Thermoelectric conversion element and method for manufacturing a thermoelectric conversion element

Abstract

To provide a thermoelectric conversion element miniaturized easily, and a manufacturing method for the thermoelectric conversion element.SOLUTION: A thermoelectric conversion element 100 includes a substrate 10, a thermoelectric conversion layer 30 formed on a first main surface 12 of the substrate 10, an insulating layer 40 covering the thermoelectric conversion layer 30, a first electrode 50 formed on the insulating layer 40 and connected to a first main surface 32 of the thermoelectric conversion layer 30 through a first contact hole 42 of the insulating layer 40, and a second electrode 60 formed on the insulating layer 40 and connected to the first main surface 32 of the thermoelectric conversion layer 30 through a second contact hole 44 of the insulating layer 40. At least a part of the first electrode 50 is formed of a material with a work function different from the work function of a material of the second electrode 60.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a thermoelectric conversion element and a method for manufacturing the same.

Background Art

[0002] A thermoelectric conversion element that generates a thermoelectromotive force between two electrodes due to a temperature difference is known. For example, Patent Document 1 discloses a thermoelectric conversion element including a thin-film thermoelectric conversion material layer, a first electrode provided on one main surface of the thermoelectric conversion material layer, and a second electrode provided at a position different from the first electrode in the in-plane direction of one main surface of the thermoelectric conversion material layer. In Patent Document 1, the work function of the material constituting the first electrode is different from the work function of the material constituting the second electrode.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the thermoelectric conversion element described in Patent Document 1, the short-circuit current can be increased by narrowing the distance between the first electrode and the second electrode, thus miniaturization of the thermoelectric conversion element is desirable. On the other hand, when miniaturizing the thermoelectric conversion element described in Patent Document 1 by photolithography and etching, several problems may arise. For example, when the first electrode is formed on one main surface of the thermoelectric conversion material layer, the material constituting the thermoelectric conversion material layer and the material constituting the first electrode are different, and the thermoelectric conversion material layer and the first electrode, which have different electrode potentials, are in a conductive state. As a result, a battery is formed between the thermoelectric conversion material layer and the first electrode in the etching solution. Consequently, due to the potential difference (difference in electrode potential) between the thermoelectric conversion material layer and the first electrode, a current flows between the thermoelectric conversion material layer and the first electrode, which may cause the thermoelectric conversion material layer to dissolve, abnormal dissolution of the material constituting the first electrode, etc. Similarly, when the second electrode is formed on one main surface of the thermoelectric material layer on which the first electrode is formed, there is a risk that current will flow between the thermoelectric material layer, the first electrode and the second electrode in the etching solution due to a battery action, causing dissolution of the thermoelectric material layer and the first electrode, and abnormal dissolution of the material constituting the second electrode.

[0005] This disclosure is made in view of the above circumstances and aims to provide a thermoelectric conversion element that is easily miniaturized and a method for manufacturing a thermoelectric conversion element. [Means for solving the problem]

[0006] To achieve the above objective, the thermoelectric conversion element relating to the first aspect is: circuit board and A thermoelectric conversion layer formed on the main surface of the substrate, An insulating layer covering the thermoelectric conversion layer, A first electrode is formed on the insulating layer and connected to the main surface of the thermoelectric conversion layer via a first contact hole in the insulating layer, A second electrode is formed on the insulating layer and connected to the main surface of the thermoelectric conversion layer via a second contact hole in the insulating layer, comprising: 、 before The first electrode has a first layer and a second layer, The first layer is connected to the main surface of the thermoelectric conversion layer, The second layer covers the first layer in such a way that the first layer is not exposed from the second layer. The aforementioned second layer and the aforementioned second electrode are formed from the same material, having a work function different from that of the material forming the aforementioned first layer. There are .

[0007] The method for manufacturing a thermoelectric conversion element relating to the second aspect is: A process of forming a thermoelectric conversion layer on a substrate, The steps include forming an insulating layer on the thermoelectric conversion layer, The process of forming a first contact hole in the insulating layer that exposes the main surface of the thermoelectric conversion layer, A step of forming a first electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the first contact hole, by photolithography and etching, A step of forming a second contact hole in the insulating layer on which the first electrode is formed, which exposes the main surface of the thermoelectric conversion layer, The process includes forming a second electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the second contact hole, by photolithography and etching from a material having a work function different from that of the material forming at least a portion of the first electrode. The method for manufacturing a thermoelectric conversion element relating to the third aspect is: A process of forming a thermoelectric conversion layer on a substrate, The steps include forming an insulating layer on the thermoelectric conversion layer, The process of forming a first contact hole in the insulating layer that exposes the main surface of the thermoelectric conversion layer, A step of forming a first layer of the first electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the first contact hole, by photolithography and etching, A step of forming a second contact hole in the insulating layer on which the first layer of the first electrode is formed, which exposes the main surface of the thermoelectric conversion layer, The process includes forming a second electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the second contact hole, by photolithography and etching from a material having a work function different from that of the material forming the first layer of the first electrode, The step of forming the second electrode involves forming the second electrode and forming the second layer such that the first layer of the first electrode is not exposed from the second layer of the first electrode. The aforementioned second electrode uses the same material as the material forming the aforementioned second layer. [Effects of the Invention]

[0008] According to the present disclosure, when the first layer is formed by etching, the thermoelectric conversion layer is not exposed to the etching solution. Further, when the second layer and the second electrode are formed by etching, the thermoelectric conversion layer and the first layer are not exposed to the etching solution. As a result, the battery action between the thermoelectric conversion layer and the first layer through the etching solution and the battery action between the thermoelectric conversion layer, the first layer, and the second electrode through the etching solution do not occur. Therefore, when the first layer is formed by etching and when the second layer and the second electrode are formed by etching, excessive dissolution of the thermoelectric conversion layer, the first layer, the second layer, and the second electrode caused by the battery action is suppressed, and the thermoelectric conversion element can be easily miniaturized.

Brief Description of the Drawings

[0009] [Figure 1] It is a top view showing a thermoelectric conversion element according to Embodiment 1. [Figure 2] It is a cross-sectional view of the thermoelectric conversion element shown in FIG. 1 taken along the line A-A. [Figure 3] It is a flowchart showing a method for manufacturing a thermoelectric conversion element according to Embodiment 1. [Figure 4] It is a cross-sectional view showing an underlayer according to Embodiment 1. [Figure 5] It is a top view showing a thermoelectric conversion layer according to Embodiment 1. [Figure 6] It is a top view showing an insulating layer and a thermoelectric conversion layer according to Embodiment 1. [Figure 7] It is a cross-sectional view of the insulating layer and the thermoelectric conversion layer shown in FIG. 6 taken along the line B-B. [Figure 8] It is a top view showing a first contact hole according to Embodiment 1. [Figure 9] It is a cross-sectional view of the first contact hole shown in FIG. 8 taken along the line C-C. [Figure 10] It is a top view showing a first layer of a first electrode according to Embodiment 1. [Figure 11] It is a cross-sectional view of the first layer of the first electrode shown in FIG. 10 taken along the line D-D. [Figure 12] It is a schematic diagram for explaining the formation of the first layer of the first electrode according to Embodiment 1. [Figure 13] This is a top view showing the second contact hole according to Embodiment 1. [Figure 14] Figure 13 is a cross-sectional view of the second contact hole, taken along the EE line. [Figure 15] This is a top view showing the second electrode and the second layer of the first electrode according to Embodiment 1. [Figure 16] Figure 15 is a cross-sectional view of the second electrode and the second layer of the first electrode, taken with the FF line in the direction of the arrow. [Figure 17] This is a schematic diagram illustrating the formation of the second layer of the second electrode and the first electrode according to Embodiment 1. [Figure 18] This is a top view showing a thermoelectric conversion element according to Embodiment 2. [Figure 19] Figure 18 is a cross-sectional view of the thermoelectric conversion element shown, taken along the line GG. [Figure 20] This is a flowchart showing a method for manufacturing a thermoelectric conversion element according to Embodiment 2. [Figure 21] This is a schematic diagram illustrating the formation of the first electrode according to Embodiment 2. [Figure 22] This is a top view showing the first electrode according to Embodiment 2. [Figure 23] Figure 22 is a cross-sectional view of the first electrode, taken along the HH line. [Figure 24] This is a schematic diagram showing a photoresist covering the first electrode according to Embodiment 2. [Figure 25] This is a schematic diagram showing the photoresist covering the second electrode according to Embodiment 2. [Figure 26] This is a schematic diagram illustrating the formation of the second electrode according to Embodiment 2. [Figure 27] This is a cross-sectional view after the first electrode and the second electrode according to Embodiment 2 have been formed. [Modes for carrying out the invention]

[0010] The thermoelectric conversion element according to the embodiment will be described below with reference to the drawings.

[0011] <Embodiment 1> A thermoelectric conversion element 100 according to Embodiment 1 will be described with reference to Figures 1 to 17. As shown in Figures 1 and 2, the thermoelectric conversion element 100 comprises a substrate 10, a base layer 20, a thermoelectric conversion layer 30, an insulating layer 40, a first electrode 50, a second electrode 60, and a protective layer 70. The first electrode 50 has a first layer 52 and a second layer 56. The first layer 52 is connected to the first main surface 32 of the thermoelectric conversion layer 30, and the second layer 56 covers the first layer 52 so that it is not exposed from the second layer 56. The second electrode 60 is connected to the first main surface 32 of the thermoelectric conversion layer 30. The second layer 56 and the second electrode 60 are formed from the same material, having a different work function from the material forming the first layer 52. Note that in Figure 1, the base layer 20 and the insulating layer 40 are omitted for ease of understanding. Furthermore, in the following top view diagrams, the sub-layer 20 may be omitted.

[0012] The thermoelectric element 100 generates a thermoelectric voltage due to the temperature difference in the thickness direction of the thermoelectric layer 30. In other words, the thermoelectric element 100 converts thermal energy into electrical energy. The thermoelectric element 100 can be used, for example, as a sensor to detect heat flux. For ease of understanding, in this specification, the direction to the right (right direction on the paper) of the thermoelectric element 100 in Figure 1 is described as the +X direction, the direction upward (up on the paper) is described as the +Y direction, and the direction perpendicular to the +X and +Y directions (towards the front of the paper) is described as the +Z direction (thickness direction).

[0013] The substrate 10 of the thermoelectric conversion element 100 is, for example, a flat glass substrate. The substrate 10 is preferably made from a material with high thermal conductivity in order to reduce thermal resistance in the thickness direction (+Z direction).

[0014] The base layer 20 of the thermoelectric conversion element 100 is provided on the first main surface 12 of the substrate 10. In Embodiment 1, the base layer 20 is provided over the entire surface of the first main surface 12. The base layer 20 is made of, for example, silicon oxide (SiO2). x ) is formed from.

[0015] The thermoelectric conversion layer 30 of the thermoelectric conversion element 100 is provided in a rectangular shape on the base layer 20. The thermoelectric conversion layer 30 is formed from an n-type or p-type thermoelectric conversion material. Examples of n-type thermoelectric conversion materials include zinc oxide (ZnO) with aluminum (Al) added, and indium gallium zinc oxide (InGaZnO). Examples of p-type thermoelectric conversion materials include magnesium silicide (Mg2Si) with silver (Ag) added. In Embodiment 1, the thermoelectric conversion layer 30 is formed from indium gallium zinc oxide.

[0016] The insulating layer 40 of the thermoelectric conversion element 100 covers the thermoelectric conversion layer 30 and the base layer 20. As shown in Figure 1, the insulating layer 40 has comb-shaped first contact holes 42 formed to connect the first electrode 50 (first layer 52) and the thermoelectric conversion layer 30. The insulating layer 40 also has comb-shaped second contact holes 44 formed to connect the second electrode 60 and the thermoelectric conversion layer 30. The insulating layer 40 is made of, for example, silicon oxide (SiO₂). x ) is formed from.

[0017] The first electrode 50 of the thermoelectric conversion element 100 is formed on the insulating layer 40 and is connected to the first main surface 32 (the main surface opposite to the substrate 10) of the thermoelectric conversion layer 30 via a first contact hole 42 in the insulating layer 40. The first electrode 50 has a first layer 52 and a second layer 56.

[0018] The first layer 52 of the first electrode 50 is connected to the first main surface 32 of the thermoelectric conversion layer 30 via the first contact hole 42 of the insulating layer 40. The first layer 52 covers the opening of the first contact hole 42 so that the thermoelectric conversion layer 30 exposed from the insulating layer 40 at the bottom of the first contact hole 42 is not exposed from the first layer 52.

[0019] As shown in Figure 1, the first layer 52 has a first base portion 52a extending in the Y direction and a plurality of first comb-tooth portions 52b extending from the first base portion 52a in the +X direction, and is formed in a comb-like shape. The first comb-tooth portions 52b and the second comb-tooth portions 60b of the second electrode 60, which will be described later, are arranged alternately and opposite each other on the first main surface 32 of the thermoelectric conversion layer 30. The first layer 52 is formed from, for example, titanium (Ti) having a small work function.

[0020] In Embodiment 1, the insulating layer 40 covers the thermoelectric conversion layer 30, and the first layer 52 of the first electrode 50 formed on the insulating layer 40 is connected via the first contact hole 42 of the insulating layer 40. Therefore, when the first layer 52 is formed by etching, the thermoelectric conversion layer 30 is not exposed from the insulating layer 40 and is not exposed to the etching solution. As a result, a battery formed by the first layer 52, the etching solution, and the thermoelectric conversion layer 30 is not formed. Consequently, in the thermoelectric conversion element 100, the first layer 52 can be formed by etching without causing damage (e.g., excessive dissolution) to the first layer 52 and the thermoelectric conversion layer 30 caused by battery action.

[0021] As shown in Figure 2, the second layer 56 of the first electrode 50 covers the first layer 52 in a way that prevents it from being exposed to the second layer 56, and is formed together with the second electrode 60 from the same material as the material that forms the second electrode 60. Therefore, when the second layer 56 is formed by etching, the first layer 52 is not exposed to the etching solution. As a result, a battery formed by the second layer 56, the etching solution, and the first layer 52 is not formed. Consequently, the second electrode 60 can be formed by etching without damaging the first layer 52 and the second layer 56 due to battery action. The materials used to form the second layer 56 and the second electrode 60 will be described later.

[0022] The second electrode 60 of the thermoelectric conversion element 100 is formed on the insulating layer 40 and is connected to the first main surface 32 of the thermoelectric conversion layer 30 via a second contact hole 44 in the insulating layer 40. The second electrode 60 and the first electrode 50 (first layer 52) are not connected, and the second electrode 60 is connected to the first main surface 32 at a location different from where the first electrode 50 is connected. The second electrode 60 covers the opening of the second contact hole 44 such that the thermoelectric conversion layer 30 exposed from the insulating layer 40 at the bottom of the second contact hole 44 is not exposed from the second electrode 60.

[0023] As shown in Figure 1, the second electrode 60 has a second base portion 60a extending in the Y direction and a plurality of second comb-tooth portions 60b extending from the second base portion 60a in the -X direction, and is formed in a comb-like shape. The second comb-tooth portions 60b and the first comb-tooth portions 52b of the first layer 52 of the first electrode 50 are arranged alternately and opposite each other on the first main surface 32 of the thermoelectric conversion layer 30.

[0024] The second electrode 60 and the second layer 56 of the first electrode 50 are formed together from the same material, but with a different work function from the material forming the first layer 52 of the first electrode 50. For example, the second electrode 60 and the second layer 56 of the first electrode 50 are formed from copper (Cu), which has a large work function.

[0025] In Embodiment 1, the insulating layer 40 covers the thermoelectric conversion layer 30, and the second electrode 60 formed on the insulating layer 40 is connected via the second contact hole 44 of the insulating layer 40. Therefore, when the second electrode 60 is formed by etching, the thermoelectric conversion layer 30 is not exposed to the etching solution. Also, the first layer 52 of the first electrode 50 is covered by the second layer 56 formed together with the second electrode 60. Therefore, when the second electrode 60 (second layer 56) is formed by etching, the first layer 52 is not exposed to the etching solution. As a result, a battery consisting of the second electrode 60, the etching solution, and the thermoelectric conversion layer 30, and a battery consisting of the second electrode 60, the etching solution, and the first layer are not formed. Consequently, in the thermoelectric conversion element 100, the second electrode 60 can be formed by etching without causing damage to the thermoelectric conversion layer 30, the first layer 52, and the second electrode 60 caused by battery action.

[0026] In the thermoelectric element 100, the first layer 52 of the first electrode 50 and the second electrode 60, which are formed from materials with different work functions, are connected to the first main surface 32 of the thermoelectric layer 30, and a thermoelectric voltage is generated by the temperature difference in the thickness direction (Z direction) of the thermoelectric layer 30. In the thermoelectric element 100, even if the first layer 52 of the first electrode 50 is formed by etching, the thermoelectric layer 30 and the first layer 52 are not damaged, and even if the second layer 56 and the second electrode 60 of the first electrode 50 are formed by etching, the thermoelectric layer 30, the first layer 52, the second layer 56, and the second electrode 60 are not damaged. Therefore, the thermoelectric element 100 can be easily miniaturized by photolithography and etching.

[0027] The protective layer 70 of the thermoelectric conversion element 100 protects the first electrode 50, the second electrode 60, etc. The protective layer 70 is formed from, for example, photosensitive polyimide. The protective layer 70 is provided with terminal openings 75 for connecting the first electrode 50 and the second electrode 60 to an external device.

[0028] Next, the manufacturing method of the thermoelectric conversion element 100 in Embodiment 1 will be described with reference to Figures 3 to 17. Figure 3 is a flowchart of the manufacturing method of the thermoelectric conversion element 100 in Embodiment 1. The manufacturing method of the thermoelectric conversion element 100 includes the steps of: forming a base layer 20 on the first main surface 12 of the substrate 10 (step S10); forming a thermoelectric conversion layer 30 on the base layer 20 (on the first main surface 12 of the substrate 10) (step S20); forming an insulating layer 40 on the thermoelectric conversion layer 30 (step S30); forming a first contact hole 42 in the insulating layer 40 (step S40); and forming a first layer 52 of the first electrode 50 that connects to the first main surface 32 of the thermoelectric conversion layer 30 via the first contact hole 42 on the insulating layer 40 (step S50). The method for manufacturing the thermoelectric conversion element 100 further includes the steps of: forming a second contact hole 44 in the insulating layer 40 on which the first layer 52 of the first electrode 50 is formed (step S60); forming a second electrode 60 on the insulating layer 40, which is connected to the first main surface 32 of the thermoelectric conversion layer 30 via the second contact hole 44, from a material having a different work function from the material forming the first layer 52 of the first electrode 50, and forming a second layer 56 of the first electrode 50 that covers the first layer 52 of the first electrode 50 from the same material as the material forming the second electrode 60, such that the first layer 52 is not exposed from the second layer 56 (step S70); and forming a protective layer 70 (step S80).

[0029] In step S10, first, the substrate 10 is prepared. Next, as shown in Figure 4, a base layer 20 is formed on the first main surface 12 of the substrate 10. The base layer 20 is formed, for example, from silicon oxide by sputtering over the entire surface of the first main surface 12.

[0030] In step S20, a rectangular thermoelectric conversion layer 30 is formed on the base layer 20, as shown in Figure 5. Specifically, first, a thermoelectric conversion film is formed on the entire surface of the base layer 20 from indium gallium zinc oxide by sputtering. Next, the thermoelectric conversion layer 30 is formed from the thermoelectric conversion film by photolithography and etching.

[0031] In step S30, as shown in Figures 6 and 7, an insulating layer 40 is formed on top of the thermoelectric conversion layer 30 and the base layer 20. Specifically, the insulating layer 40 is formed from silicon oxide by CVD (Chemical Vapor Deposition) over the entire surface of the base layer 20 and the thermoelectric conversion layer 30. Here, the thermoelectric conversion layer 30 is covered by the insulating layer 40 in a state where it is not exposed from the insulating layer 40.

[0032] In step S40, first contact holes 42 are formed in the insulating layer 40 by photolithography and etching. In Embodiment 1, as shown in Figures 8 and 9, the first contact holes 42 are formed in a comb-like shape to match the shape of the first layer 52 of the first electrode 50. As a result, the first main surface 32 of the thermoelectric conversion layer 30 is exposed from the insulating layer 40 in a comb-like shape.

[0033] In step S50, as shown in Figures 10 and 11, a first layer 52 of the first electrode 50 is formed on the insulating layer 40. The first layer 52 is connected to the first main surface 32 of the thermoelectric conversion layer 30 via the first contact hole 42. The first layer 52 also covers the opening of the first contact hole 42 such that the thermoelectric conversion layer 30 exposed from the insulating layer 40 at the bottom of the first contact hole 42 is not exposed from the first layer 52.

[0034] Specifically, first, a titanium thin film is deposited on the insulating layer 40 by sputtering to fill the first contact holes 42. Next, the first layer 52 is formed in a comb-like shape from the titanium thin film by photolithography and etching. In Embodiment 1, when etching the titanium thin film, as shown in Figure 12, the thermoelectric conversion layer 30 is covered by the insulating layer 40 and the first layer 52 (titanium thin film), and furthermore, the portion of the titanium thin film that will become the first layer 52 of the first electrode 50 is covered with photoresist. Therefore, the insulating layer 40 and the titanium thin film are exposed to the etching solution, while the thermoelectric conversion layer 30 is not exposed to the etching solution, allowing the first layer 52 to be formed.

[0035] In step S60, second contact holes 44 are formed in the insulating layer 40 by photolithography and etching. In Embodiment 1, as shown in Figures 13 and 14, the second contact holes 44 are formed in a comb-like shape to match the shape of the second electrode 60. As a result, the first main surface 32 of the thermoelectric conversion layer 30 is exposed from the insulating layer 40 in a comb-like shape.

[0036] In step S70, as shown in Figures 15 and 16, a second electrode 60 is formed on the insulating layer 40, and a second layer 56 of the first electrode 50 is formed. The second electrode 60 is connected to the first main surface 32 of the thermoelectric conversion layer 30 via a second contact hole 44. The second electrode 60 covers the opening of the second contact hole 44 such that the thermoelectric conversion layer 30 exposed from the insulating layer 40 at the bottom of the second contact hole 44 is not exposed from the second electrode 60. The second layer 56 of the first electrode 50 covers the first layer 52 of the first electrode 50 such that the first layer 52 is not exposed from the second layer 56. The second electrode 60 and the second layer 56 are formed from a material (copper) having a different work function from the material (titanium) that forms the first layer 52 of the first electrode 50.

[0037] Specifically, first, a copper thin film is deposited on the insulating layer 40 and the first layer 52 by sputtering to fill the second contact holes 44. Next, the second electrode 60 and the second layer 56 are formed in a comb-like shape from the copper thin film by photolithography and etching. In Embodiment 1, when etching the copper thin film, as shown in Figure 17, the thermoelectric conversion layer 30 is covered by the insulating layer 40, the first layer 52 and the second electrode 60 (copper thin film), the first layer 52 is covered by the second layer 56 (copper thin film), and furthermore, the areas of the copper thin film that become the second electrode 60 and the second layer 56 of the first electrode 50 are covered with photoresist. Therefore, the insulating layer 40 and the copper thin film are exposed to the etching solution, while the thermoelectric conversion layer 30 and the first layer 52 are not exposed to the etching solution, allowing the second electrode 60 to be formed.

[0038] In step S80, for example, a protective layer 70 is formed from photosensitive polyimide. Specifically, photosensitive polyimide is applied, and the applied photosensitive polyimide is exposed to light and developed. Then, the developed photosensitive polyimide is fired to form the protective layer 70. Through this process, the thermoelectric conversion element 100 can be manufactured.

[0039] As described above, in the thermoelectric conversion element 100 of Embodiment 1, the first layer 52 of the first electrode 50 can be formed by etching without damaging the thermoelectric conversion layer 30 and the first layer 52 of the first electrode 50, and the second layer 56 of the first electrode 50 and the second electrode 60 can be formed without damaging the thermoelectric conversion layer 30, the first layer 52, the second layer 56, and the second electrode 60. Therefore, the thermoelectric conversion element 100 can be easily miniaturized by photolithography and etching. Furthermore, by miniaturizing the comb-shaped first electrode 50 (first layer 52) and the second electrode 60, the distance between the first electrode 50 and the second electrode 60 can be narrowed, and the perimeter length of the first electrode 50 and the second electrode 60 can be increased, thereby increasing the short-circuit current of the thermoelectric conversion element 100.

[0040] The characteristics of the thermoelectric element 100 are largely determined by the work functions of the first electrode 50 and the second electrode 60. In other words, the selection of materials for forming the first layer 52 of the first electrode 50 and the second layer 56 of the first electrode 50 and the second electrode 60, based on the work function, greatly influences the characteristics of the thermoelectric element 100. On the other hand, in conventional thermoelectric elements (for example, the thermoelectric element described in Japanese Patent Publication No. 6513476), when manufacturing the thermoelectric element by photolithography and etching, the materials for forming the electrodes must be selected considering not only the work function but also the galvanic effect during etching. In Embodiment 1, when forming the first layer 52 of the first electrode 50 and the second layer 56 and second electrode 60 of the first electrode 50, only one of the materials (titanium or copper) forming each is exposed and etched. Therefore, the material forming the first layer 52 of the first electrode 50 and the material forming the second layer 56 and second electrode 60 of the first electrode 50 can be selected based on the work function without considering the galvanic effect during etching. In other words, the degree of freedom in selecting the material forming the first layer 52 of the first electrode 50 and the material forming the second layer 56 and second electrode of the first electrode 50 is increased, and the characteristics of the thermoelectric conversion element 100 can be easily improved.

[0041] In Embodiment 1, the first layer 52 of the first electrode 50 was described as being made of titanium, and the second layer 56 and second electrode 60 of the first electrode 50 were made of copper. However, the thermoelectric conversion element 100 can be manufactured using the same procedure even if the materials are swapped, with copper used for the first layer 52 of the first electrode 50 and titanium used for the second layer 56 and second electrode 60 of the first electrode 50.

[0042] <Embodiment 2> The thermoelectric element 100 may include a first electrode 50 that does not include the second layer 56. In other words, the entire first electrode 50 of the thermoelectric element 100 may be formed by using the material of the first layer 52.

[0043] In Embodiment 2, the thermoelectric conversion element 100 comprises a substrate 10, a base layer 20, a thermoelectric conversion layer 30, an insulating layer 40, a first electrode 50, a second electrode 60, and a protective layer 70, as shown in Figures 18 and 19. In this configuration, elements other than the first electrode 50 may be the same as those in Embodiment 1. In Figure 18, the +X, +Y, and +Z directions are set in the same way as in Figure 1 of Embodiment 1.

[0044] In Embodiment 2, the first electrode 50, which does not include the second layer 56, is connected to the first main surface 32 of the thermoelectric conversion layer 30 via the first contact hole 42 of the insulating layer 40. The first electrode 50 covers the opening of the first contact hole 42 such that the thermoelectric conversion layer 30 exposed from the insulating layer 40 at the bottom of the first contact hole 42 is not exposed from the first electrode 50.

[0045] In Embodiment 2, the first electrode 50 shown in Figure 18 has a first base portion 50a extending in the Y direction and a plurality of first comb-tooth portions 50b extending from the first base portion 50a in the +X direction, and is formed in a comb-like shape. The first comb-tooth portions 50b and the second comb-tooth portions 60b of the second electrode 60 are arranged alternately opposite each other on the first main surface 32 of the thermoelectric conversion layer 30. The entire first electrode 50 is formed from, for example, titanium (Ti) having a small work function, similar to the first layer 52 in Embodiment 1.

[0046] In Embodiment 2, the insulating layer 40 covers the thermoelectric conversion layer 30, and the first electrode 50 formed on the insulating layer 40 is connected via the first contact hole 42 of the insulating layer 40. Therefore, when the first electrode 50 is formed by etching, the thermoelectric conversion layer 30 is not exposed from the insulating layer 40 and is not exposed to the etching solution. As a result, a battery consisting of the first electrode 50, the etching solution, and the thermoelectric conversion layer 30 is not formed. Consequently, in the thermoelectric conversion element 100, the first electrode 50 can be formed by etching without causing damage to the first electrode 50 and the thermoelectric conversion layer 30 due to battery action (e.g., excessive dissolution).

[0047] In Embodiment 2, when the second electrode 60 is formed by etching, the first electrode 50 is covered so as not to be exposed to the photoresist, and the first electrode 50 is not exposed to the etching solution. As a result, a battery formed by the second electrode 60, the etching solution, and the first electrode 50 is not formed. Consequently, in the thermoelectric conversion element 100, the second electrode 60 can be formed by etching without causing damage to the first electrode 50 and the second electrode 60 due to battery action. For example, the second electrode 60 is formed from copper (Cu) which has a large work function.

[0048] In Embodiment 2, the thermoelectric element 100 includes a first electrode 50 and a second electrode 60 connected to the first main surface of the thermoelectric layer 30. The first electrode 50 and the second electrode 60 are formed from materials with different work functions. The thermoelectric element 100 generates a thermoelectric voltage due to the temperature difference in the thickness direction (Z direction) of the thermoelectric layer 30. In the thermoelectric element 100, forming the first electrode 50 by etching does not damage the thermoelectric layer 30 and the first electrode 50, and forming the second electrode 60 by etching does not damage the thermoelectric layer 30, the first electrode 50, and the second electrode 60. Therefore, the thermoelectric element 100 can be easily miniaturized by photolithography and etching.

[0049] Next, the method for manufacturing the thermoelectric element 100 in Embodiment 2 will be described with reference to Figures 20 to 25. Figure 20 is a flowchart showing the method for manufacturing the thermoelectric element 100 in Embodiment 2. In Embodiment 2, steps S10 to S40, S60, and S80 may be the same as in Embodiment 1.

[0050] The manufacturing method shown in Figure 20 includes, following step S40, a step (step S50A) in which a first electrode 50 is formed on the insulating layer 40 and connected to the first main surface 32 of the thermoelectric conversion layer 30 via a first contact hole 42. The step S50A includes a procedure for depositing a titanium thin film, similar to the step S50 in Embodiment 1. In the step S50A, when etching the titanium thin film, different areas are covered with photoresist compared to the step S50 in Embodiment 1. Figure 21 shows the first electrode 50 covered with photoresist in step S50A. Figures 22 and 23 show the first electrode 50 formed on the insulating layer 40 in step S50A. The first electrode 50 is connected to the first main surface 32 of the thermoelectric conversion layer 30 via a first contact hole 42. Furthermore, the first electrode 50 covers the opening of the first contact hole 42 in such a way that the thermoelectric conversion layer 30, which is exposed from the insulating layer 40 at the bottom of the first contact hole 42, is not exposed from the first electrode 50.

[0051] The manufacturing method shown in Figure 20 includes, following step S60, a step (step S70A) of forming a second electrode 60 on the insulating layer 40, which is connected to the first main surface 32 of the thermoelectric conversion layer 30 via a second contact hole 44. To form the second electrode 60, a material having a different work function from the material used to form the first electrode 50 is used. Step S70A includes a procedure for depositing a copper thin film on the insulating layer 40 by sputtering to fill the second contact hole 44. In this procedure, the first electrode 50 is covered with photoresist in a way that prevents exposure before the copper thin film is deposited. Figure 24 shows the first electrode 50 covered with photoresist. The photoresist covering the first electrode 50 may be residual photoresist used to form the second contact hole 44, or it may be newly arranged in accordance with the formation of the second electrode 60. Following the deposition of the copper thin film, the area that will become the second electrode 60 is covered with photoresist, as shown in Figure 25. Subsequently, the second electrode 60 is formed in a comb-like shape from the copper thin film by etching as shown in Figure 26. For example, a mixture containing phosphoric acid, nitric acid, and acetic acid can be used as the etching solution. In this case, since the first electrode 50 is covered with photoresist, there is no need to consider the etching selectivity with respect to the second electrode 60. The thermoelectric conversion layer 30 is covered with the insulating layer 40, the first electrode 50, and the second electrode 60, and the areas that will become the first electrode 50 and the second electrode 60 are covered with photoresist, so the insulating layer 40 and the copper thin film are exposed to the etching solution, while the thermoelectric conversion layer 30 and the first electrode 50 are not exposed to the etching solution, allowing the second electrode 60 to be formed. Figure 27 shows the first electrode 50 and the second electrode 60 formed on the insulating layer 40.

[0052] In Embodiment 2, the thermoelectric conversion element 100 allows for the formation of the first electrode 50 without causing etching damage to the thermoelectric conversion layer 30 and the first electrode 50. In addition, the thermoelectric conversion element 100 allows for the formation of the second electrode 60 without causing etching damage to the thermoelectric conversion layer 30, the first electrode 50, and the second electrode 60. Therefore, the thermoelectric conversion element 100 can be easily miniaturized by photolithography and etching. Furthermore, by miniaturizing the comb-shaped first electrode 50 and the second electrode 60, the distance between the first electrode 50 and the second electrode 60 can be narrowed, and the perimeter length between the first electrode 50 and the second electrode 60 can be increased, thereby increasing the short-circuit current of the thermoelectric conversion element 100.

[0053] In Embodiment 2, when forming the first electrode 50 and the second electrode 60, only one of the materials (titanium or copper) forming each electrode is exposed and etched. Therefore, the material forming the first electrode 50 and the material forming the second electrode can be selected based on the work function without considering the galvanic effect during etching. In other words, the degree of freedom in selecting the material forming the first electrode 50 and the material forming the second electrode 60 is increased, making it easy to improve the characteristics of the thermoelectric conversion element 100.

[0054] In Embodiment 2, titanium was used as the material for the first electrode 50 and copper as the material for the second electrode 60. However, the thermoelectric conversion element 100 can be manufactured using the same procedure even if the materials are swapped, with copper used for the first electrode 50 and titanium for the second electrode.

[0055] The first electrode 50 and the second electrode 60 may be formed by selective etching. If a combination of electrode materials and an etchant can be selected that ensures a sufficient selectivity ratio with respect to the material of the first electrode 50 during etching of the second electrode 60, the thermoelectric conversion element 100 with the structure shown in Figures 18 and 19 can be manufactured without using the photoresist shown in Figure 24. As a first example, when the first electrode 50 made of titanium is formed, dry etching may be performed using a mixed gas containing boron trichloride (BCl3) and chlorine (Cl2). Subsequently, when the second electrode 60 made of copper is formed, wet etching may be performed using a mixed solution containing sulfuric acid and hydrogen peroxide. To form the second electrode 60, wet etching may be performed using a mixed solution containing phosphoric acid, nitric acid, and acetic acid. As a second example, when the first electrode 50 made of copper is formed, wet etching may be performed using a mixed solution containing sulfuric acid (H2SO4) and hydrogen peroxide (H2O2). Subsequently, when the second electrode 60 made of titanium is formed, wet etching may be performed using an aqueous solution of acidic ammonium fluoride. In this example, silicon oxide (SiO₂) is used as the insulating layer 40. x Instead of ), silicon nitride (SiN) may be used as the material.

[0056] The thermoelectric conversion element 100 may include the first electrode 50 in Embodiment 1 so that the work function of the material differs between a part of the first electrode 50 and the second electrode 60. Alternatively, the thermoelectric conversion element 100 may include the first electrode 50 in Embodiment 2 so that the work function of the material differs between the entire first electrode 50 and the second electrode 60. Therefore, the thermoelectric conversion element 100 includes the first electrode 50, at least partially formed using a material having a work function different from that of the material forming the second electrode 60.

[0057] <Variation> While embodiments have been described above, this disclosure can be modified in various ways without departing from its essence.

[0058] For example, the substrate 10 is not limited to a glass substrate. The substrate 10 may be formed from an insulating film (for example, a polyimide film).

[0059] Furthermore, although the thermoelectric conversion element 100 in this embodiment includes a base layer 20, the thermoelectric conversion element 100 does not necessarily have to include a base layer 20. The thermoelectric conversion layer 30 may be formed directly on the first main surface 12 of the substrate 10. Moreover, the thermoelectric conversion element 100 does not necessarily have to include a protective layer 70.

[0060] In Embodiment 1, the first layer 52 of the first electrode 50 is formed from a material having a small work function, and the second layer 56 and the second electrode 60 of the first electrode 50 are formed from materials having a large work function. In the thermoelectric conversion element 100, it is sufficient that the work function of the material forming the first layer 52 of the first electrode 50 and the work function of the material forming the second layer 56 and the second electrode 60 of the first electrode 50 are different. In Embodiment 2, in the thermoelectric conversion element 100, it is sufficient that the work function of the material forming the entire first electrode and the work function of the material forming the second electrode 60 are different.

[0061] In Embodiment 1, the material forming the first layer 52 of the first electrode 50, the second layer 56 of the first electrode 50, and the second electrode 60 may be a material with a small work function such as cesium (Cs) or aluminum (Al), or a material with a large work function such as nickel (Ni). The same applies to the material forming the first electrode 50 and the second electrode 60 in Embodiment 2.

[0062] The surfaces of the protective layer 70 of the first electrode 50 (second layer 56) and the second electrode 60 that are exposed from the terminal opening 75 may be coated with protective plating.

[0063] While preferred embodiments have been described above, this disclosure is not limited to any particular embodiment, and includes the invention described in the claims and its equivalents. [Explanation of symbols]

[0064] 10 Substrate, 12 First main surface, 20 Underlayer, 30 Thermoelectric conversion layer, 32 First main surface, 40 Insulating layer, 42 First contact hole, 44 Second contact hole, 50 First electrode, 50a First base, 50b First comb teeth, 52 First layer, 52a First base, 52b First comb teeth, 56 Second layer, 60 Second electrode, 60a Second base, 60b Second comb teeth, 70 Protective layer, 75 Terminal opening, 100 Thermoelectric conversion element

Claims

1. circuit board and A thermoelectric conversion layer formed on the main surface of the substrate, An insulating layer covering the thermoelectric conversion layer, A first electrode is formed on the insulating layer and connected to the main surface of the thermoelectric conversion layer via a first contact hole in the insulating layer, The thermoelectric conversion layer comprises a second electrode formed on the insulating layer and connected to the main surface of the thermoelectric conversion layer via a second contact hole in the insulating layer, The first electrode has a first layer and a second layer, The first layer is connected to the main surface of the thermoelectric conversion layer, The second layer covers the first layer in such a way that the first layer is not exposed from the second layer. The second layer and the second electrode are formed from the same material, having a work function different from that of the material forming the first layer. Thermoelectric conversion element.

2. The first layer covers the opening of the first contact hole in such a way that the thermoelectric conversion layer is not exposed from the insulating layer. The second electrode covers the opening of the second contact hole in such a way that the thermoelectric conversion layer is not exposed from the insulating layer. The thermoelectric conversion element according to claim 1.

3. The first layer has a first base and a plurality of first comb teeth extending from the first base. The second electrode has a second base and a plurality of second comb teeth extending from the second base. The first comb-tooth portion and the second comb-tooth portion are arranged alternately and opposite to each other on the main surface of the thermoelectric conversion layer. The thermoelectric conversion element according to claim 1.

4. A process of forming a thermoelectric conversion layer on a substrate, The steps include forming an insulating layer on the thermoelectric conversion layer, The process of forming a first contact hole in the insulating layer that exposes the main surface of the thermoelectric conversion layer, A step of forming a first electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the first contact hole, by photolithography and etching, A step of forming a second contact hole in the insulating layer on which the first electrode is formed, which exposes the main surface of the thermoelectric conversion layer, The process includes forming a second electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the second contact hole, by photolithography and etching from a material having a work function different from that of the material forming at least a portion of the first electrode. A method for manufacturing a thermoelectric conversion element.

5. A step of forming a thermoelectric conversion layer on a substrate, The steps include forming an insulating layer on the thermoelectric conversion layer, The process of forming a first contact hole in the insulating layer that exposes the main surface of the thermoelectric conversion layer, A step of forming a first layer of the first electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the first contact hole, by photolithography and etching, A step of forming a second contact hole in the insulating layer on which the first layer of the first electrode is formed, which exposes the main surface of the thermoelectric conversion layer, The process includes forming a second electrode on the insulating layer, which is connected to the main surface of the thermoelectric conversion layer via the second contact hole, by photolithography and etching from a material having a work function different from that of the material forming the first layer of the first electrode, The step of forming the second electrode involves forming the second electrode and forming the second layer such that the first layer of the first electrode is not exposed from the second layer of the first electrode. The aforementioned second electrode uses the same material as the material forming the aforementioned second layer. A method for manufacturing a thermoelectric conversion element.

6. The process of forming the two adjacent electrodes is as follows: A step of forming a first insulating layer such that the area corresponding to the first electrode is covered and the second contact hole is exposed, A step of forming a specific material layer on the first insulating layer and the second contact hole, the material having a work function different from that of the material forming the first electrode, The process includes forming a second insulating layer on the specified material layer such that it covers an area corresponding to the second electrode, A method for manufacturing a thermoelectric element according to claim 4.

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