A THERMOELECTRIC MODULE FIELD OF INVENTION [0001] The present invention relates broadly, but not exclusively, to a thermoelectric module and a method for manufacturing the same. BACKGROUND [0002] A thermoelectric device operates by Peltier or thermoelectric effect to create a heat flux between opposite junctions of two different thermoelectric elements. Specifically, a thermoelectric device transfers heat from one side of the device to the other side when a DC electric current flows through the thermoelectric device. Thus, depending on the direction of the current applied to the device, a thermoelectric device can be used for either heating or cooling. [0003] Thermoelectric devices are typically connected in series and sandwiched between two sides. The cooling ability of the whole system is thus proportional to the number of thermoelectric devices. A direct stacking of two thermoelectric devices is not possible as the arrangement will create a short circuit due to the exposure of the conductive surfaces of different circuits. [0004] In some applications, multiple thermoelectric devices can be cascaded together by adding thermal interface materials between the thermoelectric devices. However, the stacking of thermoelectric devices in this manner can result in thermal conductivity loss and a reduction in efficiency. [0005] A need therefore exists to provide solutions that seek to address at least one of the problems above or to provide a useful alternative. SUMMARY [0006] According to a first aspect of the present invention, there is provided a thermoelectric module comprising: a lower thermoelectric unit comprising lower first and second thermoelectric elements electrically connected at a bottom side of the lower thermoelectric unit; an upper thermoelectric unit comprising upper first and second thermoelectric elements electrically connected at a top side of the upper thermoelectric unit; a first connector comprising a conducting material disposed between the upper first thermoelectric element and the lower second thermoelectric element, wherein the upper first thermoelectric element is directly above the first conductor; and a second connector comprising the conducting material disposed between the upper second thermoelectric element and the lower first thermoelectric element, wherein the upper second thermoelectric element is directly above the second conductor.

[0007] The upper first thermoelectric element and the first connector may be directly above the lower second thermoelectric element, and the upper second thermoelectric element and the second connector may be directly above lower first thermoelectric element.

[0008] The first and second connectors may be configured to receive a voltage to generate a temperature difference between the bottom side of the lower thermoelectric unit and the top side of the upper thermoelectric unit.

[0009] The bottom side of the lower thermoelectric unit may be configured to be in thermal contact with a first temperature and the top side of the upper thermoelectric unit may be configured to be in thermal contact with a second temperature to generate a potential difference between the first and second connectors.

[0010] The upper thermoelectric unit may have a lower heat flow transfer capacity than the lower thermoelectric unit.

[0011] The upper first thermoelectric element may be smaller in size than the lower second thermoelectric element, and the upper second thermoelectric element may be smaller in size than the lower first thermoelectric element.

[0012] The lower first and second thermoelectric elements may be electrically connected at the bottom side of the lower thermoelectric unit by a bottom conductive plate, and the upper first and second thermoelectric elements may be electrically connected at the top side of the upper thermoelectric unit by a top conductive plate. [0013] The first thermoelectric element may comprise a P-type semiconductor chip and the second thermoelectric element may comprise an N-type semiconductor chip.

[0014] The thermoelectric module may further comprise a flexible substrate disposed between the lower first and second thermoelectric elements and between the upper first and second thermoelectric elements .

[0015] According to a second aspect of the present invention, there is provided a thermoelectric device comprising a plurality of thermoelectric modules as defined in the first aspect, wherein the first connector of one thermoelectric module is connected to the second connector of an adj acent thermoelectric module.

[0016] The thermoelectric device may further comprise thermally conducting panels coupled to bottom and top sides of the thermoelectric device respectively.

[0017] According to a third aspect of the present invention, there is provided a human-wearable article comprising a thermoelectric device as defined in the second aspect, wherein the thermoelectric device is configured to modulate a temperature of air, water or contact surface.

[0018] According to a fourth aspect of the present invention, there is provided a method for manufacturing a thermoelectric module, the method comprising: forming a lower thermoelectric unit by electrically connecting lower first and second thermoelectric elements at a bottom side of the lower thermoelectric unit; forming an upper thermoelectric unit by electrically connecting upper first and second thermoelectric elements at a top side of the upper thermoelectric unit; disposing a first connector between the upper first thermoelectric element and the lower second thermoelectric element, such that the upper first thermoelectric element is directly above the first connector; and disposing a second connector between the upper second thermoelectric element and the lower first thermoelectric element, such that the upper second thermoelectric element is directly above the second connector.

[0019] The upper first thermoelectric element and the first connector may be directly above the lower second thermoelectric element; and the upper second thermoelectric element and the second connector may be directly above lower first thermoelectric element. [0020] The upper thermoelectric unit may have a lower heat flow transfer capacity than the lower thermoelectric unit.

[0021] The upper first thermoelectric element may be smaller in size than the lower second thermoelectric element, and the upper second thermoelectric element may be smaller in size than the lower first thermoelectric element.

[0022] The lower first and second thermoelectric elements may be electrically connected at the bottom side of the lower thermoelectric unit by a bottom conductive plate, and the upper first and second thermoelectric elements may be electrically connected at the top side of the upper thermoelectric unit by a top conductive plate.

[0023] The first thermoelectric element may comprise a P-type semiconductor chip and the second thermoelectric element may comprise an N-type semiconductor chip.

[0024] According to a fifth aspect of the present invention, there is provided a method of manufacturing a thermoelectric device, the method comprising: manufacturing a plurality of thermoelectric modules using the method as defined in the fourth aspect; and connecting the first connector of one thermoelectric module to the second connector of an adjacent thermoelectric module.

[0025] The method may further comprise coupling thermally conducting panels to bottom and top sides of the thermoelectric device respectively.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the invention are provided by way of example only, and will be better understood and readily apparent to one of ordinary skill in the art from the following written description and the drawings, in which:

[0027] Figure 1 shows a schematic diagram illustrating a side view of a thermoelectric module according to an example embodiment. [0028] Figure 2 A shows a schematic diagram illustrating the lower thermoelectric units of a thermoelectric device having multiple modules shown in Figure 1 according to an example embodiment.

[0029] Figure 2B shows a schematic diagram illustrating the upper thermoelectric units of the thermoelectric device of Figure 2A.

[0030] Figure 2C shows a schematic diagram illustrating a bottom assembly of the thermoelectric device of Figures 2A and 2B.

[0031] Figure 2D shows a schematic diagram illustrating a top assembly of the thermoelectric device of Figures 2A and 2B.

[0032] Figure 3A shows a perspective view of a thermoelectric device based on Figures 2A- 2D.

[0033] Figure 3B shows a top view of the thermoelectric device of Figure 3A.

[0034] Figure 3C shows a side view of the thermoelectric device of Figure 3 A.

[0035] Figure 4 shows a schematic diagram illustrating a side view of a thermoelectric module according to another example embodiment.

[0036] Figure 5A shows a schematic diagram illustrating the lower thermoelectric units of a thermoelectric device having multiple modules shown in Figure 4 according to an example embodiment.

[0037] Figure 5B shows a schematic diagram illustrating the upper thermoelectric units of the thermoelectric device of Figure 5A.

[0038] Figure 5C shows a schematic diagram illustrating a bottom assembly of the thermoelectric device of Figures 5A and 5B.

[0039] Figure 5D shows a schematic diagram illustrating a top assembly of the thermoelectric device of Figures 5A and 5B. [0040] Figure 6 shows a flowchart illustrating a method for manufacturing a thermoelectric module according to an example embodiment.

DETAILED DESCRIPTION

[0041] Embodiments of the present invention will be described, by way of example only, with reference to the drawings. Like reference numerals and characters in the drawings refer to like elements or equivalents.

[0042] The present disclosure relates to multi-stacking of N-type and P-type semiconductor chips to form a flexible thermoelectric module. In one example, the thermoelectric module includes two thermoelectric units including semiconductor chips. The semiconductor chips of opposite doping from each thermoelectric unit are stacked to form the thermoelectric module. Conductors are disposed between the semiconductor chips to allow electrons to flow through the semiconductor chips. In this configuration, the lower and upper thermoelectric units transfer heat in the same direction from a cold side to a hot side of the thermoelectric module.

[0043] Further, this configuration may advantageously allow thermoelectric units to be cascaded without the need of inserting layers of substrate and thermal interface materials between the stacked thermoelectric units to avoid short circuit. The compact structure of thermoelectric modules may advantageously increase the temperature difference between the cold side and the hot side of a thermoelectric device including the modules as compared to a single layer thermoelectric device, thereby increasing the cooling density of the thermoelectric device. Such thermoelectric devices can be used for modulating temperature of air, water or contact surfaces of a human-wearable article, such as clothing item, head gear, etc.

[0044] Figure 1 shows a schematic diagram illustrating side view of a thermoelectric module 100 according to an example embodiment. The thermoelectric module 100 has a lower thermoelectric unit 102 and an upper thermoelectric unit 104. The lower thermoelectric unit 102 has lower first and second thermoelectric elements that are electrically connected at a bottom side 106 of the lower thermoelectric unit 102. The upper thermoelectric unit 104 has upper first and second thermoelectric elements electrically connected at a top side 108 of the upper thermoelectric unit 104.

[0045] The thermoelectric module 100 further includes a first connector 110 comprising a conducting material. The first connector 110 is disposed between the upper first thermoelectric element of the upper thermoelectric unit 104 and the lower second thermoelectric element of the lower thermoelectric unit 102, such that the upper first thermoelectric element of the upper thermoelectric unit 104 is directly above the first connector 110 and lower second thermoelectric element of the lower thermoelectric unit 102.

[0046] The thermoelectric module 100 further includes a second connector 112 comprising the conducting material. The second connector 112 is disposed between the upper second thermoelectric element of the upper thermoelectric unit 104 and the lower first thermoelectric element of the lower thermoelectric unit 102, such that the upper second thermoelectric element of the upper thermoelectric unit 104 is directly above the second connector 112 and lower first thermoelectric element of the lower thermoelectric unit 102.

[0047] The thermoelectric elements used in the thermoelectric module 100 typically have low thermal conductivity to create a temperature gradient across the thermoelectric module 100 that allow effective heat transfer carried by electrons from one side of the thermoelectric module 100 to another side. As shown in Figure 1, the first thermoelectric element in the thermoelectric module 100 is an N-type semiconductor chip 114 and the second thennoelectric element in the thermoelectric module 100 is a P-type semiconductor chip 116.

[0048] The N-type and P-type semiconductor chips 114a, 116a are joined via solders joints 118a at the bottom side 106 of the lower thermoelectric unit 102 using a bottom conductive plate 120. The N-type and P-type semiconductor chips 114b, 116b are joined via solders joints 118b at the top side 108 of the upper thermoelectric unit 104 using a top conductive plate 122. In an embodiment, the bottom and top conductive plates 120, 122 and connectors 110, 112 are made of copper coated with gold or tin and silver plating.

[0049] The conductive plates 120, 122 are P-N junctions between the semiconductor chips 114a and 116a, 114b and 116b, respectively, that allow an electric current to pass through. In use, electrons moving through the conductive plates 120, 122 would either absorb heat for cooling or release heat tor heating, depending on the direction of the current applied to the thennoelectric module 100.

[0050] The N-type semiconductor chip 114b of the upper thermoelectric unit 104 and the P- type semiconductor chip 116a of the lower thermoelectric unit 102 are connected to the first connector 110 inserted between the semiconductor chips 114b, 116a using solder joints 118c. The P-type semiconductor chip 116b of the upper thermoelectric unit 104 and the N-type semiconductor chip 114a of the lower thermoelectric unit 102 are connected to the second connector 112 inserted between the semiconductor chips 114a, 116b using solder joints 118d. It will be appreciated that, instead of solder joints, the semiconductor chips 114a, 114b, 116a, 116b can be joined to the connectors 110, 112 or conductive plates 120, 122 via other methods such as eutectic bonding, anisotropic conductive paste (ASP) or thermal adhesive, etc.

[0051] The thermoelectric module 100 may further include a flexible substrate (not shown) disposed between the N-type semiconductor chip 114a and P-type semiconductor chip 116a of the lower thermoelectric unit 102, and also between the N-type semiconductor chip 114b and P-type semiconductor chip 116b of the upper thermoelectric unit 104.

[0052] The first and second connectors 110, 112 are configured to receive a voltage to generate a temperature difference between the bottom side 106 of the lower thermoelectric unit 102 and the top side 108 of the upper thermoelectric unit 104. As shown in Figure 1, the first and second connectors 110, 112 are connected to an electrical circuit 124 for receiving voltage from the electrical circuit 124. Sharing of the connectors 110, 112 between the lower and upper thermoelectric units 102, 104 may advantageously eliminate the need to insert layers of substrate and thermal interface materials between the stacked thermoelectric units.

[0053] As shown in Figure 1, DC voltage is supplied to the thermoelectric module 100 via the electrical circuit 124. Tills causes electrons to flow through the semiconductor chips 114a, 114b, 116a, 116b of the respective thermoelectric units 102, 104. At a cold side 126 of the thermoelectric module 100, heat is absorbed by the movement of electrons. The heat absorbed from the cold side 126 is subsequently released (shown as arrows 128 in Figure 1) at a hot side 130 opposite the cold side 126. It should be noted that the heat flow direction (shown as arrows 132 in Figure 1) may be reversed by changing the direction of the DC voltage applied to the electrical circuit 124.

[0054] The temperature difference across each thermoelectric unit 102, 104 can be calculated using the formula below.

DT: Temperature difference across the thermoelectric units 102, 104

Heat Load: Power generated by the thermoelectric units 102, 104 (measured in Watts) Peltier Module Rating: Max power used to transfer the heat across the thermoelectric units (measured in Watts)

ΔT _total : Actual temperature difference between the hot side 130 and cold side 126 of the thermoelectric module 100

[0055] By stacking the semiconductor chips 114a and 116b, 114b and 116a with opposite doping to form a multi-stage thermoelectric module 100, both lower and upper thermoelectric units 102, 104 transfer heat in the same direction from the cold side 126 to the hot side 130 of the thermoelectric module 100. This arrangement may advantageously increase the temperature difference between the cold side 126 and the hot side 130 as compared to a single layer thermoelectric module, thereby increasing the cooling density of the thermoelectric module 100. It should be noted that the thermoelectric module according to the example embodiment can be used as a thermoelectric generator that convert heat flux into electrical energy. Specifically, the bottom side 106 of the lower thermoelectric unit 102 is configured to be in thermal contact with a first temperature and the top side 108 of the upper thermoelectric unit 104 is configured to be in thermal contact with a second temperature such that a potential difference is generated between the first and second connectors 110, 112.

[0056] Figures 2A and 2B show diagrams illustrating the lower thermoelectric unit 102 and the upper thermoelectric unit 104 respectively of a thermoelectric device 200 according to an example embodiment. The thermoelectric device 200 includes multiple thermoelectric modules 100 that are connected in series. The details of the thermoelectric module 100 are explained above in respect of Figure 1.

[0057] As shown in Figure 2A, the first connector 110 of a first thermoelectric module 202 is connected to the second connector 112 of a second thermoelectric module 204 adjacent to the first thermoelectric module 202. An electrical power source (represented as a battery 206) is connected to the conductors at both ends of the thermoelectric device 200 to supply DC voltage. A switch 208 is also connected to the electric circuit 124 to control the DC voltage supplied to the thermoelectric device 200.

[0058] Figures 2C and 2D show diagrams illustrating a bottom assembly and a top assembly respectively of the thermoelectric device 200 of Figures 2A and 2B. Referring to Figure 2C, the thermoelectric device 200 has bottom conductive plates 120 that are attached to the bottom side 106 of the N-type and P-type semiconductor chips 114, 116 of the lower thermoelectric unit 102. Referring to Figure 2D, the thermoelectric device 200 has top conductive plates 122 that are attached to the top side 108 of the N-type and P-type semiconductor chips 114, 116 of the upper thermoelectric unit 104.

[0059] Figures 3A, 3B and 3C show the perspective view, top view and side view respectively of the thermoelectric device 200 of Figure 2A. The thermoelectric device 200 is a multi-stage device that includes multiple thermoelectric modules 100 that are electrically connected in series. As shown in Figure 3A, the conductors 110, 112 that are stacked between the lower and upper thermoelectric units 102, 104 are offset to the sides of the bottom and top conductive plates 120, 122. This structure, combined with the malleable characteristics of copper metal, may create a flexible thermoelectric device 200 that is advantageous for design purpose. For example, a portable device such as a headgear with cooling ability can be made by shaping the thermoelectric device 200 to fit into a casing (not shown). The thermoelectric device 200 may further include thermally conducting panels (not shown) coupled to bottom and top sides of the thermoelectric device 200 respectively for more efficient heat transfer.

[0060] Figure 4 shows a diagram illustrating a thermoelectric module 400 according to another example embodiment. The thermoelectric module 400 has a lower thermoelectric unit 402 and an upper thermoelectric unit 404. The lower thermoelectric unit 402 has lower first and second thermoelectric elements that are electrically connected at a bottom side 406 of the lower thermoelectric unit 402. The upper thermoelectric unit 404 has upper first and second thermoelectric elements electrically connected at a top side 408 of the upper thermoelectric unit 404.

[0061] The thermoelectric module 400 further includes a first connector 410 comprising a conducting material. The first connector 410 is disposed between the upper first thermoelectric element of the upper thermoelectric unit 404 and the lower second thermoelectric element of the lower thermoelectric unit 402, such that the upper first thermoelectric element of the upper thermoelectric unit 404 is directly above the first connector and lower second thermoelectric element of the lower thermoelectric unit 402.

[0062] The thermoelectric module 400 further includes a second connector 412 comprising the conducting material. The second connector 412 is disposed between the upper second thermoelectric element of the upper thermoelectric unit 404 and the lower first thermoelectric element of the lower thermoelectric unit 402, such that the upper second thermoelectric element of the upper thermoelectric unit 404 is directly above the second connector 412 and lower first thermoelectric element of the lower thermoelectric unit 402. [0063] As shown in Figure 4, the first thermoelectric elements in the thermoelectric module 400 are N-type semiconductor chips 414a, 414b and the second thermoelectric elements in the thermoelectric module 400 are P-type semiconductor chips 416a, 416b. The lower N-type and P- type semiconductor chips 414a, 416a are joined via solders joints 418a at the bottom side 406 of the lower thermoelectric unit 402 using a bottom conductive plate 420. The upper N-type and P-type semiconductor chips 414, 416 are joined via solders joints 418b at the top side 408 of the upper thermoelectric unit 404 using a top conductive plate 422. The first and second connectors 410, 412 are connected to an electrical circuit 424 for receiving voltage from the electrical circuit 424.

[0064] The upper thermoelectric unit 404 has a lower heat flow transfer capacity than the lower thermoelectric unit 402. As shown in Figure 4, the upper thermoelectric unit 404 has semiconductor chips 414b, 416b that are smaller in size than the semiconductor chips 414a, 416a of the lower thermoelectric unit 402. The top conductive plate 422 is also smaller in size than the bottom conductive plate 420.

[0065] Heat is absorbed at a cold side 426 of the thermoelectric module 400 adjacent the upper thermoelectric unit 404. Larger chips 414a, 416a of the lower thermoelectric unit 402 function to absorb the heat transferred from the upper thermoelectric unit 404 and release the heat (as shown with arrows 428 in Figure 4) at a hot side 430 opposite the cold side 426. Hie heat flow ⁷ direction is shown as arrows 432 in Figure 4.

[0066] The multi-stage thermoelectric module 400 having thermoelectric units 402, 404 with different heat flow transfer capacities may advantageously increase the temperature difference between the hot side 430 and the cold side 426, thus increasing heat transfer from the cold side 426 to the hot side 430 and increasing the efficiency of the thermoelectric module 400.

[0067] Figures 5A and 5B show diagrams illustrating the lower thermoelectric unit 402 and the upper thermoelectric unit 404 respectively of a thermoelectric device 500 according to an example embodiment. The thermoelectric device 500 includes multiple thermoelectric modules 400 that are connected in series. The details of the thermoelectric module 400 are explained above in respect of Figure 4.

[0068] As shown in Figure 5A, the first connector 410 of a first thermoelectric module 502 is connected to the second connector 412 of a second thermoelectric module 504 adjacent to the first thermoelectric module 502. An electrical power source (represented as a battery 506) is connected to the connectors at both ends of the thermoelectric device 500 to supply DC voltage. A switch 508 is also connected to the electric circuit 424 to control the DC voltage supplied to the thermoelectric device 500.

[0069] Figures 5C and 5D show diagrams illustrating a bottom assembly and a top assembly respectively of the thermoelectric device 500 of Figures 5A and 5B. Referring to Figure 5C, the thermoelectric device 500 has bottom conductive plates 420 that are attached to the bottom side 406 of the N-type and P-type semiconductor chips 414, 416 of the lower thermoelectric unit 402. Referring to Figure 5D, the thermoelectric device 500 has top conductive plates 422 that are attached to the top side 408 of the N-type and P-type semiconductor chips 414, 416 of the upper thermoelectric unit 404. As shown in these two figures, the size of the top conductive plates 422 is smaller than that of the bottom conductive plates 420.

[0070] Figure 6 shows a flowchart illustrating a method for manufacturing a thermoelectric module according to an example embodiment. At step 602, a lower thermoelectric unit is formed by electrically connecting lower first and second thermoelectric elements at a bottom side of the lower thermoelectric unit. At step 604, an upper thermoelectric unit is formed by electrically connecting upper first and the second thermoelectric elements at a top side of the upper thermoelectric unit. At step 606, a first connector is disposed between the upper first thermoelectric element and the lower second thermoelectric element, such that the upper first thermoelectric element is directly above the first connector and lower second thermoelectric element. At step 608, a second connector is disposed between the upper second thermoelectric element and the lower first thermoelectric element, such that the upper second thermoelectric element is directly above the second connector and lower first thermoelectric element.

[0071] Embodiments of the present invention provide multi-stacking of N-type and P-type semiconductor chips to form a flexible thermoelectric module. Due to the compact structure of the thermoelectric module as disclosed, the cooling capacity per unit volume of the thermoelectric module can be advantageously increased, or the weight and size of the thermoelectric module can be substantially reduced to achieve a particular cooling capacity. This makes it possible to manufacture portable thermoelectric products with satisfactory cooling capacity.

[0072] For example, headgears can be designed to incorporate thermoelectric products to remove heat from the interior to improve the comfort of the wearers. The popularity of motorcycles is on the rise around the globe, especially in hotter countries in Asia. The thermoelectric products can be added into the helmets of riders to transfer heat from the interior of the helmets to surroundings.

[0073] For the same purpose, thermoelectric products can also be inserted into central processing units (CPUs) of computers, portable air-conditioning (AC) units and other wearable items such as head safety equipments, respirators and apparel.

[0074] It will be appreciated by a person skilled in the art that numerous variations and/or modifications may be made to the present invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. For example, the thermoelectric module are described in the example embodiments in connection with cooling, but can be used for heating by reversing the polarity of the applied voltage. Also, the configurations can be used for generating a potential difference between a hot junction and a cold junction. The present embodiments are, therefore, to be considered in all respects to be illustrative and not restrictive.