Thermoelectric wafer

Abstract

To provide a thermoelectric wafer that facilitates planar contact with the central region and suppresses stress-induced damage.SOLUTION: A thermoelectric wafer consisting of a thermoelectric element layer containing thermoelectric semiconductor material comprises a peripheral region and a central region enclosed by the peripheral region, and the thickness of the peripheral region is thinner than the thickness of the central region.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermoelectric wafer. [Background technology]

[0002] 2. Description of the Related Art Conventionally, as one of the means for effectively utilizing energy, there has been a device that directly converts thermal energy into electrical energy and vice versa using a thermoelectric conversion module that has a thermoelectric effect such as the Seebeck effect or the Peltier effect. A known example of a thermoelectric conversion module is a so-called π-type thermoelectric conversion element. A π-type thermoelectric conversion element is configured by providing a pair of electrodes spaced apart on a substrate, with a P-type thermoelectric element layer on one electrode and an N-type thermoelectric element layer on the other electrode, also spaced apart, and connecting the top surfaces of both thermoelectric element layers to a common electrode on the opposing substrate. In recent years, in order to improve thermoelectric performance and mass productivity, thin-film P-type thermoelectric element layers and N-type thermoelectric element layers have been formed into wafers, and thermoelectric conversion modules have been mass-produced. For example, in the manufacturing process of a thermoelectric wafer, when multiple process treatments are performed on the thermoelectric wafer, defects such as chipping or damage may occur at the outer peripheral edge of the thermoelectric wafer, and these defects may progress in subsequent processes, ultimately leading to a decrease in yield, etc. For example, Patent Document 1 discloses a wafer in which the back side of the end portion has a flat shape and the front side of the end portion has an inclined surface, in order to prevent the defect of chipping of the outer periphery of the wafer when etching a semiconductor substrate in a method for manufacturing a semiconductor device. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-118298 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Document 1 is an invention originally designed to prevent etching gas from getting around to the edge and backside of the wafer. On the other hand, as mentioned above, the edge of this wafer has a flat shape on the back side of the wafer and an inclined surface on the front side of the wafer, and the edge of the wafer has a sharp shape, but it is disclosed that it is preferable that the sharpness of the edge is such that the wafer does not crack. However, in the manufacturing process, sufficient consideration has not been given to the contact of the central region of the thermoelectric wafer with the flat surface on which the thermoelectric wafer is placed in the process treatment device, handling when the thermoelectric wafer is subjected to multiple processes, and damage due to stress from the process treatment device, etc. Furthermore, unlike Patent Document 1, the thermoelectric wafer does not have a rigid support substrate such as a silicon substrate and is therefore easily damaged.

[0005] In view of the above, an object of the present invention is to provide a thermoelectric wafer in which contact with the flat surface of the central region is easy and breakage due to stress is suppressed. [Means for solving the problem]

[0006] As a result of extensive research to solve the above problems, the inventors discovered that by making the thickness of the edge region of the thermoelectric wafer thinner than the thickness of the central region surrounded by the edge region, it is easier to make contact with the flat surface of the central region of the thermoelectric wafer, and damage due to stress can be suppressed, thereby completing the present invention. That is, the present invention provides the following [1] to [3]. [1] A thermoelectric wafer comprising a thermoelectric element layer containing a thermoelectric semiconductor material, the thermoelectric wafer having edge regions and a central region surrounded by the edge regions, the thickness of the edge regions being thinner than the thickness of the central region. [2] The thermoelectric wafer according to [1] above, wherein the ratio of the minimum width of the edge region of the thermoelectric wafer to the maximum Feret diameter of the thermoelectric wafer is 0.005 or more. [3] The thermoelectric wafer according to [1] or [2] above, wherein the ratio of the thickness of the edge region to the minimum thickness of the outer peripheral edge of the central region is 0.20 or more and less than 1.00. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a thermoelectric wafer in which contact with the flat surface of the central region is easy and breakage due to stress is suppressed. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is an explanatory diagram showing an embodiment of a thermoelectric wafer of the present invention. [Figure 2] 1A to 1C are explanatory views showing an embodiment of the steps according to the method for manufacturing a thermoelectric wafer of the present invention in the order of steps. [Figure 3] 1A to 1C are cross-sectional structural views along the steps for explaining the difference between the conventional and present methods for manufacturing a thermoelectric wafer. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Thermoelectric wafer] The thermoelectric wafer of the present invention is a thermoelectric wafer consisting of a thermoelectric element layer containing a thermoelectric semiconductor material, characterized in that the thermoelectric wafer has edge regions and a central region surrounded by the edge regions, and the thickness of the edge regions is thinner than the thickness of the central region. In the present invention, by making the thickness of the edge region of the thermoelectric wafer thinner than the thickness of the central region surrounded by the edge region, it is possible to suppress, for example, in the manufacturing process, the contact of the central region of the thermoelectric wafer with the flat surface on which the thermoelectric wafer is installed in the process processing device, and damage due to handling when the thermoelectric wafer is processed in multiple processes or stresses originating from the process processing device.

[0010] In this specification, a film made of a thermoelectric semiconductor composition before drying may be simply referred to as a "composition film," and a film after drying may be simply referred to as a "coated film." Furthermore, a film obtained by compressing after heating and pressurizing treatment may be simply referred to as a "thermoelectric wafer precursor." Furthermore, a film obtained after firing a thermoelectric wafer precursor may be simply referred to as a "thermoelectric element layer" or a "thermoelectric wafer." Furthermore, chips obtained by singulating a thermoelectric wafer may be simply referred to as a "thermoelectric chip" or "chip."

[0011] In this specification, preferred definitions can be selected arbitrarily, and combinations of preferred definitions can be considered more preferred. In this specification, the expression "XX to YY" means "XX or more and YY or less." In this specification, for preferred numerical ranges (e.g., ranges of content, etc.), the lower and upper limits described in stages can be independently combined. For example, the description "preferably 10 to 90, more preferably 30 to 60" can be combined with the "preferable lower limit (10)" and the "more preferable upper limit (60)" to form "10 to 60."

[0012] FIG. 1 is an explanatory diagram showing an embodiment of a thermoelectric wafer of the present invention, in which (a) is a plan view of the thermoelectric wafer 1 and (b) is a cross-sectional view of the thermoelectric wafer 1. The thermoelectric wafer 1 is a circular wafer having an edge region 2 and a central region 3 surrounded by the edge region 2, where D is the diameter, P is the length of the edge region 2, C1 is the thickness of the edge region 2, Q is the diameter of the central region 3, and C2 is the thickness of the central region 3.

[0013] The ratio of the minimum width of the edge region of the thermoelectric wafer to the maximum Feret diameter of the thermoelectric wafer is preferably 0.005 or more, more preferably 0.01 to 0.20, and even more preferably 0.03 to 0.10. When the ratio of the minimum value of the width of the end region of the thermoelectric wafer to the maximum Feret diameter of the thermoelectric wafer is within this range, a decrease in the effective area of ​​the thermoelectric wafer is suppressed, and the number of thermoelectric chips (with the same specifications) obtained by dicing the thermoelectric wafer can be maintained. Here, "edge region width" refers to the shortest distance from any point on the outer periphery of the edge region to the inner periphery of the edge region, and "minimum edge region width" refers to the smallest measured value when the width is measured along the periphery of the edge region.

[0014] The ratio of the thickness of the edge region to the minimum thickness of the outer peripheral edge of the central region of the thermoelectric wafer is preferably 0.20 or more and less than 1.00, more preferably 0.30 or more and less than 0.90, even more preferably 0.40 or more and less than 0.80, and particularly preferably 0.50 or more and less than 0.70. When the ratio of the thickness of the edge region to the minimum thickness of the outer peripheral edge of the central region of the thermoelectric wafer is within this range, it becomes easier to make contact with the flat surface of the central region of the thermoelectric wafer, and it becomes easier to suppress breakage due to external stress. Here, the "minimum thickness of the outer periphery of the central region" refers to the minimum value of the measured distance between an arbitrary point on the periphery of the central region of the thermoelectric wafer and the rear surface of the thermoelectric wafer, which is obtained by dropping a perpendicular line from the arbitrary point to the rear surface of the thermoelectric wafer. For example, in Figure 1, this refers to the minimum value of C2.

[0015] The shape of the edge region of the thermoelectric wafer is not particularly limited, but typically, in a longitudinal cross section including approximately the center of the thermoelectric wafer, the thermoelectric wafer may have a convex shape, such as a semicircular, semielliptical, or triangular shape, extending from the outer periphery of the central region of the thermoelectric wafer toward the edge of the edge region, or may have one or more stepped steps. From the viewpoints of facilitating processing of the thermoelectric wafer and of easily suppressing damage due to external stress, including contact, the shape is preferably a semicircular, semielliptical, or stepped shape.

[0016] When the ratio of the thickness of the edge region to the minimum value of the thickness of the outer peripheral edge of the central region of the thermoelectric wafer, and the ratio of the minimum value of the width of the edge region of the thermoelectric wafer to the maximum Feret diameter of the thermoelectric wafer are both within the above ranges, the number of thermoelectric chips (with identical specifications) obtained by dicing the thermoelectric wafer can be maintained, and contact with the flat surface of the central region of the thermoelectric wafer can be facilitated, thereby suppressing breakage due to stress.

[0017] The thickness of the thermoelectric wafer made of the thermoelectric element layer obtained by the firing treatment described below, that is, the thickness of the central region of the thermoelectric wafer, is preferably 10 to 800 μm, more preferably 100 to 600 μm, and even more preferably 150 to 500 μm. When the thickness of the thermoelectric wafer is in this range, the thermoelectric wafer is mechanically stable and the contact with the flat surface of the central region of the thermoelectric wafer is facilitated. The thickness of the edge region of the thermoelectric wafer may be thinner than the thickness of the outer peripheral edge of the central region of the thermoelectric wafer, but from the viewpoint of stability including mechanical strength, it is preferably at least 55 μm or more.

[0018] The shape of the thermoelectric wafer in plan view is not particularly limited, but examples thereof include a circle, an ellipse, a square, and a rectangle. The size of the thermoelectric wafer is not particularly limited, but from the viewpoint of mass-producing multiple chips at once, the diameter is preferably 30 mm to 500 mm for a circle, and each side is preferably 10 mm to 500 mm for a square or rectangle.

[0019] (Support) In the present invention, it is preferable to use a support as a support for the coating film. The support is not particularly limited, and examples thereof include glass, silicon, ceramics, and resin films. From the viewpoint of flexibility, resin films are preferred, and from the viewpoint of heat resistance, heat-resistant resin films are more preferred. The heat-resistant resin film is not particularly limited, but polyimide film, polyamide film, polyetherimide film, polyaramid film, polyamideimide film, or fluorine-based film (polytetrafluoroethylene, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is preferred, and polyimide film is particularly preferred because of its high versatility. The thickness of the heat-resistant resin film is preferably 50 to 1000 μm, more preferably 75 to 500 μm, and even more preferably 100 to 200 μm, from the viewpoints of flexibility, heat resistance, and dimensional stability. The glass transition temperature (Tg) of the heat-resistant resin film is preferably 200°C or higher, more preferably 220°C or higher, and even more preferably 250°C or higher. Here, Tg refers to the temperature at the maximum point of tan δ (loss modulus / storage modulus) obtained by a differential scanning calorimeter (measured in the range of 0 to 500° C. at a temperature rise rate of 5° C. / min).

[0020] <Thermoelectric element layer> The thermoelectric wafer used in the present invention is composed of a thermoelectric element layer. The thermoelectric element layer is preferably formed from a thermoelectric semiconductor composition containing thermoelectric semiconductor particles made of a thermoelectric semiconductor material, a binder resin, and an ionic compound (ionic liquid, inorganic ionic compound).

[0021] (Thermoelectric semiconductor materials) The thermoelectric semiconductor material is preferably pulverized to a predetermined size using, for example, a fine grinding device and used as thermoelectric semiconductor particles. The particle size of the thermoelectric semiconductor particles is preferably 10 nm to 100 μm, more preferably 50 nm to 50 μm, and even more preferably 3 μm to 30 μm. The average particle size of the thermoelectric semiconductor particles was obtained by measurement using a laser diffraction particle size analyzer (Malvern, Mastersizer 3000) and was taken as the median value of the particle size distribution.

[0022] As the thermoelectric semiconductor material used in the present invention, there is no particular limitation as long as it can generate a thermoelectromotive force by applying a temperature difference. For example, bismuth-tellurium-based thermoelectric semiconductor materials such as P-type bismuth telluride and N-type bismuth telluride; telluride-based thermoelectric semiconductor materials such as GeTe and PbTe; antimony-tellurium-based thermoelectric semiconductor materials; zinc-antimony-based thermoelectric semiconductor materials such as ZnSb and Zn3Sb 2、 Zn4Sb3; silicon-germanium-based thermoelectric semiconductor materials such as SiGe; bismuth selenide-based thermoelectric semiconductor materials such as Bi2Se3; β-FeSi2, CrSi2, MnSi 1.73 , Mg2Si and other silicide-based thermoelectric semiconductor materials; oxide-based thermoelectric semiconductor materials; Heusler materials such as FeVAl, FeVAlSi, FeVTiAl, and sulfide-based thermoelectric semiconductor materials such as TiS2 are used.

[0023] Among these, the thermoelectric semiconductor material used in the present invention is preferably a bismuth-tellurium-based thermoelectric semiconductor material such as P-type bismuth telluride or N-type bismuth telluride. The P-type bismuth telluride has holes as carriers and a positive value for the Seebeck coefficient. For example, Bi X Te3Sb 2-X represented by is preferably used. In this case, X is preferably 0 < X ≤ 0.8, more preferably 0.4 ≤ X ≤ 0.6. When X is greater than 0 and less than or equal to 0.8, the Seebeck coefficient and electrical conductivity increase, and the characteristics as a P-type thermoelectric conversion material are maintained, which is preferable. In addition, the N-type bismuth telluride has electrons as carriers and a negative value for the Seebeck coefficient. For example, Bi2Te 3-Y Se Y represented by is preferably used. In this case, Y is preferably 0 ≤ Y ≤ 3 (when Y = 0: Bi2Te3), more preferably 0.1 < Y ≤ 2.7. When Y is 0 to 3, the Seebeck coefficient and electrical conductivity increase, and the characteristics as an N-type thermoelectric conversion material are maintained, which is preferable.

[0024] The content of the thermoelectric semiconductor particles in the thermoelectric semiconductor composition is preferably 30 to 99% by mass, more preferably 50 to 96% by mass, and even more preferably 70 to 95% by mass. When the content of the thermoelectric semiconductor particles is within the above range, the Seebeck coefficient (absolute value of the Peltier coefficient) is large, and a decrease in electrical conductivity is suppressed, with only a decrease in thermal conductivity, so that a film exhibiting high thermoelectric performance and having sufficient film strength and flexibility is obtained, which is preferable.

[0025] Furthermore, the thermoelectric semiconductor particles are preferably subjected to an annealing treatment (hereinafter sometimes referred to as "annealing treatment A"). By performing annealing treatment A, the crystallinity of the thermoelectric semiconductor particles is improved, and furthermore, the surface oxide film of the thermoelectric semiconductor particles is removed, thereby increasing the Seebeck coefficient (absolute value of the Peltier coefficient) of the thermoelectric conversion material and further improving the thermoelectric figure of merit.

[0026] (binder resin) The binder resin used in the present invention has the effect of physically binding thermoelectric semiconductor particles together, thereby increasing the flexibility of the thermoelectric conversion module and facilitating the formation of a thin film by coating or the like.

[0027] The binder resin is appropriately selected depending on the temperature of the heat treatment and the baking (annealing) temperature of the thermoelectric semiconductor material. It is preferable to heat the material at a temperature higher than the decomposition temperature of the binder resin. Furthermore, a resin that maintains various physical properties such as mechanical strength and thermal conductivity without being impaired when a coating film made of the thermoelectric semiconductor composition is subjected to heat treatment or the like to cause crystal growth of thermoelectric semiconductor particles is more preferable. In this specification, the term "decomposition temperature" refers to the temperature at which the mass loss rate by thermogravimetry (TG) is 100% (the mass after decomposition is less than 1% of the mass before decomposition). The decomposition temperature of the binder resin is preferably 150 to 400°C.

[0028] Thermoplastic resins and curable resins can be used as such binder resins. Examples of thermoplastic resins include polyolefin resins such as polyethylene, polypropylene, polyisobutylene, and polymethylpentene; polycarbonate; thermoplastic polyester resins such as polyethylene terephthalate and polyethylene naphthalate; polyvinyl polymers such as polystyrene, acrylonitrile-styrene copolymer, polyvinyl acetate, ethylene-vinyl acetate copolymer, vinyl chloride, polyvinylpyridine, polyvinyl alcohol, and polyvinylpyrrolidone; polyurethane; and cellulose derivatives such as ethyl cellulose. Examples of curable resins include thermosetting resins and photocurable resins. Examples of thermosetting resins include epoxy resins and phenolic resins. Examples of photocurable resins include photocurable acrylic resins, photocurable urethane resins, and photocurable epoxy resins. These resins may be used alone or in combination. Among these, thermoplastic resins are preferred, polycarbonate and cellulose derivatives such as ethyl cellulose are more preferred, and polycarbonate is particularly preferred.

[0029] The content of the binder resin in the thermoelectric semiconductor composition is preferably 0.1 to 20 mass %, more preferably 0.5 to 15 mass %, and even more preferably 1.0 to 10 mass %.

[0030] <Ionic compounds> (ionic liquid) The ionic liquid that can be contained in the thermoelectric semiconductor composition is a molten salt formed by combining a cation and an anion, and refers to a salt that can exist in a liquid state at any temperature range from -50°C to less than 400°C. Ionic liquids are characterized by extremely low vapor pressure, nonvolatility, excellent thermal stability and electrochemical stability, low viscosity, and high ionic conductivity. Therefore, as a conductive additive, they can effectively suppress a decrease in electrical conductivity between thermoelectric semiconductor materials. In addition, ionic liquids exhibit high polarity due to their aprotic ionic structure and excellent compatibility with binder resins, thereby enabling the electrical conductivity of the thermoelectric element layer to be uniform.

[0031] The ionic liquid may be a known or commercially available one. For example, a nitrogen-containing cyclic cationic compound such as pyridinium, pyrimidinium, pyrazolium, pyrrolidinium, piperidinium, or imidazolium, or a derivative thereof; a tetraalkylammonium-based amine-based cation and a derivative thereof; a phosphine-based cation such as phosphonium, trialkylsulfonium, or tetraalkylphosphonium, or a derivative thereof; a lithium cation and a derivative thereof; or a mixture of a cation component and a Cl cation. - , Br - , I - , AlCl4 - , Al2Cl7 - , BF4 - , PF6 - , ClO4 - , NO3 - , CH3COO - , CF3COO - , CH3SO3 - , CF3SO3 - , (FSO2)2N - , (CF3SO2)2N - , (CF3SO2)3C - , AsF6 - , SbF6 - , NbF6 - , TaF6 - , F(HF) n - , (CN)2N - , C4F9SO3 - , (C2F5SO2)2N- , C3F7COO - , (CF3SO2)(CF3CO)N - and an anion component such as the above.

[0032] The ionic liquid preferably has a decomposition temperature of 300° C. or higher. If the decomposition temperature is within the above range, the effect as a conductive additive can be maintained even when a coating film made of the thermoelectric semiconductor composition is annealed, as described below.

[0033] The content of the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.4 to 30 mass%, and even more preferably 0.8 to 20 mass%. If the content of the ionic liquid is within the above range, a decrease in electrical conductivity is effectively suppressed, and a film with high thermoelectric performance can be obtained.

[0034] (inorganic ionic compounds) The inorganic ionic compound that can be contained in the thermoelectric semiconductor composition is a compound composed of at least a cation and an anion. The inorganic ionic compound exists in a solid state over a wide temperature range from 400 to 900°C and has characteristics such as high ionic conductivity, so that it can act as a conductive additive to suppress a decrease in electrical conductivity between thermoelectric semiconductor materials.

[0035] The content of the inorganic ionic compound in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and even more preferably 1.0 to 10 mass%. If the content of the inorganic ionic compound is within the above range, a decrease in electrical conductivity can be effectively suppressed, and as a result, a film with improved thermoelectric performance can be obtained. When an inorganic ionic compound and an ionic liquid are used in combination as the ionic compound, the total content of the inorganic ionic compound and the ionic liquid in the thermoelectric semiconductor composition is preferably 0.01 to 50 mass%, more preferably 0.5 to 30 mass%, and even more preferably 1.0 to 10 mass%.

[0036] The thickness of the coating film made of the thermoelectric semiconductor composition is preferably 10 to 1000 μm, more preferably 20 to 800 μm, and even more preferably 30 to 650 μm.

[0037] <Solder acceptance layer> The solder-receiving layer has a function of joining the thermoelectric element layer and the solder material layer on the opposing electrode side that constitutes the thermoelectric conversion module, and is directly joined to the thermoelectric element layer.

[0038] The solder-receiving layer preferably contains a metal material. The metal material is preferably at least one selected from gold, silver, nickel, aluminum, rhodium, platinum, chromium, palladium, tin, and an alloy containing any of these metal materials. Among these, a two-layer structure of gold, silver, nickel, aluminum, or tin and gold is preferred, and silver, nickel, and aluminum are more preferred from the viewpoints of material cost, high thermal conductivity, and bonding stability.

[0039] The thickness of the solder-receiving layer is preferably 10 nm to 50 μm, more preferably 50 nm to 10 μm, and particularly preferably 500 nm to 3 μm. When the thickness of the solder-receiving layer is within this range, the adhesion to the surface of the thermoelectric element layer and the adhesion to the surface of the solder material layer on the electrode side that constitutes the thermoelectric conversion module are excellent, resulting in a highly reliable bond. Furthermore, high thermal conductivity as well as electrical conductivity can be maintained, and as a result, the thermoelectric performance of the thermoelectric conversion module is maintained without any deterioration. The solder-receiving layer may be formed as a single layer using a metal material, or may be formed as a multilayer using two or more metal materials laminated together.

[0040] [Method for manufacturing thermoelectric wafer] First, before describing the method for manufacturing a thermoelectric wafer according to the present invention, the differences between the conventional method for manufacturing a thermoelectric wafer and the method for manufacturing a thermoelectric wafer according to the present invention will be explained with reference to the drawings.

[0041] 3A and 3B are cross-sectional structural views illustrating steps in the manufacturing process for explaining the differences between the conventional and present thermoelectric wafer manufacturing methods. In manufacturing method (a), (a-1) is a cross-sectional structural view illustrating a state in which a heating and pressing support jig 21a equipped with a side jig 23a and a heating and pressing jig 24a are placed opposite each other with a coating film 22a formed from a thermoelectric semiconductor composition interposed therebetween, and a heating and pressing device (not shown) is used to apply heat and pressure to the coating film 22a from both sides of the heating and pressing support jig 21a and the heating and pressing jig 24a, with the upper surfaces of the side jig 23a functioning as stoppers for the upper limit of pressure. (a-2) is a cross-sectional structural view illustrating the state after the thermoelectric wafer precursor 25a obtained by the heating and pressing process has been formed. (a-3) is a cross-sectional structural view of a single thermoelectric wafer precursor 25a obtained after the heating and pressing jig 24a is released from the thermoelectric wafer precursor 25a. In manufacturing method (a), the entire pressure surface of the heating and pressurizing support jig is flat, and there is no narrow area between the upper and lower jigs, so that the appropriate pressure is not applied to the coating film until it reaches the side jig. Only when the pressure surface of the heating and pressurizing jig reaches the side jig does uniform pressure begin to be applied, so that the coating film wraps around the top and bottom of the side jig, and as a result, a thermoelectric wafer with convex portions on the top and bottom is obtained.

[0042] In the manufacturing method (b) of FIG. 3 , (b-1) is a cross-sectional view showing a state in which a heating and pressing support jig 21b equipped with a side jig 23b and a heating and pressing jig 24b are placed opposite each other with a coating film 22b formed from a thermoelectric semiconductor composition interposed therebetween, and a heating and pressing device (not shown) is used to apply a heating and pressing treatment to the coating film 22b from both sides of the heating and pressing support jig 21b and the heating and pressing jig 24b, with the upper surfaces of the side jig 23b functioning as stoppers for the upper limit of pressure. (b-2) is a cross-sectional view showing a state after forming a thermoelectric wafer precursor 25b obtained by the heating and pressing treatment. (b-3) is a cross-sectional view of a single thermoelectric wafer precursor 25b obtained after releasing the heating and pressing jig 24b from the thermoelectric wafer precursor 25b. In manufacturing method (b), in order to prevent the coating film from wrapping around the side jig, i.e., so that the coating film does not reach the side jig after heating and pressing, the edges of the coating film are positioned in advance so as to leave a space and not reach the edges of the heating and pressing support jig, and then heating and pressing is performed. However, in manufacturing method (b), although it is usually possible to make the thickness of the edge region of the obtained thermoelectric wafer thinner than the thickness of the central region, it is considered to be a difficult method to control the desired shape, including the thickness of the edge region.

[0043] In the manufacturing method (c) of FIG. 3 (corresponding to an example of a manufacturing method of a thermoelectric wafer of the present invention), (c-1) is a cross-sectional view showing a state in which a heating and pressing support jig 21c equipped with a side jig 23c and a heating and pressing jig 24c having a specific convex shape at the end of the pressing surface are arranged opposite each other with a coating film 22c formed from a thermoelectric semiconductor composition interposed therebetween, and a heating and pressing device (not shown) is used to apply a heating and pressing treatment to the coating film 22c from both sides of the heating and pressing support jig 21c and the heating and pressing jig 24c, with the upper surfaces of the side jig 23c functioning as stoppers for the upper limit of the pressure. (c-2) is a cross-sectional view showing a state after the thermoelectric wafer precursor 25c obtained by the heating and pressing treatment has been formed. (c-3) is a cross-sectional view showing a single thermoelectric wafer precursor 25c obtained after the heating and pressing jig 24c is released from the thermoelectric wafer precursor 25c. In manufacturing method (c), a heating and pressurizing jig 24c having a specific convex shape at the end of the pressure surface is used, and the vertical distance between the ends of the jig is narrowed, so that even when the coating film is pressed, the pressure is less likely to escape horizontally, and the heating and pressurizing process is completed before it reaches the side jig, or the pressure is completed by the time the coating film reaches the side jig, so the gap with the side jig does not get filled, and the thickness of the edge region of the obtained thermoelectric wafer can be made thinner than the thickness of the central region, making it possible to control it to the desired shape.

[0044] The method for producing a thermoelectric wafer of the present invention is a method for producing a thermoelectric wafer, comprising the following steps (A) to (C): (A) A step of obtaining a coating film formed from a thermoelectric semiconductor composition containing a thermoelectric semiconductor material (B) a step of heating and pressurizing the coating film to form edge regions and a central region surrounded by the edge regions, thereby obtaining a thermoelectric wafer precursor. (C) A step of firing the thermoelectric wafer precursor to obtain a thermoelectric wafer comprising a thermoelectric element layer. The thermoelectric wafer is characterized in that it comprises edge regions of the thermoelectric wafer and a central region surrounded by the edge regions, the thickness of the edge regions being thinner than the thickness of the central region.

[0045] In the following description, steps (A), (B), and (C) may also be referred to as the "coating step," the "heating and pressurizing step," and the "firing step," respectively, in that order. The method for manufacturing a thermoelectric wafer according to the present invention will now be described with reference to the drawings.

[0046] 2A and 2B are explanatory views showing, in order of steps, an embodiment of the method for producing a thermoelectric wafer of the present invention. FIG. 2A is a cross-sectional view including a coating film 12 formed from a thermoelectric semiconductor composition on a heating and pressing support jig 11. FIG. 2B is a cross-sectional view showing an embodiment in which the heating and pressing support jig 11, which is provided with a side jig 13, and a heating and pressing jig 14 are arranged opposite each other with the coating film 12 interposed therebetween. FIG. 2C is a cross-sectional view showing an embodiment in which a heating and pressing device (not shown) is used to apply heat and pressure to the coating film 12 from both sides of the heating and pressing support jig 11 and the heating and pressing jig 14, with the upper surfaces of the side jig 13 functioning as a stopper for the upper limit of pressure. FIG. 2D is a cross-sectional view showing an embodiment after the thermoelectric wafer precursor 15 obtained by the heating and pressing process has been formed. 1(e) is a cross-sectional view showing the state after the heating and pressurizing jig 14 has been released from the thermoelectric wafer precursor 15, and FIG. 1(f) is a cross-sectional view showing the thermoelectric wafer 16 after the thermoelectric wafer precursor 15 has been peeled off from the heating and pressurizing support jig 11 and subjected to a firing process. The obtained thermoelectric wafer 16 has an edge region 17 and a central region 18 surrounded by the edge region 17, and it can be seen that the thickness of the edge region 17 is thinner than the thickness of the central region 18.

[0047] Process (A): Coating process The method for manufacturing a thermoelectric wafer of the present invention includes a coating step. The coating step is a step of forming a composition film from a thermoelectric semiconductor composition containing a thermoelectric semiconductor material on a support, and drying the composition film to obtain a coated film. For example, in the above-mentioned FIG. 2(a), this is a step of obtaining a coating film 12 formed from a thermoelectric semiconductor composition on a support jig 11 for heating and pressing.

[0048] The details of the thermoelectric semiconductor composition containing the thermoelectric semiconductor material used to form the coating film are as described above.

[0049] The method for applying the thermoelectric semiconductor composition as a composition film includes, but is not limited to, known methods such as screen printing, flexographic printing, gravure printing, spin coating, dip coating, die coating, spray coating, bar coating, applicator method, and doctor blade method. The resulting composition film is then dried to form a coating film. Conventional drying methods, such as hot air drying, hot roll drying, and infrared irradiation, can be used. The heating temperature is typically 80 to 150°C, and the heating time, which varies depending on the heating method, is typically several seconds to several tens of minutes. When a solvent is used in preparing the thermoelectric semiconductor composition, the heating temperature is not particularly limited as long as it is within a temperature range that allows the solvent used to be dried.

[0050] Step (B): Heat and pressure step The method for manufacturing a thermoelectric wafer of the present invention includes a heating and pressurizing step. The heating and pressurizing step is a step of subjecting the coating film to a heating and pressurizing treatment, and is also a step of giving a desired shape to the edge region. For example, in the above-mentioned steps (b) to (e) of FIG. 2, a heating and pressing device (not shown) is used to apply a heating and pressing treatment to the coating film 12 from both sides of a heating and pressing support jig 11 equipped with a side jig 13 and a heating and pressing jig 14, thereby forming an edge region 17 of the coating film 12 (a shape having a step from the outer periphery of the central region) and a central region 18 surrounded by the edge region, and further compressing the coating film to obtain a thermoelectric wafer precursor 15 having a reduced thickness.

[0051] The heating and pressurizing treatment in the heating and pressurizing step can be carried out by a known method, for example, by using a hydraulic press, an air press, or the like. The heating and pressing jig can be made of any known material without particular limitation as long as it has heat resistance, flatness, workability (e.g., recess processing for forming edge regions), flatness, etc. From the viewpoint of heat resistance and low thermal expansion, metal, ceramic, glass, etc. can be used. The thickness of the heating and pressing jig is not particularly limited as long as it does not cause mechanical deformation or damage to the coating film or the thermoelectric wafer to be formed during the heating and pressing treatment, but is usually 2 to 100 mm. The heating temperature is 100 to 600°C, and the pressure is 40 to 300 MPa. The heating and pressurizing treatment time is not particularly limited, but is preferably from several seconds to several hours, and more preferably from several minutes to several tens of minutes. The heat-pressure supporting jig and side jigs are not particularly limited as long as they function as a support and have load-bearing capacity, heat resistance, flatness, etc., and can be made of known materials, similar to the heat-pressure jig described above. From the viewpoint of heat resistance and low thermal expansion, metals, ceramics, glass, etc. can be mentioned. The thickness of the heating and pressing support jig is not particularly limited as long as it does not undergo mechanical deformation or damage to the coating film or the thermoelectric wafer to be formed during the heating and pressing treatment, similar to the heating and pressing jig, but is usually 5 to 200 mm. The thickness of the side jig needs to be adjusted appropriately depending on the thickness of the heating and pressing support jig and the heating and pressing jig, but is usually 10 to 200 mm as long as there is no mechanical deformation during the heating and pressing treatment and no damage is caused to the coating film or the thermoelectric wafer to be formed.

[0052] Process (C): Firing process The method for manufacturing a thermoelectric wafer of the present invention includes a firing step. The firing step is a step of firing the thermoelectric wafer precursor formed from the coating film compressed in step (B) to obtain a thermoelectric wafer consisting of a thermoelectric element layer. For example, in (d) of FIG. 2 described above, the thermoelectric wafer precursor 15 obtained by the heating and pressurizing treatment and compression is peeled off from the heating and pressurizing support jig 11, and in (e) the thermoelectric wafer precursor 15 is fired to obtain a thermoelectric wafer 16 consisting of a thermoelectric element layer. By carrying out the firing treatment, the thermoelectric performance can be stabilized and the thermoelectric semiconductor particles in the thermoelectric semiconductor composition in the coating film can be caused to undergo crystal growth, thereby further improving the thermoelectric performance of the thermoelectric wafer consisting of the thermoelectric element layer.

[0053] The firing treatment is not particularly limited, but is usually carried out in an inert gas atmosphere such as nitrogen or argon, in a reducing gas atmosphere, or under vacuum conditions, with the gas flow rate controlled. The temperature of the firing treatment depends on the thermoelectric semiconductor particles, resin, ionic compound (ionic liquid, inorganic ionic compound), etc. used in the thermoelectric semiconductor composition and is adjusted appropriately, but is usually 260 to 1000°C, preferably 280 to 600°C. The time for the firing treatment is not particularly limited, but is usually from several minutes to several tens of hours, preferably from several minutes to several hours.

[0054] The method for producing a thermoelectric wafer of the present invention preferably further includes a solder-receiving layer forming step as a post-step. The solder-receiving layer forming step is a step of obtaining a solder-receiving layer by performing plating or the like on the thermoelectric wafer, that is, the thermoelectric element layer. The solder-receiving layer has a function of joining the thermoelectric element layer and the solder material layer on the opposing electrode side that constitutes the thermoelectric conversion module, and is directly joined to the thermoelectric element layer.

[0055] The metal material used to form the solder-receiving layer, the thickness of the solder-receiving layer, etc. are as described above.

[0056] The solder-receiving layer is preferably formed using the above-mentioned metal material. The solder-receiving layer is required to have high electrical conductivity and high thermal conductivity in order to maintain thermoelectric performance, and therefore it is preferable to use a solder-receiving layer formed by electroplating, electroless plating, or vacuum film formation.

[0057] The thermoelectric wafer produced by the thermoelectric wafer manufacturing method of the present invention, or the thermoelectric wafer having a solder-receiving layer formed thereon, may be further divided into individual pieces in a dicing step. The dicing step is a step of dividing the thermoelectric wafer into individual thermoelectric chips. From the viewpoint of processing accuracy and process stability, the division is preferably performed by attaching a dicing tape to the thermoelectric wafer and using a dicing blade. The thermoelectric wafer of the present invention and the thermoelectric wafer produced by the method for producing the same result in fewer chips flying off during dicing, improving the production yield of the resulting thermoelectric chips.

[0058] (Manufacturing of thermoelectric conversion modules) A thermoelectric conversion module can be manufactured by combining multiple thermoelectric chips (P-type thermoelectric chips, N-type thermoelectric chips) described above obtained by dicing a thermoelectric wafer manufactured by the thermoelectric wafer manufacturing method of the present invention or a thermoelectric wafer having a solder-receiving layer formed on the thermoelectric wafer. From the viewpoint of thermoelectric performance, the thermoelectric conversion module can be manufactured by mounting (arranging) a P-type thermoelectric chip and an N-type thermoelectric chip so that they are connected via electrodes to form a so-called π-type or in-plane type thermoelectric conversion module. [Industrial Applicability]

[0059] The thermoelectric wafer of the present invention allows for easy contact with the flat surface of the central region and minimizes stress-induced breakage. Because thermoelectric wafers can be mass-produced with high yield, they can be individually diced and used as thermoelectric chips for thermoelectric conversion modules. The resulting thermoelectric conversion modules can be used for power generation applications, such as converting exhaust heat from various combustion furnaces (e.g., factories, waste incineration furnaces, and cement combustion furnaces), exhaust heat from automobile combustion gases, and exhaust heat from electronic devices into electricity. Cooling applications in the electronics field include temperature control of various sensors, such as CPUs (Central Processing Units) used in smartphones and various computers, image sensors (e.g., CMOS (Complementary Metal Oxide Semiconductors) and CCDs (Charge Coupled Devices), and MEMS (Micro Electro Mechanical Systems) and light-receiving elements. [Explanation of symbols]

[0060] 1: Thermoelectric wafer (thermoelectric element layer) 2: End area 3: Central area 11: Heat and pressure support jig 12: Coating film 13: Side jig 14: Heat and pressure jig 15: Thermoelectric wafer precursor 16: Thermoelectric wafer 17: End area 18: Central area 21a, 21b, 21c: Heat and pressure support jig 22a, 22b, 22c: coating film 23a, 23b, 23c: Side jigs 24a, 24b, 24c: Heat and pressure jig 25a, 25b, 25c: Thermoelectric wafer precursors D: diameter of the thermoelectric wafer Q: Diameter of the central region P: Length of the end region C1: Thickness of the edge region C2: Thickness of the central region

Claims

1. A thermoelectric wafer comprising a thermoelectric element layer including a thermoelectric semiconductor material, the thermoelectric wafer having edge regions and a central region surrounded by the edge regions, the thickness of the edge regions being thinner than the thickness of the central region.

2. 2. The thermoelectric wafer of claim 1, wherein a ratio of a minimum width of the edge region of the thermoelectric wafer to a maximum Feret diameter of the thermoelectric wafer is 0.005 or greater.

3. 2. The thermoelectric wafer according to claim 1, wherein the ratio of the thickness of said edge region to the minimum thickness of the outer peripheral edge of said central region is equal to or greater than 0.20 and less than 1.00.

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