WO2021200570A1 - Sensor device, production method for sensor device, and gas determination system - Google Patents

Abstract

[Problem] To provide a sensor device, a production method for the sensor device, and a gas determination system that make it possible to increase the sensitivity with which gases are detected. [Solution] The sensor device according to one embodiment of the present invention comprises a gate electrode, an insulating film, a graphene layer, a source electrode and a drain electrode, and a conductive porous layer. The insulating film is formed on the gate electrode. The graphene layer is formed on the insulating film. The source electrode and the drain electrode are arranged on the insulating film so as to be opposite each other with the graphene layer therebetween. The porous layer is formed on the graphene layer.

Description

Sensor device, manufacturing method of sensor device and gas judgment system

The present invention relates to a sensor device, a method for manufacturing the sensor device, and a gas determination system.

The sensor described in Patent Document 1 has a gate electrode, an insulating film provided on the gate electrode, a graphene film provided on the insulating film, a first electrode, and a second electrode. It has an FET structure. In the sensor described in Patent Document 1, a constant voltage is applied between the first electrode and the second electrode before the measurement of the detection target, the gate voltage of the gate electrode is increased or decreased, and the current value Id is measured. After that, the same operation is performed during the measurement of the determination target. Then, the change ΔVg of the gate voltage Vg at which the current value Id is minimized before and after the measurement is used for the determination evaluation of the determination target.

JP-A-2018-163146

It is desired that the gas sensor determines the type of gas with high accuracy.
In view of the above circumstances, an object of the present invention is to provide a sensor device capable of increasing the detection sensitivity of gas, a method for manufacturing the sensor device, and a gas determination system.

The sensor device according to one embodiment of the present invention includes a gate electrode, an insulating film, a graphene layer, a source electrode and a drain electrode, and a conductive porous layer.
The insulating film is formed on the gate electrode.
The graphene layer is formed on the insulating film.
The source electrode and the drain electrode are arranged on the insulating film so as to face each other via the graphene layer.
The porous layer is formed on the graphene layer.

The gas determination system according to one embodiment of the present invention includes a sensor device and an information processing device.
The sensor device includes a gate electrode, an insulating film formed on the gate electrode, a graphene layer formed on the insulating film, and a source electrode arranged so as to face each other on the insulating film via the graphene layer. It also has a drain electrode and a conductive porous layer formed on the graphene layer.
The information processing apparatus determines the gas adsorbed on the porous layer based on the measurement result of the current flowing between the source electrode and the drain electrode with the control unit that controls the voltage applied to the gate electrode. It has a determination unit and a determination unit.

According to the present invention, the gas detection sensitivity can be increased.

It is a schematic diagram which shows the structure of the gas determination system which concerns on embodiment of this invention. It is a schematic diagram which shows the structure of the sensor device which constitutes a part of the said gas determination system. It is a partially enlarged schematic diagram near the channel layer explaining the state _{of the graphene layer and the CO 2} molecule when the first voltage and the second voltage are applied to the gate electrode. It is the schematic which shows the structure of a channel layer. It is a graph which shows the change of the current which flows between a source electrode and a drain electrode when a sweep voltage is applied to a gate electrode after the application of the 1st voltage and after the application of the 2nd voltage in the gas determination system. The amount of charge transfer between the channel layer and the gas molecule in the range of CNPD when _{CO 2} , C ₆ H ₆ , CO, NH ₃ , and O _{2 are used as the gas is shown.} It is a graph which shows the result of having measured the range of CNPD of acetone and ammonia as a gas by shaking a gas concentration using the said gas determination system. It is a flow figure explaining the schematic procedure for gas determination in the said gas determination system. It is a flow chart explaining the gas determination method. It is a figure which shows the signal waveform of the 1st voltage, the 2nd voltage, and the sweep voltage in the gas sensor of the said gas determination system. FIG. 11 is a diagram showing the experimental results of the graphene sensor. (A) is an experimental result of a gas sensor having a channel layer not decorated with activated carbon, and (B) is an experimental result of a gas sensor having a channel layer decorated with activated carbon. (A) is an experimental result showing the detection ability for ammonia gas (5 ppb) in the presence of air in a gas sensor having a channel layer decorated with activated carbon, and (B) is an experimental result in the presence of air in a gas sensor having a channel layer decorated with activated carbon. It is an experimental result which shows the detection ability with respect to ammonia gas (500 ppt). It is schematic cross-sectional view of each step explaining the manufacturing method of the sensor device which concerns on embodiment of this invention. It is schematic cross-sectional view of each step explaining the manufacturing method of the sensor device which concerns on embodiment of this invention. It is schematic cross-sectional view of each step explaining the manufacturing method of the sensor device which concerns on embodiment of this invention. It is schematic cross-sectional view of each step explaining the manufacturing method of the sensor device which concerns on embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Overview of gas judgment system]
FIG. 1 is a schematic diagram showing the configuration of a gas determination system. FIG. 2 is a schematic view showing the configuration of the sensor 10 that constitutes a part of the gas determination system.

As shown in FIG. 1, the gas determination system 1 includes a sensor device 2, an information processing device 4, a display device 5, and a storage unit 6.
The sensor device 2 includes a storage chamber 20, a sensor 10 (sensor device), a UV (ultraviolet) light source 23, and a heating unit 26.

The storage chamber 20 houses the sensor 10, the UV light source 23, and the heating unit 26. The accommodation chamber 20 has an intake port 21 for sucking gas from the outside and an exhaust port 22 for exhausting the gas introduced into the accommodation chamber 20 from the accommodation chamber 20 to the outside. The intake port 21 is provided with a valve 24 for adjusting the inflow of gas into the accommodation chamber 20, and the exhaust port 22 is provided with a valve 25 for adjusting the outflow of gas in the accommodation chamber 20 to the outside.

The UV light source 23 emits ultraviolet rays (UV) to irradiate the sensor 10. The channel layer 15 is cleaned by irradiating the channel layer 15 of the sensor 10, which will be described later, with UV.
The heating unit 26 is, for example, a heater and heats the sensor 10.

As shown in FIG. 2, the sensor 10 has a gate electrode 13, an insulating film 14, a source electrode 11, a drain electrode 12, and a channel layer 15.
The gate electrode 13 is made of highly doped conductive silicon.
The insulating film 14 is formed on the gate electrode 13. The insulating film 14 is composed of _{, for example, SiO 2.}
The source electrode 11 and the drain electrode 12 are formed on the insulating film 14 and are arranged to face each other via the channel layer 15. The source electrode 11 and the drain electrode 12 are composed of, for example, a laminated structure of a Cr film and an Au film.

The channel layer 15 is formed on the insulating film 14 and is arranged to face the gate electrode 13 via the insulating film 14. As shown in FIG. 4, the channel layer 15 has a graphene layer 16 and a porous layer 17 formed on the graphene layer 16.

In the present embodiment, the graphene layer 16 is composed of a single layer film, but may be a multilayer film. Further, a part of the multilayer film may be composed of a conductive material other than graphene.

The porous layer 17 is formed by decorating the surface of the graphene layer 16 with activated carbon. The material constituting the porous layer 17 is not limited to activated carbon, and may be more porous than the graphene layer 16 and may have conductive properties similar to the graphene layer 16. As the conductive material constituting the porous layer 17, for example, a carbon-based material, a conductive polymer, conductive ceramics, or porous silicon may be used.

Since the porous layer 17 functions to promote gas adsorption, the porosity increases the adsorption surface area, and since it has many dangling bonds, it can efficiently adsorb gas.
Since the porous layer 17 has conductive properties, the adsorption surface area is larger and the surface has many dangling bonds as compared with the case where a film having no conductive properties is provided on the graphene layer 16 as an adsorption film. Therefore, the adsorption of gas molecules is promoted, and the shift amount of the charge neutral point becomes large.

Preferably, the porous layer 17 is made of the same carbon-based material as the graphene layer 16. A carbon-based material is a substance containing carbon as a main component. In this embodiment, the porous layer 17 is porous and is a carbon-based material, that is, activated carbon.
As a result, as compared with the case where a non-carbon material is used for the porous layer 17, the formation of a potential barrier formed between different materials having different electron affinities is suppressed, and charge neutrality is facilitated in order to facilitate charge transfer. The difference between the points becomes large.

The thickness of the porous layer 17 is not particularly limited, and may be the same as the thickness of the graphene layer 16, or may be thinner or thicker than the thickness of the graphene layer 16. Typically, the graphene layer 16 has a thickness of 0.35 nm and the porous layer 17 has a thickness of 30 nm.
The porous layer 17 is formed so as to cover the entire surface of the graphene layer 16, but is not limited to this, and may be formed so as to cover at least a part of the surface of the graphene layer 16.

As shown in FIG. 1, the information processing device 4 includes an acquisition unit 41, a determination unit 42, an output unit 43, and a control unit 44.
The acquisition unit 41 acquires change information of the current flowing between the source electrode 11 and the drain electrode 12. Hereinafter, the current flowing between the source electrode 11 and the drain electrode 12 may be referred to as a drain current.
The determination unit 42 determines the type of gas by using the current change information acquired by the acquisition unit 41. Specifically, the information processing device 4 acquires current change information for each of a plurality of different types of gas in advance and stores it in the storage unit 6. The determination unit 42 identifies and determines the type of gas detected by the sensor 10 with reference to the current change information stored in the storage unit 6. The gas concentration can also be determined by the determination unit 42. Details will be described later.
The output unit 43 outputs the current change information acquired by the acquisition unit 41 and the determination result such as the type and concentration of the gas determined by the determination unit 42 to the display device 5.
As shown in FIG. 2, the control unit 44 controls the voltage applied to the gate electrode 13 of the sensor 10.

The display device 5 has a display unit, and displays the type and concentration of gas output from the information processing device 4 on the display unit. The user can grasp the gas determination result by checking the display unit.
The storage unit 6 acquires in advance current change information for each of a plurality of known gases of different types detected by the gas determination system 1 and stores them as reference data. The storage unit 6 may be on a cloud server on which the information processing device 4 can communicate, or may be provided in the information processing device 4.

(Details of sensor)
The sensor 10 is a field effect transistor type sensor device.
3 (A) and 3 (B) show the channel layer 15 whose state changes depending on the voltage applied to the gate electrode 13 and the vicinity of the channel layer 15 for explaining the charge state _{of CO 2 as an example of the gas adsorbed on the channel layer 15.} It is a partially enlarged schematic diagram.

Figure 3 (A) shows a case where the gate electrode 13 and the first tuning voltage V _T1 as a first voltage is applied for a predetermined time. In the present embodiment, the first tuning voltage V _T1 is a constant voltage at a predetermined time, a -40 V. The value of the first tuning voltage V _T1 is not limited to -40 V, by applying a first tuning voltage V _T1, the negative charge is supplied to the channel layer 15, channel layer 15 valence band Any voltage value may be used as long as it has.
Figure 3 (B) shows when the gate electrode 13 and the second tuning voltage V _T2 of the second voltage is applied for a predetermined time. In the present embodiment, the second tuning voltage _VT2 is a constant voltage at a predetermined time, which is 40V. The value of the second tuning voltage V _T2 is not limited to 40V, by applying a second tuning voltage V _T2, the positive charges are supplied to the channel layer 15, channel layer 15 has a conduction band Any voltage value like this may be used.
In the present embodiment, the first and second tuning voltages are set to a constant voltage, and an example in which the voltage changes in a rectangular wave shape as shown in FIG. 11 is given, but the present invention is not limited to this. For example, the voltage value may fluctuate slightly within a predetermined time, for example, the rise and fall of the voltage becomes dull, the voltage value changes with a slight gradient, and the channel layer 15 changes the valence band or the conduction band by application. It suffices as long as it has a voltage value.

Both the channel layer 15 when the first tuning voltage is applied and the channel layer 15 when the second tuning voltage is applied attract gas. As shown in FIG. 3, when the first tuning voltage is applied and when the second tuning voltage is applied, the gas molecules adsorbed on the channel layer 15, here the CO ₂ molecules, are the distances and bond angles from the channel layer 15. The combined state is different. As a result, CO ₂ functions as a donor _{when the first tuning voltage VT1 is applied.} When the second tuning voltage _{VT2 is} applied, CO ₂ functions as an acceptor.

When gas is supplied to the channel layer, it is considered that the number of naturally adsorbed gas molecules is small in the channel layer when no voltage is applied to the gate electrode.
On the other hand, in the present embodiment, by applying the first tuning voltage and the second tuning voltage to the gate electrode, the gas molecules that have come to the vicinity of the channel layer are indicated by arrows in FIG. It is guided to the surface of the channel layer by the electric field, and gas adsorption is accelerated.
Further, in the present embodiment, as shown in FIG. 3, by applying the first tuning voltage and the second tuning voltage, the direction of the electric field near the surface of the channel layer is changed, and the gas molecules to the channel layer are different. The binding state of can be changed.

The values of the preferred first tuning voltage _VT1 and the second tuning voltage _VT2 can be appropriately set depending on the thickness of the insulating film 14. In this embodiment, an insulating film 14 having a thickness of 285 nm is used, and in this case, a voltage of about −40 V (40 V) is required so that the channel layer 15 has a valence band (conduction band).
Further, in order to channel layer 15 to confirm that the switching between the conduction band and the valence band, a first tuning voltage V _T1 and the second tuning voltage V _T2 is negative, the voltage on both sides of the positive side It is preferable to shake. Further, it is more preferable to shake the voltage so that the absolute values of the negative and positive voltages are the same.
The application time of each of the first tuning voltage _VT1 and the second tuning voltage _VT2 is several seconds to several minutes.

FIG. 5 shows the gate electrode 13 when the sweep voltage is applied to the gate electrode 13 after _{the first tuning voltage VT1} is applied for a predetermined time in the gas determination system 1 _{and after the second tuning voltage VT2} is applied for a predetermined time. It is a graph which shows the change of the current which flows between a source electrode 11 and a drain electrode 12 when a sweep voltage is applied to.
The voltage applied to the gate electrode 13 is controlled by the control unit 44.
The sweep voltage changes in a range of a first tuning voltage and a second tuning voltage different from the first tuning voltage. In this embodiment, a sweep voltage that linearly changes the voltage from −40 V to 40 V in about 1 minute is used, and the sweep voltage is a voltage that changes on both the positive and negative sides.

_{In the present embodiment, after applying the first tuning voltage VT1} to the gate electrode 13 of the sensor 10 to which the gas is supplied for a _{predetermined time, the drain current Id} (first current) while applying the sweep voltage to the gate electrode 13 I _d1 ) is measured.
The solid line curve 51 shown in FIG. 5 shows the change characteristic of _{the first current I d1.} In the obtained curve 51, _{the point when the first current I d1} becomes the minimum value is referred to as the first charge neutral point 31. The gate voltage value when the first current I _d1 becomes the minimum value is referred to as a first gate voltage.
As described above, the channel layer 15 has a valence band by applying the first tuning voltage _{VT1 to the gate electrode 13.} As a result, the gas is sufficiently attracted to the channel layer 15 and the gas becomes a donor.

_{Further, in the present embodiment, after applying the second tuning voltage VT2} to the gate electrode 13 of the sensor 10 to which the gas is supplied for a _{predetermined time, the drain current Id} (second) while applying the sweep voltage to the gate electrode 13. The current I _d2 ) is measured.
The long broken line curve 52 shown in FIG. 5 shows the change characteristic of _{the second current I d2.} In the obtained curve 52, _{the point when the second current I d2} becomes the minimum value is referred to as the second charge neutral point 32. The gate voltage value when the second current I _d2 becomes the minimum value is referred to as a second gate voltage.

In FIG. 5, the broken line curve 50 having a short line length is a curve located at the center of the curve 51 and the curve 52 in the horizontal axis direction. The point at which the current I _{d on the} curve 50 becomes the minimum value is defined as the center point 30.

As shown in FIG. 5, the _{curve 52 showing the characteristics of the second current I d2} with respect to the sweep voltage (gate voltage Vg) is the curve 51 showing the characteristics _{of the first current I d1 with respect to the sweep voltage (gate voltage Vg).} It almost matches the shape moved in the horizontal axis direction.
In FIG. 5, V _CNP indicates the gate voltage value when the charge neutrality point is taken, and ΔV _CNP indicates the difference between the first gate voltage and the second gate voltage.

Here, the first gate voltage at the first charge neutral point 31 and the second gate voltage at the second charge neutral point 32 are unique to each type of gas adsorbed on the channel layer 15. The band indicating the range from the gate voltage of 1 to the second gate voltage is different for each type of gas. It is considered that this is because the bonding state of the gas attracted to the channel layer 15 and functioning as an acceptor or donor and the channel layer 15 differs depending on the type of gas.

FIG. 6 is a diagram showing that the band indicating the range from the first gate voltage to the second gate voltage differs depending on the type of gas. In FIG. 6, bands in a total of five types of gases _{, CO 2} (carbon dioxide), C ₆ H ₆ (benzene), CO (carbon monoxide), NH ₃ (ammonia), and O _{2 (oxygen), are shown.} There is. FIG. 6 shows the charge state of the channel layer in the range of CNPD (Charge Neutrality Point Disparity: | ΔVCNP | in FIG. 5). CNPD shows the difference between the first charge neutral point 31 and the second charge neutral point 32, and corresponds to the band.

In FIG. 6, the strip extending in the vertical direction indicates a band indicating a range from the first gate voltage to the second gate voltage. The upper part of the strip corresponds to the first gate voltage at the second charge neutral point 32, and the lower part corresponds to the second gate voltage at the first charge neutral point 31. The center point 30 is located at the center of a band extending in the vertical direction. In each band, the upper half of the center point 30 indicates the range in which the gas is an acceptor, and the lower half indicates the range in which the gas is a donor.

As shown in FIG. 6, the first gate voltage and the second gate voltage are different depending on the type of gas, and the bandwidth and the band range are different. Therefore, the type of gas can be determined by using this band data.
For example, in the present embodiment, band data of a plurality of known gases are acquired in advance and stored in the storage unit 6. Then, by referring to the data stored in the storage unit 6, the type of gas can be determined from the band data obtained for the unknown gas.
In this way, it is possible to determine the type of gas by acquiring the change characteristics of the drain current corresponding to the sweep voltage after applying the two-value tuning voltage of -40V and 40V as data.

Further, the band indicating the range from the first gate voltage to the second gate voltage changes substantially linearly according to the change in the gas concentration. FIG. 7 shows the first gate voltage at the first charge neutral point 31 obtained by applying a sweep voltage after applying the first tuning voltage by varying the concentration of the gas, and sweeping after applying the second tuning voltage. It is a figure which shows the result of having measured the 2nd gate voltage at the 2nd charge neutral point 32 obtained by applying a voltage. In the figure, the bar graph shows the gate voltage value at the center point 30. The straight line extending in the vertical direction indicates the band from the first gate voltage to the second gate voltage.
FIG. 7 (A) shows the case where acetone is used as the gas, and FIG. 7 (B) shows the case where ammonia is used, and the results of varying the concentration in the range of 1 to 200 ppm are shown.

As shown in FIG. 7, the band indicating the range from the first gate voltage to the second gate voltage changes substantially linearly according to the concentration of the gas to be determined, and the determination of the gas concentration using the band is performed. Is possible.
For example, in the present embodiment, the data of known gas bands having different concentrations are acquired in advance and stored in the storage unit 6. Then, by referring to the data of the storage unit 6, the gas concentration can be determined from the band data obtained from the unknown gas.

[Gas judgment method]
The gas determination method in the gas determination system 1 will be described with reference to FIGS. 8 to 11.
FIG. 8 is a flow chart illustrating a schematic procedure for gas determination in the gas determination system 1.
FIG. 9 is a flow chart illustrating a gas determination method in the information processing apparatus 44.
FIG. 10 is a diagram showing signal waveforms of a _{first tuning voltage VT1} , a second tuning voltage _VT2 , and a sweep voltage applied to the gate electrode. As shown in FIG. 10, the first tuning voltage _VT1 and the second tuning voltage _VT2 are step functions with respect to time.

First, as shown in FIG. 8, gas is supplied into the accommodation chamber 20 (S1). The pressure inside the containment chamber 20 is normal.

Next, UV is irradiated from the UV light source 23 toward the sensor 10 and the inside of the accommodation chamber 20 for 1 minute (S2).
By performing UV irradiation, the gas is efficiently adsorbed on the channel layer. _{This is because O 2} , H ₂ O, etc. are removed from the surface of the channel layer by UV irradiation (cleaning effect), and the movement between the adsorption of gas molecules on the surface of the channel layer and the photoexcited desorption. It is considered that this is because the equilibrium is guided and the number of effective adsorption sites for gas in the channel layer increases, and the adsorption is accelerated by the state change (ionization, etc.) of the adsorbed molecules.

Next, the sensor 10 is heated by the heating unit 26 (S3). The heating temperature is preferably 95 ° C. or higher. In this embodiment, the sensor 10 is heated to a heating temperature of 110 ° C.
By UV irradiation and heating, obtained by applying a sweep voltage after application first tuning voltage V _T1, the curve 51 showing the variation of the first current I _d1 for sweep voltage, the second tuning voltage V _The curve 52 showing the change _{of the second current I d2} with respect to the sweep voltage obtained by applying the sweep voltage after applying T2 can be more clearly distinguished. Details will be described later.

Next, the gas determination is performed (S4). The details of the gas determination will be described below with reference to FIGS. 9 and 10.

The gas determination is started from a state in which a voltage of 5 to 10 mV is applied between the source electrode 11 and the drain electrode 12. The voltage value applied to each electrode is controlled based on the control signal from the control unit 44.
The voltage applied between the source electrode 11 and the drain electrode 12 uses the linear region of the output. If the voltage applied between the source electrode 11 and the drain electrode 12 is too high or too low, noise will be generated. Therefore, it is preferable to set the voltage to 5 to 10 mV, which suppresses the generation of noise.

As shown in FIGS. 9 and 10, when the gas determination is started, the first tuning voltage _VT1 is applied to the gate electrode 13 for a predetermined time (S41). In the present embodiment, the first tuning voltage _{V T1} of -40V is applied for several seconds to several minutes.
As a result, the channel layer 15 has a valence band, the gas is sufficiently attracted to the channel layer 15, and the gas functions as a donor.
The application time of the first tuning voltage _VT1 is appropriately set depending on the thickness of the insulating film 14 and the like. In the present embodiment, it is preferably 5 s (seconds) or more, more preferably 30 s or more, and preferably 120 s or less, further preferably 60 s or less, in a time sufficient for the channel layer 15 to have a valence band. All you need is. Further, the application time can be appropriately set to a preferable value depending on the heating temperature of the sensor 10 and the like.

Next, a sweep voltage is applied to the gate electrode 13, and the first current I _d1 flowing between the source electrode 11 and the drain electrode 12 while the sweep voltage is being applied is measured (S42). In this embodiment, the voltage is swept with a resolution of 50 mV to 100 mV, a range of 80 V, and a sweep time of 1 minute. As shown in FIG. 10, the gate voltage is gradually changed from negative to positive, such as -40V to 40V. The gate voltage may be gradually changed from positive to negative, such as from 40V to −40V.
The measurement result of the first current I _d1 with respect to the sweep voltage is acquired by the acquisition unit 41.

Next, based on the measurement result acquired by the acquisition unit 41, the determination unit 42 determines the first gate voltage, which is the gate voltage value when _{the first current I d1 becomes the minimum value (S43).} ..

Next, a second tuning voltage _VT2 is applied to the gate electrode 13 for a predetermined time (S44). In this embodiment, the second tuning voltage V _T2 of 40V is applied for several seconds to several minutes.
As a result, the channel layer 15 has a conduction band, the gas is sufficiently attracted to the channel layer 15, and the gas functions as an acceptor. The coupling state of the channel layer 15 and the gas after the application of the second tuning voltage is different from the coupling state of the channel layer 15 and the gas after the application of the first tuning voltage.
The application time of the second tuning voltage _VT2 is appropriately set depending on the thickness of the insulating film 14 and the like. In the present embodiment, it is preferably 5 s (seconds) or more, more preferably 30 s or more, and preferably 120 s or less, further preferably 60 s or less, and the time is sufficient for the channel layer 15 to have a conduction band. Just do it. Further, the application time can be appropriately set to a preferable value depending on the heating temperature of the sensor 10 and the like.

Next, a sweep voltage is applied to the gate electrode 13, and a second current I _d2 flowing between the source electrode 11 and the drain electrode 12 while the sweep voltage is being applied is measured (S45). In this embodiment, the voltage was swept with a resolution of 50 mV to 100 mV, a range of 80 V, and a sweep time of 1 minute. As shown in FIG. 10, the gate voltage is gradually changed from negative to positive, such as -40V to 40V. The gate voltage may be gradually changed from positive to negative, such as from 40V to −40V.
The measurement result of the second current I _d2 with respect to the sweep voltage is acquired by the acquisition unit 41.

Next, based on the measurement result acquired by the acquisition unit 41, the determination unit 42 determines the second gate voltage, which is the gate voltage value when _{the second current I d2 becomes the minimum value (S46).} ..

Next, the determination unit 42 determines the type and concentration of the gas by referring to the data stored in the storage unit 6 based on the first gate voltage and the second gate voltage determined in S43 and S46. It is determined (S47). In addition, although an example of determining both the type and the concentration of the gas is given here, either one may be used.

S43, S46, and S47 correspond to gas determination steps for determining gas based on the measurement results of _{the first current I d1} and the second current I _d2.
In the present embodiment, _{after the measurement of the first current I d1} of S42, a step of determining the first gate voltage V _{g1 at} which the first current I _{d1 becomes the minimum value is provided.} This may be performed at the step of determining the second gate voltage V _{g2 at} which the second current I _{d2 of the above is the minimum value.}

_{In the present embodiment, the curve 51 showing the change of the first current I d1} with respect to the sweep voltage and the curve 52 showing the change _{of the second current I d2} with respect to the sweep voltage are more clearly defined by performing UV irradiation and heating. Identifiable data is obtained. This enables more accurate gas determination.

FIG. 11 shows a series of measuring _{the first current I d1} while applying the first tuning voltage and the sweep voltage, applying the second tuning voltage, and measuring the second current I _{d2 while applying the sweep voltage.} The results of measuring the change _{of the first current I d1} with respect to the sweep voltage and the change of the second current I _d2 with respect to the sweep voltage when the above steps are repeated 5 times are shown.

In FIG. 11, the solid line is a curve 51 showing the characteristics of the drain current (first current) and the gate voltage obtained when the sweep voltage is applied to the gate electrode after the first tuning voltage is applied. The broken line is a curve 52 showing the characteristics of the drain current (second current) and the gate voltage obtained when the sweep voltage is applied to the gate electrode after the second tuning voltage is applied.

FIG. 11A is an experimental result showing the change characteristic of the current flowing between the source electrode and the drain electrode with respect to the sweep voltage when the gas determination is performed without UV light irradiation and heating.
FIG. 11B is an experimental result showing the change characteristic of the current flowing between the source electrode and the drain electrode with respect to the sweep voltage when the gas determination is performed without UV light irradiation and heating.
FIG. 11C is an experimental result showing the change characteristics of the current flowing between the source electrode and the drain electrode with respect to the sweep voltage when the gas is determined with UV light irradiation and heating.

As shown in FIG. 11A, the curve 52 shown by the broken line has a shape in which the curve 51 shown by the solid line is moved to the right along the horizontal axis direction on the drawing. The difference between the first gate voltage and the second gate voltage when the drain current I _{d in each curve becomes the minimum value can be taken.}

As shown in FIG. 11B, in the curve 52 shown by the broken line, the curve 51 shown by the solid line moves to the right along the horizontal axis direction in the drawing and slightly upward along the vertical axis direction. It is almost in the form of moving. The difference between the first gate voltage and the second gate voltage when the drain current I _{d in each curve becomes the minimum value can be taken.}

As shown in FIG. 11C, in the curve 52 shown by the broken line, the curve 51 shown by the solid line moves to the right along the horizontal axis direction on the drawing and moves upward along the vertical axis direction. The curve 51 and the curve 52 can be clearly distinguished from each other.

As described above, in any of the drawings of FIGS. 11A to 11C, a curve showing the characteristics of the drain current and the gate voltage obtained when the sweep voltage is applied to the gate electrode after the first tuning voltage is applied. The curve 52 showing the characteristics of the drain current and the gate voltage obtained when the sweep voltage is applied to the gate electrode after applying the 51 and the second tuning voltage has a shape deviated in the horizontal axis direction, and the first The type of gas can be determined by the gate voltage and the second gate voltage.
Then, as shown in FIG. 11C, by UV irradiation and heating, the difference between the first gate voltage and the second gate voltage in the horizontal axis direction can be further increased, and the first gate can be further increased. The band indicating the range from the voltage to the second gate voltage can be made clearer. Thereby, the accuracy of determining the type of gas can be further improved.

As described above, in the gas determination method of the present invention, the type or concentration of gas can be determined with high accuracy by using a gas sensor having a field effect transistor structure using graphene as a channel. Further, since the gas sensor can be made small, the sensor device 2 can be made small.

Further, in the present embodiment, the channel layer 15 is composed of a laminate of the graphene layer 16 and the porous layer 17. Since the porous layer 17 is more porous than the graphene layer 16, the gas adsorption efficiency is high. Moreover, since the porous layer 17 is made of the same carbon-based material (activated carbon) as the graphene layer 16, the conductive properties of the channel layer 15 can be maintained satisfactorily. As a result, the accuracy of gas detection in the channel layer 15 can be improved.

Here, FIG. 12 shows a comparison between the drain current characteristic when the channel layer has a single-layer structure of a graphene layer and the drain current characteristic when the channel layer has a laminated structure of a graphene layer and a porous layer. ..
12 (A) and 12 (B) show the current characteristics (dashed line) between the source and drain when the gate voltage is swept under vacuum, and the gate voltage in the presence of 3 ppm of ammonia _{with the carrier gas as N 2.} The current characteristics (solid line) between the source and drain during sweeping are shown. FIG. 12 (A) shows the current characteristics when the channel layer has a single-layer structure of a graphene layer, and FIG. 12 (B) shows the current characteristics when the channel layer has a laminated structure of a graphene layer and a porous layer. Shown.

When the channel layer has a single-layer structure of a graphene layer, as shown in FIG. 12 (A), the shift amount of the charge neutral point at the time of introducing the ammonia gas was about 1.5 V, whereas the channel When the layer had a laminated structure of a graphene layer and a porous layer, as shown in FIG. 12 (B), the shift amount of the charge neutral point at the time of introducing the ammonia gas was about 5 V.
From this, according to the sensor 10 of the present embodiment having the porous layer 17, the sensitivity to gas can be increased as compared with the sensor having no porous layer 17, so that even when the gas concentration is low. It can be detected with high accuracy.

Further, according to the present embodiment, since the channel layer 15 has the porous layer 17, the channel layer 15 can have the selectivity of the detection target gas. 13 (A) and 13 (B) are diagrams showing the same drain current characteristics as in FIG. 12, showing the results of detecting ammonia gas in the presence of air by the sensor 10 provided with the porous layer 17 made of activated carbon. be.
FIG. 13A shows the drain current characteristic of the sensor 10 in an air atmosphere and the drain current characteristic of the sensor 10 in an atmosphere in which 5 ppb of ammonia is mixed with the air. A clear shift in the charge neutral point was confirmed before and after the introduction of ammonia.
Similarly, FIG. 13B shows the drain current characteristic of the sensor 10 in an air atmosphere and the drain current characteristic of the sensor 10 in an atmosphere in which 500 ppt of ammonia is mixed with the air. In this example as well, a clear shift in the charge neutral point was detected before and after the introduction of ammonia.
It is considered that these results are due to the fact that the pores of the porous layer 17 _{do not pass the O 2} gas having a relatively large molecule, but pass only the ammonia gas having a relatively small molecule to filter _{the O 2 gas.} From this, it was confirmed that gas selectivity can be obtained by using the porous layer 17 which is activated carbon.

[Sensor manufacturing method]
Subsequently, a method of manufacturing the sensor 10 of the present embodiment configured as described above will be described.

First, as shown in FIG. 14A, a graphene layer 160 is formed on the surface of the copper foil 101 by a CVD (chemical vapor deposition) method or the like. The graphene layer 160 corresponds to the graphene layer 16 in the sensor 10 shown in FIG.

A commercially available product in which the graphene layer 160 is laminated on the copper foil 101 may be used. In this case, a copper foil 101 having graphene layers 160 formed on both sides may be used. In this case, only one side graphene layer 160 formed on the surface of the copper foil 101 is used, the other side graphene layer 160 formed on the surface of the copper foil 101, a copper foil 101 with O ₂ plasma etching or the like Will be removed.

Subsequently, as shown in FIG. 14 (B), the protective layer 103 is formed on the surface of the graphene layer 160 by, for example, a spin coating method. The protective layer 103 is for protecting the graphene layer 160, and can be omitted if necessary. The resin constituting the protective layer 103 is not particularly limited, and for example, a photosensitive resist resin can be used. In the present embodiment, for example, polymethylmethacrylate (PMMA) is used as the protective layer 103.

Subsequently, as shown in FIG. 14C, the laminate of the copper foil 101, the graphene layer 160, and the resist resin layer 103 is floated on the solvent 105 in the container 104 to dissolve only the copper foil 101. As the solvent 105, for example, ammonium peroxodisulfate or the like is used.

Then, as shown in FIG. 14D, the graphene layer 160 floating on the solvent 105 is scooped up and placed on the substrate 110 to dry the graphene layer 160 and the resist resin layer 103. As the substrate 110, a silicon substrate having a silicon oxide film formed on its surface is used, and the graphene layer 160 is placed on the silicon oxide film.
The silicon substrate and the silicon oxide film correspond to the gate electrode 13 and the insulating film 14 in the sensor 10 shown in FIG. 2, respectively (see FIG. 15 (A)).

After that, as shown in FIG. 14 (E), the protective layer 103 is melted with acetone, washed, and then annealed at a predetermined temperature to improve the adhesion between the substrate 110 and the graphene layer 160.

Subsequently, as shown in FIG. 15A, the resist resin layer 106 is formed on the graphene layer 160 by the spin coating method. Then, by exposing and developing the resist resin layer 106, the resist resin layer 106 is patterned into a predetermined shape as shown in FIG. 15 (B). The exposure method of the resist resin layer 106 is not particularly limited, and an exposure method using an exposure mask, a maskless exposure method such as electron beam drawing, and the like can be adopted.

Subsequently, as shown in FIG. 15C, the graphene layer 160 exposed from the opening of the resist resin layer 106 is removed by dry etching. For the dry etching method of the graphene layer 160, for example, O ₂ plasma is used.

Subsequently, as shown in FIG. 15 (D), the first metal layer 107a is formed on the surface of the resist resin layer 106 and inside the opening thereof. Then, as shown in FIG. 15 (E), the first metal layer 107a is patterned (lifted off) by removing the resist resin layer 106, and the pattern of the first metal layer 107a adjacent to the graphene layer 160 is formed on the substrate 110. To form.

The first metal layer 107a may be a single layer or a multilayer structure. In the present embodiment, chromium (Cr) having a thickness of about 5 nm is formed as an adhesion material, and gold (Au) having a thickness of about 70 nm is formed on the chromium (Cr) as an electrode material. The film forming method of the first metal layer 107a is not particularly limited, and may be a sputtering method or a vacuum vapor deposition method. In this embodiment, the first metal layer 107a is formed by the electron beam deposition method.

Subsequently, as shown in FIG. 16A, the first resist resin layer 108a is formed on the substrate 110, and the second resist resin layer 108b is formed on the first resist resin layer 108a. For the first resist resin layer 108a, for example, a methyl methacrylate (MMA) film is used, and for the second resist resin layer 108b, for example, a polymethylmethacrylate (PMMA) film is used. Used.

Subsequently, as shown in FIG. 16B, the graphene layer 160 and the metal layer 107 are formed by exposing and developing the first resist resin layer 108a and the second resist resin layer 108b using electron beam lithography technology or the like. A resist pattern is formed in which the boundary portion of the surface is exposed.
In the present embodiment, an opening pattern in which the opening width of the first resist resin layer 108a is larger than the opening width of the second resist resin layer 108b is formed.

Subsequently, as shown in FIG. 16C, the first metal layer 107b is formed on the surface of the second resist resin layer 108b and inside the opening thereof. Then, as shown in FIG. 16D, the second metal layer 107b is patterned (lifted off) by removing the first and second resist resin layers 108a and 108b, and the graphene layer 160 and the first metal layer 107a are formed. A pattern of the second metal layer 107b straddling the boundary portion of the above is formed on the substrate 110.

The second metal layer 107b may be a single layer or a multilayer structure. In the present embodiment, chromium (Cr) having a thickness of about 5 nm is formed as an adhesion material, and gold (Au) having a thickness of about 20 nm is formed on the chromium (Cr) as an electrode material. The film forming method of the second metal layer 107b is not particularly limited, and may be a sputtering method or a vacuum vapor deposition method. In this embodiment, the second metal layer 107b is formed by the electron beam deposition method.

The first metal layer 107a and the second metal layer 107b form a common metal layer 107. The metal layer 107 corresponds to the source electrode 11 and the drain electrode 12 in the sensor 10 shown in FIG. In the present embodiment, since the opening width of the first resist resin layer 108a is larger than the opening width of the second resist resin layer 108b, the second metal layer 107b is less likely to come into contact with the side surface of the opening of the first resist resin layer 108a. As a result, the patterning accuracy of the second metal layer 107b at the time of lift-off can be improved.

Subsequently, as shown in FIG. 17A, a resist resin layer 121 for coating the graphene layer 160 and the metal layer 107 is formed on the substrate 10 by spin coating or the like.
In FIG. 17A, the upper part is a cross-sectional view of the substrate 110, and the lower part is a plan view thereof (the same applies to FIGS. 17B to 17D).

Subsequently, as shown in FIG. 17B, the resist resin layer 121 is exposed and developed using electron beam lithography technology or the like, and the graphene layer 160 located between two adjacent metal layers 107 is partially formed. A resist pattern to be coated is formed.

Subsequently, as shown in FIG. 17C, the graphene layer 160 not coated with the resist resin layer 121 is removed from the substrate 110 by _{O 2 plasma etching.}
The etching conditions are not particularly limited, and in the present embodiment, the gas flow rate is 20 sccm, the pressure is 6 Pa, the power is RF 20 W (13.56 MHz), and the processing time is 35 seconds. The thickness of the resist resin layer 121 after the etching treatment is, for example, 30 nm.

Subsequently, as shown in FIG. 17 (D), the resist resin layer 121 is carbonized by performing an annealing treatment of the resist resin layer 121 in vacuum. As a result, the activated carbon layer 170 made of the carbon composition constituting the resist resin layer 121 is formed on the graphene layer 160. The activated carbon layer 170 corresponds to the porous layer 17 in the sensor 10 shown in FIG.

As described above, in the present embodiment, the activated carbon layer 170 is formed on the graphene layer 160 by carbonizing the resist resin layer 121, which is a mask for patterning the graphene layer 160. The annealing conditions of the resist resin layer 121 are not particularly limited, and for example, the annealing temperature is 300 ° C. and the annealing time is 3 hours and 30 minutes.

The thickness of the activated carbon layer 170 can be adjusted by adjusting the thickness of the resist resin layer 121. For example, when the pattern etching of the graphene layer 160, the resist resin layer 121 may be thinned to a predetermined thickness by the O ₂ plasma etch. Alternatively, after the activated carbon layer 170 is formed, the thickness of the activated carbon layer 170 may be adjusted by etching again.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

For example, in the above-described embodiment, the gate electrodes to which the first and second tuning voltages and the sweep voltage are applied are common gate electrodes, but the present invention is not limited to this. A gate electrode to which a sweep voltage is applied may be provided separately from the gate electrode to which the first and second tuning voltages are applied, and both gate electrodes are arranged so as to face the graphene layer via an insulating film. I just need to be there.

Further, in the above-described embodiment, the tuning voltage (fixed voltage) is set to two values of the first tuning voltage and the second tuning voltage, but at least two values may be sufficient, and three or more values may be used. By setting the value to 3 or more, the gas information is increased, and more accurate gas determination becomes possible.

Further, in the above-described embodiment, the gate is in the order of the negative (-40V in the above-described embodiment) first tuning voltage, the sweep voltage, the positive (40V in the above-described embodiment) second tuning voltage, and the sweep voltage. Although the example in which the voltage is applied to the electrode is given, the voltage may be applied to the gate electrode in the order of the positive second tuning voltage, the sweep voltage, the negative first tuning voltage, and the sweep voltage.

Further, the porous layer may cover the entire surface of the graphene layer or may partially cover it.

1 ... Gas judgment system 4 ... Information processing device 10 ... Sensor (sensor device)
11 ... Source electrode 12 ... Drain electrode 13 ... Gate electrode 14 ... Insulating film 15 ... Channel layer 16,160 ... Graphene layer 17 ... Porous layer 42 ... Judgment unit 44 ... Control unit 170 ... Activated carbon layer

Claims (5)

1. With the gate electrode
   The insulating film formed on the gate electrode and
   The graphene layer formed on the insulating film and
   A source electrode and a drain electrode arranged to face each other on the insulating film via the graphene layer,
   A sensor device including a conductive porous layer formed on the graphene layer.
2. The sensor device according to claim 1.
   The porous layer is a sensor device made of a carbon-based material.
3. A gate electrode, an insulating film formed on the gate electrode, a graphene layer formed on the insulating film, and a source electrode and a drain electrode arranged to face each other on the insulating film via the graphene layer. Prepare and
   A resin layer is formed on the graphene layer,
   A method for manufacturing a sensor device that carbonizes the resin layer.
4. The method for manufacturing a sensor device according to claim 3.
   Further having a dry etching step of patterning the graphene layer into a predetermined shape,
   A method for manufacturing a sensor device in which the resin layer is formed on the graphene layer as a mask for patterning the graphene layer.
5. A gate electrode, an insulating film formed on the gate electrode, a graphene layer formed on the insulating film, and a source electrode and a drain electrode arranged to face each other on the insulating film via the graphene layer. A sensor device having a conductive porous layer formed on the graphene layer, and
   A control unit that controls the voltage applied to the gate electrode and a determination unit that determines the gas adsorbed on the porous layer based on the measurement result of the current flowing between the source electrode and the drain electrode. A gas determination system including an information processing device having the same.

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