Gas detector and gas detector array

Abstract

Provided is a gas detector (100) comprising: an insulating layer (3); a first electrode (2a) that is positioned on the insulating layer; a two-dimensional material layer (1) that is electrically connected to the first electrode; and a second electrode (2b) that is electrically connected to the first electrode via the two-dimensional material layer. The two-dimensional material layer has an exposed surface that is exposed to the outside. The two-dimensional material layer is provided so as to perform photoelectric conversion when an electromagnetic wave in a wavelength region that is absorbed by a gas to be detected is incident.

Description

Gas detectors and gas detector arrays

[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.

[0002] Japanese Patent Laid-Open Publication No. 2019-102567 (Patent Document 1) discloses a field effect transistor (FET) including a gate and a gate insulating film made of graphene. The FET described in Patent Document 1 functions 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.

[0003] Japanese Patent Application Laid-Open No. 2019-102567

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

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

[0006] According to an embodiment of the present disclosure, a gas detector 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 configured to perform photoelectric conversion when electromagnetic waves in a wavelength range absorbed by a gas to be detected are incident thereon.

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

[0008] 10 is a schematic cross-sectional view of a gas detector according to a first embodiment; FIG. 11 is a schematic cross-sectional view taken along arrows II-II in FIG. 1; FIG. 12 is a flowchart for explaining a manufacturing method of the gas detector according to the first embodiment; FIG. 13 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; FIG. 14 is a diagram for specifically explaining the operating principle of gas detection by an adsorption method in the gas detector according to the first embodiment; FIG. 15 is a schematic cross-sectional view of a gas detector according to a second embodiment; FIG. 16 is a schematic cross-sectional view of a gas detector according to a third embodiment; FIG. 17 is a schematic cross-sectional view of a gas detector according to a fourth embodiment; FIG. 18 is a schematic cross-sectional view of a gas detector according to a fifth embodiment; FIG. 19 is a schematic cross-sectional view of a gas detector according to a sixth embodiment; FIG. 19 is a schematic cross-sectional view taken along arrows XI-XI in FIG. 10; FIG. 20 is a schematic plan view showing a first modified example of the gas detector according to the sixth embodiment; FIG. 21 is a schematic cross-sectional view of a gas detector array according to a seventh embodiment; FIG. 22 is a schematic diagram showing an example of a readout circuit for reading out electrical signals obtained from the gas detector array according to the seventh embodiment; and FIG. 23 is a top view of a first modified example of the gas detector array according to the seventh embodiment.

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

[0010] In the embodiments described below, the drawings are schematic and are intended 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 embodiments. Furthermore, components with the same reference numerals are the same or equivalent as described above. This applies throughout the entire specification.

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

[0012] The gas detector according to the present disclosure detects, as gas detection signals, changes in the electrical properties of the two-dimensional material layer associated with photoelectric conversion that occurs at least in the two-dimensional material layer when electromagnetic waves in a wavelength range absorbed by a gas to be detected are incident thereon, and changes in the electrical properties of the two-dimensional material layer associated with adsorption of the gas to be detected onto the two-dimensional material layer, and further measures the amounts of each change. In this specification, gas detection based on the former change in electrical properties will also be referred to as gas detection by an electromagnetic wave detection method, and gas detection based on the latter change in electrical properties will also be 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 electromagnetic waves 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 detectors that detect 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 description, graphene is used as an example of the material of the two-dimensional material layer, but the material constituting the two-dimensional material layer is not limited to graphene. For example, transition metal dichalcogenides (TMDs), black phosphorus, silicene (a two-dimensional honeycomb structure of silicon atoms), germanene (a two-dimensional honeycomb structure of germanium atoms), and the like can be used as the material of the two-dimensional material layer. Examples of transition metal dichalcogenides include MoS, WS, and WSe.

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

[0016] The two-dimensional material layer may be composed of two-dimensional materials arranged in a single layer (e.g., single-layer graphene). Alternatively, the two-dimensional material layer may be composed of two-dimensional materials arranged in multiple layers (e.g., multi-layer graphene). The latter two-dimensional material layer increases the photoelectric conversion efficiency and enhances the sensitivity of the gas detector. Furthermore, a band gap is formed in the latter two-dimensional material layer. As a result, the latter two-dimensional material layer can be configured 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. Furthermore, as the number of layers of secondary raw materials contained in the two-dimensional material layer increases, the carrier mobility in the channel region decreases, but the two-dimensional material layer becomes less susceptible to carrier scattering from underlying structures such as a substrate, resulting in a lower noise level. Therefore, a gas detector including a two-dimensional material layer including two-dimensional materials arranged in multiple layers can enhance the detection sensitivity of electromagnetic waves. 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 layers of graphene may or may not be aligned with 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 natural graphite 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, methane, or the like as a carbon source on graphene and growing graphene by a CVD method.

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

[0019] In the following, the terms n-type and p-type may be used to refer to materials of components in contact with the two-dimensional material layer. Here, for example, n-type materials refer to materials with electron-donating properties, and p-type materials refer to materials with electron-withdrawing properties. Furthermore, a material in which there is a bias in the charge throughout the molecule, with electrons predominating, may be referred to as n-type, and a material in which holes predominate may be referred to as p-type. These materials may be either organic or inorganic, or a mixture thereof.

[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 electrode material, 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 operated in an electronically conductive state in this state, the influence of the holes doped from the electrode into the two-dimensional material layer reduces the mobility of electrons flowing into the channel region of the two-dimensional material layer, increasing the contact resistance between the two-dimensional material layer and the electrode. This increase in contact resistance may reduce the electron (carrier) mobility due to the field effect in the gas detector, resulting in a deterioration in the performance of the gas detector. In particular, when the two-dimensional material layer is composed of single-layer graphene, the amount of doped carriers injected from the electrode is greater than when the two-dimensional material layer is composed of multi-layer graphene. Therefore, the decrease in electron mobility in the gas detector is particularly significant when single-layer graphene is used as the two-dimensional material layer. Therefore, when the entire two-dimensional material layer is composed of single-layer graphene, the performance of the gas detector may be reduced. Therefore, at least the contact area of ​​the secondary raw material layer with the electrode may be made of multilayer graphene. Multilayer graphene reduces carrier doping from the electrode compared to single-layer graphene. Therefore, an increase in contact resistance between the two-dimensional material layer and the electrode can be suppressed. As a result, the aforementioned decrease in electron mobility 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 nanoribbons). The two-dimensional material layer may be, for example, a single graphene nanoribbon, a composite in which multiple graphene nanoribbons are stacked, or a structure in which graphene nanoribbons are periodically arranged on a plane (e.g., 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 manipulating specific wavelengths using 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 phenomena. In this specification, these resonances are referred to as 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 that does not generate a tunnel current.

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

[0025] 1 and 2 includes a plurality of detectors. The plurality of detectors includes a first detector 100A and a second detector 100B. The first detector 100A and the second detector 100B basically have the same configuration.

[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 portion located on the opposite side of the semiconductor layer 4 will be referred to as the upper portion of each, and the portion located on the semiconductor layer 4 side of each will be referred to as the lower portion of each.

[0028] The semiconductor layer 4 is sensitive to electromagnetic waves in a wavelength range that is 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 that is 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] 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, or a phototransistor.

[0031] Although a silicon substrate has been described above 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 dots, a Type II superlattice, or a combination thereof.

[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 a third portion 1c of the two-dimensional material layer 1, the first electrode 2a, and the second electrode 2b, which will be described later. Note that the upper surface of the insulating layer 3 may have a recess that is recessed relative to the portions that are 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, which will be described later, may bridge over the recess of the insulating layer 3.

[0034] The material constituting the insulating layer 3 may be any material having electrical insulation properties, including, for example, silicon oxide (SiO). The material constituting the insulating layer 3 may include, for example, at least one selected from the group consisting of SiO, tetraethyl orthosilicate (Si(OCH)), silicon nitride (SiN), hafnium oxide (HfO), aluminum oxide (AlO), 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 even when boron nitride comes into contact with the two-dimensional material layer 1 made of graphene, it does not adversely affect charge mobility. Therefore, boron nitride is a suitable material for constituting the insulating layer 3 from the viewpoint of preventing the insulating layer 3 from impairing the performance of the two-dimensional material layer 1, such as electron mobility.

[0035] The plurality of first electrodes 2a and the plurality of second electrodes 2b are arranged at intervals from one another on the upper surface of the insulating layer 3. The plurality of first electrodes 2a and the plurality of 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 one another. 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 conductive material, 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). Furthermore, 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 to enhance adhesion therebetween. The material constituting the adhesion layer is not particularly limited, but may include at least one of chromium (Cr) and titanium (Ti), for example.

[0037] 2, the first electrode 2a and the second electrode 2b are formed, for example, in the lower part of the two-dimensional material layer 1. Note that the first electrode 2a and the second electrode 2b may also be formed in 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 the 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 second surface 42 of the semiconductor layer 4. It is sufficient that the third electrode 2c is in contact with at least a portion of the semiconductor layer 4. For example, the third electrode 2c may be provided so as to be in contact with a portion of a side surface of the semiconductor layer 4 extending in a direction intersecting with the first surface 41. Such a gas detector 100 is capable of detecting electromagnetic waves incident from the second surface 42 side. As shown in FIG. 2 , the gas detector 100 in which the third electrode 2c is provided on the entire second surface 42 of the semiconductor layer 4 is suitable for cases in which electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident only from the first surface 41 side. In the gas detector 100 shown in FIG. 2 , the electromagnetic waves incident from the first surface 41 side and transmitted through the semiconductor layer 4 are reflected by the second electrode 2b and reach the two-dimensional material layer 1 again, thereby increasing the absorption rate of the electromagnetic waves in the two-dimensional material layer 1.

[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 multiple two-dimensional material layers 1 include a first two-dimensional material layer 11 and a second two-dimensional material layer 12. The first two-dimensional material layer 11 electrically connects a first set of first electrodes 2a and second electrodes 2b. The second two-dimensional material layer 12 electrically connects a second set of first electrodes 2a and second electrodes 2b. 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.

[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 two-dimensional material layer 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, which will be described later. 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 a first electrode 2a. The second portion 1b is connected to a 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, if a recess is formed in the upper surface of the insulating layer 3, the third portion 1c may bridge over the recess. The lower surface of the third portion 1c does not have to 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 1 a, the second portion 1 b, and the third portion 1 c of each two-dimensional material layer 1 are, for example, equal to each other. The thicknesses of the first portion 1 a, the second portion 1 b, and the third portion 1 c 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 not only covers the second two-dimensional material layer 12 but also the second set of first electrodes 2 a and second electrodes 2 b of the second detection unit 100B, for example. 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, for example, at least one selected from the group consisting of silicon oxide (SiO), tetraethyl orthosilicate (Si(OCH)), silicon nitride (SiN), hafnium oxide (HfO), aluminum oxide (AlO), nickel oxide (NiO), boron nitride (BN), siloxane-based polymer materials, polyethylene terephthalate (PET), polyvinylidene chloride (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 composed 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 the same overall thickness as the first coating film 5. 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 the same gas barrier properties.

[0050] <Method of Manufacturing Gas Detector 100> Fig. 3 is a flowchart for explaining a method of manufacturing the gas detector 100 according to embodiment 1. A method of manufacturing the gas detector 100 shown in Figs. 1 and 2 will be described with reference to Fig. 3.

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

[0052] Second, a step (S2) of forming a third electrode 2c is performed. In this step (S2), the third electrode 2c is formed on the second surface 42 (see FIG. 2 ) of the semiconductor layer 4. Specifically, first, a protective film is 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, for example, at least one selected from the group consisting of 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 may be formed on the second surface 42 of the semiconductor layer 4 to improve adhesion between the semiconductor layer 4 and the third electrode 2c. 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 below, as long as the first surface 41 of the semiconductor layer 4 is protected.

[0054] Third, a step (S3) of forming an insulating layer 3 is performed. 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 can 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 includes Si, the insulating layer 3 may be, for example, SiO formed by partially thermally oxidizing the first surface 41 of the semiconductor layer 4.

[0055] Fourth, a step (S4) of forming the first electrode 2 a and the second electrode 2 b is performed. In this step (S4), the first electrode 2 a and the second electrode 2 b 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, and 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, EB lithography, or the like. Openings are formed in the resist mask in regions where the first electrode 2a and the second electrode 2b are to be formed. Second, a conductive film that will become the first electrode 2a and the second electrode 2b is formed on the upper surface of the resist mask using a method such as vapor deposition or sputtering. The conductive film is formed so as to extend from the interior of the openings in the resist mask to the upper surface of the resist mask. Third, the resist mask is removed together with a portion of the conductive film that was disposed on the upper surface of the resist mask. As a result, the other portion of the conductive film that was disposed in the openings in 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 may be formed on the first surface 41 of the semiconductor layer 4 to improve adhesion between the semiconductor layer 4 and the first electrode 2a or the second electrode 2b. 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 2 a, the second electrode 2 b, 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 FIGS. 1 and 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 2 a, the insulating layer 3, and a portion of the semiconductor layer 4 by, for example, epitaxial growth or screen printing. Alternatively, the two-dimensional material layer 1 may be formed by transferring and attaching a film-like two-dimensional material layer formed on a substrate different from the semiconductor layer 4 by CVD or the like, or a film-like two-dimensional material layer peeled from graphite or the like by mechanical peeling or the like, onto the first electrode 2 a, the insulating layer 3, and a portion of the semiconductor layer 4. The method for patterning the two-dimensional material layer 1 is not particularly limited, and photolithography, EB lithography, or the like may be employed. 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, the coating film is formed by at least one of sputtering, vapor deposition, and MOD coating (MOD: Metal Organic Composition). Second, a mask is formed on the upper surface of the coating film by photolithography, covering the region where the first coating film 5 is to be formed. Third, the portion of the coating film exposed from the mask is removed by, for example, a dry etching method. Examples of dry etching include oxygen plasma or tetrafluoromethane (CF ４ 1 and 2. Fourth, the mask is removed, forming the coating film 5 shown in FIG.

[0060] The gas detector 100 shown in FIGS. 1 and 2 can be manufactured by the above steps (S1 to S6). In the manufacturing method described above, 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 also be formed on the two-dimensional material layer 1. However, if 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, a possible approach is to form a protective film to protect the two-dimensional material layer 1 except for the region where the first electrode 2a or the second electrode 2b is formed, 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 serves as a transistor channel, each first electrode 2a and the first portion 1a of each two-dimensional material layer 1 serves as a source, each second electrode 2b and the second portion 1b of each two-dimensional material layer 1 serves as a drain, and the third electrode 2c serves as a gate. Hereinafter, the currents Isd1 and Isd2 flowing through each two-dimensional material layer 1 will also be referred to as source-drain currents, and the voltage Vg applied to the third electrode 2c will also be referred to as a gate voltage.

[0062] The gas detector 100 can detect changes in the source-drain currents Isd1 and 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 flowing.

[0064] The gas detector 100 is also capable of detecting 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 resonant 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 target gas is adsorbed to the third portion 1c of the two-dimensional material layer 1. Therefore, the gas detector 100 can also detect the concentration of the target gas by converting the amount of change in the resonant frequency of the third portion 1c when a DC voltage is applied into the amount of electromagnetic wave irradiation applied 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] 4 is a schematic diagram showing changes in electrical characteristics that occur in each two-dimensional material layer 1 of the gas detector 100 when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the two-dimensional material layer 1. 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 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 currents Isd1 and Isd2 flowing through each two-dimensional material layer 1, which is detected when the gas to be detected is not present around the gas detector 100. Furthermore, FIG. 4 shows the change Vph in the gate voltage Vg and the change Iph in 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 may be selected depending on the doping type of the semiconductor layer 4; a positive voltage is applied if the semiconductor layer 4 is p-type, and a negative voltage is applied if the semiconductor layer 4 is n-type.

[0069] Each of the two-dimensional material layers 1 and the semiconductor layer 4 is sensitive 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 via 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 in response to the amount of change Vph in the gate voltage Vg, causing the source-drain currents Isd1 and Isd2 to change. Furthermore, the gas detector 100 can also detect the amount of change Iph in 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 where the target gas is not present on the optical path. By detecting this current change Iph, it is possible to detect a change in the light intensity of the electromagnetic wave incident on the gas detector 100 due to the electromagnetic wave being absorbed by the target gas. Detecting this change in light intensity makes it possible to detect the presence or absence of the target gas on the optical path of the electromagnetic wave, measure the concentration of the target gas, 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 showing changes in electrical characteristics of the two-dimensional material layer 1 caused by the adsorption of a target gas 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 target gas 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 target gas is not present around the gas detector 100. Note that 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 target gas is present around the gas detector 100. Furthermore, FIG. 5 shows the change Vph in the gate voltage Vg and the change Iph in the source-drain current Isd1 depending on the presence or absence of the target gas.

[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 in this current Iad 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 enables 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 a change in the electrical properties of the two-dimensional material layer 1, which is referred to as the gas adsorption gate effect.

[0074] <Advantages of the Gas Detector 100> The gas detector 100 can simultaneously perform gas detection using an electromagnetic wave detection method and gas adsorption. Therefore, the gas detector 100 can detect or identify specific gas species in a mixed gas, which was difficult with conventional FETs that only perform gas detection using the gas adsorption method. Furthermore, gas detection using the electromagnetic wave detection method by the gas detector 100 can be performed using the optical gating effect, as described above. Therefore, the gas detection sensitivity of the gas detector 100 is significantly higher than that of typical gas detectors that only perform gas detection using the electromagnetic wave detection method.

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

[0076] In addition, typical gas detectors that only perform gas detection using electromagnetic wave detection pass electromagnetic waves in a specific wavelength range through an enclosed space (such as a gas cell) and measure the attenuation of the electromagnetic waves using a single element. Therefore, it is difficult to measure (map) the spatial distribution of gas concentration using such gas detectors, and it is particularly impossible to measure the gas concentration distribution at a position far 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 that is externally exposed, and a second detection unit 100B having a second two-dimensional material layer 12 that is covered by a coating film 5 and has no exposed surface that is externally exposed. The first detection unit 100A can simultaneously perform gas detection using electromagnetic wave detection and gas adsorption. The second detection unit 100B can only perform gas detection using gas adsorption. 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 an extremely high surface-to-volume ratio compared to 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 by utilizing the gas adsorption gate effect in the gas detector 100 is extremely high compared to gas detection performed using other materials other than the two-dimensional material layer as the adsorbent.

[0078] <Modifications> The gas detector according to the present disclosure does not need to include the semiconductor layer 4. Even in this case, the gas adsorption gate effect can occur. Furthermore, when electromagnetic waves in a wavelength range absorbed by the gas to be detected are 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 that does not include the semiconductor layer 4 can also simultaneously perform gas detection by the electromagnetic wave detection method and gas adsorption method.

[0079] The gas detector according to the present disclosure may not include the second detection unit 100B. Such a gas detector can simultaneously perform gas detection using an electromagnetic wave detection method and a gas adsorption method. Therefore, like the gas detector 100, it can detect specific gas species in a mixed gas, identify gas species, and detect the presence or absence of a target gas at a position away from the upper surface of the two-dimensional material layer 1. In this case, the gas detector 100 preferably includes multiple first detection units 100A. Some of the multiple first detection units 100A receive electromagnetic waves in a wavelength range absorbed by the target gas, which have passed through a comparison container filled with a specific comparison gas different from the target gas. The surface of the two-dimensional material layer may be modified to enable binding and capture of the specific gas. For example, an antibody that binds to the target gas as an antigen may be bound to the surface of the two-dimensional material layer. In this manner, a gas detector capable of specific detection can be realized. The antibodies 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 target gas as an antigen and examines the distribution of the fluorescent substance and enzyme on the surface of the two-dimensional material layer, thereby enabling detection by staining to be performed in parallel with the gas molecule detection described in the operating principle of the present invention, and enabling the detection accuracy and spatial concentration distribution of gas molecular species to be measured.

[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 covalently bond with the gas molecule species to be detected, thereby enabling highly specific gas detection of 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 and 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 promotes interaction between the two-dimensional material layer and the gas molecules to be detected, thereby improving detection accuracy.

[0083] The gas detector 100 may further include a light source that irradiates each of the plurality of 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 the gas to be detected. In this way, deterioration of signal quality due to erroneous detection of gases other than the target gas can be suppressed.

[0085] The gas detector 100 may further include a column capable of separating gas components, and may be configured so that the gas components separated by the column are supplied to the periphery of each of the plurality of 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 can 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 surroundings of each of the plurality of detection units. As described above, the gas generator may be a heating device for generating an aerosol. Such a gas detector 100 can detect 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 waves 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 waves to be irradiated and detected based on the above-mentioned operating principle, it becomes possible to detect multiple types of electromagnetic waves and therefore 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 first electrodes 2a and second electrodes 2b, a third two-dimensional material layer, and a second coating film covering the third two-dimensional material layer. 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, respectively. 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, respectively, and electrically connects the third set of first electrodes 2a and second electrodes 2b. The second coating film is configured to block 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 embodiment 2 has the same configuration, operating principle, and effects as those of the above-described embodiment 1. Therefore, the same components as those of the above-described embodiment 1 are denoted by the same reference numerals, and 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 includes 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. Note that the ferroelectric layer 6 may also be disposed, for example, on the upper surface of the third portion 1c of the two-dimensional material layer 1. Furthermore, the ferroelectric layer 6 may not be in contact with the two-dimensional material layer 1, but 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 undergoes polarization when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident on the ferroelectric layer. Examples of the material constituting the ferroelectric layer 6 include barium titanate (BaTiO3), lithium niobate (LiNbO ３ ), lithium tantalate (LiTaO ３ ), strontium titanate (SrTiO ３), lead zirconate titanate (PZT), strontium tantalate bismuthate (SBT), bismuth ferrite (BFO), zinc oxide (ZnO), hafnium oxide (HfO ２ ) and organic polymer polyvinylidene fluoride ferroelectrics (PVDF, P(VDF-TrFE), P(VDF-TrFE-CTFE), etc.). The ferroelectric layer may be formed by stacking or mixing a plurality of different ferroelectric materials.

[0093] The material forming the ferroelectric layer 6 may be, for example, a material that is polarized when electromagnetic waves in a wavelength range different from the wavelength range to which the semiconductor layer 4 is sensitive are incident on the ferroelectric layer 6. The gas detector 101 having such a configuration is suitable for detecting multiple 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 that exhibits the pyroelectric effect. Specifically, the material of the ferroelectric layer may be a ferroelectric 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 is sensitive to a wide band of electromagnetic waves.

[0095] The gas detector 101 includes, 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, the same configuration as the first ferroelectric layer 61.

[0096] <Operation Principle> In the gas detector 101, when an electromagnetic wave is irradiated onto the ferroelectric layer 6, a change in dielectric polarization occurs within the ferroelectric layer 6 due to the pyroelectric effect of the ferroelectric layer 6. The change in polarization in the ferroelectric layer 6 due to the pyroelectric effect applies a change in the electric field 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 optical gating effect of the semiconductor layer 4 and the optical gating effect of the ferroelectric layer 6 can be utilized for gas detection using an electromagnetic wave detection method.

[0097] <Effects> The gas detector 101 can utilize the optical gate effect of the semiconductor layer 4 and the optical gate effect of the ferroelectric layer 6, and therefore can achieve 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 is sensitive 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 gating effect.

[0099] <Modifications> The gas detector 101 can also be modified in the same manner as the gas detector 100 .

[0100] Embodiment 3 Unless otherwise specified, the gas detector according to embodiment 3 has the same configuration, operating principle, and effects as those of the above-described embodiment 1. Therefore, the same components as those of the above-described embodiment 1 are denoted by the same reference numerals, and 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 includes 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 is in contact with the two-dimensional material layer 1 and can supply holes or electrons to 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] The contact layer 7 can be formed, for example, from a composition called a positive photoresist, which contains a photosensitizer having a quinone diazide group and a novolac resin. The material constituting the contact layer 7 can also be a material having a polar group. For example, a material having an electron-withdrawing group, which is an example of such a material, has the effect of reducing the electron density of the two-dimensional material layer 1. A material having an electron-donating group, which is an example of such a material, has the effect of increasing the electron density of the two-dimensional material layer 1. Examples of materials having electron-withdrawing groups include materials having halogens, nitriles, carboxyl groups, or carbonyl groups. Examples of materials having electron-donating groups include materials having alkyl groups, alcohols, amino groups, or hydroxyl groups. In addition to the above, materials that cause charge imbalance throughout the molecule due to polar groups can also be used as the material for the contact layer 7.

[0104] Furthermore, any material that exhibits polarity due to charge imbalance within the molecule, such as organic materials, metals, semiconductors, insulators, or mixtures of these materials, can be used as the material for the contact layer 7. When the inorganic contact layer 7 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 if the work function of the contact layer 7 is larger than that of the two-dimensional material layer 1, and n-type if the work function is smaller. On the other hand, when the contact layer 7 is organic, the organic material that constitutes the contact layer 7 does not have a clear work function. Therefore, it is preferable to determine whether the two-dimensional material layer 1 will be n-type doped or p-type doped by determining the polar group of the material of the contact layer 7 based on the polarity of the organic molecules used for the contact layer 7.

[0105] For example, when a composition containing a photosensitive agent having a quinone diazide group and a novolac resin, known as 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 eliminates the need for a mask formation process 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 structure similar to that of the first contact layer 71.

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

[0108] <Effects> The gas detector 102 includes the contact layer 7 that can supply 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, it is possible to control the carrier doping of the two-dimensional material layer 1 without considering the influence of carrier doping associated with 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 in 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] Furthermore, a plurality of 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. A plurality of 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 plurality of contact layers 7 may be the same or different materials.

[0111] Furthermore, in the gas detector according to this embodiment, the film 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 into the two-dimensional material layer 1 from the contact layer 7. 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 materials described above, materials that cause polarity conversion may also be used as the material for the contact layer 7. In this case, when the contact layer 7 undergoes polarity conversion, electrons or holes generated during the conversion are supplied to the two-dimensional material layer 1. As a result, the portion of the two-dimensional material layer 1 that is in contact with the contact layer 7 is doped with electrons or holes. Therefore, even if the contact layer 7 is removed, the portion of the two-dimensional material layer 1 that was in contact with the contact layer 7 remains doped with electrons or holes. 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 period of time has elapsed. In this case, the opening area of ​​the two-dimensional material layer 1 is increased compared to when the contact layer 7 is present. This improves the detection sensitivity of the gas detector. Here, polarity conversion refers to a phenomenon in which a polar group is chemically converted, such as an electron-withdrawing group changing to an electron-donating group, an electron-donating group changing to an electron-withdrawing group, a polar group changing to a non-polar group, or a non-polar group changing to a polar group.

[0113] Alternatively, 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 enabling doping into 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 for the contact layer 7. In this case, the two-dimensional material layer 1 can be doped with electrons or holes generated during the oxidation-reduction reaction.

[0115] <Modifications> The gas detector 102 can 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 other embodiments.

[0116] Embodiment 4 Unless otherwise specified, the gas detector according to embodiment 4 has the same configuration, operating principle, and effects as those of the above-described embodiment 1. Therefore, the same components as those of the above-described embodiment 1 are denoted by the same reference numerals, and 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 the 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 conductive material can be used to form 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 supply circuit or the like and is floating.

[0119] The plurality of conductors 8 have a one-dimensional or two-dimensional periodic structure. For example, an example of a one-dimensional periodic structure may be a structure in which the plurality of conductors 8 are arranged at intervals (periodically) in the horizontal direction or the depth direction of the paper of FIG. 8 . Another example of a two-dimensional periodic structure may be a structure in which the conductors 8 are arranged at positions corresponding to lattice points of a square lattice, a triangular lattice, or the like in a plan view of the gas detector. Furthermore, in a plan view of the gas detector, the planar shape of each conductor 8 may be any shape, such as a circle, a triangle, a square, a polygon, or an ellipse. Furthermore, the arrangement of the conductors 8 in a plan view is not limited to the periodic symmetry described above, and may also be an asymmetrical arrangement in a plan view. Here, any specific method may be used to form the conductors 8. For example, a method similar to the manufacturing method of the first electrode 2 a and the second electrode 2 b 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 coating film 5 .

[0121] <Effects of the Gas Detector 103> The gas detector 103 includes conductors 8, which are floating electrodes, 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, thereby extending the lifetime of the photocarriers. This improves the detection sensitivity of the gas detector 103.

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

[0123] Furthermore, by arranging the 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 the 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 the specific wavelength with high sensitivity.

[0124] Furthermore, when the plurality of conductors 8 are formed so as to be arranged asymmetrically in a plan view, polarization dependency occurs in the conductors 8 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 and also improve the contrast by detecting only light of a specific polarization.

[0125] Furthermore, in the gas detector 103, a conductor 8 may be disposed below the two-dimensional material layer 1. Even 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-described plurality of conductors 8. In this case, the same effect as when a plurality of conductors 8 is formed can be obtained.

[0127] <Modifications> 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 other embodiments.

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

[0129] 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 bridges between the first portion 1a and the second portion 1b. The insulating layer 3 has a plurality of recesses 30 formed therein that are recessed relative to the upper surface of the insulating layer 3. Each recess 30 is formed as, for example, an opening (through-hole) that exposes 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 the pair of contact portions 1d. The bridging portion 1e is not in contact with the insulating layer 3 or the semiconductor layer 4.

[0131] The recess 30 in the insulating layer 3 only needs to be provided so that even when the third portion 1c is bent 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 in the insulating layer 3 is formed as an opening, the semiconductor layer 4 may have a second recess (not shown) formed therein that is recessed relative to the first surface 41 and that is continuous with the recess 30 in the insulating layer 3 in the vertical direction.

[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 Gas Detector 104> In the gas detector 104, the third portion 1 c 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 higher than that of the gas detector 100, etc. As a result, the detection sensitivity of the gas detector 104 is improved.

[0134] <Modifications> The gas detector 104 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 other embodiments.

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

[0136] 10 and 11 , in a gas detector 105 according to the sixth embodiment, at least one opening 31 exposing a portion 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 an interval from each other. The gas detector 105 has, for example, a first first electrode 2a1 and a second first electrode 2a2 arranged at an interval 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 that is 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 with a coating film 5 (third coating film).

[0138] Each of the fourth two-dimensional material layer 13 and the fifth two-dimensional 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 in 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 set to zero when no electromagnetic waves are incident by adjusting the voltage V and applying a reverse bias to the Schottky junction. Furthermore, the Fermi level of the two-dimensional material layer 1 is modulated by the photovoltaic force generated when the electromagnetic waves are incident on the semiconductor layer 4, thereby lowering the energy barrier between the two-dimensional material layer 1 and the semiconductor layer 4. As a result, only when the electromagnetic waves are irradiated does a current flow 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 that detects changes in current in the two-dimensional material layer 1. For example, the gas detector 105 can also detect changes in each of the voltages Vd1 and Vd2 in a state where a constant current is flowing between each of the first electrodes 2 a and the second electrodes 2 b.

[0146] The gas detector 105 can also detect frequency changes in the source-drain current value in the third portion 1 c of the two-dimensional material layer 1 .

[0147] <Effects of Gas Detector 105> The gas detector 105 is capable of being turned off, and is therefore expected to reduce power consumption and improve the signal S / N ratio.

[0148] 12 and 13 show modifications 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 areas occupied by the first portion 1a and the third portion 1c in 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 have been removed in at least a direction intersecting 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). 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 1 a, the second portion 1 b, and the third portion 1 c are symmetrical with respect to a line that passes through the center of the two-dimensional material layer 1 in the direction intersecting the extension direction and extends along the extension direction. In a cross section passing through the center of the two-dimensional material layer 1 in the direction intersecting the extension 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 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 the 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 depending on 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] Furthermore, in gas detectors 106 and 107, the sum of the areas of the end faces of second portions 1b is larger than the sum of the areas of the end faces of second portions 1b of gas detector 105 shown in FIG. 10. The end faces of second portions 1b are surfaces extending along the thickness direction of two-dimensional material layer 1, in other words, along a direction perpendicular to the sheet formed by two-dimensionally arranged atoms in two-dimensional material layer 1. In other words, the end face area of ​​the two-dimensional crystal structure in each of second portions 1b shown in FIGS. 12 and 13 is larger than the end face area of ​​the two-dimensional crystal structure in second portion 1b shown in FIG. 10. Therefore, in each of two-dimensional material layers 1 shown in FIGS. 12 and 13, the proportion of unbonded bonds (dangling bonds) in the two-dimensional crystal structure is increased 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, resulting in an increase in carrier mobility and a larger change in current I. As a result, the detection sensitivity of the gas detectors 106 and 107 shown in Figures 12 and 13 is higher than the sensitivity 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. Graphene nanoribbons have a band gap that varies depending on their width. Therefore, the wavelength range of electromagnetic waves that can be photoelectrically converted in the second portion 1b can be adjusted depending on the width of the second portion 1b in the intersecting direction, and can be narrower than the wavelength range of electromagnetic waves that can be photoelectrically converted in other regions. In this case, photocarriers generated by photoelectric conversion in the second portion 1b can be detected separately from photocarriers generated by photoelectric conversion in other regions. Furthermore, detecting photocarriers generated by photoelectric conversion in the second portion 1b improves the sensitivity of the gas detector. In such a gas detector, a Schottky junction is formed between the second portion 1b made of the graphene nanoribbon and the semiconductor layer 4, thereby reducing dark current and improving sensitivity by detecting photocarriers generated by electromagnetic waves 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, the insulating layer 3 may further include a third opening 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 configured to block transmission of electromagnetic waves in a wavelength range absorbed by the gas to be detected.

[0158] The configuration of the gas detector of 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 in the two-dimensional material layer 1.

[0159] Here, examples of materials that change in properties when irradiated with electromagnetic waves and impart 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 that exhibits a polarization effect (pyroelectric effect) due to 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 imparted 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 properties change when irradiated with electromagnetic waves, the properties 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 such materials, can change when irradiated with electromagnetic waves, causing a change in potential in 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 have 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] Seventh Embodiment Fig. 14 is a top view of a gas detector array according to a seventh embodiment. Fig. 15 is a schematic diagram showing an example of a readout circuit that reads out electrical signals obtained from the gas detector array according to the seventh embodiment. Fig. 16 is a top view showing a first modified example of the gas detector array according to the seventh embodiment.

[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 to 107 according to any one 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 the same. 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 arranged gas detectors 100 is not limited to this. For example, the multiple gas detectors 100 may be arranged in a 3×3 or more array. Furthermore, each of the multiple detectors included in the two gas detectors 100 may be arranged in an array. For example, the first detector 100A, the second detector 100B, and the third detector described above may be arranged in a 2×2 array.

[0166] 14, the plurality of gas detectors 100 are periodically arranged two-dimensionally, but the plurality of gas detectors 100 may be periodically arranged in one direction. The plurality of gas detectors 100 may be spaced 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, as long as the gas detectors 100 can be separated from one another. By using the first electrode 2a and the third electrode 2c as common electrodes, it is possible to reduce the amount of wiring required for the pixels 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 the plurality of gas detectors 100 from one another, for example, an insulating layer may be provided so as to surround the outer periphery of each gas detector 100.

[0168] The gas detector array 1000 using a plurality of gas detectors 100 in this manner 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 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 that reads out electrical signals obtained from each of the plurality of gas detectors 100. The detection circuit is preferably arranged, for example, outside the plurality of gas detectors 100 arranged in an array. The detection circuit may be provided on a semiconductor chip that is separate from the plurality of gas detectors 100, and may be electrically connected to each of the plurality of gas detectors 100 via bumps or the like.

[0172] 15 is a schematic diagram showing an example of a gas detector array 1000 equipped with the above-described detection circuit. Hereinafter, each gas detector 100 (or each detection unit) constituting the gas detector array 1000 will also be referred to as a pixel. The gas detector array 1000 includes a vertical scanning circuit 301 that scans the pixels 100 in the vertical direction, a horizontal scanning circuit 302 that scans the pixels 100 in the horizontal direction, 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 pixel by 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 sequentially applied to the horizontal scanning circuit 302, thereby reading out all pixel responses of that row. Thereafter, a voltage is similarly applied to the vertical scanning circuit 301 to select another row, and voltages are sequentially applied to the horizontal scanning circuit 302, thereby reading out all pixel responses of that other row. By repeating this process, the responses of all 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 easily detecting 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 basically the same configuration as the gas detector array 1000 shown in Fig. 14 and can achieve the same 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. Furthermore, 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 in one direction. Furthermore, 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, and 203 according to any of the above-described embodiments 1 to 6 are arranged in a one-dimensional or two-dimensional array, thereby enabling the array to function as a gas image sensor.

[0179] The gas detectors 200, 201, 202, and 203 are, for example, gas detectors having different detection wavelengths. 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. In this case, the gas detector array can detect electromagnetic waves of at least two or more different wavelengths.

[0180] By arranging gas detectors 200, 201, 202, and 203 having different detection wavelengths in an array, 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 range, etc. As a result, it is possible to obtain a color image in which differences in wavelength are displayed as different colors.

[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 sensitive to different wavelength ranges. For example, a semiconductor material whose detection wavelength is that of visible light and a semiconductor material whose detection wavelength is that of infrared light may be used as the constituent materials. In this case, for example, when the gas detector is applied to an on-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, there is no need to use different cameras with image sensors depending on the detection wavelength of electromagnetic waves.

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

[0183] Furthermore, a polarization-discriminating image sensor can be formed by arraying gas detectors 200, 201, 202, and 203 that detect different polarizations. For example, polarization-discriminating image sensors can be realized by arranging multiple gas detectors, each of which has four pixels that detect polarization angles of 0°, 90°, 45°, and 135°. The polarization-discriminating image sensor can, for example, distinguish between artificial and natural objects, distinguish between materials, distinguish between objects with the same temperature in the infrared wavelength range, distinguish between boundaries between objects, or provide equivalent resolution improvement.

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

[0185] 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 spirit of the invention. Furthermore, the above-described embodiments include disclosures of various stages, and various disclosures may be extracted by appropriately combining the disclosed constituent elements.

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

[0187] 1 Two-dimensional material layer, 1a First portion, 1b Second portion, 1c Third portion, 1d Contact portion, 1e Bridge portion, 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 section, 100B second detection section, 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; and at least one second electrode electrically connected to the at least one first electrode through the at least one two-dimensional material layer, wherein the at least one two-dimensional material layer has an exposed surface exposed to the outside, and the at least one two-dimensional material layer is provided to perform photoelectric conversion when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident thereon.

2. Further comprising: a semiconductor layer having a first surface and a second surface located on the opposite side of the first surface; and a third electrode disposed on the second surface, wherein the insulating layer is disposed on the first surface, the at least one second electrode is disposed on the insulating layer, and the semiconductor layer is provided to perform photoelectric conversion when an electromagnetic wave in a wavelength range absorbed by the gas to be detected is incident thereon. The gas detector according to claim 1.

3. The at least one first electrode and the at least one second electrode include a first set of first and second electrodes and a second set of first and second electrodes spaced apart from the first set of first and second electrodes, and the at least one two-dimensional material layer includes a first two-dimensional material layer electrically connecting the first set of first and second electrodes and a second two-dimensional material layer spaced apart from the first two-dimensional material layer and electrically connecting the second set of first and second electrodes, the first two-dimensional material layer has the exposed surface, and further includes a first coating film covering the second two-dimensional material layer, and the first coating film is provided to inhibit transmission of the gas to be detected. The gas detector according to claim 1 or 2.

4. The at least one first electrode and the at least one second electrode further include a third set of first and second electrodes that are spaced apart from each of the first and second electrodes of the first set and the first and second electrodes of the second set, and the at least one two-dimensional material layer further includes a third two-dimensional material layer that is spaced apart from each of the first two-dimensional material layer and the second two-dimensional material layer and electrically connects between the third set of first and second electrodes. The gas detector according to claim 3 further includes a second coating film covering the third two-dimensional material layer, and the second coating film is provided to inhibit transmission of electromagnetic waves in a wavelength range absorbed by the gas to be detected.

5. The gas detector according to claim 3 or 4 further includes a first ferroelectric layer that is in contact with the first two-dimensional material layer or connected to the first two-dimensional material layer via the insulating layer, and a second ferroelectric layer that is in contact with the second two-dimensional material layer or connected to the second two-dimensional material layer via the insulating layer. The materials constituting the first ferroelectric layer and the second ferroelectric layer are materials in which polarization occurs when electromagnetic waves in a wavelength range absorbed by the gas to be detected are incident.

6. The gas detector according to any one of claims 3 to 5 further includes a first contact layer in contact with the first two-dimensional material layer and a second contact layer in contact with the second two-dimensional material layer. The materials constituting the first contact layer and the second contact layer are materials capable of supplying electrons or holes to the first two-dimensional material layer or the second two-dimensional material layer.

7. The gas detector according to any one of claims 3 to 6 further includes a first conductor in contact with the first two-dimensional material layer and a second conductor in contact with the second two-dimensional material layer.

8. Each of the first two-dimensional material layer and the second two-dimensional material layer has a first portion and a second portion that are spaced apart from each other on the insulating layer, and a third portion that is cross-linked between the first portion and the second portion. The gas detector according to any one of claims 3 to 7.

9. The gas detector according to claim 1, further comprising a semiconductor layer having a first surface and a second surface located on the side opposite to the first surface, wherein the insulating layer is disposed on the first surface, at least one opening for exposing a part of the first surface is formed in the insulating layer, the at least one two-dimensional material layer electrically connects between the at least one first electrode and the semiconductor layer, and extends from within the at least one opening onto the insulating layer, and 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.

10. The at least one opening has a first opening and a second opening which are spaced apart from each other, the at least one first electrode has a first first electrode and a second first electrode which are spaced apart from each other, the at least one two-dimensional material layer includes a fourth two-dimensional material layer that extends from within the first opening onto the insulating layer and electrically connects between the first first electrode and the semiconductor layer, and a fifth two-dimensional material layer that extends from within the second opening onto the insulating layer and electrically connects between the second first electrode and the semiconductor layer, and further includes a third coating film covering the fifth two-dimensional material layer, and the third coating film is provided to inhibit the permeation of the gas to be detected.

11. The at least one opening further has a third opening which is spaced apart from each of the first opening and the second opening, the at least one first electrode further has a third first electrode which is spaced apart from each of the first first electrode and the second first electrode, the at least one two-dimensional material layer includes a sixth two-dimensional material layer that extends from within the third opening onto the insulating layer and electrically connects between the third first electrode and the semiconductor layer, and further includes a fourth coating film covering the sixth two-dimensional material layer, and the fourth coating film is provided to inhibit the permeation of electromagnetic waves in a wavelength range absorbed by the gas to be detected.

12. The portion of the fourth two-dimensional material layer disposed on the insulating layer has a first end face extending in a direction intersecting the first face, the portion of the fourth two-dimensional material layer disposed in the first opening has a second end face extending in the intersecting direction, the portion of the fifth two-dimensional material layer disposed on the insulating layer has a third end face extending in the intersecting direction, the portion of the fifth two-dimensional material layer disposed in the second opening has a fourth end face extending in the intersecting direction, the sum of the areas of the second end faces is larger than the sum of the areas of the first end faces, and the sum of the areas of the fourth end faces is larger than the sum of the areas of the third end faces. The gas detector according to claim 10 or 11.

13. A gas detector array comprising a plurality of the gas detectors according to any one of claims 1 to 12, wherein each of the plurality of gas detectors is arranged in an array.

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