Measurement system, sensor recovery method, and measurement method

Abstract

This invention provides a measurement system that can recover the CNP of a sensor having a graphene layer toward 0V using an appropriate amount of ultraviolet irradiation. [Solution] The measurement system 1 includes a sensor 3 comprising an insulating layer 12 having a front and back surface, a graphene layer 14 provided on the front surface of the insulating layer 12, a source electrode 15 and a drain electrode 16 electrically connected to each other by the graphene layer 14, and a gate electrode made of a conductive semiconductor substrate 10 provided on the back side of the insulating layer 12; a UV light source 5 that irradiates the graphene layer 14 of the sensor 3 with ultraviolet light; a detection circuit 45 that measures the drain current Id flowing between the source electrode 15 and the drain electrode 16; and a control circuit 43 that starts irradiating the graphene layer 14 with ultraviolet light from the UV light source 5 based on the measured value of the drain current Id, and stops irradiating the graphene layer 14 with ultraviolet light from the UV light source 5 based on the measured value of the drain current Id.

Description

Technical Field

[0001] The present invention relates to a measurement system including a sensor having a graphene layer, a method for recovering the sensor, and a measurement method.

Background Art

[0002] Graphene is a single-atom layer material composed of carbon atoms and has excellent electrical and mechanical properties, so it is expected to be applied to various electronic devices. In particular, a graphene field-effect transistor (hereinafter referred to as "GFET") using graphene as a channel material has an Id (drain current)-Vg (gate voltage) characteristic due to the electronic state peculiar to graphene. In an ideal state, Id becomes minimum at Vg = 0V. Further, the Vg at which Id takes the minimum is called the charge neutral point, that is, CNP (charge neutral point). The CNP is the point where electron conduction and hole conduction switch. Since the Id-Vg characteristic changes sensitively with respect to gas adsorption, an electric field, and light, it is expected to be applied to a highly sensitive sensor platform.

[0003] A device is known in which an insulating film, graphene as a channel, and source-drain electrodes are formed on a semiconductor substrate including a doped silicon material to form a GFET. When gas is adsorbed on the graphene serving as the channel in this device, charge transfer occurs between the gas molecules and the graphene channel, and p-doping (the CNP shifts in the positive direction) or n-doping (the CNP shifts in the negative direction) occurs depending on the sign of the charge, and it operates as a gas sensor. Further, it is known that the gas sensitivity and gas selectivity for a specific gas can be improved by providing a specific metal, metal compound, or activated carbon on the graphene surface. A device using a substrate including a pyroelectric material instead of the semiconductor substrate of the GFET is known. This device applies the so-called "optical gate effect" in which the spontaneous polarization of the pyroelectric body arranged near the graphene acts as a gate voltage, and the spontaneous polarization changes due to infrared irradiation and acts as a change in the gate voltage of the graphene, and operates as an IR bolometer.

[0004] Patent Document 1 describes a sensor having an FET structure comprising a first electrode as a source electrode, a second electrode as a drain electrode, a gate electrode, a gate insulating film, and a graphene film as a channel. In this sensor, before measuring the object to be detected, a constant voltage is applied between the first and second electrodes, the gate voltage Vg of the gate electrode is increased or decreased, and the current value of the drain current Id is measured. Subsequently, the same operation is performed during the measurement of the object to be detected. From the change in Id-Vg characteristics before and after measurement, the amount of carriers injected into the graphene film from sources other than the gate electrode, i.e., the number of objects to be detected that are the sources of these carriers, is calculated. Non-patent documents 1 and 2 describe a technique for irradiating a graphene film with ultraviolet light to improve a condition in which CNPs are displaced by carriers injected from the object to be detected attached to the graphene film, thereby reducing sensor sensitivity. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2018-163146 [Non-patent literature]

[0006] [Non-Patent Document 1] Alvaro Pena, Daniel Matatagui, Filiberto Ricciardella, Leandro Sacco, Sten Vollebregt, Daniel Otero, Jesus Lopez-Sanchez, Pilar Marin, Mari Carmen Horrillo “Optimization of multilayer graphene-based gas sensors by ultraviolet photoactivation” Applied Surface Science 610 (2023) 155393 [Non-Patent Document 2] Xin Yan, Yanan Wu, Rui Li, Chengqian Shi, Ramiro Moro, Yanqing Ma, Lei Ma "High-Performance UV-Assisted NO2 Sensor Based on Chemical Vapor Deposition Graphene at Room Temperature" ACS Omega 2019, 4, 14179-14187 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] While GFET-type sensor platforms offer high sensitivity, they are susceptible to disturbances and manufacturing variations, resulting in significant variations and drift in Id-Vg characteristics, which poses practical problems for applications. In particular, in gas sensor applications, the graphene channel is exposed to air, making it prone to p-doping due to oxygen adsorption. This phenomenon inhibits the adsorption sites of the target gas, causing drift in the reference CNP and significantly degrading the gas sensor characteristics. Furthermore, in infrared sensor applications, graphene is packaged in a vacuum, but outgassing from the inner wall of the package and the surface of the printed circuit board poses a problem, leading to changes in CNP. Additionally, when CNP drift occurs, sweeping the gate voltage to return CNP to near 0V before measurement is considered. However, if the CNP drift is too large, a wide-range gate voltage sweep is required, leading to increased detection time, larger drive circuits, and higher power consumption. One known method for recovering CNPs (returning them to near 0V) is annealing in an Ar+H2 atmosphere, but this requires a large annealing apparatus, resulting in a large system. The techniques described in Non-Patent Documents 1 and 2 above improve gas sensitivity by irradiating with ultraviolet (UV) light, but because sensing is done using the resistance value between Id and Vg, the true reference value of the resistance is unknown, which can lead to damage to the graphene channel or charge transfer from the insulating substrate due to insufficient or excessive UV irradiation. The present invention has been made in view of the above problems, and aims to provide a measurement system, a sensor recovery method, and a measurement method that can recover the CNP of a sensor having a graphene layer toward 0V with an appropriate amount of ultraviolet irradiation. [Means for solving the problem]

[0008] A measurement system according to one aspect of the present invention includes a sensor comprising: an insulator having a front surface and a back surface; a graphene layer provided on the front surface of the insulator; a first electrode and a second electrode electrically connected to each other by the graphene layer; and a third electrode provided on the back surface of the insulator; a light source that irradiates the graphene layer of the sensor with ultraviolet light; a measurement unit that measures the current flowing from one of the first electrode and the second electrode to the other; and a control unit that starts irradiating ultraviolet light from the light source based on the measured value of the current and stops irradiating ultraviolet light from the light source based on the measured value of the current. In the above configuration, the control unit may be configured to stop the irradiation of ultraviolet light from the light source when the voltage at the charge neutral point where the measured value of the current is minimized when the voltage is changed approaches zero, in the measured value of the current when a voltage is applied to the third electrode by irradiation of ultraviolet light from the light source. In the above configuration, the control unit may be configured to stop the irradiation of ultraviolet light when the voltage at the charge neutral point approaches a predetermined range from zero.

[0009] Furthermore, a measurement system according to one aspect of the present invention includes a sensor comprising an insulator, a graphene layer provided on the surface of the insulator, and a first electrode and a second electrode electrically connected to each other by the graphene layer; a light source that irradiates the graphene layer of the sensor with ultraviolet light; a measurement unit that measures the current flowing from one of the first electrode and the second electrode to the other; and a control unit that starts irradiating ultraviolet light from the light source based on the measured value of the current and stops irradiating ultraviolet light from the light source based on the measured value of the current. In the above configuration, the control unit may be configured to stop the irradiation of ultraviolet light when the measured value of the current decreases to a predetermined reference value. In the above configuration, the graphene layer may have nanoparticles provided on its surface. In the above configuration, the light source may be configured to irradiate ultraviolet light with a wavelength of 265 nm or more and 400 nm or less.

[0010] Furthermore, a sensor recovery method according to one aspect of the present invention comprises the steps of measuring a current flowing from one of the first electrode and the second electrode to the other of a sensor comprising an insulator having a front surface and a back surface, a graphene layer provided on the front surface of the insulator, a first electrode and a second electrode electrically connected to each other by the graphene layer, and a third electrode provided on the back surface of the insulator; and starting irradiation of the graphene layer with ultraviolet light from a light source based on the measured value of the current, and stopping the irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current.

[0011] Furthermore, a sensor recovery method according to one aspect of the present invention is a sensor recovery method comprising the steps of: measuring the current flowing from one of the first electrode and the second electrode to the other of a sensor comprising an insulator, a graphene layer provided on the surface of the insulator, and a first electrode and a second electrode electrically connected to each other by the graphene layer; and starting irradiation of the graphene layer with ultraviolet light from a light source based on the measured value of the current, and stopping the irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current. Furthermore, a measurement method according to one aspect of the present invention comprises the steps of the recovery method described above, and a step of measuring the current after the ultraviolet irradiation has been stopped following the execution of the recovery method. [Effects of the Invention]

[0012] According to the present invention, since the CNP of the sensor having a graphene layer can be recovered to near 0 V with an appropriate UV irradiation amount, the measurement can be performed from the state near 0 V of the CNP, and the reproducibility of the measurement can be improved.

Brief Description of the Drawings

[0013] [Figure 1] It is a schematic diagram showing the configuration of the measurement system according to the first embodiment. [Figure 2] It is a schematic diagram showing the configuration of the sensor according to the first embodiment. [Figure 3] It is a block diagram showing the connection configuration of each component of the measurement system according to the first embodiment. [Figure 4] (a) is a diagram showing a state where the sensor is irradiated with ultraviolet rays from the UV light source 5, and (b) is a diagram showing the relationship between the irradiation time of ultraviolet rays and the CNP. [Figure 5] It is a diagram showing the drain current Id with respect to the gate voltage Vg in the first embodiment. [Figure 6] (a) to (b) are diagrams showing the experimental results of changes in CNP in different environments including in vacuum, in air, and during UV irradiation. [Figure 7] It is a flowchart showing the recovery process and the gas measurement process according to the first embodiment. [Figure 8] It is a schematic diagram showing the configuration of the sensor according to the second embodiment. [Figure 9] (a) to (c) are diagrams showing the experimental results of changes in CNP in different environments including in vacuum, in air, and during UV irradiation with a peak wavelength of 265 nm. [Figure 10] It is a schematic diagram showing the configuration of the sensor 3B according to the third embodiment. [Figure 11] It is a diagram showing the changes in the gate voltage Vg and the drain current Id due to the optical gate effect in the third embodiment. (a) shows the changes when CNP = 0 V, and (b) shows the changes when CNP ≠ 0 V. [Figure 12]It is a flowchart showing the calibration process and the infrared measurement process according to the third embodiment. [Figure 13] It is a flowchart showing the calibration process according to the third embodiment.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. Note that the embodiments described below are examples of means for realizing the present invention, and should be appropriately modified or changed according to the configuration and various conditions of the apparatus to which the present invention is applied. The present invention is not limited to the following embodiments.

[0015] In addition, in the description of the following drawings, the same or similar parts are denoted by the same or similar reference numerals. However, it should be noted that the drawings are schematic, and the vertical and horizontal dimensions and scales of the members or parts are different from the actual ones. Therefore, specific dimensions and scales should be determined in consideration of the following description. Also, it is a matter of course that there are parts where the dimensional relationships and ratios are different between the drawings. 〔First Embodiment〕 〔Configuration〕 First, the first embodiment of the present invention will be described. FIGS. 1 to 7 are diagrams showing the first embodiment. The measurement system 1 according to the first embodiment corresponds to an embodiment of the measurement system of the present invention, and as an example, detects the type and concentration of gas. FIG. 1 is a schematic diagram showing the configuration of the measurement system 1 according to the first embodiment. FIG. 2 is a schematic diagram showing the configuration of the sensor 3 according to the first embodiment. FIG. 3 is a block diagram showing the connection configuration of each component of the measurement system 1 according to the first embodiment. As shown in FIG. 1, the measurement system 1 according to the first embodiment includes a housing 2, a sensor 3, a circuit board 4, and a UV light source 5. In FIG. 1, the height direction of the housing 2 is the Z direction, and the direction orthogonal to the length direction, the Z direction, and the X direction of the housing 2 is the Y direction.

[0016] The housing 2 has a hollow, roughly rectangular chamber 6, which houses a sensor 3, a circuit board 4, and a UV light source 5. The housing 2 has an intake port 21 for drawing gas in from the outside and an exhaust port 22 for exhausting the gas introduced into the chamber 6 to the outside. The intake port 21 is provided with an electromagnetic valve 23 to regulate the inflow of gas into the chamber 6, and the exhaust port 22 is provided with an electromagnetic valve 24 to regulate the outflow of gas from the chamber 6 to the outside. Instead of electromagnetic valves 23 and 24, a pump or fan may be provided at the intake port 21 or exhaust port 22 to draw gas into the chamber 6 and exhaust gas from the chamber 6.

[0017] Figure 2 is a schematic diagram showing the configuration of the sensor according to the first embodiment. In Figure 2, the thickness direction of the semiconductor substrate 10 is the Z direction, the arrangement direction of the source electrode 15 and the drain electrode 16 is the X direction, and the direction perpendicular to the Z direction and the X direction is the Y direction. The same applies to subsequent diagrams with the same viewpoint.

[0018] As shown in Figure 2, sensor 3 comprises a semiconductor substrate 10, an insulating layer 12, a graphene layer 14, a source electrode 15, and a drain electrode 16. The insulating layer 12 is provided on the main surface of the semiconductor substrate 10. The insulating layer 12 has a surface on the +Z direction side and a back surface on the -Z direction side, and is provided on the semiconductor substrate 10 with its back surface in contact with the substrate, while the graphene layer 14 is provided on the surface of the insulating layer 12. The semiconductor substrate 10 and the graphene layer 14 are not in contact with each other because they are provided via the insulating layer 12. As will be described later, the semiconductor substrate 10 is a semiconductor substrate containing impurities such as silicon, and therefore functions as a gate electrode.

[0019] The source electrode 15 and the drain electrode 16 are positioned on the surface of the insulating layer 12, sandwiching the graphene layer 14. The source electrode 15 and the drain electrode 16 are electrically connected by contacting the X-direction end of the graphene layer 14. The graphene layer 14 corresponds to a channel through which current flows. The gate terminal Tg is electrically connected to the semiconductor substrate 10, and the source terminal Ts and drain terminal Td are electrically connected to the source electrode 15 and drain electrode 16, respectively. Sensor 3 functions as a transistor that controls the drain current Id flowing between the source electrode 15 and the drain electrode 16 by a gate voltage Vg applied to the gate terminal Tg connected to the semiconductor substrate 10.

[0020] The semiconductor substrate 10 is, for example, an n-type or p-type silicon substrate doped with impurities. The insulating layer 12 is, for example, an inorganic insulating film such as a silicon oxide film or a silicon nitride film. The source electrode 15 and the drain electrode 16 each have, for example, an adhesion film that adheres closely to the insulating layer 12 and a low-resistance film provided on the adhesion film. The adhesion film is, for example, a titanium film or a chromium film, and the low-resistance film is, for example, a gold film, a copper film, or an aluminum film.

[0021] The graphene layer 14 is, for example, a so-called monolayer (with a thickness of approximately 0.34 nm) consisting of one atomic layer of graphene. The graphene layer 14 may also be a film consisting of multiple atomic layers, rather than a monolayer. Furthermore, the graphene layer 14 may be a single crystal or a polycrystalline material consisting of multiple grains.

[0022] As shown in Figure 3, the circuit board 4 includes a control circuit 43, a detection circuit 45, and a drive circuit 47. The control circuit 43 is electrically connected to the sensor 3, the UV light source 5, the detection circuit 45, and the drive circuit 47. The drive circuit 47 is electrically connected to the sensor 3 and the electromagnetic valves 23 and 24. Note that one or more of the control circuit 43, the detection circuit 45, and the drive circuit 47 may be configured on a separate circuit board from the circuit board 4 and communicate with each other wirelessly or via wired connections. Alternatively, one or more of the functions of the control circuit 43, the detection circuit 45, and the drive circuit 47 may be implemented by an integrated circuit such as a microcomputer.

[0023] A microcomputer consists of a CPU (Central Processing Unit) that controls calculations and the entire device based on a control program, a ROM (Read Only Memory) that stores the CPU's control program and other information in a predetermined area, a RAM (Random Access Memory) for storing data read from the ROM and other memory, as well as calculation results necessary for the CPU's calculation process, and an I / F (Interface) that mediates data input and output to external devices. These components are connected to each other and enable data exchange via a bus, which is a signal line for data transfer.

[0024] The drive circuit 47 is electrically connected to the gate terminal Tg, the source terminal Ts, and the drain terminal Td. The drive circuit 47 applies a drive voltage to the drain terminal Td and the gate terminal Tg to drive the sensor 3. Specifically, the drive circuit 47 applies a drain voltage Vd to the drain terminal Td and a sweep voltage that changes within a predetermined range to the gate terminal Tg. In the first embodiment, for example, a sweep voltage that changes linearly from -40V to 40V in about 1 minute is used, and the sweep voltage is a voltage that changes on both the positive and negative sides.

[0025] The detection circuit 45 is electrically connected to the gate terminal Tg, the source terminal Ts, and the drain terminal Td. The detection circuit 45 detects the drain current Id flowing between the source electrode 15 and the drain electrode 16 when a sweep voltage is applied to the gate terminal Tg by the drive circuit 47.

[0026] The detection circuit 45 measures the change in CNP before and after gas inhalation based on the sweep voltage applied to the gate electrode in the drive circuit 47 before and after gas inhalation, and the drain current Id detected by the detection circuit 45 while the sweep voltage is applied. Based on the measurement results, it then detects the type and concentration of the gas.

[0027] The drive circuit 47 applies a sweep voltage to the gate terminal Tg before starting the gas measurement process, and the detection circuit 45 measures CNP based on the detected drain current Id and gate voltage Vg. Furthermore, if the measured CNP is not 0V, the control circuit 43 controls the UV light source 5 to irradiate the sensor 3 with ultraviolet light and performs a process to recover CNP to 0V. In this recovery process, CNP is monitored during ultraviolet irradiation, and ultraviolet light is irradiated until CNP is reduced to 0V or approaches 0V. UV light source 5 is a light source that emits ultraviolet light with a peak wavelength of 265 nm to 400 nm. UV light source 5 is composed of, for example, a UV-LED (light-emitting diode). As an example, UV light source 5 is a light source that emits ultraviolet light with a peak wavelength of 265 nm. [Regarding the irradiation of sensor 3 with ultraviolet light] Figure 4(a) shows how ultraviolet light is irradiated onto sensor 3 from UV light source 5, and Figure 4(b) shows the relationship between ultraviolet irradiation time and CNP. In Figure 4(b), the vertical axis is CNP (V), and the horizontal axis is ultraviolet irradiation time (min).

[0028] As shown in Figures 1 and 4(a), the UV light source 5 is positioned at a height that allows ultraviolet light to be irradiated onto an area of ​​the inner wall in the +Z direction within the chamber 6, including at least the entire surface area of ​​the graphene layer 14 of the sensor 3. The UV light source 5 is controlled to turn on and off according to a control signal from the control circuit 43. The UV light source 5 lights up in response to a control signal from the control circuit 43 instructing it to light up during the recovery process of the CNP, and irradiates ultraviolet light onto the entire surface area of ​​the graphene layer 14 of the sensor 3, as shown in Figure 4(a).

[0029] Here, the graphene layer 14 undergoes a change in CNP due to the injection of electrons or holes from gas molecules upon adsorption. In addition to gas molecule adsorption, variations in the initial CNP also occur due to the process conditions of the sensor 3 (residue of resist and solvent). Furthermore, the CNP changes due to the injection of holes caused by oxygen in the air. Therefore, in the first embodiment, the CNP is measured before executing the gas measurement process, and it is determined whether the measured CNP is, for example, 0V, or whether it is above or below a preset upper threshold or lower threshold. If it is determined that it is not 0V, or is above or below the upper threshold or lower threshold, a CNP recovery process is executed.

[0030] By irradiating the graphene layer 14 with ultraviolet light, gas molecules and oxygen molecules can be released. On the other hand, excessive irradiation of the graphene layer 14 with ultraviolet light can damage the graphene layer 14 and may induce charge transfer in the semiconductor substrate 10. Therefore, it is necessary to avoid excessive irradiation of the graphene layer 14 with ultraviolet light. Accordingly, in this invention, as shown in Figure 4(b), the irradiation time of ultraviolet light is controlled so that the CNP becomes 0V.

[0031] Figure 5 shows the drain current Id with respect to the gate voltage Vg in the first embodiment. The horizontal axis represents the gate voltage Vg applied by the drive circuit to the gate terminal Tg. The vertical axis represents the drain current Id that flows from the drain terminal Td to the source terminal Ts when the drive circuit applies a drain voltage Vd to the drain terminal Td. [Regarding the properties of a charge neutral point (CNP)] Figure 5 shows the drain current Id as a function of the gate voltage Vg in the first embodiment. In Figure 5, the horizontal axis represents the gate voltage Vg, and the vertical axis represents the drain current Id.

[0032] The conduction band and valence band of graphene are cone-shaped, and the bottom of the conduction band and the top of the valence band are in contact at the Dirac point. The current-voltage characteristics 52a when graphene is neutral will be described below based on Figure 5. When the gate voltage Vg is approximately 0V, the Fermi level is located at the Dirac point. At the Dirac point, the carrier density contributing to conduction is low. Therefore, when the gate voltage Vg = 0V, the drain current Id is minimal. That is, the point where the drain current Id is minimal is the CNP. Hereafter in the first embodiment, the point where the drain current Id is minimal will be described as the charge neutral point, but in order to realize the first embodiment, instead of measuring the point where the drain current Id is minimal, a point near the point of minimality may be measured, and the measured point may be considered as the CNP. In the current-voltage characteristics 52a, when the gate voltage Vg is 0V, it is CNP 53a, and when the gate voltage Vg is positive or negative, the drain current Id increases.

[0033] When specific molecules in a gas are adsorbed onto the graphene layer 14 and the molecules supply electrons to the graphene, the molecules function as donors. In this case, the Fermi level becomes higher than the Dirac point, meaning the work function of graphene decreases. The work function of graphene is the energy difference between the Fermi level and vacuum. Therefore, as shown in Figure 5, in the current-voltage characteristic 52b, CNP 53b becomes negative than Vg = 0. When specific molecules in a gas are adsorbed onto the graphene layer 14 and the molecules accept electrons from the graphene, the molecules function as acceptors. In this case, the Fermi level becomes lower than the Dirac point, meaning the work function of graphene increases. Therefore, in the current-voltage characteristic 52c, CNP 53c becomes positive than Vg = 0.

[0034] The control circuit 43 measures ΔCNP54b, which is the difference between CNP53a and 53b, or ΔCNP54c, which is the difference between CNP53a and 53c. The magnitude of ΔCNP54b or 54c is proportional to the amount of a specific molecule adsorbed on the graphene layer 14. Therefore, the concentration of a specific molecule can be measured from the magnitude of the difference 54b or 54c. [Regarding changes in CNP in vacuum, air, and under ultraviolet irradiation]

[0035] Figure 6 shows experimental results of changes in CNP under different environments, including vacuum, air, and ultraviolet irradiation. Figure 6(a) shows the result when irradiated with ultraviolet light with a peak wavelength of 340 nm, and Figure 6(b) shows the result when irradiated with ultraviolet light with a peak wavelength of 265 nm.

[0036] In the experiment, a graphene layer 14 with a channel size of 200 nm was formed, a sensor 3 was placed on a vacuum prober, a gate voltage Vg was applied to the gate terminal Tg, and the source current Is was measured. As UV light sources 5, a light source with a peak wavelength of 340 nm and a light source with a peak wavelength of 265 nm were used.

[0037] As shown in Figure 6(a), when sensor 3 was initially placed in a vacuum and sufficiently annealed, the CNP was approximately -14V. Subsequently, when sensor 3 was placed in air, it was p-doped due to the influence of oxygen molecules, and the CNP rose to approximately 0V. After that, even when sensor 3 was placed in a vacuum, the CNP did not recover and rose to approximately 12V. Next, sensor 3 was irradiated with ultraviolet light with a peak wavelength of 340nm from a UV light source. Irradiation with ultraviolet light shifted the CNP from approximately 12V to approximately -10V. The amount of CNP shift after 10 minutes of irradiation with ultraviolet light at a wavelength of 340nm was 18V. Subsequently, when sensor 3 was placed in a vacuum, the CNP shifted slightly to the positive side.

[0038] On the other hand, as shown in Figure 6(b), when sensor 3 was initially placed in a vacuum and sufficiently annealed, the CNP was 0V. Subsequently, when sensor 3 was placed in air, it was p-doped due to the influence of oxygen molecules, and the CNP rose to approximately 30V. After that, even when sensor 3 was placed in a vacuum, the CNP did not recover and rose to approximately 32V. Next, sensor 3 was irradiated with ultraviolet light with a peak wavelength of 265nm from a UV light source. Irradiation with ultraviolet light shifted the CNP from approximately 32V to approximately -25V. The amount of CNP shift when irradiated with ultraviolet light at a wavelength of 265nm for 10 minutes was 22V. Subsequently, when sensor 3 was placed in a vacuum, the CNP shifted slightly to the positive side.

[0039] From the experimental results above, it was found that irradiating the p-doped sensor 3 with ultraviolet light in the atmosphere causes a shift in CNP that crosses CNP=0V. In other words, by monitoring CNP during the ultraviolet irradiation for recovery and ending the irradiation when CNP=0V, gas measurements can be performed from the CNP=0V state. Furthermore, since the ultraviolet irradiation is stopped when CNP=0V, excessive or insufficient irradiation of the graphene layer 14 with ultraviolet light can be avoided. It was also found that the recovery speed is faster with ultraviolet light at a wavelength of 265 nm than with ultraviolet light at a wavelength of 340 nm. [Recovery process and gas measurement process] Next, we will describe the recovery process and gas measurement process performed by the measurement system 1. Figure 7 is a flowchart showing the recovery process and gas measurement process according to the first embodiment. The measurement system 1 executes the recovery process and gas measurement process shown in the flowchart of Figure 7, in accordance with the control of the control circuit 43. Once the recovery process and gas measurement process are performed in the measurement system 1, the system first proceeds to step S100, as shown in Figure 7.

[0040] In step 100, before the gas measurement process is executed, the drive circuit 47 applies a sweep voltage to the gate terminal Tg and a drain voltage Vd to the drain terminal Td. Furthermore, the control circuit 43 measures CNP, which is the gate voltage Vg at which the drain current Id is minimized, based on the drain current Id detected by the detection circuit 45 for the sweep voltage while the sweep voltage is being applied. Then, it is determined whether the measured CNP is not 0V or not. If it is determined that it is not 0V (Yes), the process proceeds to step S102; otherwise, it proceeds to step S108. In the CNP0V determination process, for example, a lower threshold (e.g., -0.2V) and an upper threshold (e.g., +0.2V) are set. If the measured CNP is less than the upper threshold and greater than the lower threshold, it is determined to be 0V. If it is above the upper threshold or below the lower threshold, it is determined not to be 0V. The sweep voltage is applied in increments of 0.2V, for example, from -40V to +40V. If the process proceeds to step S102, the control circuit 43 sends a control signal to the UV light source 5 to turn it on, and the irradiation of the sensor 3 with ultraviolet light begins. After that, the process proceeds to step S104.

[0041] In step S104, similar to step S100, a sweep voltage is applied to the gate terminal Tg to measure CNP and determine whether CNP has reached 0V. If it is determined that CNP has reached 0V (Yes), the process proceeds to step S106. If it is determined that CNP has not reached 0V (No), the process of continuing ultraviolet irradiation and applying a sweep voltage to determine whether CNP has reached 0V is repeated until CNP reaches 0V. Here, the repeated application of the sweep voltage may be, for example, by applying -40V to +40V from negative to positive, and then again by applying -40V to +40V from negative to positive. Alternatively, the voltage may be applied alternately from positive to negative, starting with -40V to +40V and then applying +40V to -40V. If the process proceeds to step S106, the control circuit 43 sends a control signal to the UV light source 5 to instruct it to turn off, thereby stopping the irradiation of ultraviolet light to the sensor 3. After that, the process proceeds to step S108. In step S108, the control circuit 43 sends a control signal to the electromagnetic valve 23 to open the valve, opening the electromagnetic valve 23 and introducing the sample gas into the chamber 6 from the intake port 21. Then, the process proceeds to step S110.

[0042] In step S110, a sweep voltage is applied to the gate terminal Tg, similar to step S100, to measure the CNP after the sample gas is introduced. Then, the control circuit 43 measures the difference ΔCNP between the CNP before and after the introduction of the sample gas. After that, the process proceeds to step S112. From this ΔCNP, the type and concentration of the sample gas can be determined. In step S112, the control circuit 43 sends a control signal to the electromagnetic valve 24 to open the valve, opening the electromagnetic valve 24 and exhausting the sample gas in the chamber 6 through the exhaust port 22. This completes the gas measurement and the process proceeds to step S114.

[0043] In step S114, the control circuit 43 determines whether or not to perform continuous measurement. If continuous measurement is performed (Yes), the process proceeds to step S100; otherwise, the series of processes ends. Here, the measurement system 1 allows setting a continuous measurement mode. If the continuous measurement mode is set, the process from step S100 is repeated. On the other hand, if the continuous measurement mode is not set, the process ends after a single measurement. Furthermore, recovery processing may be performed not only immediately before performing gas measurement processing or while gas measurement processing is being repeated, but also periodically while the power is on and gas measurement processing is not being performed. [Effects of the First Embodiment]

[0044] As described above, the measurement system 1 according to the first embodiment includes a sensor 3 comprising an insulating layer 12 having a front and a back surface, a graphene layer 14 provided on the front surface of the insulating layer 12, a source electrode 15 and a drain electrode 16 electrically connected to each other by the graphene layer 14, and a gate electrode made of a conductive semiconductor substrate 10 provided on the back side of the insulating layer 12; a UV light source 5 that irradiates ultraviolet light onto the graphene layer 14 of the sensor 3; a detection circuit 45 that measures the drain current Id flowing between the source electrode 15 and the drain electrode 16; and a control circuit 43 that starts irradiating the graphene layer 14 with ultraviolet light from the UV light source 5 based on the measured value of the drain current Id, and stops irradiating with ultraviolet light from the UV light source 5 based on the measured value of the drain current Id. Furthermore, the control circuit 43 is configured to stop the irradiation of ultraviolet light from the UV light source 5 when the measured value of the drain current Id when a voltage is applied to the gate electrode by irradiation of ultraviolet light from the UV light source 5 approaches zero (0V) in the charge neutral point where the measured value of the drain current Id when the gate voltage Vg is changed is minimized. Specifically, the control circuit 43 is configured to stop the irradiation of ultraviolet light when the gate voltage Vg at the charge neutral point approaches zero (0V) to a predetermined range.

[0045] With this configuration, ultraviolet light can be irradiated until the CNP reaches 0V or approximately 0V, and the irradiation can be stopped once the CNP reaches 0V or approximately 0V. This allows measurements to be performed each time using the CNP at which the gate voltage is 0V or approximately 0V as a reference, thereby improving the reproducibility of the measurements. In other words, the point where the graphene is in equilibrium, close to a state that is neither n-type nor p-type conduction, is taken as the zero point, and the difference from this zero point is taken, resulting in a more accurate and stable difference compared to taking the difference from a point other than the zero point. Furthermore, since oxygen and other gas molecules adsorbed on the graphene layer 14 can be desorbed by ultraviolet irradiation, sufficient adsorption sites for the target gas molecules on the graphene layer 14 can be secured, improving sensitivity. In addition, since the gas measurement process can be started after the CNP reaches 0V or approximately 0V, the sweep range of the gate voltage Vg applied to the gate electrode can be minimized. This eliminates the need for boost circuits, etc., allowing for simplification of the control circuit and reduction of measurement time. Furthermore, since ultraviolet light is irradiated while monitoring CNP, it is possible to prevent insufficient or excessive irradiation of the graphene layer 14 with ultraviolet light. [Correspondence in the first embodiment] In the first embodiment, the insulating layer 12 corresponds to an insulator, the source electrode 15 corresponds to a first electrode, the drain electrode 16 corresponds to a second electrode, and the semiconductor substrate 10 (gate electrode) corresponds to a third electrode. In the first embodiment, the UV light source 5 corresponds to the light source, the detection circuit 45 corresponds to the measurement unit, and the control circuit 43 corresponds to the control unit. [Second Embodiment] Next, a second embodiment of the present invention will be described. Figures 8 and 9 show the second embodiment. 〔composition〕 Figure 7 is a schematic diagram showing the configuration of the sensor 3A according to the second embodiment.

[0046] The second embodiment differs from the first embodiment in that it includes a sensor 3A having nanoparticles arranged on a graphene layer 14. Hereinafter, the same reference numerals will be used for components similar to those in the first embodiment, and explanations of parts similar to those in the first embodiment will be omitted as appropriate, while the different parts will be described in detail. As shown in Figure 8, the measurement system 1 according to the second embodiment is equipped with a sensor 3A in place of the sensor 3 in the measurement system 1 of the first embodiment. In the sensor 3A of the first embodiment described above, a plurality of metal nanoparticles 17 are provided on the graphene layer 14. A channel 18 is formed from the graphene layer 14 and the plurality of nanoparticles 17.

[0047] The nanoparticles 17 consist of a metal, a metal oxide, or a mixture of a metal and a metal oxide that readily binds selectively to specific molecules in the detection gas. The nanoparticles 17 may also play a role in improving the reactivity when specific molecules in the detection gas bind to them. When the nanoparticles consist of tin, tin oxide, or a mixture of tin and tin oxide, ethanol and ammonia are mainly adsorbed, thus enabling a detection device that selectively detects ethanol and ammonia. The nanoparticles 17 may contain impurities other than tin, tin oxide, or a mixture of tin and tin oxide, whether intentional or unintentional.

[0048] In addition to tin, the nanoparticles 17 may be at least one metal selected from, for example, zinc, gold, silver, copper, scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, zinc, aluminum, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, hafnium, tantalum, tungsten, osmium, iridium, and platinum, an oxide of this metal, or a mixture of this metal and an oxide of this metal. Besides the above, semiconductor nanoparticles such as silicon, germanium, or III-V semiconductors can also be used as nanoparticles 17. Furthermore, the particle size of the nanoparticles 17 is, for example, 0.5 nm to 100 nm, and typically 0.5 nm to 20 nm. [Method for forming thin films of nanoparticles]

[0049] A method for forming a thin film of nanoparticles on a graphene layer 14 will be described. First, a resist material is applied to the graphene layer 14 and the source electrode 15 and drain electrode 16 to form a resist film. The resist film is, for example, a photosensitive resin film such as a methyl methacrylate film. The resist film is applied by, for example, a spin coater or a spray coater.

[0050] Next, using a photomask that masks the graphene layer 14, the resist film is exposed to light except for the graphene layer 14 using electron beam lithography. Then, development is performed with a developer to remove the unexposed graphene layer 14 portion of the resist film. This forms a resist pattern in which only the graphene layer 14 portion is exposed.

[0051] Next, a thin film consisting of nanoparticles 17 is formed on the unremoved portion of the resist film and on the graphene layer 14. Afterward, the formed thin film is allowed to oxidize naturally. Vacuum deposition is used to form the thin film. When the nanoparticles 17 are tin, the thin film is preferably 2 nm or smaller. If it is 2 nm or smaller, a region where the nanoparticles 17 aggregate is formed when the thin film is created.

[0052] Next, the resist film is removed along with the thin film of nanoparticles 17. This forms a thin film of nanoparticles 17 on the graphene layer 14. The lift-off method is used to remove the resist film. The thin film of nanoparticles 17 has crack-like gaps in places, and the graphene layer 14 is exposed through these gaps. [Regarding changes in CNP in vacuum, air, and under ultraviolet irradiation]

[0053] Figure 9 shows experimental results of CNP changes under different environments, including vacuum, air, and ultraviolet irradiation with a peak wavelength of 265 nm. Figure 9(a) shows the case where a thin film of aluminum nanoparticles is provided on the graphene layer 14, Figure 9(b) shows the case where a thin film of tin nanoparticles is provided on the graphene layer 14, and Figure 9(c) shows the case where no thin film of nanoparticles is provided on the graphene layer 14. Note that the graphene layer 14 of sensor 3 in Figure 9(c) is formed by the CVD method. In the experiment, a graphene layer 14 with a channel size of 200 nm was formed, a sensor 3 was placed on a vacuum prober, a gate voltage Vg was applied to the gate terminal Tg, and the source current Is was measured. A UV light source 5 with a peak wavelength of 265 nm was used.

[0054] First, when a thin film of aluminum nanoparticles was formed on the graphene layer 14, as shown in Figure 9(a), the CNP was approximately -2V when the sensor 3 was initially placed in a vacuum and sufficiently annealed. Subsequently, when the sensor 3 was placed in air, it was p-doped due to the influence of oxygen molecules, and the CNP rose to approximately 10V. After that, even when the sensor 3 was placed in a vacuum, the CNP did not recover and rose to approximately 12V. Next, the sensor 3 was irradiated with ultraviolet light with a peak wavelength of 265nm from a UV light source. Irradiation with ultraviolet light shifted the CNP from approximately 12V to approximately -20V. Subsequently, when the sensor 3 was placed in a vacuum, the CNP shifted slightly to the positive side.

[0055] Furthermore, when a thin film of tin nanoparticles was formed on the graphene layer 14, as shown in Figure 9(b), the CNP was 0V when the sensor 3 was initially placed in a vacuum and sufficiently annealed. Subsequently, when the sensor 3 was placed in air, it was p-doped due to the influence of oxygen molecules, and the CNP rose to approximately 60V. After that, even when the sensor 3 was placed in a vacuum, the CNP did not recover and rose slightly to approximately 61V. Subsequently, the sensor 3 was irradiated with ultraviolet light with a peak wavelength of 265nm from a UV light source. Irradiation with ultraviolet light shifted the CNP from approximately 61V to approximately -2V. After that, when the sensor 3 was placed in a vacuum, there was no change in the CNP.

[0056] Furthermore, when a thin film of nanoparticles was not formed, as shown in Figure 9(c), the CNP was approximately 40V when the sensor 3 was initially placed in a vacuum and sufficiently annealed. Subsequently, when the sensor 3 was placed in air, it was p-doped due to the influence of oxygen molecules, and the CNP rose to approximately 80V. After that, even when the sensor 3 was placed in a vacuum, the CNP did not recover and remained at approximately 80V. Next, the sensor 3 was irradiated with ultraviolet light with a peak wavelength of 265nm from a UV light source. Irradiation with ultraviolet light shifted the CNP from approximately 80V to approximately 47V. Subsequently, when the sensor 3 was placed in a vacuum, the CNP rose to approximately 50V.

[0057] From the experimental results above, it was found that when a thin film of nanoparticles is formed, irradiating the p-doped sensor 3 with ultraviolet light in air causes a CNP shift that crosses CNP=0V. On the other hand, when a thin film of nanoparticles is not formed, irradiating the p-doped sensor 3 with ultraviolet light in air does not reach CNP=0V. This is because, although the irradiation time was the same in both cases, it is thought that this irradiation time was insufficient to reach CNP=0V when a thin film of nanoparticles is not formed. In any case, it was found that forming a thin film of nanoparticles shortens the time it takes to reach CNP=0V during the recovery process. The recovery process and gas measurement process described in the first embodiment can also be applied to the measurement system 1 equipped with the sensor 3A having the configuration described above. [Effects of the second embodiment] As described above, the measurement system 1 according to the second embodiment is equipped with a sensor 3A in place of the sensor 3 of the first embodiment, and the sensor 3A is configured such that nanoparticles 17 are provided on the surface of the graphene layer 14 in the sensor 3.

[0058] This configuration allows for selective binding to specific molecules in the detected gas, and also improves the reactivity when those molecules bind. In addition, the thin film of nanoparticles increases the rate at which the CNP approaches 0V when irradiated with ultraviolet light, thus shortening the time required for the CNP to recover to 0V. The reason for this is as follows: Nanoparticles impart gas selectivity to graphene alone. Because the surface energy of nanoparticles is lower than that of graphene, the binding energy between the nanoparticles and gas molecules is similarly lower, and the energy required to dissociate that bond is also lower. Therefore, sensors with nanoparticles attached to graphene exhibit a higher recovery effect from ultraviolet irradiation. [Third Embodiment] Next, a third embodiment of the present invention will be described. Figures 10 to 13 show the third embodiment. 〔composition〕 Figure 10 is a schematic diagram showing the configuration of the sensor 3B according to the third embodiment.

[0059] The third embodiment differs from the first and second embodiments in that it includes a sensor 3B having a pyroelectric layer 120 instead of sensor 3, and monitors the current Id flowing between contact electrodes 115 and 116, stopping ultraviolet irradiation when the value reaches a predetermined reference value. Hereinafter, parts similar to the first and second embodiments will be omitted as appropriate, and the differing parts will be described in detail.

[0060] The infrared measurement system according to the third embodiment, although not shown in the figures, comprises a measurement system equipped with a sensor 3B having a graphene layer and a dark box for calibration, and the sensor 3B detects infrared radiation. In other words, the measurement system according to the third embodiment is configured as an infrared bolometer. The measurement system 1 according to the third embodiment is the same as the measurement system 1 of the first embodiment, but with the housing 2 and UV light source 5 removed, and sensor 3B replaced with sensor 3.

[0061] As shown in Figure 10, sensor 3B comprises a gate electrode layer 110, an insulating layer 112, a graphene layer 114, contact electrodes 115 and 116, and a pyroelectric layer 120. The insulating layer 112 is provided on the main surface of the pyroelectric layer 120. The insulating layer 112 has a surface on the +Z direction side and a back surface on the -Z direction side, and is provided on the pyroelectric layer 120 with its back surface in contact with it, while the graphene layer 114 is provided on the surface of the insulating layer 112. The pyroelectric layer 120 and the graphene layer 114 are not in contact with each other because they are provided via the insulating layer 112. The gate electrode layer 110 is provided on the side of the pyroelectric layer 120 opposite to the side of the insulating layer 112. The gate electrode layer 110 is made of, for example, Si.

[0062] The contact electrodes 115 and 116 are provided on the surface of the insulating layer 112, sandwiching the graphene layer 114. Each of the contact electrodes 115 and 116 is in contact with the X-direction end of the graphene layer 114 and is electrically connected. The graphene layer 114 corresponds to a channel through which the current Id flows. The gate terminal Tg is electrically connected to the gate electrode layer 110, and the contact terminals Tc are electrically connected to the contact electrodes 115 and 116, respectively. The insulating layer 112 and the graphene layer 114 have the same configuration as the insulating layer 12 and the graphene layer 14 in the first embodiment. The contact electrodes 115 and 116 have the same configuration as the source electrode 15 and the drain electrode 16 in the first embodiment.

[0063] The pyroelectric layer 120 is, for example, a layer of LiNbO3, which is both a type of ferroelectric and a type of pyroelectric. LiNbO3 absorbs infrared radiation in the wavelength range of 6 μm to 20 μm and generates heat, causing a change in polarization due to the pyroelectric effect. When the sensor 3B detects infrared radiation or light of other wavelengths, a ferroelectric material other than LiNbO3 is used as the material for the pyroelectric layer 120. Examples of ferroelectric materials that can be used for the pyroelectric layer 120 include BaTiO3 (barium titanate), LiTaO3 (lithium tantalate), SrTiO3 (strontium titanate), PZT (lead zirconate titanate), SBT (strontium bismuth tantalate), BFO (bismuth ferrite), ZnO (zinc oxide), and HfO2 (hafnium oxide).

[0064] In the graphene layer 114, a current Id flows between the contact electrodes 115 and 116. The pyroelectric effect generates a voltage when the pyroelectric layer 120 receives infrared light, causing a change in the current Id flowing between the contact electrodes 115 and 116. In other words, the current Id flowing through the graphene layer 114 changes due to the polarization change in the pyroelectric layer 120 due to light reception. Thus, the graphene layer 114, the pair of contact electrodes 115 and 116, and the pyroelectric layer 120 constitute a FET, and the polarization change in the pyroelectric layer 120 acts as a change in the gate voltage Vg.

[0065] The dark box, although not shown in the diagram, is made of materials that block light, including infrared light, from the outside. Inside the dark box, a UV light source 5 is provided on the ceiling, and by installing the measurement system 1 in the installation area provided inside the dark box, ultraviolet light can be irradiated onto the graphene layer 114 of the sensor 3B.

[0066] The circuit board 4 according to the third embodiment is equipped with a detection circuit 145 in place of the detection circuit 45 in the circuit board 4 of the first embodiment. The detection circuit 145 is electrically connected to each pair of contact terminals Tc. The detection circuit 145 receives the current Id flowing through the graphene layer 114 as an input signal. The detection circuit 145 performs signal processing such as amplification on this input signal and outputs it to the control circuit 43. The control circuit 43 receives the output from the detection circuit 145 and performs infrared detection based on the received current Id. Because the graphene layer 114 has high charge mobility, it has high sensitivity in infrared detection, i.e., high temperature resolution.

[0067] The control circuit according to the third embodiment, although not shown in the figures, measures the difference ΔId between the current Id detected by the detection circuit 145 and a reference current Idr. Based on this measurement result, it detects infrared radiation. Here, the reference current Idr corresponds to the current Id when CNP=0V, and its value is a known value at the time of design.

[0068] In addition, the control circuit 43 determines whether calibration is necessary based on the current Id detected by the detection circuit 145 and the reference current Idr. Furthermore, if calibration is necessary, it controls the UV light source 5 to irradiate the sensor 3B installed in the dark box with ultraviolet light and performs a calibration process to bring the measured value of current Id closer to the reference value, which is the value of the reference current Idr. In this calibration process, the current Id is monitored while ultraviolet light is irradiated, and ultraviolet light is irradiated until the measured value of current Id reaches the reference value. [Regarding the characteristics of the reference current Idr]

[0069] Figure 11 shows the changes in gate voltage Vg and current Id due to the optical gate effect in the third embodiment. Figure 11(a) shows the changes when CNP = 0V, and Figure 11(b) shows the changes when CNP ≠ 0V. In Figures 11(a) and (b), the horizontal axis is the gate voltage Vg and the vertical axis is the current Id.

[0070] As shown in Figure 11(a), the current Id that is minimum when the gate voltage Vg is 0V is the reference current Idr when CNP = 0V. At this time, the change in current Id from the reference current Idr when the gate voltage Vg changes by ΔVg due to the photo-gate effect is ΔId.

[0071] On the other hand, as shown in Figure 11(b), the current Id when CNP≠0V does not reach its minimum value when the gate voltage Vg=0V, as shown by the solid curve in Figure 11(b). Therefore, if the minimum value when CNP≠0V is taken as the reference current Idr', the change in current Id from the reference current Idr' when the gate voltage Vg changes by ΔVg due to the photo-gate effect is ΔId', and ΔId≠ΔId'. For this reason, when CNP≠0V, ultraviolet light is irradiated onto the graphene layer 114 to calibrate the reference current Idr so that it returns from the position shown by the solid curve in Figure 11(b) to the position shown by the dashed curve. [Calibration process and infrared measurement process] Next, the calibration process and infrared measurement process according to the third embodiment will be described. Figure 12 is a flowchart showing the calibration process and infrared measurement process according to the third embodiment.

[0072] In step S200, the measurement system 1 is placed in the dark box, and the process proceeds to step S202. The procedure for placing the measurement system 1 into the dark box is controlled by the control circuit 43 if there is a mechanism, such as an electric motor, to mechanically place and remove the measurement system 1 from the dark box. If such a mechanism is not available, the procedure is performed manually. In step S202, the current current Id is obtained via the detection circuit 145, and the process proceeds to step S204.

[0073] In step S204, the measured value of current Id obtained in step S202 is compared with the reference value, which is the reference current Idr. If the measured value is greater than the reference value, it is determined that calibration is required (Yes), and the process proceeds to step S206. On the other hand, if the measured value equals the reference value, it is determined that calibration is not required (No), and the process proceeds to step S208. This determination process can be performed by the control circuit 43. If the process proceeds to step S206, the control circuit 43 controls the calibration process to calibrate the reference current Idr, and then the process proceeds to step S208.

[0074] If the measurement system 1 is placed in the dark box manually, a calibration start command is sent to the control circuit 43 of the measurement system 1 via an input device (not shown). On the other hand, if the measurement system 1 is placed in the dark box automatically by the above mechanism, the control circuit 43 confirms that calibration is required and automatically performs the calibration process. In step S208, the measurement system 1 is removed from the dark box, and the process proceeds to step S210. The procedure for removing the measurement system 1 from the dark box is controlled by the control circuit 43 if the above mechanism is present, otherwise it is done manually.

[0075] In step S210, the infrared measurement process is started, and the process proceeds to step S212. Specifically, the detection circuit 145 detects the current Id, and the control circuit 43 measures the difference ΔId between the detected current Id and the reference current Idr. Then, infrared radiation is detected based on the measured ΔId. That is, since the current Id changes due to the optical gate effect caused by the incidence of infrared radiation, infrared radiation can be detected by the difference ΔId between this changed current Id and the reference current Idr. In step S212, it is determined whether the measurement has finished or not. If it is determined that the measurement has finished (Yes), the series of processes is terminated. If it is determined that the measurement has not finished (No), the process proceeds to step S200. [Calibration process] Next, the calibration process according to the third embodiment will be described. Figure 13 is a flowchart showing the calibration process according to the third embodiment. The control circuit 43 performs the calibration process shown in the flowchart of Figure 13. Once the calibration process is performed in step S206, the process proceeds to step S250, as shown in Figure 13.

[0076] In step S250, a control signal is sent to the UV light source 5 to turn it on, and the irradiation of the sensor 3B with ultraviolet light begins. Then, the process proceeds to step S252. As a result, the entire surface area of ​​the graphene layer 114 of the sensor 3B is irradiated with ultraviolet light. In step S252, the current current Id is obtained via the detection circuit 145, and the process proceeds to step S254.

[0077] In step S254, it is determined whether the value of current Id obtained in step S252 has reached a reference value. If it is determined that it has reached the reference value (Yes), the process proceeds to step S256; otherwise, ultraviolet irradiation continues and the process proceeds to step S252. Here, the determination of whether or not the reference value has been reached is not limited to determining whether or not the current value of Id has reached the reference value, but may also be determined to determine whether or not the value has fallen within a predetermined range relative to the reference value. If the process proceeds to step S256, a control signal is sent to the UV light source 5 to instruct it to turn off, thereby stopping the irradiation of ultraviolet light onto the sensor 3B. After that, the series of processes is terminated and the process returns to its original state. [Effects of the third embodiment]

[0078] As described above, the measurement system 1 according to the third embodiment includes a sensor 3B comprising an insulating layer 112, a graphene layer 114 provided on the surface of the insulating layer 112, contact electrodes 115 and 116 electrically connected to each other by the graphene layer 114, a pyroelectric layer 120 provided on the back side of the insulating layer 112, and a gate electrode layer 110 provided on the back side of the pyroelectric layer 120; a UV light source 5 that irradiates the graphene layer 114 of the sensor 3B with ultraviolet light; a detection circuit 145 that measures the current Id flowing between the contact electrodes 115 and 116; and a control circuit 43 that starts irradiating the graphene layer 114 with ultraviolet light from the UV light source 5 based on the measured value of current Id, and stops irradiating the graphene layer 114 with ultraviolet light from the UV light source 5 based on the measured value of current Id. Furthermore, the control circuit 43 is configured to stop irradiating ultraviolet light when the measured value of current Id decreases to the value of a reference current Idr (reference value).

[0079] With this configuration, ultraviolet light is irradiated until the measured value of the current Id flowing between the contact electrodes 115 and 116 reaches a reference value or approximate reference value when the CNP becomes 0V, and the ultraviolet light irradiation is stopped when the measured value reaches the reference value or approximate reference value. This improves the reproducibility of the measurement because each measurement can be performed based on the reference value. In addition, since ultraviolet light is irradiated while monitoring the measured value of the current Id, it is possible to prevent insufficient or excessive irradiation of the graphene layer 114 with ultraviolet light. Furthermore, since the calibration process can be performed without contact, it is also effective even when the measurement system 1 is vacuum packaged. [Correspondence in the third embodiment] In the third embodiment, the insulating layer 112 corresponds to an insulator, the contact electrodes 115 and 116 correspond to the first electrode and the second electrode, the UV light source 5 corresponds to a light source, the detection circuit 145 corresponds to a measurement unit, and the control circuit 43 corresponds to a control unit. [Variation]

[0080] In the third embodiment described above, the gate electrode layer 110 is provided on the side of the pyroelectric layer 120 opposite to the insulating layer 112 in the sensor 3B. However, the configuration is not limited to this, and a configuration in which the gate electrode layer 110 is removed is also possible. Alternatively, a configuration in which both the gate electrode layer 110 and the pyroelectric layer 120 are removed is also possible. [Explanation of Symbols]

[0081] 1...Measurement system, 2...Housing, 3,3A,3B...Sensors, 4...Circuit board, 5...UV light source, 6...Chamber, 10...Semiconductor substrate, 12,112...Insulating layer, 14,114...Graphene layer, 15...Source electrode, 16...Drain electrode, 17...Nanoparticles, 18...Channel, 21...Intake port, 22...Exhaust port, 23,24...Solenoid valve, 43...Control circuit, 45,145...Detection circuit, 47...Drive circuit, 110...Gate electrode layer, 120...Pyroelectric layer

Claims

1. A sensor comprising: an insulator having a front surface and a back surface; a graphene layer provided on the front surface of the insulator; a first electrode and a second electrode electrically connected to each other by the graphene layer; and a third electrode provided on the back surface of the insulator. A light source that irradiates the graphene layer with ultraviolet light, A measuring unit for measuring the current flowing from one of the first electrode and the second electrode to the other, A control unit that starts irradiating ultraviolet light from the light source based on the measured value of the current, and stops irradiating ultraviolet light from the light source based on the measured value of the current, A measurement system equipped with the following features.

2. The measurement system according to claim 1, wherein the control unit stops irradiating the third electrode with ultraviolet light when a voltage is applied to the third electrode by irradiation with ultraviolet light from the light source, and the voltage at the charge neutral point where the measured value of the current is minimized when the voltage is changed approaches zero.

3. The measurement system according to claim 2, wherein the control unit stops the irradiation of ultraviolet light when the voltage at the charge neutral point approaches zero within a predetermined range.

4. A sensor comprising an insulator, a graphene layer provided on the surface of the insulator, and a first electrode and a second electrode electrically connected to each other by the graphene layer, A light source that irradiates the graphene layer of the sensor with ultraviolet light, A measuring unit for measuring the current flowing from one of the first electrode and the second electrode to the other, A control unit that starts irradiating ultraviolet light from the light source based on the measured value of the current, and stops irradiating ultraviolet light from the light source based on the measured value of the current, A measurement system equipped with the following features.

5. The measurement system according to claim 4, wherein the control unit stops the irradiation of ultraviolet light when the measured value of the current decreases to a predetermined reference value.

6. The measurement system according to claim 1 or 4, wherein the graphene layer has nanoparticles provided on its surface.

7. The measurement system according to claim 1 or 4, wherein the light source irradiates ultraviolet light with a wavelength of 265 nm or more and 400 nm or less.

8. A sensor comprising an insulator having a front surface and a back surface, a graphene layer provided on the front surface of the insulator, a first electrode and a second electrode electrically connected to each other by the graphene layer, and a third electrode provided on the back surface of the insulator, the steps of measuring the current flowing from one of the first electrode and the second electrode to the other, The steps include: starting irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current, and stopping irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current; A recovery method for a sensor having [a certain characteristic].

9. A sensor comprising an insulator, a graphene layer provided on the surface of the insulator, and a first electrode and a second electrode electrically connected to each other by the graphene layer, the steps of measuring the current flowing from one of the first electrode and the second electrode to the other; The steps include: starting irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current, and stopping irradiation of the graphene layer with ultraviolet light from the light source based on the measured value of the current; A recovery method for a sensor having [a certain characteristic].

10. Each step of the recovery method according to claim 8 or 9, The steps include: measuring the current after the ultraviolet irradiation has been stopped following the execution of the recovery method; A measurement method having

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