Thermoelectric semiconductor having a porous structure deaerated into a vacuum and thermoelectric panel

Abstract: A thermoelectric semiconductor device having a porous structure and an air-tight sealing structure maintaining it in a derated state is disclosed. A refrigeration panel comprising two rectangular plates (13) and a plurality of p-type (12) and n-type (11) semiconductor elements arranged between said two plates (13) in a matrix form. These semiconductor elements have a porous structure and are arranged alternatively and connected electrically in series by elongated Ni plates (14).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor element and to a thermoelectric semiconductor unit as defined in the preambles of claims 1 and 3 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 a and thermal conductivity k of the semiconductive material. As is apparent form the above equation, the semiconductive material therefore is preferably demanded to have a large Seebeck coefficient, 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 occuring 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. JP-A-61-065487 describes an n-type semiconductor powder and a p-type semiconductor powder which are encapsulated in a glass tube. The powders are molded by sintering under high temperature and high pressure. JP-A-02-071 568 describes a method for improving the heat resistance of a thermoelectric conversion material powder by forming boron carbide on the surfaces of silicon carbides particles. SUMMARY OF THE INVENTION It is the object of the present invention to provide thermoelectric semiconductor elements that are suitable for use in an electronic refrigeration device and/or a thermoelectric power generation device. This object is solved by a semicondicutor element according to claim 1 and by a thermoelectric semiconductor unit according to claim 3. Preferred embodiments of these devices are defined in the respective subclaims. The invention provides a p-type or n-type semiconductor element useful for a thermoelectric semiconductor unit. The element comprises a p-type or n-type semiconductor porous body and electrodes which made of an air-tight material, wherein side surfaces of said porous body are coated with an air-tight insulation material and wherein said porous body has been deaerated. The electrodes are formed on upper and lower end surfaces of said element, and said porous body is made of a gas permeable thermoelectric semiconductive material which is supported by gas permeable support particles. According to a preferred embodiment of said element, said gas permeable thermoelectric semiconductive material is provided as a thermoelectric semiconductive layer on the outher surface of said porous body. The invention also provides a thermoelectric semiconductor unit comprising at least one pair of the above described p-type and n-type semiconductor elements, wherein one of said air tight metal electrodes is a common electrode made of an air-tight metal which electrically connects said pair of semiconductor elements at one end thereof, whereas each of said semiconductor elements is covered by an electrode of an air-tight metal at the other end thereof. An insulation sheet material is inserted between said pair of semiconductor elements, and the other surfaces of said pair of semiconductor elements are covered by an air-tight insulation material. According to a preferrd embodiment of said unit, said insulation sheet material is gas-permeable. According to another preferred embodiment, an assembly of a predetermined number of said p-type and n-type semiconductor elements is arranged alternatingly in a two-dimensional configuration, each semiconductor element having electrodes of an air-tight metal formed on both end surfaces thereof and other side surfaces thereof being covered with an insulating material. Junction electrodes are formed on upper and lower surfaces of said assembly, each of which is made of an air-tight metal and electrically connects said electrodes of a pair of said semiconductor elements at each end surface of said assembly alternatingly in series. An air-tight insulation material is provided covering the outer surfaces of said assembly not covered by said junction electrodes, said air-tight insulation material and said junction electrodes maintaining said assembly in a deaerated state. 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 an enlarged partial cross-sectional view showing a texture of a semiconductive material according to a first preferred embodiment of the present invention, Fig. 2 is an enlarged partial cross-sectional view showing a txture of a semiconductive material according to a second preferred embodiment of the present invention, Fig. 3 is an enlarged perspective view of a semiconductor element partially cut according to a third preferred embodiment of the present invention, Fig. 4 is an enlarged perspective view of a unit of p-type and n-type semiconductor elements according to a fourth preferred embodiment of the present invention, Fig. 5 is a perspective view of an assembly of semiconductor elements according to a fifth preferred embodiment of the present invention, Fig. 6 is an enlarged perspective view of a semiconductor element according to a sixth preferred embodiment of the present invention, Fig. 7 is an enlarged perspective view of a unit of p-type and n-type semiconductor elements according to a seventh preferred embodiment of the present invention, Fig. 8 is an enlarged partial perspective view of a refrigeration panel according to a eighth preferred embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [First preferred embodiment] Fig. 1 shows an enlarged schematic cross-sectional view of a thermoelectric semiconductor material which is desirably available to semiconductor elements of the invention. (Bi, Sb) 2 Te 3 and Bi 2 (Te, Se) 3 are used for p-type and n-type semiconductive materials and glass balloon material having an average particle size of 8 µm and a film thickness of 0.5 µm is used as support particles. Each glass balloon 61 is hollow but is not air-tight. Therefore, glass balloons 61 form a porous material. After crushing a solidified poly-crystalline semiconductive material of p-type or n-type as a starting material, it is milled into a powder having an average particle size of 0.08 µm by a ball mill using zirconia balls of 2 mm and an organic solvent. After drying the powder, it is mixed with a suitable viscous solvent to make a slurry. Then, the glass balloon material is mixed into the slurry and the mixture is dried. By repeating the mixing into the slurry and drying the mixture, the thickness of the semiconductive layer 62 supported by each glass balloon 61 can be varied. The dried mixture is molded into cubic semiconductor elements and they are subjected to a heat treatment for two hours at 500 °C in argon gas. The p-type and n-type semiconductor elements are submerged into a slurry after applying an insulation resin on the side surfaces of each element and, then, dried repeatedly. Then, these p-type and n-type semiconductor elements are arranged alternatively and in contact with each other to form a rectangular and, thereafter, the insulation resin is hardened to joint them each other. Further, they are connected in series by Ni plates. For comparison, semiconductor elements made of a solid semiconductive material are also prepared. In order to measure temperature properties of individual refrigeration panels, a Cu plate of a thickness of 0.3 mm is adhered to the lower temperature side of each panel after applying an insulation grease and a thermocouple is adhered onto the Cu plate. At the higher temperature side of each panel, a heat radiation plate is mounted after applying an insulation grease and thermocouple is adhered to the heat radiation plate. As the heat radiation plate, the following three plates were prepared to measure temperature properties of the panel; Type 1 [Heat radiation condition (1)] Cu heat radiation plate of a thickness of 0.5 mm having a heat radiation area same as the cross-section of the joined semiconductor elements and the surface of which is oxidized. Cooling condition is spontaneous radiation. Type 2 [Heat radiation condition (2)] Cu heat radiation plate of a thickness of 0.5 mm having a size equal to the cross-section of the joined semiconductor elements on which Cu radiation fins are planted at a pitch of 7 mm. Each radiation fin has a thickness of 0.3 mm and a width of 7 mm. The total heat radiation area is three times as large as that of the sole Cu heat radiation plate. Surfaces of the Cu heat radiation plate and fins are oxidized. Cooling condition is spontaneous radiation. Type 3 [Heat radiation condition (3)] Cu heat radiation plate of a thickness of 0.5 mm having a size four times as large as that of Type 1 or 2 Cu heat radiation plate on which Cu radiation fins each having a thickness of 0.3 mm and a width of 7 mm are planted at a pitch of 5 mm. The total heat radiation area is twenty times as large as the cross-section of the joined semiconductor elements. Surfaces of Cu heat radiation plate and fins are oxidized. Cooling condition is spontaneous radiation . There was sought for the condition under which the temperature of the Cu plate at the lower temperature side becomes lowest by varying a current amount of a DC power source under heat radiation conditions (1), (2) and (3), respectively. The measurement was done at a room temperature of 300 K. Table 1 shows the volume percentage a (%) of each thermoelectric semiconductor material, the volume percentage b (%) of the pore, the apparent resistivity c (Ωcm) of the semiconductor element (a, b and c are mean values averaged with respect to p-type and n-type semiconductor elements), the lowest achievable temperature d (K) at the of the heat radiation fin at the time when the lowest achievable temperature was realized and the current quantity f (A) at that time. [Cooling condition (1)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c(Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 46 100 0 0.0010 300.0 300.0 0.0 47 72.5 22 0.0015 299.8 301.8 0.2 48 51.3 43.6 0.0021 299.3 302.3 0.5 49 27.9 67.3 0.0045 298.7 304.4 0.5 50 5.2 90.6 0.0250 295.0 314.5 0.4 51 1.8 93.2 0.1020 290.7 330.8 0.3 [Cooling condition (2)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c (Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 52 100 0 0.0010 298.6 301.5 1.0 53 72.5 22 0.0015 298.0 301.8 1.5 54 51.3 43.6 0.0021 297.1 305.7 1.5 55 27.9 67.3 0.0045 294.6 308.2 1.3 56 5.2 90.6 0.0250 284.5 323.7 1.0 51 1.8 93.2 0.1020 283.9 319.7 0.4 [Cooling condition (3)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c (Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 58 100 0 0.0010 289.1 310.3 8.3 59 72.5 22 0.0015 287.6 312.2 7.8 60 51.3 43.6 0.0021 281.8 315.4 7.2 61 27.9 67.3 0.0045 273.1 320.0 5.8 62 5.2 90.6 0.0250 263.9 313.2 2.2 63 1.8 93.2 0.1020 279.0 304.3 0.5 As is apparent from Table 1, the semiconductor elements made of a semiconductive material comprised of glass balloon supports and a semiconductive player supported thereby is able to make the lowest achievable temperature reasonably lower than that of the semiconductor with no pores therein. [Second preferred embodiment] (Bi, Sb) 2 Te 3 and SrTiO 3-X are used for p-type and n-type semiconductive materials, respectively, and foam alumina balloons having a mean particle size of 1 mm, a porosity of 95 % and a mean pore size of 4 µm are used as support particles for the semiconductive material in a second preferred embodiment. Solidified poly-crystalline mass of (Bi, Sb) 2 Te 3 and sintered mass of SrTiO 3-X as starting materials are crushed separately and each material is milled into a powder having a mean grain size of 0.08 µm by a ball mill using zirconia balls of 0.2 mm and an organic solvent. After drying the same, it is mixed with a viscous solvent to make a slurry having a density in which the semiconductive material is adhered to surfaces of the alumina balloons. Then, the mixture in a slurry state is dried. The thickness of the semiconductor layer can be increased by repeating the mixing process and drying process. After drying the material obtained, the same is subjected to a heat treatment for two hours at a temperature of 500 °C in argon atmosphere. Fig. 1 shows an enlarged schematic cross-sectional view of the semiconductor obtained according to the manufacturing process mentioned above. As shown in Fig. 1, the semiconductor is comprised of alumina balloons 71 and a thermoelectric semiconductor layer 72. After forming semiconductor elements in a configuration of a cube, they are assembled so as to constitute a refrigeration panel by a method similar to that stated in the first preferred embodiment and physical quantities same as those cited in Table 1 were measured under the same cooling conditions (1), (2) and (3) as those of the first preferred embodiment. Table 2 shows results of the measurement. [Cooling condition (1)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c(Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 64 100 0 0.0010 300.0 300.0 0.0 65 54.6 38.3 0.0025 299.6 301.8 0.5 66 33.3 60.6 0.0034 299.5 301.4 0.3 67 15.3 77.9 0.0073 298.8 304.2 0.4 68 8.3 86.0 0.0125 298.1 305.1 0.3 69 1.4 90.6 0.1250 294.3 318.3 0.2 [Cooling condition (2)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c(Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 70 100 0 0.0010 299.3 301.1 1.0 71 54.6 38.3 0.0025 298.5 302.3 1.2 72 33.3 60.6 0.0034 297.9 303.4 1.3 73 15.3 77.9 0.0073 295.7 307.5 1.0 74 8.3 86.0 0.0125 293.2 310.2 0.8 75 1.4 90.6 0.1250 289.1 313.9 0.4 [Cooling condition (3)] Case No. Volume % of Semicon. a(%) Volume % of pore b(%) Resistivity c(Ωcm) Lowest achiev Temp. d(K) Temp. at radiat side e(K) Current amount f(A) 76 100 0 0.0010 294.4 305.0 6.3 77 54.6 38.3 0.0025 290.3 303.3 5.5 78 33.3 60.6 0.0034 287.2 310.2 5.0 79 15.3 77.9 0.0073 278.8 312.4 3.2 80 8.3 86.0 0.0125 277.0 311.1 2.5 81 1.4 90.6 0.1250 284.4 303.5 0.4 As is apparent from Table 2, cases in that the porous semiconductor elements are used can make the lowest achievable temperature much lower than that of the case using the solid semiconductor elements. This effect is enhanced under the cooling conditions (1), (2) and (3) mentioned above in each of which the heat radiation surface area per the cross-section of the semiconductor element is small and the cooling condition is spontaneous radiation having a radiation efficiency lower than that of an ordinary electronic refrigeration device. [Third preferred embodiment] In this preferred embodiment, (Bi, Sb) 2 Te 3 and Bi 2 (Te, Se) 3 are also used for p-type and n-type semiconductive materials and, as support particles, glass balloon material having a mean particle size of 500 µm and a shell thickness of 1.5 µm. The glass balloon material has a hollow structure and a structure of porous pellets having a mean pore size of 25 µm partially. Since the glass material itself is porous, the glass balloon material form a porous material. After crushing a solidified poly-crystalline semiconductive material of p-type or n-type as a starting material, it is milled into a powder having a mean particle size of 0.08 µm by a ball mill using zirconia balls of 0.2 mm and an organic solvent. After drying the powder, it is mixed into a suitable viscous solvent to make a slurry. By repeating the mixing into the slurry and drying the mixture, the thickness of the semiconductive layer supported by the glass balloon material can be varied. The dried mixture is molded into cubic semiconductor elements and they are subjected to a heat treatment for two hours at 500 °C in argon atmosphere. The p-type and/or n-type semiconductor element thus manufactured has a volume percentage of 5.3 %, a porosity of 90.6 %, a resistivity of 0.0250 Ωcm and a Seebeck coefficient of 200 µV/deg. Fig. 3 is an enlarged perspective view of a semiconductor element partially cut off according to the third preferred embodiment. Each cubic semiconductor element 81 is subjected to an Ni electrolytic plating treatment to form electrodes on the upper and bottom surfaces thereof and, thereafter, Cu plates 82 are adhered to respective plated surfaces to form upper and lower electrodes 82. Further, an air-tight insulation resin 83 of ultraviolet curing type is coated on side surfaces thereof in a vacuum and is cured by irradiation of ultraviolet rays. The p-type and n-type semiconductor elements are alternatively arranged in a rectangular with no gap and fixed using a suitable bonding agent with each other to form the main body of a refrigeration panel. Thereafter, these are connected in series using Ni plates. On the lower temperature side of the refrigeration panel, insulation grease is applied thinly and a Cu plate of a thickness of 0.3 mm is bonded. On the Cu plate, a thermocouple is mounted to measure thermal properties. On the higher temperature side thereof, insulation grease is coated and a heat radiation plate having a thickness of 0.5 mm is adhered. The heat radiation plate has a size four times as large as the cross-section of the main body comprised of the semiconductor elements. This radiation plate provides with Cu radiation fins planted thereof at a pitch of 5 mm each of which has a thickness of 0.3 mm and a width of 10 mm. A thermocouple is mounted on the heat radiation plate to measure thermal properties of the refrigeration panel. The cooling condition is spontaneous radiation. The measurement was made at an ambient temperature of 300 K to seek for a condition under that the lowest achievable temperature was obtained at the lower temperature side while varying a current amount of an electric power source. Since it is possible to cool the lower temperature side of the panel down to about 0 °C in the cases in that the porous semiconductor elements are used, bedewing occurs usually. Therefore, bedewing was caused repeatedly by applying an electric current for 20 minutes every two hours to measure variations of various physical quantities. Table 3 shows each compositional condition of each sample tested, the lowest achievable temperature at the lower temperature side thereof, a temperature of the fin at a time when the lowest achievable temperature is obtained, a current amount at that time and a number of times of repetition of bedewing at which any detorioration was observed. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 82 solid semiconductor elements 288.3K 310.3K 8.3A 83 porous semiconductor but not air-tight 263.9K 313.2K 2.2A 138 84 porous semiconductor air-tight at 50 Pa 259.2K 314.6K 2.2A over 500 times 85 porous semiconductor air-tight at 100 Pa 259.5K 314.7K 2.2A over 500 times 86 porous semiconductor air-tight at 1,000 Pa 263.5K 313.2K 2.2A over 500 times 87 porous semiconductor air-tight at 10,000 Pa 263.7K 313.6K 2.2A 413 As is easily understood from Table 3, when porous semiconductor elements are used, the lowest achievable temperature at the lower temperature side can be lowered in comparison with the case using solid semiconductor elements. But, deterioration due to the bedewing may be caused in the case of the porous semiconductor element. Further, if semiconductor elements deaerated individually were used as in the present preferred embodiment, the lowest achievable temperature could be lowered further and lifetime against the detorioration due to the bedewing could be elongated much more. The present preferred embodiment is advantageous especially under the cooling conditions mentioned above. Further, since each semiconductor element is formed to have an air-tight structure in the present preferred embodiment, it becomes possible to assemble the elements in an arbitrary configuration resulting in a wide use. [Fourth preferred embodiment] Fig.3 is an enlarged perspective view of a unit comprised of a pair of p-type and n-type semiconductor elements 94 and 95. These semiconductor elements 94 and 95 are manufactured according to the same method as that of the first preferred embodiment. Between the pair of p-type and n-type semiconductor elements 94 and 95, an insulation film 96 such as a ceramic film is inserted and, on upper surfaces of them, Cu electrode plates 97, are soldered respectively, but insulated by the above insulation film 96. The lower surfaces of them are commonly connected by a common Cu electrode plate 98 of thickness of 0.3 mm soldered thereon. These units thus formed are set in a vacuum chamber and ultraviolet-curing resin is applied to all side surfaces of each unit therein. Thereafter, the resin is cured by irradiation of ultraviolet rays. The cured resin layer 99 maintains each unit in an air-tight structure. A predetermined number of the units are arranged so as to be able to connect them in series, joined tightly and connected in series using Ni plates. Two alumina plates are adhered on upper and lower surfaces of the joined body of the units to form heat radiation surfaces similarly to the preferred embodiment. Measurements of respective physical quantities were done under the same condition as those in the third preferred embodiment. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 88 solid semiconductor elements 288.3K 310.3K 8.3A 89 porous semiconductor but not air-tight 263.9K 313.2K 2.2A 138 90 porous semiconductor air-tight at 50 Pa 258.3K 314.6K 2.2A over 500 times 91 porous semiconductor air-tight at 100 Pa 256.2K 314.7K 2.2A over 500 times 82 porous semiconductor air-tight at 1,000 Pa 263.8K 314.1K 2.2A over 500 times 93 porous semiconductor air-tight at 10,000 Pa 263.6K 314.6K 2.2A over 500 times As is easily understood from Table 4, when porous semiconductor elements are used, the lowest achievable temperature at the lower temperature side can be lowered in comparison with the case using solid semiconductor elements. Further, if semiconductor units deaerated individually were used as in the present preferred embodiment, the lowest achievable temperature could be lowered further and lifetime against the detorioration due to the bedwing could be elongated much more. The present preferred embodiment is advantageous especially under the cooling conditions mentioned above. The porous insulation film 96 inserted between the p-type and n-type semiconductor elements 94 and 95 serves to deaerate said two elements equally and to lower the thermal conductivity of the refrigeration panel. [Fifth preferred embodiment] Fig. 5 shows a main body of a refrigeration panel according to a fifth preferred embodiment of the present invention. Porous semiconductor elements 100 and 101 of p-type and n-type are manufactured using the same method as that of the third preferred embodiment. After subjecting each element to Ni electrolytic plating to form Ni films on upper and lower surfaces thereof, an insulation porous resin 102 is applied to side surfaces thereof. Then, a predetermined number of p-type and n-type semiconductor elements are arranged alternatively in a contacted state. By soldering a plurality of Cu plates 104 on the upper and lower surfaces of the assembled body, the semiconductor elements are electrically connected in series. Then, the assembled body is put into a vacuum chamber and a ultraviolet-curing air-tight insulation resin 103 is applied to all surfaces not covered by the Ni films therein. This resin is cured by irradiation of ultraviolet rays in a deaerated state. Table 5 shows physical quantities of each refrigeration panel measured under radiation conditions same as those of the third preferred embodiment of the present invention. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 94 solid semiconductor elements 288.3K 310.3K 8.3A 95 porous semiconductor but not air-tight 263.9K 313.2K 2.2A 138 96 porous semiconductor air-tight at 50 Pa 256.1K 315.6K 2.2A over 500 times 97 porous semiconductor air-tight at 100 Pa 256.1K 315.1K 2.2A over 500 times 98 porous semiconductor air-tight at 1,000 Pa 263.3K 314.0K 2.2A 499 times 99 porous semiconductor air-tight at 10,000 Pa 263.6K 313.8K 2.2A over 500 times As is apparent from Table 5, the present preferred embodiment can enjoy advantages substantially same as those obtained by the third or fourth preferred embodiments. In addition, according to the present preferred embodiment, since semiconductor elements are deaerated in an assembled state, the deaeration process can be simplified and they can be deaerated uniformly. [Sixth preferred embodiment] Fig. 6 shows a semiconductor element according to a sixth preferred embodiment. The semiconductor element is substantially comprised of a thermoelectric semiconductor layer 111 supported by alumina balloons 114. Thermoelectric semiconductive material used for p-type and n-type semiconductors are (Bi, Sb) 2 Te 3 and Bi 2 (Te, Se) 3 , respectively. The alumina balloon 114 has a mean particle size of 200 µm and a shell thickness of 1.0 µm. This alumina balloon material is partly hollow and partly porous pellet having a pore size of 25 µm and shells forming balloons are porous. The alumina balloon material is formed into cubic support blocks after adding an organic binder and these blocks are burned at 1,400 °C. After crushing a solidified poly-crystalline semiconductive material as the starting material, it is milled into a powder having a mean particle size of 0.08 µm by a ball mill using zirconia balls of 0.2 mm and an organic solvent. After drying the powder, it is mixed with a viscous solvent to make a slurry. Thereafter, each support blocks are immersed into the slurry and, then, dried. The support blocks thus manufactured are subjected to a heat treatment for two hours at 500 °C in argon gas. An area ratio of the semiconductive layer 111 to the support block 114 is 5.3 %, the porocity thereof is 90.6 %, the resistivity is 0.0250 Ωcm and the Seebeck coefficient is 200 µV/deg. The semiconductor layer 111 has many pores therein and, therefore, the semiconductor element has an air permeability as a whole. After subjecting the upper and lower surfaces of each semiconductor element, Cu electrode plates 112 are soldered thereon. Further, an air-tight insulation resin 113 of ultraviolet-curing type is applied to all side surfaces thereof in a vacuum chamber and cured by irradiation of ultraviolet rays. A predetermined number of the p-type and n-type semiconductor elements are arranged alternatively so as to form a rectangular and fixed by applying a bonding agent to end faces of the assembled body. Further, they are connected in series using Ni plates. After applying an insulation grease on the lower temperature side of the assembled body, a Cu plate of a thickness of 0.3 mm is adhered thereto and a thermocouple is mounted thereon to measure a temperature. A heat radiation plate is mounted on the higher temperature side thereof after applying an insulation grease thereon. A thermocouple is adhered on the heat radiation plate. The heat radiation plate has an area four times as large as the cross-section of the assembled body and many Cu fins planted thereon at a pitch of 5 mm. Thicknesses of the heat radiation plate and fin are 0.5 mm and 0.3 mm, respectively. The width of the fin is 10 mm. The heat radiation plate including the fins has a radiation area twenty times as large as the cross-section of the assembled body. All radiation surfaces thereof have been oxidized. The radiation condition is spontaneous radiation. The measurement was done at an ambient temperature of 300 K to measure the lowest achievable temperature by varying a current amount of a DC power source. Table 6 shows physical quantities same as those shown in Table 5. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 100 solid semiconductor elements 288.3K 310.3K 8.3A 101 porous semiconductor but not air-tight 262.9K 314.5K 2.4A 259 102 porous semiconductor air-tight at 50 Pa 258.6K 312.6K 2.3A over 500 times 103 porous semiconductor air-tight at 100 Pa 258.3K 311.3K 2.3A over 500 times 104 porous semiconductor air-tight at 1,000 Pa 261.7K 315.9K 2.4A 413 times 105 porous semiconductor air-tight at 10,000 Pa 262.0K 314.9K 2.8A 436 times As is apparent from Table 6, according to the sixth preferred embodiment, the merits are substantially the same as those of the third preferred embodiment. [Seventh preferred embodiment] Fig. 7 shows an enlarged perspective view of a unit comprised of a pair of p-type and n-type semiconductor elements each of which has a structure substantially same as that of the semiconductor element shown in Fig. 6. Namely, this unit has a pair of p-type and n-type semiconductor elements 123 and 124 joined via a porous ceramic sheet 129 having a thickness of 200 µm. Each semiconductor element has a porous semiconductor layer 125 supported by a porous support 128 and a Cu plate 126 is soldered on the upper surface thereof. On the lower surface of the unit, a common electrode Cu plate 130 is soldered. The side surfaces of the unit are covered by an air-tight insulation resin 127. The measurement was done under radiation conditions same as those in the third preferred embodiment. Table 7 shows physical quantities same as those shown in Tables 3, 4, 5 or 6. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 106 solid semiconductor elements 288.3K 310.3K 8.3A 107 porous semiconductor but not air-tight 261.6K 312.2K 2.2A 312 108 porous semiconductor air-tight at 50 Pa 257.3K 313.6K 2.4A over 500 times 109 porous semiconductor air-tight at 100 Pa 257.0K 316.7K 2.6A over 500 times 110 porous semiconductor air-tight at 1,000 Pa 268.6K 311.6K 2.4A 439 times 111 porous semiconductor air-tight at 10,000 Pa 268.6K 311.6K 2.4A 439 times According to this preferred embodiment, the merits are substantially the same as those obtained by the fourth preferred embodiment. [Eighth preferred embodiment] Fig. 8 shows a eighth preferred embodiment of the present invention. In this preferred embodiment, p-type and n-type semiconductor elements 131 and 132 each having a structure same as that of the sixth preferred embodiment are used and electrically connected in series using Cu electrode plates 133 and 134 in a manner similar to that shown in Fig. 5. Each Cu electrode plate has an area two times as large as that of one face of the semiconductor element so as to be able to connect a pair of the semiconductor elements in common. Side surfaces of the assembled body and portions not covered by Cu electrode plates 133 and 134 are covered by an air-tight insulation resin 135 similarly to Fig. 5. Table 8 shows physical quantities measured under radiation conditions same as those in the sixth preferred embodiment. Case No. State of sample L.A. Temp. Temp. of fin Current amount Number of times of repetition 112 solid semiconductor elements 288.3K 310.3K 8.3A 113 porous semiconductor but not air-tight 263.6K 310.2K 2.8A 138 114 porous semiconductor air-tight at 50 Pa 254.6K 314.6K 2.7A over 500 times 115 porous semiconductor air-tight at 100 Pa 259.6K 313.9K 2.7A over 500 times 116 porous semiconductor air-tight at 1,000 Pa 264.3K 315.9K 2.6A over 499 times 117 porous semiconductor air-tight at 10,000 Pa 264.8K 316.3K 2.7A over 500 times According to the eighth preferred embodiment of the present invention, the merits are the same as those obtained by the sixth preferred embodiment. Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications are apparent to those skilled in the art.

Claims: A p-type or n-type semiconductor element (81; 114) for a thermoelectric semiconductor unit, said element (81; 114) comprising a p-type or n-type semiconductor porous body and electrodes (82; 112) made of an air-tight metal, wherein side surfaces of said porous body are coated with an air-tight insulation material (83; 113) and said porous body has been deaerated, characterized in that said electrodes (82; 112) are formed on upper and lower end surfaces of said element (81; 114) and said porous body is made of a gas permeable thermoelectric semiconductive material supported by gas permeable support particles. The element of claim 1, characterized in that said gas permeable thermoelectric semiconductive material is provided as a thermoelectric semiconductive layer (111) at the outer surface of said porous body. A thermoelectric semiconductor unit comprising at least one pair of p-type and n-type semiconductor elements according to claim 1 or 2, characterized in that one of said air tight metal electrodes is a common electrode (98; 130) made of an air-tight metal electrically connecting said pair of semiconductor elements (94, 95; 123, 124) at one end thereof, whereas each of said semiconductor elements (94, 95; 123, 124) is covered by an electrode (97; 126) of an air tight metal at the other end thereof; an insulation sheet material (96; 129) is inserted between said pair of semiconductor elements (94; 95); and the other surfaces of said pair of semiconductor elements (94, 95; 123, 124) are covered by an air-tight insulation material (99; 127). The unit of claim 3, characterized in that said insulation sheet material (96; 129) is gas-permeable. The unit of claim 3 or 4, characterized in that an assembly of a predetermined number of said pair of p-type and n-type semiconductor elements (100, 101) is arranged alternatingly in a two-dimensional configuration, each semiconductor element (100, 101) having electrodes of an air-tight metal formed on both end surfaces thereof and other side surfaces thereof being covered with an insulating material (102); junction electrodes (104) formed on upper and lower surfaces of said assembly, each of which is made of an air-tight metal and electrically connects said electrodes of a pair of said semiconductor elements (100, 101) at each end surface of said assembly alternatingly in series; and an air-tight insulation material (103) covering the outer surfaces of said assembly not covered by said junction electrodes (104), said air-tight insulation material (103) and said junction electrodes (104) maintaining said assembly in a deaerated state.

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