Gas detectors and gas detector arrays

Abstract

The gas detector (100) includes an insulating layer (3), a first electrode (2a) disposed on the insulating layer, a two-dimensional material layer (1) electrically connected to the first electrode, and a second electrode (2b) electrically connected to the first electrode via the two-dimensional material layer. The two-dimensional material layer has an exposed surface exposed to the outside. The two-dimensional material layer is provided so that photoelectric conversion is performed when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the two-dimensional material layer.

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present disclosure relates to gas detectors and gas detector arrays, and more particularly to gas detectors and gas detector arrays comprising two-dimensional layers of material. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2019-102567 (Patent Document 1) discloses a field effect transistor (FET) having a gate and a gate insulating film made of graphene. The FET described in Patent Document 1 acts as a gas sensor that detects a gas based on a drain current change caused by a threshold voltage change resulting from a work function change when a detection target gas such as ammonia is adsorbed to graphene. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-102567 A Summary of the Invention [Problem to be solved by the invention]

[0004] Various gases are adsorbed to graphene. Therefore, in the above-mentioned FET, the drain current changes even when a gas other than the detection target is adsorbed to graphene. In other words, it is difficult to detect a specific gas species in a mixed gas or to identify a gas species using the above-mentioned FET.

[0005] In this disclosure, techniques are proposed for detecting specific gas species or for identifying gas species. [Means for solving the problem]

[0006] A gas detector according to an embodiment of the present disclosure includes an insulating layer, at least one first electrode disposed on the insulating layer, at least one two-dimensional material layer electrically connected to the at least one first electrode, and at least one second electrode electrically connected to the at least one first electrode via the at least one two-dimensional material layer. The at least one two-dimensional material layer has an exposed surface exposed to the outside. The at least one two-dimensional material layer is provided so as to perform photoelectric conversion when an electromagnetic wave having a wavelength range absorbed by a gas to be detected is incident thereon. Effect of the Invention

[0007] In accordance with the present disclosure, specific gas species can be detected or gas species can be identified. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic plan view of a gas detector according to a first embodiment. [Diagram 2] FIG. 2 is a schematic cross-sectional view taken along the line of arrows II-II in FIG. [Diagram 3] 4 is a flowchart illustrating a method for manufacturing the gas detector according to the first embodiment. [Figure 4] FIG. 2 is a diagram for specifically explaining the operating principle of gas detection by an electromagnetic wave detection method in the gas detector according to the first embodiment. [Diagram 5] FIG. 2 is a diagram for specifically explaining the operating principle of adsorption-type gas detection in the gas detector according to the first embodiment. [Figure 6] FIG. 11 is a schematic cross-sectional view of a gas detector according to a second embodiment. [Figure 7] FIG. 11 is a schematic cross-sectional view of a gas detector according to a third embodiment. [Figure 8] FIG. 11 is a schematic cross-sectional view of a gas detector according to a fourth embodiment. [Figure 9] FIG. 11 is a schematic cross-sectional view of a gas detector according to a fifth embodiment. [Figure 10] FIG. 13 is a schematic cross-sectional view of a gas detector according to a sixth embodiment. [Figure 11] FIG. 11 is a schematic cross-sectional view taken along the line of arrows XI-XI in FIG. [Figure 12] FIG. 23 is a schematic plan view showing a first modified example of the gas detector according to the sixth embodiment. [Figure 13] FIG. 23 is a schematic plan view showing a second modified example of the gas detector according to the sixth embodiment. [Figure 14] FIG. 13 is a top view of a gas detector array according to a seventh embodiment. [Figure 15] FIG. 13 is a schematic diagram showing an example of a readout circuit that reads out an electrical signal obtained from the gas detector array according to the seventh embodiment. [Figure 16] FIG. 23 is a top view showing a first modified example of the gas detector array according to the seventh embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. In the following, the same or corresponding parts are denoted by the same reference characters, and overlapping descriptions will not be repeated.

[0010] In the embodiments described below, the drawings are schematic and are used to conceptually explain functions or structures. Furthermore, the present disclosure is not limited to the embodiments described below. Unless otherwise specified, the basic configuration of the gas detector is common to all the embodiments. Furthermore, the same reference numerals are attached to the same or equivalent parts as described above. This is common throughout the entire specification.

[0011] The gas detector according to the present disclosure is a gas detector for detecting a gas to be detected. The gas to be detected by the gas detector according to the present disclosure includes any gas or any fine particles suspended in any gas. The fine particles include any liquid fine particles or any solid fine particles suspended in any gas in the form of an aerosol.

[0012] The gas detector according to the present disclosure detects, as gas detection signals, a change in the electrical properties of the two-dimensional material layer associated with photoelectric conversion occurring at least in the two-dimensional material layer when an electromagnetic wave in a wavelength range absorbed by a gas to be detected is incident thereon, and a change in the electrical properties of the two-dimensional material layer associated with adsorption of the gas to be detected to the two-dimensional material layer, and further measures the amount of each change. In this specification, gas detection based on the former change in electrical properties is also referred to as gas detection by an electromagnetic wave detection method, and gas detection based on the latter change in electrical properties is also referred to as gas detection by an adsorption method.

[0013] In the embodiments described below, the configuration of a gas detector that detects visible light or infrared light as an electromagnetic wave in a wavelength range absorbed by the gas to be detected is described, but the electromagnetic waves detected by the gas detector of the present disclosure are not limited to visible light and infrared light. The embodiments described below are also effective as a detector that detects radio waves such as X-rays, ultraviolet light, near-infrared light, terahertz (THz) waves, and microwaves in addition to visible light and infrared light. In the embodiments described below, these lights and radio waves are collectively referred to as electromagnetic waves.

[0014] In the following, the material of the two-dimensional material layer is described as graphene, but the material constituting the two-dimensional material layer is not limited to graphene. For example, the material of the two-dimensional material layer can be a transition metal dichalcogenide (TMD), black phosphorus, silicene (two-dimensional honeycomb structure of silicon atoms), germanene (two-dimensional honeycomb structure of germanium atoms), etc. Examples of the transition metal dichalcogenide include MoS2, WS2, WSe2, etc.

[0015] These materials have a structure similar to that of graphene, and are capable of arranging atoms in a single layer on a two-dimensional surface. Therefore, even when these materials are applied to a two-dimensional material layer, the same effects as when graphene is applied to the two-dimensional material layer can be obtained.

[0016] The two-dimensional material layer may be composed of two-dimensional materials arranged in a single layer (e.g., single-layer graphene). The two-dimensional material layer may be composed of two-dimensional materials arranged in multiple layers (e.g., multi-layer graphene). In the latter two-dimensional material layer, the photoelectric conversion efficiency increases, and the sensitivity of the gas detector increases. In addition, a band gap is formed in the latter two-dimensional material layer. As a result, the latter two-dimensional material layer can be provided so that photoelectric conversion occurs in the two-dimensional material layer 1 only when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident on the two-dimensional material layer 1. In addition, when the number of layers of the secondary raw material contained in the two-dimensional material layer increases, the mobility of carriers in the channel region decreases, but the two-dimensional material layer becomes less susceptible to carrier scattering from an underlying structure such as a substrate, and as a result, the noise level decreases. Therefore, in a gas detector including a two-dimensional material layer including two-dimensional materials arranged in multiple layers, the detection sensitivity of electromagnetic waves can be increased. In addition, among the multiple graphenes stacked on top of each other in the two-dimensional material layer, the directions of the hexagonal lattice vectors between any two graphene layers may or may not match each other.

[0017] When the two-dimensional material layer is composed of multilayer graphene, the stacking orientation angle may be not only AB stacking seen in graphite in its natural state, but also turbostratic stacking. Turbostratic stacking is also called random stacking or turbostratic graphene. The method for producing the turbostratic structure portion may be determined appropriately. For example, the turbostratic structure portion may be formed by transferring a single layer of graphene produced by a CVD method multiple times and stacking multilayer graphene. Furthermore, the turbostratic structure portion may be formed by arranging ethanol or methane as a carbon source on the graphene and growing the graphene by a CVD method.

[0018] In addition, in the following, the terms p-type and n-type may be used for the two-dimensional material layer. In the following embodiments, a two-dimensional material layer having more holes than the intrinsic two-dimensional material layer is called p-type, and a two-dimensional material layer having more electrons than the intrinsic two-dimensional material layer is called n-type. The two-dimensional material layer may be intrinsic, not doped with impurities, and may have a conductivity type of p-type or n-type.

[0019] In the following, the terms n-type and p-type may be used for the materials of the members in contact with the two-dimensional material layer. Here, for example, n-type material refers to a material having electron donating properties, and p-type material refers to a material having electron withdrawing properties. In addition, there are cases where there is a bias in the charge throughout the molecule, and electrons are predominant, and holes are predominant, and these are called n-type and p-type, respectively. As these materials, either organic or inorganic substances or a mixture thereof can be used.

[0020] Furthermore, when the two-dimensional material layer is in contact with an electrode, carriers are doped from the electrode into the two-dimensional material layer. For example, when gold (Au) is used as the material of the electrode, holes are doped into the two-dimensional material layer near the electrode due to the difference in work function between the two-dimensional material layer and Au. When the gas detector is driven in an electronically conductive state in this state, the mobility of electrons flowing into the channel region of the two-dimensional material layer decreases due to the influence of the holes doped from the electrode into the two-dimensional material layer, and the contact resistance between the two-dimensional material layer and the electrode increases. This increase in contact resistance may decrease the mobility of electrons (carriers) due to the field effect in the gas detector, resulting in a decrease in performance of the gas detector. In particular, when the two-dimensional material layer is made of single-layer graphene, the doping amount of carriers injected from the electrode is larger than when the two-dimensional material layer is made of multi-layer graphene. Therefore, the decrease in the mobility of electrons in the gas detector is particularly noticeable when single-layer graphene is used as the two-dimensional material layer. Therefore, when the entire two-dimensional material layer is made of single-layer graphene, the performance of the gas detector may decrease. Therefore, at least the contact area of ​​the secondary raw material layer with the electrode may be made of multi-layer graphene. In the multi-layer graphene, carrier doping from the electrode is smaller than in the single-layer graphene. Therefore, an increase in the contact resistance between the two-dimensional material layer and the electrode can be suppressed. As a result, the above-mentioned decrease in the mobility of electrons in the gas detector can be suppressed, and the performance of the gas detector can be improved.

[0021] The two-dimensional material layer may also include nanoribbon-shaped graphene (hereinafter also referred to as graphene nanoribbon). The two-dimensional material layer may be, for example, a single graphene nanoribbon, a composite in which a plurality of graphene nanoribbons are stacked, or a structure in which graphene nanoribbons are periodically arranged on a plane (for example, a graphene metamaterial). In a two-dimensional material layer configured as a structure in which graphene nanoribbons are periodically arranged on a plane, plasmon resonance may occur. As a result, the sensitivity of the gas detector can be improved.

[0022] In this specification, the following plasmon resonance phenomena, such as surface plasmon resonance, which is an interaction between a metal surface and light, the phenomenon called pseudo-surface plasmon resonance, which means resonance on a metal surface outside the visible light and near-infrared light regions, and the phenomenon called metamaterial or plasmonic metamaterial, which means manipulation of a specific wavelength by a structure with dimensions smaller than the wavelength, are not particularly distinguished by name, but are treated as equivalent in terms of the effects of the phenomenon. In this specification, these resonances are called surface plasmon resonance, plasmon resonance, or simply resonance.

[0023] In this specification, what is referred to as an insulating layer is an insulating film layer having a thickness at which no tunnel current occurs.

[0024] Embodiment 1 Fig. 1 is a schematic plan view of a gas detector 100 according to embodiment 1. Fig. 2 is a schematic cross-sectional view taken along line II-II in Fig. 1. Fig. 2 also shows typical electrical connections of the gas detector 100.

[0025] The gas detector 100 shown in Figures 1 and 2 includes a plurality of detection sections. The plurality of detection sections includes a first detection section 100A and a second detection section 100B. The first detection section 100A and the second detection section 100B basically have the same configuration as each other.

[0026] Each of the first detection unit 100A and the second detection unit 100B mainly includes a two-dimensional material layer 1, a first electrode 2a, a second electrode 2b, a third electrode 2c, an insulating layer 3, and a semiconductor layer 4. The first detection unit 100A and the second detection unit 100B share, for example, the third electrode 2c, the insulating layer 3, and the semiconductor layer 4. The second detection unit 100B differs from the first detection unit 100A in that it further includes a first coating film 5. From a different perspective, the gas detector 100 includes a plurality of two-dimensional material layers 1, a plurality of first electrodes 2a, a plurality of second electrodes 2b, one insulating layer 3, one semiconductor layer 4, and one first coating film 5.

[0027] The semiconductor layer 4 has a first surface 41 and a second surface 42 located on the opposite side to the first surface 41. The two-dimensional material layer 1, the first electrode 2a, the second electrode 2b, and the insulating layer 3 are disposed on the first surface 41 of the semiconductor layer 4. The third electrode 2c is disposed on the second surface 42 of the semiconductor layer 4. Hereinafter, for each of the two-dimensional material layer 1, the first electrode 2a, the second electrode 2b, and the insulating layer 3, the portions located on the opposite side to the semiconductor layer 4 with respect to each other will be referred to as the upper portions of each, and the portions located on the semiconductor layer 4 side with respect to each other will be referred to as the lower portions of each.

[0028] The semiconductor layer 4 has sensitivity to electromagnetic waves in a wavelength range absorbed by the gas to be detected. In other words, the semiconductor layer 4 is provided so as to perform photoelectric conversion when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the semiconductor layer 4.

[0029] The semiconductor layer 4 is made of a semiconductor material such as silicon (Si), etc. Specifically, the semiconductor layer 4 may be a silicon substrate doped with impurities.

[0030] Here, the semiconductor layer 4 may have a multi-layer structure, and may be a pn junction photodiode, a pin photodiode, a Schottky photodiode, an avalanche photodiode, etc. Also, a phototransistor may be used as the semiconductor layer 4.

[0031] Although the above description has been given of a silicon substrate as an example of the semiconductor material constituting the semiconductor layer 4, other materials may be used as the material constituting the semiconductor layer 4. For example, the material constituting the semiconductor layer 4 may be a compound semiconductor such as germanium (Ge), a III-V group or II-V group semiconductor, mercury cadmium telluride (HgCdTe), indium antimony (InSb), lead selenium (PbSe), lead sulfur (PbS), cadmium sulfur (CdS), gallium nitride (GaN), silicon carbide (SiC), gallium phosphide (GaP), indium gallium arsenide (InGaAs), indium arsenide (InAs), a substrate including a quantum well or quantum dot, a Type II superlattice, or a combination of these materials.

[0032] The semiconductor layer 4 is preferably doped with impurities so that the electrical resistivity of the semiconductor layer 4 is 100 Ω·cm or less. By doping the semiconductor layer 4 at a high concentration, the carrier movement speed (read speed) in the semiconductor layer 4 increases. As a result, the response speed of the gas detector 100 improves.

[0033] The insulating layer 3 is disposed on the first surface 41 of the semiconductor layer 4. The lower surface of the insulating layer 3 is in contact with the first surface 41 of the semiconductor layer 4. The upper surface of the insulating layer 3 is in contact with, for example, the lower surfaces of the third portion 1c of the two-dimensional material layer 1, the first electrode 2a, and the second electrode 2b described later. Note that the upper surface of the insulating layer 3 may have a recess recessed relative to the portion in contact with the lower surfaces of the first electrode 2a and the second electrode 2b. The recess may be formed as an opening that exposes the first surface 41 of the semiconductor layer 4. In this case, the third portion 1c of the two-dimensional material layer 1 described later may be bridged over the recess of the insulating layer 3.

[0034] The material constituting the insulating layer 3 may be any material having electrical insulation properties, and includes, for example, silicon oxide (SiO2). The material constituting the insulating layer 3 includes, for example, at least one selected from the group consisting of SiO2, tetraethyl orthosilicate (Si(OC2H5)4), silicon nitride (Si3N4), hafnium oxide (HfO2), aluminum oxide (Al2O3), nickel oxide (NiO), boron nitride (BN) (boron nitride), and siloxane-based polymer materials. For example, the atomic arrangement of boron nitride is similar to that of graphene, so that even if boron nitride comes into contact with the two-dimensional material layer 1 made of graphene, it does not adversely affect the mobility of charges. Therefore, boron nitride is suitable as a material constituting the insulating layer 3 from the viewpoint of suppressing the insulating layer 3 from impairing the performance of the two-dimensional material layer 1, such as electron mobility.

[0035] The first electrodes 2a and the second electrodes 2b are arranged at intervals from each other on the upper surface of the insulating layer 3. The first electrodes 2a and the second electrodes 2b include a first set of first electrodes 2a and second electrodes 2b included in the first detection unit 100A and a second set of first electrodes 2a and second electrodes 2b included in the second detection unit 100B. The first set of first electrodes 2a and second electrodes 2b are arranged at intervals from each other. The second set of first electrodes 2a and second electrodes 2b are arranged at intervals from the first set of first electrodes 2a and second electrodes 2b.

[0036] The material constituting the first electrode 2a and the second electrode 2b may be any material having electrical conductivity, and may include, for example, at least one selected from the group consisting of gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), chromium (Cr), and palladium (Pd). In addition, an adhesion layer (not shown) may be formed between at least one of the first electrode 2a and the second electrode 2b and the insulating layer 3 in order to enhance adhesion therebetween. The material constituting the adhesion layer is not particularly limited, and may include, for example, at least one of chromium (Cr) and titanium (Ti).

[0037] 2, the first electrode 2a and the second electrode 2b are formed, for example, on the lower part of the two-dimensional material layer 1. The first electrode 2a and the second electrode 2b may be formed on the upper part of the two-dimensional material layer 1.

[0038] As shown in FIG. 2, a power supply circuit for applying a bias voltage Vsd1 to the two-dimensional material layer 1 of the first detection unit 100A is electrically connected between the first electrode 2a and the second electrode 2b of the first set. A power supply circuit for applying a bias voltage Vsd2 to the two-dimensional material layer 1 of the second detection unit 100B is electrically connected between the first electrode 2a and the second electrode 2b of the second set. Each power supply circuit includes a voltage source and an ammeter (not shown). Each voltage source applies the bias voltage Vsd1 between the first electrode 2a and the second electrode 2b of the first set, or applies a bias voltage Vsd2 between the first electrode 2a and the second electrode 2b of the second set. Each ammeter detects a current Isd1 that flows when the bias voltage Vsd1 is applied between the first electrode 2a and the second electrode 2b of the first set, or a current Isd2 that flows when the bias voltage Vsd2 is applied between the first electrode 2a and the second electrode 2b of the second set.

[0039] The third electrode 2c is provided, for example, on the entire surface of the second surface 42 of the semiconductor layer 4. The third electrode 2c may be in contact with at least a part of the semiconductor layer 4. For example, the third electrode 2c may be provided so as to be in contact with a part of the side surface of the semiconductor layer 4 extending in a direction intersecting with the first surface 41. Such a gas detector 100 can detect an electromagnetic wave incident from the second surface 42 side. As shown in FIG. 2, the gas detector 100 in which the third electrode portion 2c is provided on the entire surface of the second surface 42 of the semiconductor layer 4 is suitable when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident only from the first surface 41 side. In the gas detector 100 shown in FIG. 2, the electromagnetic wave incident from the first surface 41 side and transmitted through the semiconductor layer 4 is reflected by the second electrode 2b and reaches the two-dimensional material layer 1 again, so that the absorption rate of the electromagnetic wave in the two-dimensional material layer 1 is increased.

[0040] As shown in FIG. 2, a power supply circuit that applies a voltage Vg to the semiconductor layer 4 is electrically connected to the third electrode 2c.

[0041] The plurality of two-dimensional material layers 1 includes a first two-dimensional material layer 11 and a second two-dimensional material layer 12. The first two-dimensional material layer 11 electrically connects the first electrode 2a and the second electrode 2b of the first set. The second two-dimensional material layer 12 electrically connects the first electrode 2a and the second electrode 2b of the second set. The second two-dimensional material layer 12 is disposed at an interval from the first two-dimensional material layer 11. The first two-dimensional material layer 11 and the second two-dimensional material layer 12 have the same configuration as each other.

[0042] Each two-dimensional material layer 1 has sensitivity to electromagnetic waves in a wavelength range absorbed by the gas to be detected. In other words, each two-dimensional material layer 1 is provided so that photoelectric conversion occurs when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the two-dimensional material layer 1. Preferably, each two-dimensional material layer 1 is provided so that photoelectric conversion occurs in the two-dimensional material layer 1 only when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the two-dimensional material layer 1.

[0043] Each of the two-dimensional material layers 1 has an upper surface extending along its two-dimensional plane. The upper surface of the first two-dimensional material layer 11 is exposed to the outside and has an adsorption region capable of adsorbing the gas to be detected. The upper surface of the second two-dimensional material layer 12 is covered with a first coating film 5 described below. Therefore, the upper surface of the second two-dimensional material layer 12 does not have an adsorption region capable of adsorbing the gas to be detected.

[0044] Each two-dimensional material layer 1 has a first portion 1a, a second portion 1b, and a third portion 1c. The first portion 1a is connected to the first electrode 2a. The second portion 1b is connected to the second electrode 2b. The third portion 1c electrically connects the first portion 1a and the second portion 1b. The lower surfaces of the first portion 1a, the second portion 1b, and the third portion 1c are in contact with, for example, the upper surface of the insulating layer 3. As described above, when a recess is formed on the upper surface of the insulating layer 3, the third portion 1c may be bridged over the recess. The lower surface of the third portion 1c may not be in contact with the upper surface of the insulating layer 3. The upper surface of the two-dimensional material layer 1 has unevenness due to, for example, the first electrode 2a and the second electrode 2b.

[0045] 2, the entire upper surface of the first two-dimensional material layer 11 is exposed to the outside and is capable of adsorbing the gas to be detected. The entire upper surface of the second two-dimensional material layer 12 is covered with the first coating film 5. It is sufficient that the upper surface of at least the third portion 1c of the first two-dimensional material layer 11 is exposed to the outside and is capable of adsorbing the gas to be detected.

[0046] The thicknesses of the first portion 1a, the second portion 1b, and the third portion 1c of each two-dimensional material layer 1 are, for example, equal to each other. The thicknesses of the first portion 1a, the second portion 1b, and the third portion 1c of each two-dimensional material layer 1 may be different from each other.

[0047] The first coating film 5 covers the second two-dimensional material layer 12. The first coating film 5 is provided so as to block the transmission of the gas to be detected. Specifically, the first coating film 5 is provided so as to block the gas to be detected from being adsorbed to the second two-dimensional material layer 12. The first coating film 5 is provided so as not to block the transmission of electromagnetic waves in a wavelength range that is absorbed by the gas to be detected, for example.

[0048] The first covering film 5, for example, covers not only the second two-dimensional material layer 12 but also the second set of the first electrode 2a and the second electrode 2b of the second detection unit 100B. The first covering film 5 does not cover the first two-dimensional material layer 11.

[0049] The material constituting the first coating film 5 includes at least one selected from the group consisting of, for example, silicon oxide (SiO2), tetraethyl orthosilicate (Si(OC2H5)4), silicon nitride (Si3N4), hafnium oxide (HfO2), aluminum oxide (Al2O3), nickel oxide (NiO), boron nitride (BN), siloxane-based polymer materials, polyethylene terephthalate (PET), polyvinylidene chloride resin (PVDC), and biaxially oriented polypropylene (OPP). The material constituting the first coating film 5 may be the same as the material constituting the insulating layer 3. Pores may be formed inside the first coating film 5. In this case, the first coating film 5 is preferably a dense and thick film. The first coating film 5 being dense means that its average pore diameter is smaller than the outer diameter of the molecules or particles of the gas to be detected. The first coating film 5 may be configured as a laminate of multiple layers made of different materials. Such a first coating film 5 can have improved gas barrier properties compared to a first coating film 5 made of a single material and having a comparable overall thickness. From a different perspective, the first coating film 5 can be made thinner than a first coating film 5 made of a single material and having comparable gas barrier properties.

[0050] <Method of Manufacturing Gas Detector 100> Fig. 3 is a flow chart for explaining a method for manufacturing the gas detector 100 according to the embodiment 1. With reference to Fig. 3, a method for manufacturing the gas detector 100 shown in Figs.

[0051] First, a step (S1) is performed of preparing a semiconductor layer 4. In this step (S1), the semiconductor layer 4 is prepared as a flat substrate made of, for example, Si.

[0052] Secondly, a step (S2) of forming the third electrode 2c is carried out. In this step (S2), the third electrode 2c is formed on the second surface 42 of the semiconductor layer 4 (see FIG. 2). Specifically, a protective film is first formed to cover the first surface 41 of the semiconductor layer 4. The protective film is, for example, a resist. Next, the third electrode 2c is formed on the second surface 42 of the semiconductor layer 4. The material constituting the third electrode 2c includes at least one selected from the group consisting of, for example, gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), and chromium (Cr).

[0053] In this step (S2), before forming the third electrode 2c, an adhesion layer for improving adhesion between the semiconductor layer 4 and the third electrode 2c may be formed on the second surface 42 of the semiconductor layer 4. The material constituting the adhesion layer includes, for example, at least one of copper (Cr) and titanium (Ti). In addition, this step (S2) may be performed after the steps (S3 to S7) described later, as long as the first surface 41 of the semiconductor layer 4 is protected.

[0054] Thirdly, a step (S3) of forming an insulating layer 3 is carried out. In this step (S3), the insulating layer 3 is formed on the first surface 41 of the semiconductor layer 4. The method of forming the insulating layer 3 is not particularly limited and may be arbitrarily selected from, for example, a thermal oxidation method, a CVD (Chemical Vapor Deposition) method, and a sputtering method. When the material constituting the semiconductor layer 4 is Si, the insulating layer 3 may be, for example, SiO2 formed by partially thermally oxidizing the first surface 41 of the semiconductor layer 4.

[0055] Fourth, a step (S4) of forming the first electrode 2a and the second electrode 2b is performed. In this step (S4), the first electrode 2a and the second electrode 2b are formed on the insulating layer 3.

[0056] The method for forming the first electrode 2a and the second electrode 2b is not particularly limited, but for example, the following lift-off method can be adopted. First, a resist mask is formed on the upper surface of the insulating layer 3 using photolithography or EB drawing. In the resist mask, openings are formed in the regions where the first electrode 2a and the second electrode 2b are to be formed. Second, a conductive film to become the first electrode 2a and the second electrode 2b is formed on the upper surface of the resist mask using a deposition method, a sputtering method, or the like. The conductive film is formed so as to extend from the inside of the opening of the resist mask to the upper surface of the resist mask. Third, the resist mask is removed together with a part of the conductive film disposed on the upper surface of the resist mask. As a result, the other part of the conductive film disposed in the opening of the resist mask remains on the surface of the insulating layer 3 and becomes the first electrode 2a or the second electrode 2b. Note that, before forming the first electrode 2a and the second electrode 2b, an adhesion layer for improving adhesion between the semiconductor layer 4 and the first electrode 2a or the second electrode 2b may be formed on the first surface 41 of the semiconductor layer 4. Alternatively, the first electrode 2a and the second electrode 2b may be formed by an etching method using a mask formed on a conductive film that is to become the first electrode 2a and the second electrode 2b.

[0057] Fifth, a step (S5) of forming a two-dimensional material layer 1 is performed. In this step (S5), for example, a two-dimensional material layer is formed so as to cover the first electrode 2a, the second electrode 2b, and the insulating layer 3, and then the two-dimensional material layer is patterned. As a result, the two-dimensional material layer 1 shown in FIG. 1 and FIG. 2 is formed.

[0058] The method for forming the two-dimensional material layer 1 is not particularly limited. The two-dimensional material layer 1 may be formed on the first electrode 2a, the insulating layer 3, and a part of the semiconductor layer 4 by, for example, an epitaxial growth method or a screen printing method. The two-dimensional material layer 1 may also be formed by transferring and attaching a film-like two-dimensional material layer formed on a substrate different from the semiconductor layer 4 by a CVD method or the like, or a film-like two-dimensional material layer peeled off from graphite or the like by mechanical peeling or the like, onto the first electrode 2a, the insulating layer 3, and a part of the semiconductor layer 4. The method for patterning the two-dimensional material layer 1 is not particularly limited, but photolithography or EB drawing or the like may be adopted. When patterning is performed using a mask, the mask is removed after the two-dimensional material layer 1 is formed.

[0059] Next, a step (S6) of forming a first coating film 5 is performed. In this step (S6), the first coating film 5 is formed on the upper surface of the second two-dimensional material layer 12. The method of forming the first coating film 5 is not particularly limited. The first coating film 5 is formed, for example, by the following etching method. First, a coating film is formed by at least one of sputtering, deposition, and MOD coating method (MOD: Metal Organic Composition). Second, a mask is formed on the upper surface of the coating film by photolithography to cover the area where the first coating film 5 is to be formed. Third, a part of the coating film exposed from the mask is removed, for example, by a dry etching method. An example of dry etching is reactive ion etching using oxygen plasma or tetrafluoromethane (CF4) plasma. Fourth, the mask is removed. As a result, the coating film 5 shown in FIG. 1 and FIG. 2 is formed.

[0060] The gas detector 100 shown in FIG. 1 and FIG. 2 can be manufactured by the above steps (S1 to S6). In the above-mentioned manufacturing method, the two-dimensional material layer 1 is formed on the first electrode 2a and the second electrode 2b, but the first electrode 2a and the second electrode 2b may be formed on the two-dimensional material layer 1. However, when the first electrode 2a and the second electrode 2b are formed on the two-dimensional material layer 1, care must be taken not to cause process damage to the two-dimensional material layer 1 when forming the first electrode 2a and the second electrode 2b. For example, it is possible to form a protective film for protecting the two-dimensional material layer 1 other than the region where the first electrode 2a or the second electrode 2b is formed in an overlapping manner, and then form the first electrode 2a and the second electrode 2b.

[0061] <Operation principle> Next, the operation principle of the gas detector 100 will be described. The gas detector 100 functions as a 2:1 field effect transistor in which the third portion 1c of each two-dimensional material layer 1 is a transistor channel, each first electrode 2a and the first portion 1a of each two-dimensional material layer 1 is a source, each second electrode 2b and the second portion 1b of each two-dimensional material layer 1 is a drain, and the third electrode 2c is a gate. Hereinafter, the currents Isd1 and Isd2 flowing through each two-dimensional material layer 1 are also referred to as source-drain currents, and the voltage Vg applied to the third electrode 2c is also referred to as gate voltage.

[0062] The gas detector 100 is capable of detecting changes in the source-drain currents Isd1, Isd2 flowing through each of the two-dimensional material layers 1 when each of the voltages Vg, Vds1, and Vds2 is applied.

[0063] The gas detector 100 is also capable of detecting changes in each of the voltages Vds1 and Vds2 when the voltage Vg is applied and constant source-drain currents Isd1 and Isd2 are allowed to flow.

[0064] The gas detector 100 can also detect a change in frequency of the source-drain current value in the third portion 1c of the two-dimensional material layer 1 when each of the voltages Vg, Vds1, and Vds2 is applied. The electrical resonance frequency of the third portion 1c of the two-dimensional material layer 1 depends on the total mass of the third portion 1c of the two-dimensional material layer 1. The mass of the third portion 1c of the two-dimensional material layer 1 increases when the gas to be detected is adsorbed to the third portion 1c of the two-dimensional material layer 1. Therefore, the gas detector 100 can detect the concentration of the gas to be detected by converting the change in the resonance frequency of the third portion 1c when a DC voltage is applied into the amount of electromagnetic radiation irradiated to the two-dimensional material layer 1.

[0065] As described above, the gas detector 100 can simultaneously perform gas detection by the electromagnetic wave detection method and gas detection by the gas adsorption method.

[0066] First, the operating principle of gas detection by the electromagnetic wave detection method in the gas detector 100 will be described with reference to FIG.

[0067] FIG. 4 is a schematic diagram showing the change in electrical characteristics that occurs in each two-dimensional material layer 1 when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident on each two-dimensional material layer 1 of the gas detector 100. In FIG. 4, the solid line graph shows the relationship between the gate voltage Vg and the source-drain currents Isd1 and Isd2 flowing through each two-dimensional material layer 1, which are detected when the gas to be detected is present around the gas detector 100. The dashed line graph shows the relationship between the gate voltage Vg and the source-drain currents Isd1 and Isd2 flowing through each two-dimensional material layer 1, which are detected when the gas to be detected is not present around the gas detector 100. Furthermore, FIG. 4 shows the change amount Vph of the gate voltage Vg and the change amount Iph of each source-drain current depending on the presence or absence of the gas to be detected.

[0068] When a voltage Vg is applied to the semiconductor layer 4 via the third electrode 2c, a depletion layer is formed at the interface between the semiconductor layer 4 and the insulating layer 3. The positive and negative voltages of the voltage Vg can be selected according to the doping type of the semiconductor layer 4. A positive voltage is applied if the semiconductor layer 4 is of p-type, and a negative voltage is applied if the semiconductor layer 4 is of n-type.

[0069] Each of the two-dimensional material layers 1 and the semiconductor layer 4 has sensitivity to electromagnetic waves in a wavelength range absorbed by the gas to be detected. Therefore, when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on each of the two-dimensional material layers 1 and the semiconductor layer 4, photoelectric conversion occurs in each of the two-dimensional material layers 1 and the semiconductor layer 4, and photocarriers are generated in each of the two-dimensional material layers 1 and the depletion layer. The photocarriers generated in each of the two-dimensional material layers 1 change the source-drain currents Isd1 and Isd2.

[0070] Furthermore, the photocarriers generated in the depletion layer cause a change in the field effect in the third portion 1c of each two-dimensional material layer 1 through the insulating layer 3. As a result, the gate voltage Vg applied to the third portion 1c of each two-dimensional material layer 1 changes. The current flowing through the third portion 1c of each two-dimensional material layer 1 changes according to the amount of change Vph of this gate voltage Vg, and the source-drain currents Isd1 and Isd2 change. Furthermore, according to the gas detector 100, the amount of change Iph of the source-drain currents Isd1 and Isd2 detected when the electromagnetic wave is incident on each two-dimensional material layer 1 and the semiconductor layer 4 in a state in which the gas to be detected is not present on the optical path can also be detected. By detecting this current change Iph, it is possible to detect a change in the amount of light of the electromagnetic wave caused by the electromagnetic wave incident on the gas detector 100 being absorbed by the gas to be detected. By detecting this change in the amount of light, it is possible to detect the presence or absence of the gas to be detected on the optical path of the electromagnetic wave, measure the concentration of the gas to be detected, and identify the type of gas present on the optical path of the electromagnetic wave. Hereinafter, a change in the electrical properties of the material in contact with the two-dimensional material layer 1 causes a field effect in the two-dimensional material layer 1, and the change in the electrical properties of the two-dimensional material layer 1 is referred to as an optical gate effect.

[0071] Next, the operating principle of gas detection by gas adsorption in the gas detector 100 will be described with reference to FIG.

[0072] FIG. 5 is a schematic diagram of the change in electrical characteristics that occurs in the two-dimensional material layer 1 due to the adsorption of the gas to be detected to the two-dimensional material layer 1. In FIG. 5, the solid line graph shows the relationship between the gate voltage Vg and the source-drain current Isd1 flowing through the first two-dimensional material layer 11, which is detected when the gas to be detected is present around the gas detector 100. The dashed line graph shows the relationship between the gate voltage Vg and the source-drain current Isd1 flowing through the first two-dimensional material layer 11, which is detected when the gas to be detected is not present around the gas detector 100. The dashed line graph is equal to the relationship between the gate voltage Vg and the source-drain current Isd2 flowing through the second two-dimensional material layer 12, which is detected when the gas to be detected is present around the gas detector 100. Furthermore, FIG. 5 shows the change amount Vph of the gate voltage Vg and the change amount Iph of the source-drain current Isd1 depending on the presence or absence of the gas to be detected.

[0073] When the gas to be detected is physically adsorbed to the third portion 1c of the first two-dimensional material layer 11, charge transfer occurs between the gas and the first two-dimensional material layer 11. As a result, a gate voltage Vad is applied to the third portion 1c of the first two-dimensional material layer 11, and the source-drain current Isd1 flowing through the first two-dimensional material layer 11 changes. The amount of change Iad in this current correlates with the amount of gas adsorbed to the first two-dimensional material layer 11. The amount of gas adsorbed to the first two-dimensional material layer 11 correlates with the gas concentration around the first two-dimensional material layer 11. Therefore, the gas detector 100 allows quantitative analysis of the gas present around the two-dimensional material layer 1. Hereinafter, the gas adsorbed to the two-dimensional material layer 1 applies an electric field effect to the two-dimensional material layer 1, causing the electrical properties of the two-dimensional material layer 1 to change, which is referred to as the gas adsorption gate effect.

[0074] <Effects of the Gas Detector 100> The gas detector 100 can simultaneously perform gas detection by the electromagnetic wave detection method and gas detection by the gas adsorption method. Therefore, the gas detector 100 can detect a specific gas species in a mixed gas or identify a gas species, which was difficult to do with a conventional FET that performs gas detection only by the gas adsorption method described above. Furthermore, gas detection by the gas detector 100 using the electromagnetic wave detection method can be performed by utilizing the optical gate effect, as described above. Therefore, the gas detection sensitivity of the gas detector 100 is extremely high compared to that of a general gas detector that performs gas detection only by the electromagnetic wave detection method.

[0075] Furthermore, in a conventional FET that only performs gas detection by the above-mentioned gas adsorption method, it is difficult to detect gas at a position away from the surface of graphene. In contrast, the gas detector 100 is capable of gas detection by an electromagnetic wave detection method, and therefore can detect the presence or absence of a gas to be detected at a position away from the upper surface of the two-dimensional material layer 1 as long as it is on the optical path of the electromagnetic wave as described above.

[0076] Moreover, a general gas detector that only performs gas detection by an electromagnetic wave detection method passes electromagnetic waves in a specific wavelength range through a closed space (such as a gas cell) and measures the attenuation of the electromagnetic waves with a single element. Therefore, it is difficult for the gas detector to measure (map) the spatial distribution of gas concentration, and it is particularly impossible to measure the gas concentration distribution at a position away from the single element. In contrast, the gas detector 100 includes a first detection unit 100A having a first two-dimensional material layer 11 that is not covered by a coating film 5 and has an exposed surface exposed to the outside, and a second detection unit 100B having a second two-dimensional material layer 12 that is covered by a coating film 5 and does not have an exposed surface exposed to the outside. The first detection unit 100A can simultaneously perform gas detection by an electromagnetic wave detection method and gas detection by a gas adsorption method. The second detection unit 100B can only perform gas detection by a gas adsorption method. Therefore, based on the difference between the detection results from both detection units, it is possible to detect the spatial distribution of the gas to be detected, and more specifically, to determine whether the gas to be detected is present within an area where it can be adsorbed by the two-dimensional material layer 1.

[0077] Furthermore, the two-dimensional material layer 1 has a much higher surface-to-volume ratio than other materials other than the two-dimensional material layer, and all components exposed on the upper surface can contribute to gas adsorption. Therefore, the sensitivity of gas detection performed in the gas detector 100 using the gas adsorption gate effect is much higher than gas detection performed using other materials other than the two-dimensional material layer as the adsorbent.

[0078] <Modification> The gas detector according to the present disclosure may not include the semiconductor layer 4. Even in this case, the gas adsorption gate effect can occur. Furthermore, when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident, photocarriers are generated in the two-dimensional material layer 1, and the source-drain currents Isd1 and Isd2 change. Therefore, the gas detector 100 not including the semiconductor layer 4 can simultaneously perform gas detection by the electromagnetic wave detection method and gas adsorption method.

[0079] The gas detector according to the present disclosure does not need to include the second detection unit 100B. Since such a gas detector can simultaneously perform gas detection by the electromagnetic wave detection method and gas detection by the gas adsorption method, it can detect a specific gas species in a mixed gas, identify the gas species, and detect the presence or absence of a detection target gas at a position away from the upper surface of the two-dimensional material layer 1, just like the gas detector 100. In this case, the gas detector 100 preferably includes a plurality of first detection units 100A. Some of the plurality of first detection units 100A receive electromagnetic waves in a wavelength range that is absorbed by the gas to be detected and that have passed through a comparison container filled with a specific comparison gas different from the gas to be detected. The surface of the two-dimensional material layer may be modified to allow binding and capture of a specific gas. For example, an antibody that has the gas to be detected as an antigen may be bound to the surface of the two-dimensional material layer. In this way, a gas detector capable of specific detection can be realized. The antibody bound to the surface of the two-dimensional material layer may include a primary antibody that binds to the gas to be detected and a secondary antibody that is labeled with a fluorescent substance or an enzyme and binds to the primary antibody. In this case, the gas detector detects the primary antibody that has the gas to be detected as an antigen and examines the distribution of the fluorescent substance and enzyme on the surface of the two-dimensional material layer, thereby making it possible to perform detection by dyeing in parallel in addition to the gas molecule detection described in the operating principle of the present invention, and to measure the detection accuracy and spatial concentration distribution of gas molecular species.

[0080] The antibody bound to the surface of the two-dimensional material layer may have a reactive functional group, such as a silyl group, a carboxyl group, or an amine group, on the surface of the two-dimensional material layer that can be covalently bonded to the gas molecule species to be detected, thereby enabling highly specific gas detection with a specific type of gas molecule as the target molecule.

[0081] The surface of the two-dimensional material layer may be coated with a peptide specific to the gas molecules to be detected, which promotes binding between the surface of the two-dimensional material layer 1 and the gas to be detected, thereby improving the detection accuracy of the gas to be detected while suppressing deterioration of the detection accuracy due to gases other than the target gas.

[0082] The surface of the two-dimensional material layer may be modified with a hydrogel, which can promote the interaction between the two-dimensional material layer and the gas molecules to be detected, thereby improving the detection accuracy.

[0083] The gas detector 100 may further include a light source that irradiates each of the multiple two-dimensional material layers 1 with electromagnetic waves in a wavelength range that is absorbed by the gas to be detected.

[0084] The gas detector 100 may further include a container that is disposed on the optical path of the electromagnetic waves incident on the multiple detection units shown in Figures 1 and 2 and that can enclose a gas to be detected. In this way, deterioration of signal quality due to erroneous detection of a gas that is not the target of detection can be suppressed.

[0085] The gas detector 100 may further include a column capable of separating gas components, and may be provided such that the gas components separated by the column are supplied to the periphery of each of the multiple detection units. The column may be capable of separating multiple types of gas components contained in the gas to be detected. Such a gas detector 100 may sequentially detect the multiple types of gas components separated by the column.

[0086] The gas detector 100 may further include a gas generator for generating a gas to be detected and supplying the gas to the periphery of each of the multiple detection units. As described above, the gas generator may be a heating device for generating an aerosol. Such a gas detector 100 can detect fine particles suspended in the gas in the form of an aerosol.

[0087] The gas detector 100 may further include an optical filter that controls the wavelength range of the electromagnetic wave incident on each of the multiple detection units. The optical filter may be attached to the container, for example. In such a gas detector 100, by controlling the wavelength of the electromagnetic wave to be irradiated and detected according to the above-mentioned operating principle, it becomes possible to detect multiple types of electromagnetic waves and thus multiple types of gas molecules.

[0088] The gas detector 100 may further include a third detection unit. The gas detector 100 may further include a third set of the first electrode 2a and the second electrode 2b, a third two-dimensional material layer, and a second coating film covering the third two-dimensional material layer. The third set of the first electrode 2a and the second electrode 2b are spaced apart from the first electrode 2a and the second electrode 2b of the first set and the first electrode 2a and the second electrode 2b of the second set. The third two-dimensional material layer is spaced apart from the first two-dimensional material layer 11 and the second two-dimensional material layer 12, and electrically connects the third set of the first electrode 2a and the second electrode 2b. The second coating film is provided so as to block the transmission of electromagnetic waves in a wavelength range absorbed by the gas to be detected.

[0089] Embodiment 2 Unless otherwise specified, the gas detector according to the embodiment 2 has the same configuration, operating principle, and effects as those of the above-mentioned embodiment 1. Therefore, the same components as those of the above-mentioned embodiment 1 are given the same reference numerals, and the description thereof will not be repeated.

[0090] <Configuration of Gas Detector 101> As shown in FIG. 6, the gas detector 101 according to the second embodiment comprises a ferroelectric layer 6 in contact with at least a part of the two-dimensional material layer 1 .

[0091] The ferroelectric layer 6 is disposed, for example, between the third portion 1c of the two-dimensional material layer 1 and the insulating layer 3. The ferroelectric layer 6 may be disposed, for example, on the upper surface of the third portion 1c of the two-dimensional material layer 1. The ferroelectric layer 6 may not be in contact with the two-dimensional material layer 1, and may be connected to the two-dimensional material layer 1 via the insulating layer 3.

[0092] The material constituting the ferroelectric layer 6 may be any material that generates polarization when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the ferroelectric layer. The material constituting the ferroelectric layer 6 includes, for example, at least one of barium titanate (BaTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), strontium titanate (SrTiO3), lead zirconate titanate (PZT), strontium tantalate bismuthate (SBT), bismuth ferrite (BFO), zinc oxide (ZnO), hafnium oxide (HfO2), and polyvinylidene fluoride ferroelectrics (PVDF, P(VDF-TrFE), P(VDF-TrFE-CTFE), etc.), which are organic polymers. The ferroelectric layer may also be formed by stacking or mixing a plurality of different ferroelectric materials.

[0093] The material constituting the ferroelectric layer 6 may be, for example, a material that undergoes polarization when an electromagnetic wave having a wavelength range different from the wavelength range to which the semiconductor layer 4 has sensitivity is incident on the ferroelectric layer 6. The gas detector 101 having such a configuration is suitable for detecting a plurality of types of gases.

[0094] The material of the ferroelectric layer 6 is not limited to the above materials as long as it is a pyroelectric body that exhibits a pyroelectric effect. Specifically, the material of the ferroelectric layer may be a ferroelectric body that undergoes a polarization change in response to a change in thermal energy inside the ferroelectric layer. In the pyroelectric effect, electromagnetic waves simply act as a heat source. Therefore, the pyroelectric effect is basically not wavelength-dependent. Therefore, the ferroelectric layer is basically not wavelength-dependent. Therefore, the ferroelectric layer has sensitivity to a wide band of electromagnetic waves.

[0095] The gas detector 101 comprises, for example, a first ferroelectric layer 61 in contact with the first two-dimensional material layer 11 and a second ferroelectric layer 62 in contact with the second two-dimensional material layer 12. The second ferroelectric layer 62 has, for example, a configuration similar to that of the first ferroelectric layer 61.

[0096] <Operation principle> In the gas detector 101, when the ferroelectric layer 6 is irradiated with an electromagnetic wave, a change in dielectric polarization occurs inside the ferroelectric layer 6 due to the pyroelectric effect of the ferroelectric layer 6. The change in polarization occurring in the ferroelectric layer 6 due to the pyroelectric effect applies an electric field change to the third portion 1c of the two-dimensional material layer 1. As a result, the gate voltage applied to the third portion 1c of the two-dimensional material layer 1 changes, and the source-drain current value changes. That is, in the gas detector 101, an electric field effect is applied to the two-dimensional material layer 1 due to the pyroelectric effect of the ferroelectric layer 6, and the electrical characteristics of the two-dimensional material layer 1 change. Therefore, in the gas detector 101, the above-mentioned optical gate effect by the semiconductor layer 4 and the optical gate effect by the ferroelectric layer 6 can be used for gas detection by the electromagnetic wave detection method.

[0097] <Effects> According to the gas detector 101, since the above-mentioned optical gate effect by the semiconductor layer 4 and the optical gate effect by the ferroelectric layer 6 can be utilized, it is possible to realize even higher sensitivity than the gas detector 100.

[0098] As described above, the material constituting the ferroelectric layer 6 may be a material that undergoes polarization when electromagnetic waves in a wavelength range different from the wavelength range to which the semiconductor layer 4 has sensitivity are incident on the ferroelectric layer 6. In this case, highly sensitive gas detection is possible in a plurality of electromagnetic wavelength ranges by utilizing the optical gate effect.

[0099] <Modification> The gas detector 101 may be modified in the same manner as the gas detector 100 .

[0100] Embodiment 3 Unless otherwise specified, the gas detector according to the embodiment 3 has the same configuration, operating principle, and effects as those of the above-mentioned embodiment 1. Therefore, the same components as those of the above-mentioned embodiment 1 are given the same reference numerals, and the description thereof will not be repeated.

[0101] <Configuration of Gas Detector 102> As shown in FIG. 7, the gas detector 101 according to the second embodiment comprises a contact layer 7 in contact with at least a part of the two-dimensional material layer 1 .

[0102] 7, a contact layer 7 is provided under the two-dimensional material layer 1. The contact layer 7 is made of a material that can supply holes or electrons to the two-dimensional material layer 1 by contacting the two-dimensional material layer 1. The contact layer 7 allows the two-dimensional material layer 1 to be doped with holes or electrons as desired.

[0103] For example, a composition containing a photosensitive agent having a quinone diazide group and a novolac resin, which is called a positive photoresist, can be used as the contact layer 7. For example, a material having a polar group can be used as the material constituting the contact layer 7. For example, a material having an electron-withdrawing group, which is one example of the material, has the effect of reducing the electron density of the two-dimensional material layer 1. For example, a material having an electron-donating group, which is one example of the material, has the effect of increasing the electron density of the two-dimensional material layer 1. For example, a material having an electron-withdrawing group can be a material having a halogen, a nitrile, a carboxyl group, or a carbonyl group. For example, a material having an electron-donating group can be a material having an alkyl group, an alcohol, an amino group, or a hydroxyl group. In addition to the above, a material in which a charge bias occurs in the entire molecule due to a polar group can also be used as the material of the contact layer 7.

[0104] In addition, any material that generates polarity by causing charge imbalance in the molecule, such as organic matter, metal, semiconductor, insulator, two-dimensional material, or a mixture of any of these materials, can be used as the material of the contact layer 7. Here, when the contact layer 7 made of an inorganic material is brought into contact with the two-dimensional material layer 1, the conductivity type of the two-dimensional material layer 1 to be doped is p-type when the work function of the contact layer 7 is larger than that of the two-dimensional material layer 1, and is n-type when the work function is smaller. On the other hand, when the contact layer 7 is an organic material, the organic material constituting the contact layer 7 does not have a clear work function. Therefore, it is preferable to determine whether the two-dimensional material layer 1 is n-type doped or p-type doped by determining the polar group of the material of the contact layer 7 depending on the polarity of the molecules of the organic material used in the contact layer 7.

[0105] For example, when a composition containing a photosensitive agent having a quinone diazide group and a novolac resin, which is called a positive photoresist, is used as the contact layer 7, the region in the two-dimensional material layer 1 where the resist is formed by a photolithography process becomes a p-type two-dimensional material layer region. This makes it unnecessary to form a mask that contacts the surface of the two-dimensional material layer 1. As a result, it is possible to reduce process damage to the two-dimensional material layer 1 and simplify the process.

[0106] The gas detector 102 comprises, for example, a first contact layer 71 in contact with the first 2D material layer 11 and a second contact layer 72 in contact with the second 2D material layer 12. The second contact layer 72 has, for example, a configuration similar to that of the first contact layer 71.

[0107] The method for manufacturing the gas detector 102 may, for example, further comprise the step of forming a contact layer 7 prior to the step of forming the two-dimensional material layer 1 .

[0108] <Effects> The gas detector 102 includes a contact layer 7 capable of supplying holes or electrons to the two-dimensional material layer 1. Therefore, in the gas detector 102, the conductivity type of the two-dimensional material layer 1 can be intentionally set to n-type or p-type. Therefore, the carrier doping of the two-dimensional material layer 1 can be controlled without considering the influence of carrier doping accompanying the contact between the two-dimensional material layer 1 and the electrode 2 and the insulating layer 3. As a result, the performance of the gas detector 102 can be improved.

[0109] Furthermore, by forming the contact layer 7 only on either the first electrode 2a side or the semiconductor layer 4 side on the upper surface of the two-dimensional material layer 1, a gradient of charge density is formed in the two-dimensional material layer 1. As a result, the mobility of carriers in the two-dimensional material layer 1 is improved, and the sensitivity of the gas detector 102 can be increased.

[0110] Also, multiple contact layers 7 may be formed on the two-dimensional material layer 1. The number of contact layers 7 may be three or more, and may be any number. Multiple contact layers 7 may be formed on the two-dimensional material layer 1 located between the first electrode 2a and the semiconductor layer 4. In this case, the materials of the multiple contact layers 7 may be the same material or different materials.

[0111] In the gas detector according to the present embodiment, the thickness of the contact layer 7 is preferably thin enough to perform photoelectric conversion when the two-dimensional material layer 1 is irradiated with electromagnetic waves. On the other hand, the contact layer 7 is preferably formed to have a thickness that allows carriers to be doped from the contact layer 7 into the two-dimensional material layer 1. The contact layer 7 may have any configuration as long as carriers such as molecules or electrons are introduced into the two-dimensional material layer 1. For example, the two-dimensional material layer 1 may be immersed in a solution to supply carriers to the two-dimensional material layer 1 at the molecular level, thereby doping the two-dimensional material layer 1 with carriers without forming a solid contact layer 7 on the two-dimensional material layer 1.

[0112] In addition to the above-mentioned materials, materials that cause polarity conversion may be used as the material of the contact layer 7. In that case, when the contact layer 7 changes polarity, electrons or holes generated during the conversion are supplied to the two-dimensional material layer 1. Therefore, doping of electrons or holes occurs in the part of the two-dimensional material layer 1 that is in contact with the contact layer 7. Therefore, even if the contact layer 7 is removed, the part of the two-dimensional material layer 1 that was in contact with the contact layer 7 remains in a state where the electrons or holes are doped. Therefore, when a material that causes polarity conversion is used as the contact layer 7, the contact layer 7 may be removed from the two-dimensional material layer 1 after a certain time has passed. In this case, the opening area of ​​the two-dimensional material layer 1 is increased compared to when the contact layer 7 is present. Therefore, the detection sensitivity of the gas detector can be improved. Here, polarity conversion is a phenomenon in which a polar group is chemically converted, and means, for example, a phenomenon in which an electron-withdrawing group changes to an electron-donating group, or an electron-donating group changes to an electron-withdrawing group, or a polar group changes to a non-polar group, or a non-polar group changes to a polar group.

[0113] The contact layer 7 may be formed of a material that undergoes polarity conversion when irradiated with electromagnetic waves. In this case, by selecting a material that undergoes polarity conversion at a specific electromagnetic wavelength as the material for the contact layer 7, polarity conversion can be caused in the contact layer 7 only when irradiated with electromagnetic waves of the specific electromagnetic wavelength, thereby allowing doping to be performed on the two-dimensional material layer 1. As a result, the photocurrent flowing into the two-dimensional material layer 1 can be increased.

[0114] Furthermore, a material that undergoes an oxidation-reduction reaction when irradiated with electromagnetic waves may be used as the material of the contact layer 7. In this case, the two-dimensional material layer 1 can be doped with electrons or holes that are generated during the oxidation-reduction reaction.

[0115] <Modification> The gas detector 102 can also be modified in the same manner as the gas detector 100. Moreover, the configuration of the gas detector according to this embodiment can also be applied to the other embodiments.

[0116] Embodiment 4 Unless otherwise specified, the gas detector according to the embodiment 4 has the same configuration, operating principle, and effects as those of the above-mentioned embodiment 1. Therefore, the same components as those of the above-mentioned embodiment 1 are given the same reference numerals, and the description thereof will not be repeated.

[0117] <Configuration of Gas Detector 104> As shown in Fig. 8, the gas detector 103 according to the fourth embodiment includes at least one conductor 8 in contact with at least a portion of the two-dimensional material layer 1. In the gas detector 103 shown in Fig. 8, a plurality of conductors 8 are disposed on an upper surface of the third portion 1c of the two-dimensional material layer 1. The plurality of conductors 8 are disposed at intervals from one another. Each conductor 8 is a floating electrode.

[0118] Any material that is a conductor can be used as the material for the conductor 8. For example, metal materials such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), chromium (Cr), or palladium (Pd) can be used as the material for the conductor 8. Here, the conductor 8 is not connected to a power circuit or the like and is floating.

[0119] The plurality of conductors 8 have a one-dimensional or two-dimensional periodic structure. For example, as an example of the one-dimensional periodic structure, a structure in which the plurality of conductors 8 are arranged (periodically) at intervals from each other in the horizontal direction on the paper surface of FIG. 8 or in the depth direction of the paper surface may be adopted. Also, as an example of the two-dimensional periodic structure, a structure in which the conductors 8 are arranged at positions corresponding to lattice points of a square lattice or a triangular lattice in a plan view of the gas detector may be adopted. Also, in a plan view of the gas detector, the planar shape of each conductor 8 may be any shape such as a circular shape, a triangular shape, a square shape, a polygonal shape, or an elliptical shape. Also, the arrangement of the conductors 8 in a plan view is not limited to the above-mentioned arrangement having periodic symmetry, and may be an arrangement having asymmetricity in a plan view. Here, a specific method for forming the conductors 8 may be any method, but for example, a method similar to the manufacturing method of the first electrode 2a and the second electrode 2b described in the first embodiment may be used.

[0120] The method for manufacturing the gas detector 103 may further include, for example, a step of forming the conductor 8 after the step of forming the two-dimensional material layer 1 and before the step of forming the covering film 5.

[0121] <Effects of Gas Detector 103> The gas detector 103 includes a conductor 8 that is a floating electrode on the two-dimensional material layer 1. Therefore, surface carriers generated in the two-dimensional material layer 1 by irradiation with electromagnetic waves can move between the multiple conductors 8, which results in a longer life of the photocarriers. This improves the detection sensitivity of the gas detector 103.

[0122] Furthermore, by arranging a plurality of conductors 8 to form a one-dimensional periodic structure and using a material for conductors 8 that generates surface plasmon resonance, the irradiated electromagnetic wave causes polarization dependence in conductors 8. As a result, only electromagnetic waves of a specific polarization can be irradiated onto semiconductor layer 4 of gas detector 103. In this case, gas detector 103 according to this embodiment can detect only light of a specific polarization.

[0123] Furthermore, by arranging a plurality of conductors 8 to form a two-dimensional periodic structure and using a material for the conductors 8 that generates surface plasmon resonance, electromagnetic waves of a specific wavelength can be resonated by the plurality of conductors 8. In this case, only electromagnetic waves having a specific wavelength can be detected by the gas detector 103. In this case, the gas detector 103 according to this embodiment can detect only electromagnetic waves of a specific wavelength with high sensitivity.

[0124] Furthermore, when the plurality of conductors 8 are formed to be arranged asymmetrically in a plan view, the conductors 8 exhibit polarization dependency with respect to the irradiated electromagnetic waves, as in the case where the plurality of conductors 8 are arranged in a one-dimensional periodic structure. As a result, only electromagnetic waves of a specific polarization can be irradiated onto the semiconductor layer 4. In this case, the gas detector 103 according to this embodiment can improve the signal-to-noise ratio of the detection signal by detecting only light of a specific polarization, and can also improve the contrast.

[0125] In addition, in the gas detector 103, a conductor 8 may be disposed under the two-dimensional material layer 1. With such a configuration, the same effect as that of the gas detector 103 shown in Fig. 8 can be obtained. Furthermore, in this case, since the two-dimensional material layer 1 is not damaged when the conductor 8 is formed, a decrease in the mobility of carriers in the two-dimensional material layer 1 can be suppressed.

[0126] Furthermore, a concave-convex portion may be formed in the two-dimensional material layer 1. In this case, the concave-convex portion of the two-dimensional material layer 1 may have a periodic structure or an asymmetric structure, similar to the above-mentioned multiple conductors 8. In this case, the same effect as when multiple conductors 8 are formed can be obtained.

[0127] <Modification> The gas detector 103 can also be modified in the same manner as the gas detector 100. The configuration of the gas detector according to this embodiment can also be applied to the other embodiments.

[0128] Embodiment 5. Unless otherwise specified, the gas detector according to the embodiment 5 has the same configuration, operating principle, and effects as those of the above-mentioned embodiment 1. Therefore, the same components as those of the above-mentioned embodiment 1 are given the same reference numerals, and the description thereof will not be repeated.

[0129] <Configuration of Gas Detector 104> 9, in the gas detector 104 according to the fourth embodiment, the third portion 1c of each of the first two-dimensional material layer 11 and the second two-dimensional material layer 12 is bridged between the first portion 1a and the second portion 1b. The insulating layer 3 is formed with a plurality of recesses 30 recessed with respect to the upper surface of the insulating layer 3. Each recess 30 is formed as, for example, an opening (through hole) exposing the first surface 41 of the semiconductor layer 4. In this case, the lower surface of the third portion 1c is disposed opposite the first surface 41 of the semiconductor layer 4 with a gap therebetween.

[0130] The third portion 1c of each two-dimensional material layer 1 has, for example, a pair of contact portions 1d in contact with the upper surface of the insulating layer 3 and a bridging portion 1e bridging between the pair of contact portions 1d. The bridging portion 1e is not in contact with the insulating layer 3 and the semiconductor layer 4.

[0131] Note that the recess 30 of the insulating layer 3 only needs to be provided so that even when the third portion 1c is deflected by its own weight, the lower surface of the third portion 1c does not come into contact with the insulating layer 3 or the semiconductor layer 4. When the recess 30 of the insulating layer 3 is formed as an opening, a second recess (not shown) that is recessed with respect to the first surface 41 and is continuous with the recess 30 of the insulating layer 3 in the up-down direction may be formed in the semiconductor layer 4.

[0132] The method for manufacturing the gas detector 104 may further include a step of forming a recess 30 in the insulating layer 3 before the step of forming the two-dimensional material layer 1.

[0133] <Effects of the gas detector 104> In the gas detector 104, the third portion 1c of the two-dimensional material layer 1 acting as a transistor channel has a portion that is not in contact with other materials, and therefore the mobility of electrons and holes is increased compared to the gas detector 100, etc. As a result, the detection sensitivity of the gas detector 104 is improved.

[0134] <Modification> The gas detector 104 can also be modified in the same manner as the gas detector 100. Moreover, the configuration of the gas detector according to this embodiment can also be applied to the other embodiments.

[0135] Embodiment 6 Unless otherwise specified, the gas detector according to the embodiment 6 has the same configuration, operating principle, and effects as those of the above-mentioned embodiment 1. Therefore, the same components as those of the above-mentioned embodiment 1 are given the same reference numerals, and the description thereof will not be repeated.

[0136] <Configuration of Gas Detector 105> 10 and 11, in a gas detector 105 according to the sixth embodiment, at least one opening 31 exposing a part of the first surface of the semiconductor layer 4 is formed in the insulating layer 3. In the gas detector 105 shown in Fig. 10, a first opening 31A and a second opening 31B are formed at a distance from each other. The gas detector 105 has, for example, a first first electrode 2a1 and a second first electrode 2a2 arranged at a distance from each other.

[0137] The gas detector 105 includes a fourth two-dimensional material layer 13 and a fifth two-dimensional material layer 14 instead of the first two-dimensional material layer 11 and the second two-dimensional material layer 12. The fourth two-dimensional material layer 13 extends from within the first opening 31A onto the insulating layer 3 and electrically connects between the first first electrode 2a1 and the semiconductor layer 4. The fourth two-dimensional material layer 13 has an exposed surface exposed to the outside. The fifth two-dimensional material layer 14 extends from within the second opening 31B onto the insulating layer 3 and electrically connects between the second first electrode 2a2 and the semiconductor layer 4. The fifth two-dimensional material layer 14 is covered by a coating film 5 (third coating film).

[0138] Each of the fourth 2D material layer 13 and the fifth 2D material layer 14 has a first portion 1a, a second portion 1b, and a third portion 1c.

[0139] The second portion 1b of each of the fourth two-dimensional material layer 13 and the fifth two-dimensional material layer 14 is in contact with the part of the first surface 41 exposed in the opening 31 in the semiconductor layer 4. Preferably, the second portion 1b of the two-dimensional material layer 1 forms a Schottky junction with the semiconductor layer 4. For example, the semiconductor layer 4 is made of a p-type material, silicon, and the two-dimensional material layer 1 is made of an n-type material, graphene.

[0140] The second electrode 2 b is disposed on the second surface 42 of the semiconductor layer 4 and is electrically connected to the two-dimensional material layer 1 via the semiconductor layer 4 .

[0141] In the gas detector 105, similarly to the gas detector 100, the third portion 1c of each two-dimensional material layer 1 acts as a transistor channel, each first electrode 2a and the first portion 1a of each two-dimensional material layer 1 act as a source, and each second electrode 2b and the second portion 1b of each two-dimensional material layer 1 act as a drain. Furthermore, in the gas detector 105, the contact region between the second portion 1b of the two-dimensional material layer 1 and the semiconductor layer 4 functions as a Schottky barrier diode.

[0142] 11, a power supply circuit for applying a voltage Vd is electrically connected between the first first electrode 2a1 and the second electrode 2b, and between the second first electrode 2a2 and the second electrode 2b. Preferably, the voltage Vd is set to be a reverse bias with respect to the Schottky junction between the two-dimensional material layer 1 and the semiconductor layer 4. When the voltage Vd is applied, currents Id1 and Id2 flow through each of the two-dimensional material layers 1. The currents Id1 and Id2 are measured by an ammeter (not shown) included in the power supply circuit.

[0143] The above-mentioned optical gate effect and gas adsorption gate effect may also occur in the gas detector 105 .

[0144] Furthermore, in the gas detector 105, when the two-dimensional material layer 1 and the semiconductor layer 4 form a Schottky junction, the currents Id1 and Id2 can be made zero when no electromagnetic waves are incident by adjusting the voltage V and applying a reverse bias to the Schottky junction. In addition, the Fermi level of the two-dimensional material layer 1 is modulated by the photoelectromotive force generated when the electromagnetic wave is incident on the semiconductor layer 4, and the energy barrier between the two-dimensional material layer 1 and the semiconductor layer 4 is lowered. As a result, only when the electromagnetic wave is irradiated, a current flows through the semiconductor layer 4, and the currents Id1 and Id2 are detected. That is, the gas detector according to this embodiment is capable of OFF operation.

[0145] The gas detector 105 according to the present embodiment is also not limited to a configuration for detecting a change in current in the two-dimensional material layer 1. The gas detector 105 can also detect changes in each of the voltages Vd1 and Vd2, for example, in a state in which a constant current flows between each of the first electrodes 2a and the second electrodes 2b.

[0146] Moreover, the gas detector 105 can also detect a change in the source-drain current value in the third portion 1 c of the two-dimensional material layer 1 with respect to frequency.

[0147] <Effects of Gas Detector 105> According to the gas detector 105, since the OFF operation is possible, it is expected that the power consumption will be reduced and the signal-to-noise ratio will be improved.

[0148] <Modifications of the Gas Detector 105> 12 and 13 show modified examples of the gas detector 105. In a gas detector 106 shown in FIG 12 and a gas detector 107 shown in FIG 13, the planar shape of the second portion 1b of the two-dimensional material layer 1 is different from that of the gas detector 105 shown in FIG 10.

[0149] The area of ​​the contact region between the second portion 1b of the two-dimensional material layer 1 and the semiconductor layer 4 in each of the gas detectors 106 and 107 is smaller than the area of ​​the contact region between the second portion 1b and the semiconductor layer 4 in the gas detector 105. In the gas detectors 106 and 107, the area of ​​the contact region between the second portion 1b and the semiconductor layer 4 is smaller than the sum of the occupied areas of the first portion 1a and the third portion 1c in a plan view.

[0150] The second portion 1b of each of the gas detectors 106 and 107 corresponds to the second portion 1b of the gas detector 105 from which a plurality of regions spaced apart from one another at least in a direction intersecting with the extending direction of the two-dimensional material layer 1 (the direction in which the first portion 1a, the third portion 1c, and the second portion 1b are arranged side by side) are removed. In the gas detector 106, each of the regions has a rectangular planar shape. In the gas detector 107, each of the regions has a regular planar shape.

[0151] In each of the gas detectors 106 and 107, the planar shapes of the first portion 1a, the second portion 1b, and the third portion 1c are symmetrical with respect to a line extending along the extending direction passing through the center of the two-dimensional material layer 1 in the direction intersecting with the extending direction. In addition, in a cross section passing through the center of the two-dimensional material layer 1 in the direction intersecting with the extending direction, the gas detectors 106 and 107 have a structure equivalent to that of, for example, the gas detector 105.

[0152] 12 has a comb-shaped (ladder-shaped) planar shape. In the gas detector 106, the sum of the widths of the second portions 1b in a direction intersecting with the extending direction of the two-dimensional material layer 1 is narrower than the widths of the first portions 1a and the third portions 1c in the intersecting direction. In the gas detector 106, a plurality of openings exposing the semiconductor layer 4 are formed, and the plurality of openings are arranged side by side in the intersecting direction.

[0153] 13 has a lattice shape in plan view. In the gas detector 107, a plurality of openings exposing the semiconductor layer 4 are formed in the two-dimensional material layer 1, and the plurality of openings are arranged side by side in both the extending direction of the two-dimensional material layer 1 and a direction intersecting therewith. In the gas detector 107, the minimum value of the sum of the widths of the second portion 1b in a direction intersecting the extending direction of the two-dimensional material layer 1 is narrower than the minimum widths of the first portion 1a and the third portion 1c in the intersecting direction.

[0154] In the gas detectors 106 and 107, the area of ​​the contact region between the two-dimensional material layer 1 and the semiconductor layer 4 is adjusted according to the width of the second portion 1b in the extension direction of the two-dimensional material layer 1. Therefore, in the gas detectors 106 and 107, the contact resistance between the two-dimensional material layer 1 and the semiconductor layer 4, and therefore the resistance of the gas detector, can be adjusted. In the gas detectors 106 and 107, the variation in the characteristics of the gas detector can be reduced and the dark current can be reduced compared to the gas detector 105 shown in FIG.

[0155] In addition, in the gas detectors 106 and 107, the sum of the areas of the end faces of the second portion 1b is larger than the sum of the areas of the end faces of the second portion 1b of the gas detector 105 shown in FIG. 10. The end face of the second portion 1b is a surface extending along the thickness direction of the two-dimensional material layer 1, in other words, along a direction perpendicular to the sheet in which atoms are two-dimensionally arranged in the two-dimensional material layer 1. In other words, the end face area of ​​the two-dimensional crystal structure in each of the second portions 1b shown in FIG. 12 and FIG. 13 is larger than the end face area of ​​the two-dimensional crystal structure in the second portion 1b shown in FIG. 10. Therefore, in each of the two-dimensional material layers 1 shown in FIG. 12 and FIG. 13, the ratio of unbonded hands (dangling bonds) of the two-dimensional crystal structure increases compared to the two-dimensional material layer 1 shown in FIG. 10. As a result, when carriers generated in the semiconductor layer 4 by electromagnetic wave irradiation are transported to each first electrode 2a through the two-dimensional material layer 1, the rate of change in carrier density is larger in each of the two-dimensional material layers 1 shown in Figures 12 and 13 than in the two-dimensional material layer 1 shown in Figure 10, and the carrier mobility is increased, resulting in a larger change in the current I. As a result, the detection sensitivity of the gas detectors 106 and 107 shown in Figures 12 and 13 is higher than that of the gas detector 105 shown in Figure 10.

[0156] In the gas detectors 106 and 107, the second portion 1b of the two-dimensional material layer 1 may be a graphene nanoribbon. The graphene nanoribbon has a band gap that changes depending on its width. Therefore, depending on the width of the second portion 1b made of the graphene nanoribbon in the crossing direction, the wavelength range of the electromagnetic wave that can be photoelectrically converted in the second portion 1b can be adjusted, and can be narrower than the wavelength range of the electromagnetic wave that can be photoelectrically converted in other regions. In this case, the photocarriers generated by the photoelectric conversion in the second portion 1b can be detected separately from the photocarriers generated by the photoelectric conversion in other regions. Furthermore, the sensitivity of the gas detector is improved by detecting the photocarriers generated by the photoelectric conversion in the second portion 1b. Furthermore, in such a gas detector, the second portion 1b made of the graphene nanoribbon and the semiconductor layer 4 form a Schottky junction, so that the dark current is reduced, and the sensitivity is improved by detecting the photocarriers generated by the electromagnetic wave absorbed at the Schottky junction.

[0157] The gas detectors 105-107 may further include a third detection unit. The gas detectors 105-107 may further include a third first electrode 2a, a sixth two-dimensional material layer, and a fourth coating film covering the sixth two-dimensional material layer. In the gas detectors 105-107, a third opening may be further formed in the insulating layer 3, the third opening being spaced apart from the first opening and the second opening. The third set of first electrodes 2a and second electrodes 2b are spaced apart from the first set of first electrodes 2a and second electrodes 2b, and the second set of first electrodes 2a and second electrodes 2b. The sixth two-dimensional material layer extends from within the third opening onto the insulating layer 3, and electrically connects the third first electrode and the semiconductor layer 4. The fourth coating film is provided so as to block the transmission of electromagnetic waves in a wavelength range absorbed by the gas to be detected.

[0158] The configuration of the gas detector according to this embodiment can also be applied to the other embodiments. <Modifications of Gas Detectors 100 to 107> In each of the gas detectors 100 to 107, it is preferable that at least one of the materials constituting the insulating layer 3, the semiconductor layer 4, the ferroelectric layer 6, the contact layer 7, and the conductor 8 is a material whose properties change when irradiated with electromagnetic waves, causing a change in potential to the two-dimensional material layer 1.

[0159] Here, examples of materials that change in characteristics when irradiated with electromagnetic waves and cause a change in potential to the two-dimensional material layer 1 include quantum dots, ferroelectric materials, liquid crystal materials, fullerenes, rare earth oxides, semiconductor materials, pn junction materials, metal-semiconductor junction materials, and metal-insulator-semiconductor junction materials. For example, when a ferroelectric material having a polarization effect (pyroelectric effect) caused by electromagnetic waves is used as the ferroelectric material, a change in polarization occurs in the ferroelectric material when irradiated with electromagnetic waves. As a result, a change in potential can be caused to the two-dimensional material layer 1.

[0160] As described above, when at least one of the materials constituting the insulating layer 3, the semiconductor layer 4, the ferroelectric layer 6, the contact layer 7, and the conductor 8 is a material whose characteristics change when irradiated with electromagnetic waves, the characteristics of at least one of the insulating layer 3, the semiconductor layer 4, the ferroelectric layer 6, the contact layer 7, and the conductor 8, which are made of the material, can change when irradiated with electromagnetic waves, causing a change in electric potential to be applied to the two-dimensional material layer 1.

[0161] More preferably, each of the materials constituting the insulating layer 3, the semiconductor layer 4, the ferroelectric layer 6, the contact layer 7, and the conductor 8 is a material whose properties change when irradiated with electromagnetic waves, causing a change in potential in the two-dimensional material layer 1.

[0162] When a material whose properties change when irradiated with electromagnetic waves and which imparts a change in potential to the two-dimensional material layer 1 is used for the contact layer 7, the contact layer 7 does not necessarily need to be in direct contact with the two-dimensional material layer 1. For example, as long as a change in potential can be imparted to the two-dimensional material layer 1, the contact layer 7 may be provided on the upper or lower surface of the two-dimensional material layer 1 via an insulating film or the like.

[0163] Embodiment 7 Fig. 14 is a top view of the gas detector array according to embodiment 7. Fig. 15 is a schematic diagram showing an example of a readout circuit that reads out an electrical signal obtained from the gas detector array according to embodiment 7. Fig. 16 is a top view showing a first modified example of the gas detector array according to embodiment 7.

[0164] 14, the gas detector array 1000 according to the seventh embodiment is an assembly of a plurality of gas detectors 100. The gas detector array 1000 has a plurality of gas detectors 100-107 according to any of the first to sixth embodiments as detection elements. The gas detector array 1000 includes, for example, a plurality of gas detectors 100 according to the first embodiment as gas detectors.

[0165] In the gas detector array 1000, the detection wavelengths of the multiple gas detectors 100 are equal. As shown in FIG. 14, in the gas detector array 1000, the multiple gas detectors 100 are arranged in a two-dimensional array. In other words, the multiple gas detectors 100 are arranged side by side in a first direction and a second direction intersecting the first direction. In the gas detector array 1000 shown in FIG. 14, four gas detectors 100 are arranged in a 2×2 array. However, the number of gas detectors 100 arranged is not limited to this. For example, the multiple gas detectors 100 may be arranged in a 3 or more×3 or more array. Also, each of the multiple detectors included in the two gas detectors 100 may be arranged in an array. For example, the two first detectors 100A, the second detectors 100B, and the third detectors described above may be arranged in a 2×2 array.

[0166] 14, the gas detectors 100 are periodically arranged two-dimensionally, but the gas detectors 100 may be periodically arranged along one direction. The gas detectors 100 may be spaced apart at equal intervals or at different intervals.

[0167] Furthermore, when arranging a plurality of gas detectors 100 in an array, the first electrode 2a and the third electrode 2c may be common electrodes, so long as each gas detector 100 can be separated. By making the first electrode 2a and the third electrode 2c common electrodes, the wiring of the pixels can be reduced compared to a configuration in which the first electrode 2a and the third electrode 2c are independent in each gas detector 100. As a result, it is possible to increase the resolution of the gas detector array. As a method for separating each of the plurality of gas detectors 100, for example, an insulating layer may be provided so as to surround the outer periphery of each gas detector 100.

[0168] In this manner, the gas detector array 1000 using a plurality of gas detectors 100 can also be used as an image sensor by arranging the plurality of gas detectors 100 in an array.

[0169] The gas detector array 1000 may include any of the gas detectors according to the first to sixth embodiments as the gas detector 100. The gas detector array 1000 may include any of the gas detectors according to the first to sixth embodiments as the gas detector 100.

[0170] The gas detector array 1000 may include a plurality of gas detectors according to any one of embodiments 1 to 6, or may include a plurality of gas detectors according to two or more of embodiments 1 to 6.

[0171] <Modifications of the Gas Detector Array 1000> The gas detector array 1000 preferably further includes a detection circuit such as a readout circuit or a matrix selection circuit for reading out an electric signal obtained from each of the plurality of gas detectors 100. The detection circuit is preferably arranged, for example, on the outer side of the plurality of gas detectors 100 arranged in an array. The detection circuit may be provided on a semiconductor chip separate from the plurality of gas detectors 100, and may be electrically connected to each of the plurality of gas detectors 100 by bumps or the like.

[0172] 15 is a schematic diagram showing an example of a gas detector array 1000 including the above-mentioned detection circuit. Hereinafter, each gas detector 100 (or each detection unit) constituting the gas detector array 1000 is also called a pixel. The gas detector array 1000 includes a vertical scanning circuit 301 that vertically scans the pixels 100, a horizontal scanning circuit 302 that horizontally scans the pixels 100, a power supply circuit 303 that supplies bias voltages to each circuit, and an output circuit 304 that outputs a signal from the horizontal scanning circuit 302 to the outside of the gas detector array 1000.

[0173] The gas detector array 1000 shown in Fig. 15 can detect the response of the gas detector 100 for each pixel. Specifically, a voltage is applied to the vertical scanning circuit 301 to select one row, and a voltage is applied to the horizontal scanning circuit 302 to select one column, thereby reading out the response of one pixel. The row selected by the vertical scanning circuit 301 is fixed, and voltages are applied sequentially to the horizontal scanning circuit 302, thereby reading out all the pixel responses of that row. Thereafter, similarly, a voltage is applied to the vertical scanning circuit 301 to select another row, and voltages are applied sequentially to the horizontal scanning circuit 302, thereby reading out all the pixel responses of that other row. By repeating this process, the responses of all the pixels can be read out.

[0174] In this embodiment, a method of reading the response for each pixel using the vertical scanning circuit 301 and the horizontal scanning circuit 302 has been described, but this is not limited to this, and the response may be read for each row or column, or other methods may be used.

[0175] <Effects> The gas detector array 1000 shown in FIG. 15 is capable of detecting the response of each pixel and can easily detect the difference between pixels, which is particularly effective for detecting multiple types of gases or measuring their spatial distribution, for example.

[0176] The gas detector array 2000 shown in Fig. 16 has a configuration basically similar to that of the gas detector array 1000 shown in Fig. 14, and can obtain similar effects, but differs from the gas detector array shown in Fig. 14 in that it includes different types of gas detectors 200, 201, 202, and 203 as the multiple gas detectors. That is, in the gas detector array 2000 shown in Fig. 16, the different types of gas detectors 200, 201, 202, and 203 are arranged in an array (matrix).

[0177] In the gas detector array 2000 shown in Fig. 16, the gas detectors 200, 201, 202, and 203 are arranged in a 2 x 2 matrix, but the number of gas detectors to be arranged is not limited to this. In addition, in the gas detector array 2000 shown in Fig. 16, the gas detectors 200, 201, 202, and 203 are periodically arranged two-dimensionally, but the gas detectors 200, 201, 202, and 203 may be periodically arranged along one direction. In addition, the intervals between the gas detectors 200, 201, 202, and 203 may be equal or different.

[0178] In the gas detector array 2000 shown in FIG. 16, different types of gas detectors 200, 201, 202, 203 according to any of the above-mentioned embodiments 1 to 6 are arranged in a one-dimensional or two-dimensional array, so that the gas detector array 2000 can function as a gas image sensor.

[0179] The gas detectors 200, 201, 202, and 203 are, for example, gas detectors having different detection wavelengths from each other. Specifically, the gas detectors 200, 201, 202, and 203 may be gas detectors according to any one of the first to sixth embodiments and may be prepared as gas detectors having different detection wavelength selectivities from each other. In this case, the gas detector array can detect electromagnetic waves of at least two or more different wavelengths.

[0180] By arranging the gas detectors 200, 201, 202, and 203 having different detection wavelengths in an array in this manner, it is possible to distinguish the wavelength of electromagnetic waves in any wavelength range, such as ultraviolet light, infrared light, terahertz waves, radio wave wavelength ranges, etc. As a result, it is possible to obtain a colored image in which differences in wavelength are shown as differences in color, for example, in the same way as an image sensor used in the visible light range.

[0181] Furthermore, the constituent materials of the semiconductor layer 4 included in each of the gas detectors 200, 201, 202, and 203 may be semiconductor materials having sensitivity in different wavelength ranges. For example, a semiconductor material having a detection wavelength of visible light and a semiconductor material having a detection wavelength of infrared light may be used as the constituent materials. In this case, for example, when the gas detector is applied to an in-vehicle sensor, the gas detector can be used as a visible light image camera during the day. Furthermore, the gas detector can be used as an infrared camera at night. In this way, it is not necessary to use different cameras having image sensors depending on the detection wavelength of the electromagnetic waves.

[0182] As an application of the gas detector other than an image sensor, the gas detector can be used as a gas mapping sensor capable of detecting the concentration distribution of gas even with a small number of pixels. For example, by using the gas detectors 200, 201, 202, and 203 with different detection wavelengths as described above due to the structure of the gas detector array, an image sensor that detects the intensity of electromagnetic waves of multiple wavelengths can be obtained. This makes it possible to detect electromagnetic waves of multiple wavelengths and obtain a color image without using color filters that were previously required for CMOS image sensors, etc.

[0183] Furthermore, a polarization discrimination image sensor can be formed by arraying gas detectors 200, 201, 202, and 203 that detect different polarizations. For example, four pixels with polarization angles of 0°, 90°, 45°, and 135° are regarded as one unit, and multiple gas detectors of this unit are arranged to enable polarization imaging. The polarization discrimination image sensor makes it possible to distinguish between man-made and natural objects, to distinguish materials, to distinguish between objects with the same temperature in the infrared wavelength range, to distinguish between boundaries between objects, or to improve equivalent resolution.

[0184] As described above, the gas detector array 2000 can detect electromagnetic waves in a wide wavelength range. Also, the gas detector array 2000 can detect electromagnetic waves of different wavelengths.

[0185] Each of the above-described embodiments may be modified or omitted as appropriate. Furthermore, the above-described embodiments may be modified in various ways in the implementation stage without departing from the gist of the embodiment. Furthermore, the above-described embodiments include disclosures of various stages, and various disclosures may be extracted by appropriate combinations of the disclosed constituent elements.

[0186] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. Unless inconsistent, at least two of the embodiments disclosed herein may be combined. The scope of the present disclosure is indicated by the claims, not the above description, and is intended to include all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0187] 1 Two-dimensional material layer, 1a first part, 1b second part, 1c third part, 1d contact part, 1e crosslinked part, 2a,2a1,2a2 first electrode, 2b second electrode 2c third electrode, 3 insulating layer, 4 semiconductor layer, 5 covering film, 6 ferroelectric layer, 7 contact layer, 8 conductor, 11 first two-dimensional material layer, 12 second two-dimensional material layer, 13 fourth two-dimensional material layer, 14 fifth two-dimensional material layer, 30 recess, 31 opening, 31A first opening, 31B second opening, 41 first surface, 42 second surface, 61 first ferroelectric layer, 62 second ferroelectric layer, 71 first contact layer, 72 second contact layer, 100, 101, 102, 103, 104, 105, 106, 107, 200, 201, 202, 203 gas detector, 100A first detection unit, 100B second detection unit, 301 vertical scanning circuit, 302 horizontal scanning circuit, 303 power supply circuit, 304 Output circuit, 1000,2000 gas detector array.

Claims

1. A gas detector for detecting a gas to be detected, comprising: An insulating layer; at least one first electrode disposed on the insulating layer; at least one two-dimensional material layer electrically connected to the at least one first electrode; at least one second electrode electrically connected to the at least one first electrode through the at least one two-dimensional material layer; the at least one two-dimensional material layer has an exposed surface that is exposed to an exterior; When electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the at least one two-dimensional material layer, photoelectric conversion is performed in the at least one two-dimensional material layer, the at least one first electrode and the at least one second electrode include a first set of first electrodes and second electrodes and a second set of first electrodes and second electrodes spaced apart from the first set of first electrodes and second electrodes; the at least one two-dimensional material layer comprises a first two-dimensional material layer electrically connecting between the first set of first electrodes and the second electrodes, and a second two-dimensional material layer spaced apart from the first two-dimensional material layer and electrically connecting between the second set of first electrodes and the second electrodes; the first two-dimensional material layer having the exposed surface; a first coating overlying the second layer of two-dimensional material; A gas detector, wherein the first coating film is provided so as to prevent permeation of the gas to be detected.

2. the at least one first electrode and the at least one second electrode further include a third set of first and second electrodes spaced apart from each of the first and second electrodes of the first set and the second set of first and second electrodes; the at least one two-dimensional material layer further comprises a third two-dimensional material layer spaced apart from each of the first two-dimensional material layer and the second two-dimensional material layer and electrically connecting between the third set of first electrodes and second electrodes; a second coating overlying the third two-dimensional material layer; 2. The gas detector according to claim 1, wherein the second coating film is provided so as to block transmission of electromagnetic waves in a wavelength range that is absorbed by the gas to be detected.

3. a first ferroelectric layer in contact with the first two-dimensional material layer or connected to the first two-dimensional material layer via the insulating layer; a second ferroelectric layer in contact with the second two-dimensional material layer or connected to the second two-dimensional material layer via the insulating layer; 3. The gas detector according to claim 1, wherein a material constituting the first ferroelectric layer and the second ferroelectric layer is a material that undergoes polarization when an electromagnetic wave having a wavelength range that is absorbed by the gas to be detected is incident thereon.

4. a first contact layer in contact with the first layer of two-dimensional material; a second contact layer in contact with the second layer of two-dimensional material; 3. The gas detector according to claim 1, wherein the first contact layer and the second contact layer are made of a material capable of supplying electrons or holes to the first two-dimensional material layer or the second two-dimensional material layer.

5. a first electrical conductor in contact with the first layer of two-dimensional material; 3. The gas detector of claim 1, further comprising a second electrical conductor in contact with the second layer of two-dimensional material.

6. 3. The gas detector of claim 1, wherein each of the first and second two-dimensional material layers has a first portion and a second portion spaced apart from each other on the insulating layer, and a third portion bridging between the first portion and the second portion.

7. A gas detector for detecting a target gas, comprising: An insulating layer; at least one first electrode disposed on the insulating layer; at least one two-dimensional material layer electrically connected to the at least one first electrode; at least one second electrode electrically connected to the at least one first electrode through the at least one two-dimensional material layer; the at least one two-dimensional material layer has an exposed surface that is exposed to an exterior; When electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the at least one two-dimensional material layer, photoelectric conversion is performed in the at least one two-dimensional material layer, a semiconductor layer having a first surface and a second surface opposite the first surface; the insulating layer is disposed on the first surface; the insulating layer has at least one opening that exposes a portion of the first surface; the at least one two-dimensional material layer electrically connects between the at least one first electrode and the semiconductor layer and extends through the at least one opening onto the insulating layer; the at least one second electrode is disposed on the second surface and is electrically connected to the at least one two-dimensional material layer through the semiconductor layer; the at least one opening includes a first opening and a second opening spaced apart from one another; The at least one first electrode includes a first first electrode and a second first electrode spaced apart from one another; the at least one two-dimensional material layer includes a fourth two-dimensional material layer extending from within the first opening onto the insulating layer and electrically connecting between the first first electrode and the semiconductor layer, and a fifth two-dimensional material layer extending from within the second opening onto the insulating layer and electrically connecting between the second first electrode and the semiconductor layer; a third coating overlying the fifth two-dimensional material layer; A gas detector, wherein the third coating film is provided so as to prevent permeation of the gas to be detected.

8. the at least one opening further comprises a third opening spaced apart from each of the first opening and the second opening; the at least one first electrode further comprises a third first electrode spaced apart from each of the first first electrode and the second first electrode; the at least one two-dimensional material layer comprises a sixth two-dimensional material layer extending from within the third opening onto the insulating layer and electrically connecting between the third first electrode and the semiconductor layer; a fourth coating film covering the sixth two-dimensional material layer; 8. The gas detector according to claim 7, wherein the fourth coating film is provided so as to block transmission of electromagnetic waves in a wavelength range that is absorbed by the gas to be detected.

9. a portion of the fourth two-dimensional material layer disposed on the insulating layer having a first end surface extending in a direction intersecting the first surface; a portion of the fourth two-dimensional material layer disposed within the first opening has a second end surface extending in the intersecting direction; a portion of the fifth two-dimensional material layer disposed on the insulating layer having a third end surface extending in the intersecting direction; a portion of the fifth two-dimensional material layer disposed within the second opening has a fourth end surface extending in the intersecting direction; a sum of areas of the second end faces is greater than a sum of areas of the first end faces, 9. The gas detector according to claim 7, wherein a sum of areas of the fourth end faces is greater than a sum of areas of the third end faces.

10. A gas detector comprising a plurality of gas detectors according to claim 1 or 7, A gas detector array, wherein each of the plurality of gas detectors is arranged in an array.

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