Light sensor

Abstract

To provide an optical sensor capable of reducing a noise equivalent power.SOLUTION: An optical sensor including: a supporting film having a first main surface and a second main surface that is positioned opposite in a thickness direction to the first main surface; a thermoelectric conversion material part that incudes a plurality of band-like first material layers composed of SiGe with a p-type conductive type, and converting thermal energy into electric energy, and a plurality of band-like second material layers composed of SiGe having an n-type conductive type, and converting the thermal energy into the electric energy, and is arranged on the first main surface; a heat sink arranged on the second main surface; and a light absorption film that is arranged so as to from a temperature difference in each of a longer direction of the first material layer and a longer direction of the second material layer in view of a direction vertical to the first main surface, and converts the received light into the thermal energy. The plurality of first material layers and the plurality of second material layers are constructed by a first phononic structure having a plurality of vacancies.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] This disclosure relates to an optical sensor. [Background technology]

[0002] Thermoelectric elements having thermoelectric materials composed of compound semiconductors are known (see, for example, Patent Documents 1 and 2). In addition, infrared sensors using a phononic structure are known (see, for example, Non-Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] International Publication No. 2021 / 039074 [Patent Document 2] Japanese Patent Publication No. 2017-223644 [Non-patent literature]

[0004] [Non-Patent Document 1] Tambo, Naoki, et al. “Sensitivity improved thermal infrared sensor cell applying the heat insulating phononic crystals.” Image Sensing Technologies: Materials, Devices, Systems, and Applications VIII. Vol. 11723. International Society for Optics and Photonics, 2021. [Overview of the project] [Problems that the invention aims to solve]

[0005] When using an optical sensor, for example, as an infrared sensor, it is required that the noise equivalent power (NEP) be good, that is, that its value be low. Therefore, one of the objectives of this disclosure is to provide an optical sensor that can reduce noise equivalent power. [Means for solving the problem]

[0006] A light sensor according to this disclosure includes a support film having a first main surface and a second main surface located opposite the first main surface in the thickness direction; a plurality of strip-shaped first material layers made of p-type conductive SiGe that convert thermal energy into electrical energy; a plurality of strip-shaped second material layers made of n-type conductive SiGe that convert thermal energy into electrical energy; a thermoelectric conversion material portion disposed on the first main surface; a heat sink disposed on the second main surface; and a light absorption film disposed so as to form a temperature difference in the longitudinal direction of the first material layer and the longitudinal direction of the second material layer, respectively, when viewed in a direction perpendicular to the first main surface, and converts received light into thermal energy. The plurality of first material layers and the plurality of second material layers are composed of a first phononic structure having a large number of voids. [Effects of the Invention]

[0007] The above-mentioned optical sensor makes it possible to reduce noise equivalent power. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a schematic plan view of the external appearance of the optical sensor in Embodiment 1. [Figure 2] Figure 2 is a schematic plan view of the external appearance of the optical sensor in Embodiment 1. [Figure 3] Figure 3 is a schematic cross-sectional view showing a section along the line segment III-III in Figures 1 and 2. [Figure 4] Figure 4 is a schematic cross-sectional view showing a part of the optical sensor in Embodiment 1. [Figure 5]FIG. 5 is a schematic diagram showing an enlarged view of a part of a first material layer composed of a first phononic structure. [Figure 6] FIG. 6 is a flowchart showing typical steps of a method for manufacturing an optical sensor in Embodiment 1. [Figure 7] FIG. 7 is a schematic plan view of the appearance of an optical sensor in Embodiment 2. [Figure 8] FIG. 8 is a schematic plan view showing an enlarged view of a partial region VIII of the optical sensor shown in FIG. 7. [Figure 9] FIG. 9 is a schematic cross-sectional view of the optical sensor shown in Embodiment 3. [Figure 10] FIG. 10 is a flowchart showing typical steps of a method for manufacturing an optical sensor in Embodiment 3. [Figure 11] FIG. 11 is a graph showing the relationship between the sensitivity of an optical sensor and the difference between length D1 and length D2. [Figure 12] FIG. 12 is a graph showing the relationship between the noise of an optical sensor and the difference between length D1 and length D2. [Figure 13] FIG. 13 is a graph showing the relationship between the noise equivalent power (NEP) of an optical sensor and the difference between length D1 and length D2. [Figure 14] FIG. 14 is a graph showing the relationship between the porosity and the NEP. Embodiments for Carrying Out the Invention

[0009] [Description of Embodiments of the Present Disclosure] First, embodiments of the present disclosure will be listed and described. The optical sensor according to the present disclosure is (1) A support film having a first main surface and a second main surface located opposite to the first main surface in the thickness direction, a plurality of strip-shaped first material layers made of SiGe having a p-type conductivity type and converting thermal energy into electrical energy, and a plurality of strip-shaped second material layers made of SiGe having an n-type conductivity type and converting thermal energy into electrical energy, a thermoelectric conversion material part disposed on the first main surface, a heat sink disposed on the second main surface, and a light absorption film disposed so as to form a temperature difference in the longitudinal direction of the first material layer and the longitudinal direction of the second material layer when viewed in a direction perpendicular to the first main surface, and converting the received light into thermal energy. The plurality of first material layers and the plurality of second material layers are composed of a first phononic structure having a large number of pores.

[0010] Regarding 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, it may include a light absorption film that converts light energy into thermal energy and a thermoelectric conversion material part (thermopile) that converts thermal energy into electrical energy. In the thermoelectric conversion material part, for example, a thermocouple formed by connecting an n-type thermoelectric conversion material of the first conductivity type and a p-type thermoelectric conversion material part of the second conductivity type different from the first conductivity type may be used. By connecting a plurality of strip-shaped n-type thermoelectric conversion material parts and a plurality of strip-shaped p-type thermoelectric conversion material parts in series alternately, the output is increased.

[0011] Here, when the optical sensor is used as, for example, an infrared sensor, it is required that the Noise Equivalent Power (NEP), which is an important index, is good, that is, its value is low. NEP is represented by a value obtained by dividing noise by sensitivity (NEP = noise / sensitivity). The sensitivity in the optical sensor is represented by the formula (1) shown in Equation 1 below.

[0012]

Equation

[0013] D* represents sensitivity, η represents emissivity, n is the logarithm of the thermocouple, α is the Seebeck coefficient, and Gth represents thermal conductance. As can be seen from equation (1), if the thermal conductance can be reduced, the sensitivity of the optical sensor can be improved.

[0014] Furthermore, the noise in the optical sensor is expressed by equation (2) shown in Equation 1 below.

[0015]

number

[0016] Vn represents noise (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 equation (2), Johnson noise is dependent on resistance, and if the resistance can be reduced, noise in the optical sensor can be reduced.

[0017] Here, the inventors considered reducing the noise and increasing the sensitivity of the optical sensor in order to improve NEP, that is, to reduce NEP. They found that among the components included in the optical sensor, the material layer included in the thermoelectric conversion material section, which converts thermal energy into electrical energy, has a high thermal conductivity, making it difficult to increase its sensitivity. Therefore, the inventors focused on the fact that reducing the thermal conductivity of the material layer would solve the problem, and came up with the configuration of the present disclosure.

[0018] In the optical sensor according to this disclosure, the plurality of first material layers and the plurality of second material layers are composed of a first phononic structure having a large number of voids. With such a configuration, the thermal conductivity of each of the plurality of first material layers and the plurality of second material layers can be reduced. This makes it possible to increase the sensitivity of the optical sensor. As a result, with such an optical sensor, the noise equivalent power can be reduced. Here, the first phononic structure refers to a structure that has a periodic structure on the order of nanometers to several microns and artificially inhibits the propagation of phonons. In this disclosure, the first phononic structure is a structure having a plurality of regularly arranged through holes. However, it includes through holes with residual film.

[0019] (2) In (1) above, the support film may be composed of a second phononic structure having a large number of pores. By doing so, the thermal conductivity of the support film can be reduced in addition to the multiple first material layers and the multiple second material layers. This makes it possible to increase the sensitivity. As a result, with such an optical sensor, the noise equivalent power can be reduced.

[0020] (3) In (1) or (2) above, if the pitch spacing of the vacancies constituting the first phononic structure is length D1 and the diameter of the vacancies constituting the first phononic structure is length D2, the difference between length D1 and length D2 may be 5 nm or more and 500 nm or less. By doing so, it is possible to reduce the thermal conductance and increase sensitivity while appropriately balancing the resistance of the first material layer and the second material layer themselves with the contact resistance to reduce noise. As a result, with such an optical sensor, it is possible to further reduce the noise equivalent power.

[0021] (4) In (3) above, the difference between length D1 and length D2 may be 10 nm or more and 200 nm or less. By doing so, the noise equivalent power can be further reduced.

[0022] (5) In any of (1) to (4) above, the pitch spacing of the vacancies constituting the first phononic structure may be 20 nm or more and 1200 nm or less. By doing so, the reduction of thermal conductivity in the first phononic structure can be made more certain. Therefore, the sensitivity of the optical sensor can be increased and the noise equivalent power can be reduced further.

[0023] (6) In any of (1) to (5) above, the diameter of the vacancies constituting the first phononic structure may be 15 nm or more and 200 nm or less. By doing so, the reduction of thermal conductivity in the first phononic structure can be made more certain. Therefore, the sensitivity of the optical sensor can be increased and the noise equivalent power can be reduced further.

[0024] (7) In any of (1) to (6) above, a base film may be further provided between the thermoelectric conversion material and the light absorption film. By doing so, the first phononic structure can be easily formed in a plurality of first material layers and a plurality of second material layers, thereby improving productivity.

[0025] (8) In any of (1) to (7) above, the thickness of the undercoat may be 10 nm or more and 50 nm or less. By doing so, it is possible to more reliably achieve both a reduction in the noise equivalent power of the optical sensor and good productivity.

[0026] (9) In (2) above, the pitch spacing and diameter of the voids constituting the first phononic structure may be the same as the pitch spacing and diameter of the voids constituting the second phononic structure. By doing so, the first phononic structure and the second phononic structure can be formed at once after the support film, the first material layer and the second material layer have been formed. Therefore, productivity can be improved.

[0027] (10) In any of (1) to (9) above, SiGe may have at least one of a nanocrystalline structure and an amorphous structure with a particle size of 3 nm or more and 200 nm or less. By doing so, the thermoelectric conversion efficiency can be improved. Therefore, sensitivity can be improved and noise equivalent power can be reduced.

[0028] (11) In any of (1) to (9) above, SiGe may be polycrystalline. Such polycrystalline SiGe is also suitably used in the optical sensor of this disclosure. The crystallinity of the polycrystalline material in the optical sensor of this disclosure is 99% or higher.

[0029] (12) In any of (1) to (11) above, at least one of the first superimposed portion of the plurality of first material layers overlapping the light-absorbing film and the second superimposed portion of the plurality of second material layers overlapping the light-absorbing film may be composed of a first phononic structure. By doing so, the thermal conductivity can be reduced in the portion where the first material layer, the second material layer and the light-absorbing film overlap, thereby increasing sensitivity and reducing noise equivalent power.

[0030] (13) In any of (1) to (11) above, the first superimposed portion of the multiple first material layers overlapping the light-absorbing film and the second superimposed portion of the multiple second material layers overlapping the light-absorbing film do not have to have a first phononic structure. By doing so, the formation of the light-absorbing film is not affected by the phononic structure, and thus productivity can be improved.

[0031] [Details of the embodiments of this disclosure] Next, embodiments of the optical sensor of the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0032] (Embodiment 1) The optical sensor according to Embodiment 1 of this disclosure will now be described. Figures 1 and 2 are schematic plan views of the external appearance of the optical sensor in Embodiment 1. For ease of understanding, the infrared absorbing film and insulating film, which will be described later, are omitted from Figure 1. In Figure 1, the outer edge 23a where the infrared absorbing film is positioned is shown by a dashed line. Figure 3 is a schematic cross-sectional view showing a cross section along the line segment III-III in Figures 1 and 2. Figure 4 is a schematic cross-sectional view showing a part of the optical sensor in Embodiment 1. Figure 4 is a schematic cross-sectional view showing an enlarged portion including the first region, second region, third region and fourth region, which will be described later.

[0033] Referring to Figures 1, 2, 3, and 4, the optical sensor 11a is, for example, an infrared sensor. The optical sensor 11a comprises a support film 13, a thermoelectric conversion material part 12, a heat sink 14, an infrared absorption film 23 as a light absorption film, a first electrode 24, and a second electrode 25. The optical sensor 11a detects infrared radiation irradiated onto the optical sensor 11a by detecting the potential difference generated between the first electrode 24 and the second electrode 25. If the entire optical sensor 11a is in the shape of a plate, its thickness direction is indicated by the Z direction. In Figures 1 and 2, the direction perpendicular to the plane of the paper is the Z direction.

[0034] In this embodiment, the support film 13 has a rectangular shape when viewed in the thickness direction (Z direction). The support film 13 supports the thermoelectric conversion material portion 12, the infrared absorption film 23, the first electrode 24, and the second electrode 25. The support film 13 includes a main surface 13b located on one side in the thickness direction and a main surface 13a located on the other side in the thickness direction. Other components of the support film 13 will be described in detail later.

[0035] The heat sink 14 includes a surface 14a and a surface 14b that are spaced apart in the thickness direction of the optical sensor 11a. The heat sink 14 is positioned on the main surface 13a of the support film 13. Specifically, the heat sink 14 is positioned so that the surface 14a of the heat sink 14 and the main surface 13a of the support film 13 are in contact. The surface 14b of the heat sink 14 is exposed. In this embodiment, the shape of the heat sink 14 is annular. The outer edge 14c of the entire heat sink 14 and the outer edge 13c of the support film 13 extend in a continuous line in the Z direction. In the cross-section shown in Figure 3, the heat sink 14 appears as two trapezoidal shapes spaced apart in the X direction. The heat sink 14 is sufficiently thick compared to the support film 13. For example, the thickness of the heat sink 14 is 10 times or more the thickness of the support film 13. In this embodiment, the heat sink 14 is a so-called substrate. The heat sink 14 is made of, for example, silicon (Si).

[0036] The optical sensor 11a has a recess 16 that is recessed in the thickness direction. In the region corresponding to the recess 16 when viewed from the surface 14b side, the support film 13, specifically the main surface 13a of the support film 13, is exposed. In Figure 1, the inner edge 16a of the heat sink 14, which is the boundary between the heat sink 14 and the support film 13 when viewed in the Z direction, is shown by a dashed line in Figure 1. As shown in Figure 1, in this embodiment, the inner edge 16a of the heat sink 14 has a square shape when viewed in the Z direction. The heat sink 14 is arranged to surround the recess 16. The inner circumferential surface 14d of the heat sink surrounding the recess 16 is tapered, with the opening on the surface 14b side being larger. The recess 16 is formed, for example, by anisotropic wet etching of a flat substrate. By forming such a recess 16, heat escape from the infrared absorption film 23 to the heat sink 14 can be suppressed. Therefore, the longitudinal temperature difference between the first material layer 21 and the second material layer 22, which will be described later, can be made larger.

[0037] The first electrode 24 and the second electrode 25 are positioned on the main surface 13b of the support film 13, outside the region 15 described later. The second electrode 25 is positioned at a distance from the first electrode 24. The first electrode 24 and the second electrode 25 are, for example, pad electrodes. The materials used for the first electrode 24 and the second electrode 25 are, for example, gold (Au), titanium (Ti), platinum (Pt), etc.

[0038] The thermoelectric conversion material section 12 is arranged on the main surface 13b of the support film 13. The thermoelectric conversion material section 12 includes a plurality of first material layers 21, including first material layers 21a, 21b, 21c, and 21d, and a second material layer 22, including second material layers 22a, 22b, 22c, and 22d. The plurality of first material layers 21 and the plurality of second material layers 22 included in the thermoelectric conversion material section 12 are each composed of SiGe. That is, the first material layer 21 and the second material layer 22 are each composed of a compound semiconductor with Si and Ge as constituent elements. The first material layer 21 is composed of an n-type thermoelectric conversion material, which is a first conductivity type. The second material layer 22 is composed of a p-type thermoelectric conversion material, which is a second conductivity type different from the first conductivity type.

[0039] The first material layer 21 has a strip-like shape. The first material layer 21 includes a first region 28a that includes a first end 28c in the longitudinal direction, and a second region 28b that includes a second end 28d opposite to the first end 28c in the longitudinal direction. The direction in which the line connecting the first region 28a and the second region 28b extends is the longitudinal direction of the strip-shaped first material layer 21.

[0040] Multiple first material layers 21 are arranged on the main surface 13b of the support film 13. Multiple first material layers 21 are arranged so as to fit within the region 15 shown by the dotted-dash rectangle in Figure 1. Multiple first material layers 21 are arranged with intervals between them. Except for first material layers 21a, 21b, 21c, and 21d, multiple first material layers 21 are arranged so that their longitudinal direction is either in the X direction or the Y direction. Except for first material layers 21a, 21b, 21c, and 21d, multiple first material layers 21 are arranged so that they extend from one side of the square-shaped region 15 toward the opposite side (with their longitudinal direction aligned in that direction). When viewed in the Z direction, multiple first material layers 21 are arranged such that the first region 28a is located closer to the inner edge 16a of the heat sink 14, and the second region 28b is located closer to the outer edge 23a of the infrared absorption film 23.

[0041] The thermoelectric conversion material section 12 includes an insulating film 26. For example, SiO2 is selected as the material for the insulating film 26. The insulating film 26 is placed on the first material layer 21 in the portion where the first material layer 21 is placed, and on the main surface 13b of the support film 13 in the portion where the first material layer 21 is not placed. The insulating film 26 is placed so as not to cover the first region 28a and the second region 28b of the first material layer 21.

[0042] The second material layer 22 also has a strip-like shape, similar to the first material layer 21. The second material layer 22 includes a third region 29a that includes a third end 29c in the longitudinal direction, and a fourth region 29b that includes a fourth end 29d opposite to the third end 29c in the longitudinal direction. The direction in which the line connecting the third region 29a and the fourth region 29b extends is the longitudinal direction of the strip-shaped second material layer 22.

[0043] The multiple second material layers 22 are arranged to fit within the region 15 shown by the dotted rectangle in Figure 1, similar to the arrangement of the multiple first material layers 21. Each of the multiple second material layers 22 is arranged so that its longitudinal direction is inclined with respect to the X or Y direction. The multiple second material layers 22 are placed on a portion of the main surface 13b of the support film 13, on a portion of the insulating film 26, and on a portion of the first material layer 21. The second material layers 22 are arranged such that, when viewed in the thickness direction of the support film 13, the third region 29a is located on the side closer to the inner edge 16a of the heat sink 14, and the fourth region 29b is located on the side closer to the outer edge 23a of the infrared absorption film 23.

[0044] Except for the first region 28a connected to the first electrode 24 and the third region 29a connected to the second electrode 25, the multiple first material layers 21 and the multiple second material layers 22 are connected alternately. Specifically, this will be explained using the arrangement on the right side of Figure 1. The first region 28a of the first material layer 21 is connected to the third region 29a of the second material layer 22 which is adjacent to the first material layer 21 in a clockwise direction. The second region 28b of the first material layer 21 is connected to the fourth region 29b of the second material layer 22 which is adjacent to the first material layer 21 in a counterclockwise direction. The multiple first material layers 21 and the multiple second material layers 22 are 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, respectively, with the second region 28b and the fourth region 29b being connected to each other and the first region 28a and the third region 29a being connected to each other. In other words, the first material layer 21 and the second material layer 22 are paired, and adjacent first material layer 21 and second material layer 22 are electrically connected alternately in series in regions including their ends. In this embodiment, the third region 29a is located on the first region 28a and is in ohmic contact with the first region 28a. The fourth region 29b is located on the second region 28b and is in ohmic contact with the second region 28b. With respect to the direction of the temperature gradient generated when light is irradiated onto the light sensor 11a, specifically the infrared absorption film 23, the polarity of the voltage generated in the first region 28a, including the first end 28c of the first material layer 21, and the polarity of the voltage generated in the third region 29a, including the third end 29c of the second material layer 22, are opposite.

[0045] Of the alternately connected first material layer 21 and multiple second material layers 22, the first material layer 21 located at the outermost edge is connected to the first electrode 24 in the first region 28a. Of the alternately connected first material layer 21 and multiple second material layers 22, the second material layer 22 located at the outermost edge is connected to the second electrode 25 in the third region 29a.

[0046] The infrared absorbing film 23 converts infrared radiation into heat. For example, carbon (C) is selected as the material for the infrared absorbing film 23.

[0047] The infrared absorbing film 23 is positioned in the region surrounded by the inner edge 16a of the heat sink 14 when viewed in the Z direction. In this embodiment, the outer edge 23a of the infrared absorbing film 23 has a square shape when viewed in the Z direction. The infrared absorbing film 23 is positioned such that the center of the square shape formed by the outer edge 23a of the infrared absorbing film 23 coincides with the center of the square shape formed by the inner edge 16a of the heat sink 14.

[0048] The infrared absorbing film 23 is positioned to form a temperature difference in the longitudinal direction of the first material layer 21, specifically between the first region 28a and the second region 28b. The infrared absorbing film 23 is also positioned to form a temperature difference in the longitudinal direction of the second material layer 22, specifically between the third region 29a and the fourth region 29b. In this embodiment, the infrared absorbing film 23 is positioned to expose the first region 28a and the third region 29a and to cover the second region 28b and the fourth region 29b. That is, the second region 28b and the fourth region 29b overlap with the infrared absorbing film 23 when viewed in the Z direction. The first region 28a and the third region 29a are not covered by the infrared absorbing film 23. The first region 28a and the third region 29a overlap with the heat sink 14 when viewed in the Z direction. The first material layer 21 and the second material layer 22 are thermally connected to the infrared absorbing film 23 such that a temperature difference is formed in the respective longitudinal directions of the first material layer 21 and the second material layer 22.

[0049] The first material layer 21 converts the temperature difference (thermal energy) between the first region 28a and the second region 28b into electrical energy. The second material layer 22 converts the temperature difference (thermal energy) between the third region 29a and the fourth region 29b into electrical energy. A temperature difference is formed in the longitudinal direction for each of the multiple first material layers 21 and the multiple second material layers 22. The thermoelectric conversion material section 12 converts the temperature difference (thermal energy) into electrical energy using the multiple first material layers 21 and the multiple second material layers 22 configured as described above. The optical sensor 11a can efficiently detect infrared rays by utilizing the temperature difference formed by the infrared absorption film 23 and the heat sink 14.

[0050] The configurations of the multiple first material layers 21 and the multiple second material layers 22 will now be described. Each of the multiple first material layers 21 is composed of a first phononic structure having a large number of voids 31. That is, each of the multiple first material layers 21 has a first phononic structure having a large number of voids 31. Similarly, each of the multiple second material layers 22 is composed of a first phononic structure having a large number of voids 31. That is, each of the multiple second material layers 22 has a first phononic structure having a large number of voids 31. In Embodiment 1, the first material layer 21 and the second material layer 22 have the first phononic structure over their entire surfaces. That is, when viewed in the Z direction, the first superimposed portion of the first material layer 21 that overlaps with the infrared absorption film 23 has the first phononic structure. When viewed in the Z direction, the second superimposed portion of the second material layer 22 that overlaps with the infrared absorption film 23 has the first phononic structure. The large number of voids 31 refers to a void density of 25 voids / μm². 2 ~2500 pieces / μm 2 It means...

[0051] Figure 5 is a schematic diagram showing an enlarged view of a part of the first material layer 21, which is composed of the first phononic structure. Figure 5 shows the first material layer 21 as viewed in the Z direction. In the schematic diagram shown in Figure 5, the outer shape of the voids 31 is shown as a perfect circle for ease of understanding, but the outer shape of the voids 31 is not limited to a perfect circle; it may be elliptical or polygonal. Referring to Figure 5 as well, the first material layer 21 is configured such that a number of voids 31 penetrating in the Z direction are formed at intervals on a strip-shaped member. The first material layer 21 can be formed, for example, by forming a resist pattern and depositing a deposition material. This will be described later. The same applies to the first phononic structure that constitutes the second material layer 22.

[0052] In Figure 5, the length D1, which indicates the pitch spacing of the voids 31, is between 20 nm and 1200 nm. In this embodiment, the length D1 indicating the pitch spacing of the voids 31 is 40 nm. The length D1 indicating the pitch spacing of the voids 31 is the distance between the centers 33a and 33b of adjacent voids 31. Also, the length D2 indicating the diameter of the voids 31 shown in Figure 5 is between 15 nm and 200 nm. In this embodiment, the length D2 indicating the diameter of the voids 31 is 15 nm.

[0053] The difference between length D1, which indicates the pitch spacing of the pores 31, and length D2, which indicates the diameter of the pores 31, is between 5 nm and 500 nm. Preferably, the difference between length D1 and length D2 is between 10 nm and 200 nm. This will be explained later.

[0054] The specific configuration of the support film 13 will now be described. The support film 13 includes a first portion 19a having a second phononic structure with a large number of voids, and a second portion 19b not having a second phononic structure. In Embodiment 1, the first portion 19a is arranged in contact with a plurality of first material layers 21 and a plurality of second material layers 22. In Embodiment 1, the second portion 19b is arranged around the first portion 19a. The first portion 19a is, specifically, the portion shown in region 15 in Figure 1 when viewed in the Z direction. The support film 13 is an insulating film. The material of the support film 13 is, for example, SiO2 or SiN. The thickness of the support film 13 is 200 nm or more and 2000 nm or less.

[0055] The first portion 19a is composed of a second phononic structure having a large number of voids. That is, the first portion 19a of the support film 13 has a second phononic structure having a large number of voids. The configuration of the second phononic structure is the same as that of the first phononic structure described above, so its explanation is omitted.

[0056] The optical sensor 11a includes an underlayer 20 placed between the thermoelectric conversion material and the infrared absorption film 23. The underlayer 20 is a silicon (Si)-based insulating film, such as SiO2 or SiN. The thickness T of the underlayer 20 shown in Figure 4 is between 10 nm and 50 nm.

[0057] A brief explanation will be given of the manufacturing method of the optical sensor 11a in Embodiment 1. Figure 6 is a flowchart showing a typical process of the manufacturing method of the optical sensor 11a in Embodiment 1. Referring to Figure 6, in the manufacturing method of the optical sensor 11a in Embodiment 1, the substrate preparation process is carried out as step (S10). In this step (S10), first, a flat substrate made of Si, which will serve as the base for the heat sink 14, is prepared.

[0058] Next, as step (S20), a support film formation step is carried out. In this step (S20), a film of SiO2 is formed on the substrate. In this case, for example, this is carried out by depositing an SiO2 deposition material onto the substrate.

[0059] Subsequently, a thermoelectric conversion material formation process is carried out as step (S30). In this step (S30), a thermoelectric conversion material 12 is formed on the support film 13. Specifically, for example, layers are formed in the following order: a first material layer 21, an insulating film layer 26, and a second material layer 22. When forming each layer, for example, resist coating, photolithography, vapor deposition, or lift-off is used.

[0060] Next, as step (S40), a phononic structure formation step is carried out. In this step (S40), both the first phononic structure contained in the first material layer 21 and the second material layer 22, and the second phononic structure contained in the support film 13 are formed. In this case, the phononic structure is drawn using an EB (ion beam) to form a resist pattern. In this case, the second portion 19b of the support film 13 is masked and covered. Then, the first phononic structure and the second phononic structure are formed by dry etching using a fluorine-based gas such as CHF3 or CF4. After that, the mask covering the second portion 19b is removed.

[0061] Subsequently, an electrode formation process is carried out as step (S50). In this step (S50), a first electrode 24 and a second electrode 25 are formed on the substrate. In this case, the first electrode 24 and the second electrode 25 are formed such that the first region 28a of the first material layer 21 located at the very edge is in contact with the first electrode 24, and the third region 29a of the second material layer 22 is in contact with the first electrode 24.

[0062] Next, as step (S60), a base film formation step is carried out. In this step (S60), a base film 20 is formed on the first material layer 21 and the second material layer 22 on which the first phononic structure is formed, and on the first portion 19a of the support film 13 on which the second phononic structure is formed. By forming this base film 20, the infrared absorption film 23 to be formed later can be reliably held on the thermoelectric conversion material part 12. The base film 20 is formed by using a deposition material and depositing SiO2 at a high angle, specifically, for example, 45 degrees or more with respect to the direction in which the material to be deposited is ejected from the substrate side. In this way, the base film 20 can be efficiently formed on the first phononic structure and the second phononic structure.

[0063] Subsequently, an infrared absorption film formation process is carried out as step (S70). In this step (S70), an infrared absorption film 23 is formed on the formed base film 20 by vapor deposition or the like.

[0064] Finally, as step (S80), a heat sink formation step is carried out. In this step (S80), a recess 16 is formed by performing anisotropic etching on the substrate. In this way, the optical sensor 11a with the above configuration is obtained.

[0065] In this type of optical sensor 11a, the multiple first material layers 21 and the multiple second material layers 22 are composed of a first phononic structure having a large number of voids 31. With this configuration, the thermal conductivity of each of the multiple first material layers 21 and the multiple second material layers 22 can be reduced. As a result, while reducing thermal conductance and increasing sensitivity, the balance between the resistance of the first material layers 21 and the second material layers 22 themselves and the contact resistance can be properly adjusted to reduce noise. Consequently, with this type of optical sensor 11a, the noise equivalent power can be further reduced.

[0066] In this embodiment, the support film 13 is composed of a second phononic structure having a large number of pores. Therefore, in addition to the multiple first material layers 21 and the multiple second material layers 22, the thermal conductivity of the support film 13 can be reduced. This allows for an increase in sensitivity. As a result, such an optical sensor can reduce noise equivalent power.

[0067] In this embodiment, the pitch spacing of the voids 31 constituting the first phononic structure is between 20 nm and 1200 nm. Therefore, the reduction of thermal conductivity in the first phononic structure can be made more reliable. Consequently, the sensitivity of the optical sensor 11a can be increased, and the noise equivalent power can be further reduced.

[0068] In this embodiment, the diameter of the voids 31 constituting the first phononic structure is between 15 nm and 200 nm. Therefore, the reduction of thermal conductivity in the first phononic structure can be made more reliable. Consequently, the sensitivity of the optical sensor 11a can be increased, and the noise equivalent power can be further reduced.

[0069] In this embodiment, the optical sensor 11a further includes an underlayer 20 disposed between the thermoelectric conversion material portion 12 and the infrared absorption film 23. Therefore, the first phononic structure can be easily formed in the plurality of first material layers 21 and the plurality of second material layers 22, thereby improving productivity.

[0070] In this embodiment, the thickness of the undercoat 20 is 10 nm to 50 nm. Therefore, it is possible to more reliably achieve both a reduction in the noise equivalent power of the optical sensor 11a and good productivity.

[0071] In this embodiment, the pitch spacing and diameter of the voids constituting the first phononic structure are the same as the pitch spacing and diameter of the voids constituting the second phononic structure. Therefore, after forming the support film 13, the first material layer 21, and the second material layer 22, the first and second phononic structures can be formed in one step. Consequently, productivity can be improved.

[0072] In this embodiment, if the pitch spacing of the voids constituting the first phononic structure is length D1 and the diameter of the voids constituting the first phononic structure is length D2, then the difference between length D1 and length D2 is between 5 nm and 500 nm. Therefore, while reducing thermal conductance and increasing sensitivity, noise can be reduced by appropriately balancing the resistance of the first material layer 21 and the second material layer 22 themselves with the contact resistance. As a result, with such an optical sensor 11a, the noise equivalent power can be further reduced.

[0073] (Embodiment 2) Embodiment 2, another embodiment, will now be described. Figure 7 is a schematic plan view of the external appearance of the optical sensor in Embodiment 2. Figure 8 is a schematic plan view showing an enlarged view of a part of region VIII of the optical sensor shown in Figure 7. For ease of understanding, the infrared absorbing film and insulating film are not shown in Figures 7 and 8. Figure 7 corresponds to Figure 1. The optical sensor in Embodiment 2 has basically the same configuration as in Embodiment 1 and produces the same effects. However, the optical sensor in Embodiment 2 differs from that of Embodiment 1 in the configuration of the first material layer and the second material layer, etc.

[0074] Referring to Figures 7 and 8, the first material layer 21 and the second material layer 22 included in the optical sensor 11b of Embodiment 2 are not arranged overlapping in the thickness direction, as in the optical sensor 11a of Embodiment 1, but rather on the same plane, specifically on the support film 13. The strip-shaped first material layer 21 and the strip-shaped second material layer 22 are arranged on the support film 13 so that their longitudinal directions are the X direction or the Y direction, respectively. The first material layer 21 and the second material layer 22 are arranged alternately with spacing between them.

[0075] The thermoelectric conversion material section 12 includes a third material layer 36 and a third material layer 37 made of metal. Examples of metals that make up the third material layer 36 and the third material layer 37 include nickel (Ni), tungsten (W), molybdenum (Mo), titanium (Ti), gold (Au), palladium (Pd), germanium (Ge), hafnium (Hf), and aluminum (Al). The third material layer 36 is arranged to span adjacent first region 28a and third region 29a on the outer edge side of the first material layer 21 and the outer edge side of the second material layer 22, and to be in ohmic contact with the first region 28a and the third region 29a. The third material layer 36 is arranged to cover the first region 28a, the third region 29a, a part of the side surface of the first region 28a, and a part of the side surface of the third region 29a. The third material layer 37 is positioned on the inner edge side of the first material layer 21 and the inner edge side of the second material layer 22, straddling the adjacent second region 28b and fourth region 29b, and in ohmic contact with the second region 28b and fourth region 29b. The first region 28a and the third region 29a overlap with the heat sink 14 when viewed in the Z direction. The second region 28b and the fourth region 29b overlap with the infrared absorption film 23 when viewed in the Z direction. The first material layer 21 and the second material layer 22 are composed of a first phononic structure.

[0076] By doing so, it is possible to increase sensitivity and reduce noise while simultaneously reducing noise equivalent power.

[0077] (Embodiment 3) Another embodiment, Embodiment 3, will now be described. Figure 9 is a schematic cross-sectional view of the optical sensor shown in Embodiment 3. The optical sensor in Embodiment 3 has basically the same configuration as in Embodiment 1 and produces the same effects. However, the optical sensor in Embodiment 3 differs from that of Embodiment 1 in the configuration of the first phononic structure formed in the first material layer 21 and the second material layer 22, and the second phononic structure formed in the support film 13.

[0078] The explanation will be given with reference to Figure 9. The first material layer 21 includes a region having a first phononic structure and a region not having a first phononic structure. The second material layer 22 includes a region having a first phononic structure and a region not having a first phononic structure. In both the first material layer 21 and the second material layer 22, the region having the first phononic structure is formed in a position that does not overlap with the infrared absorption film 23, and the region not having the first phononic structure is formed in a position that overlaps with the infrared absorption film 23. In Embodiment 3, when viewed in the Z direction, the first superimposed portion of the first material layer 21 that overlaps with the infrared absorption film 23 does not have a first phononic structure. When viewed in the Z direction, the second superimposed portion of the second material layer 22 that overlaps with the infrared absorption film 23 does not have a first phononic structure. The support film 13 includes a first portion 19a having a second phononic structure and a second portion 19b not having a second phononic structure. The first portion 19a is positioned between the centrally located second portion 19b and the surrounding second portion 19b. In other words, the support film 13 has a second phononic structure in the first portion 19a, in a position that does not overlap with the infrared absorption film 23 and the outer edge 13c when viewed in the Z direction. The second portion 19b of the support film 13 that overlaps with the infrared absorption film 23 when viewed in the Z direction does not have a first phononic structure.

[0079] By doing so, it is possible to increase sensitivity and reduce noise while simultaneously reducing noise equivalent power.

[0080] The optical sensor 11c shown in Embodiment 3 is manufactured by, for example, the following steps. Figure 10 is a flowchart showing a typical process for manufacturing the optical sensor 11c in Embodiment 3. Referring to Figure 10, in the manufacturing method of the optical sensor 11c in Embodiment 3, the following steps (S10) are performed: substrate preparation step (S10), support film formation step (S20), and thermoelectric conversion material part formation step (S30). After that, an infrared absorption film formation step (S41) is performed. That is, an infrared absorption film 23 is formed on the thermoelectric conversion material part 12. After that, a phononic structure formation step (S51) is performed. In this case, the area where the infrared absorption film 23 is placed is masked to form the first phononic structure and the second phononic structure. Then, after performing the electrode formation step (S61), a heat sink formation step (S71) is performed.

[0081] In this way, the optical sensor 11c according to Embodiment 3 is manufactured. With this manufacturing method, the optical sensor 11c according to Embodiment 3 can be manufactured efficiently without forming a base film 20. The infrared absorption film formation step (S41) may be performed between the electrode formation step (S61) and the heat sink formation step (S71). In this case, in the phononic structure formation step (S51), for example, a resist pattern is formed at the position where the infrared absorption film 23 will be formed in a later step. In this way, the first phononic structure and the second phononic structure can be prevented from being formed at positions that overlap with the infrared absorption film 23 when viewed in the Z direction.

[0082] Here, we will explain the relationship between the sensitivity of the optical sensor 11a of Embodiment 1, the optical sensor 11c of Embodiment 3, and the optical sensor according to this disclosure, in which only the first phononic structure is formed on the first material layer 21 and the second material layer 22, and the second phononic structure is not formed on the support film 13, and the difference between the length D1 and the length D2.

[0083] Figure 11 is a graph showing the relationship between the sensitivity of the optical sensor and the difference between lengths D1 and D2. In Figure 11, the horizontal axis represents the difference (nm) between lengths D1 and D2, and the vertical axis represents the sensitivity Rv (V / W). In Figure 11, Sample 1 represents the optical sensor of Embodiment 1, Sample 2 represents the optical sensor of Embodiment 3, and Sample 3 represents the optical sensor in which only the first phononic structure is formed on the first material layer 21 and the second material layer 22, and the second phononic structure is not formed on the support film 13. The same applies to Figures 12, 13, and 14.

[0084] Referring to Figure 11, the sensitivity increases in all cases as the difference between length D1 and length D2 increases.

[0085] Figure 12 is a graph showing the relationship between the noise of the optical sensor and the difference between lengths D1 and D2. In Figure 11, the horizontal axis represents the difference (nm) between lengths D1 and D2, and the vertical axis represents the noise Vn (V / W).

[0086] Referring to Figure 12, as the difference between length D1 and length D2 increases, the contact resistance increases, but the resistance of the first and second material layers themselves decreases, resulting in a downward convex shape in a certain range for each sample.

[0087] Figure 13 is a graph showing the relationship between the noise equivalent power (NEP) of the optical sensor and the difference between lengths D1 and D2. In Figure 13, the horizontal axis represents the difference between lengths D1 and D2 (nm), and the vertical axis represents NEP (V / W).

[0088] Referring to Figure 13, since NEP is derived from noise / sensitivity, the trend shown in the graph in Figure 12 is pronounced, and the NEP value decreases within a certain range. Furthermore, by setting the difference between lengths D1 and D2 to between 5 nm and 500 nm, the NEP can be reduced to 3.5E-0.2 or less. This further reduces the noise equivalent power. Moreover, by setting the difference between lengths D1 and D2 to between 10 nm and 200 nm, the NEP can be reduced to 3.0E-0.2 or less. This further reduces the noise equivalent power.

[0089] Figure 14 is a graph showing the relationship between porosity and NEP. In Figure 14, the horizontal axis represents porosity (%), and the vertical axis represents NEP (V / W). The porosity represents the ratio of the volume of all through-holes to the total volume of the first phononic structure.

[0090] Referring to Figure 14, NEP can also be reduced within a certain range by adjusting the porosity. Specifically, NEP can be reduced by setting the porosity between 2% and 72%.

[0091] (Other embodiments) In the above embodiment, at least one of the first material layer and the second material layer may be composed of SiGe having at least one of a nanocrystalline structure and an amorphous structure with a particle size of 3 nm to 200 nm. By doing so, the thermoelectric conversion efficiency can be improved. Therefore, sensitivity can be improved and noise equivalent power can be reduced.

[0092] The crystal grain size was measured by observing TEM (Transmission Electron Microscope) images. A JEM-2100F (manufactured by JEOL Ltd.) was used, with an acceleration voltage of 200kV. The electron probe diameter was set to 0.2nm, and the EDX mapping conditions were 256 pixels × 256 pixels, a dwell time of 0.5ms / pixel, and 15 integration cycles.

[0093] Furthermore, regarding the SiGe that constitutes the first material layer 21 and the second material layer 22, for example, amorphous SiGe may be heat-treated at a temperature of about 500°C to create a nanocrystalline structure in part of it. The SiGe may also have a nanocrystalline or amorphous structure. The SiGe may also be polycrystalline. Such polycrystalline SiGe is also suitably used in the optical sensor of this disclosure. The crystallinity of the polycrystalline material in the optical sensor of this disclosure is 99% or higher. The crystallinity was measured as follows: A HORIBA LabRam HR-PL was used as the apparatus. The measurement conditions were a laser wavelength of 532 nm and a laser power of 2.5 mW. The analysis conditions were 400 cm². -1 The nearby peaks were analyzed. For the analysis, a Gaussian function and a pseudo-Voigt function were fitted. The Gaussian function G(x) is expressed by equation (3) shown in Equation 3 below.

[0094]

number

[0095] Furthermore, the pseudo-Voigt function F(x) is expressed by equation (4) shown in equation 4 below.

[0096]

number

[0097] Gaussian function G(x): Variable Ag , W g , x g , the initial value of x0 was set to 400 cm -1 For the pseudo-Fokt function F(x): variable A f , W f , x f , for m, the initial value of x0 was set to 380 cm -1 and g was set to 0.5. Each parameter was optimized by the least squares method, and the pseudo-Fokt function and the Gaussian function were integrated to obtain the area. Regarding the crystallization rate, it was calculated as crystallization rate = area derived using the pseudo-Fokt function / (area derived using the pseudo-Fokt function + area derived using the Gaussian function), assuming that the area derived using the Gaussian function corresponds to the amorphous phase and the area derived using the pseudo-Fokt function corresponds to the crystal phase.

[0098] It should be understood that the embodiments disclosed herein are illustrative in all respects and not restrictive in any way. The scope of the present invention is defined by the claims rather than the above description, and it is intended that all modifications within the meaning and scope equivalent to the claims be included.

Explanation of Reference Numerals

[0099] 11a, 11b photosensors 12 thermoelectric conversion material section 13 support film 13a, 13b, 17a, 17b, 18a, 18b main surfaces 13c, 14c, 23a outer edges 14 heat sink 14a, 14b surfaces 14d inner peripheral surface 15 region 16 recess 16a inner edge '19a first part 19b second part<00004|01>20 base film [[ID=5|4]]21, 21a, 21b, 21c, 21d first material layer 22, 22a, 22b, 22c, 22d second material layer 23 Infrared absorbing film 24 1st electrode 25 2nd electrode 26 Insulating film 28a 1st area 28b 2nd area 28c First end 28d Second end 29a Third area 29b 4th area 29c Third end 29d Fourth end 31 Holes 32 Base section 33a,33b center 36,37 Third material layer D1, D2 Length F pseudo-Voight function G Gaussian function T thickness

Claims

1. A support film having a first main surface and a second main surface located opposite the first main surface in the thickness direction, A thermoelectric conversion material portion comprising a plurality of strip-shaped first material layers composed of p-type conductive SiGe that convert thermal energy into electrical energy, and a plurality of strip-shaped second material layers composed of n-type conductive SiGe that convert thermal energy into electrical energy, disposed on the first main surface, A heat sink disposed on the second main surface, The material comprises a light-absorbing film that is positioned to form a temperature difference in the longitudinal direction of the first material layer and the longitudinal direction of the second material layer, respectively, when viewed in a direction perpendicular to the first main surface, and which converts received light into thermal energy, The plurality of first material layers and the plurality of second material layers are composed of a first phononic structure having a large number of voids. An optical sensor in which the first superimposed portion of the plurality of first material layers overlapping the light-absorbing film and the second superimposed portion of the plurality of second material layers overlapping the light-absorbing film do not have the first phononic structure.

2. The optical sensor according to claim 1, wherein the support film is composed of a second phononic structure having a large number of pores.

3. If the pitch spacing of the holes constituting the first phononic structure is length D1, and the diameter of the holes constituting the first phononic structure is length D2, The optical sensor according to claim 1 or claim 2, wherein the difference between length D1 and length D2 is 5 nm or more and 500 nm or less.

4. The optical sensor according to claim 3, wherein the difference between the length D1 and the length D2 is 10 nm or more and 200 nm or less.

5. The optical sensor according to claim 1 or claim 2, wherein the pitch spacing of the vacancies constituting the first phononic structure is 20 nm or more and 1200 nm or less.

6. The optical sensor according to claim 1 or claim 2, wherein the diameter of the vacancies constituting the first phononic structure is 15 nm or more and 200 nm or less.

7. The optical sensor according to claim 1 or claim 2, further comprising a base film disposed between the thermoelectric conversion material portion and the light absorbing film.

8. The optical sensor according to claim 7, wherein the thickness of the underlayer film is 10 nm or more and 50 nm or less.

9. The optical sensor according to claim 2, wherein the pitch spacing and diameter of the voids constituting the first phononic structure are the same as the pitch spacing and diameter of the voids constituting the second phononic structure, respectively.

10. The optical sensor according to claim 1 or claim 2, wherein the SiGe has at least one of a nanocrystalline structure and an amorphous structure with a particle size of 3 nm or more and 200 nm or less.

11. The light sensor according to claim 1 or claim 2, wherein the SiGe is a polycrystalline material.

12. The optical sensor according to claim 1 or claim 2, wherein at least one of the first superimposed portion of the plurality of first material layers overlapping with the light-absorbing film and the second superimposed portion of the plurality of second material layers overlapping with the light-absorbing film is composed of the first phononic structure.

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