JP7215347B2 - Gas sensor and method for manufacturing gas sensor - Google Patents

Description

The present invention relates to a gas sensor and a method for manufacturing a gas sensor.

There are various types of gas sensors that detect gases contained in exhaled breath and air. Among others, graphene-based gas sensors utilize the fact that the electronic state of graphene changes with gas molecules, and are expected to detect gases with high sensitivity and ease.

However, gas molecules that have a weak electrostatic interaction with graphene are difficult to change the electronic state of graphene, so the gas that can be detected by a gas sensor using graphene is limited. In particular, nitric oxide (NO) has a weak electrostatic interaction with graphene, so it is difficult to detect it with a graphene-based gas sensor.

F. Schedin et al., “Detection of individual gas molecles adsorbed on graphene”, Nature Materials, 6, 652 (2007) M. Gautam et al., “Gas sensing properties of graphene synthesized by chemical vapor deposition”, Materials Science and Engineering C 31, 1405 (2011) R. Pearce et al., “Epitaxially grown graphene based gas sensors for ultra sensitive NO2 detection”, Sensors and Actuators B, 155, 451 (2011)

International publication WO2017/002854

The disclosed technique has been made in view of the above, and aims to provide a gas sensor capable of detecting nitric oxide, and a method for manufacturing the gas sensor.

According to one aspect of the following disclosure, a semiconductor substrate, a source region formed on a surface layer of the semiconductor substrate, a drain region formed on the surface layer of the semiconductor substrate, and between the source region and the drain region a gate insulating layer formed on the semiconductor substrate of, a graphene layer formed on the gate insulating layer, a gate electrode formed on a surface of the graphene layer in a first region, and the graphene layer and a metal phthalocyanine layer, which is a chromium phthalocyanine layer formed on the surface in the second region of. a semiconductor substrate, a source region formed in a surface layer of the semiconductor substrate, a drain region formed in the surface layer of the semiconductor substrate, and formed on the semiconductor substrate between the source region and the drain region. a gate insulating layer formed on the gate insulating layer, a graphene layer formed on the gate insulating layer, a gate electrode formed on the surface in the first region of the graphene layer, and on the back surface of the graphene layer in the second region A gas sensor having a formed metal phthalocyanine layer is provided.

According to the present invention, the metal phthalocyanine layer increases the amount of change in the work function of the graphene layer when nitrogen monoxide molecules are bound, so that nitric oxide can be detected.

FIG. 1 is a plan view showing the crystal structure of graphene. FIG. 2 is a cross-sectional view of a gas sensor using graphene examined by the inventors of the present application. FIG. 3 is an energy band diagram of the gas sensor. FIG. 4 is a schematic diagram showing the relationship between gate voltage and drain current in a gas sensor. 5(a) to 5(c) are cross-sectional views of the graphene layer according to the first embodiment during production. 6A to 6C are cross-sectional views (Part 1) of the gas sensor according to the first embodiment during manufacturing. 7A to 7C are cross-sectional views (part 2) of the gas sensor according to the first embodiment during manufacturing. FIG. 8 is a cross-sectional view (No. 3) of the gas sensor according to the first embodiment during manufacturing. 9 is a plan view of the gas sensor according to the first embodiment. FIG. FIG. 10 is a schematic diagram for explaining how to use the gas sensor according to the first embodiment. FIG. 11 is a plan view showing the molecular structure of metal phthalocyanine. FIG. 12 is a schematic diagram (part 1) showing a mechanism for detecting gas molecules with the gas sensor according to the first embodiment; FIG. 13 is a schematic diagram (part 2) showing a mechanism for detecting gas molecules with the gas sensor according to the first embodiment; FIGS. 14A and 14B are energy band diagrams obtained by simulating a single graphene layer without forming a metal phthalocyanine layer. FIG. 15(a) is a plan view of a calculation model before nitrogen monoxide gas molecules are adsorbed on the metal phthalocyanine layer according to the first embodiment, and FIG. 15(b) is a side view thereof. FIG. 16(a) is a plan view of a calculation model after nitrogen monoxide gas molecules are adsorbed on the metal phthalocyanine layer according to the first embodiment, and FIG. 16(b) is a side view thereof. FIGS. 17A to 17C are energy band diagrams showing simulation results when a copper phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIGS. 18A to 18C are energy band diagrams showing simulation results when a nickel phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIGS. 19A to 19C are energy band diagrams showing simulation results when a cobalt phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIGS. 20A to 20C are energy band diagrams showing simulation results when a manganese phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIGS. 21A to 21C are energy band diagrams showing simulation results when a chromium phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIGS. 22A to 22C are energy band diagrams showing simulation results when a titanium phthalocyanine layer is formed as the metal phthalocyanine layer according to the first embodiment. FIG. 23 is a table summarizing the results of FIGS. 17-22. 24A to 24C are cross-sectional views (Part 1) of the gas sensor according to the second embodiment during manufacturing. 25A to 25C are cross-sectional views (part 2) of the gas sensor according to the second embodiment during manufacturing. FIG. 26 is a cross-sectional view (No. 3) of the gas sensor according to the second embodiment during manufacturing. FIG. 27 is a plan view of the gas sensor according to the second embodiment. FIG. 28 is a cross-sectional view for explaining how to use the gas sensor according to the second embodiment. FIG. 29 is a schematic diagram (part 1) showing a mechanism for detecting gas molecules with the gas sensor according to the second embodiment; FIG. 30 is a schematic diagram (Part 2) showing a mechanism for detecting gas molecules with the gas sensor according to the second embodiment. FIG. 31(a) is a side view of a calculation model before nitrogen monoxide gas molecules are adsorbed on the graphene layer in the second embodiment, and FIG. FIG. 4 is a side view of the calculation model after nitrogen oxide gas molecules are adsorbed. FIGS. 32A and 32B are energy band diagrams showing simulation results in the second embodiment. FIG. 33 is a diagram showing the amount of change in drain current assumed in the second embodiment. FIGS. 34A and 34B are cross-sectional views (Part 1) of the gas sensor according to the third embodiment during manufacture. 35A to 35C are cross-sectional views (part 2) of the gas sensor according to the third embodiment during manufacturing. FIG. 36 is a cross-sectional view (part 3) of the gas sensor according to the third embodiment during manufacturing.

Prior to the description of the present embodiment, matters examined by the inventors of the present application will be described.

As described above, there is a sensor using graphene as a gas sensor for detecting gases contained in exhaled breath and the atmosphere.

FIG. 1 is a plan view showing the crystal structure of graphene.
As shown in FIG. 1, graphene is a sheet-like substance corresponding to one atomic layer of graphite, and has a crystal structure in which carbon atoms are bonded like a honeycomb. Due to such a crystal structure, the specific surface area of graphene is larger than that of graphite, and the electronic state of graphene is greatly affected by the external atmosphere and the like. By using this feature, it is thought that the electronic state of graphene changes with a specific gas contained in the atmosphere or exhaled air, and that gas can be detected.

FIG. 2 is a cross-sectional view of a gas sensor using graphene examined by the inventors of the present application.

This gas sensor 1 has an n-type source region 3 and a drain region 4 on the surface layer of a p-type silicon substrate 2 , and a gate insulator on the surface of the silicon substrate 2 between the source region 3 and the drain region 4 . A silicon oxide layer is formed as layer 5 .

A graphene layer 6 for detecting gas is formed on the gate insulating layer 5 . Then, the gate electrode 7 is formed on the surface of the first region R1 of the graphene layer 6, and the second region R2 of the graphene layer 6 is exposed to the atmosphere. The gate electrode 7 is formed by patterning an aluminum layer, for example, and the source electrode 8 and the drain electrode 9 are formed simultaneously with the gate electrode 7 .

According to such a gas sensor 1, a structure similar to that of a MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is obtained by forming the silicon substrate 2, the gate insulating layer 5, and the gate electrode 7 in this order. Then, the gas molecules to be detected are bound to the graphene layer 6 exposed in the second region R2, and the electronic state of the graphene layer 6 is thereby changed. Reflecting this change in electronic state, the drain current _Id flowing through the channel 2a between the source region 3 and the drain region 4 changes as follows.

FIG. 3 is an energy band diagram of this gas sensor 1. As shown in FIG.
As shown in FIG. 3, the work function φ _m of the gate electrode 7 is defined by the difference between the vacuum level _{E 0} and the Fermi level EF. In the silicon substrate ₂ , the Fermi level _EF is located in the band gap _G between the valence band _BSV and the conduction band _BSC . The difference becomes the work function φ _s of the silicon substrate 2 .

FIG. 4 is a schematic diagram showing the relationship between the gate voltage and the drain current in this gas sensor 1. As shown in FIG.

The MOSFET flat-band voltage V _FB can be written as V _FB = φ _m - φ _s using the respective work functions φ _m and φ _s . Here, when gas molecules are adsorbed on the graphene layer 6, the work function of the graphene layer 6 changes, and the work function of the gate electrode 7 also changes from φ _m to φ _m +Δφ. In this case, the change amount ΔV _FB of the flat band voltage V _FB described above also becomes Δφ.

As a result, for example, if a constant bias voltage V _bias is applied to the gate electrode 7, the drain current increases from I _d1 to I _d2 by _ΔId . Therefore, gas molecules can be detected by detecting the amount of increase ΔI _d in the drain current.

If the bias voltage V _bias is set in the subthreshold region, the drain current changes exponentially, so even if the work function change Δφ is small, the increase ΔI _d can be increased, and the gas molecules can be detected with high sensitivity. It is thought that it can be detected at

If the amount of change in the drain current is defined as I _d2 /I _d1 , the amount of change satisfies I _d2 /I _d1 =10 ^(Δφ/SS) . SS is the amount of change in drain current per unit voltage (sub-threshold swing). According to this, in a MOSFET with a subthreshold swing SS of about 65 mV/decade, the drain current increases by one digit when the amount of change Δφ in the work function is 60 mV.

Based on this principle, in the gas sensor 1, each molecule of nitrogen dioxide and ammonia binds to the graphene layer 6 to increase the amount of increase ΔI _d , and these gas molecules can be detected with high sensitivity.

However, gas molecules that have little electrostatic interaction with the graphene layer 6 hardly change the work function of the graphene layer 6 , and it is difficult for the gas sensor 1 to detect the gas molecules.

In particular, nitric oxide is preferably detectable with high sensitivity for pathological judgment of asthma.

Embodiments capable of detecting nitric oxide are described below.

(First embodiment)
The gas sensor according to this embodiment will be described while following the manufacturing process. The gas sensor uses graphene layers to detect nitric oxide. Therefore, first, a method for forming a graphene layer will be described.

5A to 5C are cross-sectional views of the graphene layer according to the present embodiment during production.

First, as shown in FIG. 5A, a copper foil is prepared as a catalytic metal foil 20, and the catalytic metal foil 20 is placed in a chamber of a CVD (Chemical Vapor Deposition) apparatus. Then, the pressure in the chamber is reduced to 10 ⁻¹ Pa or less, and while the catalyst metal foil 20 is heated to a temperature of 1000° C. or more, hydrogen gas is supplied to the chamber to remove the oxide on the surface of the catalyst metal foil 20 . Restore and remove. After that, methane gas and hydrogen gas are supplied into the chamber while maintaining the state where the catalyst metal foil 20 is heated to a temperature of 1000° C. or higher. By maintaining this state for about 60 minutes, methane is decomposed by the catalytic action of copper, and the carbon atoms generated thereby are reconfigured on the surface of the catalytic metal foil 20 to form the graphene layer 21 .

Since the graphene layer 21 isolates methane in the atmosphere from the catalyst metal foil 20, no new graphene grows on the graphene layer 21, and the graphene layer 21 having a thickness of one atomic layer is formed. can be done.

Next, as shown in FIG. 5B, a support layer 22 is formed by applying a resist or a polymer such as PDMS (polydimethylsiloxane) to the surface 21a of the graphene layer 21 and baking it.

Subsequently, as shown in FIG. 5C, the catalyst metal foil 20 is dissolved and removed with an etchant such as an iron chloride solution to expose the rear surface 21b of the graphene layer 21. Next, as shown in FIG.

Next, a method for manufacturing a gas sensor according to this embodiment using this graphene layer 21 will be described.

6 to 8 are cross-sectional views of the gas sensor according to the present embodiment during manufacturing.

First, as shown in FIG. 6A, a p-type silicon substrate is prepared as a semiconductor substrate 30, and an n-type source region is formed by ion-implanting an n-type impurity such as phosphorus or arsenic into the surface layer of the semiconductor substrate 30. As shown in FIG. 31 and a drain region 32 are formed. In the ion implantation, a resist layer is used as a mask, and n-type impurities are not implanted into the semiconductor substrate 30 in the portion covered with the resist layer.

Moreover, the conductivity type of the semiconductor substrate 30 is not limited to the p-type, and the p-type source region 31 and the drain region 32 may be formed in the n-type semiconductor substrate 30 .

After that, the surface of the semiconductor substrate 30 is oxidized to form a silicon oxide layer having a thickness of about 1 nm to 100 nm as the gate insulating layer 33 .

Next, as shown in FIG. 6B, the rear surface 21b of the graphene layer 21 obtained in the step of FIG. Graphene layer 21 is pressed onto layer 33 .

At this time, it is preferable to heat the semiconductor substrate 30 to evaporate moisture on the surface of the graphene layer 21 in order to increase the adhesion between the graphene layer 21 and the gate insulating layer 33 . Although the substrate temperature at this time is not particularly limited, the semiconductor substrate 30 can be heated at a temperature of 100° C. or higher, for example.

After that, as shown in FIG. 6C , the support layer 22 is dissolved in an organic solvent such as acetone and removed, leaving the graphene layer 21 on the gate insulating layer 33 .

Subsequently, as shown in FIG. 7A, a resist is applied on the graphene layer 21, and the resist is exposed and developed to form an island-shaped first resist layer 35. Next, as shown in FIG. Using the first resist layer 35 as a mask, RIE (Reactive Ion Etching) using oxygen gas as an etching gas is performed to remove portions of the graphene layer 21 that are not covered with the first resist layer 35 .

After that, the first resist layer 35 is removed with an organic solvent.

Next, as shown in FIG. 7B, a resist is applied again to the entire upper surface of the semiconductor substrate 30, exposed and developed to form a second resist so as to cover the side surfaces 21c and 21d of the graphene layer 21. Next, as shown in FIG. A resist layer 36 is formed. Then, while leaving the gate insulating layer 33 between the source region 31 and the drain region 32, the portion of the gate insulating layer 33 not covered with the second resist layer 36 is etched with a hydrofluoric acid solution and removed.

After that, the second resist layer 36 is removed with an organic solvent.

In this example, the second resist layer 36 is formed to cover the side surface 21c of the graphene layer 21 near the source region 31 as described above. Therefore, the side surface 21c recedes from the side surface 33a of the gate insulating layer 33 closer to the source region 31 toward the drain region 32 side. As a result, the graphene layer 21 is separated from the source region 31, and electrical connection between the source region 31 and the graphene layer 21 can be suppressed. Similarly, the side surface 21d of the graphene layer 21 closer to the drain region 32 recedes from the side surface 33b of the gate insulating layer 33 closer to the drain region 32 toward the source region 31 side. This makes it possible to suppress electrical connection between the drain region 32 and the graphene layer 21 .

Next, the process shown in FIG. 7(c) will be described.
First, a resist layer (not shown) having electrode-shaped openings is formed on the upper side of the semiconductor substrate 30, and an aluminum layer having a thickness of about 10 nm to 1000 nm is formed in the openings by vapor deposition. Then, by removing the resist layer, the aluminum layer on the source region 31 and the drain region 32 becomes the source electrode 37 and the drain electrode 38 , and the aluminum layer on the graphene layer 21 becomes the gate electrode 39 . Such an electrode patterning method is also called a lift-off method.

In this embodiment, the gate electrode 39 is formed only on the surface 21a of the first region R1 of the graphene layer 21, and the surface 21a of the second region R2 of the graphene layer 21 is exposed.

Next, as shown in FIG. 8, the semiconductor substrate 30 is placed in a vapor deposition chamber whose pressure is reduced to 10 ⁻¹ Pa or less, and the semiconductor substrate 30 is heated to about room temperature to 200° C. in the vapor deposition chamber. Then, the metal phthalocyanine vaporized at a temperature of about 200° C. to 300° C. is supplied to the vapor deposition chamber to form the metal phthalocyanine layer 40 on the surface 21a of the graphene layer 21 in the second region R2 at a growth rate of 1 Å/sec or less. do.

The metal phthalocyanine layer 40 is also formed on each of the source electrode 37, the drain electrode 38 and the gate electrode 39. As shown in FIG.

The intermolecular force between the metal phthalocyanine molecules is weaker than the intermolecular force between the graphene layer 21 and the metal phthalocyanine molecules. Therefore, when the semiconductor substrate 30 is heated in this way, after the metal phthalocyanine molecules are deposited on the graphene layer 21 by the thickness of one molecular layer, excess metal phthalocyanine molecules are released by heat. Thereby, the thickness of the metal phthalocyanine layer 40 in the second region R2 can be made a monomolecular layer.

Note that the method for forming the metal phthalocyanine layer 40 is not limited to the above. For example, the metal phthalocyanine layer 40 may be formed by applying an organic solvent in which metal phthalocyanine molecules are dissolved on the graphene layer 21 by spin coating or dipping.

With the above, the basic structure of the gas sensor 50 according to the present embodiment is completed.

The gas sensor 50 is an n-type MOSFET in which a p-type semiconductor substrate 30, a gate insulating layer 33, and a gate electrode 39 are laminated in this order, and the second region R2 functions as a gas detection region.

FIG. 9 is a plan view of this gas sensor 50. As shown in FIG.
Note that the metal phthalocyanine layer 40 is omitted in FIG. Also, FIG. 8 described above corresponds to a cross-sectional view taken along line II in FIG.

As shown in FIG. 9, the graphene layer 21 has a rectangular planar shape in the second region R2. The size of the second region R2 is not particularly limited, but in this example, the length of one side of the second region R2 is approximately 1 μm to 100 μm.

Next, how to use this gas sensor 50 will be described.
FIG. 10 is a cross-sectional view for explaining how to use the gas sensor 50. As shown in FIG.

As shown in FIG. 10, in actual use, a first terminal 45 and a second terminal 46 are connected to the source electrode 37 and the drain electrode 38, respectively. At the same time, the gate electrode 39 is brought into contact with the third terminal 47 . These terminals 45 to 47 may be clip-shaped metal terminals that sandwich the semiconductor substrate 30, or thin metal wires such as bonding wires.

Since the thickness of the metal phthalocyanine layer 40 is as thin as one molecular layer as described above, the third terminal 47 easily penetrates the metal phthalocyanine layer 40 and contacts the gate electrode 39 . The same applies to the first terminal 45 and the second terminal 46 .

A bias voltage V _bias is applied from the third terminal 47 to the gate electrode 39 , and a drain voltage V _d is applied between the first terminal 45 and the second terminal 46 .

As a result, the drain current _Id flows through the channel 30a between the source region 31 and the drain region 32. However, when the gas molecules 48 bind to the metal phthalocyanine layer 40 in the second region R2, the drain current _Id increases. also change. This will be explained below.

FIG. 11 is a plan view showing the molecular structure of metal phthalocyanine.

As shown in FIG. 11, a metal phthalocyanine is a cyclic compound in which four phthalimides are bridged with nitrogen atoms around a metal atom M. The metal atom M is not particularly limited, and metal phthalocyanine in which any one of titanium, vanadium, chromium, manganese, iron, and cobalt is arranged as the metal atom M can be used.

FIG. 12 is a schematic diagram showing a mechanism for detecting gas molecules 48 with the gas sensor 50. As shown in FIG. 12 illustrates HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital) of metal phthalocyanine layer 40 and gas molecule 48, respectively. For the graphene layer 21, energy band curves of the valence band B _GV and the conduction band B _GC are also shown. It is assumed that the valence band B _GV and the conduction band B _GC extend above and below the Dirac point D and are filled with electrons up to the hatched energy of dots. This also applies to FIG. 13, which will be described later.

When gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 , electrons e ⁻ move from the HOMO of the gas molecules 48 to the graphene layer 21 via the HOMO of the metal phthalocyanine layer 40 . This increases the number of electrons in the conduction band B _GC of the graphene layer 21 .

FIG. 13 is a schematic diagram when electrons move in the direction opposite to that in FIG.

In this case, the electron e ⁻ moves from the conduction band B _GC of the graphene layer 21 to the LUMO of the gas molecule 48 via the LUMO of the metal phthalocyanine layer 40, and the number of electrons in the conduction band B _GC of the graphene layer 21 decreases.

Which electron transfer occurs between FIG. 12 and FIG. 13 is determined by various factors. Such factors include, for example, the adsorption energy of the gas molecules 48 to the metal phthalocyanine layer 40, the difference in electronegativity between the two, and the band alignment between the graphene layer 21 and the metal phthalocyanine layer 40.

In both cases of FIG. 12 and FIG. 13, the Fermi level E _F of the graphene layer 21 changes by ΔE _F due to the change in the number of electrons in the conduction band B _GC . Assuming that the amount of change in the carrier concentration of the conduction band B _GC that accompanies the change in the number of electrons is ρ, the amount of change ΔE _F in the Fermi level _EF is approximately ρ/D. Note that D is the electron density of states. In particular, in the graphene layer 21, the state density of electrons in the vicinity of the Dirac point _D is smaller than that of a metal, so that such a change in the number of electrons causes a significant change in the Fermi level EF. Then, the work function of the graphene layer 21 changes due to the combination of the change in the _Fermi level EF and the resulting dipole effect. As a result, the threshold voltage of the MOSFET of the gas sensor 50 is modulated and the drain current is changed.

In particular, when the thickness of the graphene layer 21 is one atomic layer as in the present embodiment, the energy band curve of the graphene layer 21 becomes linear. As a result, even a slight change in the number of electrons in the conduction band B _GC causes a large change in the Fermi level _EF , making it possible to increase the amount of change in the drain current due to the adsorption of gas molecules 48. .

Moreover, since the metal phthalocyanine layer 40 has a greater electrostatic interaction with the nitrogen monoxide gas molecules 48 than the graphene layer 21, the gas sensor 50 can measure the presence and concentration of nitrogen monoxide. .

If the metal phthalocyanine layer 40 is too thick, the gas molecules 48 and the graphene layer 21 are largely separated by the metal phthalocyanine layer 40, and the change in the electronic state of the graphene layer 21 due to the adsorption of the gas molecules 48 becomes slight. . Therefore, it is preferable to set the thickness of the metal phthalocyanine layer 40 to a monomolecular layer as in the present embodiment so that the adsorption of the gas molecules 48 greatly changes the electronic state of the graphene layer 21 .

The inventor of the present application conducted a simulation to confirm how the Fermi level EF of the _graphene layer 21 changes when the gas molecules 48 of nitrogen monoxide are adsorbed. The simulation will be described below.

FIGS. 14A and 14B are energy band diagrams obtained by simulating a single graphene layer 21 without forming the metal phthalocyanine layer 40. FIG.

Among them, FIG. 14A is an energy band diagram of the graphene layer 21 to which no nitrogen monoxide gas molecules 48 are adsorbed. FIG. 14(b) is an energy band diagram of the graphene layer 21 on which the nitrogen monoxide gas molecules 48 are adsorbed. In these energy band diagrams, the horizontal axis indicates the electron wave number in the reciprocal space, and the vertical axis indicates the electron energy. This also applies to each energy band diagram described later.

As shown in FIGS. 14A and 14B, the Fermi level EF of the graphene layer 21 before the adsorption of the nitrogen monoxide gas molecules 48 is _−3.879 eV, and after the adsorption of the gas molecules 48 The Fermi level E _F is −3.922 eV. As a result, the amount of change ΔE _F in the Fermi level EF before and after the nitrogen monoxide gas molecules 48 are adsorbed is −43 meV (= _−3.922 eV−(−3.879 eV)).

Next, simulation results when the metal phthalocyanine layer 40 is formed on the graphene layer 21 as in the present embodiment will be described.

FIG. 15(a) is a plan view of a calculation model before nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40, and FIG. 15(b) is a side view thereof.

Note that FIGS. 15A and 15B show unit cells, and actual calculations were performed using a 3×3 supercell. This also applies to FIGS. 16(a) and 16(b), which will be described later.

As shown in FIG. 15B, in the calculation model before the gas molecules 48 are adsorbed, the distance Z1 between the graphene layer 21 and the metal phthalocyanine layer 40 is used.

On the other hand, FIG. 16(a) is a plan view of a calculation model after nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40, and FIG. 16(b) is a side view thereof.

As shown in FIG. 16B, in the calculation model after the gas molecules 48 are adsorbed, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 is used.

The simulation results when various metal atoms M of the metal phthalocyanine layer 40 are changed will be described below using the calculation models of FIGS. 15 and 16 .

·Copper phthalocyanine FIGS. 17A to 17C are energy band diagrams showing simulation results when a copper phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 17A is an energy band diagram of the graphene layer 21 alone. FIG. 17B is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a copper phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 (see FIG. 15(b)) between the graphene layer 21 and the metal phthalocyanine layer 40 was set to 3.00 Å.

FIG. 17C is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide are adsorbed on the metal phthalocyanine layer 40 . In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.36 Å.

As shown in FIGS. 17B and 17C, the Fermi level EF of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is _−3.741 eV, and after adsorption The Fermi level E _F of is −3.764 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is −23 meV (= _−3.764 eV−(−3.741 eV)). Become.

• Nickel phthalocyanine FIGS. 18A to 18C are energy band diagrams showing simulation results when a nickel phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 18A is an energy band diagram of the graphene layer 21 alone. FIG. 18(b) is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a nickel phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 15(b)) was set to 3.12 Å.

FIG. 18C is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide have been adsorbed on the metal phthalocyanine layer 40 . In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.23 Å.

As shown in FIGS. 18B and 18C, the Fermi level E _F of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is −3.703 eV, and after adsorption The Fermi level E _F of is −3.745 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is −42 meV (= _−3.745 eV−(−3.703 eV)). Become.

Cobalt phthalocyanine FIGS. 19A to 19C are energy band diagrams showing simulation results when a cobalt phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 19A is an energy band diagram of the graphene layer 21 alone. FIG. 19(b) is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a cobalt phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 (see FIG. 15(b)) between the graphene layer 21 and the metal phthalocyanine layer 40 was set to 3.07 Å.

FIG. 19C is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide are adsorbed on the metal phthalocyanine layer 40 . In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.26 Å.

As shown in FIGS. 19B and 19C, the Fermi level EF of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is _−3.651 eV, and after adsorption The Fermi level E _F of is −3.731 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is −80 meV (= _−3.731 eV−(−3.651 eV)). Become. From this result, it has been clarified that when a cobalt phthalocyanine layer is formed as the metal phthalocyanine layer 40, the Fermi level EF changes more than when the graphene layer 21 alone is used (-43 _meV ).

Manganese phthalocyanine FIGS. 20A to 20C are energy band diagrams showing simulation results when a manganese phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 20A is an energy band diagram of the graphene layer 21 alone. FIG. 20(b) is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a manganese phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 (see FIG. 15(b)) between the graphene layer 21 and the metal phthalocyanine layer 40 was set to 3.04 Å.

FIG. 20C is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide have been adsorbed on the metal phthalocyanine layer 40 . In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.32 Å.

As shown in FIGS. 20B and 20C, the Fermi level EF of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is _−3.556 eV, and after adsorption The Fermi level E _F of is −3.763 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is ₋₂₀₇ meV (=−3.763 eV−(−3.556 eV)). Become.

From this result, it is clear that when a manganese phthalocyanine layer is formed as the metal phthalocyanine layer 40, the change in the Fermi level EF is greater than in the case of the graphene layer 21 alone (-43 _meV ).

• Chromium phthalocyanine FIGS. 21A to 21C are energy band diagrams showing simulation results when a chromium phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 21A is an energy band diagram of the graphene layer 21 alone. FIG. 21(b) is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a chromium phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 15(b)) was set to 3.36 Å.

FIG. 21C is an energy band diagram of the graphene layer 21 when the gas molecules 48 of nitrogen monoxide are adsorbed on the metal phthalocyanine layer 40 . In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.36 Å.

As shown in FIGS. 21(b) and (c), the Fermi level EF of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is _−3.603 eV, and after adsorption The Fermi level E _F of is −3.819 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is −216 meV (= _−3.819 eV−(−3.603 eV)). Become.

From this result, it has been clarified that when a chromium phthalocyanine layer is formed as the metal phthalocyanine layer 40, the Fermi level EF changes more than when the graphene layer 21 alone is used (-43 _meV ).

• Titanium phthalocyanine FIGS. 22A to 22C are energy band diagrams showing simulation results when a titanium phthalocyanine layer is formed as the metal phthalocyanine layer 40. FIG.

Among them, FIG. 22A is an energy band diagram of the graphene layer 21 alone. FIG. 22(b) is an energy band diagram of the graphene layer 21 before adsorption of nitrogen monoxide gas molecules 48 when a titanium phthalocyanine layer is formed as the metal phthalocyanine layer 40 . The distance Z1 (see FIG. 15(b)) between the graphene layer 21 and the metal phthalocyanine layer 40 was set to 2.29 Å.

FIG. 22C is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide are adsorbed on the metal phthalocyanine layer 40. As shown in FIG. In this case, the distance Z2 between the graphene layer 21 and the metal phthalocyanine layer 40 (see FIG. 16(b)) was set to 3.38 Å.

As shown in FIGS. 22B and 22C, the Fermi level EF of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is _−3.801 eV, and after adsorption The Fermi level E _F of is −3.728 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is 73 meV (= _−3.728 eV−(−3.801 eV)). .

From this result, it has been clarified that when a titanium phthalocyanine layer is formed as the metal phthalocyanine layer 40, the Fermi level EF changes more than when the graphene layer 21 alone is used (-43 _meV ).

FIG. 23 is a table summarizing the results of FIGS. 17-22.
In FIG. 23, in addition to the variation ΔE _F in the Fermi level _EF , the variation I _d2 /I _d1 in the binding energy E _bin and the drain current is also shown. Of these, the binding energy E _bin is the binding energy between the metal phthalocyanine layer 40 and the nitrogen monoxide gas molecules 48 . Its binding energy E _bin was particularly strong in the chromium phthalocyanine layer 40, suggesting that nitric oxide gas molecules 48 adsorb to the chromium atoms.

Also, the amount of change in drain current I _d2 /I _d1 is the ratio of drain currents before and after flat band voltage V _FB changes by ΔV _FB due to adsorption of gas molecules 48, as described with reference to FIG. be. As described above, the amount of change I _d2 /I _{d1 satisfies} I _d2 /I _d1 =10 ^(Δφ/SS) _. and

Furthermore, FIG. 23 also shows the results for vanadium phthalocyanine and iron phthalocyanine.

As shown in FIGS. 14A and 14B, when the metal phthalocyanine layer 40 is not formed, the variation ΔE _F of the Fermi level _EF of the graphene layer 21 is −43 meV. According to FIG. 23, the absolute value of variation ΔE _F exceeds 43 meV for each of titanium phthalocyanine, vanadium phthalocyanine, chromium phthalocyanine, manganese phthalocyanine, iron phthalocyanine, and cobalt phthalocyanine. As a result, the amount of change in drain current I _d2 /I _d1 when these metal phthalocyanines were used was 10 or more, and it was clarified that the presence or absence of nitrogen monoxide gas molecules 48 can be measured with high sensitivity by the gas sensor 50. .

In particular, the variation I _d2 /I _d1 exceeds 2,000 for chromium phthalocyanine. The amount of change ΔE _F when the metal phthalocyanine layer 40 is not formed is −43 meV, and the amount of change I _d2 /I _d1 in this case is about 4.5. Therefore, when a chromium phthalocyanine layer is formed as the metal phthalocyanine layer 40, the sensitivity to nitric oxide is about 450 times higher than when the metal phthalocyanine layer 40 is not formed. In the case of metal atoms with a negative variation ΔE _F , electrons move from the metal phthalocyanine layer 40 to the graphene layer 21 due to the adsorption of nitrogen monoxide gas molecules 48, suggesting that the graphene layer 21 is doped n-type. are doing. This also revealed that the electron transfer of the model of FIG. 12 actually occurs.

In addition, even if a molecular layer having a molecular structure similar to that of metal phthalocyanine is formed in place of the metal phthalocyanine layer 40, it is considered that the amount of change in drain current I _d2 /I _d1 increases in the same manner as described above. Such molecules include porphyrin containing a metal element and its isomers, and these molecular layers may be formed instead of the metal phthalocyanine layer 40 . Porphyrin isomers include, for example, porphycene, colphycene, and hemiporphycene.

According to the present embodiment described above, by forming the metal phthalocyanine layer 40 on the graphene layer 21, the Fermi level EF of the graphene layer 21 when the nitrogen monoxide gas molecules 48 are _adsorbed changes greatly. do. As a result, the gas sensor 50 can measure the presence or absence of nitric oxide and its concentration with high accuracy, and the gas sensor 50 can be applied to pathological determination of asthma.

The metal phthalocyanine layer 40 includes a titanium phthalocyanine layer, a vanadium phthalocyanine layer, a chromium phthalocyanine layer, a manganese phthalocyanine layer, an iron phthalocyanine layer, and a cobalt phthalocyanine layer. According to the results of FIG. 23, by using these metal phthalocyanine layers 40, the amount of change in drain current I _d2 /I _d1 is 10 times or more. detection sensitivity is greatly increased.

(Second embodiment)
After the gas molecules are detected by the gas sensor, it is preferable that the gas sensor is refreshed by heating to desorb the gas molecules from the gas sensor so that the gas sensor can be reused. In this embodiment, a gas sensor from which gas molecules are easily desorbed by refreshing will be described.

24 to 26 are cross-sectional views of the gas sensor according to this embodiment during manufacturing. 24 to 26, the same elements as those explained in the first embodiment are given the same reference numerals as in the first embodiment, and the explanation thereof will be omitted below.

First, a structure in which a gate insulating layer 33 is formed on a semiconductor substrate 30 is obtained as shown in FIG.

Subsequently, as shown in FIG. 24(b), the semiconductor substrate 30 is placed in a vapor deposition chamber, and the semiconductor substrate 30 is heated to about room temperature to 200° C. in the vapor deposition chamber. The pressure inside the vapor deposition chamber is set to 10 ⁻¹ Pa or less. Then, the metal phthalocyanine vaporized at a temperature of about 200° C. to 300° C. is supplied to the deposition chamber to form the metal phthalocyanine layer 40 on the gate insulating layer 33 at a growth rate of 1 Å/sec or less. The thickness of the metal phthalocyanine layer 40 is not particularly limited, but in this example, the metal phthalocyanine layer 40 is formed with a thickness of one molecular layer.

As in the first embodiment, the metal phthalocyanine layer 40 may be replaced with a molecular layer of porphyrin containing a metal element or an isomer thereof. The porphyrin isomers include, for example, porphycene, colphycene, and hemiporphycene.

Next, the process shown in FIG. 24(c) will be described.
First, a structure in which the graphene layer 21 is formed on the support layer 22 is produced by performing the steps of FIGS. 5A to 5C of the first embodiment. Then, the back surface 21 b of the graphene layer 21 is brought into close contact with the metal phthalocyanine layer 40 , and the support layer 22 is pressed to press the graphene layer 21 onto the metal phthalocyanine layer 40 .

In order to prevent the metal phthalocyanine layer 40 from being oxidized, it is preferable to perform this step in a reduced pressure atmosphere or an inert gas atmosphere. After the metal phthalocyanine layer 40 is formed in the step of FIG. 24(b), the metal phthalocyanine layer 40 is not exposed to the air, and the graphene layer 21 is adhered thereon, thereby preventing the metal phthalocyanine layer 40 from being oxidized. can be effectively suppressed.

Next, as shown in FIG. 25A, the support layer 22 is dissolved in an organic solvent such as acetone and removed, leaving the graphene layer 21 on the metal phthalocyanine layer 40 .

Subsequently, as shown in FIG. 25B, a resist is applied on the graphene layer 21, and the resist is exposed and developed to form a first island-shaped resist layer 35. Next, as shown in FIG. Then, while using the first resist layer 35 as a mask, the graphene layer 21 and the metal phthalocyanine layer 40 in the portions not covered with the first resist layer 35 are removed by RIE using oxygen gas as an etching gas. .

After that, the first resist layer 35 is removed with an organic solvent.

Next, as shown in FIG. 25(c), a resist is applied again to the entire upper surface of the semiconductor substrate 30, exposed and developed to form a second resist so as to cover the side surfaces 21c and 21d of the graphene layer 21. Next, as shown in FIG. A resist layer 36 is formed.

Then, while leaving the gate insulating layer 33 between the source region 31 and the drain region 32, the portion of the gate insulating layer 33 not covered with the second resist layer 36 is etched with a hydrofluoric acid solution and removed.

After that, the second resist layer 36 is removed with an organic solvent.

As in the first embodiment, the second resist layer 36 is formed so as to cover the side surfaces 21c and 21d of the graphene layer 21 in the present embodiment as well, so that the side surfaces 21c and 21d are aligned with the side surfaces 33a of the gate insulating layer 33. , 33b. As a result, the graphene layer 21 is separated from each of the source region 31 and the drain region 32 , and electrical connection of the graphene layer 21 with the source region 31 and the drain region 32 can be suppressed.

Next, as shown in FIG. 26, a source electrode 37 and a drain electrode 38 are formed on the source region 31 and the drain region 32, respectively, by performing the same step as in FIG. 7C of the first embodiment. . Along with this, the gate electrode 39 is formed on the surface 21a in the first region R1 of the graphene layer 21 so that the second region R2 of the graphene layer 21 is exposed.

With the above, the basic structure of the gas sensor 60 according to the present embodiment is completed.

27 is a plan view of this gas sensor 60. FIG. Note that FIG. 26 described above corresponds to a cross-sectional view taken along line II--II in FIG.

As shown in FIG. 27, each of the graphene layer 21 and the metal phthalocyanine layer 40 is patterned into a rectangular shape in the second region R2. The second region R2 functions as a gas detection region, and the drain current of the gas sensor 60 changes due to gas molecules adsorbed on the graphene layer 21 in the second region R2.

Next, a method of using the gas sensor 60 according to this embodiment will be described.

FIG. 28 is a cross-sectional view for explaining how to use the gas sensor 60 according to this embodiment. In FIG. 28, the same reference numerals as in the first embodiment denote the same elements as those described in the first embodiment, and the description thereof will be omitted below.

As shown in FIG. 28, in actual use, a bias voltage V is applied from the third terminal 47 to the gate electrode 39 while applying a drain voltage V _d between the first terminal 45 and the second terminal 46 . _{Apply bias} .

At this time, when the gas molecules 48 bind to the graphene layer 21 in the second region R2, the work function of the graphene layer 21 changes. As a result, the drain current I _d flowing between the source region 31 and the drain region 32 changes, and by measuring the amount of change, the presence and concentration of nitrogen monoxide gas molecules 48 can be known.

Moreover, since the metal phthalocyanine layer 40 is formed under the graphene layer 21 in this example, the bonding force acting between the metal phthalocyanine layer 40 and the gas molecules 48 is weakened by the graphene layer 21 . Therefore, by heating the gas sensor 60 after measurement, the gas molecules 48 are easily desorbed from the graphene layer 21, and the gas sensor 60 can be easily refreshed.

Furthermore, since the metal phthalocyanine layer 40 is covered with the graphene layer 21, it is possible to prevent the metal phthalocyanine layer 40 from being oxidized by atmospheric oxygen or the like. In addition, since the metal phthalocyanine layer 40 is not directly contacted by the gas molecules 48, chemical change of the metal phthalocyanine layer 40 by the gas molecules 48 can be prevented.

Next, the mechanism by which the gas sensor 60 detects the gas molecules 48 will be described in more detail.

FIG. 29 is a schematic diagram showing a mechanism for detecting gas molecules 48 with the gas sensor 60. As shown in FIG.

Note that FIG. 29 illustrates the HOMO and LUMO of the gas molecules 48 . For the graphene layer 21, energy band curves of the valence band B _GV and the conduction band B _GC are also shown. As in FIG. 12, the valence band B _GV and the conduction band B _GC extend above and below the Dirac point D, and are filled with electrons up to the hatched energies of dots. This also applies to FIG. 30, which will be described later.

As shown in FIG. 29 , when gas molecules 48 are adsorbed on the surface of the graphene layer 21 , electrons e ⁻ move from the HOMO of the gas molecules 48 to the conduction band B _GC of the graphene layer 21 . As a result, the number of electrons in the conduction band B _GC of the graphene layer 21 increases as in the first embodiment.

FIG. 30 is a schematic diagram when electrons move in the direction opposite to that in FIG.

In this case, the electron e ⁻ moves from the conduction band B _GC of the graphene layer 21 to the LUMO of the gas molecule 48 .

30 or 29 depends on the adsorption energy of the gas molecules 48 to the graphene layer 21, the difference in electronegativity between the two, the band alignment between the graphene layer 21 and the gas molecules 48, and the like.

In both cases of FIG. 30 and FIG. 29, the Fermi level EF of the _graphene layer 21 changes as the number of electrons in the conduction band B _GC changes. Also, the metal phthalocyanine layer 40 under the graphene layer 21 has the effect of changing the electronic state of the graphene layer 21 . This changes the relative energy position between the gas molecules 48 such as band alignment and the graphene layer 21, and makes it possible to control the amount of electrons e ⁻ moving between them.

Next, simulation results when the metal phthalocyanine layer 40 is formed under the graphene layer 21 as in the present embodiment will be described.

FIG. 31( a ) is a side view of the calculation model before the nitrogen monoxide gas molecules 48 are adsorbed on the graphene layer 21 . Note that FIG. 31(a) shows a unit cell, and the actual calculation was performed using a 3×3 super cell. This also applies to FIG. 31(b), which will be described later.

In addition, in the calculation model of FIG. 31(a), the distance between the graphene layer 21 and the metal phthalocyanine layer 40 is Z3.

On the other hand, FIG. 31( b ) is a side view of the calculation model after the gas molecules 48 of nitric oxide are adsorbed on the graphene layer 21 . In this calculation model, the distance between the graphene layer 21 and the metal phthalocyanine layer 40 is Z4. Also, the distance between the gas molecules 48 and the graphene layer 21 was Z5.

The inventors of the present application used the calculation models of FIGS. 31(a) and (b) to determine how the Fermi level EF of the _graphene layer 21 changes when the gas molecules 48 of nitric oxide are adsorbed. A simulation was performed to confirm.

FIGS. 32(a) and 32(b) are energy band diagrams showing the simulation results.

In the simulation, a chromium phthalocyanine layer was formed as the metal phthalocyanine layer 40 .

FIG. 32( a ) is an energy band diagram of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the graphene layer 21 . The interval Z3 (see FIG. 31(a)) in this case was set to 2.32 Å.

On the other hand, FIG. 32B is an energy band diagram of the graphene layer 21 after the gas molecules 48 of nitrogen monoxide have been adsorbed on the graphene layer 21 . The interval Z4 (see FIG. 31(b)) in this case was set to 2.36 Å. Also, the distance Z5 between the gas molecules 48 and the graphene layer 21 (see FIG. 31(b)) was set to 2.38 Å.

As shown in FIGS. 32A and 32B, the Fermi level E _F of the graphene layer 21 before the nitrogen monoxide gas molecules 48 are adsorbed on the metal phthalocyanine layer 40 is −3.603 eV, and the gas molecules The Fermi level E _F after adsorption of 48 is −3.668 eV. As a result, the amount of change ΔE _F in the Fermi level EF of the graphene layer 21 before and after the nitrogen monoxide gas molecules 48 are adsorbed is −65 meV (= _−3.668 eV−(−3.603 eV)). Become.

The absolute value of this change is larger than the absolute value of the change (−43 _meV ) of the Fermi level EF of the graphene layer 21 when the metal phthalocyanine layer 40 is not formed. This shows that forming the metal phthalocyanine layer 40 under the graphene layer 21 is effective in increasing the amount of change ΔE _F in the Fermi level _EF associated with the adsorption of the nitrogen monoxide gas molecules 48 . It became clear.

FIG. 33 is a diagram showing the variation I _d2 /I _d1 of the drain current assumed in this embodiment. For comparison, FIG. 33 also shows the amount of change I _d2 /I _d1 in the single graphene layer 21 without the metal phthalocyanine layer 40 .

As described in the first embodiment, the variation I _d2 /I _d1 satisfies I _d2 /I _d1 =10 ^(Δφ/SS) . In calculating the amount of change I _d2 /I _d1 in FIG. 33, it was assumed that the subthreshold swing SS was equal to 65 mV/decade.

As shown in FIG. 33, when the metal phthalocyanine layer 40 is formed under the graphene layer 21 as in the present embodiment, the variation I _d2 /I _d1 is more than doubled compared to the case where the metal phthalocyanine layer 40 is not formed. became. From this result, it became clear that even if the metal phthalocyanine layer 40 is formed under the graphene layer 21, nitric oxide can be detected with high sensitivity.

(Third Embodiment)
In this embodiment, the graphene layer 21 and the metal phthalocyanine layer 40 are laminated by a method different from that of the second embodiment.

34 to 36 are cross-sectional views of the gas sensor according to this embodiment during manufacturing. 34 to 36, the same elements as those described in the first and second embodiments are assigned the same reference numerals as in these embodiments, and the description thereof will be omitted below.

First, by performing the steps of FIGS. 5A to 5C described in the first embodiment, a structure in which the graphene layer 21 is formed on the support layer 22 as shown in FIG. make.

Next, as shown in FIG. 34(b), a metal phthalocyanine layer 40 having a thickness of one molecular layer is formed on the back surface 21b of the graphene layer 21 by vapor deposition. The growth conditions of the metal phthalocyanine layer 40 are not particularly limited, and the metal phthalocyanine layer 40 can be formed, for example, under conditions in which the temperature of the graphene layer 21 is from room temperature to about 200° C. in a vapor deposition chamber with a pressure of 10 ⁻¹ Pa or less. . In that case, the metal phthalocyanine layer 40 is grown at a growth rate of 1 Å/sec or less by supplying metal phthalocyanine vaporized at a temperature of about 200° C. to 300° C. to the vapor deposition chamber.

Subsequently, as shown in FIG. 35(a), a structure in which a gate insulating layer 33 is formed on the semiconductor substrate 30 is obtained in the same manner as in the step of FIG. 24(a) of the second embodiment.

Then, as shown in FIG. 35B, the surface 40a of the metal phthalocyanine layer 40 formed in the step of FIG. Then, by pressing the support layer 22 , the metal phthalocyanine layer 40 is pressure-bonded to the gate insulating layer 33 together with the graphene layer 21 .

Next, as shown in FIG. 35C, the supporting layer 22 is dissolved in an organic solvent such as acetone and removed, leaving the graphene layer 21 and the metal phthalocyanine layer 40 on the gate insulating layer 33 .

After that, the steps of FIGS. 25B to 26 of the second embodiment are performed to obtain the basic structure of the gas sensor 60 according to the present embodiment, as shown in FIG.

In the gas sensor 60, the surface 21a of the graphene layer 21 is exposed in the second region R2, and nitrogen monoxide molecules can be detected by binding to the surface 21a.

According to the present embodiment described above, in the step of FIG. 35B, the graphene layer 21 and the metal phthalocyanine layer 40 are simultaneously transferred to the gate insulating layer 33 in a laminated state. Therefore, there is less room for impurities such as moisture to enter between the graphene layer 21 and the metal phthalocyanine layer 40, and the adhesion between the graphene layer 21 and the metal phthalocyanine layer 40 is improved.

Furthermore, since the metal phthalocyanine layer 40 is formed under the graphene layer 21 in this embodiment as well as in the second embodiment, the gas molecules can be separated from the graphene layer 21 by heating to refresh the gas sensor 60.

The following supplementary remarks are further disclosed regarding each of the embodiments described above.
(Appendix 1) A semiconductor substrate;
a source region formed in a surface layer of the semiconductor substrate;
a drain region formed in the surface layer of the semiconductor substrate;
a gate insulating layer formed on the semiconductor substrate between the source region and the drain region;
a graphene layer formed on the gate insulating layer;
a gate electrode formed on the surface of the first region of the graphene layer;
a metal phthalocyanine layer formed on either the front surface or the back surface of the second region of the graphene layer;
A gas sensor comprising:
(Appendix 2) The gas sensor according to Appendix 1, wherein the graphene layer has a thickness of one atomic layer.
(Appendix 3) The gas sensor according to appendix 1, wherein the metal phthalocyanine layer is formed on the surface to have a thickness of one molecular layer.
(Appendix 4) The gas sensor according to appendix 1, wherein the metal phthalocyanine layer is any one of a titanium phthalocyanine layer, a vanadium phthalocyanine layer, a chromium phthalocyanine layer, a manganese phthalocyanine layer, an iron phthalocyanine layer, and a cobalt phthalocyanine layer. .
(Appendix 5) The metal phthalocyanine layer is formed on the back surface,
The gas sensor according to appendix 1, wherein the graphene layer in the second region is exposed.
(Appendix 6) The gas sensor according to appendix 1, wherein the metal phthalocyanine layer is formed on the surface, and the metal phthalocyanine layer is exposed in the second region.
(Appendix 7) The gas sensor according to appendix 1, wherein a side surface of the graphene layer closer to the source region recedes from a side surface of the gate insulating layer closer to the source region toward the drain region.
(Appendix 8) forming a source region in a surface layer of a semiconductor substrate;
forming a drain region in the surface layer of the semiconductor substrate;
forming a gate insulating layer over the semiconductor substrate between the source and drain regions;
forming a graphene layer on the gate insulating layer;
forming a gate electrode on the surface of the graphene layer in the first region;
forming a metal phthalocyanine layer on the surface in the second region of the graphene layer;
A method of manufacturing a gas sensor, comprising:
(Appendix 9) The step of forming the graphene layer includes
pressing the graphene layer formed on the support layer to the gate insulating layer while heating the graphene layer;
and removing the support layer after the pressure bonding.
(Appendix 10) The method of manufacturing a gas sensor according to appendix 8, wherein the step of forming the metal phthalocyanine layer is performed by vapor deposition while heating the semiconductor substrate.
(Appendix 11) forming a source region in a surface layer of a semiconductor substrate;
forming a drain region in the surface layer of the semiconductor substrate;
forming a gate insulating layer on the surface of the semiconductor substrate between the source region and the drain region;
forming a metal phthalocyanine layer on the gate insulating layer;
forming a graphene layer on the metal phthalocyanine layer;
forming a gate electrode on the surface of the first region of the graphene layer such that the second region of the graphene layer is exposed;
A method of manufacturing a gas sensor, comprising:
(Appendix 12) The step of forming the metal phthalocyanine layer and the step of forming the graphene layer are
forming the graphene layer on a support layer;
forming the metal phthalocyanine layer on the graphene layer;
pressing the metal phthalocyanine layer together with the graphene layer to the gate insulating layer;
12. The method of manufacturing a gas sensor according to appendix 11, further comprising: removing the support layer after the pressure bonding.

Reference Signs List 1 Gas sensor 2 Silicon substrate 2a Channel 3 Source region 4 Drain region 5 Gate insulating layer 6 Graphene layer 7 Gate electrode 8 Source electrode 9 Drain electrode 20 Catalyst metal foil 21 Graphene layer 21a Front surface 21b Back surface 21c, 21d Side surface 22 Support layer 30 Semiconductor substrate 30a Channel 31 Source region 32 Drain region 33 Gate insulating layer 33a, 33b Side surface 35 First resist layer 36 Second resist layer 37 Source electrode 38 Drain electrode 39 Gate electrode 40 Metal phthalocyanine layer 40a Surface , 45... first terminal, 46... second terminal, 47... third terminal, 48... gas molecule, 50, 60... gas sensor.

Claims (6)

a semiconductor substrate;
a source region formed in a surface layer of the semiconductor substrate;
a drain region formed in the surface layer of the semiconductor substrate;
a gate insulating layer formed on the semiconductor substrate between the source and drain regions;
a graphene layer formed on the gate insulating layer;
a gate electrode formed on the surface of the first region of the graphene layer;
a metal phthalocyanine layer that is a chromium phthalocyanine layer formed on the surface in the second region of the graphene layer;
A gas sensor comprising: a semiconductor substrate;
a source region formed in a surface layer of the semiconductor substrate;
a drain region formed in the surface layer of the semiconductor substrate;
a gate insulating layer formed on the semiconductor substrate between the source and drain regions;
a graphene layer formed on the gate insulating layer;
a gate electrode formed on the surface of the first region of the graphene layer;
a metal phthalocyanine layer formed on the back surface of the second region of the graphene layer;
A gas sensor comprising: 3. The gas sensor according to claim 1 , wherein the graphene layer has a thickness of one atomic layer. 3. The gas sensor according to claim 1 , wherein said metal phthalocyanine layer is formed to have a thickness of one molecular layer. forming a source region in a surface layer of a semiconductor substrate;
forming a drain region in the surface layer of the semiconductor substrate;
forming a gate insulating layer over the semiconductor substrate between the source and drain regions;
forming a graphene layer on the gate insulating layer;
forming a gate electrode on the surface of the graphene layer in the first region;
forming a metal phthalocyanine layer , which is a chromium phthalocyanine layer, on the surface of the second region of the graphene layer;
A method of manufacturing a gas sensor, comprising: forming a source region in a surface layer of a semiconductor substrate;
forming a drain region in the surface layer of the semiconductor substrate;
forming a gate insulating layer over the semiconductor substrate between the source and drain regions;
forming a metal phthalocyanine layer on the gate insulating layer;
forming a graphene layer on the metal phthalocyanine layer;
forming a gate electrode on the surface of the first region of the graphene layer such that the second region of the graphene layer is exposed;
A method of manufacturing a gas sensor, comprising:

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