Abstract:
A flexible thermoelectric device and a manufacturing method thereof are provided. Flexible substrates are formed by using LIGA process, micro-electro-mechanical process or electroforming technique. The flexible substrates are used to produce thermoelectric device. The structure and the material property of the substrates offer flexible property and tensile property to the thermoelectric device. Thermal transfer enhancement structures such as thermal via or metal diffusion layer are formed on the flexible substrates to overcome the low thermal transfer property of the flexible substrates.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 96125383, filed Jul. 12, 2007. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a thermoelectric device. More particularly, the present invention relates to a flexible thermoelectric device and a manufacturing method thereof. 
     2. Description of Related Art 
     Thermoelectric devices produced by using thermoelectric semiconductor material do not require any liquid or gas as coolant, and thus having advantages of being capable of working continuously, no contamination, no moving parts, no noises, long service life, small volume, and light weight, etc., so the thermoelectric device is widely applied on cooling or heating devices. 
     Generally, the thermoelectric device includes a plurality of N-type semiconductor members and P-type semiconductor members arranged in order. Then, the solder is used to joint the N-type semiconductor members and the P-type semiconductor members on a metal electrode. The N-type semiconductor members and the P-type semiconductor members are alternatively connected on the metal electrode from the upper side and the lower side, and they are connected in series to form a complete circuit. The metal electrodes on the upper side and the lower side are respectively connected onto the substrate after being processed by the electroplating process. The substrate is used to contact with a heat source, so the substrate must have desirable electrical insulation property and heat transfer property, and the material is generally ceramic or silicon. 
     When a power source is connected between the electrodes on two ends of the thermoelectric device, and the current flows from the N-type semiconductor member to the P-type semiconductor member, such that the thermal absorption occurs on one side of the thermoelectric device, and heat release occurs on the other side. At this time, if the connection direction of the power source is arranged inversely, the directions of the thermal absorption and the thermal release are changed. Therefore, the thermoelectric device can be used for the cooling device or heating device by this phenomenon. 
     However, the conventional thermoelectric device takes ceramic or silicon as the substrate. The ceramic substrate or silicon substrate does not have flexibility, so it cannot be applied on the heat source with a curved surface or changeable surface. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a flexible thermoelectric device. Buffer structures are formed on substrates, so as to offer flexible and tensile properties to the thermoelectric device. Meanwhile, a thermal transfer enhancement structure is formed on the flexible substrate, so as to overcome disadvantages of the conventional thermoelectric device such as low thermal transfer property, large volume, fixed device layout structure, and limited application fields, etc. 
     The present invention provides a method for manufacturing a flexible thermoelectric device. The substrates are produced by performing press molding process, so buffer structures are formed while the substrates are produced, and thus the manufacturing process is relatively simple. 
     The present invention provides a flexible thermoelectric device, which includes a first substrate, a second substrate, a plurality of thermoelectric pairs, a plurality of first electrodes, and a plurality of second electrodes. At least one of the first substrate and the second substrate has flexibility. The plurality of thermoelectric pairs is disposed between the first substrate and the second substrate. Each thermoelectric pair is respectively composed of a first type thermoelectric member and a second type thermoelectric member. The plurality of first electrodes is disposed between the first substrate and the thermoelectric pairs. The plurality of second electrodes is disposed between the second substrate and the thermoelectric pairs. The first type thermoelectric member and the second type thermoelectric member of each thermoelectric pair are alternatively connected in series by the first electrodes and the second electrodes. 
     The present invention provides a method for manufacturing a flexible thermoelectric device, which includes the following steps. Firstly, a first substrate and a second substrate are provided. At least one of the first substrate and the second substrate has a plurality of buffer structures. Next, a plurality of first electrodes is formed on the first substrate, and a plurality of second electrodes is formed on the second substrate. A plurality of thermoelectric pairs is formed on the first electrodes, and each thermoelectric pair is respectively composed of a first type thermoelectric member and a second type thermoelectric member. Then, the second electrodes and the thermoelectric pairs are jointed, and the first type thermoelectric member and the second type thermoelectric member of each thermoelectric pair are alternatively connected with each other in series by the first electrodes and the second electrodes. 
     In the flexible thermoelectric device of the present invention, buffer structures (concave structures, for example, a V-shaped groove, a square groove; convex structures, for example, a square, an inverted V-shaped, or a semicircular structure; and trenches) are disposed on at least one of the first substrate and the second substrate, which can be deformed along the substrate direction when the thermoelectric device substrate is warped or stretched. The concave structures or the convex structures can enlarge the heat transfer areas, and together with the thermal diffusion layers, the heat dissipation speed is increased. 
     Furthermore, thermal vias are disposed on at least one of the first substrate and the second substrate, such that the heat dissipation speed is increased. 
     In the method for manufacturing the flexible thermoelectric device of the present invention, the first substrate and the second substrate are produced by performing the pressing molding process, the buffer structures (including concave structures, for example, a V-shaped groove and a square groove; convex structures, for example, a square, an inverted V-shaped, or a semicircular structure; trenches; through holes; or bind holes) can be formed while the first substrate and the second substrate are produced, so the manufacturing process is relatively simple. The buffer structures can be deformed along the substrate direction when the thermoelectric device substrate is warped or stretched. The through holes or the blind holes on the first substrate and the second substrate can be used as the thermal vias, so as to enlarge the heat transfer area and to increase the heat dissipation speed. 
     In order to make the aforementioned and other objects, features, and advantages of the present invention comprehensible, preferred embodiments accompanied with figures are described in detail below. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
         FIG. 1A  is a top view of a flexible thermoelectric device according to a first embodiment of the present invention. 
         FIG. 1B  is a sectional view of the flexible thermoelectric device taken along a line A-A′ of  FIG. 1A . 
         FIG. 2A  is a sectional view of a flexible thermoelectric device according to a second embodiment of the present invention. 
         FIGS. 2B to 2F  show other variations of the flexible thermoelectric device according to the second embodiment of the present invention. 
         FIG. 3A  is a top view of a flexible thermoelectric device according to a third embodiment of the present invention. 
         FIG. 3B  is a sectional view of the flexible thermoelectric device taken along the line A-A′ of  FIG. 3A . 
         FIG. 4  is a flow chart of an embodiment of a method for manufacturing a flexible thermoelectric device of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
       FIG. 1A  is a top view of a flexible thermoelectric device according to a first embodiment of the present invention, and  FIG. 1B  is a sectional view of the flexible thermoelectric device taken along a line A-A′ of  FIG. 1A . 
     Referring to  FIGS. 1A and 1B , a flexible thermoelectric device  100   a  includes a first substrate  102 , a second substrate  104 , a plurality of thermoelectric pairs  106   a - 106   c , a plurality of first electrodes  110   a - 110   c , and a plurality of second electrodes  112   a - 112   b . Each of the thermoelectric pairs  106   a - 106   c  is respectively composed of an N-type thermoelectric member  108   a  and a P-type thermoelectric member  108   b . The N-type thermoelectric members  108   a  and the P-type thermoelectric members  108   b  are, for example, arranged alternatively with each other, that is, two adjacent thermoelectric members may have different configurations. 
     The first substrate  102  and the second substrate  104  are for example respectively formed with a plurality of buffer structures  102   a - 102   b  and  104   a - 104   c , so as to make the first substrate  102  and the second substrate  104  have flexibility. The first substrate  102  and the second substrate  104  are made of polymer material, for example, polymethacrylate (PMMA), polydimethylsiloxane (PDMS), or polyimide (PI), etc. . . . 
     The buffer structures  102   a - 102   b  on the first substrate  102  are, for example, disposed on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . For example, the buffer structure  102   a  is disposed between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   b . The buffer structure  102   b  is disposed between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   c.    
     The buffer structures  104   a - 104   c  on the second substrate  104  are, for example, disposed on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . For example, the buffer structure  104   a  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a . The buffer structure  104   b  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b . The buffer structure  104   c  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   c.    
     In this embodiment, the buffer structures  102   a - 102   b  and  104   a - 104   c  of the first substrate  102  and the second substrate  104  include concave structures. The buffer structures  102   a - 102   b  can also be formed by one or more concave structures. The concave structure is, for example, a V-shaped groove. Definitely, the concave structure can also be a square groove or a semicircular groove, etc. 
     The plurality of thermoelectric pairs  106   a - 106   c  is, for example, disposed between the first substrate  102  and the second substrate  104 . The N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  can be in the form of a thin film, a thick film, or a bulk material. The N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  are made of a semiconductor material, for example, Bi—Te compound, Fe—Si compound, or Co—Sb compound etc. 
     The plurality of first electrodes  110   a - 110   c  is, for example, disposed between the first substrate  102  and the thermoelectric pairs  106   a - 106   c . Each of the first electrodes  110   a - 110   c  is respectively connected to the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . For example, the first electrode  110   a  is connected to the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a . The first electrode  110   b  is connected to the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b . The first electrode  110   c  is connected to the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   c.    
     The plurality of second electrodes  112   a - 112   c  is, for example, disposed between the second substrate  104  and the thermoelectric pairs  106   a - 106   c . Each of the second electrodes  112   a - 112   b  is respectively connected to the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . For example, the second electrode  112   a  is connected between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   b . The second electrode  112   b  is connected between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   c . The N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c  are alternatively connected to each other in series by the first electrodes  110   a - 110   c  and the second electrodes  112   a - 112   b.    
     In addition, the flexible thermoelectric device  100   a  can be selectively disposed with a plurality of thermal diffusion layers  114   a - 114   c  and  116   a - 116   b . The plurality of thermal diffusion layers  114   a - 114   c  and  116   a - 116   b  are, for example, respectively disposed on an external surface of the first substrate  102  and the second substrate  104 . The thermal diffusion layers  114   a - 114   c  and  116   a - 116   b  can completely or partially cover the external surfaces of the first substrate  102  and the second substrate  104 . In the present invention, the external surface of the first substrate  102  refers to a back surface of the surface where the first electrodes of the first substrate  102  are disposed thereon, and the external surface of the second substrate  104  refers to a back surface of the surface where the second electrodes of the second substrate  104  are disposed thereon. The thermal diffusion layer is made of, for example, a metal material. 
     The flexible thermoelectric device  100   a  can selectively dispose a plurality of through holes  122  and through holes  124  in the first substrate  102  and the second substrate  104 . Thermal vias  126  and thermal vias  128  are respectively formed in the through holes  122  and the through holes  124 . 
     The plurality of through holes  122  in the first substrate  102  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  114   a - 114   c  is, for example, disposed on the external surface of the first substrate  102 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  126  is, for example, disposed in the through holes  122 , for respectively connecting the first electrodes  110   a - 110   c  to the thermal diffusion layers  114   a - 114   c . For example, the first electrode  110   a  and the thermal diffusion layer  114   a  are connected together by the thermal via  126 . The first electrode  110   b  and the thermal diffusion layer  114   b  are connected together by the thermal via  126 . The first electrode  110   c  and the thermal diffusion layer  114   c  are connected together by the thermal via  126 . The thermal diffusion layers  114   a - 114   c  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. 
     The plurality of through holes  124  in the second substrate  104  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  116   a - 116   b  is, for example, disposed on the external surface of the second substrate  104 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  128  is, for example, disposed in the through holes  124 , for respectively connecting the second electrodes  112   a - 112   b  to the thermal diffusion layers  116   a - 116   b . For example, the second electrode  112   a  and the thermal diffusion layer  116   a  are connected together by the thermal via  128 . The second electrode  112   b  and the thermal diffusion layer  116   b  are connected together by the thermal via  128 . The thermal diffusion layers  116   a - 116   c  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. 
     In the flexible thermoelectric device of the first embodiment, the concave structure, for example, the V-shaped groove or the square groove is disposed on the first substrate and the second substrate to serve as a stress buffer structure for the substrate, such that when the thermoelectric device substrate is warped or stretched, it can be deformed along the substrate direction. The concave structure can enlarge the heat transfer area, and together with the thermal diffusion layers, the heat dissipation speed is increased. 
     In the flexible thermoelectric device of the first embodiment, the thermal vias are disposed on the first substrate and the second substrate, so as to increase the heat dissipation speed. In this embodiment, the thermal vias  126  and the thermal vias  128  for filling up the through holes  122  and the through holes  124  are taken as an example for illustration. Definitely, the thermal vias  126  and the thermal vias  128  may also not fill up the through holes  122  and the through holes  124 , but merely cover the surfaces and side walls of the through holes, and the objective of increasing the heat dissipation speed can also be achieved similarly. 
     In addition, in another embodiment, blind holes can also be used to replace the through holes. The blind holes are disposed on an external surface of at least one of the first substrate and the second substrate. Furthermore, the blind holes can enlarge the heat transfer area, and together with the thermal diffusion layers, the heat dissipation speed is increased. 
     Second Embodiment 
       FIG. 2A  is a sectional view of a flexible thermoelectric device according to a second embodiment of the present invention, and  FIGS. 2B to 2F  show other variations of the flexible thermoelectric device according to the second embodiment of the present invention. In  FIGS. 2A to 2E , the same numerals are used to indicate the members the same as that of the first embodiment, and the illustrations are omitted here. In order to simplify the drawings, in  FIGS. 2B to 2F , the plurality of thermoelectric pairs  106   a - 106   c  is collectively called the thermoelectric pair  106 , the plurality of first electrodes  116   a - 116   c  is collectively called the first electrode  110 , and the plurality of second electrodes  112   a - 112   b  is collectively called the second electrode  112 . The difference between this embodiment and the first embodiment lies in that, the second substrate  104  is a flat plate, and a convex structure is disposed on the first substrate  102  to serve as buffer structures  130   a  and  130   b.    
     As shown in  FIG. 2A , a flexible thermoelectric device  100   b  is, for example, formed by a first substrate  102 , a second substrate  104 , a plurality of thermoelectric pairs  106   a - 106   c , a plurality of first electrodes  110   a - 110   c , and a plurality of second electrodes  112   a - 112   b.    
     The buffer structures  130   a  and  130   b  of the first substrate  102  include a convex structure, for example, a square protrusion. Definitely, the buffer structure  120  of the first substrate  102  can also be convex structure in other configurations. For example, the first substrate  102  can have a buffer structure  120   a  of an inverted V-shaped protrusion (as shown in  FIG. 2B ) or a buffer structure  120   b  of a semicircular protrusion (as shown in  FIG. 2C ). The buffer structure  120  of the first substrate  102  can also be formed by one or more convex structures. For example, the first substrate  102  can also include a buffer structure  120   c  having two square protrusions (as shown in  FIG. 2D ), a buffer structure  120   d  having two inverted V-shaped protrusions (as shown in  FIG. 2E ), or a buffer structure  120   e  having two semicircular protrusions (as shown in  FIG. 2F ). 
     As shown in  FIG. 2A , in the flexible thermoelectric device  100   b , the thermal diffusion layers  114   a - 114   c  and  116   a - 116   c  are selectively disposed on the external surface of the first substrate  102  or the second substrate  104  respectively. The thermal diffusion layers  114   a - 114   c  and  116   a - 116   c  can completely or partially cover the external surface of the first substrate  102  or the second substrate  104 . The first substrate  102  is a substrate having the convex structure, such that the heat transfer area is increased. The thermal diffusion layers  114   a - 114   c  further enable the convex structure of the first substrate  102  to have the functions of a heat sink fin. 
     In the flexible thermoelectric device  100   b , a plurality of through holes  122  and through holes  124  is selectively disposed in the first substrate  102  and the second substrate  104  respectively. Thermal vias  126  and thermal vias  128  are respectively formed in the through holes  122  and the through holes  124 . 
     The plurality of through holes  122  in the first substrate  102  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  114   a - 114   c  is, for example, disposed on the external surface of the first substrate  102 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  126  is, for example, disposed in the through holes  122 , for respectively connecting the first electrodes  110   a - 110   c  to the thermal diffusion layers  114   a - 114   c . For example, the first electrode  110   a  and the thermal diffusion layer  114   a  are connected together by the thermal via  126 . The first electrode  110   b  and the thermal diffusion layer  114   b  are connected together by the thermal via  126 . The first electrode  110   c  and the thermal diffusion layer  114   c  are connected together by the thermal via  126 . The thermal vias  126  do not fill up the through holes  122 , but only cover the surfaces and the side walls of the through holes  122 . The thermal diffusion layers  114   a - 114   c  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. In this embodiment, the thermal diffusion layers  114   a - 114   c  are broken from the top of the buffer structures  130   a  and  130   b  of the square protrusion. In addition, the thermal diffusion layers  114   a - 114   c  and the thermal vias  126  can be manufactured by the same process, that is, the thermal diffusion layers  114   a - 114   c  and the thermal vias  126  can be integrated as a whole. 
     The plurality of through holes  124  in the second substrate  104  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  116   a - 116   b  is, for example, disposed on the external surface of the second substrate  104 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  128  is, for example, disposed in the through holes  124 , for respectively connecting the second electrodes  112   a - 112   b  to the thermal diffusion layers  116   a - 116   b . For example, the second electrode  112   a  and the thermal diffusion layer  116   a  are connected together by the thermal via  128 . The second electrode  112   b  and the thermal diffusion layer  116   b  are connected together by the thermal via  128 . The thermal vias  128  do not fill up the through holes  124 , but merely cover the surfaces and the side walls of the through holes  124 . The thermal diffusion layers  116   a - 116   b  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. In addition, the thermal diffusion layers  116   a - 116   c  and the thermal vias  128  can be manufactured by the same process, that is, the thermal diffusion layers  116   a - 116   c  and the thermal vias  128  are integrated as a whole. 
     In addition, in this embodiment, a plurality of trenches  134  may be selectively disposed on the external surface of the second substrate  104  in parallel to serve as the buffer structures  134   a - 134   c . The buffer structures  134   a - 134   c  are, for example, disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . For example, the buffer structure  134   a  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a . The buffer structure  134   b  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b . The buffer structure  134   c  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   c.    
     In the flexible thermoelectric device of this embodiment, the thermal vias are disposed on the first substrate and the second substrate, so as to increase the heat dissipation speed. In this embodiment, the thermal vias  126  and the thermal vias  128  do not fill up the through holes  122  and the through holes  124 , but merely cover the surfaces and the side walls of the through holes, so as to enlarge the heat dissipation area. The first substrate  102  has a convex structure, such that the heat transfer area is increased. The thermal diffusion layers further enable the convex structure of the first substrate  102  to have the functions of a heat sink fin. 
     In the flexible thermoelectric device of this embodiment, a plurality of trenches at least extending along a Y direction is disposed on the second substrate to serve as stress buffer structures, which can be at least deformed along an X direction when the thermoelectric device substrate is warped or stretched. In addition, a plurality of trenches extending along the X direction can also be disposed on the second substrate to serve as the stress buffer structures, which can be deformed along the X direction and the Y direction when the thermoelectric device substrate is warped or stretched. 
     Third Embodiment 
       FIG. 3A  is a top view of a flexible thermoelectric device according to a third embodiment of the present invention, and  FIG. 3B  is a sectional view of the flexible thermoelectric device taken along the line A-A′ of  FIG. 3A . In  FIGS. 3A and 3B , the same numerals are given to indicate members the same as that of the first embodiment, and the illustrations are omitted here. The difference between this embodiment and the first embodiment lies in that, the first substrate  102  and the second substrate  104  are both flat plates, and a plurality of trenches  132  and  134  arranged in parallel is respectively disposed on the external surfaces of the first substrate  102  and the second substrate  104  to serve as buffer structures  132   a - 132   b  and  134   a - 134   c.    
     Referring to  FIGS. 3A and 3B , the flexible thermoelectric device  100   c  is, for example, formed by a first substrate  102 , a second substrate  104 , a plurality of thermoelectric pairs  106   a - 106   c , a plurality of first electrodes  110   a - 110   c , and a plurality of second electrodes  112   a - 112   b.    
     The buffer structures  132   a - 132   b  of the first substrate  102  are formed by a plurality of trenches  132 . The buffer structures  132   a - 132   b  are located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . For example, the buffer structure  132   a  is disposed between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   b . The buffer structure  132   b  is disposed between the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b  and the N-type thermoelectric member  108   a  of the thermoelectric pair  106   c.    
     The buffer structures  134   a - 134   c  of the second substrate  104  are formed by a plurality of trenches  134 . The buffer structures  134   a - 134   c  are, for example, located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . For example, the buffer structure  134   a  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   a . The buffer structure  134   b  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   b . The buffer structure  134   c  is disposed between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the thermoelectric pair  106   c.    
     As shown in  FIG. 3A , the plurality of trenches  132  and  134  extends along the Y direction. The trenches  132  and  134  are respectively used as the stress buffer structures for the first substrate  102  and the second substrate  104 , which can be deformed along the X direction when the thermoelectric device substrate is warped or stretched. In addition, as shown in  FIG. 5A , the thermoelectric device of this embodiment can selectively dispose a plurality of trenches  136  extending along the X direction on the first substrate  102  and the second substrate  104 . The plurality of trenches  136  is located between the adjacent thermoelectric pairs, and the X direction and the Y direction are crossed with each other. The trenches  136  are similarly used as the stress buffer structures for the first substrate  102  and the second substrate  104 , which can be deformed along the Y direction when the thermoelectric device substrate is warped or stretched. 
     In addition, the first substrate  102  and the second substrate  104  can be selectively disposed with a plurality of through holes  122  and through holes  124 . Thermal vias  126  and thermal vias  128  are respectively formed in the through holes  122  and the through holes  124 . 
     The plurality of through holes  122  in the first substrate  102  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  114   a - 114   c  is, for example, disposed on the external surface of the first substrate  102 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  126  is, for example, disposed in the through holes  122 , for respectively connecting the first electrodes  110   a - 110   c  to the thermal diffusion layers  114   a - 114   c . For example, the first electrode  110   a  and the thermal diffusion layer  114   a  are connected together by the thermal via  126 . The first electrode  110   b  and the thermal diffusion layer  114   b  are connected together by the thermal via  126 . The first electrode  110   c  and the thermal diffusion layer  114   c  are connected together by the thermal via  126 . The thermal vias  126  do not fill up the through holes  122 , but merely cover the surfaces and the side walls of the through holes  122 . The thermal diffusion layers  114   a - 114   c  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. 
     The plurality of through holes  124  in the second substrate  104  is located between the N-type thermoelectric member  108   a  and the P-type thermoelectric member  108   b  of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal diffusion layers  116   a - 116   b  is, for example, disposed on the external surface of the second substrate  104 , and respectively located on corresponding positions between the N-type thermoelectric member  108   a  and the P-type thermoelectric member of each of the adjacent thermoelectric pairs  106   a - 106   c . The plurality of thermal vias  128  is, for example, disposed in the through holes  124 , for respectively connecting the second electrodes  112   a - 112   b  to the thermal diffusion layers  116   a - 116   b . For example, the second electrode  112   a  and the thermal diffusion layer  116   a  are connected together by the thermal via  128 . The second electrode  112   b  and the thermal diffusion layer  116   b  are connected together by the thermal via  128 . The thermal vias  128  do not fill up the through holes  124 , but only cover the surfaces and the side walls of the through holes  124 . The thermal diffusion layers  116   a - 116   b  are electrically isolated from each other, so as to prevent the short circuit of the thermoelectric device. 
     In the flexible thermoelectric device in this embodiment, a plurality of trenches at least extending along the Y direction is disposed on at least one of the first substrate and the second substrate to serve as the stress buffer structures, which can be at least deformed along the X direction when the thermoelectric device substrate is warped or stretched. A plurality of trenches  136  extending along the X direction can also be disposed on the first substrate and the second substrate to serve as the stress buffer structures, which can be at least deformed along the X direction and the Y direction when the thermoelectric device substrate is warped or stretched. 
     In the flexible thermoelectric device of this embodiment, the thermal vias are disposed on the first substrate and the second substrate, so as to increase the heat dissipation speed. 
     In addition, the flexible thermoelectric device of the present invention is not limited to the configurations in the first to third embodiments, but also can be any combination of the configurations in the first embodiment to the third embodiment. For example, the first substrate (or the second substrate) can be selected from the above substrates using any one of the concave structure, the convex structure, and the trench as the buffer structure, and the second substrate (or the first substrate) can be selected from the above substrates using any one of the concave structure, the convex structure, and the trench as the buffer structure or selected from flat plate substrates without buffer structures. The through holes and the blind holes can also be selectively disposed on the first substrate or the second substrate to serve as the thermal vias, so as to increase the heat dissipation speed. 
     The structure of the flexible thermoelectric device is illustrated above, and then the method for manufacturing the flexible thermoelectric device of the present invention is illustrated below.  FIG. 4  is a flow chart of an embodiment of a method for manufacturing a flexible thermoelectric device of the present invention. 
     Referring to  FIG. 4 , firstly, the first substrate and the second substrate are provided, and at least one of the first substrate and the second substrate has a plurality of buffer structures (Step  200 ). The first substrate and the second substrate having the plurality of buffer structures are produced by performing a press molding process. For example, firstly, a master mold of a substrate is produced by a semiconductor process, a LIGA process, and an electroforming process. Then, the first substrate and the second substrate are produced by selecting PMMA, PDMS, and PI, or other polymer molding materials, and by means of hot pressing or other manners such as exposure and curing. 
     If the buffer structures of the first substrate and the second substrate are concave structures ( FIG. 1B ) or convex structures ( FIGS. 2A to 2F ), the concave structures and the convex structures can be directly made by the master mold of the substrate. That is, the concave structure and the convex structure can be produced simultaneously during the press molding process of the first substrate and the second substrate. 
     If the buffer structures of the first substrate and the second substrate are trenches ( FIGS. 2A ,  3 A, and  3 B), the trenches can be directly formed by the master mold of the substrate. That is, the trenches can be formed simultaneously during the press molding process of the first substrate and the second substrate. Alternatively, after the first substrate and the second substrate are molded, a cutting step is performed to the first substrate and the second substrate, so as form the trenches extending along the X direction and the Y direction ( FIG. 3A ). The cutting step is achieved by, for example, a laser cutting process or a conventional cutting process. 
     When the first substrate and the second substrate has at least one of the plurality of through holes and the plurality of blind holes ( FIGS. 1A ,  1 B,  2 A,  2 B,  3 A, and  3 B), the plurality of through holes or the plurality of blind holes can be directly formed by the master mold of the substrate. That is, the through holes or the blind holes can be formed simultaneously during the press molding process of the first substrate and the second substrate. Alternatively, after the first substrate and the second substrate have been molded, a drilling step is performed on the first substrate and the second substrate, so as to form the plurality of through holes or the plurality of blind holes. The drilling step is achieved by, for example, a laser drilling process or a conventional drilling process. 
     Next, a plurality of first electrodes is formed on the first substrate, and a plurality of second electrodes is formed on the second substrate (Step  202 ). The process of forming the plurality of first electrodes and the plurality of second electrodes on the first substrate and the second substrate respectively includes, for example, a printed circuit board manufacturing process. Alternatively, the semiconductor process can also be adopted, for example, firstly, a metal layer is sputtered or deposited on the first substrate and the second substrate, and then a lithography and etching step is performed, so as to pattern the metal layer to form the plurality of first electrodes and the plurality of second electrodes. 
     Then, a plurality of thermoelectric pairs is formed on the first electrode. Each of the thermoelectric pairs is respectively formed by a first type thermoelectric member and a second type thermoelectric member, and each of the first electrodes is respectively connected to the first type thermoelectric member and the second type thermoelectric member of each of the thermoelectric pairs (Step  204 ). The first type thermoelectric member and the second type thermoelectric member can be in the form of a thin film, a thick film, and a bulk material. The first type thermoelectric member and the second type thermoelectric member are made of, for example, semiconductor materials doped by N-type dopant or P-type dopant. The first type thermoelectric member and the second type thermoelectric member are formed by sputtering, evaporation, metal-organic chemical vapor deposition (MOCVD), and molecular beam epitaxy (MBE) processes. The first type thermoelectric member and the second type thermoelectric member are, for example, formed on the first electrode by soldering. 
     Then, the second electrodes and the thermoelectric pairs are jointed, and each of the second electrodes is respectively connected to the first type thermoelectric member and the second type thermoelectric member of the adjacent thermoelectric pairs (Step  206 ). The second electrodes and the thermoelectric pairs are jointed by, for example, a soldering process. 
     Next, a plurality of first thermal diffusion layers is formed on an external surface of the first substrate, and a plurality of second thermal diffusion layers is formed on an external surface of the second substrate (Step  208 ). The first thermal diffusion layer and the second thermal diffusion layer are produced by a semiconductor process, for example, electroplating, sputtering, or printed circuit board manufacturing process. 
     In addition, if the first substrate and the second substrate have the plurality of through holes or blind holes thereon ( FIGS. 1A ,  1 B,  2 A,  2 B,  3 A, and  3 B), before the first thermal diffusion layers and the second thermal diffusion layers are formed, the electroplating or sputtering process is used to apply the metal on inner walls of the through holes or the blind holes, or to completely fill up the through holes or the blind holes so as to form the thermal vias. After the first thermal diffusion layers and the second thermal diffusion layers are formed, a patterning process is performed, so as to make the first thermal diffusion layers be respectively located on corresponding positions between the first type thermoelectric member and the second type thermoelectric member of the adjacent thermoelectric pairs, and to make the second thermal diffusion layers be respectively located on corresponding position between the first type thermoelectric member and the second type thermoelectric member of each of the thermoelectric pairs. The first thermal diffusion layers are respectively connected to the first electrodes by the thermal via. The second thermal diffusion layers are respectively connected to the second electrodes by the thermal via. 
     In the method for manufacturing the flexible thermoelectric device of the present invention, the substrates (the first substrate and the second substrate) are produced by the press molding process, and the buffer structures (including the concave structures, for example, the V-shaped groove and the square groove etc.; the convex structures, for example, the square, the inverted V-shaped or the semicircular structures, etc.; the trenches; the through holes; or the blind holes) are formed while the substrates are produced, so the manufacturing process is relatively simple. The buffer structures can be deformed along the substrate direction when the thermoelectric device substrate is warped or stretched. 
     The through holes or the blind holes on the substrates (the first substrate and the second substrate) can be used as the thermal vias, so as to enlarge the heat transfer area, and to increase the heat dissipation speed. 
     To sum up, in the method for manufacturing the flexible thermoelectric device of the present invention, the concave structures, for example, a V-shaped groove and a square groove etc., the convex structures, for example, a square, an inverted V-shaped or a semicircular structure etc., and the trenches are disposed on the substrate to use as the stress buffer structure for the substrate, which can be deformed along the substrate direction when the thermoelectric device substrate is warped or stretched. The concave structures or the convex structures can enlarge the heat transfer area, and increase the heat dissipation speed. 
     The thermal vias are disposed on the substrates, so as to increase the heat dissipation speed. 
     In addition, in the method for manufacturing the flexible thermoelectric device of the present invention, the press molding manner is used to produce the substrate, so the buffer structures can be formed while the substrates are produced, so the manufacturing process is relatively simple. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention cover modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.