JP3500374B2 - Thermoelectric element and thermoelectric module - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric element and a thermoelectric module which are preferably used for cooling a heating element such as a semiconductor and have excellent thermoelectric characteristics, and in particular, small variations in characteristics and excellent reliability.

[0002]

2. Description of the Related Art Conventionally, a thermoelectric element utilizing the Peltier effect has been widely used as a thermoelectric module for controlling the temperature of a laser diode and cooling a thermostat or a refrigerator. The cooling thermoelectric module used near this room temperature has an A ₂ B ₃ type crystal (A is Bi and / or Sb, B is Te and / or Se) from the viewpoint of excellent cooling characteristics.
A thermoelectric element composed of is generally used.

Furthermore, it is necessary to use the p-type and n-type thermoelectric elements in pairs, and for the p-type, Bi ₂ Te ₃ and Sb ₂ T are used.
e ₃ (antimony telluride) is a solid solution with n-type B
Since the solid solution of i ₂ Te ₃ and Bi ₂ Se ₃ (bismuth selenide) exhibits particularly excellent performance, this A ₂ B ₃ type crystal (A is Bi and / or Sb, B is Te and / or Se) )
Are widely used as thermoelectric elements for cooling thermoelectric modules.

This A ₂ B ₃ type crystal has been produced as an ingot or a single crystal having a large crystal grain size by a melting method such as a zone melting method or a unidirectional solidification, and a sliced one has been used for a long time. The thermoelectric element used in the thermoelectric module has a problem in that most of these crystals having a cleavage plane when they are cut into a size of several mm square easily cause chipping at the element edge portion and the processing yield is extremely low. . Therefore, in recent years, a polycrystalline body produced by hot pressing or the like has been used in order to maintain the strength against processing.

By using a powder having a particle size distribution of 10 to 200 μm in an n-type solid solution raw material of Bi ₂ Te ₃ and Bi ₂ Se ₃ , doping control can be facilitated and thermoelectric properties can be improved. JP-A 64-37456
It has been proposed in the publication.

Similarly, in the p-type solid solution raw material of Bi ₂ Te ₃ and Sb ₂ Te ₃ , it is possible to improve the thermoelectric properties by adjusting the particle size to 10 to 200 μm.
No. 1 publication.

[0007]

However, in the methods described in JP-A-64-37456 and JP-A-3-16281, chipping is somewhat suppressed and the processing yield is increased as compared with the single crystal material. However, there is a large variation in the characteristics, especially when the ON /
There is a problem that module performance deteriorates when it is repeatedly used for a long time and used for a long time.

Therefore, it is an object of the present invention to realize a thermoelectric element and a thermoelectric module which have excellent thermoelectric characteristics, particularly small variations in characteristics, and excellent reliability.

[0009]

According to the present invention, characteristic variations in polycrystalline thermoelectric elements and performance deterioration after long-term use of thermoelectric modules are correlated with the size of the chip formed on the surface of the thermoelectric elements, And it is based on the knowledge that variations in thermoelectric performance and changes over time can be reduced by reducing the maximum depth of the chip, the electronic module using the thermoelectric element of the present invention, the characteristics change even after repeated use. The number is small, the long-term reliability is extremely high, and the reliability variation can be increased.

That is, the thermoelectric element of the present invention has a figure of merit of 2.8 × 10 ^-3 / K or more and an output factor of 3.5 × 10 ^-3 W.
In a thermoelectric element made of a polycrystal having a density of / mK ² or more, the maximum depth of the chip existing on the surface is 50 μm or less. As a result, when used as a thermoelectric module, it has excellent thermoelectric characteristics and small variations in characteristics.
It is possible to provide a highly reliable thermoelectric element.

Particularly, it is preferable that the average particle size is 20 μm or less and the relative density is 97% or more. By reducing the particle size and increasing the relative density, it is possible to increase the processing yield, prevent the particles from falling off, and reduce the maximum surface roughness.

Further, the thermoelectric elements are Bi, Sb, T
It is preferable to include at least two of e and Se.
This makes it possible to obtain a thermoelectric element having excellent thermoelectric characteristics.

Furthermore, the hardness of the surface is 0.
It is preferably at least 5 GPa. Due to this high hardness, it is possible to suppress a reduction in processing yield.

Further, the thermoelectric module of the present invention includes a supporting substrate, a plurality of the thermoelectric elements arranged on the supporting substrate, a wiring conductor for electrically connecting the plurality of thermoelectric elements, and the supporting substrate. An external connection terminal provided on the wiring conductor and electrically connected to the wiring conductor is provided. By adopting such a configuration, it is possible to realize a thermoelectric module having excellent thermoelectric characteristics, small variations in characteristics, and high reliability.

Particularly, the form factor of the thermoelectric element is 2000.
/ M or more, and the device density is preferably 100 / cm ² or more. As a result, the amount of heat absorbed per unit area can be increased and the cooling capacity can be increased.

Further, a cooling substrate is provided on the surface of the plurality of thermoelectric elements opposite to the supporting substrate, and the supporting substrate is placed at 60 ° C.
The temperature difference between the cooling substrate and the supporting substrate is kept at a maximum by keeping current at the temperature of 100 ° C. and the temperature difference between the cooling substrate and the supporting substrate is maximized, and then the current is stopped 10,000 times. The rate of change is preferably 8% or less. Such a thermoelectric module having a small resistance change has high reliability and can be suitably used as a cooling module that requires long-term reliability such as laser diode cooling.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION When a thermoelectric element having a figure of merit of 2.8 × 10 ^-3 / K or more and an output factor of 3.5 × 10 ^-3 W / mK ² or more is built into a thermoelectric module, It is possible to increase the maximum temperature difference and the amount of heat absorption and to show a high cooling capacity.

The figure of merit Z is Z = S ² / where S is the Seebeck coefficient, ρ is the resistivity, and k is the thermal conductivity.
It is defined by ρk and shows the efficiency when the thermoelectric element is used as a cooling element or a power generation element. Further, the output factor is a numerical value represented by PF = S ² / ρ and has a particular effect on the heat absorption amount.

When the thermoelectric element is used by incorporating the supporting substrate and the cooling substrate into the thermoelectric module such that the thermoelectric element is sandwiched between the thermoelectric element and the thermoelectric module, when the thermoelectric element is energized, a temperature difference between the cooling substrate and the supporting substrate is produced. Of 60 ° C. or higher, the thermoelectric element itself is easily distorted, and the difference between the coefficient of thermal expansion of the thermoelectric element and the coefficient of thermal expansion of the cooling substrate or the supporting substrate is large, so that the thermoelectric element is deformed.

That is, warpage occurs on the upper and lower surfaces of the module, and as a result, a large strain occurs in the element. Although this stress is slight, stress concentration occurs in the defect portion where the particles are shed, so that the crack progresses by repeating the energization. In addition, since it becomes a barrier (gap) when a current is passed, it is likely to cause a short circuit.

Therefore, when a thermoelectric element having a large number of chips or a thermoelectric element having a large number of chips is used, the initial characteristics are excellent, but the O is kept for a long time such as cooling the laser diode.
It is not preferable in a module that repeats N-OFF cooling.

Those having excellent characteristics with a figure of merit of 2.8 × 10 ^-3 / K or more and an output factor of 3.5 × 10 ^-3 / K or more have a large characteristic deterioration due to the above deformation.
It is important for the thermoelectric element of the present invention that the maximum depth of the chip existing on the surface is 50 μm or less in order to maintain the characteristics of the thermoelectric element even if there is repeated deformation caused by repeated energization and stop of energization. Is.

Further, according to the present invention, it is necessary that the maximum defect depth of both N-type and P-type elements used in the thermoelectric module is 50 μm or less.
If the maximum defects of either N-type or P-type devices are small, the same effect as when the maximum defects of all devices are reduced can be expected. For example, the maximum defects of N-type devices are all 50 μm
Even if the maximum defects of all P-type elements are 10 μm or less, the same long-term reliability as when the maximum defects of all N-type and P-type elements are 10 μm can be secured. This is because the total amount of deformation can be reduced by reducing the maximum defects of half the elements used in the module.

Further, according to the present invention, it is preferable that the maximum depth is small in order to improve the reliability, but in order to suppress the processing cost, the lower limit of the maximum depth is 0.5 μm, particularly 1 μm.
m, more preferably 2 μm, and the upper limit is preferably 20 μm, more preferably 15 μm, and more preferably 10 μm in order to obtain high characteristics and high reliability.

The change in the characteristics due to the above deformation occurs because the crack gradually progresses from the chip included in the thermoelectric element, so that the area through which the current flows is substantially reduced. Is caused by the shedding of. The defects due to the grain removal reduce the yield at the time of module assembly, and the defects grow during ON-OFF energization, which lowers the reliability.

Therefore, by making the average particle size small, it is possible to reduce the dropout of particles and to make the maximum depth of the chip small, in particular 20 μm or less, further 15 μm or less, and more preferably 10 μm or less. It is preferable that the maximum depth of the chip is 20 μm or less and 15
It becomes easy to reduce the thickness to 10 μm or less.

According to the present invention, the average particle size is 20 μm.
By setting m or less, the thermal conductivity can be further reduced, and as a result, the effect of further improving the thermoelectric figure of merit can be expected.

Further, although the lower limit of the average particle diameter is not directly related to the reliability of the thermoelectric characteristics, it is particularly 0.5 μm, more preferably 1 μm in view of easiness of handling and raw material cost.
It is preferably μm, and more preferably 2 μm.

The average particle diameter in the present invention is measured from the SEM photograph of the fracture surface of the thermoelectric element by the intercept method or the like with the minor axis of 200 particles as the average particle diameter.

According to the present invention, the relative density is 97% or more,
In particular, it is preferably 98% or more, further preferably 99% or more. By increasing the relative density in this way, the dropout of crystal grains can be further reduced. It should be noted that by increasing the compactness, it is possible to reduce the specific resistance and easily reduce the performance index and the output factor.

The shape of the thermoelectric element is not limited, but it is preferably a long shape in consideration of mounting on the thermoelectric module. This is because when the elements are arranged in series on the rectangular substrate, a square element cross-sectional area ensures a higher cross-sectional area, and the heat absorption amount can be increased accordingly.

The thermoelectric element may be formed by firing a molded body by extrusion molding, cutting it, machining it, or forging the sintered body by a forging method. However, when it is produced by sintering in a die such as hot pressing or pulse current sintering, it is preferably obtained by cutting the sintered body. Further, it is also effective to remove the chip generated at the end by the R processing or the C surface processing.

In the present invention, the term "chips present on the surface" refers to the surface of the thermoelectric module excluding the surface to be joined to the supporting substrate or the cooling substrate. For example, in the case of a long rectangular parallelepiped, the longitudinal direction It means a side surface consisting of four surfaces facing to each other, and does not include both end portions joined to the substrate via the electrodes.

The thermoelectric element of the present invention comprises Bi, Sb, Te and S.
It is preferable to include at least two of e, and especially A
It is preferably composed of a ₂ B ₃ type intermetallic compound. here,
A is a semiconductor crystal composed of Bi and / or Sb, B is Te and / or Se, and particularly, the composition ratio B / A is 1.4 to
When it is 1.6, the thermoelectric property at room temperature can be improved.

A₂B₃Known intermetallic compounds of the type
Bi₂Te₃, Sb₂Te₃, Bi₂Se₃At least one of
Seed is preferable, and Bi is used as a solid solution.₂Te₃And B
i₂Se₃Is a solid solution of Bi₂Te_3-xSe_x(X = 0.
05-0.25), or Bi ₂Te₃And Sb₂Te₃Solid solution of
Bi that is the body_xSb_2-xTe₃(X = 0.1-0.6) etc.
Can be illustrated.

Impurities can be added as dopants in order to efficiently convert the above intermetallic compound into a semiconductor. For example, by incorporating a compound containing a halogen element such as I, Cl and Br into the raw material powder,
An n-type semiconductor can be manufactured.

Examples of such compounds include AgI and CuB.
r, SbI₃, SbCl₃, SbBr ₃, HgBr₂Etc. as an example
Can be shown, and by adding these, the intermetallic compound semiconductor
You can adjust the carrier concentration in the body, and as a result,
It is possible to improve thermoelectric properties. Halogen source above
The element is 0.01 to 5% by weight in terms of efficient semiconductor formation,
In particular, it is preferable that the content is 0.1 to 4% by weight.

Further, when manufacturing a p-type semiconductor,
Te can be added to adjust the carrier concentration,
Like the n-type semiconductor, the thermoelectric property can be improved.

The surface hardness is preferably 0.5 GPa or more, particularly 0.6 GPa or more, and further 0.7 GPa or more. If the hardness is high, there is an effect of suppressing shedding during processing, making it difficult to deform, suppressing the development of cracks, and further improving reliability.

The maximum depth of the chip in the present invention is
It refers to the difference between the flat portion and the concave portion on the surface of the sintered body formed by the scratches or the dropped portions of the particles. The maximum depth is either a large value obtained by directly observing a particle falling portion observed with a microscope or the like with an SEM or the like, or by measuring with a non-contact type surface roughness measuring instrument. The measurement points depend on the state of particle loss, but can be obtained by measuring two or more points per 1 mm ² and determining the maximum value.

Next, a method for manufacturing the thermoelectric element of the present invention will be described.

First, a raw material powder is prepared. The raw material powder to be used may be an ingot prepared by a melting method or the like, and a commercially available powder having a large particle size may be classified. For example, a relatively inexpensive commercially available powder having a nonuniform particle size is prepared into a desired composition, and an organic solvent is used. The powder used in the present invention can be easily obtained by adding and pulverizing.

It is preferable to heat-treat the above raw material powder in advance in a hydrogen stream before firing. This heat treatment is performed in a hydrogen stream, and the impurity oxygen on the surface of the raw material powder is reduced and removed by hydrogen gas, and the oxides with high specific resistance are reduced, so the specific resistance of the sintered body obtained by firing is reduced. Can be reduced.

The raw material powder subjected to the heat treatment in hydrogen is filled in a firing mold and fired, and it is preferable to pressurize during firing in order to obtain a dense body. For example, pulse current sintering method (PE
CS), hot press method (HP), gas pressure sintering method (GP
S), hot isostatic pressing (HIP), etc. can be used.

By applying pressure during firing, the firing temperature can be lowered and the firing time can be shortened, so that grain growth during firing can be suppressed, particles can be made uniform, and thermoelectric characteristics can be improved. . In order to obtain a more compact and more compact sintered body more easily, PECS and HP are particularly preferable. Further, when the PECS is performed, the sintering time is completed within 30 minutes including the temperature increase, so that the microstructure control is easy, PECS is preferable because excellent characteristics can be obtained.

The firing temperature is in a temperature range lower than the melting point (T) by about 150 ° C., particularly (T-120 ° C.) to (T-20).
The temperature range of (° C.) is preferred. For example, about 400 to 500 ° C. is preferable for Bi ₂ Te ₃ and about 400 to 480 ° C. is preferable for Bi _0.5 Sb _1.5 Te ₃ .

If desired, the raw material powder may be molded before firing. For the molding, known molding methods such as a die pressing method, a cold isostatic pressing (CIP method), a doctor blade method, a calender roll method, a rolling method, an extrusion molding method, a casting molding method and an injection molding method may be used. it can. Among these, especially die pressing method, CIP
The method is preferable in terms of simplicity and mass production. Note that crystal orientation is also effective in improving thermoelectric characteristics by applying a high magnetic field during molding.

The sintered body obtained by firing is cut into a long element shape by a dicing saw or the like. At this time, in order to suppress particle shedding, methods such as making the blade of the diamond saw thin and slowing the cutting speed are effective for reducing the chip and the depth of the chip.

If desired, the cut surface can be processed by a known method. In particular, polishing the surface by lapping or polishing or removing a chip generated at the edge of the end is also effective for improving reliability.

The thermoelectric element thus produced has a figure of merit of 2.8 × 10 ^-3 / K or more and an output factor of 3.5 × 10 ^-3.
It is possible to obtain the thermoelectric element of the present invention having W / mK ² or more and having a high reliability in which the maximum depth of the chip existing on the surface is 50 μm or less.

The thermoelectric module of the present invention comprises a support substrate,
A plurality of thermoelectric elements arranged on the support substrate, a wiring conductor electrically connecting the plurality of thermoelectric elements, and an external connection terminal provided on the support substrate and electrically connected to the wiring conductor. And a thermoelectric module.

That is, the same number and a plurality of n-type thermoelectric elements and p-type thermoelectric elements are arranged at appropriate intervals, and they are electrically connected in series such as n-type, p-type, n-type and p-type, respectively. Furthermore, it has a structure in which both ends of the thermoelectric element are connected to external electrodes and are sandwiched by heat exchange substrates.

It is important for obtaining high reliability that the thermoelectric element used in the thermoelectric module is the above-mentioned thermoelectric element of the present invention.

When the thermoelectric module is actually used for cooling, it is necessary to provide a cooling substrate on the surface of the thermoelectric element opposite to the supporting substrate. This cooling substrate is bonded on a thermoelectric element via an electrode, and a heating element, a device for cooling, or the like is placed on the cooling substrate for use.

Further, in the thermoelectric module of the present invention, it is preferable that the shape factor of the long thermoelectric element is 2000 / m or more and the element density is 100 pieces / cm ² or more in order to improve thermoelectric characteristics. By increasing the form factor, the amount of current to be applied can be reduced, and by increasing the element density of the ceramic substrate of the thermoelectric module to 100 or more, the heat absorption amount can be increased.

Here, the shape factor is L / S represented by the ratio of the element thickness L to the element cross-sectional area S, and the element density is the number of thermoelectric elements existing per unit area (cm ² ). is there.

In this case, since the cross-sectional area of the element becomes small, the reliability was poor when a large element having a maximum chip depth exceeding 50 μm was used, but the element density was improved by using the thermoelectric element of the present invention. The reliability does not deteriorate even when the value is increased.

Further, in the thermoelectric module of the present invention, the resistance change rate of the thermoelectric module after the output cycle test of 10,000 times is 8% or less, particularly 6% or less, and further 5% or less. Is preferable for ensuring. As described above, when the change in resistance is small after the output cycle test of 10,000 times, the laser diode can be suitably used for a long time as a cooling application.

The output cycle test of the thermoelectric module according to the present invention will be described in detail below. First, a test sample is prepared. That is, a support substrate, a plurality of thermoelectric elements arranged on the support substrate, a wiring conductor for electrically connecting the plurality of thermoelectric elements, and provided on the support substrate,
A cooling substrate is provided on the surface of the thermoelectric module opposite to the support substrate of the thermoelectric module, which is provided with the wiring conductor and the external connection terminal electrically connected, to obtain a sample.

The temperature is adjusted so that the supporting substrate is kept at a temperature of 60.degree. A current is passed through the thermoelectric element via the external connection terminal. The energization cools the cooling substrate, and the maximum temperature difference between the support substrate and the cooling substrate occurs when a maximum current is applied. The temperature difference between the cooling substrate and the supporting substrate is maximized by energization and maintained for 90 seconds, then the energization is stopped and left as it is for 270 seconds. In this way, when one cycle from energization to the next energization is performed, this is repeated 10,000 times.

[0061]

As EXAMPLES N-type material, the ingot containing SbI ₃ 0.06 wt% as a dopant fabricated purity of 99.99% or higher Bi ₂ Te _{2 .85} Se _0.15 in pulling method, similar to the P-type Bi _0.5 Sb _1.5 produced by the process
A Te ₃ ingot was prepared.

The above ingot was crushed by a stamp mill and then crushed by a ball mill as shown in Table 1. The obtained slurry was taken out, dried and sieved with 40 mesh.

The powder was heated at 350 ° C. to 400 ° C. for 5 hours,
After heat treatment in a hydrogen stream, it was filled in a carbon mold, and the hot pressing method (HP) and pulse current sintering method (PECS) were performed under the conditions shown in Table 1 for the P type and Table 2 for the N type. Baked.

If desired, the powder may be pressed at a pressure of 15
After being molded at 0 MPa into a diameter of 20 mm and a thickness of 15 mm, and heat-treating the molded body in a hydrogen stream, Table 1 shows the case of P type.
In the case of N type, the gas pressure sintering method (GP
S), and was fired by hot isostatic pressing (HIP).

The relative density of the sintered body was calculated as a ratio to the density of the ingot by measuring the density by the Archimedes method. HP and PECS are the pressing direction during sintering,
In the GPS and HIP methods, thermal conductivity (k) and Seebeck coefficient (S) in the direction perpendicular to the pressing direction during molding
In order to measure the resistivity and the resistivity (ρ), measurement samples were prepared. For thermal conductivity measurement, diameter 10 mm, thickness 1
For a disk sample having a size of 3 mm, a rectangular column sample having a length of 3 mm, a width of 3 mm, and a length of 15 mm was prepared for measuring Seebeck coefficient and resistivity.

The thermal conductivity was measured by the laser flash method.
The Seebeck coefficient and the resistivity were measured under the conditions of 20 ° C. by a thermoelectric power evaluation device manufactured by Vacuum Riko Co., Ltd., respectively.

The figure of merit Z is expressed by the formula Z = S ² / ρk
(S is the Seebeck coefficient, ρ is the resistivity, and k is the thermal conductivity). The output factor is PF = S ² /
It was calculated by ρ.

After the surface of the sample whose thermal conductivity was measured was mirror-finished, a part of the sample was chemically etched, and several SEM photographs were taken at a magnification at which the particle diameter could be confirmed. The average minor axis particle size of 300 pieces was measured and defined as the average particle size. Furthermore, the hardness was measured by the micro Vickers method.

Next, the sintered body was sliced with a wire saw so that the direction perpendicular to the above-mentioned pressing surface was the thickness direction, and the side surface was subjected to surface grinding with a diamond grindstone of # 600 or more to obtain electroless Ni. After plating, Au plating was applied.

Thereafter, the sample was diced into the width shown in Table 3 with a dicing saw. The blade width, processing speed and rotation speed of the dicing saw were set to the conditions shown in Tables 1 and 2. Each dicing thermoelectric element is observed with a scanning electron microscope (SEM) at the end of the side surface of the thermoelectric element, a photograph is taken, the size of the chip is measured, and the maximum size (R ₁ ) is selected. In addition, the surface roughness (R _max ) was obtained with a surface roughness meter, and the larger of R ₁ and R _max was taken as the maximum depth of the defect.

A plurality of the obtained n-type and p-type thermoelectric elements are arranged on a supporting substrate on which copper electrodes are formed in a pattern, and S
A thermoelectric module was manufactured by bonding using n-Pb solder.

The shape factor and the element density were calculated from the substrate shape and the number of elements of the thermoelectric module, and shown in Table 3. The substrate used had several copper electrode patterns in order to change the device density.

A thermoelectric module is installed in a vacuum, a copper heat sink is adhered to its supporting substrate with a heat conductive grease, and circulating water temperature is set to 2 while circulating water is flowing through the heat sink.
The temperature difference (ΔT _max ) that maximizes the cooling surface temperature was determined by changing the current value flowing in the module when the temperature was kept constant at 7 ° C.

Similarly, the supporting substrate is held at 27 ° C., a heater is installed on the cooling substrate, and the thermoelectric module is operated to heat the cooling substrate to 27 ° C. (Qcmax). Was measured.

The module further has a circulating water temperature of 60 ° C.
And energize for 1.5 minutes with the maximum current flow (O
N), an ON-OFF repeated test of turning OFF for 4.5 minutes was performed for 10,000 cycles, the resistance of the thermoelectric module was measured before and after the above test, and the change rate thereof was calculated. For the resistance measurement, the resistance of the entire internal circuit including the thermoelectric element was measured at the external connection terminal of the thermoelectric module. The results are shown in Tables 1 to 3.
In Table 3, the smaller of the maximum depths of defects of the p-type and n-type thermoelectric elements is shown as d.

[0076]

[Table 1]

[0077]

[Table 2]

[0078]

[Table 3]

Sample No. of the present invention of p type. 1-5, 7-1
1, 13, 14, 16 and 17 have a chip depth of 43μ
m or less, the thermoelectric figure of merit was 3.04 × 10 ⁻³ / K, and the output factor was 3.55 × 10 ⁻³ W / mK ² or more.

Further, the n-type sample No. of the present invention was used. 19-2
3, 25-29, 31, 32, 34 and 35 have a chip depth of 40 μm or less and a thermoelectric figure of merit of 2.87 × 10 ^−3.
/ K, and the output factor was 3.5 × 10 ⁻³ W / mK ² or more.

Sample N produced by combining these
o. The thermoelectric modules 37 to 41 and 43 to 51 had a resistance change rate of 5.7% or less. Especially, d is 20 μm
The following sample No. The thermoelectric modules 37-40 and 43-51 had a resistance change rate of 2.9% or less. Furthermore, the sample No. with d of 15 μm or less. 37-40 and 43
The rate of change in resistance of the thermoelectric modules of ˜50 was 2.3% or less. Furthermore, the sample No. with d of 10 μm or less.
The thermoelectric modules 37-39, 43-47 and 48 are
The rate of resistance change was 1.8% or less.

On the other hand, p-type sample No. 1 having a maximum defect depth of more than 50 μm. Nos. 6, 12, 15, 18 and n-type sample No. having a maximum defect depth exceeding 50 μm. 24, 30,
Even if 33 and 36 were combined to form a thermoelectric module, the resistance change rate exceeded 8%, or the element was destroyed.

[0083]

EFFECTS OF THE INVENTION According to the present invention, by controlling the size of the chip generated on the surface, especially on the edge, to 50 μm or less, even if the thermoelectric element is deformed by a heat load as a thermoelectric module, the thermoelectric element can be used for a long time High performance can be maintained, and variations in thermoelectric characteristics can be reduced. Further, the thermoelectric module of the present invention is very excellent in long-term reliability in repeated use, and it is possible to reduce variations in reliability of the thermoelectric module.

Front page continuation (51) Int.Cl. ⁷ identification code FI H01L 35/34 H01L 35/34 (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 35/16 C22C 12/00 C22C 28 / 00 H01L 35/18 H01L 35/32 H01L 35/34

Claims (7)

(57) [Claims] 1. A thermoelectric element made of a polycrystal having a figure of merit of 2.8 × 10 ⁻³ / K or more and an output factor of 3.5 × 10 ⁻³ W / mK ² or more, which is free from defects existing on the surface. A thermoelectric element having a maximum depth of 50 μm or less. 2. An average particle size of 20 μm or less and a relative density of 97%.
It is above, The thermoelectric element of Claim 1 characterized by the above-mentioned. 3. The thermoelectric element according to claim 1, wherein the thermoelectric element contains at least two kinds of Bi, Sb, Te and Se. 4. The thermoelectric element according to claim 1, wherein the surface has a hardness of 0.5 GPa or more. 5. A support substrate, a plurality of thermoelectric elements according to claim 1 arranged on the support substrate, a wiring conductor electrically connecting the plurality of thermoelectric elements, A thermoelectric module, comprising: an external connection terminal provided on a support substrate and electrically connected to the wiring conductor. 6. The thermoelectric module according to claim 5, wherein the shape factor of the thermoelectric element is 2000 / m or more and the element density is 100 pieces / cm ² or more. 7. A cooling substrate is provided on the surface of the plurality of thermoelectric elements opposite to the supporting substrate, the supporting substrate is maintained at a temperature of 60 ° C., and a current is passed through the thermoelectric elements to cool the thermoelectric elements. 7. The resistance change rate is 8% or less after an output cycle test in which the temperature difference between the substrate and the supporting substrate is kept to a maximum and then the energization is stopped 10,000 times. The thermoelectric module described.