JP7359793B2 - Field effect transistor, gas sensor, and manufacturing method thereof - Google Patents

Description

The present disclosure relates to a field effect transistor, a gas sensor, and a method of manufacturing the same.

BACKGROUND OF THE INVENTION Among metal organic frameworks (MOFs) there are materials with semiconducting properties, and such materials can be applied as semiconductor layers of field effect transistors (also referred to as FETs). Furthermore, some metal-organic structures have gas adsorption ability in addition to semiconductor properties, and such materials can be used in gas sensors.

For example, Patent Document 1 includes a field effect transistor, a detection region provided on the field effect transistor, and a sensitive film provided in the detection region, and the sensitive film includes a metal-organic structure. A chemical sensor is disclosed. Patent Document 1 describes that this chemical sensor can accurately detect a component to be detected in a sample.

WO2016/185679

As mentioned above, field effect transistors using metal-organic structure films can be applied to various devices including gas sensors, and there is a desire for the development of further novel field effect transistors. In particular, there is a need for field effect transistors that can realize low voltage drive.

Therefore, an object of the present disclosure is to provide a field effect transistor that uses a metal-organic structure film as a semiconductor layer and has a novel structure.

Example aspects of this embodiment are described as follows.

(1) A field effect transistor including a substrate, a source electrode, a drain electrode, a gate electrode, and a metal-organic structure film as a semiconductor layer,
A metal-organic structure film has a plurality of crystal structures in which organic ligands and metal ions having a π-conjugated skeleton are coordinated so as to extend in the plane direction of the substrate. Including a laminated structure laminated on top,
Each crystal structure has pores formed by coordination of organic ligands and metal ions, and in the layered structure, pores of adjacent crystal structures communicate in the film thickness direction,
A top contact type field effect transistor.
(2) The field effect transistor according to (1), which is a bottom gate-top contact type.
(3) The field effect transistor according to (1) or (2), wherein the π-conjugated skeleton includes at least one aromatic ring.
(4) The field effect transistor according to any one of (1) to (3), wherein the π-conjugated system skeleton is a polycyclic aromatic hydrocarbon structure.
(5) The field effect transistor according to any one of (1) to (4), wherein the organic ligand has three-fold symmetry.
(6) The field effect transistor according to any one of (1) to (5), wherein the metal ion is a metal ion that can have a coordination number of 4 or more.
(7) The field effect transistor according to any one of (1) to (6), wherein the gate electrode is an aluminum electrode.
(8) The field effect transistor according to (7), wherein aluminum oxide is formed as a gate insulating layer on the surface of the aluminum electrode.
(9) The metal-organic structure film includes a step of applying a metal ion-containing solution containing metal ions onto a substrate, and a step of applying an organic ligand-containing solution containing an organic ligand onto the substrate. The field effect transistor according to any one of (1) to (8), which is formed by an LBL method including:
(10) A gas sensor comprising the field effect transistor according to any one of (1) to (9).
(11) A method for manufacturing the field effect transistor according to any one of (1) to (8), comprising: a metal-organic structure film;
applying a metal ion-containing solution containing metal ions onto the substrate;
applying an organic ligand-containing solution containing an organic ligand onto the substrate;
A method comprising the step of forming by an LBL method comprising:

According to the present disclosure, it is possible to provide a field effect transistor that uses a metal-organic structure film as a semiconductor layer and has a novel structure.

FIG. 1 is a schematic cross-sectional view for explaining the basic structure of a bottom gate-top contact field effect transistor 10, which is an example of a field effect transistor according to the present embodiment. FIG. 2 is a schematic cross-sectional view for explaining the basic structure of a bottom gate-bottom contact field effect transistor 200, which is an example of a field effect transistor. 1 is an AFM image of the metal-organic structure film obtained in Example 1. 1 is an AFM image (enlarged) of the metal-organic structure film obtained in Example 1. 1 is an FE-SEM image of a cross section of the metal-organic structure film obtained in Example 1. 1 is an FT-IR spectrum of the metal-organic structure film obtained in Example 1. 2 is a graph showing the results of electrical resistance evaluation of the metal-organic structure film obtained in Example 1. FIG. 7 is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3. FIG. 6A is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3, following FIG. 6A. Continuing from FIG. 6B, it is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3. FIG. 6C is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3, continuing from FIG. 6C. FIG. 6D is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3, continuing from FIG. 6D. Continuing from FIG. 6E, it is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (top contact type) in Example 2 or 3. 1 is an FT-IR spectrum of a particulate MOF obtained in Comparative Example 1. 1 is an XRD spectrum of a particulate MOF obtained in Comparative Example 1. 7 is a graph showing the results of evaluating the transfer characteristics of the field effect transistor E1 obtained in Example 2. 5 is a graph showing the results of evaluating the output characteristics of the field effect transistor E1 obtained in Example 2. 3 is a graph showing the results of evaluating the transfer characteristics of the field effect transistor C1 obtained in Comparative Example 1. FIG. 7 is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (bottom contact type) in Comparative Example 2. FIG. 10A is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (bottom contact type) in Comparative Example 2, following FIG. 10A. Continuing from FIG. 10B, it is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (bottom contact type) in Comparative Example 2. FIG. 10C is a schematic cross-sectional process diagram for explaining the manufacturing process of a field effect transistor (bottom contact type) in Comparative Example 2, continuing from FIG. 10C. 3 is a graph showing the results of evaluating the transfer characteristics of field effect transistor E2 (Example 3). 3 is a graph showing the results of evaluating the transfer characteristics of field effect transistor C2 (Comparative Example 2).

This embodiment is a field effect transistor including a substrate, a source electrode, a drain electrode, a gate electrode, and a metal-organic structure film as a semiconductor layer, in which the metal-organic structure film is an organic structure having a π-conjugated skeleton. It includes a layered structure in which a plurality of crystal structures in which atoms and metal ions are coordinated so as to expand in the plane direction of the substrate are stacked on the substrate via π-π interaction, and each crystal structure is , has pores formed by coordination of organic ligands and metal ions, and in the laminated structure, pores of adjacent crystal structures communicate in the film thickness direction, and are of a top contact type. , which is a field effect transistor.

According to this embodiment, it is possible to provide a field effect transistor that uses a metal-organic structure film as a semiconductor layer and has a novel structure. Further, the field effect transistor according to this embodiment can preferably be driven at a low voltage.

Hereinafter, the present embodiment will be described with reference to the drawings, but the present disclosure is not limited to the following embodiment.

1. Field-Effect Transistor The field-effect transistor of this embodiment includes, as a semiconductor layer, the metal-organic structure film of this embodiment, the details of which will be described later. In addition to the semiconductor layer, the field effect transistor of this embodiment includes a substrate, a source electrode, a drain electrode, and a gate electrode. The field effect transistor of this embodiment is a top contact type. The field effect transistor of this embodiment is preferably used as an insulated gate FET in which the gate and channel are insulated.

The thickness of the field effect transistor of this embodiment excluding the substrate is not particularly limited, but is, for example, 150 to 350 nm.

The field effect transistor of this embodiment preferably includes a substrate, a gate electrode on the substrate, a metal-organic structure film, a gate insulating layer between the gate electrode and the metal-organic structure film, and a metal-organic structure film. It has a source electrode and a drain electrode that are provided in contact with and connected to each other via a metal-organic structure film. In this field effect transistor, a metal-organic structure film and a gate insulating layer are provided adjacent to each other.

The structure of the field effect transistor of this embodiment is a top contact type. Examples of the top contact type include a bottom gate-top contact type and a top gate-top contact type. The field effect transistor of this embodiment is a top contact type, more preferably a bottom gate-top contact type. When the field effect transistor of this embodiment is a top contact type, it can be driven more effectively at a low voltage. This is presumably because the top contact structure has high adhesion between the semiconductor layer and the electrode and can achieve higher mobility than the bottom contact structure. Note that this embodiment is not limited by this assumption.

FIG. 1A is a schematic cross-sectional view for explaining the basic structure of a bottom gate-top contact type field effect transistor 10, which is an example of the field effect transistor of this embodiment. On the other hand, FIG. 1B is a schematic cross-sectional view for explaining the basic structure of a bottom contact type field effect transistor 200 (bottom gate-bottom contact type), which is not the present embodiment.

As shown in FIG. 1A, the field effect transistor 10 (bottom gate-top contact type) includes a substrate 1, a gate electrode 2, a gate insulating layer 3, a metal organic structure film 5 as a semiconductor layer, and a source. It has an electrode 4A and a drain electrode 4B in this order. This structure may be covered with a sealing layer (not shown). The sealing layer can be made of a gas-permeable material, for example.

The field effect transistor 200 (bottom gate-bottom contact type) differs from the field effect transistor 10 in the stacking mode. As shown in FIG. 1B, the field effect transistor 200 (bottom gate-bottom contact type) includes a substrate 201, a gate electrode 202, a gate insulating layer 203, a source electrode 204A, a drain electrode 204B, and a semiconductor layer. and metal-organic structure film 205 in this order.

The substrate, gate electrode, gate insulating layer, source electrode, drain electrode, and metal-organic structure film will be described below.

(substrate)
The substrate plays a role of supporting a gate electrode, a source electrode, a drain electrode, and the like.

The type of substrate is not particularly limited, and examples thereof include a plastic substrate, a silicon substrate, a glass substrate, and a ceramic substrate. Among these, from the viewpoint of device applicability and cost, a glass substrate or a plastic substrate is preferable.

(gate electrode)
The gate electrode is not particularly limited, and for example, a general electrode used as a gate electrode of a field effect transistor can be used.

The material of the gate electrode is not particularly limited, and examples thereof include metals such as gold, silver, aluminum, copper, chromium, nickel, cobalt, titanium, platinum, magnesium, calcium, barium, and sodium, InO ₂ , and SnO ₂ or conductive oxides such as indium tin oxide (ITO), conductive polymers such as polyaniline, polypyrrole, polythiophene, polyacetylene or polydiacetylene, semiconductors such as silicon, germanium or gallium arsenide, or fullerenes, carbon nanotubes or Examples include carbon materials such as graphite. Among these, metal is preferred, and aluminum is preferred. Since aluminum has a lower sublimation temperature than other metals, it can be formed into a film under mild conditions. Furthermore, a metal oxide film (aluminum oxide film) can be formed on the surface of the metal electrode under mild conditions. Furthermore, since the obtained aluminum oxide film has a large capacitance, low voltage driving can be effectively achieved.

The method for forming the gate electrode is not particularly limited, but examples include a method of vapor depositing or sputtering an electrode material on a substrate, and a method of applying an electrode forming composition containing an electrode material. . Further, when patterning the electrode, the patterning method includes, for example, a printing method such as inkjet printing, screen printing, offset printing, or letterpress printing (flexo printing), a photolithography method, or a mask vapor deposition method.

(gate insulating layer)
The gate insulating layer is not particularly limited as long as it is a layer having insulating properties. Further, the gate insulating layer may be a single layer or a multilayer.

Materials for the gate insulating layer are not particularly limited, but include, for example, inorganic oxides such as aluminum oxide, silicon nitride, silicon dioxide, or titanium oxide, polymethyl methacrylate, polystyrene, polyvinylphenol, melamine resin, polyimide, Examples include polymers such as polycarbonate, polyester, polyvinyl alcohol, polyvinyl acetate, polyurethane, polysulfone, polybenzoxazole, polysilsesquioxane, epoxy resin, or phenolic resin. The materials for the gate insulating layer may be used alone or in combination of two or more. Among these, inorganic oxides are preferred, and aluminum oxide is preferred in terms of film uniformity. In order to achieve sufficient charge induction in the semiconductor by applying a low voltage to the gate electrode, it is desirable to increase the capacitance of the gate insulating film. Therefore, low voltage driving can be achieved by introducing an aluminum oxide film having a large capacitance into the top contact structure. The aluminum oxide film can be formed by oxidizing aluminum under relatively mild conditions (for example, oxygen plasma irradiation energy: approximately 150 W, irradiation time from several minutes to several tens of minutes). Further, since the aluminum oxide film has excellent insulation properties even if it is a thin film, it can contribute to low voltage driving. Furthermore, when manufacturing a MOF transistor with a top contact structure, the hydroxyl groups present on the surface of the aluminum oxide film can bond with metal ions and become the basis for constructing the MOF film.

The method for forming the gate insulating layer is not particularly limited, but examples include a method of applying a composition for forming a gate insulating layer containing the above-mentioned material onto a substrate on which a gate electrode is formed, Examples include methods of vapor deposition or sputtering. In addition, it is also possible to oxidize the surface of the metal serving as the gate electrode to form an oxide, and use this oxide as the gate insulating layer. For example, the gate electrode can be formed of aluminum, and the surface of this aluminum can be oxidized to aluminum oxide by reactive ion etching or the like to form an insulating layer.

(source electrode and drain electrode)
The source electrode is an electrode into which a current flows from the outside through wiring. Further, the drain electrode is an electrode that sends a current to the outside through wiring.

The material for forming the source electrode and the drain electrode can be the same as the electrode material for forming the gate electrode described above. Among these, metal is preferred, and gold or silver is preferred.

The distance between the source electrode and the drain electrode (gate length) can be determined as appropriate, but is preferably 200 μm or less, and particularly preferably 100 μm or less, for example. Furthermore, although the gate width can be determined as appropriate, it is preferably 5000 μm or less, particularly preferably 2000 μm or less, for example. Further, the ratio between the gate width W and the gate length L is not particularly limited, but for example, the ratio W/L is preferably 10 or more, and preferably 20 or more.

The method for forming the source electrode and the drain electrode is not particularly limited, but for example, the electrode material may be deposited on the substrate on which the gate electrode, the gate insulating layer, and optionally the metal-organic structure film are formed. Examples include a sputtering method and a method of applying or printing an electrode forming composition. In the case of patterning, the patterning method may be the same as the method for forming the gate electrode described above.

(Metal-organic structure film)
The field effect transistor of this embodiment includes a metal-organic structure film as a semiconductor layer. The metal-organic structure film has a π- It includes a stacked structure stacked on a substrate via π interaction. Each crystal structure has pores formed by the coordination of organic ligands and metal ions, and in the layered structure, the pores of adjacent crystal structures communicate in the film thickness direction, forming communicating pores. are doing.

The metal-organic structure film in this embodiment can be formed by an LBL (Layer By Layer) method using an organic ligand having a π-conjugated skeleton and a metal ion. In the LBL method, a metal ion-containing solution containing metal ions and an organic ligand-containing solution containing organic ligands are alternately applied onto a region where a metal-organic structure film is to be formed by drop casting or the like. This is a method of forming a thin film while coating. The metal-organic structure film in this embodiment can be preferably obtained by the LBL method using an organic ligand having a π-conjugated skeleton and a metal ion. That is, the metal-organic structure film formed by the LBL method includes a plurality of crystal structures in which organic ligands having a π-conjugated skeleton and metal ions are coordinated so as to expand in a plane direction. In such a crystal structure, pores are formed by coordination of an organic ligand having a π-conjugated skeleton and a metal ion. Multiple crystal structures in which organic ligands and metal ions are coordinated in a planar direction are created by connecting the pores of the crystal structure in the film thickness direction due to the π-π interaction of the organic ligands, creating communicating pores. Stack them to form a . That is, a plurality of crystal structures in which organic ligands and metal ions are coordinated in a planar direction are stacked in the film thickness direction to form a metal-organic structure film. Delocalized π electrons exist in the metal-organic structure film in this embodiment. During conduction, these delocalized π electrons flow out, and the molecule as a whole conducts with a negative charge. Further, the communicating pores of the metal-organic structure film may have the property of adsorbing gas, for example. When gas is adsorbed to the communicating holes, the resistance of the metal-organic structure film changes.

The organic ligand used to form the metal-organic framework film has a π-conjugated skeleton. One type of organic ligand may be used alone, or two or more types may be used in combination. From the viewpoint of uniformity of the membrane and communicating pores, it is preferable to use one type of organic ligand alone.

The π-conjugated skeleton constituting the organic ligand is preferably configured to include at least one aromatic ring. In this embodiment, the skeleton preferably means a portion of the organic ligand other than the coordinating functional group.

The number of coordinating functional groups of the organic ligand is preferably two or more, three or more, four or more, five or more, and six or more. Examples of the coordinating functional group include a hydroxy group, a carboxylic acid group, and an amine group.

The π-conjugated skeleton of the organic ligand is preferably a polycyclic aromatic hydrocarbon structure. Examples of the polycyclic aromatic hydrocarbon structure include a triphenylene structure, a pyrene structure, a perylene structure, and a mellitic acid triimide structure. When the π-conjugated system skeleton is a polycyclic aromatic hydrocarbon structure, a crystal structure in which organic ligands and metal ions are coordinated so as to expand in a plane direction can be easily formed by the LBL method.

The organic ligand preferably has three-fold symmetry or four-fold symmetry. Three-fold symmetry refers to the fact that when the structural formula of an organic ligand is rotated by 120° C. around the center, the structure becomes the same as the original structure. Similarly, 4-fold symmetry means that when the structural formula of an organic ligand is rotated by 120° C. around the center, the structure becomes the same as the original structure.

For example, the following compounds are exemplified as organic ligands having three-fold symmetry.

Even when these compounds are rotated by 120° C., there is no difference in the positions of each part of the skeleton and each coordinating functional group before and after rotation. Therefore, the compound has 3-fold symmetry.

It is preferable that the organic ligand has a π-conjugated skeleton having a polycyclic aromatic hydrocarbon structure and has three-fold symmetry. In this case, a crystal structure in which organic ligands and metal ions are coordinated in a planar direction can be easily formed by the LBL method, and metals with high carrier mobility and stable in the atmosphere can be used. An organic structure film can be obtained. The large number of recognition points of organic ligands contributes to the expansion of the conjugated region, and the molecular structure with high rigidity and conjugated region can lead to a regular three-dimensional structure.

An example of an organic ligand whose π-conjugated skeleton is a polycyclic aromatic hydrocarbon structure and has three-fold symmetry is 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP). It will be done.

The metal ion used to form the metal-organic structure film is not particularly limited, and can be appropriately selected depending on the type of organic ligand. The metal ion is preferably a metal ion that can have four or more coordinations, for example. Examples of metal ions that can have 4 or more coordinations, that is, metal ions that can have a coordination number of 4 or more, include copper ions, nickel ions, zinc ions, cobalt ions, and cadmium ions. Metal ions may exist as clusters.

In this embodiment, an organic ligand whose π-conjugated skeleton is a polycyclic aromatic hydrocarbon structure and has 3-fold symmetry is used as the organic ligand, and an organic ligand with 4-coordination is used as the metal ion. It is preferable to use the metal ions obtained. Further, in one embodiment, three metal ions are coordinated to one molecule of an organic ligand having three-fold symmetry. Examples of metal ions that can be four-coordinated include copper ions.

A metal-organic structure film formed using HTTP as an organic ligand and a metal ion capable of having four coordinations as a metal ion contains a structural unit of the following formula (I).

（式中、Ｍは、４配位を取り得る金属イオンを示す。）

(In the formula, M represents a metal ion that can be 4-coordinated.)

In the structural unit of formula (I), M is, for example, a copper ion. In the structural unit of formula (I), three metal ions are coordinated to one organic ligand (HHTP). Each metal ion is also coordinated with other organic ligands (not shown), and the organic ligands and metal ions are coordinated so that the structural unit of formula (I) expands in the plane direction. and form a crystal structure. A countless number of crystal structures formed by coordination of organic ligands and metal ions in a planar direction are included in the metal-organic structure film. One crystal structure is stacked with another crystal structure adjacent to it upwardly or downwardly by π-π interaction so that the pores in the two crystal structures are connected to form a communicating pore. A metal-organic structure film is constituted by a laminate having such a crystal structure.

For example, specifically, in a metal-organic structure film formed by a combination of HHTP and copper ions (Cu ²⁺ ), Cu ²⁺ is coordinated to three diol sites of HHTP, and Cu ²⁺ is Since Cu ²⁺ is four-coordinated, it coordinates with two HHTPs. We believe that the MOF exhibits excellent semiconductor properties due to the two-dimensional film formation caused by the large number of coordination bonding points caused by HHTP, combined with the π-π interaction that occurs when the MOF is constructed in the vertical direction. It will be done.

The organic ligand may be added to the solution in the form of a hydrate or a salt.

The thickness of the metal-organic structure film is not particularly limited, but is preferably, for example, 10 to 500 nm, more preferably 20 to 200 nm. The thickness of the metal-organic structure film can be adjusted as appropriate by, for example, the number of cycles of a coating process such as drop casting during formation by the LBL method.

The field-effect transistor of this embodiment can be used, for example, in a gas sensor, although its application is not particularly limited. That is, in the field effect transistor of this embodiment, the included gas molecules are included in the MOF film, thereby changing the conductivity and changing the semiconductor characteristics. For example, when ammonia enters the MOF film, the semiconductor characteristics of the MOF film change due to the unpaired electrons of the ammonia. When gas molecules enter the MOF film, it is expected that the semiconductor properties will behave differently depending on the size and molecular structure of the gas molecules. Therefore, for example, by combining pattern learning algorithms, it is considered possible to quantitatively identify the types of gas molecules contained in a mixed gas.

2. Method for Manufacturing Field Effect Transistor The method for manufacturing the field effect transistor of this embodiment is not particularly limited, but as described above, the metal-organic structure film in this embodiment is preferably formed by the LBL method. can.

The gate electrode, the gate insulating layer, the source electrode, and the drain electrode can all be produced or deposited by the method described above.

The process of forming a metal-organic structure film by the LBL method will be described below.

Note that in this embodiment, applying a certain composition onto a substrate is not limited to applying the composition directly to the substrate, but also applying the composition above the substrate through another layer provided on the substrate. It shall also include a mode of applying. The further layer to which the composition is applied (the underlying layer of the metal-organic framework film) is necessarily determined by the structure of the field-effect transistor. The layer serving as the base of the metal-organic structure film is, for example, a gate insulating layer in the case of a bottom gate type.

In forming a metal-organic structure film by the LBL method, first, a metal ion-containing solution containing metal ions is applied onto the substrate, that is, a base layer (for example, a gate insulating layer), and dried (metal ion containing solution application step). Application may be performed once or multiple times. Next, an organic ligand-containing solution containing an organic ligand is applied onto the substrate and dried (organic ligand-containing solution application step). Application may be performed once or multiple times. The metal-organic structure film in this embodiment can be formed by alternately performing the metal ion-containing solution application step and the organic ligand-containing solution application step multiple times. Regarding the LBL method, for example, "Ming-Shui Yao et al., Layer-by-Layer Assembled Conductive Metal-Organic Framework Nanofilms for Room-Temperature Chemiresistive Sensing, Angew. Chem. Int., Ed. 2017, 56, 16510-16514" It is also stated.

A metal ion-containing solution can be prepared, for example, by dissolving a metal salt containing the above metal ions in a solvent.

Examples of metal salts include metal acetates, metal formates, metal nitrates, metal sulfates, metal chlorides, metal bromides, metal iodides, metal fluorides, metal carbonates, metal phosphates, metal sulfides, or Examples include, but are not limited to, metal hydroxides. One type of metal salt may be used alone, or two or more types may be used in combination.

The content of metal ions in the metal ion-containing solution is not particularly limited, but is, for example, 1 to 50 mmol/L. The amount of the metal ion-containing solution applied is not particularly limited, but is, for example, 6×10 ⁻⁶ to 7×10 ⁻⁴ μl/μm ² .

The solvent used in the metal ion-containing solution is not particularly limited, and can be appropriately selected in consideration of the type and volatility of the metal salt, film-forming properties, and the like. Examples of the solvent include alcohol solvents such as methanol, ethanol, propanol, butanol, pentanol, hexanol, cyclohexanol, methyl cellosolve, ethyl cellosolve, or ethylene glycol, hexane, octane, decane, toluene, xylene, mesitylene, ethylbenzene, amyl Hydrocarbon solvents such as benzene, decalin, 1-methylnaphthalene, 1-ethylnaphthalene, 1,6-dimethylnaphthalene or tetralin; ketone solvents such as acetone, methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, acetophenone, propiophenone or butyrophenone; Examples include ester solvents such as ethyl acetate, butyl acetate, amyl acetate, 2-ethylhexyl acetate, γ-butyrolactone or phenyl acetate, and nitrile solvents such as acetonitrile or benzonitrile. One type of solvent may be used alone, or two or more types may be used in combination.

The organic ligand-containing solution can be prepared, for example, by dissolving the above-mentioned organic ligand in a solvent.

The content of the organic ligand in the organic ligand-containing solution is not particularly limited, but is, for example, 1 to 50 mmol/L. The amount of the organic ligand-containing solution applied is not particularly limited, but is, for example, 6×10 ⁻⁶ to 7×10 ⁻⁴ μl/μm ² .

The solvent used in the organic ligand-containing solution is not particularly limited, and can be appropriately selected in consideration of the type and volatility of the organic ligand, film formability, and the like. Examples of the solvent include those exemplified as solvents used in metal ion-containing solutions.

The method for applying the solution is not particularly limited, and examples thereof include drop casting, casting, dip coating, die coater, roll coater, bar coater, and spin coating. The solution can also be applied by a so-called printing method, and examples of the printing method include an inkjet method, screen printing, gravure printing, flexography printing, offset printing, or microcontact printing. In this embodiment, it is preferable to apply the solution by drop casting.

The method for drying the solution applied onto the substrate is not particularly limited, and examples thereof include natural drying, heat drying, reduced pressure drying, or a combination thereof. The drying time is, for example, 10 seconds to 1 hour.

By the above method, the metal-organic structure film in this embodiment can be formed. In the LBL method, growth of metal-organic structures occurs multiple times simultaneously on a substrate. As a result, a metal-organic structure film is formed in which a crystal structure expanded in a plane direction is grown at multiple points.

In this embodiment, the field effect transistor to be manufactured is preferably of a bottom gate-top contact type. That is, it is preferable that the gate electrode be disposed on the substrate side with respect to the semiconductor layer, and the source/drain electrodes be disposed on the opposite side of the semiconductor layer from the substrate (ie, on the front surface side). Specifically, a gate electrode is placed on a substrate, a gate insulating layer is placed on the gate electrode, a metal-organic structure film as a semiconductor layer is placed on the gate insulating layer, and a metal-organic structure film is placed on the gate insulating layer. Preferably, source/drain electrodes are arranged on the film. In particular, in the case of this configuration, it is preferable that the gate electrode is made of metal (preferably aluminum) and the gate insulating layer is made of the metal oxide (aluminum oxide). By employing such a configuration, the metal-organic structure film can be uniformly formed on the gate electrode. By forming source/drain electrodes on the metal organic structure film, a field effect transistor that can be driven at a low voltage can be effectively obtained.

Hereinafter, the present embodiment will be described with reference to examples, but the present disclosure is not limited to these examples.

[Example 1]
In this example, a metal-organic structure film was formed and evaluated by the following method.

(1) Materials/Silicon substrate/Copper acetate hydrate/2,3,6,7,10,11-hexahydroxytriphenylene hydrate (HHTP hydrate)

(2) Formation of metal-organic framework film First, the silicon substrate was cleaned with a piranha solution. Next, a metal-organic structure film was formed on the silicon substrate. Formation of the metal-organic framework film consists of two steps: immersing the substrate in an ethanol solution (5 mM) of copper acetate, washing, and drying; and immersing the substrate in an ethanol solution (5 mM) of HHTP hydrate and drying. This was carried out by repeating one cycle consisting of the steps of 15 times. Note that the copper acetate ethanol solution (5 mM) and the HHTP hydrate ethanol solution (5 mM) were each filtered in advance using a 200 nm PTFE filter. Further, drying in each step was performed by spraying nitrogen gas for at least 30 seconds. Through the above steps, a metal-organic structure film (thickness: 209±38 nm) was obtained. For reference, metal-organic structure films were also produced using 5, 10, or 20 cycles. The respective film thicknesses were 79±12 nm, 135±21 nm, or 192±40 nm, respectively.

[evaluation]
(1) Observation using an atomic force microscope (AFM), observation using a field emission scanning electron microscope (FE-SEM), and analysis using FT-IR Figures 2A and 2B show AFM images of the obtained metal-organic structure film. shows. FIG. 2B was acquired at a higher resolution than the AFM image in FIG. 2A. It can be seen from FIGS. 2A and 2B that pores with diameters of about several hundred nm are formed in the metal-organic structure film.

FIG. 3 shows an FE-SEM image of a cross section of the obtained metal-organic structure film taken by FE-SEM. It can be seen from FIG. 3 that a metal-organic structure film (MOF film) is formed.

FIG. 4 shows the results of FT-IR analysis of the obtained metal-organic structure film. As shown in FIG. 4, peaks were observed around 1450 cm ⁻¹ indicating ring expansion and contraction and around 1370 cm ⁻¹ indicating CO expansion and contraction. Also, in the XRD spectrum (not shown), peaks were observed near (100), (200), and (210).

From the above results, it was confirmed that a metal-organic structure film was formed.

(2) Evaluation of IV characteristics by four-probe measurement Four gold electrodes were formed on the surface of the metal-organic structure film described above, and the electrical resistance of the metal-organic structure film was evaluated by the four-probe measurement method.

σ=(I/V)×(L/WT) [S/cm]
I represents the current, V represents the voltage, L represents the distance between the electrodes (actually measured value: 100 μm), W represents the electrode width (actually measured value: 1000 μm), and T represents the film thickness of the metal-organic structure film. T was the average value of the thicknesses at multiple locations obtained from the AFM images.

As shown in FIG. 5, a linear IV curve derived from ohmic contact and rectification characteristics near 0 V were observed. In the case of resistance measurement of semiconductor materials, since a Schottky barrier exists at the semiconductor-metal interface, it exhibits diode-like characteristics, that is, rectification characteristics, near 0V. Therefore, it can be seen that the obtained metal-organic structure film has semiconductor properties.

[Example 2]
(1) Materials/Glass substrate (Eagle glass, dimensions: 2 x 2.5 cm)
・Aluminum for vapor deposition (gate electrode)
・Vapourized gold (source electrode, drain electrode)
・Teflon・Copper acetate hydrate ・2,3,6,7,10,11-hexahydroxytriphenylene hydrate (HHTP hydrate)

(2) Equipment - Vacuum evaporation equipment: SVC700TMSG/SVC-7PS80 vacuum evaporator, made by Sanyu Electronics Co., Ltd. - Dry etching device: RIE-10NG reactive ion etching system, made by SAMCO Co., Ltd. - Robotic dispenser: Imagemast er 350 dispenser equipment, Musashi Engineering Co., Ltd. Made

(3) Manufacturing process of field effect transistor (top contact type) FIGS. 6A to 6F are schematic cross-sectional process diagrams for explaining the manufacturing process of the field effect transistor (top contact type) in Example 1.

First, as shown in FIG. 6A, a glass substrate 101 as a substrate was cleaned with a piranha solution.

Next, as shown in FIG. 6B, an aluminum electrode 102 to be a gate electrode was deposited on the glass substrate 101 using a vacuum deposition apparatus using a shadow mask. The thickness of the aluminum electrode 102 was 50 nm.

Next, as shown in FIG. 6C, a reactive ion etching (RIE) process was performed using a dry etching apparatus at 150 W for 5 minutes to form an aluminum oxide film 103 that would become an insulating layer.

Next, as shown in FIG. 6D, a Teflon bank 104 was formed using a robotic dispenser to define a region where a semiconductor layer was to be formed.

Next, as shown in FIG. 6E, a metal-organic structure film 105 as a semiconductor layer was formed. Formation of the metal-organic framework film 105 involves repeating the steps of drop-casting 0.3 μL of a copper acetate ethanol solution (5 mM) onto the substrate and drying it four times, and 0.3 μL of an ethanol solution of HHTP hydrate ( This was carried out by repeating one cycle four times, consisting of a step of drop-casting 5mM) onto the substrate and drying it four times. Note that the copper acetate ethanol solution (5 mM) and the HHTP ethanol solution (5 mM) were each filtered using a 200 nm PTFE filter before drop casting. Further, drying in each step was performed by allowing the product to stand for at least 30 seconds.

Next, as shown in FIG. 6F, a source electrode 106A and a drain electrode 106B were formed on the metal-organic structure film 105 by vacuum deposition using a shadow mask (channel width/channel length=1000 μm/50 μm). Gold was used for the source electrode 106A and the drain electrode 106B.

Through the above steps, a top contact type field effect transistor E1 was obtained.

[Example 3]
In Example 3, a metal organic framework film was formed using 1,3,5-benzenetricarboxylic acid (BTC) as an organic ligand. Specifically, a top-contact field effect transistor E2 was formed in the same manner as in Example 2, except that the step of forming a metal-organic structure film as a semiconductor layer shown in FIG. 6E was performed in the following manner. Obtained.

In the process of forming a metal-organic structure film as a semiconductor layer shown in FIG. 6E, the metal-organic structure film 105 is formed by drop-casting 0.2 μL of a copper acetate ethanol solution (1 mM) onto the substrate and drying it. This was carried out by repeating 16 times one cycle consisting of the step of drop-casting 0.2 μL of BTC in ethanol solution (1 mM) onto the substrate and drying it. Note that the copper acetate ethanol solution (1 mM) and the BTC ethanol solution (1 mM) were each filtered using a 200 nm PTFE filter before drop casting. Further, drying in each step was performed by allowing the product to stand for at least 30 seconds.

[Comparative example 1]
HHTP hydrate and copper acetate were mixed in methanol and reacted at 65° C. for 24 hours to form a particulate metal-organic framework. FIG. 7A shows the FT-IR spectrum of the obtained particulate MOF, and FIG. 7B shows the XRD spectrum. It can be seen from FIGS. 7A and 7B that a particulate metal-organic structure composed of HHTP and copper ions was obtained.

Using the obtained particulate MOF, a top-contact field effect transistor C1 was formed according to the steps described in Example 2 except for forming the metal-organic structure film. The specific steps are described below.

First, as shown in FIG. 6A for reference, a glass substrate as a substrate was cleaned with a piranha solution.

Next, as shown in FIG. 6B for reference, an aluminum electrode that would become a gate electrode was deposited on the glass substrate using a vacuum deposition apparatus using a shadow mask. The thickness of the aluminum electrode was 50 nm.

Next, as shown in FIG. 6C for reference, a reactive ion etching (RIE) process was performed using a dry etching device at 150 W for 5 minutes to form an aluminum oxide film that would become an insulating layer.

Next, as shown in FIG. 6D for reference, a Teflon bank was formed using a robotic dispenser to define a region where a semiconductor layer was to be formed.

Next, as shown in FIG. 6E for reference, a layer of metal-organic framework was formed using particulate MOF. Formation of the layer of metal-organic framework was carried out by drop-casting an amount of 0.25 μL of particulate MOF in aniline solution (0.16 wt %) onto the substrate and drying.

Next, as shown in FIG. 6F for reference, source and drain electrodes were formed on the layer of metal-organic structure by vacuum evaporation using a shadow mask (channel width/channel length = 1000 μm/50 μm). . Gold was used for the source electrode and the drain electrode.

Through the above steps, a field effect transistor C1 was obtained.

[Comparative example 2]
(1) Materials/Silicon substrate (dimensions: 2 x 2.5 cm)
・Vapourized gold (source electrode, drain electrode)
・Teflon・Copper acetate hydrate ・2,3,6,7,10,11-hexahydroxytriphenylene hydrate (HHTP hydrate)
・2,3,5,6-tetrafluoro-4-mercaptobenzoic acid (TFMBA)
Note that since TFMBA has a bonding site with gold and a bonding site with copper ions, it was used to ensure the adhesion between the metal-organic structure film and the gold electrode.

(2) Equipment - Vacuum evaporation equipment: SVC700TMSG/SVC-7PS80 vacuum evaporator, made by Sanyu Electronics Co., Ltd. - Dry etching device: RIE-10NG reactive ion etching system, made by SAMCO Co., Ltd. - Robotic dispenser: Imagemast er 350 dispenser equipment, Musashi Engineering Co., Ltd. Made

(3) Manufacturing process of field effect transistor (bottom contact type) FIGS. 10A to 10D are schematic cross-sectional process diagrams for explaining the manufacturing process of a field effect transistor (bottom contact type) in Comparative Example 2.

First, as shown in FIG. 10A, a silicon substrate 201 as a substrate was cleaned with a piranha solution.

Next, as shown in FIG. 10B, a source electrode 206A and a drain electrode 206B were formed using a vacuum evaporation apparatus using a shadow mask. Gold was used for the source electrode 206A and the drain electrode 206B. The thickness of each electrode was 50 nm. Further, the substrate on which gold was deposited was immersed for 10 minutes in a TFMBA solution (10 mM) dissolved in 2-propanol to perform TFMBA treatment. After immersion, the substrate was washed with 2-propanol and then blown with nitrogen.

Next, as shown in FIG. 10C, a Teflon bank 204 was formed using a robotic dispenser to define a region where a semiconductor layer would be formed.

Next, as shown in FIG. 10D, a metal organic structure film 205 as a semiconductor layer was formed. Formation of the metal-organic framework film 205 involves drop-casting 3 μL of a copper acetate ethanol solution (50 mM) onto the substrate and drying it, and drop-casting 3 μL of an ethanol solution of HHTP hydrate (50 mM) onto the substrate. This was carried out by repeating one cycle consisting of the steps of drying and drying seven times. Note that the copper acetate ethanol solution (50 mM) and the HHTP ethanol solution (50 mM) were each filtered using a 200 nm PTFE filter before drop casting. Further, drying in each step was performed by allowing the product to stand for at least 5 minutes.

Through the above steps, a bottom contact type field effect transistor C2 was obtained. Note that in the field effect transistor C2, silicon functions as a gate electrode, and the silicon oxide film functions as an insulator layer.

[evaluation]
(1) Transfer characteristics and output characteristics The transfer characteristics and/or output characteristics of the produced field effect transistors E1, E2, C1, and C2 were evaluated in the atmosphere using a source meter (manufactured by KEITHLEY). Specifically, the evaluation was performed as follows. Current and voltage were measured by applying the short needle of the probe to the gate electrode, source electrode, and drain electrode. The transfer characteristic is the correlation between the gate voltage (V GS ) and the drain current (I _{DS ) obtained when the drain voltage is set constant and the gate voltage (V GS ) is} modulated and swept through a source meter. (eg, FIG. 8A). Further, the output characteristics are indicated by the correlation between the drain voltage and drain current obtained when the gate voltage is set constant and the drain voltage (V _DS ) is modulated and swept (for example, FIG. 8B). In this case, the source for both is always grounded. In this measurement, a gate voltage of −5 V or lower, which is lower than the voltage applied to a normal organic transistor, was applied. Note that the output characteristics were measured with V _GS set to 0, -1, -2, and -3V.

FIG. 8A is a graph showing the results of evaluating the transfer characteristics of the field effect transistor E1 (Example 2). FIG. 8B is a graph showing the results of evaluating the output characteristics of the field effect transistor E1 (Example 2). FIG. 9 is a graph showing the results of evaluating the transfer characteristics of the field effect transistor C1 (Comparative Example 1). FIG. 11 is a graph showing the results of evaluating the transfer characteristics of the field effect transistor E2 (Example 3). FIG. 12 is a graph showing the results of evaluating the transfer characteristics of the field effect transistor C2 (Comparative Example 2).

As shown in FIG. 8A, in the transfer characteristics, a rise in the ON current was observed near −2.5 V, and it was confirmed that the field effect transistor E1 exhibited good FET characteristics. Regarding the output characteristics, FET characteristics depending on the applied voltage were also obtained (FIG. 8B). Since organic semiconductor materials are usually unstable in the atmosphere, evaluation of transfer characteristics and output characteristics is generally performed in a nitrogen atmosphere. However, the field effect transistor obtained in this example The transistor exhibited stable transistor characteristics in the atmosphere even without special treatment such as encapsulants. Further, as understood from FIGS. 8A and 8B, driving at a low voltage of 5 V or less was confirmed. Furthermore, as shown in FIG. 11, a nonlinear increase in drain current value was observed.

On the other hand, as understood from FIG. 9, the field effect transistor C1 of Comparative Example 1 did not exhibit semiconductor characteristics. Moreover, as understood from FIG. 12, the field effect transistor C2 of Comparative Example 2 also did not exhibit semiconductor characteristics. Note that the transistor characteristics are characterized by a current change from off to on due to the application of a gate voltage. Since such characteristics were not observed in the graph of FIG. 12, it was determined that transistor characteristics were not obtained. The reason why the field effect transistor of the comparative example did not exhibit semiconductor characteristics is presumed to be due to the following reasons. In the case of the bottom contact type, it is necessary to form a metal-organic structure film in the channel (between the source and drain) in a microscopic space. However, the adhesion between the electrode and the metal-organic structure film in the bottom contact type is lower than that in the top contact type. Therefore, it is presumed that transistor characteristics could not be obtained with the bottom contact type. Note that the above speculation does not limit the present disclosure.

(2) Evaluation as a gas sensor As a gas sensing evaluation device, a small glove box for gas sensing evaluation was designed in cooperation with UNICO. This glove box is equipped with a flange on the back, making it possible to evaluate transistor characteristics in a gas atmosphere. At that time, the transistor was evaluated with the self-made connector connected to the source meter via a flange. The gas flow rate is adjusted using a permeator (manufactured by Gastech). This permeator makes it possible to achieve a quantitative gas flow rate. Examples of gas components to be detected include ammonia, ethanol, acetone, n-decane, n-dodecane, ethylbenzene, toluene, acetaldehyde, phenol, and propylamine.

The gas sensing ability of the field effect transistor E1 (Cu-HHTP MOF) obtained in Example 1 was evaluated using the gas sensing evaluation apparatus described above. Specifically, a field effect transistor was placed in a glove box, ammonia gas was injected into the glove box to each predetermined concentration, and after 5 minutes, the electrical resistance was measured by the above-mentioned four-terminal measurement method. The results are shown in Table 1.

As shown in Table 1, the field effect transistor E1 exhibits different electrical resistances depending on the concentration of ammonia gas, and it can be seen that the conductivity of the MOF changes depending on the concentration of ammonia gas. This confirmed that the field effect transistor of this embodiment has gas sensing ability.

The upper limits and/or lower limits of the numerical ranges described herein can be arbitrarily combined to define a preferable range. For example, a preferable range can be defined by arbitrarily combining the upper and lower limits of a numerical range, a preferable range can be defined by arbitrarily combining the upper limits of a numerical range, and the lower limit of a numerical range Preferred ranges can be defined by arbitrarily combining values.

Although this embodiment has been described in detail above, the specific configuration is not limited to this embodiment, and even if there are design changes within the scope of the gist of the present disclosure, they are not included in the present disclosure. It is something that can be done.

1 Substrate 2 Gate electrode 3 Gate insulating layer 4A Source electrode 4B Drain electrode 5 Metal-organic structure film (semiconductor layer)
101 Glass substrate 102 Aluminum electrode 103 Aluminum oxide film 104 Teflon bank 105 Metal-organic structure film (semiconductor layer)
106A Source electrode 106B Drain electrode 201 Substrate 202 Gate electrode 203 Gate insulating layer 204A Source electrode 204B Drain electrode 205 Metal-organic structure film

Claims (9)

A field effect transistor comprising a substrate, a source electrode, a drain electrode, a gate electrode, and a metal-organic structure film as a semiconductor layer,
A metal-organic structure film has a plurality of crystal structures in which organic ligands and metal ions having a π-conjugated skeleton are coordinated so as to extend in the plane direction of the substrate. Including a laminated structure laminated on top,
Each crystal structure has pores formed by coordination of organic ligands and metal ions, and in the layered structure, pores of adjacent crystal structures communicate in the film thickness direction,
It is a top contact type,
A field effect transistor in which the organic ligand is 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) or 1,3,5-benzenetricarboxylic acid (BTC) . The field effect transistor according to claim 1, which is of the bottom gate-top contact type. 3. The field effect transistor according to claim 1, wherein the π-conjugated skeleton includes at least one aromatic ring. The field effect transistor according to any one of claims 1 to 3, wherein the π-conjugated system skeleton is a polycyclic aromatic hydrocarbon structure. The field effect transistor according to any one of claims 1 to 4 , wherein the gate electrode is an aluminum electrode. 6. The field effect transistor according to claim 5 , wherein aluminum oxide is formed as a gate insulating layer on the surface of the aluminum electrode. The metal-organic framework film is produced using an LBL method, which includes the steps of applying a metal ion-containing solution containing metal ions onto a substrate, and applying an organic ligand-containing solution containing an organic ligand onto the substrate. The field effect transistor according to any one of claims 1 to 6 , which is formed by. A gas sensor comprising the field effect transistor according to any one of claims 1 to 7 . A method for manufacturing a field effect transistor according to any one of claims 1 to 6 , comprising:
metal-organic framework film,
applying a metal ion-containing solution containing metal ions onto the substrate;
applying an organic ligand-containing solution containing an organic ligand onto the substrate;
A method comprising the step of forming by an LBL method comprising:

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