JPH0936440A - Production of thermoelectric material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the production process of thermoelectric material while preventing mixture of oxygen by arranging a plurality of specified targets oppositely to an objective substrate in a filming chamber sustained in evacuated state, irradiating the plurality of targets with laser light to generate a plurality of plumes and depositing the plume on the substrate. SOLUTION: A pair of targets 10 are prepared containing at least one kind of material selected from bismuth, tellurium, antimony and selenium at a specified compositional ratio. The targets 10 are disposed oppositely to an objective substrate 3 in a filming chamber 6 sustained in evacuated state. The targets 10 are then irradiated with laser light 5 to generate plumes 15 which are eventually deposited on the substrate 3 thus producing a thermoelectric material. This method simplifies the process greatly as compared with a conventional process employing powder sintering. Mixture of oxygen in the crushing process can also be prevented.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a thermoelectric material. Such thermoelectric materials include, for example, cooling using the Peltier effect, cooling and heating using the Peltier effect, temperature control using the Peltier effect, thermoelectric generation using the Seebeck effect, heat using the Seebeck effect, or an infrared sensor, etc. Used in the field. When such a thermoelectric material is used as a thin film or a small element, for example, a thin film cooling element integrated with a semiconductor element such as an IC, an integrated cooling element of a semiconductor laser,
It can be used as a temperature control element of an optical element, a temperature control element of a printer head, a battery of a wristwatch, and various sensors using thermoelectric conversion such as an infrared sensor and a flow sensor. Now, in this thermoelectric material, the present application is a thermoelectric material containing at least two or more kinds of components selected from bismuth, tellurium, antimony, and selenium, which are attracting attention today in view of the relationship with the applicable temperature range. Relates to a method of making.

[0002]

2. Description of the Related Art Heretofore, a powder sintering method has been known as a practical method for producing this type of thermoelectric material.

[0003]

This method involves obtaining a device through a solid solution forming step, a pulverizing step, a particle size sieving step, a sintering step, and a slicing step, and there is a problem that the steps are complicated. . Further, oxygen and the like are easily mixed in the material in the crushing process.

In such a thermoelectric material, the figure of merit changes depending on the temperature. In other words, when it is used as a thermoelectric element, the operating temperature will be different. At each site in the thickness direction of the thermoelectric element, the component ratio of the components that make up the element material is changing, or the impurity concentration is changing. Thus, it is possible to obtain a good thermoelectric element that can maintain a high figure of merit in each part. However, it is very difficult to obtain such a structure by the powder sintering method. Therefore, in view of the above problems, the object of the present invention is that the process is simple and can avoid the inclusion of oxygen and the like, and when used as a thermoelectric material, a thermoelectric element showing a high figure of merit as a whole element. It is to obtain a method for manufacturing a thermoelectric material capable of obtaining an element.

[0005]

The first characteristic means of the method for producing a thermoelectric material according to the present invention for achieving this object is to provide any one or more of the four components in different composition ratios. While making multiple targets to contain,
In the film forming chamber maintained under reduced pressure vacuum, the plurality of targets are arranged facing the substrate to be film-formed, and the plurality of targets are irradiated with laser light to generate a plurality of plumes from the plurality of targets. The vapor deposition is performed on the substrate, and the thermoelectric material is produced by a laser ablation method. This relates to claim 1. Further, in the first characteristic means, in producing the thermoelectric material,
The amount of the deposits deposited on the substrate from each of the multiple targets is changed between the targets as the thermoelectric material is formed, so that the thermoelectric material has different gradients in composition in the forming direction. It is preferable to use it as a material. This is the second characteristic means of the present invention according to claim 2. Further, in the first characteristic means, the thermoelectric material is an impurity semiconductor material containing impurities in the material, and one of the plurality of targets is a material containing impurities as a main component. It is preferable that the thermoelectric material is a graded material in which the impurity concentration in the forming direction is changed in a gradient manner by changing the vapor deposition amount of the impurities along with the formation. This is the third characteristic means of the present invention according to claim 3. Furthermore, in any one of the first to third characteristic means, in order to apply the laser ablation method, the wavelength of the laser beam is 193 to 1064 nm, the laser power density is 100 to 100,000 mJ / cm ² , and It is preferable that the thermoelectric material is manufactured by setting the degree of vacuum in the film chamber to be higher than 10 ^-2 Torr and the temperature of the substrate from room temperature to 600 ° C or lower. This is the fourth characteristic means of the present invention according to claim 4. The operation and effect are as follows.

[0006]

In the first characteristic means, the thermoelectric material is formed on the substrate by the laser ablation method. In the production, a target is produced, and the target is placed in a film forming chamber maintained at a predetermined degree of vacuum, and the target is provided with laser light to face the target. A film made of a thermoelectric material is formed on top. Therefore, the process is greatly simplified, and oxygen and the like are not mixed in the thermoelectric material due to the method.
Furthermore, when this laser ablation method is adopted, its morphology can be easily controlled and a grain structure can be obtained. Therefore, the figure of merit can be improved. Now, in this method, a plurality of targets are prepared. And when making thermoelectric materials,
The plurality of targets are irradiated with laser light, and plumes are simultaneously generated from the plurality of targets to form a thermoelectric material. For example, when a plurality of targets have different components, the thermoelectric material having an arbitrary component composition ratio can be easily manufactured by relatively controlling the vapor deposition amount from each target. Furthermore, even when producing a thermoelectric material with a constant composition,
For example, it is not necessary to prepare in advance a solid solution containing each component in a predetermined composition ratio, as is necessary when using a single target. In addition, if one target is provided with a material serving as a semiconductor base material of an impurity semiconductor and the other target is provided with a material serving as an impurity, and this method is used, a thermoelectric material with an appropriately adjusted impurity concentration can be easily prepared. Can be obtained.

Next, the characteristic means according to claim 2 will be described. In carrying out this method, the vapor deposition amounts from the plurality of targets are relatively changed over time as the material is formed. Therefore, it is possible to easily obtain a graded material having a different component composition ratio in the material thickness direction, which is the direction in which the thermoelectric material is formed. As described above, when used as a thermoelectric element, such a material can be configured so that each component of the element has a composition ratio showing the maximum figure of merit at the operating temperature. Can be very good.

Next, the characteristic means according to claim 3 will be described. In carrying out this method, the amount of vapor deposition from a target containing impurities as a main component for obtaining semiconductor characteristics is relatively changed over time as the material is formed. Therefore, it is possible to easily obtain the graded material with the impurity concentration changed in the thickness direction of the material, which is the direction of forming the thermoelectric material. As described above, when used as a thermoelectric element, such a material can be configured such that each part of the element has a composition ratio showing the maximum figure of merit at the operating temperature, and therefore the element as a whole. The characteristics can be very good.

When the fourth characteristic means of the present application is adopted, the thermoelectric material can be obtained by the laser ablation method, but if the wavelength of the laser, the power density, the degree of vacuum, and the substrate temperature deviate from the ranges described. However, the following problems will occur. Laser wavelength is 1064
If the wavelength is longer than nm, the composition shift becomes large and it is difficult to control. On the other hand, if the wavelength is shorter than 193 nm, it becomes difficult to handle the laser light. Laser power density is 10 mJ / cm
^{If it is} less than ² , the formation speed is extremely reduced and it becomes difficult to ablate. On the other hand, if it is larger than 100,000 mJ / cm ² , the formation is too fast, the grain structure is broken, and the figure of merit tends to decrease. If the degree of vacuum in the film forming chamber is lower than 10 ^-2 Torr (the degree of vacuum is poor), it is difficult to perform stable ablation. On the other hand, the higher the degree of vacuum, the better, but 10
Keeping higher than ^-9 Torr (good vacuum)
At present, it is not practical and the equipment system tends to be expensive.
Even if the film formation substrate temperature is low, the formation rate does not decrease. However, if the temperature is too high, re-evaporation of the formed material from the substrate occurs and compositional deviation easily occurs. Even if the temperature is lower than room temperature, there is no negative effect, but it is not necessary to cool in manufacturing. Further, when the temperature is higher than 600 ° C., the melting point of the bismuth-tellurium-based material exceeds the melting point, so that the compositional deviation becomes remarkable and it becomes unsuitable for film formation. Further, with respect to the number of repetitions of laser light, the higher this is, the more the productivity can be improved.

[0010]

Therefore, by adopting the first characteristic means of the present application, compared with the powder sintering method, it is preferable from the point of view of simplification of the process, and it is preferable that the thermoelectric power has a preferable figure of merit with less oxygen and the like mixed therein. Now you can get the material. Furthermore, it has become possible to easily obtain thermoelectric materials having different composition ratios and thermoelectric materials having different impurity concentrations. Furthermore, when the second characteristic means of the present application is adopted, it has become possible to easily obtain a gradient material having a different component composition in the thickness direction, which is the direction in which the thermoelectric material is formed. Furthermore, when the third characteristic means of the present application is adopted, it has become possible to easily obtain a gradient material having different impurity concentrations in the thickness direction, which is the direction in which the thermoelectric material is formed. Further, by adopting the fourth characteristic means of the present application, it has become possible to stably obtain a thermoelectric material having a grain structure while ensuring the formation rate of the thermoelectric material.

[0011]

EXAMPLES Examples of the present application will be described below. In the description, the configuration of the laser ablation apparatus 1 and laser ablation conditions will be described.

1 Laser Ablation Device 1 FIG. 1 shows a situation in which the laser ablation device 1 is used to produce a thermoelectric material 2 containing bismuth telluride as a main component on a silicon substrate 3. The apparatus 1 comprises a neodymium (Nd ³⁺ ) YAG laser 4 and a film forming chamber 6 for forming a film by a laser beam 5 emitted from the laser 4. The neodymium (Nd ³⁺ ) YAG laser 4 has a pulse of 1000
mJ, a fundamental wave (1064 nm) having an irradiation area of 0.5 cm ² , and a pulse repetition rate of 10 Hz, and the fundamental wave is 266 n by using a nonlinear optical element 40.
Convert to m for use. Therefore, the energy is 100 mJ per pulse and the energy density is 200 mJ / cm ^2.
The laser light is reduced to. The apparatus 1 is provided with a total reflection type mirror 7a and a half mirror 7b for guiding a laser beam 5 emitted from the laser 4 into the film forming chamber 6 at predetermined locations. Further, molding lens systems 9a and 9b for laser light molding are provided in front of the quartz entrance window 8 provided in the film forming chamber 6, and laser light irradiated to the target 10 in front of this molding lens system. A damping device 9c for adjusting the energy density of 5 as required,
9d is provided. In the film forming chamber 6, a pair of target holding bases 11 for holding the target 10,
A substrate holding table 12 is provided facing the holding table 11 and capable of maintaining the substrate 3 at a predetermined film formation substrate temperature. Further, the film forming chamber 6 has an exhaust mechanism 1 equipped with a vacuum pump 13 in order to maintain the chamber at a predetermined degree of vacuum.
It is equipped with 4. When manufacturing the thermoelectric material 2, a different type of target 1 is attached to each of the pair of target holding bases 11.
While holding 0, the substrate 3 is held on the substrate holding table 12 to fabricate the material. In this case, laser light 5
However, laser ablation can be performed by being irradiated (applied) to each target 10.

Therefore, in producing the thermoelectric material 2,
A pair of targets 10 containing various raw material elements (in this case, at least one or more selected from bismuth, tellurium, antimony, and selenium) in a predetermined composition ratio.
(The composition ratios of the targets are different from each other), and the targets 10 are arranged facing the substrate 3 to be film-formed in the film-forming chamber 6 maintained under reduced pressure and vacuum. The target 10 is irradiated with the laser light 5, and the target 10 emits a plume 15.
Are generated and vapor-deposited on the substrate 3 to produce a thermoelectric material. The above is the schematic configuration of the apparatus and the thermoelectric material when the method of the present invention is employed.

1 First, the production of the material 16 shown in FIG. 2 will be described. This material 16 is a so-called Bi-Te-based material, and its composition is Bi ₂ Te ₃ . Reference numeral 17 denotes a high temperature side electrode and 18 denotes a low temperature side electrode. In the example shown in FIG. 1, the target holder 1 located on the upper side.
The target 10 made of a material containing bismuth (Bi) as a main component is provided in 1a, and the target 10 made of a material containing tellurium (Te) as a main component is provided in the target holding material 11b located on the lower side. To be done. Hereinafter, specific manufacturing conditions and characteristics of the manufactured products are listed in Table 1 below.

[0015]

[Table 1] Fabrication object Thermoelectric material (Bi ₂ Te ₃ ) Target Bi side Bi simple substance Te side Te simple substance Substrate material Si (100) P type production substrate temperature room temperature deposition chamber vacuum degree 10 ⁻⁶ Torr laser wavelength 266 nm laser power Density Bi side 40 mJ / cm ² constant Te side 60 mJ / cm ² constant Laser pulse repetition rate 10 Hz Substrate-target distance 20 mm Film formation time 60 min Product Bi ₂ Te ₃ Target film thickness 5 to 10 μm Vapor deposition particle size 2 μm or less

The material thus produced showed thermoelectric properties.

Next, a further embodiment of the present application will be described. The composition of the graded material of this example is shown in FIG.
The gradient material 20 is a so-called P-type Bi-Te-based material, and has a different impurity concentration (specifically, Sb concentration) between the vicinity of the surface 21 of the material and the inner side portion 22 thereof. Therefore, the impurity concentration is set to be higher at the front surface side portion 23. Then, the impurity concentration changes in a gradient in the thickness direction of the material. When manufacturing such a gradient material 20, a plurality of targets 10 are used.
Among them, one is provided with a target 24 composed of a material containing impurities as a main component, and the amount of impurities deposited is changed in accordance with the formation of the thermoelectric material, so that such a gradient is provided. is there. The device configuration is shown in FIG. 3 corresponding to FIG. Practically, the target 24 containing impurities as a main component
By changing the laser energy density of the laser light irradiated toward the target, the change in the deposition amount can be controlled. In the example shown in FIG. 3, antimony (Sb) is added to the target holding table 11a located on the upper side.
The target composed of a material containing tellurium (Te) as a main component has a target holding material 11b positioned on the lower side.
A target, which is a solid solution of bismuth (Bi) and tellurium (Te), is provided in the. Hereinafter, specific production conditions and characteristics of the produced products are listed in Table 2 below.

[0018]

[Table 2] Manufacturing target P-type thermoelectric material (impurity concentration is changed in the thickness direction) Target composition ratio Bi-Te side Bi: Te 2: 3 Sb-Te side Sb: Te 2: 3 Substrate material Si (100 ) P-type production substrate temperature room temperature deposition chamber vacuum degree 10 ^-6 Torr laser wavelength 266 nm laser power density Bi-Te side 60 mJ / cm ² constant Sb-Te side (20 mJ / cm ² at the start of production, at the end of production) 6
0 mJ / cm ² to be continuously changed) laser pulse repetition rate 10Hz substrate - between target distance 20mm film formation time 60min prepared target thickness 5~10μm deposition particle size 2μm or less

In order to investigate the morphology of the thermoelectric material produced under the above conditions, the morphology of the material surface was observed by SEM. What was obtained by the laser ablation method of the present application had a so-called grain structure. These had a high figure of merit as a thermoelectric material.

[Further Examples] In the above examples, an example of producing a Bi-Te-based thermoelectric material containing bismuth telluride as a main component was shown.
The method of the present application can be applied to the production of a thermoelectric material containing at least two kinds selected from bismuth, tellurium, antimony and selenium such as i-Sb type and Bi-Se type. In the above example, neodymium (Nd ³⁺ ) YA
Although the G laser is adopted, an excimer laser or the like may be used. In this case, the number of pulse repetitions is increased, which has the advantage of improving the film formation rate. Also, the Ar ⁺ laser is suitable because of its high power density. Further, when the KrF excimer laser is used, only the portions corresponding to the film forming conditions shown in Table 1 are as shown in Table 3 below.

[0021]

[Table 3] Vacuum degree of film forming chamber 2.0 × 10 ⁻⁶ Torr Laser wavelength 248 nm Laser power density 200 mJ / cm ² Laser pulse repetition rate 50 Hz Film forming time 60 min Target film thickness 80 to 90 μm Vapor deposition particle diameter 1 μm or less

Therefore, when using this laser,
Since the particle size is small, high speed film formation is possible. Further, as the substrate, other than a silicon substrate, any smooth material such as glass can be used. In the case of glass, there is an advantage that the product is inexpensive. In the above-mentioned embodiment, the attenuator was used to adjust the power density of the laser light with which the target was irradiated, but other methods can also be adopted. As another method, the number of laser light sources and the number of targets are provided, and the irradiation light amount from these light sources is changed and adjusted. Furthermore, as the half mirror used in the above embodiment, a mirror whose transmittance and reflectance can be relatively adjusted is adopted. For example, in the device system shown in FIG. It is also possible to change the composition ratio of the components in the material by adopting a material whose transmittance / reflectance can be adjusted and changing the transmittance ratio as the material is formed. Further, in the above-described embodiment, an example in which a pair of targets is used as a target has been described. However, in the present application, if there are a plurality of targets, the operation and effect of the present application can be achieved.

It should be noted that although reference numerals are given in the claims for convenience of comparison with the drawings, the present invention is not limited to the configuration of the accompanying drawings by the entry.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a laser ablation apparatus.

FIG. 2 is a diagram showing a configuration of a thermoelectric material.

FIG. 3 is a diagram showing a configuration of a laser ablation device.

FIG. 4 is a diagram showing the structure of a material in which the impurity concentration changes in the thickness direction of the thermoelectric material.

[Explanation of symbols]

 2 Thermoelectric material 3 Substrate 4 Laser 5 Laser light 6 Film forming chamber 10 Target 15 Plume 20 Gradient material

Front page continuation (72) Shigeru Morikawa Inventor Shigeru-ku, Kyoto City, Kyoto Prefecture 17 Kyodoji-Minami-cho, Ltd.Kansai Research Institute of Technology (72) Inventor Yoshiyuki Yamada 17 Chudo-ji, Minami-cho, Kyoto-shi, Kyoto Prefecture Inside the New Technology Research Center (72) Hisashi Sakai Hisashi Sakai 17 Nakadoteran-Minami-cho, Shimogyo-ku, Kyoto Prefecture Incorporated Kansai New Technology Research Center (72) Inventor Takatomo Sasaki 2-8 Yamada Nishi, Suita-shi, Osaka A9-310 (72) ) Inventor Yusuke Mori 8-16-9 Private City, Katano City, Osaka Prefecture

Claims (4)

[Claims] 1. A method for producing a thermoelectric material comprising a thermoelectric material containing at least two or more selected from bismuth, tellurium, antimony and selenium, wherein any one or more of the four components is A plurality of targets (10) containing different composition ratios are produced, and the plurality of targets (10) are faced to a substrate (3) to be film-formed in a film-forming chamber (6) which is maintained under reduced pressure and vacuum. ) Is provided, and a plurality of plumes (15) are generated from the plurality of targets (10) by irradiating the plurality of targets (10) with a laser beam (5) and vapor-deposited on the substrate (3). hand,
A method for producing a thermoelectric material, which comprises producing the thermoelectric material by a laser ablation method. 2. When producing the thermoelectric material, the amount of the deposit deposited on each of the plurality of targets (10) on the substrate (3) is set between the targets according to the formation of the thermoelectric material. 2. The method for producing a thermoelectric material according to claim 1, wherein the thermoelectric material is made a gradient material having a different component composition in the forming direction. 3. The thermoelectric material is an impurity semiconductor material containing impurities in the material, and the plurality of targets (1
0) is a material containing the impurity as a main component, and the deposition amount of the impurity is changed in accordance with the formation of the thermoelectric material, so that the thermoelectric material is formed in the direction of formation of the impurity. The method for producing a thermoelectric material according to claim 1, wherein the gradient material (20) has a concentration that changes in a gradient. 4. A laser beam having a wavelength of 193 to 1064 nm for applying the laser ablation method.
And laser power density of 100,000 to 100,000 mJ / cm
² , the degree of vacuum in the film forming chamber (6) is set higher than 10 ^-2 Torr, and the temperature of the substrate (3) is increased from room temperature to 600.
4. The thermoelectric material is produced by setting the temperature to ℃ or below.
The method for producing a thermoelectric material according to any one of 1.