ENERGY HARVESTER AND METHOD FOR MANUFACTURING AN ENERGY HARVESTER - Patent application

Abstract

The present invention relates to a method for manufacturing an energy harvester and an energy harvester for converting thermal energy into electrical energy. The energy harvester comprises an electrically conductive and flexible substrate, a plurality of thermoelectric legs, and an opposing electrode layer. Bonding the substrate to the opposing electrode layer provides a series electrical connection of alternating N-type and P-type thermoelectric legs.

Description

[Technical field]

[0001] The present invention relates to a method for manufacturing an energy harvester for converting thermal energy into electrical energy, and to an energy harvester for converting thermal energy into electrical energy. [Background technology]

[0002] Thermoelectric devices have steadily gained traction as a viable energy source for sensors and other Internet of Things (IoT) devices. Thermoelectric devices are formed from alternating N and P elements / legs made of semiconductor materials. The thermoelectric legs are placed on a substrate and another substrate is arranged on top to connect the thermoelectric legs with each other in series.

[0003] Electrical current may be generated by the thermoelectric device through the Seebeck effect, where a temperature difference across the thermoelectric device causes electrical current to be generated through alternating N and P elements / legs.

[0004] US Patent No. 10,553,773 discloses a method of encapsulating a thin film-based thermoelectric module, comprising forming a thin film-based thermoelectric module by sputter depositing pairs of N-type and P-type thermoelectric legs in electrical contact with each other on a flexible substrate having a dimensional thickness of 25 μm or less, and imparting flexibility and a dimensional thickness of 100 μm or less to the formed thin film-based thermoelectric module based on the selection of a fabrication process for the layers of the formed thin film-based thermoelectric module. The method also comprises encapsulating the formed thin film-based thermoelectric module with an elastomer to impart flexibility thereto. The elastomer encapsulation has a dimensional thickness of 15 μm or less, and the flexibility allows an array of thin film-based thermoelectric modules to be fully wrapped and bent around a system element from which the array is configured to extract thermoelectric power.

[0005] In certain applications, a ceramic housing may encapsulate the thermoelectric device mentioned above. However, conventional implementations of thermoelectric devices may be limited in application due to their associated stiffness, bulk, size, and high cost. In addition, the stiffness of the ceramic housing and substrate may impair the flexibility of the thermoelectric device. Summary of the Invention

[0006] It is an object of the present invention to overcome these problems and to provide an improved energy harvester, which overcomes or at least reduces the problems highlighted in the prior art.

[0007] According to a first aspect of the present invention, this and other objects are achieved by a method of manufacturing an energy harvester, the method comprising the steps of: Providing a conductive, flexible substrate having a substrate surface; providing a plurality of thermoelectric legs, each having a substrate end and an opposing end, the plurality of thermoelectric legs including an N-type thermoelectric leg and a P-type thermoelectric leg; arranging substrate ends of a plurality of thermoelectric legs on a substrate surface; bonding substrate ends of a plurality of thermoelectric legs to a substrate to form a plurality of pairs of adjacent thermoelectric legs, each pair of adjacent thermoelectric legs having an N-type thermoelectric leg electrically connected to a P-type thermoelectric leg via an N-type thermoelectric leg and a substrate end of the P-type thermoelectric leg; providing an opposing electrode layer having an opposing electrode layer surface; arranging opposing electrode layers on opposing ends of the plurality of thermoelectric legs; bonding opposite ends of the plurality of thermoelectric legs to opposite electrode layer surfaces; and separating the opposing electrode layer into several segments to electrically connect adjacent pairs of N-type and P-type thermoelectric legs, thereby forming a series electrical connection between adjacent pairs of thermoelectric legs.

[0008] As a result, a simple and efficient method for manufacturing the energy harvester is achieved. The simple manufacturing method allows the manufacturing of the energy harvester to be compatible with manufacturing facilities used in the electronics industry, thus facilitating expansion in the production of energy harvesters and facilitating cheaper manufacturing of the energy harvester.

[0009] The energy harvester produced in this manner comprises a series-connected pair of adjacent N-type and P-type thermoelectric legs. Thus, the energy harvester may be viewed as having a series of alternating N-type and P-type thermoelectric legs. In general, the substrate end of an N-type thermoelectric leg is electrically connected to the substrate end of a P-type thermoelectric leg, and the opposite end of the N-type thermoelectric leg is electrically connected to the opposite end of another P-type thermoelectric leg other than the one to which the N-type thermoelectric leg is electrically connected via its substrate end.

[0010] In the energy harvester, a plurality of thermoelectric legs are arranged on a substrate surface with the substrate ends of the N-type thermoelectric legs electrically connected to the substrate ends of the P-type thermoelectric legs, and the electrically connected N-type and P-type thermoelectric legs are considered to be a pair of adjacent thermoelectric legs, e.g., a pair of adjacent N-type and P-type thermoelectric legs. Correspondingly, an N-type thermoelectric leg electrically connected to a P-type thermoelectric leg via an opposite end of the thermoelectric leg is also considered to be a pair of adjacent electric legs, e.g., a pair of adjacent N-type and P-type thermoelectric legs. In this context, a pair of adjacent thermoelectric legs may be described in relation to the ends of the thermoelectric legs. Thus, a pair of adjacent thermoelectric legs may be a pair of substrate ends of adjacent thermoelectric legs, or a pair of adjacent thermoelectric legs may be a pair of opposite ends of adjacent thermoelectric legs. When a pair of adjacent thermoelectric legs is referred to without specifying the associated ends of the thermoelectric legs, that end may be either the substrate end or the opposite end, and the associated end will be clear from the context.

[0011] Generally, the N-type thermoelectric leg and the P-type thermoelectric leg of an adjacent thermoelectric leg pair are adjacent to one another. However, the N-type thermoelectric leg is not limited to being adjacent to the P-type thermoelectric leg to represent an adjacent thermoelectric leg pair, since the electrical connection between the ends of the thermoelectric legs dictates that the thermoelectric legs should be an adjacent thermoelectric leg pair.

[0012] An opposing electrode layer is arranged on the opposing ends of the plurality of adjacent thermoelectric legs, and then the opposing ends of the plurality of thermoelectric legs are bonded to the opposing electrode layer surface. The substrate ends of the plurality of thermoelectric legs can be considered to be arranged on the substrate surface, such that the opposing ends of the plurality of thermoelectric legs extend from the substrate surface, allowing the opposing electrode layer to be arranged on the opposing ends of the plurality of thermoelectric legs. In general, the opposing electrode layer has a size sufficient for the opposing electrode layer to be arranged on several pairs of adjacent N-type and P-type thermoelectric legs. For example, the opposing electrode layer may be arranged on all of the thermoelectric legs of an energy harvester, such that the method would utilize a single opposing electrode layer for a single energy harvester, for example. However, it is also contemplated that the method may utilize more than one opposing electrode layer for an energy harvester, where each opposing electrode layer is arranged on an opposing electrode layer on the opposing ends of the plurality of adjacent thermoelectric legs.

[0013] After bonding the opposite ends of the multiple thermoelectric legs to the opposite electrode layer surface, the opposite electrode layer is separated into segments, such as several segments, to electrically connect adjacent pairs of N-type and P-type thermoelectric legs, thereby forming a series electrical connection between adjacent pairs of thermoelectric legs. In this context, a segment comprises a single pair of adjacent N-type and P-type thermoelectric legs. Thus, the opposite end of the N-type thermoelectric leg is electrically connected to the opposite end of the P-type thermoelectric leg. Although the step of separating the opposite electrode layer into segments may be performed using any procedure, the step of separating the opposite electrode layer into segments generally involves removing material. Thus, by removing material, electrical connection through the opposite electrode layer is prevented due to the removal of material of the opposite electrode layer. The combination of arranging and subsequently bonding opposing electrode layers on opposing ends of a plurality of adjacent thermoelectric legs and separating the opposing electrode layers into segments provides for greatly simplified manufacturing of the energy harvester, particularly as compared to processes in which individual portions of electrode material must be disposed on opposing ends of N-type and P-type thermoelectric legs to be electrically connected. For example, opposing ends of a plurality of thermoelectric legs can be bonded to opposing electrode layer surfaces in a single operation, e.g., by soldering or sintering, without consideration of how the N-type and P-type thermoelectric legs are arranged on a substrate layer with respect to forming pairs of adjacent N-type and P-type thermoelectric legs on the substrate surface, providing a more robust manufacturing process.

[0014] The step of separating the opposing electrode layer into segments and electrically connecting adjacent pairs of N-type and P-type thermoelectric legs may be based on knowledge of locating adjacent pairs of N-type and P-type thermoelectric legs on the substrate surface. The N-type thermoelectric legs may be electrically connected to P-type thermoelectric legs located anywhere on the substrate surface. For example, after arranging the opposing electrode layer on the opposing ends of the plurality of thermoelectric legs and bonding the opposing ends of the plurality of thermoelectric legs to the opposing electrode layer surface, the opposing electrode layer may be cut based on knowledge of locating adjacent pairs of N-type and P-type thermoelectric legs on the substrate surface to electrically connect adjacent pairs of thermoelectric legs in series. Thus, the method is not specifically limited to require that the N-type thermoelectric legs of adjacent pairs of N-type and P-type thermoelectric legs be adjacent to the P-type thermoelectric legs of adjacent pairs of N-type and P-type thermoelectric legs on the substrate surface. This makes the step of cutting the opposing electrode layers to separate the opposing electrode layers into segments and forming a series electrical connection between pairs of adjacent thermoelectric legs more flexible than if the series electrical connection were made using individual pieces of connecting material.

[0015] The series electrical connections formed between pairs of adjacent thermoelectric legs are not limited to connecting one P-type thermoelectric leg in series with one N-type thermoelectric leg, and in particular one P-type thermoelectric leg may be connected in series with two or more N-type thermoelectric legs, or one N-type thermoelectric leg may be connected in series with two or more P-type thermoelectric legs. Correspondingly, groups of N-type thermoelectric legs, e.g., groups of 2 to 10, may be connected in series with groups of P-type thermoelectric legs of the same size, and vice versa. For example, the step of separating the opposing electrode layers into segments to electrically connect pairs of adjacent N-type thermoelectric legs and P-type thermoelectric legs, thereby forming a series electrical connection between pairs of adjacent thermoelectric legs, may be such that one P-type thermoelectric leg is connected in series with a plurality of N-type thermoelectric legs, e.g., 2-10, e.g., 2, 3, 4, 5, 6, 7, 8, or 9 N-type thermoelectric legs, or one N-type thermoelectric leg is connected in series with a plurality of N-type thermoelectric legs, e.g., 2-10, e.g., 2, 3, 4, 5, 6, 7, 8, or 9 N-type thermoelectric legs. This may be done, inter alia, by cutting the opposing electrode layer such that a group of N-type thermoelectric legs, such as 5, 6, 7, 8 or 9 N-type thermoelectric legs, are connected in series with a plurality of P-type thermoelectric legs, or a group of 2-10, such as 2, 3, 4, 5, 6, 7, 8 or 9 N-type thermoelectric legs, are connected in series with a group of P-type thermoelectric legs, or a group of 2-10, such as 2, 3, 4, 5, 6, 7, 8 or 9 P-type thermoelectric legs, are connected in series with a group of N-type thermoelectric legs. When one N-type thermoelectric leg is connected in series with a plurality of P-type thermoelectric legs, or when one P-type thermoelectric leg is connected in series with a plurality of N-type thermoelectric legs, or when a group of P-type thermoelectric legs is connected in series with a group of N-type thermoelectric legs, the N-type thermoelectric leg and the P-type thermoelectric leg are still considered to be a pair of adjacent N-type thermoelectric legs and P-type thermoelectric legs in this context.When one N-type thermoelectric leg is connected in series with multiple P-type thermoelectric legs, or when one P-type thermoelectric leg is connected in series with multiple N-type thermoelectric legs, the number of N-type thermoelectric legs and the number of P-type thermoelectric legs for the energy harvester may be selected to match the ratio of N-type thermoelectric legs to P-type thermoelectric legs and / or the ratio of P-type thermoelectric legs to N-type thermoelectric legs. Due to the series connection between the N-type thermoelectric legs and the P-type thermoelectric legs, there is a risk that the connection between the thermoelectric legs and the opposite layer will be broken so that current cannot flow through the energy harvester. However, when an N-type thermoelectric leg or group of N-type electrical legs are connected in series with multiple P-type thermoelectric legs, or when an P-type thermoelectric leg or group of P-type thermoelectric legs are connected in series with multiple N-type thermoelectric legs, the risk of failure of the energy harvester due to loss of connection between the thermoelectric leg and the opposing electrode layer is significantly reduced. This is particularly relevant when the energy harvester does not utilize another layer on the opposing electrode layer. Thus, in one example of an energy harvester, the series electrical connection of alternating N-type thermoelectric legs and P-type thermoelectric legs comprises individual N-type thermoelectric legs connected in series with a group of P-type thermoelectric legs, individual P-type thermoelectric legs connected in series with a group of N-type thermoelectric legs, or a group of N-type thermoelectric legs connected in series with a group of P-type thermoelectric legs, and the energy harvester does not comprise another layer arranged on the opposing electrode layer opposite the multiple thermoelectric legs. A group of either or both of the N-type and P-type thermoelectric legs may comprise 2 to 10, e.g., 4, of each type of thermoelectric leg. Where the disclosed energy harvester includes a series electrical connection including a group of either or both of the N-type and P-type thermoelectric legs, the step of separating the opposing electrode layers into segments and electrically connecting adjacent pairs of N-type and P-type thermoelectric legs is advantageously performed by cutting the opposing electrode layers.For example, with knowledge of the placement of N-type thermoelectric legs and P-type thermoelectric legs within the substrate, as prepared in a pick and place process, cutting may be performed to form serial electrical connections between individual thermoelectric legs or groups of thermoelectric legs as intended, thereby providing a simplified process.

[0016] The arrangement of the plurality of thermoelectric legs on top of the substrate surface may be performed in numerous ways. Preferably, the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs are provided as a large component. Providing the thermoelectric legs as a large component allows the thermoelectric legs to be picked up and placed at a desired location on the substrate. The thermoelectric legs may be placed manually by a person or automatically by a machine configured to pick up and place components, for example, using a pick-and-place process. If the N-type and P-type thermoelectric legs are arranged using an automated machine, the automated machine will generally map the location of the N-type and P-type thermoelectric legs and how the substrate ends are connected, for example, to adjacent pairs of thermoelectric legs. The mapped locations of the N-type and P-type thermoelectric legs may then be used in separating the opposing electrode layers into segments. For example, a pick-and-place process may be used in conjunction with cutting, for example, laser cutting, of the opposing electrode layers.

[0017] The step of bonding the thermoelectric legs to the substrate and / or top electrode may be accomplished by providing a bonding agent on the substrate and / or top electrode. The bonding agent may be disposed on the substrate and / or top electrode prior to the thermoelectric legs, for example, by disposing the bonding agent on the substrate and / or top electrode and then contacting the thermoelectric legs with the bonding agent. The bonding agent may be disposed on the substrate and / or top electrode after the thermoelectric legs, for example, by disposing the thermoelectric legs on the substrate and / or top electrode and then bonding with the bonding agent. The bonding agent may be an adhesive, solder, or a sintering agent that allows bonding to be achieved by sintering. Alternatively, bonding may be achieved by welding.

[0018] The substrate may have a plurality of bonding areas thereon. The bonding areas may be formed by depositing a bonding agent on the substrate. The bonding areas may be formed by etching the substrate, for example the substrate may have a conductive surface with an insulating base layer underneath, and thus the bonding areas may be formed by etching the conductive surface. The bonding areas may be formed by printing, as known from printed circuit boards. Each bonding area is configured to receive one N-type thermoelectric leg and one adjacent P-type thermoelectric leg, thus forming adjacent pairs of N-type and P-type thermoelectric legs on each bonding area. The bonding areas are electrically conductive, such that when one N-type and one P-type thermoelectric leg are arranged on the bonding area, an electrically connected adjacent pair of N-type and P-type thermoelectric legs is formed on the bonding area. In a preferred embodiment, the number of bonding areas on the substrate is in the range of 4 to 1000, preferably in the range of 60 to 80.

[0019] Forming the serial electrical connection between adjacent pairs of N-type and P-type thermoelectric legs may be performed by separating the opposing electrode layer into several segments and electrically connecting adjacent pairs of N-type and P-type thermoelectric legs with each other in series. The segments may bridge between different pairs of adjacent N-type and P-type thermoelectric legs and connect them with each other in series. The segments of the opposing electrode layer are preferably arranged to extend from the N-type thermoelectric leg of a first adjacent pair of thermoelectric legs to the P-type thermoelectric leg of a second adjacent pair of thermoelectric legs. Separating the opposing electrode layer into different segments may be performed before or after bonding to the thermoelectric legs, and is preferably performed after bonding to reduce the number of parts that need to be handled. Forming the serial electrical connection, e.g., separating the opposing electrode layer into segments, may be performed by cutting, etching, or dissolving the opposing electrode layer.

[0020] A series electrical connection between adjacent pairs of N-type and P-type thermoelectric legs may be formed by electrically connecting an N-type thermoelectric leg of a first adjacent pair of thermoelectric legs to a P-type thermoelectric leg of a second adjacent pair of thermoelectric legs.

[0021] In one embodiment, the step of joining the thermoelectric legs to the substrate and / or the opposing electrode layer is performed by soldering, sintering or welding. Soldering and sintering are techniques widely used in the production of electronic components, thus further increasing the compatibility between the energy harvester according to the invention and existing production techniques used in electronic components. Soldering and sintering is particularly advantageous when combined with cutting of the opposing electrode layer to separate the opposing electrode layer into segments, as this combination provides a simplified process.

[0022] Soldering is preferably used as a joining technique in situations where the energy harvester is to be used at temperatures below 230° C. Sintering is preferably used as a joining technique in situations where the energy harvester is to be used at temperatures above 230° C. The sintering may be silver sintering.

[0023] Soldering or sintering may be performed by forming solder pads on the substrate, each solder pad configured to receive one N-type thermoelectric leg and one P-type thermoelectric leg. The solder pads may be formed in any desired shape. The solder pads may be formed in a generally rectangular or elliptical shape on the substrate when viewed from above. The solder pads may be formed in a generally rectangular shape having a width in the range of 0.5 mm to 20 mm, preferably in the range of 2 mm to 10 mm, and a length in the range of 0.5 mm to 10 mm, preferably in the range of 1 to 5 mm. The solder pads may function as bonding areas on the substrate.

[0024] In one embodiment, the step of forming a series electrical connection between a pair of adjacent thermoelectric legs includes cutting the opposing electrode layers, such that the formation of the opposing electrode layers is performed by readily available methods, and the cutting may be performed by laser cutting or blade cutting.

[0025] The cutting of the opposing electrode layer may be performed before the opposing electrode layer is arranged on the thermoelectric legs. Preferably, however, the opposing electrode layer is arranged on and covers the opposing ends of the thermoelectric legs, and then subsequently bonded to the thermoelectric legs and finally cut to electrically connect the multiple thermoelectric legs with each other in series. The opposing electrode layer serves to electrically connect pairs of thermoelectric legs formed on the substrate in series.

[0026] In one embodiment, the step of arranging the plurality of thermoelectric legs on top of the substrate is performed by a pick-and-place process. Pick-and-place processes and pick-and-place machines are widely used in the electronics industry, thus further facilitating compatibility of the energy harvester with machine processes already present in the electronics industry. For the production of the energy harvester, a pick-and-place process can be particularly advantageous since only surface mount devices are required to create an energy harvester according to the invention. The energy harvester according to the invention may be assembled in layers on the substrate, the assembly of layers being compatible with pick-and-place processes and pick-and-place machines. This is in contrast to more conventional through-hole techniques, where holes through the substrate are required to place the electrical components, and in this case it is sufficient to place the surface mount devices on top of the substrate.

[0027] The combination of bonding opposing electrode layers to opposing ends of multiple thermoelectric legs and then separating the opposing electrode layers into segments by cutting to electrically connect adjacent pairs of N-type and P-type thermoelectric legs is particularly advantageous when combined with a pick-and-place process for arranging the substrate ends of the multiple thermoelectric legs on a substrate surface to greatly simplify the manufacture of the energy harvester.

[0028] In one embodiment, the method further includes arranging an insulating layer on the opposing electrode layer opposite the plurality of thermoelectric legs. Providing an insulating layer on the opposing electrode layer ensures that no unexpected short circuit occurs. The insulating layer on the opposing electrode layer may also be referred to as a top layer. However, it is preferred that no other layer is arranged on the opposing electrode layer opposite the plurality of thermoelectric legs. If no other layer is arranged on the opposing electrode layer, the opposing electrode layer may also be referred to as a heat receiving surface. The heat receiving surface is the surface of the energy harvester facing the heat source, and the substrate of the energy harvester faces away from any heat source, such that the energy harvester can generate electricity from a thermal gradient between the opposing electrode layer and the substrate.

[0029] In one embodiment, an insulating layer is provided on the thermally conductive base layer. The thermally conductive base layer ensures a good thermal connection to the external environment and thus facilitates a possible increase in temperature difference across the energy harvester. The thermally conductive base layer may be graphite or other material with high thermal conductivity. Furthermore, the thermally conductive base layer may facilitate the opposite electrode layer to function as the hot side of the energy harvester and the substrate to function as the cold side of the energy harvester.

[0030] The insulating layer may be provided on the thermally conductive base layer as a spray layer.The insulating layer may be provided on the thermally conductive base layer as a boron nitride spray.

[0031] According to a second aspect of the present invention, the object is achieved by an energy harvester for converting thermal energy into electrical energy, the energy harvester comprising: a conductive, flexible substrate having a substrate surface; a plurality of thermoelectric legs, each having a substrate end and an opposite end, arranged on the substrate surface and joined to the substrate surface by soldering or sintering, the plurality of thermoelectric legs comprising an N-type thermoelectric leg and a P-type thermoelectric leg; an opposing electrode layer arranged on an opposing end of the plurality of thermoelectric legs and joined to the plurality of thermoelectric legs by soldering or sintering; Bonding to the substrate and opposing electrode layers provides a series electrical connection of alternating N-type and P-type thermoelectric legs.

[0032] The opposing electrode layer may also be referred to as the heat receiving surface. Preferably, the opposing electrode layer does not include another layer.

[0033] The substrate may be made of metal foil or metallized sheets of paper or plastic. The substrate may comprise multiple materials and / or layers. The substrate may comprise a non-conductive flexible base on top of which the electrodes are placed. Alternatively, the substrate may comprise a base layer coated with a conductive layer, which may be etched away to form the desired electrical connections. Preferably, the substrate comprises multiple bonding areas to allow multiple thermoelectric legs to be bonded to the substrate. The multiple bonding areas may be formed as electrodes, which are configured to electrically connect thermoelectric legs arranged on the same electrode. The substrate may be formed in any desired shape, for example, to have a generally rectangular or oval shape when the substrate is viewed from above. The substrate may be formed in a box shape. The box shape of the substrate may be formed in any desired dimensions. In a preferred embodiment, the box shape is formed with a height in the range of 0.1 mm to 2 mm, a width in the range of 20 mm to 30 mm, and a length in the range of 20 mm to 30 mm. The small footprint of the substrate may facilitate utilization of the energy harvester for a wide variety of applications, such as in hard-to-reach, space-limited areas, and the energy harvester may even be arranged as an integrated component within a circuit. During use of the energy harvester, the substrate is configured to function as the cold side of the energy harvester.

[0034] The material of the thermoelectric legs may be selected from any thermoelectric material capable of converting a heat difference into an electric current. The material of the thermoelectric legs may be selected depending on the application of the energy harvester. The P-type thermoelectric legs may include one or more of the following thermoelectric materials: Mg3Sb2, ZnSb, Zn4Sb3, Bi2Te3, PbTe, and SiGe. The N-type thermoelectric legs may include one or more of the following thermoelectric materials: Mg3Sb2, Bi2Te3, PbTe, SiGe, and Mg2SiSn. The thermoelectric legs are preferably formed as rectangular pillars. However, the thermoelectric legs may be formed as pillars having any desired cross-section. The thermoelectric legs may be formed as box-shaped pillars having a width in the range of 0.5 mm to 5 mm, a length in the range of 0.5 mm to 5 mm, and a height in the range of 0.5 mm to 100 mm. The number of thermoelectric legs arranged on the substrate may be selected depending on the desired application and power output of the energy harvester. In a preferred embodiment, 60-80 N-type thermoelectric legs and 60-80 P-type thermoelectric legs are arranged on the substrate.

[0035] The thermoelectric leg may comprise multiple layers. In a preferred embodiment, the thermoelectric leg comprises a first electrode for electrically connecting the thermoelectric leg to a substrate, a first barrier layer acting as a diffusion barrier between the first electrode and the thermoelectric layer, a thermoelectric layer for generating an electric current as a result of a temperature difference across the thermoelectric leg, a second barrier layer acting as a diffusion barrier between the second electrode and the thermoelectric layer, and a second electrode for electrically connecting the thermoelectric leg to an opposing electrode layer. The electrode of the thermoelectric leg may be made of Ag or Au. The barrier layer may be made of Ti, CrN, Mo or Ni. The electrode and / or barrier layer may be formed on the thermoelectric layer by physical vapor deposition or other similar sputtering techniques, preferably the electrode and / or barrier layer are formed by sputtering outside of a clean room.

[0036] The opposing electrode layer may be made of metal foil or a metallized sheet of paper or plastic. The opposing electrode layer may comprise multiple materials and / or layers. The opposing electrode layer may comprise a non-conductive flexible base on which the electrode rests. The opposing electrode layer is preferably formed in a shape corresponding to the substrate. Preferably, the opposing electrode layer is formed by a flexible, thin, conductive layer that is easy to separate into different segments. During use of the energy harvester, the opposing electrode layer is configured to function as the hot side of the energy harvester.

[0037] In the method of the present invention, the opposing electrode layer is divided into segments to electrically connect pairs of adjacent N-type and P-type thermoelectric legs, and correspondingly, the energy harvester comprises a divided surface facing a heat source, e.g., a heat receiving surface. Each segment of the surface represents a series electrical connection of an N-type and a P-type thermoelectric leg, i.e., in the divided opposing electrode layer. The substrate layer is flexible, and due to the divided surface of the opposing electrode layer, where each segment represents a connection between pairs of adjacent N-type and P-type thermoelectric legs, the opposing electrode layer is also flexible. Thus, the divided opposing electrode layer increases the flexibility of the energy harvester compared to conventional energy harvesters that do not have a divided surface.

[0038] In one embodiment, the substrate comprises a flexible circuit board (CB). Having the substrate formed from a CB facilitates compatibility between the energy harvester and other electronic components and production equipment used in electronics factories.

[0039] The flexible CB may be formed of a flexible base layer, such as polyamide, with one or more electrodes disposed on the flexible base layer. The electrodes disposed on the flexible CB may serve as bonding areas for the thermoelectric legs. In a preferred embodiment, the substrate comprises a flexible printed circuit board (PCB).

[0040] In one embodiment, the opposing electrode layer preferably comprises a conductive foil having a thickness in the range of 1 μm to 500 μm. For example, the conductive foil, e.g. a metal foil, may have a thickness in the range of 10 μm to 500 μm, e.g., 50 μm to 400 μm, or 100 μm to 200 μm.

[0041] As a result, a flexible, electrically conductive, cuttable material is provided for the opposing electrode layer. Additionally, the conductive foil may exhibit a sagging behavior between the thermoelectric legs, i.e., when the foil is aligned over the thermoelectric legs, the foil may begin to sag between the legs. The sagging behavior may be advantageous in further improving the flexibility of the energy harvester, as the opposing electrode layer allows for a greater degree of bending of the energy harvester before the opposing electrode layer is strained or even breaks.

[0042] The conductive foil may be a metal foil, such as for example Ag-foil, Au-foil, Cu-foil, Al-foil or Fe-foil.

[0043] In one embodiment, the energy harvester is obtainable by a method of manufacture according to the first aspect of the present invention.

[0044] It should be noted that the present invention relates to all possible combinations of features recited in the claims. Other objects, features and advantages of the inventive concept will be apparent from the following detailed disclosure, from the appended claims, and from the drawings. A feature described in relation to one of the embodiments may also be incorporated in other embodiments, and the advantages of the feature are applicable to all embodiments in which it is incorporated.

[0045] In the following, the invention is explained in more detail by means of examples and with reference to schematic drawings. [Brief description of the drawings]

[0046] [Figure 1a]FIG. 1a is a schematic perspective view of an energy harvester according to one embodiment of the present invention. [Figure 1b] FIG. 1b is a schematic enlarged perspective view of the energy harvester shown in FIG. 1a with the top layer removed. [Diagram 2] FIG. 2 is a schematic top view of a substrate and an enlarged top view of a bonding area on the substrate, according to one embodiment of the present invention. [Diagram 3] FIG. 3 is a cross-sectional side view of an energy harvester according to one embodiment of the present invention. [Figure 4] FIG. 4 is a flow diagram of a method for manufacturing an energy harvester according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0047] The present invention is not limited to the embodiments illustrated in the drawings. Thus, when features recited in the appended claims are followed by reference signs, it will be understood that such signs are included solely for the purpose of enhancing comprehension of the claims and do not in any way limit the scope of the claims.

[0048] The term "comprising" as used herein means "consisting at least in part of." In interpreting statements in this specification and claims that include the term "comprising," there may be other features present than those that precede this term in the respective statement. Related terms such as "comprise" and "comprised" should be interpreted in a similar manner.

[0049] The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which presently preferred embodiments of the invention are shown. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein, but rather, these embodiments are provided for thoroughness and completeness and to fully convey the scope of the invention to those skilled in the art.

[0050] Please refer first to Fig. 1a and Fig. 1b, which show different schematic perspective views of an energy harvester 1 according to an embodiment of the present invention. The energy harvester 1 is for converting thermal energy into electrical energy. The energy harvester 1 comprises a substrate 2, a plurality of thermoelectric legs 3, 4, an opposing electrode layer 5, and a top layer 6. The substrate 2 is an electrically conductive and flexible PCB. The substrate 2 comprises a plurality of electrodes 21 disposed on the substrate 2. The plurality of electrodes 21 are disposed on a substrate surface 23. The substrate surface 23 is planar. The plurality of electrodes 21 serve as bonding areas for bonding the thermoelectric legs 3, 4 to the substrate 2. The substrate 2 is formed to have a generally box-like shape. During use of the energy harvester 1, the substrate 2 serves as the cold side of the energy harvester 1. The substrate 2 further comprises two electrical terminals 7 for electrically connecting the energy harvester 1 to an external component, thus enabling the energy harvester to supply power to the external component. The two electrical terminals 7 are formed as two prongs 7 connected in series with the multiple thermoelectric legs 3, 4.

[0051] The plurality of thermoelectric legs 3, 4 comprises a plurality of N-type thermoelectric legs 3 and a plurality of P-type thermoelectric legs 4. The plurality of N-type thermoelectric legs 3 and the plurality of P-type thermoelectric legs 4 each comprise a substrate end for bonding to the substrate 2 and an opposite end for bonding to an opposite electrode 5. The thermoelectric legs 3, 4 are arranged on top of the substrate 2 and bonded to the substrate 2 by soldering or sintering. The soldering or sintering of the thermoelectric legs 3, 4 is performed by depositing a conductive bonding agent on the electrode 21 of the substrate 2, thereby allowing the thermoelectric legs 3, 4 to be electrically connected to the substrate. The plurality of thermoelectric legs 3, 4 are provided as a plurality of box-like columns. The plurality of thermoelectric legs 3, 4 are arranged in electrically connected pairs, each pair comprising an N-type thermoelectric leg 3 and a P-type thermoelectric leg 4. The electrically connected pairs are electrically connected by being placed on the same electrode 21 of the substrate 2. An electrode 21 formed on the substrate 2 is configured to receive at least two thermoelectric legs 3, 4. The thermoelectric legs 3, 4 may include one or more of the following thermoelectric materials: MgSb, Mg3Sb2, ZnSb, Zn4Sb3, Bi2Te3, PbTe and SiGe.

[0052] The opposing electrode layer 5 is arranged on the opposing ends of the plurality of N-type thermoelectric legs 3 and the plurality of P-type thermoelectric legs 4. The opposing electrode layer 5 is arranged on the opposite side of the substrate 2 with respect to the thermoelectric legs 3, 4. The opposing electrode layer 5 is bonded to the plurality of N-type thermoelectric legs 3 and the plurality of P-type thermoelectric legs 4 by soldering or sintering. The opposing electrode layer 5, together with the substrate 2, serves to electrically connect the plurality of N-type thermoelectric legs 3 and the plurality of P-type thermoelectric legs 4 with each other in series. The opposing electrode layer 5 comprises a conductive foil. The opposing electrode layer 5 preferably has a thickness of 100 μm. However, in other embodiments, the opposing electrode layer may be as thin as 1 μm or as thick as 500 μm. In the embodiment shown, the opposing electrode layer 5 is separated into different segments, so that it electrically connects the pairs of electrically connected thermoelectric legs 3, 4 with each other in series. During use of the energy harvester 1, the opposing electrode layer 5 serves as the hot side of the energy harvester 1. As a result, the temperature difference between the hot side, i.e., the opposing electrode layer 5, and the cold side, i.e., the substrate 2, causes the thermoelectric legs 3, 4 to generate an electric current via the Seebeck effect. The generated electric current may be delivered to an external component via an electrical terminal 7 connected in series with the thermoelectric legs 3, 4.

[0053] Atop the opposing electrode layer is a top layer 6. The top layer 6 is arranged to cover the opposing electrode layer 5 and the thermoelectric legs 3, 4. The top layer 6 is described in more detail with reference to FIG.

[0054] Please refer to FIG. 2, which shows a schematic top view of the substrate 2 and an enlarged top view of a bonding area 21 on the substrate 2, according to an embodiment of the present invention. The substrate 2 is arranged in a grid-like structure formed by a plurality of electrodes 21. The plurality of electrodes 21 are formed as rectangular patches on the substrate 2. The electrodes 21 are formed with a width of 4 mm and a length of 1 mm. The electrodes 21 are arranged on the substrate 2 such that, in cooperation with the opposing electrode layer 5, the electrodes 21 are electrically connected to each other in series. The plurality of electrodes 21 are electrically insulated from each other by the substrate 2, such that no direct electrical connection is formed within the substrate 2 between the electrodes 21. Each electrode 21 is configured to receive a pair of thermoelectric legs 3, 4 and electrically connects the associated pair of thermoelectric legs 3, 4. The substrate 2 is a flexible PCB, in which case the plurality of electrodes 21 are provided by a plurality of solder pads on the flexible PCB.

[0055] Please refer to FIG. 3, which shows a cross-sectional side view of an energy harvester 1 according to an embodiment of the present invention. The substrate 2 is arranged on the cold side of the energy harvester 1, and thus the energy harvester 1 is preferably arranged such that the substrate 2 faces away from any heat source during use of the energy harvester 1. The substrate 2 preferably comprises a non-conductive base layer on which a plurality of electrodes 21 are arranged. Each electrode 21 has an N-type thermoelectric leg 3 and a P-type thermoelectric leg 4 arranged thereon. The electrodes 21 electrically connect the associated thermoelectric legs 3, 4 arranged on and bonded to the associated electrode 21. A bonding agent 22 is used to bond the thermoelectric legs 3, 4 to the electrodes 21. The bonding agent 22 can be a solder used for soldering or a sintering powder used for sintering.

[0056] Each thermoelectric leg 3, 4 bonded to an electrode 21 comprises multiple layers proceeding from the substrate 2 towards the opposing electrode layer 5. The first layer, starting with the layer closest to the substrate 2, is the first leg electrode 31, 41, the second layer is the first barrier layer 32, 42, the third layer is the thermoelectric layer 33, 43, the fourth layer is the second barrier layer 34, 44, and finally the fifth layer, closest to the opposing electrode layer 5, is the second leg electrode 35, 45. The first leg electrode 31, 41 serves to electrically connect the thermoelectric leg 3, 4 to the electrode 21 of the substrate 2. The first leg electrode 31, 41 is connected to the electrode 21 via a bonding agent 22. The first barrier layer 32, 42 prevents diffusion of atoms between the first leg electrode 31, 41 and the thermoelectric layer 33, 43. The thermoelectric layers 33, 34 are configured to generate an electric current as a result of a temperature difference across the thermoelectric layers 33, 43. The second barrier layers 34, 44 prevent atomic diffusion between the second leg electrodes 35, 45 and the thermoelectric layers 33, 43. The second leg electrodes 35, 45 function to electrically connect the thermoelectric legs 3, 4 to the opposing electrode layer 5. The second leg electrodes 35, 45 are bonded to the opposing electrode layer 5 via a bonding agent 51. The bonding agent 22 used between the first leg electrodes 31, 41 and the electrode 21 of the substrate 2 may be the same type of bonding agent 51 as that used between the second leg electrodes 35, 45 and the opposing electrode layer 5. The electrode layers 31, 35 for the multiple N-type thermoelectrics 3 may be different or the same as the electrode layers 41, 45 for the multiple P-type thermoelectrics 4. The barrier layers 32 , 34 for the plurality of N-type thermoelectrics 3 may be different from or the same as the barrier layers 42 , 44 for the plurality of P-type thermoelectrics 4 .

[0057] The opposing electrode layer 5 serves to electrically connect pairs of thermoelectric legs from different electrodes 21 in series with each other. The opposing electrode layer 5 comprises a flexible conductive foil. The opposing electrode layer 5 is formed as a segment extending from an N-type thermoelectric leg 3 on one electrode 21 to a P-type thermoelectric leg 4 arranged on a different electrode 21, thus electrically connecting pairs of different thermoelectric legs from different electrodes 21 with each other.

[0058] A top layer 6 is arranged on the opposing electrode layer 5 opposite the thermoelectric legs 3, 4. The top layer 6 comprises an insulating layer 61. The top layer 6 further comprises a thermally conductive base layer 62. The insulating layer 61 serves to insulate the opposing electrode layer 5 from the thermally conductive base layer 62. The insulating layer 61 is provided as a sprayed on boron nitride layer on the thermally conductive base layer 62.

[0059] Please refer to FIG. 4 which shows a flow diagram of a method 100 for manufacturing an energy harvester 1 according to one embodiment of the present invention.

[0060] The method 100 includes a first step 101 of providing a substrate, where the substrate is conductive and flexible. The method 100 includes a second step 102 of arranging a plurality of N-type thermoelectric legs and a plurality of P-type thermoelectric legs on top of the substrate. The second step 102 may be performed by a pick-and-place process, for example by a pick-and-place machine configured for surface mount devices. The method 100 includes a third step 103 of bonding the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs to the substrate. The third step 103 may be performed by soldering or sintering the thermoelectric legs to the substrate. The method 100 includes a fourth step 104 of arranging an opposing electrode layer on the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs on an opposing side of the substrate. The method 100 includes a fifth step 105 of bonding the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs to opposing electrode layers. The fifth step 105 may be performed by soldering or sintering the thermoelectric legs to the opposing electrode layers. The method 100 includes a sixth step 106 of separating the opposing electrode layers to electrically connect the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs with each other in series. The sixth step 106 may be performed by cutting the opposing electrode layers, for example by laser cutting or blade cutting.

[0061] The method 100 may further include arranging an insulating layer on an opposing electrode layer opposite the plurality of N-type thermoelectric legs and the plurality of P-type thermoelectric legs. The insulating layer may be provided on the thermally conductive base layer.

[0062] Although specific embodiments of the present invention have been described herein, several alternatives are possible, as would be apparent to one of ordinary skill in the art. [Explanation of symbols]

[0063] 1 Energy Harvester 2. Board 3, 4 Thermoelectric Legs 5 Opposite electrode layer 6 Top layer 21 electrodes 23 Board surface 7 Electrical terminals 22 Bonding agent 32, 42 First barrier layer 33, 43 Thermoelectric layer 34, 44 Second barrier layer 35, 45 Second leg electrode 31, 41 First leg electrode 51 Bonding Agent 61 Insulating layer 62 Thermally conductive base layer 100 ways 101 First Step of the Method 102 Second step of the method 103 Third step of the method 104 Fourth Step of the Method 105 Fifth Step of the Method 106 Sixth Step of the Method

Claims

1. 1. A method of manufacturing an energy harvester, comprising: providing a conductive, flexible substrate having a substrate surface; providing a plurality of thermoelectric legs each having a substrate end and an opposite end, the plurality of thermoelectric legs comprising an N-type thermoelectric leg and a P-type thermoelectric leg; arranging the substrate ends of the plurality of thermoelectric legs on a surface of the substrate; bonding the substrate ends of the plurality of thermoelectric legs to the substrate to form a plurality of pairs of adjacent thermoelectric legs, each pair of adjacent thermoelectric legs having an N-type thermoelectric leg electrically connected to the P-type thermoelectric leg via an N-type thermoelectric leg and the substrate end of the P-type thermoelectric leg; providing an opposing electrode layer having an opposing electrode layer surface; arranging the opposing electrode layer on the opposing ends of the plurality of thermoelectric legs; bonding the opposing ends of the plurality of thermoelectric legs to the opposing electrode layer surface; and separating the opposing electrode layer into segments to electrically connect adjacent pairs of N-type and P-type thermoelectric legs, thereby forming a series electrical connection between adjacent pairs of thermoelectric legs.

2. 2. The method for manufacturing an energy harvester of claim 1, wherein the step of joining the plurality of thermoelectric legs to the substrate and / or the opposing electrode layer is performed by soldering or sintering.

3. 2. The method for manufacturing an energy harvester of claim 1, wherein the step of separating the opposing electrode layers into segments includes cutting the opposing electrode layers.

4. 10. The method for manufacturing an energy harvester of claim 1, wherein the step of arranging the plurality of thermoelectric legs on the surface of the substrate is performed by a pick-and-place process.

5. The method for manufacturing an energy harvester of claim 1 , further comprising the step of arranging an insulating layer on said opposing electrode layer opposite said plurality of thermoelectric legs.

6. 6. A method for manufacturing an energy harvester as claimed in claim 5, wherein the insulating layer is provided on a thermally conductive base layer.

7. 1. An energy harvester for converting thermal energy into electrical energy, comprising: a conductive, flexible substrate having a substrate surface; a plurality of thermoelectric legs, each having a substrate end and an opposite end, arranged on the substrate surface and joined to the substrate surface by soldering or sintering, the plurality of thermoelectric legs comprising an N-type thermoelectric leg and a P-type thermoelectric leg; an opposing electrode layer disposed on the opposing ends of the plurality of thermoelectric legs and joined to the plurality of thermoelectric legs by soldering or sintering; An energy harvester, wherein bonding to the substrate and the opposing electrode layer provides a series electrical connection of alternating N-type thermoelectric legs and P-type thermoelectric legs.

8. The energy harvester of claim 7 , wherein the substrate comprises a flexible circuit board, CB.

9. 8. An energy harvester according to claim 7, wherein the opposing electrode layer comprises a conductive foil preferably having a thickness in the range of 1 μm to 500 μm.

10. The series electrical connection of alternating N-type thermoelectric legs and P-type thermoelectric legs comprises: an individual N-type thermoelectric leg connected in series with a group of P-type thermoelectric legs; an individual P-type thermoelectric leg connected in series with a group of N-type thermoelectric legs; or 8. The energy harvester of claim 7, comprising a group of N-type thermoelectric legs connected in series with a group of P-type thermoelectric legs.

11. 8. The energy harvester of claim 7, wherein the energy harvester does not include another layer disposed on the opposing electrode layer opposite the plurality of thermoelectric legs.

12. An energy harvester according to claim 7, obtainable by the method according to any one of claims 1 to 6.

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