Thermoelectric semiconductor deaerated into a vacuum and thermoelectric panel using p-type and n-type thermoelectric semiconductors

Abstract: A thermoelectric semiconductor device is disclosed having a structure wherein a predetermined number of p-type and n-type semiconductor elements (21,22) is arranged in a two-dimensional configuration and is alternatingly electrically connected in series. The device utilizes a heat generation and/or an adsorption phenomenon caused by supplying a DC current to said semiconductor elements or an electromotive force caused by a temperature difference given at each junction between said semiconductor elements. The device is characterized in that the semiconductor elements are arranged with a space between them, each space being either filled with an adiabatic insulation material (25) and being deaerated to a vacuum. Each of said semiconductor elements may be made of a porous material. The application also discloses an electronic refrigeration panel comprising said therporous material semiconductor device, wherein the semiconductor elements are made of a thermoelectric semiconductive material supported by support particles.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric semiconductor device and an electronic refrigeration panel as defined in the preambles of claims 1 and 8 respectively. 2. Description of the Prior Art Recently, electronic devices such as electronic refrigeration, heating and thermoelectric power generation devices which utilize the Peltier effect and/or the Seeback effect have been highly demanded from various demands such as inhibition of freon due to the global atmospheric problem, local refrigeration for electronic apparatuses, small refrigerator for dehumidification, utilization of waste heat of a small amount and the like. In a conventional electronic refrigeration panel, p-type and n-type semiconductor elements each made of a Bi-Te system single or poly-crystalline solid material are arranged alternatively in a two-dimensional configuration and electrically connected in series using Cu plates as electrodes. In a conventional thermoelectric device, poly-crystalline sintered material such as Fe 2 Si or the like is used and p-type and n-type semiconductor elements are jointed with each other directly. It has been known that a heat absorption amount per a consumed power at the refrigerating side of the electronic refrigeration panel is determined by the performance factor of the semiconductive material used and that the performance factor is represented -by Z =S 2. σ/k using Seebeck coefficient S, electrical conductivity σ and thermal conductivity k of the semiconductive material. As is apparent form the above equation, the semiconductive material therefor is preferably demanded to have a large Seebeck coefficients, a high electric conductivity σ and a low thermal conductivity K. Further, in driving a method of the refrigerator of this type, it is driven intermittently after reaching a predetermined refrigeration temperature. In such a case, it is demanded to have a high adiabatic property at the time when no voltage is applied thereto. In the thermoelectric power generation device, each semiconductor element is demanded to have a low thermal conductivity in order to maintain a temperature difference between higher and lower temperature sides. Further, in a semiconductive material such as Bi-Te system material, there have been proposed various technics such that Sb and/or Se are added thereto to reduce a lattice vibration in a heat conduction and that a polycrystalline solidified body with a controlled grain size is made without making a single crystal grow from a molten state to lower the thermal conductivity thereof. In an electronic refrigeration device, it is said theoretically that it is possible to obtain a temperature difference of about 60 °C between the higher and lower temperature sides in a Bi-Te system semiconductive material. However, there is the problem that the lowest achievable temperature at the lower temperature side becomes higher due to an increase of the temperature at the higher temperature side if the amount of heat radiation occurring there is small. The thermal resistance between an ordinary radiation plate and an ambient atmosphere is about 0.0002 to 0.0005 W/cm 2 ·deg under spontaneous cooling and about 0.0004 to 0.0002 W/cm 2 ·deg under forcible air cooling. Accordingly, temperature rise at the radiation side (higher temperature side) is a serious problem. To solve this problem, in a conventional refrigeration panel, a plurality of p-type and n-type semiconductor elements are arranged alternatively in a rectangular configuration, but with a gap therebetween to give a cross section two or three times as large as the sum of their cross sections obtained when they are arranged in contact with each other. Moreover a heat radiation plate having an area about ten times as large as the above sum of their cross sections and fins each having an area about 5 to 7 times as large as the above sum are provided to give a total radiation area about 100 to 200 times as large as the above sum. The heat radiation plate and fins are forcibly air-cooled by a fan or water cooled. However, there is a strong demand to cool a large refrigeration plane to a low temperature without using a large radiation plane and forcible cooling. If such a demand is realized such devices can be widely used for a refrigeration panel of a large size and a wall of a cold reserving chamber. Further, in a conventional structure, bedewings are apt to occur at the lower temperature side and disconnections are often caused at junctions between the element and the electrode by corrosions due to bedewings. EP-A-0 122 121 discloses a thermoelectric device including a plurality of thermoelectric elements, coupling means on opposite sides of the elements interconnecting the elements electrically according to a predetermined pattern, and encapsulant means including an encapsulant material covering the exposed surfaces of the elements. The encapsulant forms void spaces between the elements for effective thermal insulation and confining substantially all of the heat flow from the temperature gradient to and through the elements. The coupling means include electrically conductive plate segments for interconnecting the elements. The segments are joined to the elements on respective opposite sides and are contacted and held in fixed relative relation by the encapsulant. The segments define an outer periphery of the device and the encapsulant material bridge across the segments at the periphery of the device. SUMMARY OF THE INVENTION It is the object of the present invention to provide a thermoelectric semiconductor device that are suitable for use in an electronic refrigeration device and/or a thermoelectric power generation device. An aspect of this object is to provide an electronic refrigeration panel. This object is solved by a thermoelectric semiconductor device according to claim 1 and by an electronic refrigeration panel according to claim 8. Preferred embodiments of the device and panel are defined in the respective subclaims. The invention provides a thermoelectric semiconductor device having a structure wherein a predetermined number of p-type and n-type thermoelectric semiconductor elements is arranged in a two-dimensional configuration and is alternatingly electrically connected in series, wherein the device utilizes a heat generation and/or adsorption phenomenon caused by supplying a DC current to said p-type or n-type thermoelectric semiconductor elements or an electromotive force caused by a temperature difference given at each junction between said p-type and n-type thermoelectric semiconductor elements. The p-type and n-type thermoelectric semiconductor elements are arranged such that a space is provided between each pair of them, each space being filled with an adiabatic insulation material and being deaerated to a vacuum by an air-tight sealing. According to a preferred embodiment, each of said p-type and n-type thermoelectric semiconductor elements is made of a porous material. According to another preferred embodiment of their thermoelectric semiconductor device, the adiabatic insulation material is an inorganic material which may be an inorganic porous material or an inorganic powder material. According to a further preferred embodiment, the spaces filled with said inorganic material are deaerated to a vacuum of 1.3 mbar (1 mm Hg) or less. According to still a further embodiment, the pores in the p-type and n-type thermoelectric semiconductor elements are deaerated to a vacuum of 1.3 mbar (1 mm Hg) or less. The invention also provides an electronic refrigeration panel comprising a thermoelectric semiconductor device wherein the p-type and n-type semiconductor elements are made of a thermoelectric semiconductive material supported by support particles. According to a preferred embodiment of the refrigeration panel, the thermoelectric semiconductor material forms a continuous layer made by sintering it. The support particles may be hollow particles or porous particles. BRIEF DESCRIPTION OF THE DRAWINGS These and other objects and features of the present invention will become clear from the following description taken in conjunction with the preferred embodiments thereof with reference to the accompanying drawings in which: Fig. 1 is a view of a refrigeration panel Fig. 2 is a cross-sectional view of a refrigeration panel in which gaps between p-type and n-type semiconductive elements are filled with an adiabatic material, Fig. 3 is a cross-sectional view of a refrigeration panel in which the inner space of the panel is evacuated to a vacuum, Fig. 4 is a cross-sectional view of a refrigeration panel according to a preferred embodiment of the present invention, Fig. 5 is a cross-sectional view showing a variation of the preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig.1 shows a thermoelectric refrigeration panel. The refrigeration panel is comprised of two rectangular alumina plates 13 and 13 and p-type and n-type semiconductor elements 11 and 12 arranged between said two alumina plates 13 and 13 in a matrix form of 15 × 15 regularly and alternatively. These semiconductor elements 11 and 12 are connected in series by elongated Ni plates 14. Each element is a cube of, for example, 1.5 × 1.5 × 1.5 mm 3 . As semiconductive materials for manufacturing these elements, Bi-Te system materials are used. More concretely, (Bi, Sb) 2 Te 3 and Bi 2 (Te, Se) 3 are chosen. In a manufacturing method therefor, after crushing poly-crystalline solidified bodies of these materials as starting materials, they are milled into a powder by a ball mill using zirconia balls of a diameter of 2mm and a solvent of ethanol. After drying the powder, it is- filled in a tube of platinum and sealed therein after deaeration and then subjected to an HIP treatment at 500 °C and under a pressure of 10 to 1000 Kg/cm 2 . The sample thus formed was taken out from the tube and cut into pieces of 3 mm × 3 mm × 20 mm. The bulk density of the sample was measured at a room temperature and the porosity thereof was determined. The Seebeck coefficient thereof was also determined by measuring the electromotive force and temperatures at both ends of each piece while maintaining a temperature difference of 5 °C between both ends thereof at a room temperature. Further, the electric conductivity thereof was determined by measuring a resistance of the piece by the four terminal method while maintaining it at room temperature. Also, the performance factor Z of the piece was measured according to the Harmer method while hanging both ends of the piece with conductive wires of 0.07 mm in a vacuum at room temperature and the thermal conductivity was determined from the electric conductivity and the Seebeck coefficient. Table 1 indicates the porosity, electric conductivity, Seebeck coefficient, thermal conductivity and performance factor of the p-type semiconductor element 11 and Table 2 indicates those of the n-type semiconductor element 12. Further, by measuring the thermal conduction between the upper and lower alumina plates 13, the thermal conductivity of the panel per unit area was determined. Table 3 indicates the porosity of the semiconductor element and the thermal conductivity of the panel. Sample No. Porosity Vol% Electric conductivity 10 -3 Ωcm Thermal conductivity W/cm·deg Seebeck coefficient µV/deg Performance factor 10 -3 /deg 11 0 1.37 0.014 171 2.86 12 1.5 1.35 0.0138 171 2.86 13 5 1.33 0.0132 172 2.98 14 10 1.28 0.0125 170 2.96 15 30 0.92 0.0092 168 2.82 16 50 0.68 0.0072 165 2.57 Sample No. Porosity Vol% Electric conductivity 10 -3 Ωcm Thermal conductivity W/cm·deg Seebeck coefficient µV/deg Performance factor 10 -3 /deg 17 0 1.16 0.0151 -192 2.83 18 1.5 1.15 0.0150 -191 2.80 19 5 1.12 0.0142 -192 2.91 20 10 1.07 0.0132 -188 2.87 21 30 0.76 0.0099 -179 2.46 22 50 0.59 0.0076 -175 2.38 Sample No. Porosity Thermal conductivity 23 0 0.0372 24 1.5 0.0367 25 5 0.0354 26 10 0.0335 27 30 0.0268 28 50 0.0207 As is apparent from Tables 1 to 3, the semiconductor having pores therein has a lower thermal conductivity and that of the refrigeration panel using the same is also low. Further, it is to be noted that the performance factor of the semiconductor having a porosity higher than 5 % does not become so low though the thermal conductivity thereof is much lowered. Fig. 2 is a schematic cross-sectional view of another thermoelectrical refrigeration panel. This refrigeration panel has substantially the same structure as that shown in Fig. 1. In this embodiment, respective gaps between p-type and n-type semiconductor elements 21 and 22 arranged between two alumina plates 23 are filled with an adiabatic material 25 such as glass fibre having a bulk density of 0.04 g/cm 2 or powder of pearlite having an average diameter of 15 µm. Each side of the panel is sealed with an inorganic adhesive agent 26. Reference numeral 24 indicates an Ni plate connecting adjacent elements. Semiconductor elements 21 and 22 are made of a semiconductive material having a porosity of 30 %. Table 4 shows respective thermal conductivities of-the refrigeration panel. Case No. Composition Thermal conductivity W/cm 2 ·deg *23 Porosity 0 % gaps: not filled 0.0372 29 Porosity 30 % gaps: not filled 0.0268 30 Porosity 0 % gaps filled with glass fibre 0.0361 31 Porosity 30 % gaps filled with glass fibre 0.0254 32 Porosity 0 % gaps filled with pearlite powder 0.0357 33 Porosity 30 % gaps filled with pearlite powder 0.0251 As is easily understood from Table 4, the thermal conductivity of the refrigeration panel can be lowered in the case that gaps are filled with an inorganic porous material or powder since no thermal conduction due to neumatic convection flow occurs therein. Also, it is to be noted that the thermal conductivity of the refrigeration panel using porous semiconductor elements is smaller than that using nonporous semiconductor elements. Fig. 3 shows a schematic cross-sectional view of a further thermoelectric refrigeration panel. The refrigeration panel has a structure substantially the same as that of the refrigeration panel shown in Fig. 2. Namely, p-type and n-type semiconductor elements 31 and 32 are regularly arranged between alumina plates 33 and connected in series by Ni plates 34. Instead of filling gaps with an adiabatic material, the inner space of the panel is evacuated to a vacuum of about 4.3 × 10 -3 mbar (0.001 mmHg) by heating the panel so as to melt a sealing glass 36 arranged around the periphery thereof and then cooling the same. Table 5 shows respective thermal conductivities of the refrigeration panels. Case No. Composition Thermal conductivity W/cm 2 ·deg *23 Porosity 0 % gaps filled with air 0.0372 34 Porosity 30 % gaps filled with air 0.0268 35 Porosity 0 % gaps in a vacuum 0.0351 36 Porosity 30 % gaps in a vacuum 0.0233 As is apparent from Table 5, the refrigeration panels wherein the inner space thereof is kept in a vacuum exhibit small thermal conductivities since no heat conduction due to neumatic convection flow occurs therein. The third embodiment is advantageous in that it is possible to prevent connecting portions between the element and the Ni plate from corrosion and detorioration since no dew condensation occurs in a vacuum. Fig. 4 shows a cross-sectional view of a thermoelectrical refrigeration panel according to a preferred embodiment of the present invention. In this preferred embodiment, gaps between p-type and n-type semiconductor elements 41 and 42 arranged between two alumina plates 43 and connected by Ni plates 44 are filled with an inorganic adiabatic material 45 such as glass fibre having a bulk density of 0.04 g/cm 3 or pearlite powder having an average grain size of 15 µm and the inside thereof is kept in an evacuated state to 1.3×10 -2 mbar (0.01 mmHg) by a glass sealing 46 according to a method similar to that of the third embodiment. Fig. 5 shows a variation of Fig. 4. In this variation, the inner side of the refrigeration panel is deaerated to a vacuum of about 1.3 mbar (1 mmHg) after sealing the periphery thereof with a resin layer of about 1 mm thickness and, thereafter, sealed airtightly. Table 6 shows the thermal conductivity per unit area with respect to refrigeration panels prepared according to the preferred embodiment together with a comparison example. Case No. Composition Thermal conductivit y W/cm 2 ·deg porosity filling material sealing state *23 0 % no (air) 0.0372 37 30 % no (air) 0.0268 38 0 % glass fibre glass seal 0.01 mmHg 0.0351 39 30 % glass fibre glass seal 0.01 mmHg 0.0235 40 0 % pearlite powder glass seal 0.01 mmHg 0.0352 41 30 % pearlite powder glass seal 0.01 mmHg 0.0235 42 0 % pearlite powder resin seal 1.00 mmHg 0.0352 43 30 % pearlite powder resin seal 1.00 mmHg 0.0240 44 0 % no (air) resin seal 1.00 mmHg 0.0364 45 30 % no (air) resin seal 1.00 mmHg 0.0260 0.01 mmHg = 1.3 × 10 -2 mbar 1 mmHg = 1.3 mbar As is apparent from Table 6, the preferred embodiment can enjoy advantages similar to those obtained in the second and third embodiments.

Claims: A thermoelectric semiconductor device having a structure wherein a predetermined number of p-type and n-type thermoelectric semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52) is arranged in a two-dimensional configuration and is alternatingly electrically connected in series, wherein the device utilizes a heat generation and/or adsorption phenomenon caused by supplying a DC current to said p-type or n-type thermoelectric semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52) or an electromotive force caused by a temperature difference given at each junction between said p-type and n-type thermoelectric semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52), characterized in that said p-type and n-type thermoelectric semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52) are arranged such that a space is provided between each pair of them, each space being filled with an adiabatic insulation material (25) and being deaerated to a vacuum by an air-tight sealing. The device of claim 1, wherein each of said p-type and n-type thermoelectric semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52) is made of a porous material. The device of claim 1 or 2, wherein said adiabatic insulation material is an inorganic material (45, 55). The device of claim 3, wherein said inorganic material (45, 55) is an inorganic porous material. The device of claim 3, wherein said inorganic material (45, 55) is an inorganic powder material. The device of any one of claim 3 to 5, wherein said spaces filled with said inorganic material are deaerated to a vacuum of 1.3 mbar (1 mm Hg) or less. The device of claims 2 and 3, wherein the pores in said p-type and n-type thermoelectric semiconductor elements are deaerated to a vacuum of 1.3 mbar (1 mm Hg) or less. An electronic refrigeration panel comprising a thermoelectric semiconductor device according to claim 2, characterized in that said p-type and n-type semiconductor elements (11, 12; 21, 22; 31, 32; 41, 42; 51, 52) are made of a thermoelectric semiconductive material supported by support particles. The refrigeration panel of claim 8, wherein said thermoelectric semiconductor material forms a continuous layer made by sintering the same. The refrigeration panel of claim 8, wherein said support particles are hollow particles. The refrigeration panel of claim 8, wherein said support particles are porous particles.

Inventors: ANDO HAMAE, KUGIMIYA KOUICHI, YOKOTANI YOUICHIROU, ANDO, HAMAE, KUGIMIYA, KOUICHI, YOKOTANI, YOUICHIROU
Applicants: MATSUSHITA ELECTRIC IND CO LTD, MATSUSHITA ELECTRIC INDUSTRIAL CO., LTD.
Application year: 1991
Main classification: H01L35
IPC codes: H01L35