Sensor device capable of measuring electric field intensity and method for measuring external electric field

Abstract

Provided is a sensor device having a small size and capable of measuring a small electric field intensity.　A sensor device comprising: a first dielectric layer; a first atomic layer material film that is disposed on the first dielectric layer and that has one or more atomic layers formed of a first material; a channel layer that is disposed on the first atomic layer material film, that has a channel region, and that has one or more atomic layers of graphene; a second atomic layer material film that is disposed on the channel layer and that has one or more atomic layers formed of a second material; and a first electrode and a second electrode that are disposed on the channel layer so as to face each other across the channel region, wherein the second atomic layer material film has a first surface and a second surface, and the first surface is disposed on the channel layer and a portion that faces the channel region in the second surface is exposed to the outside, or a second dielectric layer is disposed on the second surface and a portion, of the second dielectric layer, that is on the surface on the opposite side of the second atomic layer material film and that faces the channel region is exposed to the outside.

Description

Sensor device capable of measuring electric field strength and method for measuring external electric field

[0001] The present invention relates to a sensor device capable of measuring electric field strength and a method for measuring an external electric field.

[0002] Conventionally, a sensor device has been used to measure the electric field strength in the atmosphere, and by measuring the electric field strength in the atmosphere, the occurrence, approach, and passage of thunderclouds can be monitored (see, for example, Patent Document 1).

[0003] Sensor devices are also used to measure the electric field strength in the atmosphere indoors. By measuring the electric field strength, the static electricity generated in the room can be monitored and accidents caused by static electricity can be prevented.

[0004] Sensor devices for measuring electric field strength include mechanical sensor devices and semiconductor sensor devices. Mechanical sensor devices are relatively large and heavy (see, for example, Patent Document 1). Semiconductor sensor devices are relatively small and light (see, for example, Non-Patent Document 1).

[0005] The mechanical sensor device includes an electrode in which a charge is induced when an external electric field is applied, a rotating plate with an opening through which the electrode can be exposed to the outside, and a drive unit that rotates the rotating plate. In the mechanical sensor device, as the rotating plate rotates, the electrode is repeatedly exposed to the outside and then covered by the rotating plate, so that an electrostatic field is intermittently applied to the electrode, and the field strength of the external electric field is measured as an AC signal generated at the electrode.

[0006] The semiconductor sensor device includes a transistor disposed on a substrate, and the field strength of an external electric field applied to the substrate is measured as the magnitude of a current flowing between the source and drain electrodes of the transistor when it is in an on-state.

[0007] Japanese Patent Application Laid-Open No. 2020-46213

[0008] WANG et al. , High-performance graphene-based electrostatic field sensor, IEEE ELECTRON DEVICE LETTERS, VOL38, No. 8. AUGUST 2017

[0009] The mechanical sensor device described above has a problem that it cannot be installed in a narrow space because it is large and heavy, while the semiconductor sensor device has a problem that it can be installed in a narrow space because it is small and light, but has a problem that the lower limit of the electric field strength that can be measured is high.

[0010] The present specification aims to propose a sensor device that is small in size and capable of measuring small electric field intensities.

[0011] a first atomic layer material film disposed on the first dielectric layer and having one or more atomic layers of graphene; a channel layer disposed on the first atomic layer material film, the channel layer having a channel region and having one or more atomic layers of graphene; a second atomic layer material film disposed on the channel layer and having one or more atomic layers formed of a second material; and a first electrode and a second electrode disposed on the channel layer to face each other with the channel region interposed therebetween, the second atomic layer material film having a first surface and a second surface, the first surface being disposed on the channel layer and a portion of the second surface facing the channel region being exposed to the outside, or a second dielectric layer being disposed on the second surface and a portion of the second dielectric layer on a surface opposite to the second atomic layer material film being exposed to the outside, the second surface being exposed to the outside, or a second dielectric layer being disposed on the second surface.

[0012] According to one aspect of a method for measuring an external electric field disclosed in the present specification, the external electric field is measured using the sensor device described above. This method is characterized by including: measuring a current value flowing between the first electrode and the second electrode while the external electric field is applied to the sensor device; and determining the field intensity of the external electric field based on the current value.

[0013] The sensor device disclosed in the present specification described above has small dimensions and is capable of measuring small electric field strengths.

[0014] Furthermore, according to the method for measuring an external electric field disclosed in the present specification, it is possible to measure a small electric field intensity using a small sensor device.

[0015] 1A is a cross-sectional view of a first embodiment of a sensor device disclosed herein, and FIG. 1B is a plan view thereof. FIG. 1A is a diagram showing the relationship between the strength of an external electric field applied to a sensor device having a channel layer of p-type graphene and the drain current, and FIG. 1B is a diagram showing the relationship between the strength of an external electric field applied to a sensor device having a channel layer of n-type graphene and the drain current. FIG. 1B is a diagram showing a state in which an external electric field is applied to the sensor device in a direction (negative direction) from the sensor device toward the outside. FIG. 1C is a diagram showing the relationship between the drain current and time when an external electric field in a positive direction is applied to the sensor device. FIG. 1D is a diagram showing the relationship between the number of atomic layers of the first atomic layer material film and the amount of change in drain current. FIG. 1E is a cross-sectional view of a second embodiment of a sensor device disclosed herein. FIG. 1F is a cross-sectional view of a third embodiment of a sensor device disclosed herein. FIG. 1F to FIG. 1C are diagrams showing manufacturing steps of an embodiment of a method for manufacturing a sensor device disclosed herein. FIG. 1F and FIG. 1B are diagrams showing manufacturing steps of an embodiment of a method for manufacturing a sensor device disclosed herein. 1A and 1B are diagrams (part 3) showing a manufacturing process of an embodiment of a manufacturing method for a sensor device disclosed in this specification; FIG. 1 is a flowchart of an embodiment of a method for measuring an external electric field disclosed in this specification;

[0016] A first preferred embodiment of the sensor device disclosed in this specification will be described below with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, but extends to the inventions set forth in the claims and their equivalents.

[0017] Fig. 1A shows a first embodiment of the sensor device disclosed in this specification, and is a cross-sectional view taken along line X-X in Fig. 1B, and Fig. 1B is a plan view. Fig. 1A shows a state in which an external electric field is applied in a direction (positive direction) toward the sensor device from the outside.

[0018] The sensor device 10 of this embodiment can measure the strength of an external electric field E1 applied from the outside. The external electric field E1 refers to an electric field generated from a source outside the sensor device 10. The sensor device 10 has high sensitivity and can measure small electric field strengths.

[0019] The sensor device 10 includes a substrate 11, a dielectric layer 12, a first atomic layer material film 13, a channel layer 14, a second atomic layer material film 15, a source electrode 16, and a drain electrode 17. As will be described in detail later, the sensor device 10 has high sensitivity due to the channel layer 14 being formed using single-layer or multi-layer graphene, and is therefore capable of measuring a small external electric field E1. The sensor device 10 of this embodiment operates as an ambipolar transistor when an external electric field is applied, and is therefore able to measure the magnitude of the external electric field E1 as a current.

[0020] The substrate 11 has the mechanical strength to support the other components of the sensor device 10. The substrate 11 has a first surface 11A and a second surface 11B. For example, a semiconductor substrate such as a silicon substrate, silicon carbide, or compound semiconductor can be used as the substrate 11. An amorphous, polycrystalline, or single-crystalline substrate can be used as the semiconductor substrate. The substrate 11 may have p-type polarity or n-type polarity. The substrate may also be intrinsic, i.e., without doping. Note that if the dielectric layer 12 has the mechanical strength to support the other components of the sensor device 10, the sensor device 10 does not need to have the substrate 11.

[0021] The dielectric layer 12 has electrical insulation properties and is disposed on the first surface 11A of the substrate 11. The dielectric layer 12 electrically insulates the substrate 11 from the first atomic layer material film 13.

[0022] A dielectric material such as silicon dioxide, aluminum oxide, or silicon nitride can be used for the dielectric layer 12. When the substrate 11 is a silicon substrate, it is preferable to use silicon dioxide for the dielectric layer 12 from the viewpoint of manufacturing the sensor device 10.

[0023] The first atomic layer material film 13 is disposed on the dielectric layer 12. The first atomic layer material film 13 is made of a material capable of forming a monoatomic layer. The first atomic layer material film 13 has one or more atomic layers formed of this material. Examples of this material include hexagonal boron nitride, hexagonal molybdenum disulfide, and hexagonal tungsten disulfide.

[0024] The lattice mismatch of the first atomic layer material film 13 with the graphene forming the channel layer 14 is preferably 10% or less, and particularly preferably 5% or less. The lattice mismatch is a percentage value obtained by dividing the absolute value of the difference between the lattice constant of the first atomic layer material film 13 and the lattice constant of graphene by the lattice constant of graphene when the first atomic layer material film 13 is disposed on the channel layer 14 so as to maximize the degree of match between the lattice constant of the first atomic layer material film 13 and the lattice constant of graphene. For example, when the first atomic layer material film 13 is formed of boron nitride, the unit lattices of the monoatomic layers of graphene and boron nitride each have an a-axis and a b-axis extending in a two-dimensional plane and a c-axis perpendicular to the a-axis and b-axis. When the first atomic layer material film 13 is disposed on the channel layer 14 so that the a-axis and c-axis of graphene and boron nitride are aligned and the a-axis and c-axis are rotated to maximize the degree of match with the lattice constants of the monoatomic layers of graphene and boron nitride, the lattice mismatch is 1.71% when the first atomic layer material film 13 is made of boron nitride, 3.01% when the first atomic layer material film 13 is made of molybdenum disulfide, and 3.26% when the first atomic layer material film 13 is made of tungsten disulfide.

[0025] The surface of the dielectric layer 12, which is made of silicon dioxide or the like, is usually not flat but has irregularities. Furthermore, impurities may be present on the surface of the dielectric layer 12. If the channel layer 14 were disposed directly on the surface of the dielectric layer 12, the two-dimensional periodic structure of graphene forming the channel layer 14 would be distorted due to the influence of the surface condition of the dielectric layer 12, and the channel layer 14 would be electrically affected by the impurities. As a result, carriers moving within the graphene would be scattered by the distortion or impurities, resulting in a decrease in carrier mobility. Therefore, in this embodiment, the first atomic layer material film 13 is disposed on the surface of the dielectric layer 12, and the channel layer 14 is disposed on this first atomic layer material film 13. This prevents the carrier mobility in the graphene from being affected by the dielectric layer 12 and decreasing.

[0026] Here, since the first atomic layer material film 13 has a small lattice mismatch with the graphene that forms the channel layer 14, even if the channel layer 14 is disposed directly on the first atomic layer material film 13, distortion of the two-dimensional periodic structure of the graphene that forms the channel layer 14 is suppressed.

[0027] The thickness of the first atomic layer material film 13 is preferably in the range of 1 to 120 atomic layers. When the thickness of the first atomic layer material film 13 is 1 atomic layer or more, the mobility of carriers in graphene can be prevented from being affected by the dielectric layer 12.

[0028] The thicker the first atomic layer material film 13, the smaller the change in the drain current flowing between the source electrode 16 and the drain electrode 17 when an external electric field E1 is applied to the sensor device 10. The thickness of the first atomic layer material film 13 is preferably determined according to the range of the external electric field E1 to be measured. If the thickness of the first atomic layer material film 13 is too thick relative to the magnitude of the external electric field E1, a small external electric field E1 may not be accurately measured. As will be described in detail later, if the thickness of the first atomic layer material film 13 is up to 120 atomic layers, the magnitude of the external electric field E1 can be measured up to approximately 17 kV / m. Since the electric field strength near the ground surface directly under a thundercloud is typically several kV / m to 10 kV / m, from the perspective of accurately measuring the external electric field strength caused by a typical thundercloud, a thickness of the first atomic layer material film 13 in the range of 1 to 40 atomic layers is preferable in order to obtain a large change in the drain current.

[0029] The channel layer 14 has a channel region 141 and includes one or more atomic layers of graphene. The channel region 141 of the channel layer 14 is preferably disposed on at least the first atomic layer material film 13. In this embodiment, the entire channel layer 14 is disposed on the first atomic layer material film 13. The channel layer 14 may have p-type polarity or n-type polarity. Alternatively, the channel layer 14 may be intrinsic, i.e., not doped with impurities.

[0030] The lower limit of the measurable electric field strength increases as the sensitivity (gain) G of the sensor device 10 increases. The sensor device 10 has high sensitivity because the channel layer 14 is formed using one or more atomic layers of graphene.

[0031] Next, in order to improve the sensitivity of the sensor device 10, the channel layer 14 is formed using one or more atomic layers of graphene. Graphene has high carrier mobility. A monoatomic layer of graphene has a density of 2×10 5 (cm 2 ∨ -1 S -1 ) which is 1.4×10 of the electron mobility in a crystalline silicon substrate. 3 (cm 2 ∨ -1 S-1 ) is a value two or more orders of magnitude higher. From the viewpoint of obtaining high carrier mobility, the channel layer 14 is preferably formed using 1 to 10 atomic layers of graphene, particularly 1 to 4 atomic layers. In particular, the highest carrier mobility can be obtained by forming the channel layer 14 using a monoatomic layer of graphene.

[0032] The carrier mobility in the channel layer 14 decreases by 20% or more with every 1 nm increase in thickness. The mobility of the channel layer 14 gradually decreases when the number of graphene atomic layers exceeds 13, but the mobility remains relatively high up to about 10 layers.

[0033] The second atomic layer material film 15 has electrical insulation properties and is disposed on the channel layer 14. The second atomic layer material film 15 protects the channel layer 14. The second atomic layer material film 15 has a first surface 15A and a second surface 15B, with the first surface 15A being disposed on the channel layer 14 and the second surface 15B being exposed to the outside. The external electric field E1 penetrates into the sensor device 10 through the second surface 15B.

[0034] The second surface 15B of the second atomic layer material film 15 forms an input / output region 15C. At least a portion of the second surface 15B facing the channel region 141 is exposed to the outside. This allows the external electric field E1 to be input to the sensor device 10 via the input / output region 15C. The external electric field E1 can also be output from the sensor device 10 via the input / output region 15C.

[0035] The second atomic layer material film 15 is formed from a material capable of forming a monoatomic layer. The second atomic layer material film 15 has one or more atomic layers formed from this material. Examples of this material include hexagonal boron nitride, molybdenum disulfide, and tungsten disulfide. The second atomic layer material film 15 preferably has a lattice mismatch of 10% or less, and particularly preferably 5% or less, with the graphene that forms the channel layer 14. The above description of the first atomic layer material film 13 applies appropriately to the description of the lattice mismatch of the second atomic layer material film 15.

[0036] The second atomic layer material film 15 is disposed directly on the channel layer 14. However, if there is a large lattice mismatch between the material forming the second atomic layer material film 15 and the graphene forming the channel layer 14, distortion occurs in the two-dimensional periodic structure of the graphene forming the channel layer 14. This causes carriers moving within the graphene to be scattered, reducing the carrier mobility. Therefore, in this embodiment, the second atomic layer material film 15, which has a small lattice mismatch with the graphene forming the channel layer 14, is disposed on the channel layer 14, thereby suppressing the reduction in carrier mobility in the graphene due to the influence of the second atomic layer material film 15.

[0037] The thickness of the second atomic layer material film 15 is preferably in the range of 1 to 100 atomic layers. When the thickness of the second atomic layer material film 15 is one atomic layer or more, the channel layer 14 can be physically protected. From the viewpoint of preventing resist, water, or the like from being doped into the channel layer 14 during the manufacture of the sensor device 10, the thickness of the second atomic layer material film 15 is particularly preferably in the range of 60 to 90 atomic layers. The action of the external electric field E1 on the channel layer 14 will be described in detail later.

[0038] The source electrode 16 and the drain electrode 17 are disposed on the channel layer 14 so as to face each other across a channel region 141 of the channel layer 14. At least a portion of each of the pair of source electrode 16 and drain electrode 17 may be disposed on the channel layer 14. In this embodiment, the entire source electrode 16 and the entire drain electrode 17 are disposed on the channel layer 14.

[0039] The sensor device 10 operates as an ambipolar transistor. When an external electric field E1 (gate voltage) is applied to the channel region 141, the drain current flowing between the source electrode 16 and the drain electrode 17 increases.

[0040] 2A and 2B are graphs showing the relationship between the strength of an external electric field applied to a sensor device having a p-type graphene channel layer and the drain current, respectively, and the relationship between the strength of an external electric field applied to a sensor device having an n-type graphene channel layer and the drain current.

[0041] As shown in FIG. 2A, when the channel layer 14 is formed using p-type graphene, the drain current I Ｄ In an ambipolar transistor, a drain current usually flows even when no external electric field E is applied (when the gate voltage is zero). On the other hand, when the channel layer 14 is formed using p-type graphene, the drain current I decreases with an increase in the magnitude of the negative external electric field E. Ｄ increases. Here, the electric field lines of the negative external electric field E extend in a direction from the substrate 11 toward the second atomic layer material film 15. Furthermore, as shown in FIG. 2B , when the channel layer 14 is formed using n-type graphene, the drain current I Ｄ On the other hand, when the channel layer 14 is formed using n-type graphene, the drain current I Ｄ is reduced.

[0042] Next, the operation of the sensor device 10 to which the external electric field E1 is applied, measuring the magnitude of the external electric field E1 as a change in the drain current value, will be described below with reference to FIGS.

[0043] 1A , an external electric field E1 is applied to the sensor device 10 in a direction (positive direction) from the outside toward the sensor device 10. The electric field lines of the positive external electric field E1 extend in a direction from the second atomic layer material film 15 toward the substrate 11.

[0044] The external electric field E1 enters the sensor device 10 from the input / output region 15C and exits to the outside from the second surface 11B of the substrate 11. The sensor device 10 uses the second surface 15B of the second atomic layer material film 15, which is one of its components, as the input / output region 15C for the external electric field E1, and is therefore capable of measuring the external electric field E1 with a small size.

[0045] The external electric field E1 applied to the sensor device 10 causes electrons in the channel layer 14 to pass through the first atomic layer material film 13 by the tunneling effect and move to the dielectric layer 12. The number of electrons passing through the first atomic layer material film 13 due to the external electric field E1 depends on the magnitude of the external electric field E1. Therefore, it is preferable that the thickness of the first atomic layer material film 13 is thin.

[0046] The larger the area of ​​the channel region 141 of the channel layer 14, the more electrons move to the dielectric layer 12.

[0047] Furthermore, the larger the area of ​​the input / output region 15C, the more electrons move to the dielectric layer 12.

[0048] The electrons that move to the dielectric layer 12 are trapped by defects at the interface between the dielectric layer 12 and the first atomic layer material film 13. The electrons trapped at the interface generate an internal electric field E2 within the sensor device 10. This internal electric field E2 acts on the channel layer 14, changing the Fermi level of the channel layer 14. Since the Fermi level of the channel layer 14 changes, the magnitude of the drain current flowing in the channel region 141 between the source electrode 16 and the drain electrode 17 changes. If the channel layer 14 is formed of p-type graphene, the Fermi level increases. On the other hand, if the channel layer 14 is formed of n-type graphene, the Fermi level decreases. When the Fermi level increases, the drain current decreases, and when the Fermi level decreases, the drain current increases. The magnitude of the external electric field E1 can be measured based on the magnitude of the change in the drain current value relative to the drain current value when the external electric field E1 is not applied to the sensor device 10. The greater the number of carriers trapped in the defects at the interface between the dielectric layer 12 and the first atomic layer material film 13, the greater the gain of the sensor device 10.

[0049] 3, an external electric field E1 directed from the sensor device 10 to the outside (negative direction) is applied to the sensor device 10. The electric field lines of the negative external electric field E1 extend in a direction from the substrate 11 toward the second atomic layer material film 15.

[0050] The external electric field E1 enters the sensor device 10 from the second surface 11B of the substrate 11 and exits to the outside through the input / output region 15C.

[0051] The external electric field E1 applied to the sensor device 10 causes holes in the channel layer 14 to pass through the first atomic layer material film 13 by the tunneling effect and move to the dielectric layer 12. The number of holes that pass through the first atomic layer material film 13 due to the external electric field E1 depends on the magnitude of the external electric field E1.

[0052] The holes that have moved to the dielectric layer 12 are trapped by defects at the interface between the dielectric layer 12 and the first atomic layer material film 13. The holes trapped at the interface generate an internal electric field E2 within the sensor device 10. The internal electric field E2 acts on the channel layer 14, causing a change in the Fermi level of the channel layer 14. Since the Fermi level of the channel layer 14 changes, the magnitude of the drain current flowing between the source electrode 16 and the drain electrode 17 changes. The magnitude of the external electric field E1 can be measured based on the magnitude of the change in the drain current value relative to the drain current value when no external electric field E1 is applied to the sensor device 10.

[0053] In addition to the high sensitivity described above, a wide measurement range is also required for the sensor device 10. The wider the measurement range of the sensor device 10, the wider the range of electric field strength that can be measured.

[0054] The maximum number of carriers induced at the interface between the dielectric layer 12 and the first atomic layer material film 13 when an external electric field is applied increases as the thickness of the first atomic layer material film 13 decreases. The number of carriers trapped in defects at the interface of the dielectric layer 12 increases as the magnitude of the external electric field E1 increases and eventually saturates. The difference between the number of carriers at the interface of the dielectric layer 12 when no external electric field is applied and the number of carriers trapped in defects at the interface when saturated corresponds to the measurement range of the sensor device 10.

[0055] Next, a measurement example in which the external electric field E1 is measured using the sensor device 10 will be described below.

[0056] FIG. 4 shows the relationship between drain current and time when a positive external electric field E1 is applied to the sensor device 10. The vertical axis of FIG. 4 represents drain current, and the horizontal axis represents time. The relationship shown in FIG. 4 was measured by placing parallel plates spaced 3 cm apart on either side of the sensor device 10 and applying a 500 V voltage between the parallel plates (the magnitude of the external electric field was approximately 16,667 V / m). The first atomic layer material film 13 was formed using hexagonal boron nitride. A 100 mV voltage was applied between the source electrode 16 and the drain electrode 17. The drain current value when a positive external electric field E1 is applied to the sensor device 10 is lower than when no external electric field E1 is applied to the sensor device 10.

[0057] FIG. 5 is a graph showing the relationship between the number of atomic layers in the first atomic layer material film 13 and the change in drain current. FIG. 5 shows the results of measuring the change in drain current by changing the number of atomic layers in the first atomic layer material film 13 in the measurement shown in FIG. 4 . The change in drain current exponentially decreases with an increase in the number of atomic layers in the first atomic layer material film 13. From the perspective of measuring the change in drain current using the sensor device 10, the upper limit of the number of atomic layers in the first atomic layer material film 13 is 120. Furthermore, from the perspective of accurately measuring the change in drain current using the sensor device 10, the lower limit of the change in drain current is considered to be approximately 1.5 μA. In this case, the upper limit of the number of atomic layers in the first atomic layer material film 13 is 40. To accurately measure the electric field strength, it is preferable to set the number of atomic layers in the first atomic layer material film 13 to 1 to 40. To measure the electric field strength over a wide measurement range, it is preferable to set the number of atomic layers in the first atomic layer material film 13 to 1 to 120.

[0058] The sensor device 10 of the present embodiment described above is small in size and can measure small electric field strengths. Furthermore, by changing the number of atomic layers in the first atomic layer material film 13, the sensor device can accurately measure electric field strengths and can also measure electric field strengths over a wide measurement range.

[0059] Furthermore, the sensor device 10 has the following advantages over conventional mechanical sensor devices. Mechanical sensor devices are several tens of centimeters in size and weigh several kilograms, which limits their installation location. On the other hand, the sensor device 10, even when modularized to include a measurement function, is only several centimeters in size and weighs only a few grams, significantly reducing installation location restrictions. Furthermore, mechanical sensor devices have a drive unit, which can cause malfunctions and require maintenance. On the other hand, the sensor device 10 is a semiconductor sensor, which significantly reduces the likelihood of malfunction. Furthermore, mechanical sensor devices consume a lot of power and require a power supply device such as an AC power source. On the other hand, the sensor device 10 consumes little power and can be powered by a simple power supply device such as a battery.

[0060] Next, other embodiments of the sensor device described above will be described below with reference to Figures 6 and 7. The detailed description of the first embodiment described above applies to points not specifically described in other embodiments. In addition, the same components are denoted by the same reference numerals.

[0061] 6 is a cross-sectional view of a second embodiment of a sensor device 10A disclosed in this specification. A second dielectric layer 18 is disposed on the second surface 15B of the second atomic layer material film 15 in the sensor device 10A of this embodiment. The second dielectric layer 18 has electrical insulation properties and functions to protect the second atomic layer material film 15.

[0062] From the viewpoint of protecting the channel layer 13, it is preferable to use a dielectric material such as silicon dioxide, aluminum oxide, or silicon nitride as the second dielectric layer 18.

[0063] Furthermore, by using a material with a high dielectric constant for the second dielectric layer 18, the external electric field can be amplified and acted on the channel layer 14. Examples of materials that can amplify the external electric field include silicon dioxide, silicon nitride, zirconium dioxide, and hafnium dioxide.

[0064] From the viewpoint of amplifying the external electric field, it is preferable that the second dielectric layer 18 has a higher dielectric constant than the second atomic layer material film 15. The amount of charge Q stored in the second dielectric layer 18 is expressed as Q=ε ｒIt is expressed as SE, where ε ｒ is the relative dielectric constant of the second dielectric layer 18, S is the area of ​​the second dielectric layer 18, and E is the field strength of the external electric field.

[0065] By disposing the second dielectric layer 18 having a higher dielectric constant than the second atomic layer material film 15 on the second atomic layer material film 15, the external electric field can be amplified and acted on the channel layer 14.

[0066] The dielectric constant of boron nitride, which is the material for forming the second atomic layer material film 15, is 3.4. From the viewpoint of amplifying the external electric field, it is particularly preferable to use silicon nitride (dielectric constant 8.5), zirconium dioxide (dielectric constant 32), or hafnium oxide (dielectric constant 16 to 19) as the material for forming the second dielectric layer 18.

[0067] The second dielectric layer 18 has a first surface 18A and a second surface 18B, and the first surface 18A is disposed on the second atomic layer material film 15. The second surface 18B is the surface of the second dielectric layer 18 opposite the second atomic layer material film 15. At least a portion of the second surface 18B facing the channel region 141 is exposed to the outside. The second surface 18B forms an input / output region 18C through which an external electric field is input and output. This allows the external electric field to be input to the sensor device 10A via the input / output region 18C. Furthermore, the external electric field can be output from the sensor device 10A via the input / output region 18C.

[0068] According to the sensor device of the present embodiment described above, the measurement sensitivity of the external electric field can be improved by amplifying the external electric field using the second dielectric layer 18. Furthermore, according to the sensor device of the present embodiment, the same effects as those of the first embodiment can be obtained.

[0069] 7 is a cross-sectional view of a sensor device 10B according to a third embodiment of the present invention, which is a so-called bottom gate transistor.

[0070] In the sensor device 10B of this embodiment, a gate insulating layer 19 is disposed on the second surface 11B of the substrate 11, and a gate electrode 20 is disposed below the gate insulating layer 19. The gate electrode 20 is disposed on the second surface 11B of the substrate 11 so as to cover a region corresponding to the channel region 141.

[0071] The gate insulating layer 19 may be a dielectric material such as silicon dioxide, aluminum oxide, or silicon nitride.

[0072] The gate electrode 20 is made of a conductive material and may have a laminated structure of, for example, chromium and gold.

[0073] The sensor device 10B measures the external electric field while a predetermined voltage is applied to the gate electrode 20. Application of the gate voltage to the gate electrode 20 increases the drain current compared to before the application. As in the first embodiment described above, the sensor device 10B can measure the magnitude of the external electric field based on the magnitude of change in the drain current value relative to the drain current value when no external electric field is applied to the sensor device 10B.

[0074] According to the sensor device of this embodiment described above, the same effects as those of the first embodiment can be obtained.

[0075] Next, a preferred embodiment of a method for manufacturing the sensor device of the first embodiment will be described below with reference to FIGS.

[0076] 8A, a substrate 11 having a first surface 11A and a second surface 11B is prepared. The substrate 11 may be, for example, a silicon substrate, a silicon carbide substrate, a semiconductor substrate such as a compound semiconductor substrate, or the like.

[0077] 8(B), a dielectric layer 12 is formed on the first surface 11A of the substrate 11. When a silicon substrate is used as the substrate 11, for example, a silicon dioxide layer is formed as the dielectric layer 12. This silicon dioxide layer is formed using a thermal oxidation method or a CVD method. When a silicon dioxide layer is formed as the dielectric layer 12 using a thermal oxidation method, the interface between the silicon dioxide layer and silicon becomes a new first surface 11A.

[0078] 8C, a first atomic layer material film 13 is disposed on the dielectric layer 12. The first atomic layer material film 13 is formed, for example, by a peeling method or a CVD method, and transferred onto the dielectric layer 12. The thickness of the first atomic layer material film 13 is preferably in the range of 1 to 120 atomic layers.

[0079] 9A, the channel layer 14 is formed on the first atomic layer material film 13. The channel layer 14 is formed by, for example, a peeling method or a CVD method, and is transferred onto the first atomic layer material film 13. The thickness and quality of the channel layer 14 are measured by, for example, Raman spectroscopy. For example, the presence or absence of defects in the graphene forming the channel layer 14 can be determined by Raman spectroscopy at 1350 cm -1 and the number of atomic layers of graphene is 1580 cm -1 G peak intensity or 2608 cm -1 The polarization is measured by the 2D peak shape of the channel layer 14. In particular, it is preferable to form the channel layer 14 using an exfoliation method from the viewpoint of obtaining high-quality graphene with few defects. Furthermore, it is preferable to form the channel layer 14 of a monoatomic layer from the viewpoint of obtaining graphene with high carrier mobility. Polarity may be imparted to the channel layer 14 by adding impurities to the graphene.

[0080] Next, as shown in FIG. 9B , a mask (not shown) is formed on the channel layer 14 using lithography and etching. A conductive layer is then formed on the channel layer 14 with the mask formed thereon, and the conductive layer (not shown) is then patterned using a lift-off method to form the source electrode 16 and the drain electrode 17 on the channel layer 14. As the lithography method, for example, electron beam lithography can be used. As the etching method, for example, oxygen plasma dry etching can be used. The conductive layer can be formed as a laminate of chromium and gold using, for example, electron beam evaporation. The chromium can have a thickness of 5 nm, and the gold can have a thickness of 80 nm.

[0081] 10A, a second atomic layer material film 15 is formed on the channel layer 14, the source electrode 16, and the drain electrode 17. The thickness of the second atomic layer material film 15 is preferably in the range of 1 to 300 atomic layers. The second atomic layer material film 15 is formed on the channel layer 14, the source electrode 16, and the drain electrode 17 by using, for example, a peeling method or a CVD method. The above description of the first atomic layer material film 13 is applied appropriately to the formation of the second atomic layer material film 15.

[0082] Next, as shown in Fig. 10B, the second atomic layer material film 15 is patterned using lithography and etching to obtain the sensor device 10 of the first embodiment shown in Fig. 1. The second atomic layer material film 15 is formed so as to cover at least a portion of the source electrode 16 and the drain electrode 17. For example, electron beam lithography can be used as the lithography method. For example, oxygen plasma dry etching can be used as the etching method.

[0083] Furthermore, after the step of FIG. 10(B) described above, a second dielectric layer 18 is formed on the second surface 15B of the second atomic layer material film 15, thereby obtaining the sensor device 10A of the second embodiment shown in FIG. 6.

[0084] Furthermore, after the step of FIG. 10(B) described above, a gate insulating layer 19 is formed on the second surface 11B of the substrate 11, and a gate electrode 20 is formed on this gate insulating layer 19, thereby obtaining the sensor device 10B of the second embodiment shown in FIG. 7.

[0085] Next, a method for measuring an external electric field using the sensor device 10 of the first embodiment described above will be described below with reference to Fig. 11. Fig. 11 is a flowchart of one embodiment of the method for measuring an external electric field disclosed in this specification.

[0086] First, the drain current value flowing between the source electrode 16 and the drain electrode 17 is measured in each state where an external electric field of a plurality of different electric field intensities is applied (step S101). This allows the relationship between the drain current value and the electric field intensity of the external electric field (current-electric field intensity relationship) to be obtained.

[0087] Next, a drain current value (measured drain current value) flowing between the source electrode 16 and the drain electrode 17 is measured when an external electric field to be measured is applied to the sensor device 10. When measuring the external electric field, it is preferable that no voltage is applied to the substrate 11 of the sensor device 10. Furthermore, since the sensor device 10 does not have any electrodes other than the source electrode 16 and the drain electrode 17, no gate voltage is applied to the sensor device 10 when measuring the external electric field.

[0088] Next, the field strength of the external electric field is calculated based on the measured drain current value (step S102). The external electric field to be measured is input to the sensor device 10 via the input / output region 15C, or is output from the sensor device 10 via the input / output region 15C. The field strength of the external electric field can be obtained by calculating the field strength corresponding to the measured drain current value with reference to the relationship between the current and field strength.

[0089] If the relationship between the current and the electric field intensity has been acquired in advance, the process of step S101 is omitted.

[0090] According to the method for measuring an external electric field of this embodiment described above, it is possible to measure a small electric field intensity using the sensor device 10 having a small size.

[0091] The external electric field can be measured in a similar manner using the sensor device 10A of the second embodiment described above. The external electric field to be measured is input to the sensor device 10A via the input / output region 18C, or is output from the sensor device 10A via the input / output region 18C. The external electric field can also be measured in a similar manner using the sensor device 10B of the third embodiment described above. The external electric field to be measured is input to the sensor device 10B via the input / output region 15C, or is output from the sensor device 10B via the input / output region 15C.

[0092] In the present invention, the sensor device capable of measuring electric field strength and the method for measuring an external electric field of the above-described embodiments can be appropriately modified without departing from the spirit of the present invention. Furthermore, the constituent elements of one embodiment can be appropriately applied to other embodiments.

[0093] REFERENCE SIGNS LIST 10 Sensor device 11 Substrate 11A First surface 11B Second surface 12 Dielectric layer (first dielectric layer) 13 First atomic layer material film 14 Channel layer 141 Channel region 15 Second atomic layer material film 15A First surface 15B Second surface 16 Source electrode (first electrode) 17 Drain electrode (second electrode) 18 Second dielectric layer 19 Gate insulating layer 20 Gate electrode (third electrode)

Claims

1. A sensor device capable of measuring the electric field strength of an external electric field, comprising: a first dielectric layer; a first atomic layer material film disposed on the first dielectric layer and having one or more atomic layers formed of a first material; a channel layer disposed on the first atomic layer material film, having a channel region, and having one or more atomic layers of graphene; a second atomic layer material film disposed on the channel layer and having one or more atomic layers formed of a second material; a first electrode and a second electrode disposed on the channel layer so as to face each other with the channel region therebetween; and the second atomic layer material film has a first surface and a second surface, the first surface is disposed on the channel layer, a second dielectric layer is disposed on the second surface, and a portion of the second dielectric layer facing the channel region on the surface opposite to the second atomic layer material film is exposed to the outside. A sensor device characterized by this.

2. The sensor device according to claim 1, wherein the first atomic layer material film has 1 to 120 atomic layers formed of the first material.

3. The sensor device according to claim 1, wherein the second atomic layer material film has 1 to 100 atomic layers formed of the second material.

4. The sensor device according to claim 1, wherein the first material or the second material is hexagonal boron nitride, molybdenum disulfide, or tungsten disulfide.

5. The sensor device according to any one of claims 1 to 4, wherein the channel layer has 1 to 10 layers of graphene.

6. A method for measuring an external electric field using the sensor device according to claim 1, comprising: measuring a current value flowing between the first electrode and the second electrode in a state where an external electric field is applied to the sensor device; and obtaining the electric field strength of the external electric field based on the current value. A method characterized by this.

7. The method according to claim 6, wherein the electric field strength of an external electric field input from or output from the surface of the second dielectric layer opposite to the second atomic layer material film is measured.