 850 ° C. for 240 hours. Table 1 shows the Li concentration of the LiOH solution and the Li concentration (doping amount) in the single crystal.

(Comparative Examples 1 and 2) High-purity ZnO powder was not used, Li doping was not performed, and the inner coating of the growth container was Pt.
And the concentration of H ₂ O ₂ injected into the alkaline solvent is 0.2 m
The same operations as in Examples 1 to 6 were performed except that the ratio was set to ol / l and ΔT was not adjusted. (Comparative Examples 3 to 4) Examples 1 to 6 except that high-purity ZnO powder was not used, Li doping was not performed, H ₂ O ₂ was not injected into an alkaline solvent, and ΔT was not adjusted. The same operation was performed.

(Performance Evaluation) With respect to the ZnO single crystal obtained in each of the above examples, electric conductivity and its variation, mobility and acoustoelectric effect characteristics were measured, and the obtained results are shown in Table 1. The acoustoelectric effect characteristics were evaluated as follows. (Acoustoelectric effect characteristics) A ZnO single crystal is processed into a cube of 5 x 5 x 5 mm with the c-plane as the top surface and the bottom surface (other surfaces are arbitrary), and these two c-planes have constant energy. An ultrasonic pulse was vertically injected, and the acoustoelectric effect voltage value and the ratio of the acoustoelectric effect voltage value and the piezo effect voltage value obtained at this time were measured. The larger the acoustoelectric effect voltage value and the ratio of the acoustoelectric effect voltage value to the piezoelectric effect voltage value, the better the acoustoelectric effect characteristic.

[0020]

[Table 1]

[0021]

As described above, according to the present invention,
Since the ZnO single crystal is doped with Li, it is possible to provide a piezoelectric semiconductor that has characteristics such as electric conductivity suitable for use as an acoustoelectric effect element and that has a reduced manufacturing cost, and a manufacturing method thereof. Therefore, the piezoelectric semiconductor of the present invention can be suitably used as an acoustoelectric effect type probe material, and also as an ultrasonic amplification material, a surface acoustic wave filter, a piezoelectric transducer, a phosphor for low-speed electron beam emission, and the like. Can be used.

[Brief description of drawings]

FIG. 1 is a schematic perspective view showing an example of a growth container according to the present invention.

FIG. 2 is a schematic sectional view showing an example of a crystal growing apparatus according to the present invention.

[Explanation of symbols]

 1 ZnO Sintered Body 3 Baffle Plate 5 Frame 7 ZnO Seed Crystal 9 Ag Wire 10 Growth Container 12, 12 'Thermocouple Insertion Section 14 Raw Material Filling Section 16 Crystal Growth Section 18, 18' Thermocouple 20 Autoclave 22 Distilled Water 24 Cap 30 Electric furnace 32, 34 thermocouple

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 41/18 41/24 9274-4M H01L 41/22 Z

Claims (4)

[Claims] 1. A piezoelectric semiconductor composed of a single crystal containing ZnO as a main component, wherein the semiconductor contains 15 to 120 Li.
It is ppm-doped and has an electric conductivity of 10 ⁻³ to 10 ^−6.
A piezoelectric semiconductor characterized by being 1 / Ω · cm. 2. Mobility is 30 cm ² / V · sec
The piezoelectric semiconductor according to claim 1, which is the above. 3. A according to claim 1 or 2, wherein the variation of electrical conductivity in the single crystal is equal to or is within 10 ² 1 / Ω · cm piezoelectric semiconductor. 4. A ZnO sintered body raw material is placed in a raw material filling section at the bottom of a container, and a ZnO seed crystal is placed in a crystal growing section at the upper portion of the vessel, and an alkaline solvent is placed in the vessel, and the temperature of the raw material filling section is set to the crystal. A method for manufacturing a piezoelectric semiconductor, in which a ZnO single crystal is grown under hydrothermal conditions by adjusting a temperature inside a container so as to be higher than a temperature of a growing portion, wherein the grown ZnO single crystal is doped with Li to generate an electric charge. A method for manufacturing a piezoelectric semiconductor, characterized by controlling conductivity.