Infrared light receiving element and optical density measuring device

Abstract

The present invention provides an optical element that enables a gas sensor with high tolerance to fluctuations while increasing the effective light-receiving or light-emitting surface area without increasing the chip size. [Solution] The optical element has an internal wiring section (30) that electrically connects a first contact electrode section (24) of one unit element and a second contact electrode section (25) of another unit element, and a second region (212), an active layer (22), and a second conductivity semiconductor layer (23) that constitute a mesa structure, and a pad electrode (40) that is arranged to cover a plurality of unit elements (20) and electrically connected to at least one of the first contact electrode section (24) and the second contact electrode section (25), and a first insulating section (50) that is arranged between the pad electrode (40) and the side surface of the mesa structure and the first region (211) of the first conductivity semiconductor layer (21), and the diameter of the circle that circumscribes the region in contact with the pad electrode and the connection section is 15% or more of the length of the short side of the substrate.

Description

Technical Field

[0001] The present invention relates to an optical element and an optical density measuring device.

Background Art

[0002] Generally, infrared rays in the long wavelength band with a wavelength of 2 μm or more are used in gas sensors due to the effect of infrared absorption by gases. In particular, in the region from a wavelength of 2.5 μm to a wavelength of 10 μm, there are many absorption bands specific to various gases, which is a wavelength band suitable for use in gas sensors (an example of an optical density measuring device). By utilizing the fact that the wavelength of infrared rays absorbed by such gases varies depending on the type of gas, a non-dispersive infrared absorption type optical density measuring device that measures the gas concentration by detecting the amount of absorption is known.

[0003] For example, in the optical density measuring device described in Patent Document 1, in a gas cell, light emitted from a light emitting unit is incident on a light receiving unit via a light guiding member. At this time, by introducing the measurement target gas into the gas cell, the concentration of the measurement target gas is detected according to the output signal of the light receiving unit.

[0004] At this time, the larger the amount of light reaching the light receiving surface of the light receiving unit from the light emitting unit, the larger the detection signal can be obtained, so the signal-to-noise ratio is improved, and the gas concentration can be detected with high precision. Thus, in an optical density measuring device, an integrated design of the light emitting unit, the light receiving unit, and the light guiding member that efficiently guides infrared rays from the light emitting unit to the light receiving unit without leakage is important.

[0005] In addition, in optical density measuring devices, thermal type elements such as lamps as light emitting elements, pyroelectric sensors as light receiving elements, and thermopiles have been used. In recent years, SMD (Surface Mount Device) type mid-infrared LEDs and photodiodes have been developed, mass-produced, and are increasingly being used, and the miniaturization of gas sensors has been progressing.

Prior Art Documents

Patent Documents

[0006] [Patent Document 1] Patent No. 6530652 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] In recent years, the use of LEDs as light-emitting elements and photodiodes as light-receiving elements has advanced. However, because it is necessary to provide pad electrodes within the semiconductor chip for connecting wiring to apply drive current or extract signals, the light-emitting and light-receiving surfaces have a rectangular shape with the corners of the pad electrode area missing. Furthermore, with the recent trend towards miniaturization of gas sensors, the size of optical elements has also decreased, and the ratio of the pad electrode area to the chip size of the optical element has increased. The region on the light-receiving surface in which sensitivity does not change with respect to positional changes in the image of light focused by the light-collecting part is the largest circle Cd that can be defined inside the light-receiving surface, as described later. Also, the size of the image created by the light-emitting surface projected onto the light-receiving surface is smaller than the size of the image created by the smallest circle Ce that can be defined including the light-emitting surface, as described later. For this reason, the image of circle Ce needs to be smaller than that of circle Cd in order to suppress characteristic variations due to thermal deformation and variations in element mounting during the production process. For this reason, the shape of the light-emitting and light-receiving surfaces is important, but the difficulty of optical path design is increasing along with the demand for miniaturization of chip size.

[0008] This invention has been made in view of these circumstances, and aims to provide an optical element that realizes a gas sensor with high tolerance to fluctuations while increasing the effective light-receiving surface or light-emitting surface without increasing the chip size. [Means for solving the problem]

[0009] An optical element according to one embodiment of the present invention is The system comprises a substrate, multiple unit elements, an internal wiring section, a pad electrode, and a first insulating section. The aforementioned plurality of unit elements are A first conductivity type semiconductor layer including a first region and a second region disposed on the substrate, An active layer disposed on a second region of the first conductive semiconductor layer, A second conductivity type semiconductor layer disposed on the active layer, A first contact electrode portion on the first region of the first conductivity type semiconductor layer, The second contact electrode portion is located on the second conductivity semiconductor layer, The internal wiring section electrically connects the first contact electrode portion of one of the unit elements and the second contact electrode portion of the other unit element. The second region, the active layer, and the second conductive semiconductor layer constitute a mesa structure. The pad electrode is arranged to cover a plurality of the unit elements and is electrically connected to at least one of the first contact electrode portion and the second contact electrode portion. The first insulating portion is disposed between the pad electrode and the side surface of the mesa structure and the first region of the first conductivity type semiconductor layer. The substrate further comprises a connection portion provided on the pad electrode for electrical connection to the outside, and electrically connected to the pad electrode, wherein the diameter of the circle circumscribing the region where the pad electrode and the connection portion are in contact is 15% or more of the length of the short side of the substrate.

[0010] An optical concentration measuring device according to one embodiment of the present invention is The optical element described above is a light-receiving element whose side of the substrate where the first conductive semiconductor layer is not arranged is the side on which the light incident surface is, Light-emitting element and The light-emitting element comprises a light-guiding section that guides the light emitted by the light-emitting element to the light-receiving element, The light guide section includes a light concentrating section, Based on the detection signal output from the light-receiving element, the concentration of the object to be measured interposed in the optical path formed by the light guide is detected.

[0011] An optical concentration measuring device according to one embodiment of the present invention is A light-receiving element, The above optical element is a light-emitting element having a light-emitting surface on the side of the substrate where the first-conductivity-type semiconductor layer is not disposed. And a light guide unit that guides the light emitted by the light-emitting element to the light-receiving element. The light guide unit includes a condensing unit. Based on the detection signal output from the light-receiving element, the concentration of the measurement object intervening in the optical path formed by the light guide unit is detected.

Advantages of the Invention

[0012] According to the present invention, it is possible to provide an optical element that realizes a gas sensor with high fluctuation resistance while increasing an effective light-receiving surface or light-emitting surface without increasing the chip size.

Brief Description of the Drawings

[0013] [Figure 1] FIG. 1 is a schematic configuration diagram (plan view) of an optical element according to the first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of the optical element of FIG. 1. [Figure 3] FIG. 3 is a schematic configuration diagram (plan view) showing an example of a conventional optical element. [Figure 4] FIG. 4 is a cross-sectional view of the conventional optical element of FIG. 3. [Figure 5] FIG. 5 is a cross-sectional view showing an optical element according to the second embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing an optical element according to the third embodiment. [Figure 7] FIG. 7 is a plan view showing an optical element according to the fourth embodiment. [Figure 8] FIG. 8 is a diagram showing the relationship between the light-receiving surface and the circle Cd. [Figure 9] FIG. 9 is a diagram showing the relationship between the light-emitting surface and the circle Ce. [Figure 10] FIG. 10 is a diagram showing the relationship between the light-receiving surface and the image of light formed by the circle Ce. [Figure 11] FIG. 11 is a diagram showing the relationship between the region of the pad electrode and the circle Cd. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings. In the following drawings, identical or similar parts are denoted by the same or similar reference numerals. However, the drawings are schematic. For example, the relationship between thickness and planar dimensions may differ from reality. Furthermore, the embodiments shown below are illustrative of devices for realizing the technical idea of ​​the present invention and do not specify the materials, shapes, structures, arrangements, etc. of the components. The technical idea of ​​the present invention can be modified in various ways within the technical scope defined by the claims described in the patent claims.

[0015] Figure 1 is a schematic diagram showing an optical element according to a first embodiment of the present invention. Figure 1 is an overhead view. Figure 2 is a cross-sectional view taken along line AA shown in Figure 1. The optical element comprises a substrate 10, a plurality of unit elements 20, an internal wiring section 30, a pad electrode 40, and a first insulating section 50. The unit element 20 has a first conductivity type semiconductor layer 21, an active layer 22, a second conductivity type semiconductor layer 23, a first contact electrode section 24, and a second contact electrode section 25. Here, the second region 212 of the first conductivity type semiconductor layer 21, the active layer 22, and the second conductivity type semiconductor layer 23 constitute a mesa structure. Here, as shown in Figure 2, a plurality of unit elements 20 are connected by the internal wiring section 30 and covered by the first insulating section 50, but the internal wiring section 30 and the first insulating section 50 are not shown in Figure 1.

[0016] The internal wiring section 30 electrically connects the first contact electrode section 24 of one unit element 20 to the second contact electrode section 25 of another unit element 20. Here, the unit element 20 is further provided with a second insulating section 60 so that the side surface of the mesa structure and the internal wiring section 30 do not directly make electrical contact.

[0017] The second contact electrode portion 25 and the pad electrode 40 are electrically connected via a through-hole 51 on the second contact electrode portion 25 of the first insulating portion 50. The pad electrode 40 is arranged on the first insulating portion 50 so as to cover a plurality of unit elements 20. The first insulating portion 50 is arranged between the pad electrode 40 and the side surface of the mesa structure and the first region 211 of the first conductivity type semiconductor layer 21. The pad electrode 40 in the example of Figure 2 corresponds to the second pad electrode 40B (connected to the second contact electrode portion 25) of the second embodiment described later. Here, the pad electrode 40 may correspond to the first pad electrode 40A (connected to the first contact electrode portion 24) of the second embodiment described later.

[0018] Furthermore, the optical element according to the first embodiment further includes a connection part 70 and a connection wiring 71 for electrically connecting to the outside of the optical element.

[0019] Furthermore, the diameter Ld of the circle circumscribing the region where the connection portion 70 and the pad electrode 40 are in contact is 15% or more of the length of the short side Ls of the substrate 10.

[0020] [substrate] The substrate 10 of this embodiment is not limited by doping with donor or acceptor impurities. However, from the viewpoint of enabling a plurality of independent unit elements 20 formed on the substrate 10 to be connected in series or in parallel, it is desirable that it be semi-insulating or that it be electrically isolated from the first conductivity type semiconductor layer 21.

[0021] When the optical element of this embodiment is a light-receiving element, the side of the substrate 10 on which the first conductivity type semiconductor layer 21 is not arranged does not have a pad electrode 40, so it is preferable to make this side the light incident surface. When the optical element of this embodiment is a light-emitting element, the side of the substrate 10 on which the first conductivity type semiconductor layer 21 is not arranged does not have a pad electrode 40, so it is preferable to make this side the light emission surface.

[0022] In this case, since light will be incident on or emitted from the substrate 10 side, it is necessary to use a material for the substrate 10 that has a larger band gap than the active layer 22. Examples of substrates 10 include, but are not limited to, GaAs, Si, InP, and InSb substrates.

[0023] [Mesa structure] The optical element of this embodiment comprises a first conductivity type semiconductor layer 21 including a first region 211 and a second region 212 disposed on a substrate 10, an active layer 22 disposed on the second region 212 of the first conductivity type semiconductor layer 21, and a second conductivity type semiconductor layer 23 disposed on the active layer 22. The second region 212, the active layer 22, and the second conductivity type semiconductor layer 23 constitute a mesa structure.

[0024] The mesa structure is not particularly limited as long as it includes a photodiode structure with a PN junction or a PIN junction. The first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 are opposite conductivity types. For example, if the first conductivity type semiconductor layer 21 is p-type, the second conductivity type semiconductor layer 23 is n-type. For example, if the first conductivity type semiconductor layer 21 is n-type, the second conductivity type semiconductor layer 23 is p-type. The materials for the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 include, but are not limited to, InSb, InAsSb, AlInSb, etc. Furthermore, the first conductivity type semiconductor layer 21 and the second conductivity type semiconductor layer 23 may be a laminated structure made of multiple materials.

[0025] The active layer 22 preferably contains In and Sb as constituent elements. Narrow bandgap semiconductors containing In and Sb are materials with very low resistance. Therefore, when used as an LED, many of the unit elements 20 described later are often used in series or in parallel to achieve appropriate driving voltage and current. Similarly, when used as a photodiode, many of the unit elements 20 described later are often used in series or in parallel to achieve a manageable resistance value when amplifying the output signal with an amplification circuit.

[0026] In this case, the pad electrodes 40 are arranged to cover a plurality of unit elements 20, as in the optical element of this embodiment.

[0027] [Contact electrodes] The optical element of this embodiment includes a first contact electrode portion 24 disposed on a first region 211 of a first conductivity type semiconductor layer 21 and a second contact electrode portion 25 disposed on a second conductivity type semiconductor layer 23. The constituent material of the contact electrode is preferably one with low contact resistance with the semiconductor layer and low electrical resistance. Specifically, examples include Ti, Ni, Pt, Cr, Al, Cu, and Au. Furthermore, the contact electrode may be composed of a laminate of multiple electrode materials.

[0028] [Unit element] The optical element of this embodiment comprises a plurality of unit elements 20, each having a first conductivity type semiconductor layer 21, an active layer 22, a second conductivity type semiconductor layer 23, a first contact electrode portion 24, and a second contact electrode portion 25.

[0029] Furthermore, multiple unit elements 20 may be electrically connected in series or parallel. Multiple unit elements 20 are arranged in two dimensions on the substrate 10. The polygonal shape with the smallest area that encompasses all of the multiple unit elements 20 in a plan view is the same shape as the substrate 10 or a shape with one corner missing.

[0030] [Internal wiring section] The optical element of this embodiment includes an internal wiring section 30 that electrically connects a first contact electrode section 24 of one unit element 20 to a second contact electrode section 25 of another unit element 20. Multiple unit elements 20 are electrically connected in series by the internal wiring section 30. Furthermore, there may be multiple unit elements 20 electrically connected in parallel by wiring different from that of the internal wiring section 30. The constituent material of the internal wiring section 30 is preferably one with low electrical resistance. Specifically, examples include Ti, Ni, Pt, Cr, Al, Cu, Au, etc., and it may be formed together with the contact electrodes.

[0031] [Second insulation section] The unit element 20 of the optical element in this embodiment may further include a second insulating portion 60 so that the side surface of the mesa structure and the internal wiring portion 30 are not directly electrically connected. The second insulating portion 60 is disposed between the mesa structure, the first region 211 of the first conductive semiconductor layer 21, and the internal wiring portion 30. Examples of constituent materials for the second insulating portion 60 include, but are not limited to, silicon nitride, silicon oxide, and aluminum oxide. The second insulating portion 60 may be composed of a laminate of multiple materials.

[0032] [Light receiving surface] In this embodiment, when the optical element is a light-receiving element, the region where the light-receiving element receives light is called the light-receiving surface. More specifically, the light-receiving surface is on the substrate 10 and, in an overhead view of the substrate 10 from a distance perpendicular to the substrate 10, is the polygon with the smallest area that encompasses all the unit elements 20. Light emitted from the light-emitting surface, which will be described later, is focused onto the light-receiving surface by the light-collecting section, and the shape of the light-emitting surface is formed on the light-receiving surface as a light image Im. As shown in Figure 8, the largest virtual circle that can be defined inside the light-receiving surface Sr is referred to as circle Cd below. In order for the sensitivity of the light-receiving surface Sr to not fluctuate with respect to positional fluctuations of the light image Im caused by thermal deformation and variations in element mounting during the production process, the light image Im must be smaller than the shortest length of the diameter of the light-receiving surface Sr (where the diameter is the length of the line segment between two points on the outer perimeter of the figure that is perpendicular to the outer perimeter of the figure), which is equivalent to the light image Im being within circle Cd. In other words, to design a gas sensor with high tolerance to fluctuations, the optical image Im should be contained within a circle Cd, and the larger the size of the circle Cd, the more tolerance to fluctuations the gas sensor can be realized. Such a gas sensor simplifies optical path design. Here, the shape of the optical image Im in Figure 8 is an example and does not represent the shape of the optical image when using the optical elements of this embodiment.

[0033] [Emitting surface] In this embodiment, when the optical element is a light-emitting element, the region from which the light-emitting element emits light is called the light-emitting surface. More specifically, the light-emitting surface is on the substrate 10 and, in an overhead view of the substrate 10 from a distance perpendicular to the substrate 10, is the polygon with the smallest area that encompasses all the unit elements 20. Also, as shown in Figure 9, the smallest virtual circle that can be defined including the light-emitting surface Se is hereafter referred to as circle Ce. The size of the image of light focused by the light-gathering portion formed by the light-emitting surface Se, which is projected onto the light-receiving surface Sr, is generally smaller than the image of light formed by the two furthest points on the light-emitting surface Se (i.e., the two endpoints that define the largest diameter), and therefore smaller than the image formed by the light-emitting region in the shape of circle Ce. For this reason, in order to design the device so that the sensitivity does not change with respect to positional changes, as shown in Figure 10, the image Im of light formed by the light-emitting region in the shape of circle Ce on the light-receiving surface Sr should be contained within circle Cd. In this case, the larger the area of ​​the light-emitting surface Se, the greater the amount of light the light-emitting element can obtain. Therefore, the larger the area of ​​the light-emitting surface Se is relative to the circle Ce, the more stable the gas sensor with greater tolerance to fluctuations can be realized. Such a gas sensor simplifies optical path design. Here, in a rectangular substrate 10, the area of ​​the light-emitting surface Se is maximized when it is a rectangle tangent to the circle Ce. Note that the shape of the light-emitting surface Se in Figure 9 is an example and does not represent the shape of the light-emitting surface Se when using the optical element of this embodiment.

[0034] [First insulation section] As described above, the optical element of this embodiment comprises a pad electrode 40 and a first insulating portion 50 disposed between the side surface of the mesa structure and the first region 211 of the first conductivity type semiconductor layer 21. The first insulating portion 50 has the role of preventing electrical connection between the pad electrode 40 and the contact electrode portions (first contact electrode portion 24 and second contact electrode portion 25) and internal wiring portion 30 of the plurality of unit elements 20 that are not directly electrically connected to the pad electrode 40. For this reason, the first insulating portion 50 needs to be an insulating material. Examples include, but are not limited to, silicon nitride, silicon oxide, and aluminum oxide. The material of the first insulating portion 50 may be resin. Furthermore, the first insulating portion 50 may be composed of a laminate of multiple materials.

[0035] The first insulating layer 50 does not necessarily need to be formed to be thicker than the mesa structure, as shown in Figure 1. The first insulating layer 50 may be an insulating layer formed to a uniform thickness, for example, as long as it has the function of insulating the pad electrode 40 from the contact electrode portion and internal wiring portion 30 of the plurality of unit elements 20 that are not directly electrically connected to the pad electrode 40.

[0036] [Pad electrodes] The optical element of this embodiment includes a pad electrode 40 that is electrically connected to at least one of the first contact electrode portion 24 and the second contact electrode portion 25. The pad electrode 40 is arranged to cover a plurality of unit elements 20. The pad electrode 40 is electrically connected to the outside via a connection portion 70. For example, the connection portion 70 and the connecting wiring 71 can be wire-bonded. Alternatively, the connection portion 70 can be flip-chip bonded using a conductive adhesive or Au bump.

[0037] The pad electrodes do not need to completely cover two or more unit elements 20. It is sufficient that the size of the pad electrodes when viewed from above is larger than the size of the unit elements 20, and that they are arranged to cover at least 50% of the area of ​​at least two or more unit elements 20. It is more preferable that the pad electrodes are arranged to cover at least 80% of the area of ​​two or more unit elements 20.

[0038] Furthermore, the pad electrode 40 has an uneven shape that reflects the shape of the mesa structure. Specifically, the part of the pad electrode 40 that overlaps with the mesa structure when viewed from above is a convex part, and the part between the mesa structures when viewed from above is a concave part. In addition, the connection part 70 that is connected to the pad electrode 40 also has an uneven shape. Therefore, the bonding area between the pad electrode 40 and the connection part 70 is increased, so the connection part becomes stronger against lateral forces and improved reliability can be expected. Here, the maximum height difference of the pad electrode 40 is preferably 0.5 μm or more and 8 μm or less. More preferably it is 1 μm or more and 6 μm or less.

[0039] The pad electrode 40 is preferably made of a material with low electrical resistance, and specifically, like the contact electrode, examples include Ti, Ni, Pt, Cr, Al, Cu, and Au. The pad electrode 40 may be made of a different material than the contact electrode.

[0040] [Through-hole] In this embodiment, the optical element has a contact electrode portion and a pad electrode 40 that are electrically connected via a through-hole 51 on the contact electrode portion of the first insulating portion 50. The through-hole 51 is formed to penetrate the first insulating portion 50. Furthermore, it is not necessarily required that the inside of the through-hole 51 be filled with metal as shown in Figure 1; metal may be formed on the inner surface of the through-hole 51 as long as the pad electrode 40 and the contact electrode are electrically connected.

[0041] [Connection part] The optical element of this embodiment further includes a connection portion 70 for electrically connecting to the outside. Specific examples of the connection portion 70 include metal and conductive adhesive. It is conceivable to electrically connect to the outside by wire bonding the connection portion 70 and the connecting wiring 71 onto the pad electrode 40. Alternatively, the connection portion 70 could be flip-chip bonded using a conductive adhesive or Au bump.

[0042] The connection portion 70 is bonded to the pad electrode 40. The diameter Ld of the circle circumscribing the region where the connection portion 70 and the pad electrode 40 are in contact must be sufficiently large relative to the size of the substrate 10, because if it is too small, the concentration of applied impact force during the bonding process will cause damage to the substrate 10. It is desirable that the diameter Ld be 15% or more of the length of the short side Ls of the substrate 10. It is more preferable that the diameter Ld be 20% or more of the length of the short side Ls. Here, from the viewpoint of insulation from other components, it is preferable that the diameter Ld be 90% or less of the short side Ls, and more preferable that it be 80% or less.

[0043] [Light guide section] The light guide is a component that guides the light emitted by the light-emitting element to the light-receiving element, and is part of the optical system of an optical density measuring device. The light guide includes a light-collecting section that focuses the light emitted from the light-emitting surface of the light-emitting element onto the light-receiving surface of the light-receiving element. Specific examples of the light-collecting section include elliptical mirrors, concave mirrors, lenses, and diffraction gratings. Furthermore, the light guide may also include planar mirrors, convex mirrors, etc.

[0044] [Optical concentration measuring device] The optical density measuring device comprises a light-emitting element, a photodetector that receives light emitted from the light-emitting element and converts it into a detection signal, and a light guide that guides the light emitted from the light-emitting element to the photodetector. Furthermore, the light guide includes a light-collecting section. The detection signal is an electrical signal that changes according to the amount of light received. Based on the detection signal output from the photodetector, the optical density measuring device detects the concentration of the object to be measured interposed in the optical path formed by the light guide. The optical density measuring device may include a control IC that drives the light-emitting element and performs analog-to-digital conversion of the output signal from the photodetector. The optical density measuring device may include a substrate that holds at least one of the light-emitting element, the photodetector, and the control IC. In addition, if the object to be measured is a gas (hereinafter referred to as "detection gas"), i.e., if it is a gas sensor, the optical density measuring device may include a gas cell that contains the detection gas. A portion of the light emitted from the light-emitting element is absorbed by the detection gas, and the detection signal of the photodetector fluctuates in accordance with the ambient concentration of the detection gas, thereby measuring the concentration of the detection gas.

[0045] Next, the details of the optical elements of this embodiment, including their effects, will be explained with reference to the drawings.

[0046] Figures 3 and 4 show an example of a conventional optical element (Comparative Example 1). Figure 3 is an overhead view. Figure 4 is a cross-sectional view along line AA shown in Figure 3. Comparative Example 1 comprises a substrate 10, a plurality of unit elements 20, an internal wiring section 30, a pad electrode 40, and a first insulating section 50. The plurality of unit elements 20 have a first conductivity type semiconductor layer 21 including a first region 211 and a second region 212 arranged on the substrate 10, an active layer 22 arranged on the second region 212 of the first conductivity type semiconductor layer 21, a second conductivity type semiconductor layer 23 arranged on the active layer 22, a first contact electrode section 24 on the first region 211 of the first conductivity type semiconductor layer 21, and a second contact electrode section 25 of the second conductivity type semiconductor layer 23. The internal wiring section 30 electrically connects the first contact electrode section 24 of one unit element 20 to the second contact electrode section 25 of another unit element 20. The pad electrode 40 is electrically connected to the second contact electrode section 25. Similar to Figure 1, the internal wiring section 30 and the first insulating section 50 are omitted from the illustration in Figure 3.

[0047] Furthermore, the pad electrode 40 is adjacent to or close to the flat portion of the substrate 10, and there is no mesa structure formed between the pad electrode 40 and the substrate 10, nor is there a unit element 20. Conventional optical elements further include a connection portion 70 for electrical connection to the outside. The connection portion 70 is bonded to the pad electrode 40.

[0048] The pad electrodes 40 placed on the substrate 10 are formed larger than the diameter Ld of the circle circumscribing the region where the connection portion 70 and the pad electrodes 40 are in contact, taking into account the misalignment of wire bonding or flip-chip bonding. In conventional optical elements, since the unit element 20 cannot be placed in the region where the pad electrodes 40 are formed, the light-emitting surface Se or light-receiving surface Sr of the optical element becomes a shape in which the corner corresponding to the region of the pad electrodes 40 is missing from its rectangular shape. Thus, in conventional optical elements, the light-receiving surface Sr and the light-emitting surface Se are not rectangular but irregular in shape. As a result, the size of the circle Cd becomes small, and the light-emitting area within the circle Ce becomes small, resulting in a smaller usable size for the optical element. In other words, as a consequence, it has been difficult to design a gas sensor with high tolerance for fluctuations. Here, as shown in Figure 11, in an optical element having at least two or more pad electrodes 40, when the length of one side of the pad electrode 40 is less than 14.7% of the length of the short side Ls of the substrate 10, its inscribed circle is already maximized, so even if the portion missing from the rectangular shape (the area of ​​the pad electrode 40) is reduced, the inscribed circle cannot be made larger. However, when the length of one side of the pad electrode 40 is 14.7% or more of the length of the short side Ls of the substrate 10, the inscribed circle can be made larger by reducing the portion missing from the rectangular shape (the area of ​​the pad electrode 40). In other words, the circle Cd with respect to the light-receiving surface Sr becomes larger. Also, the circle Se with respect to the light-emitting surface becomes larger. In conventional optical elements, large pad electrodes 40 are used considering the misalignment of wire bonding or flip-chip bonding and the concentration of applied impact force, making it difficult to keep the length less than 14.7% of the length of the short side Ls of the substrate 10. The optical element according to this embodiment, with the above configuration, can reduce the portion missing from the rectangular shape of the light-receiving surface Sr and the light-emitting surface Se (the area of ​​the pad electrode 40). In other words, since a unit element 20 can also be placed below the pad electrode 40, the portion missing from the rectangular shape can be substantially eliminated (or at least reduced) regardless of the size of the pad electrode 40.Therefore, the optical element according to this embodiment can increase the effective light-receiving or light-emitting surface without increasing the chip size, thereby realizing a gas sensor with high tolerance for fluctuations.

[0049] Figure 5 shows a cross-sectional view representing an optical element according to the second embodiment. The second embodiment has a first pad electrode 40A and a second pad electrode 40B. The first contact electrode portion 24 and the first pad electrode 40A are electrically connected via a through-hole 51 on the first contact electrode portion 24 of the first insulating portion 50, and the second contact electrode portion 25 and the second pad electrode 40B are electrically connected via a through-hole 51 on the second contact electrode portion 25 of the first insulating portion 50. The first pad electrode 40A and the second pad electrode 40B are electrically connected to one or more internal wiring portions 30 and a unit element 20.

[0050] By adopting this second embodiment, unit elements 20 can be arranged beneath the pad electrode 40, similar to Figure 1. As a result, the areas of the light-receiving surface Sr and the light-emitting surface Se can be used efficiently without waste, and the size of the circle Cd increases. In addition, the light-emitting area within the circle Ce increases, making it possible to increase the size that can be effectively used as an optical element. Consequently, a gas sensor with high tolerance to fluctuations can be realized. Furthermore, the optical path design becomes easier in this case.

[0051] Figure 6 shows a cross-sectional view representing an optical element according to the third embodiment. While the optical elements according to the first and second embodiments have a structure that uses through-holes 51 for the electrical connection of the pad electrodes 40 (through-hole connection type), the optical element according to the third embodiment has a structure in which the electrical connection of the pad electrodes 40 is made at the end of the first insulating portion 50 (insulating portion end connection type). The optical element according to the third embodiment has a first pad electrode 40A and a second pad electrode 40B. The first contact electrode portion 24 and the first pad electrode 40A are arranged on the substrate 10 and are electrically connected via a first electrode region 31 which is electrically connected to the first contact electrode portion 24 and a second electrode region 32 which is arranged to cover the end 52 of the first insulating portion 50 and is electrically connected to the first pad electrode 40A. The second contact electrode portion 25 and the second pad electrode 40B are arranged on the substrate 10 and are electrically connected via a third electrode region 33 which is electrically connected to the second contact electrode portion 25 and a fourth electrode region 34 which is arranged to cover the end portion 52 of the first insulating portion 50 and is electrically connected to the second pad electrode 40B.

[0052] The substrate 10 and the first electrode region 31 and the third electrode region 33 do not need to be in direct contact; a second insulating portion 60 made of an insulating material may be formed between them.

[0053] Since the connection portion 70 is not bonded to the first electrode region 31 and the third electrode region 33, they can be formed smaller than the pad electrode 40 of Comparative Example 1. Therefore, by arranging the unit elements 20 within the substrate 10, the light-emitting surface Se or the light-receiving surface Sr can be utilized more effectively without increasing the chip size.

[0054] Figure 7 shows an overhead view of the optical element according to the fourth embodiment. Similar to Figure 1, the internal wiring section 30 and the first insulating section 50 are omitted from the illustration in Figure 7. In the fourth embodiment, the first pad electrode 40A, which is electrically connected to the first contact electrode section 24, is arranged to cover all the unit elements 20. Similarly, the second pad electrode 40B, which is electrically connected to the second contact electrode section 25, may be arranged to cover all the unit elements 20. Arranging to cover all the unit elements 20 means that, in an overhead view of the substrate 10 from a distance perpendicular to the substrate 10, all the unit elements 20 are included.

[0055] To prevent parasitic capacitance from occurring between the close contact electrode and the pad electrode 40, which would affect the operation of the optical element, it is desirable to cover more than 50% of the multiple unit elements 20 with pad electrodes 40 that are at the same potential. It is more preferable to cover more than 80% of the multiple unit elements 20 with pad electrodes 40 that are at the same potential. It is even more preferable that all unit elements 20 are covered. [Explanation of Symbols]

[0056] 10 circuit boards 20 unit element 21 First Conductivity Semiconductor Layer 22 Active layer 23 Second Conductivity Semiconductor Layer 24 First contact electrode section 25 Second contact electrode section 30 Internal wiring section 31 1st electrode area 32 2nd electrode area 33 Third electrode area 34 4th electrode area 40 pad electrodes 40A First Pad Electrode 40B Second Pad Electrode 50 First insulating section 51 Through Holes 52 End of the first insulating section 60 Second insulating section 70 Connection part 71 Connection Wiring 211 First Domain 212 Second Field

Claims

1. The system comprises a substrate, multiple unit elements, an internal wiring section, a pad electrode, and a first insulating section. The aforementioned plurality of unit elements are A first conductivity type semiconductor layer including a first region and a second region disposed on the substrate, An active layer disposed on a second region of the first conductive semiconductor layer, A second conductivity type semiconductor layer disposed on the active layer, A first contact electrode portion on the first region of the first conductivity type semiconductor layer, The second contact electrode portion is located on the second conductivity semiconductor layer, The internal wiring section electrically connects the first contact electrode portion of one of the unit elements and the second contact electrode portion of the other unit element. The second region, the active layer, and the second conductive semiconductor layer constitute a mesa structure. The pad electrode is arranged to cover a plurality of the unit elements and is electrically connected to at least one of the first contact electrode portion and the second contact electrode portion. The first insulating portion is disposed between the pad electrode and the side surface of the mesa structure and the first region of the first conductivity type semiconductor layer. The substrate further comprises a connection portion provided on the pad electrode for electrical connection to the outside, and electrically connected to the pad electrode, wherein the diameter of the circle circumscribing the region where the pad electrode and the connection portion are in contact is 15% or more of the length of the short side of the substrate. The pad electrode has an uneven shape that reflects the shape of the unit element, and is arranged to completely cover a plurality of the unit elements. An infrared light receiving element in which the maximum height difference of the pad electrodes is 1 μm or more.

2. The pad electrode is a first pad electrode that connects to the first contact electrode portion. The infrared light receiving element according to claim 1, wherein the first contact electrode portion and the first pad electrode are electrically connected via a through-hole on the first contact electrode portion of the first insulating portion.

3. The pad electrode is a second pad electrode that connects to the second contact electrode portion. The infrared light receiving element according to claim 1, wherein the second contact electrode portion and the second pad electrode are electrically connected via a through-hole on the second contact electrode portion of the first insulating portion.

4. The pad electrode comprises a first pad electrode connected to the first contact electrode portion and a second pad electrode connected to the second contact electrode portion. The first contact electrode portion and the first pad electrode are electrically connected via a through-hole on the first contact electrode portion of the first insulating portion. The second contact electrode portion and the second pad electrode are electrically connected via a through-hole on the second contact electrode portion of the first insulating portion. The infrared light receiving element according to claim 1, wherein the first pad electrode and the second pad electrode are electrically connected to one or more internal wiring sections via a unit element.

5. The pad electrode is a first pad electrode that is electrically connected to the first contact electrode portion. The infrared light receiving element according to claim 1, wherein the first contact electrode portion and the first pad electrode are electrically connected via a first electrode region arranged on the substrate and electrically connected to the first contact electrode portion, and a second electrode region arranged to cover the end of the first insulating portion and electrically connected to the first pad electrode.

6. The pad electrode is a second pad electrode that is electrically connected to the second contact electrode portion. The infrared light receiving element according to claim 1, wherein the second contact electrode portion and the second pad electrode are electrically connected via a third electrode region disposed on the substrate and electrically connected to the second contact electrode portion, and a fourth electrode region disposed to cover the end of the first insulating portion and electrically connected to the second pad electrode.

7. The pad electrode comprises a first pad electrode electrically connected to the first contact electrode portion and a second pad electrode electrically connected to the second contact electrode portion. The first contact electrode portion and the first pad electrode are electrically connected via a first electrode region, which is arranged on the substrate and electrically connected to the first contact electrode portion, and a second electrode region, which is arranged to cover the end of the first insulating portion and electrically connected to the first pad electrode. The infrared light receiving element according to claim 1, wherein the second contact electrode portion and the second pad electrode are electrically connected via a third electrode region disposed on the substrate and electrically connected to the second contact electrode portion, and a fourth electrode region disposed to cover the end of the first insulating portion and electrically connected to the second pad electrode.

8. The infrared light receiving element according to any one of claims 1 to 7, wherein the pad electrodes are arranged to cover at least 50% of the area of ​​at least two of the unit elements.

9. The infrared light receiving element according to any one of claims 1, 2, and 5, wherein the pad electrode is a first pad electrode electrically connected to the first contact electrode portion, and is arranged to cover 50% or more of the plurality of unit elements.

10. The infrared light receiving element according to any one of claims 1, 3, and 6, wherein the pad electrode is a second pad electrode that is electrically connected to the second contact electrode portion and is arranged to cover 50% or more of the plurality of unit elements.

11. An infrared light receiving element according to any one of claims 1 to 10, wherein the unit element is smaller than the area in contact between the pad electrode and the connection portion when viewed from above.

12. The infrared light receiving element according to any one of claims 1 to 11, wherein the active layer comprises In and Sb as constituent elements.

13. The infrared light receiving element according to any one of claims 1 to 12, wherein the side of the substrate on which the first conductive semiconductor layer is not disposed is the light incident surface.

14. The infrared light receiving element according to claim 13, Light-emitting element and The light-emitting element comprises a light-guiding section that guides the light emitted by the light-emitting element to the infrared light-receiving element, The light guide section includes a light concentrating section, An optical density measuring device that detects the density of an object to be measured interposed in the optical path formed by the light guide based on a detection signal output from the infrared light receiving element.

15. The infrared light receiving element according to claim 9, wherein the pad electrode is a first pad electrode that is electrically connected to the first contact electrode portion, and is arranged to cover all of the plurality of unit elements.

16. The infrared light receiving element according to claim 10, wherein the pad electrode is a second pad electrode that is electrically connected to the second contact electrode portion, and is arranged to cover all of the plurality of unit elements.

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