Optical sensor and method for manufacturing optical sensor

Abstract

With a view to improving the sensitivity of an optical sensor, an optical sensor according to one embodiment of the present invention comprises: a substrate that has first wiring and second wiring; a first electrode that is electrically connected to the first wiring; a second electrode that is electrically connected to the second wiring; a light-receiving layer that receives light and that is provided at a position in a manner sandwiching the first electrode and the second electrode between the substrate and the light-receiving layer; and an electric current varying layer that is positioned between the light-receiving layer and the substrate, and that is electrically connected to the first electrode and the second electrode to allow electric current to flow therethrough, the electric current being varied in association with the light received on the light-receiving layer.

Description

Optical sensor and method for manufacturing the optical sensor

[0001] The present invention relates to an optical sensor and a method for manufacturing an optical sensor.

[0002] Known conventional optical sensors include infrared sensors used in infrared cameras capable of capturing images with long-wavelength infrared radiation, for example, wavelengths of 8 μm to 15 μm. In recent years, there has been a demand for visualization of the distribution and emissions of gas species such as propane (C3H8) and methane (CH4). In particular, methane is a greenhouse gas with an absorption wavelength of 7 μm to 8 μm, so there is a demand for infrared cameras capable of capturing images with wavelengths in the 6 μm to 20 μm wavelength range, which includes the long-wavelength infrared radiation range.

[0003] Known conventional optical sensor technologies include bolometer-based and thermopile-based methods. For example, Patent Document 1 discloses a bolometer-based thermal infrared detector. Furthermore, Patent Document 2 discloses an electromagnetic wave detector that detects electromagnetic waves incident on a graphene layer by photoelectric conversion. In the electromagnetic wave detector of Patent Document 2, a gate voltage corresponding to a change in the polarization value of a ferroelectric layer due to electromagnetic waves is applied to the graphene layer. Therefore, the electromagnetic wave detector of Patent Document 2 has higher sensitivity than the infrared detector of Patent Document 1.

[0004] Patent No. 3921320 Patent No. 6297233

[0005] However, in the electromagnetic wave detector described in Patent Document 2, it is not possible to provide a ferroelectric layer that extends as widely as the graphene layer on the electromagnetic wave incident side, and the sensitivity is reduced due to reflection or absorption of the electromagnetic wave by the graphene layer. In view of the above circumstances, an object of the present invention is to improve the sensitivity of an optical sensor.

[0006] In order to solve the above problem, an optical sensor according to one embodiment of the present invention comprises a substrate having first wiring and second wiring, a first electrode electrically connected to the first wiring, a second electrode electrically connected to the second wiring, a light-receiving layer disposed between the substrate and the first electrode and the second electrode to receive light, and a current-changing layer disposed between the light-receiving layer and the substrate, electrically connected to the first electrode and the second electrode, through which a current flows and which changes in response to light received by the light-receiving layer.

[0007] In an optical sensor according to one aspect of the present invention, the substrate has an insulating layer having an internal conductive pattern including the first wiring and the second wiring, and the readout circuit receives the output signal of the current in the current change layer via the first wiring and the second wiring, amplifies the output signal, and outputs it to an external circuit.

[0008] According to an optical sensor of an aspect of the present invention, the light receiving layer is a pyroelectric layer. According to an optical sensor of an aspect of the present invention, the light receiving layer is a layer of a semiconductor compound that performs photoelectric conversion. According to an optical sensor of an aspect of the present invention, the current change layer is a graphene layer. According to an optical sensor of an aspect of the present invention, the optical sensor further includes a first support structure that supports the first electrode at one end extending away from the substrate and electrically connects the first electrode to the first wiring, and a second support structure that supports the second electrode at one end extending away from the substrate and electrically connects the second electrode to the second wiring.

[0009] In an optical sensor according to one aspect of the present invention, the light receiving layer has a first main surface located on the current change layer side and a second main surface located opposite the first main surface, and further includes a third electrode located on the second main surface side of the light receiving layer and electrically connected to a third wiring of the substrate. In an optical sensor according to one aspect of the present invention, the third electrode is provided only on a portion of the area of ​​the second main surface. In an optical sensor according to one aspect of the present invention, the third electrode is a silicon electrode. In an optical sensor according to one aspect of the present invention, the third electrode is electrically connected to the third wiring via a conductor penetrating the light receiving layer.

[0010] A method for manufacturing an optical sensor according to one aspect of the present invention is a method for manufacturing an optical sensor comprising: a first substrate having first wiring and second wiring; a first electrode electrically connected to the first wiring; a second electrode electrically connected to the second wiring; a light-receiving layer that receives light; and a current change layer that is electrically connected to the first electrode and the second electrode, through which a current flows and through which the current changes in response to light received by the light-receiving layer, the method comprising the steps of: forming the light-receiving layer on the second substrate, either directly or indirectly via another layer; forming the current change layer on the light-receiving layer, either directly or indirectly via another layer; forming the first electrode and the second electrode at locations sandwiching the current change layer; and opposing the second substrate, on which the light-receiving layer and the current change layer are formed, to the first substrate with the current change layer facing the first substrate, and electrically connecting the first electrode and the second electrode to the first wiring and the second wiring.

[0011] According to one aspect of the present invention, a method for manufacturing an optical sensor further includes a step of separating the light receiving layer from the second substrate after connecting the first electrode and the second electrode to the first wiring and the second wiring.

[0012] According to the present invention, the sensitivity of the optical sensor can be improved.

[0013] FIG. 1 is a cross-sectional view showing an optical sensor according to a first embodiment of the present invention. FIG. 2 is a view showing a method for manufacturing an optical sensor according to the first embodiment. FIG. 3 is a view showing a first step for creating a substrate. FIG. 4 is a view showing a second step for creating a substrate. FIG. 5 is a view showing a fifth step for creating a substrate. FIG. 6 is a view showing a first step for creating a FET section. FIG. 7 is a view showing a first step for creating a FET section. FIG. 8 is a view showing a second step for creating a FET section. FIG. 9 is a view showing a second step for creating a FET section. FIG. 10 is a view showing a third step for creating a FET section. FIG. 11 is a view showing a third step for creating a FET section. FIG. 12 is a view showing a step for bonding a substrate and a FET section. FIG. 13 is a cross-sectional view showing an optical sensor according to a second embodiment. FIG. 14 is a perspective view showing an optical sensor according to the second embodiment. FIG. 15 is a view showing a method for manufacturing an optical sensor according to the second embodiment. FIG. 16 is a view showing a first step for creating a supporting leg substrate. FIG. 17 is a view showing a second step for creating a supporting leg substrate. FIG. 18 is a view showing a third step for creating a supporting leg substrate. FIG. 19 is a view showing a fourth step for creating a supporting leg substrate. FIG. 20 is a view showing a sixth step for creating a supporting leg substrate. 10 is a diagram showing a seventh step of creating a support leg substrate; FIG. 11 is a diagram showing an eighth step of creating a support leg substrate; FIG. 12 is a diagram showing a step of bonding a support leg substrate and a FET section; FIG. 13 is a diagram showing a peeling step in the second embodiment; FIG. 14 is an upper perspective view showing an optical sensor of the third embodiment; FIG. 15 is a bottom perspective view showing an optical sensor of the third embodiment; FIG. 16 is a graph explaining the action of gate voltage; FIG. 17 is a cross-sectional view showing an optical sensor of the fourth embodiment; FIG. 18 is a diagram showing a manufacturing method of the optical sensor of the fourth embodiment; FIG. 19 is a cross-sectional view showing an optical sensor of the fifth embodiment; FIG. 20 is a cross-sectional view showing an optical sensor of the sixth embodiment; FIG. 21 is a perspective view showing an optical sensor of the sixth embodiment; FIG. 22 is an upper perspective view showing an optical sensor of the seventh embodiment; FIG. 23 is a bottom perspective view showing an optical sensor of the seventh embodiment.

[0014] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the present invention, and not all of the combinations of features described in the embodiments are necessarily essential to the configuration of the present invention. The configuration of the embodiments may be modified or changed as appropriate depending on the specifications of the device to which the present invention is applied and various conditions (such as usage conditions and usage environment).

[0015] The technical scope of the present invention is defined by the claims and is not limited by the individual embodiments described below. The drawings used in the following description may differ in scale and shape from the actual structure to make each configuration easier to understand. The correspondence between the drawings may also differ in some places to simplify the description. Components shown in previously described drawings may be referenced as appropriate in the description of subsequent drawings.

[0016] <First Embodiment> Fig. 1 is a cross-sectional view showing an optical sensor according to a first embodiment of the present invention. The optical sensor 100 includes a substrate 110 and a FET (Field Effect Transistor) section 120. In the case of an image sensor for an infrared camera, a single substrate 110 is provided with a plurality of FET sections 120 arranged in an array, but for the sake of convenience of explanation, Fig. 1 shows an optical sensor 100 including one substrate 110 and one FET section 120.

[0017] The substrate 110 includes a ROIC (Read Out Integrated Circuit) substrate 111, an insulating layer 113, and a wiring pattern 114. The FET section 120 includes a pyroelectric layer 121, a graphene layer 122, a contact electrode 123, and a protective layer 124. The ROIC substrate 111 includes an internal readout circuit (ROIC) 112 that receives signals output by the FET sections 120 and reads out detection signals. The function of the readout circuit 112 is to collect current signals from the multiple FET sections 120 and read out the processed detection signals from an output terminal. The readout circuit 112, for example, amplifies the signals output by the FET sections 120 and outputs them to an external circuit as detection signals. The readout circuit 112 may also have signal processing functions such as analog-to-digital conversion.

[0018] The ROIC substrate 111 has a rectangular shape in a plan view and has a certain thickness. For example, the ROIC substrate 111 includes a semiconductor substrate such as silicon, and an insulating layer is provided on the main surface of the semiconductor substrate. A conductive pattern serving as a signal line or ground is included inside the insulating layer. The conductive pattern includes two or more conductive portions serving as signal lines. Elements such as MOS transistors and diodes are configured on the semiconductor substrate or insulating layer. These elements are connected by a conductive pattern serving as a signal line to form the readout circuit 112.

[0019] The readout circuit 112 has two or more terminals 112a for connection to the FET units 120. The readout circuit 112 may have another terminal 112a for applying a voltage to a gate electrode, which will be described later. These multiple terminals 112a are connected to two or more conductive units that serve as signal lines. These multiple terminals 112a are provided to correspond to the multiple FET units 120, respectively. The readout circuit 112 also includes multiple terminals (not shown) for outputting detection signals to an external circuit.

[0020] A plurality of wiring patterns 114 are provided, each connected to a terminal 112a. The wiring patterns 114 are electrically connected to a conductive pattern that serves as a signal line of the readout circuit 112 via the terminal 112a. Specifically, the wiring patterns 114 are preferably made of, for example, Ti or TiN because of their low thermal conductivity, but may be made of a conductive material such as Au, Ag, or Cu. The wiring patterns 114 electrically connect the FET section 120 to the readout circuit 112 of the ROIC substrate 111. The insulating layer 113 is provided on, for example, the entire main surface of the ROIC substrate 111. In part of the insulating layer 113, the conductive pattern or terminal 112a of the readout circuit 112 is exposed and connected to the wiring patterns 114. The insulating layer 113 is made of, for example, SiO ２ This layer protects the read circuit 112 .

[0021] The pyroelectric layer 121 corresponds to an example of a light-receiving layer in the present invention, and has a large light-receiving area, sandwiching a pair of contact electrodes 123 between the pyroelectric layer 121 and the ROIC substrate 111. The pair of contact electrodes 123 corresponds to an example of a first electrode and a second electrode in the present invention. The pyroelectric layer 121 is made of, for example, LiNbO ３ The layer is LiNbO ３ When the optical sensor 100 detects infrared rays or light of other wavelengths, the material of the pyroelectric layer 121 is LiNbO ３ Ferroelectric materials that can be used for the pyroelectric layer 121 include, for example, BaTiO ３ (barium titanate), LiTaO ３ (lithium tantalate), SrTiO ３ (strontium titanate), PZT (lead zirconate titanate), SBT (strontium tantalate bismuthate), BFO (bismuth ferrite), ZnO (zinc oxide), HfO ２ (hafnium oxide), etc.

[0022] The graphene layer 122 is an example of a two-dimensional material layer and an example of a current change layer according to the present invention. The two-dimensional material layer may be made of, in addition to graphene, transition metal dichalcogenide, black phosphorus, silicene, germanene, or the like. The graphene layer 122 is provided between a pair of contact electrodes 123, with one end of the graphene layer 122 connected to one of the contact electrodes 123 and the other end of the graphene layer 122 connected to the other contact electrode 123. The graphene layer 122 extends along the pyroelectric layer 121 and is located between the pyroelectric layer 121 and the ROIC substrate 111. An insulating layer made of, for example, SiN may be provided between the pyroelectric layer 121 and the graphene layer 122.

[0023] In the graphene layer 122, a current flows between the contact electrodes 123. When the pyroelectric layer 121 receives infrared light, a voltage is generated due to the pyroelectric effect, which causes a change in the current flowing between the contact electrodes 123. That is, the current flowing through the graphene layer 122 changes due to a polarization change caused by light reception in the pyroelectric layer 121. In other words, a FET is configured by the pair of the graphene layer 122 and the contact electrode 123 and the pyroelectric layer 121, and the polarization change in the pyroelectric layer 121 acts as a change in the gate voltage.

[0024] The current flowing through the graphene layer 122 is input as a signal to the readout circuit 112 via the contact electrode 123 and the wiring pattern 114. The readout circuit 112 performs signal processing such as amplification on this input signal and outputs it to an external circuit. The external circuit is provided, for example, inside the housing of the image sensor, receives the output from the readout circuit 112, and detects infrared rays in a determination unit having a signal processing function including a memory and a processor. Because the graphene layer 122 has high charge mobility, the sensitivity of the FET unit 120 and the optical sensor 100 in infrared detection, i.e., the temperature resolution, is higher than when a two-dimensional material layer other than graphene is used.

[0025] The piezoelectric material of the pyroelectric layer 121 can have a crystalline structure such as amorphous or single crystal, but using a pyroelectric layer 121 with good crystallinity such as single crystal improves the speed responsiveness of the FET section 120 and the optical sensor 100 in infrared detection. Furthermore, using a thin pyroelectric layer 121 also improves the speed responsiveness of the infrared detection. The infrared incident side of the pyroelectric layer 121 is on the opposite side from the ROIC substrate 111, and the graphene layer 122 is not located on the incident side. Therefore, the infrared rays are not reflected by the graphene layer 122, and the pyroelectric layer 121 with a large light-receiving area has high light utilization efficiency, improving the speed responsiveness of the FET section 120 and the optical sensor 100.

[0026] The contact electrode 123 is, for example, an Au electrode, and may have an underlayer of Ru or Ti. The contact electrode 123 is connected to the wiring pattern 114 of the substrate 110 and transmits a current signal to the readout circuit 112. The protective layer 124 covers the surface of the graphene layer 122 to protect it.

[0027] <Method of Manufacturing the Optical Sensor 100> Next, a method of manufacturing the optical sensor 100 will be described. FIG. 2 is a diagram showing a method of manufacturing the optical sensor 100 according to the first embodiment. In manufacturing the optical sensor 100, the substrate 110 and the FET section 120 are separately manufactured. That is, the substrate 110 is manufactured as a first wafer on which a wiring pattern is formed on an ROIC, through steps S101 to S105. Meanwhile, the FET section 120 is manufactured as a second wafer on which graphene, electrodes, and pyroelectric elements are formed, through steps S201 to S207. Each step in FIG. 2 will be described below with reference to a diagram showing each step. Note that, although a large number of elements are formed simultaneously and in parallel in an array on each wafer, the following description will focus on one element.

[0028] 3A, 3B, 3C, 4A, and 4B are diagrams showing the steps of fabricating the substrate 110. In step S101, as shown in FIG. 3A, an ROIC substrate 111 having a readout circuit 112 therein is prepared. A commercially available ROIC substrate 111 can be used. Next, in step S102, as shown in FIG. 3B, an insulating layer 113 is formed on the surface of the ROIC substrate 111. Then, in step S103, as shown in FIG. 3C, the insulating layer 113 is patterned to expose connection points 116 with the readout circuit 112.

[0029] In step S104, as shown in Fig. 4A, a wiring layer 117 made of, for example, a conductor is formed on the surface of the insulating layer 113. Then, in step S105, as shown in Fig. 4B, the wiring layer 117 is patterned to form a wiring pattern 114. In this way, the substrate 110 is obtained.

[0030] 5A, 5B, 5C, 6A, 6B, 6C, 7A, and 7B are diagrams showing the steps of forming the FET section 120. In step S201, as shown in FIG. 5A, a substrate 126 having a release layer 127 on its surface is prepared. The substrate 126 is, for example, a Si substrate, and the release layer 127 is, for example, a SiO ２ This is the layer.

[0031] In step S202, as shown in FIG. 5B, a ferroelectric material such as LiNbO ３ The pyroelectric layer 121 is formed by the above method. The pyroelectric layer 121 is formed by, for example, film formation by crystal growth or transfer. In particular, by using transfer, a thin pyroelectric layer 121 with good crystallinity can be obtained.

[0032] In step S203, as shown in Fig. 5C, graphene is transferred onto the surface of the pyroelectric layer 121 to form a graphene layer 122. When transferring graphene, the surface to be transferred needs to be highly smooth. The surface of a substrate 126 such as a Si substrate has high smoothness, and the substrate 126 is coated with SiO ２ and a release layer 127 such as LiNbO ３ The surface on which the pyroelectric layer 121 is formed is also a surface with sufficiently high smoothness. Therefore, the surface of the pyroelectric layer 121 is suitable for transferring graphene, and a high-quality graphene layer 122 is formed in step S203.

[0033] As a comparative example, consider a case where layers such as a pyroelectric layer 121 and a graphene layer 122 are sequentially stacked on an ROIC substrate 111, and an FET is formed by etching, without using the bonding and peeling of two wafers as in this embodiment. The surface of the ROIC substrate 111 has irregularities due to the conductive pattern near the surface of the readout circuit 112. Therefore, when graphene is transferred to form the graphene layer 122, some irregularities remain in the graphene, which may reduce the measurement accuracy of the optical sensor. In contrast to this comparative example, this embodiment employs the bonding and peeling of two wafers as described below, thereby resolving this issue. That is, the manufacturing method of this embodiment provides good graphene transfer accuracy, which contributes to improving the measurement accuracy of the optical sensor 100.

[0034] In step S204, the graphene layer 122 is patterned as shown in Fig. 6A. In step S205, a conductor layer 128 made of, for example, Au, which serves as the contact electrode 123, is formed on the surfaces of the pyroelectric layer 121 and the graphene layer 122 as shown in Fig. 6B. The conductor layer 128 is then patterned to form a pair of contact electrodes 123 sandwiching the graphene layer 122 therebetween as shown in Fig. 6C.

[0035] In step S206, as shown in Fig. 7A, a protective layer 124 is formed on the surface of the graphene layer 122. In step S207, as shown in Fig. 7B, the pyroelectric layer 121 is patterned. As a result, the FET section 120 is obtained in a state where it is mounted on the surface of the substrate 126 having the release layer 127.

[0036] 2, the substrate 110 prepared in steps S101 to S105 is bonded to the FET section 120 prepared in steps S201 to S207. FIG. 8 is a diagram showing the process of bonding the substrate 110 and the FET section 120. Specifically, in bonding the substrate 110 and the FET section 120, the substrate 126 on which the FET section 120 is mounted is placed on the substrate 110 with the FET section 120 side of the substrate 126 facing the surface of the substrate 110. Then, the contact electrodes 123 of the FET section 120 are connected to the wiring pattern 114 of the substrate 110.

[0037] In step S302, peeling is performed at the interface between the release layer 127 and the pyroelectric layer 121, and the substrate 126 and the release layer 127 are peeled off from the pyroelectric layer 121. Specifically, for example, when the release layer 127 is made of SiO ２In the case where the exfoliation layer 127 is a layer of the pyroelectric layer 121, the exfoliation is performed by etching the exfoliation layer 127. Alternatively, for example, the exfoliation may be performed by ion implantation into the pyroelectric layer 121 without using the exfoliation layer 127. As a result of the exfoliation, the optical sensor 100 having the structure shown in FIG. 1 is obtained. When the exfoliation layer 127 is etched, the graphene layer 122 is protected from damage caused by etching because the graphene layer 122 is located between the pyroelectric layer 121 and the substrate 110. The graphene layer 122 is also protected by the protective layer 124 formed on the surface of the graphene layer 122.

[0038] Second Embodiment Next, a second embodiment of the optical sensor will be described. In the following description, duplicated explanations of the elements described above will be omitted.

[0039] Fig. 9 is a cross-sectional view showing the optical sensor 200 of the second embodiment, and Fig. 10 is a perspective view showing the optical sensor 200 of the second embodiment. Fig. 9 shows a cross section taken along line A-A shown in Fig. 10. However, for convenience of illustration, some elements are omitted from Fig. 10.

[0040] The optical sensor 200 of the second embodiment includes a FET section 120 and a support leg substrate 210. In the optical sensor 200 of the second embodiment, the graphene layer 122 is also located between the pyroelectric layer 121 and the ROIC substrate 111, and the graphene layer 122 does not block infrared rays entering from the pyroelectric layer 121 side, so that the light utilization efficiency in the pyroelectric layer 121 is high.

[0041] The support leg substrate 210 includes the ROIC substrate 111, pillars 211, and a support leg layer 215. The combination of the pillars 211 and the support leg layer 215 corresponds to an example of the support leg structure referred to in the present invention. The pillars 211 are also called studs and are made of, for example, W (tungsten). The pillars 211 are connected to the readout circuit 112 and protrude in a columnar shape from the surface of the ROIC substrate 111.

[0042] The support leg layer 215 includes a wiring layer 212 made of, for example, TiN, a support layer 213 made of, for example, SiN, and an electrode layer 214 made of, for example, Au. The support leg layer 215 extends from the pillar 211 along the surface of the ROIC substrate 111. The extended end of the support leg layer 215 is spaced apart from the surface of the ROIC substrate 111, and the electrode layer 214 at the extended end is connected to the contact electrode 123 of the FET section 120. The pillar 211 and the support leg layer 215 support the contact electrode 123 of the FET section 120, thereby holding the FET section 120 at a location spaced apart from the surface of the ROIC substrate 111. In other words, a so-called hollow structure is formed between the FET section 120 and the ROIC substrate 111.

[0043] The FET section 120 is connected to the readout circuit 112 of the ROIC substrate 111 by the pillars 211 and the wiring layer 212 and electrode layer 214 of the support leg layer 215. The support leg layer 215 has a thin, serpentine shape as shown in FIG. 10 , which suppresses heat conduction from the FET section 120 to the pillars 211.

[0044] The FET section 120 is held by the support leg layer 215 and the pillars 211 to form a hollow structure, and the FET section 120 is thermally isolated from the ROIC substrate 111, etc. As a result, the response speed of the FET section 120 to incident infrared rays is improved in the optical sensor 200 of the second embodiment compared to the optical sensor 100 of the first embodiment.

[0045] <Method of Manufacturing the Optical Sensor 200> Next, a method of manufacturing the optical sensor 200 of the second embodiment will be described. FIG. 11 is a diagram showing a method of manufacturing the optical sensor 200 of the second embodiment. In the optical sensor 200 of the second embodiment, the FET section 120 and the support leg substrate 210 are also fabricated separately. That is, the support leg substrate 210 is fabricated as a third wafer on which a support structure is formed on the ROIC, in steps S401 to S407, and the FET section 120 is fabricated as the second wafer described above, in steps S201 to S207. Each step in FIG. 11 will be described below with reference to the diagrams showing each step. However, the steps from S201 to S207 for fabricating the FET section 120 are the same as those in the first embodiment, and therefore will not be described here. Furthermore, although multiple elements are formed simultaneously and in parallel in an array on each wafer, the following description will focus on one element.

[0046] 12A, 12B, 13A, 13B, 13C, 14A, 14B, and 14C are diagrams showing the steps of fabricating the support leg substrate 210. In step S401, as shown in FIG. 12A, an ROIC substrate 111 having a readout circuit 112 therein is prepared. Next, in step S402, as shown in FIG. 12B, a sacrificial layer 216 made of, for example, polyimide is formed on the surface of the ROIC substrate 111. In step S403, as shown in FIG. 13A, the sacrificial layer 216 is patterned to expose connection points 217 with the readout circuit 112.

[0047] In step S404, as shown in Fig. 13B, a W layer 218 is formed on the surface of the sacrificial layer 216 to form pillars 211. Then, in step S405, as shown in Fig. 13C, the surfaces of the sacrificial layer 216 and pillars 211 are planarized. In step S406, as shown in Fig. 14A, a wiring layer 212 and a support layer 213 are formed on the planarized surfaces of the sacrificial layer 216 and pillars 211, and further, as shown in Fig. 14B, an electrode layer 214 is formed on the surface of the support layer 213 to form a support leg layer 215.

[0048] In step S407, as shown in Fig. 14C, the support leg layer 215 is patterned to obtain the support leg substrate 210. However, at this point, the sacrificial layer 216 remains. Because the support leg substrate 210 is produced separately from the FET section 120, the FET section 120 is not affected by, for example, the patterning of the support leg layer 215, and damage to the graphene layer 122 is avoided. In step S501 of Fig. 11, the support leg substrate 210 produced in steps S401 to S407 and the FET section 120 produced in steps S201 to S207 are bonded together.

[0049] 15 is a diagram showing a process for bonding the support leg substrate 210 and the FET section 120. Specifically, in bonding the support leg substrate 210 and the FET section 120, the substrate 126 on which the FET section 120 is mounted is placed on the support leg substrate 210 with the FET section 120 side of the substrate 126 facing the surface of the support leg substrate 210. Then, the contact electrode 123 of the FET section 120 is connected to the support leg layer 215 of the support leg substrate 210.

[0050] In step S502 of Fig. 11 , the substrate 126 is peeled off. Fig. 16 is a diagram showing the peeling process. In the peeling process, the peeling layer 127 is removed by etching or the like, and the substrate 126 and the peeling layer 127 are peeled off from the pyroelectric layer 121. When the peeling layer 127 is etched, the graphene layer 122 is located between the pyroelectric layer 121 and the support leg substrate 210, and therefore the graphene layer 122 is protected from damage caused by etching. The graphene layer 122 is also protected by the protective layer 124 formed on the surface of the graphene layer 122.

[0051] 11, the sacrificial layer 216 of the support leg substrate 210 is removed by etching, thereby obtaining the optical sensor 200 shown in Fig. 9. Even during the etching of the sacrificial layer 216, the graphene layer 122 is protected by being located between the pyroelectric layer 121 and the support leg substrate 210, and is also protected by the protective layer 124.

[0052] Third Embodiment Next, a third embodiment of the optical sensor will be described. In the following description, duplicated explanations of the elements described above will be omitted.

[0053] Fig. 17 is a top perspective view showing the optical sensor 300 of the third embodiment, and Fig. 18 is a bottom perspective view showing the optical sensor 300 of the third embodiment. However, for convenience of illustration, some elements are omitted in Figs. 17 and 18. As in the second embodiment, the optical sensor 300 of the third embodiment includes a FET section 120 and a support leg substrate 210. Furthermore, the optical sensor 300 of the third embodiment includes a gate electrode layer 301, a metal via 302, a gate wiring layer 303, and a gate pillar 304.

[0054] The gate electrode layer 301 corresponds to an example of a third electrode according to the present invention and is made of, for example, Si. The gate electrode layer 301 is provided, for example, on only a portion of the surface of the pyroelectric layer 121. The metal via 302 penetrates the pyroelectric layer 121 at a position that avoids the graphene layer 122 and the contact electrode 123. The metal via 302 is connected to the gate electrode layer 301. The metal via 302 may penetrate the gate electrode layer 301.

[0055] The gate wiring layer 303 has a structure similar to that of the support leg layer 214, and is connected to the metal via 302 on the back surface side of the pyroelectric layer 121 on which the graphene layer 122 is provided. The surface of the pyroelectric layer 121 on which the gate electrode layer 301 is provided corresponds to an example of the first main surface in the present invention, and the back surface of the pyroelectric layer 121 on which the graphene layer 122 is provided corresponds to an example of the second main surface in the present invention. The gate pillar 304 has a structure similar to that of the pillar 211. The gate electrode layer 301 is connected to, for example, the readout circuit 112 via the metal via 302, the gate wiring layer 303, and the gate pillar 304, and a gate voltage is applied to it.

[0056] FIG. 19 is a graph illustrating the effect of the gate voltage. The horizontal axis of FIG. 19 represents the gate voltage Vbg, and the vertical axis represents the current Id of the detection signal flowing through the graphene layer 122. The polarization change in the pyroelectric layer 121 acts in the same way as the change in the gate voltage Vbg. As a result, the current curves 311 and 312 change from the current curve 311 when no infrared light is incident to the current curve 312 when infrared light is incident. In other words, even if the gate voltage Vbg is zero, a signal change ΔI1 occurs, making it possible to detect infrared light. In the first and second embodiments, this signal change ΔI1 is detected. In the third embodiment, when an appropriate gate voltage V ０ is applied to the gate electrode layer 301, resulting in a larger signal change ΔI2. Therefore, the third embodiment has improved detection sensitivity compared to the first and second embodiments.

[0057] 17 and 18 , the explanation will be continued. The gate electrode layer 301 may be made of a material other than Si that transmits infrared light. When the gate electrode layer 301 is made of Si, Si has low infrared reflectivity, so the efficiency of infrared light incidence on the pyroelectric layer 121 is high, and the sensitivity of the FET section 120 and the optical sensor 300 is improved. Furthermore, the gate electrode layer 301 may be provided on the entire surface of the pyroelectric layer 121, but when it is provided on only a portion of the surface of the pyroelectric layer 121, the reflection of infrared light by the gate electrode layer 301 is reduced, and the sensitivity of the FET section 120 and the optical sensor 300 is improved.

[0058] The gate electrode layer 301 is formed in the process in which the FET section 120 is produced as a second wafer. The gate wiring layer 303 can be produced simultaneously in the process in which the support leg layer 214 is produced, and the gate pillar 304 can be produced simultaneously in the process in which the pillar 211 is produced. In other words, the connection structure via the metal via 302 enables electrical continuity to the gate electrode layer 301 through a manufacturing process similar to that in the second embodiment. This prevents an increase in the number of processes and eliminates the need to prepare a separate circuit board.

[0059] <Fourth embodiment> Next, an optical sensor 400 according to a fourth embodiment will be described. Fig. 20 is a cross-sectional view showing the optical sensor 400 according to the fourth embodiment. While the optical sensors 100, 200, and 300 according to the first to third embodiments described above are so-called thermal optical sensors, the optical sensor 400 according to the fourth embodiment is a so-called quantum optical sensor.

[0060] The optical sensor 400 of the fourth embodiment includes a substrate 110 similar to that of the first embodiment, and an FET section 410 different from that of the first embodiment. The FET section 410 of the fourth embodiment includes a graphene layer 122, a contact electrode layer 123, and a protective layer 124, similar to that of the first embodiment. The FET section 410 of the fourth embodiment includes a Si substrate 411 doped with impurities such as P, and a SiO ２ The Si substrate 411 doped with impurities such as P is a semiconductor compound layer that performs photoelectric conversion, and corresponds to an example of the light-receiving layer of the present invention.

[0061] In the optical sensor 400 of the fourth embodiment, photoelectric conversion occurs when infrared light is incident on the Si substrate 411, and a voltage is applied to the graphene layer 122. As a result, a current change occurs in the graphene layer 122, and the current change is detected as a detection signal by the readout circuit 112 of the substrate 110.

[0062] 21 is a diagram showing a manufacturing method of the optical sensor 400 of the fourth embodiment. In the manufacturing method of the optical sensor 400 of the fourth embodiment, the manufacturing process of the first wafer from step S101 to step S105 and the manufacturing process of the fourth wafer from step S202 to step S207 are the same as those in the first embodiment.

[0063] In the method for manufacturing the optical sensor 400 of the fourth embodiment, instead of step S201 in the first embodiment, a Si substrate 411 having an insulating layer 412 on its surface is prepared in step S601. Thereafter, the same processes as in the first embodiment, from step S202 to step S207, are performed to obtain the FET section 410 of the fourth embodiment.

[0064] In the method for manufacturing the optical sensor 400 of the fourth embodiment, the substrate 110 created in steps S101 to S105 and the FET section 410 created in steps S601 to S207 are bonded together to obtain the optical sensor 400 shown in Fig. 20. In other words, the method for manufacturing the optical sensor 400 of the fourth embodiment does not include the peeling step in step S302 of the first embodiment.

[0065] Fifth Embodiment Fig. 22 is a cross-sectional view showing an optical sensor according to a fifth embodiment of the present invention. The optical sensor 1100 includes a substrate 1110 and a FET (Field Effect Transistor) section 1120. In the case of an image sensor for an infrared camera, a single substrate 1110 is provided with a plurality of FET sections 1120 arranged in an array, but for the sake of convenience of explanation, Fig. 22 shows an optical sensor 1100 including one substrate 1110 and one FET section 1120.

[0066] The substrate 1110 includes a semiconductor substrate 1111, an insulating layer 1113, and a wiring pattern 1114. The FET section 1120 includes a pyroelectric layer 1121, a graphene layer 1122, a contact electrode 1123, and a protective layer 1124. The semiconductor substrate 1111 is a substrate made of, for example, Si.

[0067] A plurality of wiring patterns 1114 are provided, extending beyond the area shown in FIG. 22, and electrically connect the FET section 1120 to a readout substrate (not shown). The insulating layer 1113 is made of, for example, SiO ２ This layer is provided on, for example, the entire main surface of the semiconductor substrate 1111 .

[0068] The pyroelectric layer 1121 is an example of a light-receiving layer according to the present invention, and has a large light-receiving area, sandwiching a pair of contact electrodes 1123 between the substrate 1110 and the pyroelectric layer 1121. The pair of contact electrodes 1123 is an example of a first electrode and a second electrode according to the present invention. The pyroelectric layer 1121 is made of, for example, LiNbO ３ This is the layer.

[0069] The graphene layer 1122 corresponds to an example of a two-dimensional material layer and an example of a current change layer according to the present invention. The graphene layer 1122 is provided between a pair of contact electrodes 1123, with one end of the graphene layer 1122 connected to one of the contact electrodes 1123 and the other end of the graphene layer 1122 connected to the other of the contact electrodes 1123. The graphene layer 1122 extends along the pyroelectric layer 1121 and is located between the pyroelectric layer 1121 and the semiconductor substrate 1111. Note that an insulating layer made of, for example, SiN may be provided between the pyroelectric layer 1121 and the graphene layer 1122. However, in this embodiment, the pyroelectric layer 1121 is made of an insulating layer such as LiNbO ３ Since the layer is made of silicon, no insulating layer is required.

[0070] The infrared ray incident side of the pyroelectric layer 1121 is opposite to the semiconductor substrate 1111, and the graphene layer 1122 is not located on the incident side. Therefore, the infrared ray is not reflected by the graphene layer 1122, and the light utilization efficiency is high in the pyroelectric layer 1121 having a large light-receiving area, thereby improving the speed responsiveness of the FET section 1120 and the optical sensor 1100.

[0071] The contact electrode 1123 is, for example, an Au electrode, and may have an underlayer of Ru or Ti. The contact electrode 1123 is connected to the wiring pattern 1114 of the substrate 1110 and transmits a current signal to, for example, a readout substrate. The protective layer 1124 covers the surface of the graphene layer 1122 to protect the graphene layer 1122.

[0072] The optical sensor 1100 of the fifth embodiment is manufactured by the same manufacturing process as the optical sensor 100 of the first embodiment.

[0073] Sixth Embodiment Next, a sixth embodiment of the optical sensor will be described. In the following description, redundant explanations of the elements described above will be omitted.

[0074] Fig. 23 is a cross-sectional view showing an optical sensor 1200 according to the sixth embodiment, and Fig. 24 is a perspective view showing the optical sensor 1200 according to the sixth embodiment. Fig. 23 shows a cross section taken along line A-A shown in Fig. 24. However, for convenience of illustration, some elements are omitted from Fig. 24.

[0075] The optical sensor 1200 of the sixth embodiment includes a FET section 1120 and a support leg substrate 1210. In the optical sensor 1200 of the sixth embodiment, the graphene layer 1122 is also located between the pyroelectric layer 1121 and the semiconductor substrate 1111, and the graphene layer 1122 does not block infrared rays entering from the pyroelectric layer 1121 side, so that the light utilization efficiency in the pyroelectric layer 1121 is high.

[0076] The support leg substrate 1210 includes a semiconductor substrate 1111, pillars 1211, and a support leg layer 1215. The combination of the pillars 1211 and the support leg layer 1215 corresponds to an example of the support leg structure referred to in the present invention. The pillars 1211 are also called studs and are made of, for example, W (tungsten). The pillars 1211 protrude in a columnar shape from the surface of the semiconductor substrate 1111.

[0077] The support leg layer 1215 includes a wiring layer 1212 made of, for example, TiN, a support layer 1213 made of, for example, SiN, and an electrode layer 1214 made of, for example, Au. The support leg layer 1215 extends from the pillar 1211 along the surface of the semiconductor substrate 1111. The extended end of the support leg layer 1215 is spaced apart from the surface of the semiconductor substrate 1111, and the electrode layer 1214 at the extended end is connected to the contact electrode 1123 of the FET section 1120. The pillar 1211 and the support leg layer 1215 support the contact electrode 1123 of the FET section 1120, thereby holding the FET section 1120 at a location spaced apart from the surface of the semiconductor substrate 1111. In other words, a so-called hollow structure is formed between the FET section 1120 and the semiconductor substrate 1111.

[0078] The pillars 1211 and the wiring layer 1212 of the support leg layer 1215, together with a wiring pattern extending to areas other than those shown in Fig. 23, constitute an example of the wiring referred to in the present invention. The FET section 1120 is electrically connected to a readout substrate (not shown) or the like by the pillars 1211, the wiring layer 1212 and electrode layer 1214 of the support leg layer 1215, and the wiring pattern extending to areas other than those shown.

[0079] 24 , the support leg layer 1215 has a thin, serpentine shape, which suppresses heat conduction from the FET section 1120 to the pillars 1211. The FET section 1120 is held by the support leg layer 1215 and the pillars 1211 to form a hollow structure, which thermally isolates the FET section 1120 from the semiconductor substrate 1111 and the like. As a result, the response speed of the FET section 1120 to incident infrared rays is improved in the optical sensor 1200 of the sixth embodiment compared to the optical sensor 1100 of the fifth embodiment.

[0080] The optical sensor 1200 of the sixth embodiment is manufactured by the same manufacturing process as that of the optical sensor 200 of the second embodiment.

[0081] Seventh Embodiment Next, a seventh embodiment of the optical sensor will be described. In the following description, redundant description of the elements described above will be omitted.

[0082] Fig. 25 is a top perspective view showing the optical sensor 1300 of the seventh embodiment, and Fig. 26 is a bottom perspective view showing the optical sensor 1300 of the seventh embodiment. However, for convenience of illustration, some elements are omitted in Figs. 25 and 26. The optical sensor 1300 of the seventh embodiment includes a FET section 1120 and a support leg substrate 1210, similar to the sixth embodiment. Furthermore, the optical sensor 1300 of the seventh embodiment includes a gate electrode layer 1301, a metal via 1302, a gate wiring layer 1303, and a gate pillar 1304.

[0083] The gate electrode layer 1301 corresponds to an example of the third electrode referred to in the present invention and is made of, for example, Si. The gate electrode layer 1301 is provided, for example, only on a portion of the surface of the pyroelectric layer 1121. The metal via 1302 penetrates the pyroelectric layer 1121 at a position that avoids the graphene layer 1122 and the contact electrode 1123. The metal via 1302 is connected to the gate electrode layer 1301. The metal via 1302 may penetrate the gate electrode layer 1301.

[0084] The gate wiring layer 1303 has a structure similar to that of the support leg layer 1214, and is connected to the metal via 1302 on the back surface side of the pyroelectric layer 1121 on which the graphene layer 1122 is provided. The surface of the pyroelectric layer 1121 on which the gate electrode layer 1301 is provided corresponds to an example of the first main surface in the present invention, and the back surface of the pyroelectric layer 1121 on which the graphene layer 1122 is provided corresponds to an example of the second main surface in the present invention. The gate pillar 1304 has a structure similar to that of the pillar 1211. The gate electrode layer 1301 is connected to, for example, a wiring pattern via the metal via 1302, the gate wiring layer 1303, and the gate pillar 1304, and a gate voltage is applied to it.

[0085] Although the above description illustrates an optical sensor that detects infrared rays, and particularly illustrates an optical sensor that is suitable for detecting infrared rays in the wavelength band of 6 μm to 20 μm, the optical sensor of the present invention may be applied to an optical sensor that detects infrared rays in other wavelength bands, or may be applied to an optical sensor that detects visible light. Furthermore, the above description illustrates a graphene layer with high mobility as a suitable example of the current change layer referred to in the present invention, but the current change layer referred to in the present invention may also be a layer made of a material other than graphene.

[0086] 100, 200, 300, 400, 1100, 1200, 1300 Optical sensor 110, 1110 Substrate 1111 Semiconductor substrate 111 ROIC substrate 112 Readout circuit 113, 113 Insulating layer 114, 1114 Wiring pattern 120, 1120 FET section 121, 1121 Pyroelectric layer 122, 1122 Graphene layer 123, 1123 Contact electrode 124, 1124 Protective layer 126, 1126 Substrate 127, 1127 Release layer 210, 1210 Support leg substrate 211, 1211 Pillar 212, 1212 Wiring layer 213, 1213 Support layer 214, 1214 Electrode layer 215, 1215 Support leg layer 216, 1216 Sacrificial layer 301, 1301 Gate electrode layer 302, 1302 Metal via 303, 1303 Gate wiring layer 304, 1304 Gate pillar 410 FET section 411 Si substrate 412 Insulating layer

Claims

1. An optical sensor comprising: a substrate having first wiring and second wiring; a first electrode electrically connected to the first wiring; a second electrode electrically connected to the second wiring; a light-receiving layer disposed between the substrate and the first and second electrodes to receive light; and a current-changing layer disposed between the light-receiving layer and the substrate, electrically connected to the first and second electrodes, through which a current flows, the current changing layer changing in response to light received by the light-receiving layer.

2. The optical sensor according to claim 1, wherein the substrate has an internal readout circuit that receives an output signal of the current in the current change layer via the first wiring and the second wiring, amplifies it, and outputs it to an external circuit.

3. The optical sensor according to claim 2, wherein the substrate has an insulating layer having an internal conductive pattern including the first wiring and the second wiring, and the readout circuit receives the output signal via the first wiring and the second wiring, amplifies it, and outputs it to the external circuit.

4. The optical sensor according to claim 1, wherein the light-receiving layer is a pyroelectric layer.

5. The optical sensor according to claim 1, wherein the light-receiving layer is a layer of a semiconductor compound that performs photoelectric conversion.

6. The optical sensor of claim 1, wherein the current-changing layer is a layer of graphene.

7. The optical sensor of claim 1, further comprising: a first support structure that supports the first electrode at one end extending away from the substrate and electrically connects the first electrode to the first wiring; and a second support structure that supports the second electrode at one end extending away from the substrate and electrically connects the second electrode to the second wiring.

8. The optical sensor described in claim 1, wherein the light receiving layer has a first main surface located on the current change layer side and a second main surface located on the opposite side of the first main surface, and further comprises a third electrode located on the second main surface side of the light receiving layer and electrically connected to a third wiring of the substrate.

9. The optical sensor according to claim 8, wherein the third electrode is provided only in a part of the area of the second main surface.

10. The optical sensor according to claim 8, wherein said third electrode is a silicon electrode.

11. The optical sensor according to claim 8, wherein the third electrode is electrically connected to the third wiring via a conductor that penetrates the light-receiving layer.

12. A method for manufacturing an optical sensor comprising: a first substrate having first wiring and second wiring, a first electrode electrically connected to the first wiring, a second electrode electrically connected to the second wiring, a light-receiving layer that receives light, and a current change layer that is electrically connected to the first electrode and the second electrode, through which a current flows and through which the current changes in accordance with the light received by the light-receiving layer, the method comprising the steps of: forming the light-receiving layer on a second substrate, either directly or indirectly via another layer; forming the current change layer on the light-receiving layer, either directly or indirectly via another layer; forming the first electrode and the second electrode at locations with the current change layer sandwiched between them; and placing the second substrate, on which the light-receiving layer and the current change layer are formed, opposite the first substrate with the current change layer facing the first substrate, and electrically connecting the first electrode and the second electrode to the first wiring and the second wiring.

13. The method for manufacturing an optical sensor according to claim 12, further comprising the step of separating the light-receiving layer from the second substrate after connecting the first electrode and the second electrode to the first wiring and the second wiring.

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