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

Abstract

Provided is a sensor device having high measurement sensitivity for measuring an external electric field. The sensor device can measure the electric field intensity of the external electric field. The sensor device includes: a first dielectric layer; a channel layer disposed directly on the first dielectric layer, having a channel region, having an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal disulfide; and a first electrode and a second electrode which are in electrical contact with the channel layer and are disposed so as to face each other with the channel region therebetween, the channel layer having a first surface and a second surface, the first surface being disposed on the first dielectric layer, the second surface being exposed to the outside, or the second dielectric layer being disposed on the second surface. A Fermi level of the channel layer is in a conduction band or valence band of the channel layer and in a trap level band in the first dielectric layer that interfaces with the channel layer.

Description

Technical Field

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

[0002] Conventionally, sensor devices are used to measure the electric field strength in the atmosphere. By measuring the electric field strength in the atmosphere, the generation and movement of thunderclouds are monitored (for example, see Patent Document 1).

[0003] In addition, sensor devices are used to measure the electric field strength in the indoor atmosphere. By measuring the electric field strength, the static electricity generated in the room is monitored and accidents caused by static electricity are prevented.

[0004] As a sensor device for measuring electric field strength, there is a mechanical sensor device (for example, refer to Patent Document 1). However, the mechanical sensor device is a relatively large and heavy device.

[0005] Therefore, a semiconductor sensor device has been proposed (for example, refer to Non-Patent Document 1). The semiconductor sensor device is a relatively small and light device.

[0006] The semiconductor sensor device has a transistor including graphene as a channel layer. The electric field strength of an external electric field applied to the semiconductor sensor device is measured as the magnitude of a current flowing between a source electrode and a drain electrode. Prior art literature Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2020-46213 Non-patent literature

[0008] Non-patent literature 1: WANG et al., High-performance graphene-based electrostatic field sensor, IEEE ELECTRON DEVICE LETTERS, VOL 38, No. 8, AUGUST 2017 Summary of the invention Problem that the invention aims to solve

[0009] The measurement sensitivity of measuring the external electric field of the semiconductor sensor device is affected by the mobility of the carriers in the channel layer and the state density of the Fermi level. The greater the mobility of the carriers, the higher the measurement sensitivity. In addition, the greater the state density of the Fermi level, the higher the measurement sensitivity.

[0010] However, although graphene has high carrier mobility, the state density of the Fermi level is low. Therefore, it is expected to further improve the measurement sensitivity of the semiconductor sensor device by increasing the state density of the Fermi level in the channel layer.

[0011] An object of the present disclosure is to provide a sensor device having high measurement sensitivity for measuring an external electric field by using a channel layer having a high state density at the Fermi level. Technical means of solving problems

[0012] (1) According to one embodiment of the present invention, a sensor device is provided. The sensor device is a sensor device capable of measuring the electric field strength of an external electric field, and is characterized by comprising: a first dielectric layer; a channel layer directly disposed on the first dielectric layer, having a channel region, and having an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal dichalcogenide; and a first electrode and a second electrode electrically contacting the channel layer and disposed opposite to each other with the channel region sandwiched therebetween, the channel layer having a first surface and a second surface, the first surface being disposed on the first dielectric layer and the second surface being exposed to the outside, or the second dielectric layer being disposed on the second surface, the Fermi level of the channel layer being located in the conduction band or the valence band of the channel layer and being located above a trap level band at an interface with the channel layer in the first dielectric layer.

[0013] (2) The sensor device of (1) preferably includes a second dielectric layer, and a gate electrode disposed on the second dielectric layer and including an atomic layer material film of one or more atomic layers.

[0014] (3) According to another embodiment of the present invention, there is provided a method for measuring an external electric field. The method for measuring an external electric field comprises: using the sensor device of (1), measuring a current value flowing between a first electrode and a second electrode in a state where an external electric field is applied to the sensor device; and obtaining an electric field strength of the external electric field based on the current value.

[0015] (4) In addition, according to another embodiment of the present invention, a method for measuring an external electric field is provided. The method for measuring the external electric field comprises: using the sensor device of (2), measuring the current value flowing between the first electrode and the second electrode while changing the gate voltage applied to the gate electrode, and obtaining the first gate voltage at which the current value shows a maximum value or a minimum value; and measuring the current value flowing between the first electrode and the second electrode when the external electric field is applied to the sensor device in a state where a second gate voltage determined based on the first gate voltage is applied to the gate electrode, and obtaining the electric field strength of the external electric field based on the current value. Effects of the Invention

[0016] According to the sensor device of the present invention described above, by using a channel layer having a high state density at the Fermi level, the measurement sensitivity for measuring an external electric field is high.

[0017] Furthermore, according to the method of measuring an external electric field of the present invention described above, since a sensor device having a channel layer having a high state density at the Fermi level is used, the external electric field can be measured with high sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 (A) is a cross-sectional view of the first embodiment of the sensor device disclosed in this specification, and (B) is a plan view. Figure 2 This is a diagram showing the relationship between the energy of electrons in the channel layer and the state density. Figure 3 (A) is a diagram showing the relationship between energy levels when the channel layer and the dielectric layer are separated, (B) is a diagram showing the relationship between energy levels when the channel layer and the dielectric layer are in contact, and (C) is a diagram showing the relationship between energy levels when a voltage is applied to the gate electrode. Figure 4 This is a diagram showing a state where an external electric field in a negative direction is applied to the sensor device. Figure 5 This is a diagram showing the relationship between the sensitivity of the sensor device and the electric field strength of the external electric field. Figure 6 It is a diagram showing a sensor device according to a modified example of the first embodiment. Figure 7 (A) is a cross-sectional view of a second embodiment of a sensor device disclosed in this specification, and (B) is a plan view. Figure 8 This is a flow chart for measuring an external electric field using the sensor device according to the second embodiment. Fig. 9 It is a diagram for explaining a method of measuring an external electric field using the sensor device according to the second embodiment. Fig.10 (A) and (B) are diagrams (part 1) showing a manufacturing process of one embodiment of a method for manufacturing a sensor device disclosed in this specification. Fig.11 (A) and (B) are diagrams (part 2) showing the manufacturing process of one embodiment of the method for manufacturing a sensor device disclosed in this specification. Fig.12 (A) and (B) are diagrams (part 3) showing the manufacturing process of one embodiment of the method for manufacturing a sensor device disclosed in this specification. DETAILED DESCRIPTION

[0019] Hereinafter, a preferred first embodiment of the sensor device disclosed in this specification will be described with reference to the drawings. However, the technical scope of the present invention is not limited to these embodiments, and includes inventions described in the claims and their equivalents.

[0020] Figure 1 (A) represents the first embodiment of the sensor device disclosed in this specification, which is Figure 1 (B) is a cross-sectional view taken along the line X1-X1, Figure 1 (B) is a top view. Figure 1 (A) represents a state where an external electric field in a positive direction is applied to the sensor device from the outside.

[0021] The sensor device 10 of this embodiment can measure the electric field strength of an external electric field E1 applied from the outside. The external electric field E1 is an electric field generated from a source existing outside the sensor device 10. The sensor device 10 has high sensitivity and can therefore measure a small electric field strength.

[0022] The sensor device 10 includes a substrate 11, a dielectric layer 12, a channel layer 13, a source electrode 14, and a drain electrode 15. The sensor device 10 of this embodiment operates as a transistor by applying an external electric field, and can measure the magnitude of the external electric field E1 as a current. The sensor device 10 has high sensitivity because the channel layer 13 includes an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal dichalcogenide, as described in detail later. As a result, the sensor device 10 can measure a small external electric field E1.

[0023] The substrate 11 has the mechanical strength to support other components of the sensor device 10. The substrate 11 has a first surface 11A and a second surface 11B. As the substrate 11, for example, a semiconductor substrate such as a silicon substrate, silicon carbide, or a compound semiconductor can be used. As the semiconductor substrate, an amorphous, polycrystalline, or single crystal substrate can be used. The substrate 11 can have a p-type polarity or an n-type polarity. In addition, the substrate can also be intrinsic without adding impurities. In addition, in the case where the dielectric layer 12 has the mechanical strength to support other components of the sensor device 10, the sensor device 10 may not have the substrate 11.

[0024] The dielectric layer 12 has electrical insulating properties and is disposed on the first surface 11A of the substrate 11 . The dielectric layer 12 electrically insulates the substrate 11 from the channel layer 13 .

[0025] As the dielectric layer 12 , a dielectric such as silicon dioxide (SiO 2 ), aluminum oxide, hafnium dioxide, or silicon nitride can be used. When the substrate 11 is a silicon substrate, silicon dioxide is preferably used as the dielectric layer 12 from the viewpoint of manufacturing the sensor device 10 .

[0026] At the interface between the dielectric layer 12 and the channel layer 13, there are trap levels that can capture carriers due to defects or impurities. For example, when the dielectric layer 12 is SiO2, a trap level band consisting of a plurality of trap levels is formed near the center of the band gap of the dielectric layer 12. From the viewpoint of increasing the number of trap levels, it is preferred to irradiate the surface of the dielectric layer 12 with oxygen ions, nitrogen ions, or helium ions.

[0027] The channel layer 13 has a channel region 131 and is directly disposed on the dielectric layer 12. The channel layer 13 has a first surface 13A and a second surface 13B. The first surface 13A is disposed on the dielectric layer 12, and the second surface 13B is exposed to the outside. The second surface 13B functions as an input / output region 10a for the sensor device 10 to input or output the external electric field E1.

[0028] The channel layer 13 is directly disposed on the dielectric layer 12, which means that substantially no other layer is disposed between the channel layer 13 and the dielectric layer 12. However, an oxide layer or the like formed unintentionally on the surface of the channel layer 13 or the surface of the dielectric layer 12 is allowed to exist.

[0029] The channel region 131 is preferably disposed at least on the dielectric layer 12. In the present embodiment, the entire channel layer 13 is disposed on the dielectric layer 12. The channel layer 13 may have p-type polarity or n-type polarity.

[0030] The channel layer 13 has an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal dichalcogenide.

[0031] The channel layer 13 preferably contains molybdenum (Mo), tungsten (W) or niobium (Nb) as a transition metal. The channel layer 13 preferably contains sulfur (S), selenium (Se) or tellurium (Te) as a chalcogen. Examples of two-dimensional transition metal dichalcogenides include MoS2, MoSe2, WS2, WSe2, NbS2 and NbSe2.

[0032] The source electrode 14 and the drain electrode 15 are in electrical contact with the channel layer 13, and are arranged to face each other with the channel region 131 of the channel layer 13 interposed therebetween. In the present embodiment, a portion of each of the source electrode 14 and the drain electrode 15 is arranged on the channel layer 13. The source electrode 14 and the drain electrode 15 are conductive. When the sensor device 10 is used to measure the external electric field E1, a predetermined voltage is applied between the source electrode 14 and the drain electrode 15.

[0033] The sensor device 10 operates as a transistor. In the sensor device 10, when an external electric field E1 is applied to the channel layer 13, a drain current flowing between the source electrode 14 and the drain electrode 15 changes.

[0034] The sensitivity of the sensor device 10 operating as a transistor depends on the mobility of carriers in the channel layer 13 and the density of states of carriers near the Fermi level in the channel layer 13. The greater the mobility of carriers, the greater the sensitivity of the sensor device 10. In addition, the greater the density of states of carriers near the Fermi level, the greater the sensitivity of the sensor device 10.

[0035] The sensor device 10 of the present embodiment has high sensitivity because the state density of carriers near the Fermi level in the channel layer 13 is high.

[0036] Figure 2 This is a calculation result of the relationship between the energy of electrons and the density of states (Density Of States: expressed as DOS) when the channel layer 13 is MoS 2 . Figure 2 The horizontal axis represents the energy of the electrons in the channel layer 13, and the vertical axis represents the state density of the electrons. The state density of the electrons represents the number of states of the electrons per unit volume and per unit energy. Figure 2 In the figure, the electron state density is expressed as a relative value.

[0037] like Figure 2 As shown, in the channel layer 13, the state density in the conduction band and the valence band is high, and the state density in the band gap is low. In the case where the channel layer 13 has an n-type polarity, the Fermi level Efc is located in the conduction band of the channel layer 13 (near the lower end). On the other hand, in the case where the channel layer 13 has a p-type polarity, the Fermi level Efc is located in the valence band of the channel layer 13 (near the upper end).

[0038] Figure 2 The relationship between the energy and state density of electrons of MoS2, a two-dimensional transition metal dichalcogenide, and graphene formed by a similar atomic layer material film is shown. The state density of electrons of MoS2 is about 16 times that of electrons of graphene near the lower end of the conduction band. Therefore, the state density of electrons of MoS2 is much greater than that of graphene. Like MoS2, other two-dimensional transition metal dichalcogenides also have a greater state density of electrons than graphene. In addition, two-dimensional transition metal dichalcogenides having n-type or p-type polarity have a band gap, while graphene does not have a band gap.

[0039] From the viewpoint of improving the sensitivity of the sensor device 10, the channel layer 13 preferably has an atomic layer material film formed by one or more atomic layers. From the viewpoint of improving the sensitivity of the sensor device 10, the channel layer 13 preferably has an atomic layer material film formed by 1 to 4 layers, especially 2 layers. When the number of atomic layers forming the atomic layer material film increases, the state density of electrons near the Fermi level of the channel layer 13 decreases (for example, refer to KC Wang et.al., Journal of Applied Physics, 122, 224302, (2017)), so the sensitivity of the sensor device 10 to the external electric field E1 decreases.

[0040] Figure 3 (A) is a diagram showing the relationship between energy levels when the channel layer 13 and the dielectric layer 12 are separated. Figure 3 The left side graph of (A) shows the density of states (DOS) distribution of electrons in the channel layer 13 . Figure 3 The figure on the right side of (A) shows the trap level band of the dielectric layer 12 and the state density (DOS) distribution of the trap level band. This also applies to Figure 3 (B) and Figure 3 The channel layer 13 has an n-type polarity, and the Fermi level Efc is located at the lower end of the conduction band of the channel layer 13 .

[0041] The dielectric layer 12 has a trap level band including a plurality of trap levels at the interface with the channel layer 13. The trap level band is located near the center of the band gap of the dielectric layer 12.

[0042] Figure 3 (B) is a diagram showing the relationship between energy levels when the channel layer 13 and the dielectric layer 12 are in contact with each other. Figure 3 (B) indicates Figure 1 The state of the sensor device 10 shown in (A). Figure 3 (B) shows the state before the electrons in the channel layer 13 move to the trap level band of the dielectric layer 12. The Fermi level Efc is located at the lower end of the conduction band of the channel layer 13, as before the contact.

[0043] The Fermi level Efc of the channel layer 13 is located slightly above the trap level band at the interface between the dielectric layer 12 and the channel layer 13. By applying an external electric field E1 to the sensor device 10, electrons can move between the energy level below the Fermi level Efc of the channel layer 13 and the trap level band of the channel layer 13.

[0044] In the sensor device 10, the state density of electrons near the Fermi level Efc of the channel layer 13 is large (see Figure 2That is, since the number of electrons in the conduction band below the Fermi level Efc of the channel layer 13 is large, a large number of electrons can move between the trap level bands of the channel layer 13 and the dielectric layer 12 .

[0045] exist Figure 3 In (B), the case where the channel layer 13 is an n-type two-dimensional transition metal dichalcogenide is described, but this description is also applicable to the case where the channel layer 13 is a p-type two-dimensional transition metal dichalcogenide.

[0046] On the other hand, when the channel layer is formed of graphene, the state density of electrons at the Fermi level Efc of the channel layer is small (refer to Figure 2 That is, since the number of electrons in the conduction band below the Fermi level Efc of the channel layer 13 is small, the number of electrons that can move between the channel layer 13 and the trap level band of the channel layer 13 is small.

[0047] A case where, when the external electric field E1 is applied to the sensor device 10 , the electric field intensity is measured as a change in the drain current will be described below.

[0048] exist Figure 1 In (A), a positive external electric field E1 is applied from the outside to the sensor device 10. The lines of force of the positive external electric field E1 extend in a direction from the channel layer 13 toward the substrate 11. The lines of force of the external electric field E1 enter the sensor device 10 from the input / output region 10a and flow out from the second surface 11B of the substrate 11 to the outside.

[0049] The external electric field E1 passing through the input / output region 10 a of the sensor device 10 causes electrons in the trap level band at the interface of the dielectric layer 12 to move to the conduction band of the channel layer 13 .

[0050] The number of electrons moving to the conduction band of the channel layer 13 depends on the magnitude of the external electric field E1. In addition, the number of electrons moving to the conduction band of the channel layer 13 depends on the state density of electrons near the Fermi level Efc. The number of electrons moving to the conduction band of the channel layer 13 depends on the area of ​​the input-output region 10a.

[0051] The electrons that move to the conduction band of the channel layer 13 generate an internal electric field E2 in the sensor device 10. The internal electric field E2 acts on the channel layer 13, and the Fermi level Efc of the channel layer 13 changes. Due to the change in the Fermi level of the channel layer 13, the magnitude of the drain current flowing through the channel region 131 between the source electrode 14 and the drain electrode 15 changes.

[0052] When the channel layer 13 is an n-type channel, the drain current increases when the Fermi level Efc rises, and decreases when the Fermi level Efc falls. When the channel layer 13 is a p-type channel, the relationship between the Fermi level and the drain current is opposite.

[0053] The sensor device 10 can measure the magnitude of the external electric field E1 based on the magnitude of the change in the drain current value with reference to the drain current value when the external electric field E1 is not applied to the sensor device 10 .

[0054] Figure 4 1 is a diagram showing a state where an external electric field E1 in a negative direction is applied to the sensor device 10. The electric lines of force of the external electric field E1 in the negative direction extend in a direction from the substrate 11 toward the channel layer 13. The electric lines of force of the external electric field E1 enter the sensor device 10 from the second surface 11B of the substrate 11 and flow out from the input / output region 10a to the outside.

[0055] The external electric field E1 passing through the second surface 11B of the substrate 11 of the sensor device 10 causes electrons in the conduction band near the Fermi level of the conduction band of the channel layer 13 to move to the trap level band at the interface of the dielectric layer 12. The difference between the energy level of the conduction band and the energy level in the trap level band disappears due to an inelastic scattering process caused by lattice vibration or the like.

[0056] The electrons in the trap level band that move to the interface of the dielectric layer 12 generate an internal electric field E2 in the sensor device 10. The internal electric field E2 acts on the channel layer 13, and the Fermi level of the channel layer 13 changes. Due to the change in the Fermi level of the channel layer 13, the magnitude of the drain current flowing through the channel region 131 between the source electrode 14 and the drain electrode 15 changes.

[0057] The sensor device 10 can measure the magnitude of the external electric field E1 based on the magnitude of the change in the drain current value with reference to the drain current value when the external electric field E1 is not applied to the sensor device 10 .

[0058] Figure 5 It is a diagram showing the relationship between the sensitivity of the sensor device 10 and the electric field strength of the external electric field. Figure 5 The relationship shown is obtained by placing parallel plates 3 cm apart to sandwich the sensor device 10 and changing the voltage applied between the parallel plates. The sensitivity of the sensor device 10 represents the rate of change of the drain current value relative to the drain current value when the external electric field E1 is not applied to the sensor device 10.

[0059] The measurement result C1 shows the relationship between the sensitivity of the sensor device 10 having the channel layer 13 of MoS2 and the electric field strength of the external electric field. When a positive external electric field is applied to the sensor device 10, the sensitivity increases as the magnitude of the external electric field increases. In addition, when a negative external electric field is applied to the sensor device 10, the sensitivity also increases as the magnitude of the absolute value of the external electric field increases.

[0060] Figure 5 The measurement results C2 of a reference sensor device having a channel layer in which graphene is sandwiched between hexagonal boron nitride on top and bottom, and C3 of a reference sensor device having a channel layer of graphene are shown. The measurement results C2 and C3 also show the same relationship as C1.

[0061] C1 shows much greater sensitivity than C2 and C3. For example, in the case of an electric field strength of 16 kV / m, the sensitivity of C1 is about 7 times that of C3.

[0062] The sensitivity of the sensor device 10 depends on the state density of carriers and the mobility of carriers. The electron mobility of graphene is about 2000 cm 2V-1s-1. The electron mobility of MoS2 is 1 to 10 cm 2V-1s-1. The electron mobility of MoS2 is 1 / 2000 to 1 / 200 of that of graphene, which means that the sensitivity is about 7 times higher.

[0063] The reason why the sensor device 10 of the present embodiment exhibits high sensitivity is considered to be that the state density near the Fermi level of the channel layer 13 is much higher than that of graphene.

[0064] By using a channel layer having a high state density at the Fermi level, the measurement sensitivity for measuring the external electric field is high.

[0065] In addition, the sensor device 10 has the following advantages compared to conventional mechanical sensor devices. The size of a mechanical sensor device is several tens of centimeters and the weight is several kilograms, so its installation location is restricted. On the other hand, even if the sensor device 10 is modularized in a manner with a measuring function, the size is at most a few centimeters and the weight is at most a few grams, so the restrictions on the installation location of the sensor device 10 are greatly alleviated. In addition, since the mechanical sensor device has a drive unit, it is possible that a failure may occur and maintenance is required. On the other hand, the sensor device 10 is a semiconductor sensor, and the possibility of failure is greatly reduced. In addition, the mechanical sensor device consumes a lot of power and requires a power supply device such as an AC power supply. On the other hand, since the sensor device 10 consumes little power, it can be driven by a simple power supply device such as a battery.

[0066] Figure 6FIG. 2 is a diagram showing a sensor device 20 according to a modification of the first embodiment. In the sensor device 20 according to this modification, a second dielectric layer 16 is disposed on the second surface 13B of the channel layer 13 . The second dielectric layer 16 has electrical insulating properties and has a function of protecting the channel layer 13 .

[0067] The second dielectric layer 16 has a first surface 16A and a second surface 16B. The first surface 16A is disposed on the channel layer 13, and the second surface 16B is exposed to the outside. The second surface 16B functions as an input / output region 10b for inputting or outputting the external electric field E1 to the sensor device 10. The electric lines of force of the external electric field E1 enter the sensor device 10 from the input / output region 10b and flow out to the outside from the second surface 11B of the substrate 11.

[0068] As the second dielectric layer 16 , from the viewpoint of protecting the channel layer 13 , a dielectric such as silicon dioxide, aluminum oxide, or silicon nitride can be used.

[0069] Furthermore, by using a material with a high dielectric constant as the second dielectric layer 16, an external electric field can be amplified to act on the channel layer 13. As a material capable of amplifying an external electric field, for example, silicon dioxide, silicon nitride, zirconium dioxide, or hafnium dioxide can be used.

[0070] According to the sensor device of this modification, the external electric field can be amplified by the second dielectric layer 16, thereby improving the measurement sensitivity of the external electric field. In addition, according to the sensor device of this embodiment, the same effects as those of the first embodiment can be obtained.

[0071] Below, refer to Figure 7 (A) and Figure 7 (B) will describe a second embodiment of the sensor device. The descriptions of the first embodiment described in detail are appropriately applied to points not particularly described in the second embodiment. In addition, the same reference numerals are attached to the same components.

[0072] Figure 7 (A) represents a second embodiment of the sensor device disclosed in this specification. Figure 7 (B) is a cross-sectional view of the X2-X2 line, Figure 7 (B) is a top view. Figure 7 (A) represents a state where an external electric field in a positive direction is applied to the sensor device from the outside.

[0073] The sensor device 30 of this embodiment is different from the first embodiment in that it includes a second dielectric layer 17 disposed on the channel layer 13, and a gate electrode 18 disposed on the second dielectric layer 17 and having an atomic layer material film of one or more atomic layers. The sensor device 30 has the same configuration as the first embodiment except that it includes the second dielectric layer 17 and the gate electrode 18.

[0074] In the sensor device 30, the Fermi level Efc of the channel layer 13 can be changed by applying a gate voltage to the gate electrode 18. The distribution of the state density of carriers also moves with the movement of the Fermi level Efc. In this embodiment, the magnitude of the gate voltage is assumed to be a magnitude to the extent that the shape of the distribution of the state density of carriers does not change.

[0075] Figure 3 (C) is a diagram showing the relationship between energy levels when a voltage is applied to the gate electrode 18. By applying a voltage to the gate electrode 18, the position of the Fermi level Efc of the channel layer 13 rises compared to the first embodiment. As a result, the number of electrons in the conduction band below the Fermi level Efc of the channel layer 13 increases. Figure 3 (C) shows a state before the electrons in the channel layer 13 move to the trap level band of the dielectric layer 12 .

[0076] Therefore, in the sensor device 30 of the present embodiment, more carriers can move between the channel layer 13 and the trap level band of the dielectric 12 than in the first embodiment. As a result, the sensitivity of the sensor device 30 is improved.

[0077] The second dielectric layer 17 is preferably thin and has excellent electrical insulation. Since the second dielectric layer 17 is thin, the external electric field E1 and the gate voltage can be applied to the channel layer 13. In addition, since the second dielectric layer 17 has excellent electrical insulation, when the gate voltage is applied to the gate electrode 18, the current can be prevented from flowing between the gate electrode 18 and the channel layer 13.

[0078] The second dielectric layer 17 preferably has an atomic layer material film of one or more atomic layers, from the viewpoint of transmitting the external electric field E1 and applying a gate voltage to the channel layer 13. Specifically, the second dielectric layer 17 preferably has an atomic layer material film of 1 to 30 atomic layers.

[0079] The second dielectric layer 17 preferably does not substantially allow a tunnel current to flow between the gate electrode 18 and the channel layer 13 when a gate voltage is applied to the gate electrode 18. The second dielectric layer 17 does not substantially allow a tunnel current to flow between the gate electrode 18 and the channel layer 13, which means that when a gate voltage is applied to the gate electrode 18, the tunnel current flowing between the gate electrode 18 and the channel layer 13 is 100 pA or less.

[0080] From the above viewpoint, the second dielectric layer 17 preferably has an atomic layer material film having one or more atomic layers formed of hexagonal boron nitride, molybdenum disulfide or tungsten disulfide. The second dielectric layer 17 can also be formed using oxides such as SiO2, but is preferably formed using an atomic layer material film from the viewpoint of obtaining high electrical insulation.

[0081] The gate electrode 18 has conductivity and allows the external electric field E1 to pass through. From such a viewpoint, the gate electrode 18 is preferably formed of an atomic layer material film having one or more atomic layers. For example, the gate electrode 18 preferably has an atomic layer material film having 1 to 5 atomic layers. Specifically, the gate electrode 18 preferably has an atomic layer material film having 1 to 5 atomic layers formed of graphene.

[0082] The surface of the gate electrode 18 exposed to the outside functions as an input / output region 10c for inputting or outputting the external electric field E1 to the sensor device 10. The electric lines of force of the external electric field E1 enter the sensor device 10 from the input / output region 10c and flow out from the second surface 11B of the substrate 11 to the outside.

[0083] Figure 8 is a flow chart of measuring an external electric field using the sensor device of the second embodiment. Figure 8 A method of measuring the external electric field E1 using the sensor device 30 is described.

[0084] First, while changing the gate voltage applied to the gate 18, the drain current value flowing between the source 14 and the drain 15 is measured, and the first gate voltage ( Figure 8 Step S101). Depending on the direction of the external electric field E1 and the polarity of the channel layer 13, the drain current value may be a maximum value or a minimum value.

[0085] Here, the first gate voltage at which the drain current value shows the maximum or minimum value may be obtained when no external electric field is applied to the sensor device 10. The state where no external electric field is applied to the sensor device 10 includes the state where an unexpected external electric field is applied to the sensor device 10.

[0086] Alternatively, the first gate voltage at which the drain current value shows a maximum value or a minimum value may be obtained when a predetermined external electric field is applied to the sensor device 10. For example, a plurality of gate voltages at which the drain current value shows a maximum value or a minimum value may be obtained when a plurality of external electric fields of different magnitudes are applied. Furthermore, an average value of a plurality of gate voltages may be used as the first gate voltage.

[0087] Fig. 91 is a diagram for explaining a method of measuring an external electric field using a sensor device according to a second embodiment. The horizontal axis represents the gate voltage and the vertical axis represents the drain current value. When the gate voltage is changed, the drain current value shows a maximum value. The gate voltage at which the drain current value shows a maximum value is the first gate voltage.

[0088] Then, the measuring gate voltage is determined based on the first gate voltage. For example, the first gate voltage may be used as the measuring gate voltage. In addition, a voltage of 70% to 100% of the first gate voltage may be used as the measuring gate voltage. The measuring gate voltage is an example of the second gate voltage.

[0089] Next, when the external electric field to be measured is applied to the sensor device 10, the drain current value flowing between the source electrode 14 and the drain electrode 15 is measured while the gate voltage for measurement is applied to the gate electrode 18. The electric field strength ( Figure 8 By measuring the external electric field input or output from the input / output region 10c while applying the measurement gate voltage, the electric field intensity of the external electric field E1 can be obtained in the state with the highest sensitivity.

[0090] For example, in a state where a gate voltage for measurement is applied to the gate electrode 18, the value of the drain current flowing between the source electrode 16 and the drain electrode 17 is measured for each state where a plurality of external electric fields of different electric field strengths are applied. Thus, the relationship between the drain current value and the electric field strength of the external electric field (the relationship between the current and the electric field strength) is obtained.

[0091] Then, by referring to the relationship between current and electric field intensity, the electric field intensity corresponding to the measured drain current value is obtained to obtain the electric field intensity of the external electric field E1.

[0092] Below, refer to Figure 10 to Figure 12 Preferred embodiments of the method for manufacturing the sensor device according to the first and second embodiments described above will be described.

[0093] First, if Fig.10 As shown in (A), a substrate 11 having a first surface 11A and a second surface 11B is prepared. As the substrate 11, for example, a silicon substrate, silicon carbide, a semiconductor substrate such as a compound semiconductor, etc. can be used.

[0094] Then, if Fig.10As shown in (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, it is preferred to form a silicon dioxide layer as the dielectric layer 12. The silicon dioxide layer is formed using a thermal oxidation method or a CVD method. When the silicon dioxide layer is formed using a thermal oxidation method as the dielectric layer 12, the interface between the silicon dioxide layer and silicon becomes the first surface 11A. From the viewpoint of increasing the number of trap energy levels, the surface of the dielectric layer 12 may be irradiated with oxygen ions, nitrogen ions, or helium ions.

[0095] Then, if Fig.11 As shown in (A), channel layer 13 is formed on dielectric layer 12. Channel layer 13 has first surface 13A and second surface 13B. First surface 13A is arranged on dielectric layer 12, and second surface 13B is exposed to the outside.

[0096] As the channel layer 13, an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal dichalcogenide is formed. The channel layer 13 can be formed, for example, using a lift-off method or a CVD method. From the viewpoint of obtaining a high-quality atomic layer material film with few defects, it is preferred to form the channel layer 13 using a lift-off method.

[0097] The thickness of the channel layer 13 is preferably in the range of 1 to 20, more preferably 1 to 4 atomic layers. The thickness and quality of the channel layer 13 are measured using, for example, Raman spectroscopy.

[0098] The channel layer 13 can be formed using molybdenum (Mo), tungsten (W) or niobium (Nb) as a transition metal and sulfur (S), selenium (Se) or tellurium (Te) as a chalcogen. As two-dimensional transition metal dichalcogenides, for example, MoS2, MoSe2, WS2, WSe2, NbS2 and NbSe2 can be used.

[0099] Then, if Fig.11 As shown in (B), the source electrode 14 and the drain electrode 15 are formed on the channel layer 13, thereby obtaining the sensor device 10 of the first embodiment. The source electrode 14 and the drain electrode 15 can be formed as a stacked body of chromium and gold.

[0100] Then, if Fig.12 As shown in (A), a second dielectric layer 17 is formed on the second surface 13B of the channel layer 13. The second dielectric layer 17 is formed as an atomic layer material film having one or more atomic layers using, for example, an electrically insulating material. The second dielectric layer 17 can be formed using a lift-off method or a CVD method. From the viewpoint of obtaining an atomic layer material film of good quality with few defects, it is preferred to form the second dielectric layer 17 using a lift-off method. Specifically, the second dielectric layer 17 is formed as an atomic layer material film having one or more atomic layers formed of hexagonal boron nitride, molybdenum disulfide, or tungsten disulfide.

[0101] Then, if Fig.12 As shown in (B), a gate electrode 18 is formed on the second dielectric layer 17 to obtain the sensor device 30 of the second embodiment. The gate electrode 18 can be formed as a stack of chromium and gold. As the gate electrode 18, for example, a conductive material is used to form an atomic layer material film having one or more atomic layers. The gate electrode 18 can be formed using a lift-off method or a CVD method. From the viewpoint of obtaining a high-quality atomic layer material film with few defects, it is preferred to form the gate electrode 18 using a lift-off method. Specifically, the gate electrode 18 is formed as an atomic layer material film having one or more atomic layers formed of graphene.

[0102] In the present invention, the sensor device capable of measuring electric field strength and the method of measuring external electric field in the above-mentioned embodiments may be appropriately changed without departing from the gist of the present invention. In addition, the constituent elements of one embodiment may be appropriately applied to other embodiments. Explanation of symbols

[0103] 10Sensor device 10a, 10b, 10c Input and output areas 11 substrate 11A first side 11B Side 2 12 Dielectric layer (first dielectric layer) 13Channel layer 13A first page 13B Side 2 131 Channel area 14 Source electrode (first electrode) 15 drain electrode (second electrode) 16 Second dielectric layer 17 Second dielectric layer 18. Gate electrode.

Claims

1. A sensor device capable of measuring the electric field strength of an external electric field, characterized in that: have: a first dielectric layer; a channel layer, which is directly disposed on the first dielectric layer, has a channel region, and has an atomic layer material film of one or more atomic layers formed of a two-dimensional transition metal dichalcogenide; as well as A first electrode and a second electrode, which are in electrical contact with the channel layer and are arranged to face each other with the channel region sandwiched therebetween, The channel layer has a first surface and a second surface, the first surface is arranged on the first dielectric layer, the second surface is exposed to the outside, or the second dielectric layer is arranged on the second surface, The Fermi level of the channel layer is located in a conduction band or a valence band of the channel layer, and the Fermi level of the channel layer is located above a trap level band of an interface with the channel layer in the first dielectric layer.

2. The sensor device according to claim 1, characterized in that The channel layer has an atomic layer material film formed of one or more atomic layers.

3. The sensor device according to claim 1, characterized in that The channel layer includes molybdenum, tungsten, or niobium as a transition metal, and includes sulfur, selenium, or tellurium as a chalcogen.

4. The sensor device according to claim 1, characterized in that The second dielectric layer is disposed on the second surface of the channel layer. A gate electrode is disposed on the second dielectric layer. The gate electrode has an atomic layer material film of one or more atomic layers.

5. The sensor device according to claim 4, characterized in that The second dielectric layer includes one or more atomic layers of an atomic layer material film.

6. The sensor device according to claim 4, characterized in that The second dielectric layer substantially prevents a tunnel current from flowing between the gate electrode and the channel layer.

7. The sensor device according to claim 4, characterized in that The second dielectric layer has an atomic layer material film having one or more atomic layers formed of hexagonal boron nitride, molybdenum disulfide, or tungsten disulfide.

8. The sensor device according to claim 4, characterized in that The gate electrode has an atomic layer material film having one or more atomic layers formed of graphene.

9. A method for measuring an external electric field using the sensor device according to claim 1, characterized in that: include: 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; as well as The electric field intensity of the external electric field is obtained based on the current value.

10. A method for measuring an external electric field using the sensor device according to claim 4, characterized in that: include: while changing the gate voltage applied to the gate electrode, measuring the current value flowing between the first electrode and the second electrode, and obtaining a first gate voltage at which the current value shows a maximum value or a minimum value; as well as When a second gate voltage determined based on the first gate voltage is applied to the gate electrode, a current value flowing between the first electrode and the second electrode when an external electric field is applied to the sensor device is measured, and the electric field strength of the external electric field is calculated based on the current value.

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