Sensor and method for controlling sensor

Abstract

To provide a technique capable of continuously using a sensor for detecting fine particles.SOLUTION: A sensor for detecting fine particles includes a substrate having insulating surfaces, at least a pair of electrodes provided on the surfaces and separated from each other by 200nm or less, a detection unit for detecting a resistance value between the electrodes, and a control unit. The control unit determines that the particles are present when the resistance value decreases to a predetermined first threshold value or less in a state where the drive voltage is applied between the electrodes, applies a refresh voltage which is a voltage higher than the drive voltage between the electrodes when it is determined that the particles are present, and determines that the space between the electrodes is refreshed when the resistance value increases to a predetermined second threshold value or more in a state where the refresh voltage is applied between the electrodes.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to sensors. [Background technology]

[0002] Sensors for detecting particulate matter have been known for some time. To repeatedly use such sensors, it is necessary to remove the particulate matter trapped in the sensor. For example, Patent Document 1 proposes a refresh process in which a heater is used to raise the temperature of a charged particulate matter collecting electrode to a predetermined particulate matter incineration temperature, thereby incinerating the particulate matter accumulated on the charged particulate matter collecting electrode. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 039072 Summary of the Invention [Problem to be solved by the invention]

[0004] The technology described in Patent Document 1 requires that the electrodes be heated to high temperatures to burn off the particulates, but this requires a long time to change the temperature, which makes it difficult to use the sensor continuously. Therefore, there is a need for a technology that allows the sensor to be used continuously to detect particulates. [Means for solving the problem]

[0005] The present disclosure can be realized in the following forms.

[0006] (1) According to one aspect of the present disclosure, a sensor is provided for detecting particles. The sensor includes a substrate having an insulating surface, at least one pair of electrodes provided on the surface, the electrodes being spaced 200 nm or less apart, a detection unit for detecting the resistance between the electrodes, and a control unit. The control unit determines the presence of particles when a drive voltage is applied between the electrodes and the resistance drops below a predetermined first threshold. If the control unit determines the presence of particles, the control unit applies a refresh voltage between the electrodes that is higher than the drive voltage. If the control unit determines the presence of particles and the resistance rises above a predetermined second threshold while the control unit is applying the refresh voltage between the electrodes, the control unit determines the presence of particles and the resistance rises above a predetermined second threshold while the control unit is applying the refresh voltage between the electrodes. According to this aspect of the sensor, if the presence of particles is determined, the control unit applies a refresh voltage higher than the drive voltage between the electrodes that are spaced 200 nm or less apart, thereby removing the particles by the electric field generated between the electrodes. As a result, the sensor can be used continuously.

[0007] (2) In the sensor described in (1) above, the control unit may gradually increase the refresh voltage. According to this type of sensor, the refresh voltage is applied between the electrodes while being gradually increased, thereby preventing an excessively large voltage from being applied between the electrodes.

[0008] (3) In the sensor described in (1) above, the refresh voltage may include a first refresh voltage and a second refresh voltage higher than the first refresh voltage, and the control unit may apply the first refresh voltage between the electrodes when it is determined that particles are present, determine whether the resistance value has increased to or above the second threshold while the first refresh voltage is being applied between the electrodes, and apply the second refresh voltage between the electrodes when it is determined that the resistance value has not increased. With this type of sensor, the refresh voltage is increased in stages, which prevents the circuitry of the control unit from becoming complicated.

[0009] (4) The sensor according to any one of (1) to (3) above may further include a heating element for heating the electrodes, and the heating element may heat the electrodes while the driving voltage is applied. According to this type of sensor, the electrodes are heated by the heating element, so that it is possible to prevent particles, which act as contaminants and burn at a lower temperature than the particles to be detected, from adhering between the electrodes. As a result, it is possible to improve the selectivity of the sensor.

[0010] (5) According to another aspect of the present disclosure, there is provided a method for controlling a sensor. The method for controlling a sensor for detecting particles includes a substrate having an insulating surface and at least one pair of electrodes disposed on the surface, the electrodes being spaced apart by 200 nm or less. The method includes the steps of: applying a drive voltage between the electrodes; determining the presence of particles when a resistance value between the electrodes drops below a predetermined first threshold while the drive voltage is applied between the electrodes; applying a refresh voltage between the electrodes that is higher than the drive voltage after the presence of particles is determined; and determining that the electrodes have been refreshed when the resistance value rises above a predetermined second threshold while the refresh voltage is applied between the electrodes. According to this aspect of the control method, when the presence of particles is determined, a refresh voltage higher than the drive voltage is applied between the electrodes spaced apart by 200 nm or less, thereby removing the particles by the electric field generated between the electrodes. As a result, the sensor can be used continuously.

[0011] The present disclosure can be realized in various forms, for example, a sensor control device, a sensor manufacturing method, a sensor refreshing method, and the like. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 2 is an explanatory diagram showing a schematic configuration of a sensor. [Figure 2] FIG. 2 is an enlarged view showing the configuration of the upper part of the sensor. [Figure 3] FIG. 2 is a top view schematically illustrating the general configuration of an electrode portion. [Figure 4] 1A to 1C are explanatory diagrams showing an example of a method for manufacturing a sensor. [Figure 5] 1A to 1C are explanatory diagrams showing an example of a method for manufacturing a sensor. [Figure 6] 10 is a flowchart illustrating an example of a method for controlling a sensor. [Figure 7] 10 is a flowchart illustrating another example of a method for controlling a sensor. DETAILED DESCRIPTION OF THE INVENTION

[0013] A. Equipment configuration FIG. 1 is an explanatory diagram showing a schematic configuration of a sensor 100 according to an embodiment of the present disclosure. FIG. 1 corresponds to a cross section taken along line AA in FIG. 3 (described later). FIG. 2 is an enlarged view showing the configuration of the upper portion of the sensor 100. For convenience of explanation, FIG. 1 shows the configuration of the main parts of the sensor 100 using a schematic cross-sectional view and a block diagram. In the following description, for convenience of explanation, the up-down direction on the paper in FIGS. 1 and 2 is defined as the up-down direction. However, the up-down direction when the sensor 100 is in use may not coincide with the up-down direction on the paper. The sensor 100 detects fine particles. Examples of fine particles include, but are not limited to, viruses, bacteria, organic matter, soot, etc. Examples of organic matter include, but are not limited to, organic fluorine-containing compounds (PFAS). The sensor 100 includes a substrate 10, an insulating layer 20, a heating element 30, an electrode unit 40, a detection unit 50, and a control unit 60.

[0014] The substrate 10 of this embodiment is formed of a silicon wafer. The material of the substrate 10 is not limited to silicon, and may be, for example, a ceramic material such as sapphire, zirconia, or alumina. In this embodiment, an insulating layer 20 is laminated on the upper surface of the substrate 10. Therefore, the surface S1 of the substrate 10 has insulating properties. If the substrate 10 is formed of an insulating material such as the ceramic material described above, the insulating layer 20 may be omitted because the surface S1 is insulating.

[0015] The planar shape of the substrate 10 is not particularly limited and may be any shape, such as rectangular or circular. The size of the substrate 10 is not particularly limited and, for example, if the planar shape is rectangular, each side may be approximately 0.1 mm to 10 mm. If the planar shape is circular, the substrate 10 may have an area approximately equal to that of the rectangular shape. The thickness of the substrate 10 is also not particularly limited and may be, for example, approximately 400 μm to 500 μm. The substrate 10 of this embodiment has a space 11 formed by cutting out a portion of the substrate 10. Therefore, the substrate 10 of this embodiment has a diaphragm-type structure. The space 11 may be formed, for example, by a through-hole penetrating the substrate 10 in the vertical direction or a recess opening to the lower surface of the substrate 10. The shape of the space 11 is not particularly limited and, for example, the shape of a cross section perpendicular to the vertical direction may be rectangular, circular, or the like. The size of the space 11 is not particularly limited, but it is preferable that the cross-sectional area of ​​the cross section perpendicular to the vertical direction is larger on the lower surface side than on the upper surface side. More specifically, for example, the area of ​​the lower surface is 0.01 mm 2 ~4mm 2 Preferably, it is 0.25 mm 2 ~2mm 2 It is more preferable that the space 11 be formed as follows. The space 11 may be omitted.

[0016] The insulating layer 20 is laminated on the upper surface of the substrate 10. The insulating layer 20 may be formed over the entire upper surface of the substrate 10, or may be formed on only a part of the upper surface of the substrate 10. In this embodiment, the insulating layer 20 covers the opening of the space 11 formed in the substrate 10 and is supported by the substrate 10. The material for forming the insulating layer 20 is not particularly limited as long as it has insulating properties, but examples thereof include silicon oxide (SiO2), silicon nitride (Si3N4), SiO x N y (x and y are arbitrary values) and other silicon compounds. Insulating layer 20 of this embodiment has a two-layer structure, including a first insulating layer 21 formed of SiO2 and a second insulating layer 22 formed of Si3N4. Insulating layer 20 may also have a single-layer structure. In this embodiment, an insulating layer 25 similar to insulating layer 20 laminated on the upper surface of substrate 10 is also laminated on the lower surface of substrate 10.

[0017] The heating element 30 is provided to improve the selectivity of the sensor 100, as described below. The heating element 30 heats the electrode portion 40. In this embodiment, the heating element 30 is embedded in the insulating layer 20. More specifically, the heating element 30 is provided on the upper surface of the lower insulating layer 23 within the second insulating layer 22 and is covered by the upper insulating layer 24. From the viewpoint of thermal efficiency, the heating element 30 is preferably embedded in a region of the insulating layer 20 corresponding to the space 11, i.e., a region overlapping the space 11 when viewed from above. The shape of the heating element 30 is not particularly limited, but may be, for example, a spiral shape such as a substantially rectangular shape when viewed from above, a wave shape, a serpentine shape, or the like. The material for forming the heating element 30 is not particularly limited, but examples thereof include platinum, a platinum alloy, a nickel alloy, a chromium alloy, and a nickel-chromium alloy. The heating element 30 is electrically connected to a contact pad (not shown) and receives power from an external circuit via the contact pad. The heating element 30 generates heat when a voltage is applied.

[0018] FIG. 3 is a top view schematically illustrating the overall configuration of the electrode unit 40. In this embodiment, the electrode unit 40 is provided on the upper surface of the insulating layer 20. The electrode unit 40 has at least one pair of electrodes 43 (hereinafter simply referred to as "electrodes 43"), each consisting of a first electrode 41 and a second electrode 42. As shown in FIG. 3, the electrode unit 40 of this embodiment has a plurality of electrodes 43. The first electrode 41 and the second electrode 42 face each other in a first direction D1 with a gap G between them. The first direction D1 is a direction parallel to the upper surface of the substrate 10. The first direction D1 is a direction perpendicular to the arrangement direction of the plurality of first electrodes 41 and a direction perpendicular to the arrangement direction of the plurality of second electrodes 42. In this embodiment, the first electrode 41 and the second electrode 42 are each formed to extend in the first direction D1.

[0019] The dimension of the gap G between the first electrode 41 and the second electrode 42, i.e., the distance between the electrodes 43, is 200 nm or less. From the viewpoint of refresh efficiency, which will be described later, the distance between the electrodes 43 is preferably 20 nm or more and 200 nm or less, and more preferably 50 nm or more and 100 nm or less. The distance between the electrodes 43 is preferably set according to the size of the particles to be detected.

[0020] In the cross sections shown in FIGS. 1 and 2, only the first electrode 41 is shown as the electrode unit 40. The first electrode 41 and the second electrode 42 are each formed of one or more types of metal. Examples of metals include, but are not limited to, gold (Au) and platinum (Pt). In this embodiment, the first electrode 41 and the second electrode 42 each have a two-layer structure as shown in FIG. 2, including, for example, a lower-layer electrode 44 formed of titanium (Ti) and an upper-layer electrode 45 formed of platinum (Pt). The first electrode 41 and the second electrode 42 may also have a single-layer structure. The first electrode 41 and the second electrode 42 are each electrically connected to contact pads (not shown), and power is supplied from an external circuit via the contact pads.

[0021] The detection unit 50 is provided to detect the resistance value between the electrodes 43. There is no particular limitation on the detection unit 50, but an ammeter is an example. The resistance value between the electrodes 43 will be described in detail later.

[0022] The control unit 60 controls the overall operation of the sensor 100. More specifically, the control unit 60 drives the sensor 100 to detect particles and removes particles adhering between the electrodes 43 using an electric field. In the following description, the removal of particles adhering between the electrodes 43 is also referred to as "refreshing." The control unit 60 is realized by, for example, a control device including a microcomputer. The control unit 60 has a voltage application unit 61, a resistance value acquisition unit 62, and a determination unit 63.

[0023] The voltage application unit 61 applies a voltage between the electrodes 43. More specifically, the voltage application unit 61 applies a drive voltage or a refresh voltage between the electrodes 43. The drive voltage is a voltage that is applied when the sensor 100 is driven. The refresh voltage is a voltage that is higher than the drive voltage and is a voltage that is applied to refresh the gap between the electrodes 43. The drive voltage and the refresh voltage are preferably set according to the size of the particles to be detected. A detailed description of the drive voltage and the refresh voltage will be given later. The voltage applied by the voltage application unit 61 may be a DC voltage or an AC voltage. In addition to applying a voltage between the electrodes 43, the voltage application unit 61 of this embodiment also applies a voltage to the heating element 30.

[0024] The resistance value acquiring unit 62 acquires the resistance value between the electrodes 43 based on the detection result by the detecting unit 50. For example, if the detecting unit 50 is configured as an ammeter, the resistance value acquiring unit 62 can calculate the resistance value between the electrodes 43 from the voltage applied between the electrodes 43 by the voltage applying unit 61 and the current value measured by the detecting unit 50.

[0025] The determination unit 63 determines whether particles are present between the electrodes 43 and whether the space between the electrodes 43 has been refreshed, based on the resistance value between the electrodes 43. These determinations will be described in detail later.

[0026] B. Manufacturing method 4 and 5 are explanatory diagrams showing an example of a method for manufacturing the sensor 100. FIG. 5 shows a step performed after the step shown in FIG. 4. FIGS. 4 and 5 show only the configuration on the upper surface side of the substrate 10, and the description of the formation of the insulating layer 25 is omitted. Also, FIG. 5 omits the illustration of the configuration below the heating element 30. The manufacturing method described below includes a step of forming an electrode portion 40 on the substrate 10 by a lift-off method.

[0027] First, an insulating layer 20 and a heating element 30 are formed on a cleaned silicon wafer substrate 10. More specifically, the cleaned substrate 10 is placed in a heat treatment furnace, and a first insulating layer 21 of the insulating layer 20, which is a silicon oxide film, is formed on the entire surface of the substrate 10 by thermal oxidation treatment. Next, as shown in Fig. 4(A), a lower insulating layer 23, which is made of a silicon nitride film and which will become part of the second insulating layer 22, is formed on the first insulating layer 21 by plasma CVD using, for example, SiH4 and NH3 as source gases.

[0028] Thereafter, as shown in FIG. 4(B), the heating element 30 is formed on the upper surface of the lower insulating layer 23 by, for example, sputtering. The heating element 30 is composed of, for example, a Ti layer and a Pt layer thereon. Next, resist is patterned by photolithography, and then the pattern of the heating element 30 is formed by etching. The method for forming the heating element 30 is not particularly limited, and for example, the components that will become the heating element 30 are deposited on the upper surface of the lower insulating layer 23, and then unnecessary portions are removed by various etching methods. The etching method is not particularly limited, and for example, a method similar to the method for forming the space portion 11 described below can be used.

[0029] 4(C), an upper insulating layer 24 is formed by forming, for example, a silicon nitride film on the upper surfaces of the lower insulating layer 23 and the heating element 30. In this way, the insulating layer 20 is formed with the heating element 30 embedded therein. The insulating layer 20 may be formed by depositing components on the upper surface of the substrate 10, or a pre-formed insulating layer 20 may be attached to the upper surface of the substrate 10.

[0030] 5(A), a photoresist composition for electron beam exposure is applied onto the insulating layer 20 by spin coating and dried to form a resist film 80. The resist film 80 is formed to a thickness of, for example, 20 nm to 40 nm. The mask pattern is created by exposing the resist film 80 by electron beam lithography and developing it. The mask pattern is formed so that the distance between the electrodes 43 is 200 nm or less, for example, 50 nm. The mask pattern is formed so that the width of the first electrode 41 and the second electrode 42 is each, for example, 15 nm.

[0031] 5(B), a metal film 90 is formed so as to cover substantially the entire upper surfaces of the insulating layer 20 and the resist film 80. The metal film 90 is formed using gold (Au) or platinum (Pt). The metal film 90 is preferably formed to a thickness of 5 nm to 20 nm, for example, 15 nm. Such a metal film 90 is formed, for example, by electron beam evaporation. The mask pattern is peeled off and the metal film 90 that overlaps that portion is simultaneously removed.

[0032] 5(C), an electrode section 40 is formed, including a plurality of pairs of electrodes 43 formed by the metal film 90. The formation of the electrode section 40 is not limited to the above-described electron beam lithography technique, and a nanoimprint lithography technique in which a pattern is transferred to a resist by stamping a mold (metal mold) that serves as an original may also be used. After the electrodes 43 are formed, an annealing treatment (e.g., heat treatment at 360°C) may be performed in a vacuum.

[0033] When providing the space 11 in the substrate 10, it can be formed, for example, by removing a part of the substrate 10 by etching. The etching method is not particularly limited, and wet etching, dry etching, or the like may be used. The etching method may be anisotropic etching or isotropic etching. When forming a through-hole as the space 11 in the substrate 10, it is preferable to use wet etching using an anisotropic etching solution.

[0034] C. Sensor Operation and Control Method Fig. 6 is a flowchart showing an example of a control method for sensor 100. Fig. 6 shows a drive process and a subsequent refresh process for sensor 100. In Fig. 6, steps S100 to S140 correspond to the drive process, and steps S150 to S190 correspond to the refresh process.

[0035] The voltage application unit 61 applies a drive voltage between the electrodes 43 (step S100). The drive voltage is not particularly limited, but is preferably set to between 1 mV and 5 V, and more preferably between 10 mV and 1 V. The drive voltage may be set to, for example, 100 mV.

[0036] In this embodiment, when the sensor 100 is driven, a voltage is also applied to the heating element 30. The heating element 30 heats the electrode unit 40 (electrodes 43) while a drive voltage is applied between the electrodes 43. This makes it possible to change the ease with which particles adhere to the gap between the electrodes 43, and particles that burn at a set heating temperature will no longer adhere to the gap between the electrodes 43. This makes it possible to prevent particles acting as impurities that burn at a lower temperature than the particles to be detected from adhering to the gap between the electrodes 43. Therefore, the selectivity of the sensor 100 can be improved by heating the surface S1 of the substrate 10 by the heating element 30.

[0037] The resistance value acquiring unit 62 acquires the resistance value between the electrodes 43 (step S110). When a drive voltage is applied between the electrodes 43, if no particles to be detected are present between the electrodes 43, the electrodes 43 are electrically insulated and no current flows between them. In an electrically insulated state, the resistance value between the electrodes 43 acquired by the resistance value acquiring unit 62 is very high, for example, several tens of MΩ or more. In the following description, the resistance value between the electrodes 43 in an electrically insulated state is also referred to as an "initial value." The resistance value between the electrodes 43 is calculated, for example, from the voltage applied by the voltage applying unit 61 and the current value detected by the detecting unit 50.

[0038] The determination unit 63 determines whether the resistance value between the electrodes 43 has dropped below a predetermined first threshold value while a drive voltage is applied between the electrodes 43 (step S120). When the electrodes 43 are electrically insulated from each other, if particles adhere between the electrodes 43, the electrodes 43 become conductive. As a result, the resistance value between the electrodes 43 acquired by the resistance value acquisition unit 62 drops significantly, for example, to about 1 KΩ. The first threshold value is not particularly limited and may be set as an absolute value or as a relative value compared with an initial value.

[0039] If it is determined that the resistance value between the electrodes 43 has not decreased (step S120: NO), the determination unit 63 determines that no particles are present between the electrodes 43 (step S130), and the process returns to step S110. On the other hand, if it is determined in step S120 that the resistance value between the electrodes 43 has decreased (step S120: YES), the determination unit 63 determines that particles are present between the electrodes 43 (step S140), and the process proceeds to step S150.

[0040] After step S140, the voltage application unit 61 applies a refresh voltage between the electrodes 43 while gradually increasing it (step S150). Step S150 is a step in which, after it is determined that particles exist between the electrodes 43, a refresh voltage higher than the drive voltage is applied between the electrodes 43. The refresh voltage is not particularly limited as long as it is large enough to remove the particles, but is preferably set to between 0.501 V and 10 V, and more preferably between 1 V and 5 V. The refresh voltage is preferably higher than the drive voltage by 0.5 V or more, more preferably by 1 V or more, and even more preferably by 2 V or more. The refresh voltage is even more preferably higher than the drive voltage by at least one digit. The rate of increase of the refresh voltage in step S150 is preferably between 10 mV / sec and 10 V / sec, and more preferably between 100 mV / sec and 1 V / sec. By gradually increasing the refresh voltage, it is possible to prevent an excessively large voltage from being applied between the electrodes 43, and therefore it is possible to reduce wear on the sensor 100.

[0041] As a result of the voltage applied between the electrodes 43 being switched from the drive voltage to the refresh voltage, the voltage applied between the electrodes 43 increases. Here, even if the voltage applied between the electrodes 43 increases, up to a certain voltage, the resistance value between the electrodes 43 does not change because the conductivity is maintained due to the presence of the particles between the electrodes 43. However, as the voltage applied between the electrodes 43 increases further, a strong electric field is generated between the electrodes 43 due to the short distance between the electrodes 43 of 200 nm or less, and the particles are removed. As a result of the removal of the particles, the conductivity between the electrodes 43 is no longer maintained, and the resistance value between the electrodes 43 increases. Then, when the particles are completely removed, the resistance value between the electrodes 43 returns to its initial value (for example, several tens of MΩ or more).

[0042] The resistance value acquisition unit 62 acquires the resistance value between the electrodes 43 (step S160). The determination unit 63 determines whether the resistance value between the electrodes 43 has increased to or above a predetermined second threshold value while a refresh voltage is applied between the electrodes 43 (step S170). The second threshold value is a value higher than the first threshold value. The second threshold value is not particularly limited and may be set as an absolute value or as a relative value compared with the resistance value between the electrodes 43 in a conductive state. If it is determined that the resistance value between the electrodes 43 has not increased (step S170: NO), the determination unit 63 determines that the electrodes 43 have not been refreshed (step S180). After step S180, the process returns to step S160.

[0043] On the other hand, if it is determined in step S170 that the resistance value between the electrodes 43 has increased (step S170: YES), the determination unit 63 determines that the electrodes 43 have been refreshed (step S190). After step S190, the process returns to step S100. Therefore, after it is determined that the electrodes 43 have been refreshed, the voltage applied between the electrodes 43 is switched from the refresh voltage to the drive voltage. By such control, the sensor 100 can continuously detect particles. For example, compared to a sensor that uses a heater to burn off particles, unlike the present application, the sensor 100 can be used continuously because it does not require time to change the temperature. Furthermore, compared to a sensor that uses a heater to burn off particles, unlike the present application, an increase in power consumption can be suppressed.

[0044] Fig. 7 is a flowchart showing another example of the control method for sensor 100. In the control method shown in Fig. 7, the drive process for sensor 100 (steps S100 to S140) is the same as the control method shown in Fig. 6, but the refresh process for sensor 100 (steps S155 to S200) is different from the control method shown in Fig. 6. In the following explanation, detailed explanation of the same steps as those in the control method shown in Fig. 6 will be omitted.

[0045] After step S140, the voltage application unit 61 applies a refresh voltage between the electrodes 43 (step S155). In the control method shown in FIG. 7, the voltage application unit 61 applies a constant value of refresh voltage between the electrodes 43 in step S155. The resistance value acquisition unit 62 acquires the resistance value between the electrodes 43 (step S160). The determination unit 63 determines whether the resistance value between the electrodes 43 has increased while the refresh voltage is being applied between the electrodes 43 (step S170). If it is determined that the resistance value between the electrodes 43 has increased (step S170: YES), the determination unit 63 determines that the electrodes 43 have been refreshed (step S190).

[0046] On the other hand, if it is determined in step S170 that the resistance value between the electrodes 43 has not increased (step S170: NO), the determination unit 63 determines that the electrodes 43 have not been refreshed (step S180), and the process proceeds to step S200. The voltage application unit 61 applies a higher refresh voltage between the electrodes 43 (step S200), and the process returns to step S160. The refresh voltage applied in step S200 is a constant voltage that is higher than the refresh voltage applied in step S155. The refresh voltage applied in step S200 is preferably higher than the refresh voltage applied in step S155 by 10 mV to 100 mV, and more preferably higher by 20 mV to 50 mV.

[0047] Here, if the lower refresh voltage is designated as the "first refresh voltage" and the higher refresh voltage is designated as the "second refresh voltage," the above-described control determines whether or not the resistance value has increased while the first refresh voltage is applied between the electrodes 43, and if it is determined that the resistance value has not increased, the second refresh voltage is applied between the electrodes 43. According to this type of control, the refresh voltage is increased in stages, which prevents the circuitry of the control unit 60 from becoming complicated.

[0048] D. Variations The configuration of the sensor 100 in the above embodiment is merely an example and can be modified in various ways. For example, while the sensor 100 is formed using MEMS, the sensor is not limited to MEMS. For example, the electrode unit 40 may be formed on an alumina substrate. Furthermore, for example, the electrode unit 40 may have a single pair of electrodes 43 instead of multiple pairs of electrodes 43. That is, generally, at least one pair of electrodes 43, with the distance between the electrodes 43 being 200 nm or less, may be provided on the surface S1 of the substrate 10. Furthermore, for example, the sensor may be a stacked type sensor in which a first electrode 41 and a second electrode 42 are stacked with an insulating film interposed therebetween, as long as the distance between the electrodes 43 is 200 nm or less. Furthermore, for example, the heating element 30 may be omitted. Furthermore, for example, the resistance value acquisition unit 62 may constantly acquire the resistance value between the electrodes 43.

[0049] The present invention is not limited to the above-described embodiments and can be realized in various configurations without departing from the spirit of the present invention. For example, the technical features in the embodiments and examples corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a technical feature is not described as essential in this specification, it can be deleted as appropriate. [Explanation of symbols]

[0050] 10...substrate, 11...space portion, 20...insulating layer, 21...first insulating layer, 22...second insulating layer, 23...lower insulating layer, 24...upper insulating layer, 25...insulating layer, 30...heating element, 40...electrode portion, 41...first electrode, 42...second electrode, 43...electrode, 44...lower layer electrode, 45...upper layer electrode, 50...detection portion, 60...control portion, 61...voltage application portion, 62...resistance value acquisition portion, 63...determination portion, 80...resist film, 90...metal film, 100...sensor, D1...first direction, G...gap, S1...surface

Claims

1. A sensor for detecting particulate matter, a substrate having an insulating surface; At least one pair of electrodes provided on the surface, the distance between the electrodes being 200 nm or less; a detection unit for detecting a resistance value between the electrodes; A control unit; Equipped with The control unit determining that particles are present when the resistance value falls below a predetermined first threshold value while a drive voltage is applied between the electrodes; When it is determined that particles are present, a refresh voltage that is higher than the drive voltage is applied between the electrodes; determining that the gap between the electrodes has been refreshed when the resistance value increases to or exceeds a predetermined second threshold value while the refresh voltage is being applied between the electrodes; A sensor characterized by:

2. 2. The sensor of claim 1, The control unit gradually increases the refresh voltage. A sensor characterized by:

3. 2. The sensor of claim 1, the refresh voltage includes a first refresh voltage and a second refresh voltage that is higher than the first refresh voltage; The control unit applying the first refresh voltage between the electrodes when it is determined that particles are present; determining whether the resistance value has increased to or above the second threshold value while the first refresh voltage is applied between the electrodes; applying the second refresh voltage between the electrodes when it is determined that the resistance value has not increased; A sensor characterized by:

4. The sensor according to any one of claims 1 to 3, further comprising: a heating element for heating the electrode; The heating element heats the electrode when the driving voltage is applied. A sensor characterized by:

5. A method for controlling a sensor for detecting particulate matter, comprising: The sensor comprises a substrate having an insulating surface and at least a pair of electrodes provided on the surface, the distance between the electrodes being 200 nm or less; applying a driving voltage between the electrodes; determining that particles are present when a resistance value between the electrodes falls to a predetermined first threshold value or less while the driving voltage is applied between the electrodes; applying a refresh voltage between the electrodes after determining that particles are present, the refresh voltage being higher than the drive voltage; determining that the gap between the electrodes has been refreshed when the resistance value increases to or exceeds a predetermined second threshold value while the refresh voltage is being applied between the electrodes; A method for controlling a sensor, comprising:

Images