Optical Sensor

Abstract

This optical sensor comprises a support body and a thermoelectric conversion material part comprising a first material layer, second material layer, and third material layer. The first material layer comprises a first area comprising a first end part and a second area comprising a second end part. The second material layer comprises a third area comprising a third end part and a fourth area comprising a fourth end part. Because the first area and third area are electrically connected and the second area and fourth area are electrically connected, the first material layer and second material layer are connected alternatingly in series. The third material layer is disposed between the first area and third area so as to be in contact with the first area and third area and between the second area and fourth area so as to be in contact with the second area and fourth area. The first area provided in the first material layer, which is the first in the series connection, is electrically connected to a first electrode, and the third area provided in the second material layer, which is the last in the series connection, is electrically connected to a second electrode.

Description

[Technical field]

[0001] The present disclosure relates to an optical sensor. This application claims priority to Japanese Application No. 2021-044964 filed on March 18, 2021, and incorporates by reference all of the contents of said Japanese application. [Background technology]

[0002] There is known a thermopile in which two types of materials forming a thermocouple are joined alternately in series, and a wire bonding pad electrode made of a material different from the thermocouple is connected so as to overlap the thermocouple material (see, for example, Patent Document 1). According to Patent Document 1, an intermediate layer made of a conductive material different from the materials of the thermocouple material and the wire bonding pad electrode is interposed between the thermocouple material and the wire bonding pad electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 9-92892 Summary of the Invention

[0004] The optical sensor according to the present disclosure includes a support, a plurality of elongated first material layers made of SiGe having a first conductivity type and configured to convert thermal energy into electrical energy, a plurality of elongated second material layers made of SiGe having a second conductivity type different from the first conductivity type and configured to convert thermal energy into electrical energy, and a third material layer including a metal, and includes a thermoelectric conversion material portion disposed on one main surface of the support, a heat sink disposed on the other main surface of the support, a light absorbing film disposed to form a temperature difference in the longitudinal direction of the first material layer as viewed in the thickness direction of the support and configured to convert received light into thermal energy, a first electrode, and a second electrode disposed apart from the first electrode. Each of the first material layers includes a first region disposed in contact with one main surface of the support and including a first end, and a second region including a second end located opposite the first end in the longitudinal direction. Each of the second material layers includes a third region including a third end and a fourth region including a fourth end located on the opposite side of the third end in the longitudinal direction. The first region and the third region are electrically connected, and the second region and the fourth region are electrically connected, so that the first material layers and the second material layers are alternately connected in series. The third material layer is disposed between the first region and the third region in contact with the first region and the third region, and is disposed between the second region and the fourth region in contact with the second region and the fourth region. The first region provided in the first first material layer connected in series is electrically connected to the first electrode, and the third region provided in the last second material layer connected in series is electrically connected to the second electrode. [Brief description of the drawings]

[0005] [Figure 1] FIG. 1 is a schematic plan view of the appearance of an optical sensor in accordance with the first embodiment. [Diagram 2] FIG. 2 is a schematic plan view of the appearance of the optical sensor in the first embodiment. [Diagram 3] FIG. 3 is a schematic cross-sectional view taken along line III-III in FIGS. [Figure 4]FIG. 4 is a schematic cross-sectional view showing a part of the optical sensor in the first embodiment. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing an enlarged portion of the optical sensor shown in FIG. [Figure 6] FIG. 6 is an EDX diagram of a portion of the cross section of the photosensor shown in FIG. [Figure 7] FIG. 7 is a graph showing the relationship between the elements and the distances measured by EDX in FIG. [Figure 8] FIG. 8 is a graph showing the relationship between the contact resistivity in a portion where the first material layer and the second material layer are electrically connected and the thickness of the third material layer. [Figure 9] FIG. 9 is a graph showing the relationship between the sensitivity D* of the optical sensor and the thickness of the third material layer. [Figure 10] FIG. 10 is a graph showing the relationship between the contact resistivity in the portion where the first material layer and the second material layer are electrically connected and various metals contained in the third material layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0006] [Problem that this disclosure aims to solve] In optical sensors such as thermopile-type infrared sensors, noise reduction is required in order to improve the sensitivity of the sensors. It is difficult to meet such a demand with the technology disclosed in Patent Document 1.

[0007] Therefore, it is an object of the present invention to provide an optical sensor capable of reducing noise. [Effects of this disclosure]

[0008] The optical sensor described above can reduce noise.

[0009] [Description of the embodiments of the present disclosure] First, the embodiments of the present disclosure will be described. The optical sensor according to the present disclosure includes a support, a plurality of elongated (strip-shaped) first material layers made of SiGe having a first conductivity type and configured to convert thermal energy into electrical energy, a plurality of elongated (strip-shaped) second material layers made of SiGe having a second conductivity type different from the first conductivity type and configured to convert thermal energy into electrical energy, and a third material layer including a metal, and includes a thermoelectric conversion material part arranged on one main surface of the support, a heat sink arranged on the other main surface of the support, a light absorbing film arranged to form a temperature difference in the longitudinal direction of the first material layer as viewed in the thickness direction of the support and configured to convert received light into thermal energy, a first electrode, and a second electrode arranged separately from the first electrode. Each of the first material layers includes a first region arranged in contact with one main surface of the support and including a first end, and a second region including a second end located on the opposite side of the first end in the longitudinal direction. Each of the second material layers includes a third region including a third end and a fourth region including a fourth end located on the opposite side of the third end in the longitudinal direction. The first region and the third region are electrically connected, and the second region and the fourth region are electrically connected, so that the first material layers and the second material layers are alternately connected in series. The third material layer is disposed between the first region and the third region in contact with the first region and the third region, and is disposed between the second region and the fourth region in contact with the second region and the fourth region. The first region provided in the first first material layer connected in series is electrically connected to the first electrode, and the third region provided in the last second material layer connected in series is electrically connected to the second electrode.

[0010] A thermopile-type optical sensor using a thermoelectric conversion material that converts a temperature difference (thermal energy) into electrical energy, such as an infrared sensor, may have a light receiving section such as a light absorbing film that converts light energy into thermal energy, and a thermoelectric conversion material section (thermopile) that converts a temperature difference into electrical energy. In the thermoelectric conversion material section, a thermocouple formed by connecting a p-type thermoelectric conversion material section and an n-type thermoelectric conversion material section is used. The output is increased by alternately connecting multiple p-type thermoelectric conversion material sections and multiple n-type thermoelectric conversion material sections in series. The resistance in the optical sensor is expressed by the following formula 1.

[0011]

number

[0012] R is resistance, Rp is the resistance per pair of p-type thermoelectric conversion material sections, Rn is the resistance per pair of n-type thermoelectric conversion material sections, N is the number of pairs, and ρc is the contact resistance, i.e., the resistance of the part where the p-type thermoelectric conversion material section and the n-type thermoelectric conversion material section are electrically connected. As can be seen from this formula, if the contact resistance ρc can be reduced, the resistance in the optical sensor can be reduced. Moreover, the noise in the optical sensor is expressed by the following formula 2.

[0013]

number

[0014] Vn is Johnson noise (V), k is Boltzmann's constant (J / K), T is temperature (K), R is resistance (Ω), and Δf is bandwidth (Hz=1 / s). As can be seen from this formula, Johnson noise depends on the resistance, and if the resistance can be reduced, the noise in the optical sensor can be reduced.

[0015] The present inventors have conducted extensive research to reduce the resistance at the contact portion between the first material layer and the second material layer, both of which are thermoelectric conversion materials. They have found that when the second material layer is formed after the first material layer is formed, the natural oxide film formed on the surface of the first material layer inhibits carrier transport and increases resistance. The present inventors have focused on the idea that the increase in resistance in the oxide film can be suppressed to improve conductivity, and have come up with the configuration of the present disclosure.

[0016] The optical sensor of the present disclosure further includes a third material layer including a metal. The third material layer is disposed between the first region and the third region in contact with the first region and the third region, and is disposed between the second region and the fourth region in contact with the second region and the fourth region. This can reduce the resistance of the portion where the first material layer and the second material layer are electrically connected. Therefore, the noise of the optical sensor can be reduced.

[0017] In the optical sensor, the metal may be a transition metal. The SiGe may have at least one of a nanocrystalline structure and an amorphous structure. By using such a metal and SiGe constituting the first material layer and the second material layer, it is possible to more reliably reduce noise in the optical sensor.

[0018] In the optical sensor, the SiGe may be polycrystalline. Such polycrystalline SiGe is also suitably used in the optical sensor of the present disclosure. The crystallization rate of the polycrystalline body of the present disclosure is 99% or more.

[0019] In the optical sensor, the melting point of the metal may be equal to or higher than 1455° C. Such a metal is thermally stable and is suitable as a material contained in the optical sensor.

[0020] In the above optical sensor, the metal may be any of Ni (nickel), W (tungsten), Mo (molybdenum), Ti (titanium), Au (gold), Pd (palladium), Ge (germanium), Hf (hafnium), Al (aluminum), and alloys of combinations thereof. By using such an element as the metal, the resistance of the portion where the first material layer and the second material layer are electrically connected can be more reliably reduced. Therefore, noise can be more reliably reduced.

[0021] In the optical sensor, the metal may be any one of Ni, W, Mo, Ti, and an alloy made of a combination thereof, thereby making it possible to further reduce noise.

[0022] In the above optical sensor, the third material layer may include an oxide film containing 10 at % or more of metal. This makes it possible to more reliably reduce the resistance of the portion where the first material layer and the second material layer are electrically connected. Therefore, it is possible to reduce noise in the optical sensor.

[0023] In the optical sensor, the third material layer may have a thickness of 3 nm to 200 nm, which can reduce the resistance of the portion where the first material layer and the second material layer are electrically connected, while suppressing a reduction in the electromotive force in the thermoelectric conversion material portion.

[0024] [Details of the embodiment of the present disclosure] Next, an embodiment of an optical sensor according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference characters and the description thereof will not be repeated.

[0025] (Embodiment 1) An optical sensor according to a first embodiment of the present disclosure will be described. FIGS. 1 and 2 are schematic plan views of the exterior of the optical sensor in the first embodiment. In order to facilitate understanding, an infrared absorbing film and an insulating film, which will be described later, are omitted in FIG. 1. In FIG. 1, the outer edge of the infrared absorbing film when it is arranged is indicated by a broken line. FIG. 3 is a schematic cross-sectional view showing a cross section along line III-III in FIGS. 1 and 2. FIG. 4 is a schematic cross-sectional view showing a part of the optical sensor in the first embodiment. FIG. 4 is a schematic cross-sectional view showing an enlarged view of a part including a first region, a second region, a third region, and a fourth region, which will be described later. FIG. 5 is a schematic cross-sectional view showing an enlarged view of a part of the optical sensor shown in FIG. 4.

[0026] 1, 2, 3, 4, and 5, the optical sensor 11a is, for example, an infrared sensor. The optical sensor 11a includes a support 13, a thermoelectric conversion material part 12 arranged on one main surface 13b of the support 13, a heat sink 14, an infrared absorbing film 23 as a light absorbing film, a first electrode 24, and a second electrode 25. The thermoelectric conversion material part 12 includes a plurality of first material layers 21 including first material layers 21a, 21b, 21c, and 21d, and a plurality of second material layers 22 including second material layers 22a, 22b, 22c, and 22d. The optical sensor 11a detects the potential difference generated between the first electrode 24 and the second electrode 25 to detect infrared rays irradiated to the optical sensor 11a. If the optical sensor 11a is entirely plate-shaped, the thickness direction of the optical sensor 11a is represented by the Z direction.

[0027] The support 13 is in the form of a thin film and has a rectangular shape when viewed in the thickness direction (Z direction). The support 13 supports the thermoelectric conversion material part 12 including a plurality of first material layers 21 and a plurality of second material layers 22, the infrared absorbing film 23, the first electrode 24, and the second electrode 25. The support 13 is formed of, for example, a SiO2 / SiN / SiO2 film. That is, the support 13 is configured by laminating SiO2, SiN, and SiO2.

[0028] The outer edge 14c, which is the outer edge of the entire heat sink 14, and the outer edge 13c of the support 13 extend in a continuous manner in the Z direction. The heat sink 14 includes one surface 14a and the other surface 14b that are spaced apart in the thickness direction of the optical sensor 11a. The heat sink 14 is disposed on the other main surface 13a of the support 13. Specifically, the heat sink 14 is disposed so that the one surface 14a of the heat sink 14 and the other main surface 13a of the support 13 abut against each other. The other surface 14b of the heat sink 14 is exposed. In this embodiment, the shape of the heat sink 14 is a rectangular loop. The heat sink 14 appears as two trapezoidal shapes in the cross section shown in FIG. 3. The heat sink 14 is sufficiently thick compared to the support 13. For example, the thickness of the heat sink 14 is 10 times or more the thickness of the support 13. In this embodiment, the heat sink 14 is a so-called substrate. The heat sink 14 is made of, for example, Si.

[0029] The optical sensor 11a is formed with a recess 16 recessed in the thickness direction. In a region corresponding to the recess 16 as viewed from the surface 14b side, the support 13, specifically the other main surface 13a of the support 13, is exposed. The inner peripheral surface 14d of the heat sink 14 surrounding the recess 16 is so-called tapered in that the opening side located on the surface 14b side is wider. The recess 16 is formed, for example, by anisotropic wet etching of a flat substrate. By forming such a recess 16, it is possible to suppress the escape of heat from the infrared absorbing film 23 to the heat sink 14. Therefore, it is possible to further increase the temperature difference in the longitudinal direction of the first material layer 21 and the second material layer 22 described later.

[0030] In Fig. 1, inner edges 16a, 16b, 16c, and 16d of the heat sink 14, which are boundaries between the heat sink 14 and the support 13, are indicated by dashed lines in Fig. 1. As shown in Fig. 1, in this embodiment, the inner edges 16a, 16b, 16c, and 16d of the heat sink 14 have a square shape when viewed in the thickness direction of the support 13.

[0031] The first material layer 21 is made of SiGe having a first conductivity type, that is, n-type. That is, the first material layer 21 is made of an n-type thermoelectric conversion material, and is made of a compound semiconductor containing Si (silicon) and Ge as constituent elements.

[0032] The first material layer 21 has an elongated shape. The first material layer 21 includes a first region 28a including a first end 28c, and a second region 28b including a second end 28d located on the opposite side of the first end 28c in the longitudinal direction. The direction in which a line connecting the first region 28a and the second region 28b extends is the longitudinal direction of the elongated first material layer 21. The first material layer 21 converts the temperature difference between the first region 28a and the second region 28b into electrical energy. The first material layer 21 is disposed on one main surface 13b of the support 13. The first material layer 21 is disposed in contact with one main surface 13b of the support 13. The first material layer 21 is positioned such that, when viewed in the thickness direction of the support 13, the first region 28a is located closer to the inner edges 16a, 16b, 16c, 16d of the heat sink 14, and the second region 28b is located closer to the outer edges 23a, 23b, 23c, 23d of the infrared absorbing film 23.

[0033] The second material layer 22 is made of SiGe having a p-type conductivity type different from the first conductivity type. That is, the second material layer 22 is made of a p-type thermoelectric conversion material, and is made of a compound semiconductor containing Si and Ge as constituent elements.

[0034] The second material layer 22 has an elongated shape. The second material layer 22 includes a third region 29a including a third end 29c, and a fourth region 29b including a fourth end 29d located on the opposite side of the third end 29c in the longitudinal direction. The direction in which a line connecting the third region 29a and the fourth region 29b extends is the longitudinal direction of the elongated second material layer 22. The second material layer 22 converts the temperature difference between the third region 29a and the fourth region 29b into electrical energy. In this embodiment, the second material layer 22 is disposed on a part of the insulating film 26 described later that is disposed in contact with the support 13, and on a part of the first material layer 21. The second material layer 22 is positioned such that, when viewed in the thickness direction of the support 13, the third region 29a is located closer to the inner edges 16a, 16b, 16c, 16d of the heat sink 14, and the fourth region 29b is located closer to the outer edges 23a, 23b, 23c, 23d of the infrared absorbing film 23.

[0035] The multiple first material layers 21 and the multiple second material layers 22 are arranged on the support 13 so as to fit within an area 15 shown in the shape of a rectangular shape indicated by a two-dot chain line in FIG. 1. The thermoelectric conversion material section 12 converts a temperature difference (thermal energy) into electric energy by the multiple first material layers 21 and the multiple second material layers 22. The thermoelectric conversion material section 12 includes an insulating film 26. As a material for the insulating film 26, for example, SiO2 is selected. The arrangement of the multiple first material layers 21 and the multiple second material layers 22 will be described in detail later.

[0036] The infrared absorbing film 23 is disposed on one main surface 13b of the support 13, on a part of the first material layer 21, on a part of the second material layer 22, and on a part of the insulating film 26. The infrared absorbing film 23 is disposed so as to form a temperature difference in the longitudinal direction of the first material layer 21, that is, between the first region 28a and the second region 28b. Specifically, the infrared absorbing film 23 is disposed so as to expose the first region 28a of the first material layer 21 and the third region 29a of the second material layer 22, and to cover the second region 28b of the first material layer 21 and the fourth region 29b of the second material layer 22. In this embodiment, the infrared absorbing film 23 is disposed so as to form a temperature difference in the longitudinal direction of the second material layer 22, that is, between the third region 29a and the fourth region 29b. The infrared absorbing film 23 is disposed in a region surrounded by the inner edges 16a, 16b, 16c, and 16d of the heat sink 14 when viewed in the thickness direction of the support 13. In this embodiment, the infrared absorbing film 23 having outer edges 23a, 23b, 23c, and 23d has a square shape when viewed in the thickness direction of the support 13. The infrared absorbing film 23 is disposed such that the center of the square shape formed by the outer edges 23a, 23b, 23c, and 23d of the infrared absorbing film 23 overlaps with the center of the square shape formed by the inner edges 16a, 16b, 16c, and 16d of the heat sink 14 when viewed in the thickness direction of the support 13. The infrared absorbing film 23 converts infrared rays into heat. For example, carbon (C) is selected as the material of the infrared absorbing film 23.

[0037] Next, the arrangement of the thermoelectric conversion material part 12 and the infrared absorbing film 23 will be described. Specifically, the insulating film 26 is arranged on the first material layer 21 in the portion where the first material layer 21 is arranged, and is arranged on one main surface 13b of the support 13 in the portion where the first material layer 21 is not arranged. The insulating film 26 is arranged so as not to cover the first region 28a and the second region 28b of the first material layer 21. The second material layer 22 is arranged on a part of the one main surface 13b of the support 13, on a part of the insulating film 26, and on a part of the first material layer 21. The second material layer 22 is arranged so that the first region 28a of the first material layer 21 and the third region 29a of the second material layer 22 are electrically connected via the third material layer 31a, and the second region 28b of the first material layer 21 and the fourth region 29b of the second material layer 22 are electrically connected via the third material layer 31b. In this embodiment, the third region 29a is disposed on the first region 28a, and the fourth region 29b is disposed on the second region 28b.

[0038] The infrared absorbing film 23 is disposed on a portion of one main surface 13b of the support 13, on a portion of the insulating film 26, and on a portion of the second material layer 22. The infrared absorbing film 23 is disposed so as to expose the first region 28a of the first material layer 21 and the third region 29a of the second material layer 22. The infrared absorbing film 23 is disposed so as to cover the second region 28b of the first material layer 21 and the fourth region 29b of the second material layer 22. That is, each connection portion where the second region 28b and the fourth region 29b are connected overlaps with the infrared absorbing film 23 when viewed in the thickness direction of the support 13. The first region 28a of the first material layer 21 and the third region 29a of the second material layer 22 are not covered by the infrared absorbing film 23. That is, the first material layer 21 and the second material layer 22 are thermally connected to the infrared absorbing film 23 so as to form a temperature difference in the longitudinal direction of each of the first material layer 21 and the second material layer 22. The infrared absorbing film 23 is disposed so that heat of the infrared absorbing film 23 is transferred to the second region 28b of the first material layer 21 and the fourth region 29b of the second material layer 22. In this manner, a temperature difference is formed in the longitudinal direction of the first material layer 21 and the second material layer 22. In this way, it is possible to obtain the optical sensor 11a that efficiently utilizes the temperature difference created by the infrared absorbing film 23 and the heat sink 14.

[0039] Next, the arrangement of the multiple first material layers 21 and the multiple second material layers 22 will be described. The multiple first material layers 21 are arranged at intervals from each other. Except for the first material layers 21a, 21b, 21c, and 21d, the multiple first material layers 21 are arranged so that the X direction or the Y direction is the longitudinal direction. Except for the first material layers 21a, 21b, 21c, and 21d, the multiple first material layers 21 are arranged so that they extend from each side of the square-shaped region 15 to the opposite side (so that the longitudinal direction is along that direction). Except for the first region 28a connected to the first electrode 24 and the third region 29a connected to the second electrode 25, the first material layer 21 and the second material layer 22 are alternately electrically connected. Specifically, the first region 28a of the first material layer 21 and the third region 29a of the second material layer 22 adjacent to one side of the first material layer 21 are electrically connected via the third material layer 31a. The second region 28b of the first material layer 21 and the fourth region 29b of the second material layer 22 adjacent to the other side of the first material layer 21 are electrically connected via the third material layer 31b. In the multiple first material layers 21 and the multiple second material layers 22, the second regions 28b and the fourth regions 29b are electrically connected to each other and the first regions 28a and the third regions 29a are electrically connected to each other, except for the first region 28a and the third region 29a connected to the first electrode 24 and the second electrode 25. That is, the first material layer 21 and the second material layer 22 are paired, and the adjacent first material layers 21 and second material layers 22 are electrically connected alternately in series in the regions including the ends.

[0040] The polarity of the voltage generated in the first region 28a including the first end 28c located on one side of the first material layer 21 and the polarity of the voltage generated in the third region 29a including the third end 29c located on one side of the second material layer 22 are opposite to the direction of the temperature gradient generated when the optical sensor 11a is irradiated with light. Here, the first material layers 21 and the second material layers 22 are always connected alternately. Of the first material layers 21 and the second material layers 22 connected alternately in series, the first material layer 21 arranged at the top is electrically connected to the first electrode 24 in the first region 28a. Of the first material layers 21 and the second material layers 22 connected alternately in series, the second material layer 22 arranged at the bottom is electrically connected to the second electrode 25 in the third region 29a. The first electrode 24 and the second electrode 25 are arranged outside the region 15 on one main surface 13b of the support 13. The first electrode 24 and the second electrode 25 are arranged apart from each other. The first electrode 24 and the second electrode 25 are, for example, pad electrodes. The material of the first electrode 24 and the second electrode 25 may be, for example, gold (Au), titanium (Ti), platinum (Pt), or the like.

[0041] Here, the thermoelectric conversion material part 12 includes a third material layer 31a containing a metal. The third material layer 31a is disposed between the first region 28a and the third region 29a in contact with the first region 28a and the third region 29a. In this embodiment, the third material layer 31a is disposed between the first region 28a and the third region 29a in the Z direction. The thermoelectric conversion material part 12 also includes a third material layer 31b containing a metal. The third material layer 31b is disposed between the second region 28b and the fourth region 29b in contact with the second region 28b and the fourth region 29b. In this embodiment, the third material layer 31b is disposed between the second region 28b and the fourth region 29b in the Z direction. In this embodiment, the metal contained in the third material layers 31a and 31b is Ni. In addition, the third material layers 31a and 31b include oxide films containing Ni at 10 at % or more. In this embodiment, the third material layers 31a and 31b include an oxide film containing 10 at % or more of Ni.

[0042] The third material layer 31a has a thickness T1 of not less than 3 nm and not more than 200 nm (see FIG. 5). The thickness T1 of the third material layer 31a is indicated by the length between one surface 32a and the other surface 33a of the third material layer 31a in the Z direction, which is the thickness direction. One surface 32a of the third material layer 31a contacts one surface 34a in the thickness direction of the first material layer 21 located on the second material layer 22 side in the thickness direction. The other surface 33a of the third material layer 31a contacts one surface 35a in the thickness direction of the second material layer 22 located on the first material layer 21 side in the thickness direction. The thickness of the third material layer 31b is also equivalent to the thickness of the third material layer 31a, so a description thereof will be omitted.

[0043] Next, a manufacturing method of the optical sensor 11a in the first embodiment will be briefly described. First, a flat substrate is prepared, and the support 13 is formed on one of the main surfaces in the thickness direction. At this time, the substrate and the other main surface 13a of the support 13 are in contact with each other. Next, the first material layer 21 is formed on one of the main surfaces 13b of the support 13. The specific formation of the first material layer 21 is as follows. First, a lift-off resist is applied in a layer on one of the main surfaces 13b of the support 13. Next, a positive resist is applied in a layer on the lift-off resist. After that, the positive resist is exposed by photolithography and dissolved by a developer. Next, a semiconductor material is evaporated to form a pattern, and the resist is removed from the support 13 (lift-off). In this manner, the above-mentioned first material layer 21 is formed.

[0044] After the first material layer 21 is formed, it is immersed in a 10% by mass buffered hydrofluoric acid (BHF) solution for 1 minute, and then rinsed with water. After the rinse, a natural oxide film with a thickness of about 10 nm to 20 nm is formed on the first material layer 21. Next, a pattern of Ni is formed as an intermediate metal layer, and then Ni is deposited to form an intermediate metal layer. Next, an insulating film 26 made of SiO2 is formed, and a pattern of the second material layer 22 is formed, and then the second material layer 22 is formed by vapor deposition. The formation of each layer, such as the formation of the second material layer 22, is performed in the same procedure as the formation of the first material layer 21, and therefore a description thereof will be omitted.

[0045] After the first material layer 21, the intermediate metal layer, and the second material layer 22 are formed, an activation process is performed by heating at about 550°C. After immersion in BHF, Ni, which is a metal in the intermediate metal layer, is diffused into a natural oxide film with a thickness of about 10 nm to 20 nm formed on the first material layer 21 that has been subjected to a water washing process. In this way, third material layers 31a and 31b containing Ni are formed. That is, in this way, a third material layer 31a is formed between the first region 28a and the third region 29a in contact with the first region 28a and the third region 29a, and a third material layer 31b is formed between the second region 28b and the fourth region 29b in contact with the second region 28b and the fourth region 29b.

[0046] Thereafter, a recess 16 is formed in the central region of the substrate from the other main surface of the substrate located opposite the support 13 in the thickness direction. In this case, the recess 16 is formed so as to recess from the other main surface of the substrate to the other main surface 13a of the support 13. In this manner, the heat sink 14 made of the substrate is formed, and the optical sensor 11a is obtained. Here, the intermediate metal layer may be provided between the first region 28a and the first electrode 24.

[0047] Next, the operation of the optical sensor 11a will be described. When light, for example, infrared light, is irradiated to the optical sensor 11a, the infrared absorbing film 23 converts the light energy into heat energy. In this case, the infrared absorbing film 23 is formed in a region surrounded by the inner edges 16a, 16b, 16c, and 16d of the heat sink 14, and the portion where the infrared absorbing film 23 is arranged is the high temperature side. On the other hand, since the heat sink 14 is arranged outside the inner edges 16a, 16b, 16c, and 16d, the temperature does not rise. Here, when focusing on one first material layer 21, the second region 28b of the first material layer 21 becomes high temperature, and the first region 28a of the first material layer 21 becomes low temperature. That is, in the longitudinal direction of one first material layer 21, a temperature difference is formed between the regions including both ends. This temperature difference forms a potential difference. The second material layer 22 also has a similar elongated shape in the longitudinal direction. Therefore, a temperature difference is formed between the regions including both ends. This temperature difference forms a potential difference. Since the multiple first material layers 21 and the multiple second material layers 22 are connected in series with alternate polarities reversed, the potential difference output by the first electrode 24 and the second electrode 25 is the sum of the potential differences caused by the temperature difference between the multiple first material layers 21 and the multiple second material layers 22. By detecting the current flowing due to the potential difference between the first electrode 24 and the second electrode 25, the optical sensor 11a detects light, in this case, infrared light.

[0048] Here, the optical sensor 11a includes the third material layers 31a and 31b having the above-mentioned configuration. Therefore, the resistance in the optical sensor 11a can be reduced. Therefore, the noise of the optical sensor 11a can be reduced.

[0049] FIG. 6 is a diagram showing EDX of a part of the cross section of the optical sensor 11a shown in FIG. 5. In FIG. 6, the left region 36a shows the concentration of element Ni, and the right region 36b shows the concentration of element O (oxygen). FIG. 7 is a graph showing the relationship between the element and distance measured by EDX in FIG. 6. In FIG. 7, the horizontal axis shows the element concentration (at%), and the vertical axis shows the distance (nm). The distance is the distance from the main surface 13b in the Z direction. The measurement was performed as follows. As an apparatus, JEM-2100F (manufactured by JEOL Ltd.) was used, and the acceleration voltage was 200 kV. The electron probe diameter was 0.2 nm, and the EDX mapping conditions were 256 pixels×256 pixels, 0.5 ms / pixel, and 15 times of accumulation.

[0050] 6 and 7, the concentration of Si decreases as the distance increases, and then drops sharply at 150 nm. On the other hand, the concentration of Ge increases as the distance increases, and then suddenly increases at 150 nm. Here, the concentration of Ni is 10 at% or more at a distance of 120 nm to 180 nm. The concentration of O also increases and peaks at a distance of 120 nm to 180 nm. With reference to FIGS. 6 and 7, it can be seen that a third material layer 31a containing a metal is disposed on one surface 34a of the first material layer 21. The thickness T1 of the third material layer 31a in this embodiment is 60 nm.

[0051] Compared to the contact resistance between the first material layer and the second material layer of an optical sensor that does not include the third material layers 31a, 31b, the reduction rate of resistance at the portion where the first material layer 21 and the second material layer 22 of the optical sensor 11a of the present disclosure are electrically connected is 99%. Also, compared to the resistance of an optical sensor that does not include the third material layers 31a, 31b, the reduction rate of the resistance of the optical sensor 11a of the present disclosure is 38%. Furthermore, compared to the Johnson noise of an optical sensor that does not include the third material layers 31a, 31b, the reduction rate of the Johnson noise of the optical sensor 11a of the present disclosure is 22%.

[0052] 8 is a graph showing the relationship between the resistance at the portion where the first material layer 21 and the second material layer 22 are electrically connected and the thickness of the third material layers 31a, 31b. In Fig. 8, the horizontal axis shows the thickness (nm) of the third material layers 31a, 31b, and the vertical axis shows the contact resistivity (mΩcm) at the portion where the first material layer 21 and the second material layer 22 are electrically connected. 2 ) is shown in Fig. 9. * 9 is a graph showing the relationship between the thickness (nm) of the third material layers 31a and 31b and the sensitivity D * (cm Hz 0.5 / W).

[0053] 8 and 9, the thickness T1 of the third material layers 31a and 31b is set to 3 nm or more and 200 nm or less, thereby suppressing the decrease in electromotive force in the thermoelectric conversion material section 12 while reducing the resistance of the portion where the first material layer 21 and the second material layer 22 are electrically connected. The thickness T1 of the third material layers 31a and 31b is set to 20 nm or more and 120 nm or less, thereby allowing sufficient diffusion of metal into the oxide film, and allowing the resistance to have a more suitable value. Therefore, the sensitivity can be further improved. The thickness T1 of the third material layers 31a and 31b is set to 40 nm or more and 80 nm or less, thereby allowing sufficient diffusion of metal into the oxide film, and allowing the resistance to have a more suitable value. Therefore, the sensitivity can be further improved.

[0054] In the above embodiment, the metal contained in the third material layers 31a and 31b is Ni, but the metal contained in the third material layers 31a and 31b may be a transition metal. In addition, SiGe may have at least one of a nanocrystalline structure and an amorphous structure. By using such a metal and SiGe constituting the first material layer 21 and the second material layer 22, the noise of the optical sensor 11a can be more reliably reduced. In addition, for SiGe, which is a constituent material of the first material layer 21 and the second material layer 22, for example, SiGe having an amorphous structure may be heat-treated at a temperature of about 500° C., for example, to create a nanocrystalline structure in a part of it. In addition, SiGe may have a nanocrystalline structure or an amorphous structure. Here, the nanocrystalline structure is a structure in which SiGe partially has nano-sized crystal grains (nanocrystals). Inside the nanocrystals, atoms are regularly aligned. In addition, SiGe may be polycrystalline. Such polycrystalline SiGe is also suitably used in the optical sensor of the present disclosure. The crystallization rate of the polycrystalline body of the present disclosure is 99% or more. The crystallization rate was measured as follows. The HORIBA LabRam HR-PL was used as the device. The measurement conditions were a laser wavelength of 532 nm and a laser power of 2.5 mW. The analysis conditions were a 400 cm -1 The peaks around were analyzed. In the analysis, a Gaussian function and a pseudo-Voigt function were fitted. The Gaussian function G(x) is expressed by the following formula 3.

[0055]

number

[0056] Moreover, the pseudo-Voigt function F(x) is expressed by the following equation 4.

[0057]

number

[0058] Gaussian function G(x): variable A g , W g , x g In this example, the initial value of x0 is 400 cm -1 The pseudo-Voigt function F(x): variable A f , W f , x f , m, the initial value of x0 is 380 cm -1 and g was set to 0.5. Each parameter was optimized by the least squares method, and the pseudo-Voigt function and Gaussian function were integrated to determine the area. The crystallinity ratio was calculated by the formula: crystallinity ratio = area derived using the pseudo-Voigt function / (area derived using the pseudo-Voigt function + area derived using the Gaussian function), assuming that the area derived using the Gaussian function corresponds to amorphous and the area derived using the pseudo-Voigt function corresponds to crystal.

[0059] The melting point of the metal contained in the third material layers 31a and 31b may be equal to or higher than 1455° C. Such a metal is thermally stable and is suitable as a material contained in the optical sensor 11a.

[0060] 10 is a graph showing the relationship between the contact resistivity in the portion where the first material layer 21 and the second material layer 22 are electrically connected and various metals contained in the third material layer. In FIG. 10, the horizontal axis shows various metals, and the vertical axis shows the contact resistivity (mΩcm) in the portion where the first material layer 21 and the second material layer 22 are electrically connected. 2 ) is shown.

[0061] Referring to FIG. 10, when the third material layer is not included, the contact resistivity is 400 (mΩcm 2 In contrast, when the third material layer is made of Ni, the contact resistivity is 0.6 (mΩcm 2 In the case where the third material layer is made of W, the contact resistivity is 1.0 (mΩcm 2 ) In the case where the third material layer is made of Mo, the contact resistivity is 1.5 (mΩcm 2In the case where the third material layer is made of Ti, the contact resistivity is 2.0 (mΩcm 2 In the case where the third material layer is made of Au, the contact resistivity is 24 (mΩcm 2 In the case where the third material layer is made of Pd, the contact resistivity is 55 (mΩcm 2 In the case where the third material layer is made of Ge, the contact resistivity is 60 (mΩcm 2 In the case where the third material layer is made of Hf, the contact resistivity is 70 (mΩcm 2 In the case where the third material layer is made of Al, the contact resistivity is 200 (mΩcm 2 ).

[0062] The metal contained in the third material layers 31a and 31b is preferably selected from Ni, W, Mo, Ti, Au, Pd, Ge, Hf, Al, and alloys of combinations thereof. Such elements can more reliably reduce the resistance in the portion where the first material layer 21 and the second material layer 22 are electrically connected. Therefore, noise can be more reliably reduced.

[0063] Furthermore, by using any one of Ni, W, Mo, Ti, and alloys made of combinations of these elements as the metal contained in the third material layers 31a and 31b, noise can be further reduced.

[0064] (Other embodiments) In the above embodiment, the first conductivity type is n-type and an n-type thermoelectric conversion material is adopted for the first material layer, and a conductivity type different from the first conductivity type is p-type and a p-type thermoelectric conversion material is adopted for the second material layer. However, this is not limited to the above, and it is also possible to assume that the first conductivity type is p-type and a p-type thermoelectric conversion material is adopted for the first material layer, and a conductivity type different from the first conductivity type is n-type and an n-type thermoelectric conversion material is adopted for the second material layer.

[0065] Moreover, with regard to the oxide film formed on the first material layer 21 after the above-mentioned water washing process, taking into consideration the effect of energy filtering, it is preferable that the thickness is about 0.1 nm to 10 nm, from the viewpoint of increasing the Seebeck coefficient.

[0066] In the above embodiment, the heat sink is in the shape of a rectangular loop, but this is not limited to this. For example, the heat sink may be formed in a lattice shape when viewed in the thickness direction of the support, and a plurality of rectangular supports may be arranged in the areas corresponding to the so-called windows of the lattice-shaped heat sink. Specifically, for example, a configuration may be adopted in which a plurality of rectangular supports, which are thin parts, are arranged at intervals, and the heat sink is arranged in the area between the supports. This also makes it possible to reduce noise. Such a configuration is used, for example, when the optical sensor is used as an array sensor.

[0067] In the above embodiment, the third region is disposed on the first region, and the fourth region is disposed on the second region, but the present invention is not limited to this. The first region and the third region, and the second region and the fourth region may be disposed adjacent to each other when viewed in the thickness direction of the support. That is, a third material layer may be disposed between the first region and the third region, which are disposed adjacent to each other when viewed in the thickness direction of the support, so as to be in contact with each of the first region and the third region, and a third material layer may be disposed between the second region and the fourth region, which are disposed adjacent to each other, so as to be in contact with each of the second region and the fourth region. This can also reduce noise.

[0068] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present disclosure is defined by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0069] 11a optical sensor, 12 thermoelectric conversion material part, 13 support 13a,13b Main surface 13c, 14c, 23a, 23b, 23c, 23d Outer edge 14 Heat sink 14a,14b,32a,33a,34a,35a side 14d Inner surface 15,36a,36b area 16 Recess 16a, 16b, 16c, 16d Inner edge 21,21a,21b,21c,21d 1st material layer 22,22a,22b,22c,22d 2nd material layer 23 infrared absorbing film (light absorbing film), 24 first electrode, 25 second electrode, 26 insulating film, 28a first region, 28b second region, 28c first end, 28d second end, 29a third region, 29b fourth region, 29c third end, 29d fourth end 31a,31b 3rd material layer T1 thickness, D * sensitivity X,Y,Z direction

Claims

1. An optical sensor comprising: A support; a thermoelectric conversion material portion including: a plurality of elongated first material layers made of SiGe having a first conductivity type and configured to convert thermal energy into electrical energy; a plurality of elongated second material layers made of SiGe having a second conductivity type different from the first conductivity type and configured to convert thermal energy into electrical energy; and a third material layer including a metal, the thermoelectric conversion material portion being disposed on one main surface of the support; A heat sink disposed on the other main surface of the support; a light absorbing film arranged to create a temperature difference in a longitudinal direction of the first material layer as viewed in a thickness direction of the support and configured to convert received light into thermal energy; A first electrode and a second electrode disposed apart from the first electrode, Each of the first material layers comprises: is disposed in contact with one major surface of the support; a first region including a first end portion and a second region including a second end portion located on the opposite side of the first end portion in a longitudinal direction; Each of the second material layers comprises: a third region including a third end and a fourth region including a fourth end located on the opposite side of the third end in the longitudinal direction; the first region and the third region are electrically connected, and the second region and the fourth region are electrically connected, whereby the first material layers and the second material layers are alternately connected in series; the third material layer is disposed between the first region and the third region in contact with the first region and the third region, and is disposed between the second region and the fourth region in contact with the second region and the fourth region; the first region provided in the first material layer that is connected in series is electrically connected to the first electrode, and the third region provided in the last second material layer that is connected in series is electrically connected to the second electrode, The third material layer includes an oxide film containing 10 at % or more of the metal.

2. the metal is a transition metal; The optical sensor of claim 1 , wherein the SiGe has at least one of a nanocrystalline structure and an amorphous structure.

3. The optical sensor according to claim 1 , wherein the SiGe is polycrystalline.

4. 3. The optical sensor according to claim 1, wherein the melting point of the metal is 1455° C. or higher.

5. 3. The optical sensor according to claim 1, wherein the metal is any one of Ni, W, Mo, Ti, Au, Pd, Ge, Hf, Al, and alloys of combinations thereof.

6. 3. The optical sensor according to claim 1, wherein the metal is any one of Ni, W, Mo, Ti, and alloys of combinations thereof.

7. The optical sensor according to claim 1 , wherein the third material layer has a thickness of 3 nm to 200 nm.

8. 3. The optical sensor of claim 1, wherein the first conductivity type is n-type and the second conductivity type is p-type.

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