Patent Description:
A strain sensor using an organic semiconductor element has been known (see, for example, PTL <NUM>). The strain sensor of PTL <NUM> includes an organic semiconductor film which is formed on a substrate from a thin film of single crystal of an organic semiconductor, and a pair of electrodes which are connected to the organic semiconductor film. When a stress compressing or stretching the organic semiconductor film acts on the film, a distance between molecules of the organic semiconductor is changed to cause the molecular vibration to change, so that the mobility of carriers of the organic semiconductor film is changed. The change of the carrier mobility is detected as, for example, a change of the resistance of the organic semiconductor film, detecting strain. PTL2 discloses an organic field effect transistor, comprising an organic semiconductor layer; a source electrode and a drain electrode; a gate insulation film <NUM>; a gate electrode; and a carrier replenishing layer. PTL3 discloses an organic thin film transistor, comprising source and drain electrodes; a surface-modification layer; an organic semiconductor layer; a gate electrode; and a gate dielectric. PTL4 discloses a strain sensor using an organic transistor, comprising an organic semiconductor layer, a source electrode and a drain electrode. PTL5 discloses a force sensor, comprising a substrate and an organic field effect transistor, in which a mechanical force acting on the transistor causes a change in its source-drain voltage or its source-drain current which corresponds to the force and is detected as measurement quantity for the acting force. PTL6 discloses a shaking sensing organic field effect transistor, comprising a substrate, a cantilever beam, a source electrode, a drain electrode, a gate electrode, an organic semiconductor layer, an insulation layer and an overshoot protection layer. PTL7 discloses a pressure sensor using a transistor comprising a highly uniform single crystalline organic semiconductor film as a channel. NPTL <NUM> describes molecular doping of organic semiconductors with an emphasis on solution-processed p-type doped polymeric semiconductors.

As mentioned above, it has been known that the organic semiconductor can be used as a strain sensor or the like by detecting a change of the carrier mobility, but it is desired that the organic semiconductor for use as a sensor has a simple construction and a required resistance can be obtained from such an organic semiconductor.

In view of the above, the present invention has been made, and an object of the invention is to provide an organic semiconductor element which is advantageous in that a desired resistance can be obtained from the element having a simple construction, a strain sensor, a vibration sensor, and a method for producing an organic semiconductor element.

The organic semiconductor element of the present invention is as defined in claim <NUM>.

The strain sensor of the present invention is as defined in claim <NUM>.

The vibration sensor of the present invention is as defined in claim <NUM>.

The method for producing an organic semiconductor element of the present invention is as defined in claim <NUM>.

According to the present invention, by forming a doped layer in a surface of an organic semiconductor film formed from single crystal of an organic semiconductor, the crystal structure of the organic semiconductor film is prevented from breaking, achieving an organic semiconductor element which is advantageous in that a desired resistance can be obtained from the element having a simple construction.

Further, according to the present invention, by forming a dopant film on the surface of the organic semiconductor film, doping can be advantageously made without breaking the crystal structure of the organic semiconductor film.

In <FIG>, a vibration sensor <NUM> has a substrate <NUM>, and a sensor portion S including an organic semiconductor element <NUM> formed on the surface of the substrate <NUM>. The vibration sensor <NUM> detects vibration of an object to be detected (detection object) using the organic semiconductor element <NUM> as a strain detecting element. A sensor having the same structure as that of the vibration sensor <NUM> can be used as an acceleration sensor for detecting acceleration or various types of sensors for detecting inclination or movement of a detection object.

The substrate <NUM> is a member in a rectangular plate form having flexibility, namely, being elastically deformable. The substrate <NUM> is fixed to a leg <NUM> at one end thereof as viewed in the longitudinal direction of the substrate (Y direction), and thus the vibration sensor <NUM> has a cantilever structure. The leg <NUM> is formed from a hardmaterial, and fixed to a detection object. By virtue of this, when an acceleration in the vertical direction is caused in the detection object due to vibration, the substrate <NUM> elastically deforms in the amount and direction according to the acceleration so that another end of the substrate <NUM> moves in the vertical direction. In this example, an explanation is made on the case where the vertical vibration is detected, but the direction of the vibration detected is notlimitedtothis. For example, when vibration (acceleration) in the horizontal direction is to be detected, the vibration sensor <NUM> may be fixed to a detection object so as to be in the state in which the surface of the substrate <NUM> on which the sensor portion S is formed faces the right or left.

The sensor portion S is formedon one surface (upper surface in this example) of the substrate <NUM>. The sensor portion S has the organic semiconductor element <NUM>, a pair of electrodes <NUM>, <NUM>, and leadwires <NUM>, <NUM>. The organic semiconductor element <NUM> is formed in a rectangular form having a longer side in the width direction of the substrate <NUM> (X direction perpendicular to the Y direction). Elastic deformation of the substrate <NUM> causes the organic semiconductor element <NUM> to be stretched or compressed in the longitudinal direction of the substrate <NUM>. It is preferred that the organic semiconductor element <NUM> is placed in the position in which stretching or compression is large when the substrate <NUM> elastically deforms.

The pair of the electrodes <NUM>, <NUM> are arranged at both ends of the organic semiconductor element <NUM> as viewed in the longitudinal direction of the substrate <NUM>, namely, in the direction along which the organic semiconductor element <NUM> is stretched or compressed. An end of the lead wire <NUM> is connected to the electrode <NUM>, and an end of the lead wire <NUM> is connected to the electrode <NUM>. The lead wires <NUM>, <NUM> are formed in a pattern such that another end of each lead wire extends to the one end of the substrate <NUM>, and the organic semiconductor element <NUM> is connected to an external electric device through the lead wires <NUM>, <NUM>.

As shown in <FIG>, the substrate <NUM> in this example is of a two-layer structure having a glass plate <NUM> and a resin layer <NUM> formed on the surface of the glass plate <NUM>, and the organic semiconductor element <NUM> is formed on the surface of the resin layer <NUM>. The resin layer <NUM> is formed from, for example, polyparaxylene (Parylene (registered trademark)). The glass plate <NUM> has a thickness of, for example, <NUM> to <NUM>, and the resin layer <NUM> has a thickness of about <NUM> to <NUM>. With respect to the material and structure constituting the substrate <NUM>, there is no particular limitation, and, instead of the glass plate <NUM>, for example, a substrate in a plate form obtained from polyethylene naphthalate (PEN) may be used, or a substrate <NUM> composed solely of polyethylene naphthalate may be used.

The organic semiconductor element <NUM> has an organic semiconductor film <NUM> formed on the surface of the resin layer <NUM>, and a dopant film <NUM> formed on the upper surface of the organic semiconductor film <NUM>. At both ends of the organic semiconductor film <NUM>, the electrodes <NUM>, <NUM> are formed from gold (Au). The organic semiconductor film <NUM> is formed from crystal of an organic semiconductor (organic compound which exhibits properties of a semiconductor), and is a film formed from the single crystal. The organic semiconductor film <NUM> has a thickness of, for example, <NUM> or less. With respect to the organic semiconductor constituting the organic semiconductor film <NUM>, for example, <NUM>,<NUM>-dioctyldinaphtho[<NUM>,<NUM>-d:<NUM>',<NUM>'-d']benzo[<NUM>,<NUM>-b:<NUM>,<NUM>-b']di thiophene (C8-DNBDT) which serves as a P type organic semiconductor is used.

As the P type organic semiconductor constituting the organic semiconductor film <NUM>, there can be used the above-mentioned C8-DNBDT, or <NUM>,<NUM>-didecyldinaphtho[<NUM>,<NUM>-d:<NUM>',<NUM>'-d']benzo[<NUM>,<NUM>-b:<NUM>,<NUM>-b']di thiophene (C10-DNBDT), <NUM>,<NUM>-dihexyldinaphtho[<NUM>,<NUM>-b;<NUM>',<NUM>-d]thiophene (C6-DNT), <NUM>,<NUM>-dinaphtho[<NUM>,<NUM>-b:<NUM>',<NUM>'-f]thieno[<NUM>,<NUM>-b]thiophene (C10-DNTT), <NUM>,<NUM>-dioctylbenzothieno[<NUM>,<NUM>-b][<NUM>]benzothiophene (C8-BTBT), <NUM>,<NUM>-bis(triisopropylsilylethynyl)pentacene, or the like. The organic semiconductor constituting the organic semiconductor film <NUM> may be of an N type. With respect to the N type organic semiconductor, dicyanoperylene-<NUM>,<NUM>:<NUM>,<NUM>-bis(dicarboxyimide) or the like can be used.

The dopant film <NUM>, which is a film formed from a dopant, is used for forming a doped layer <NUM> in the surface of the organic semiconductor film <NUM> (the interface with the dopant film <NUM>). The dopant film <NUM> is formed in the form of a thin film on the surface of the organic semiconductor film <NUM> between the electrodes <NUM>, <NUM>. As a dopant material for forming the dopant film <NUM>, for example, <NUM>,<NUM>,<NUM>,<NUM>-tetrafluoro-<NUM>,<NUM>,<NUM>,<NUM>-tetracyano-quinodimethane (F<NUM>TCNQ, <NPL>)) is used.

By forming the dopant film <NUM>, a charge transfer complex of the dopant and the organic semiconductor is formed at the interface between the organic semiconductor film <NUM> and the dopant film <NUM>. Specifically, as shown in <FIG>, charge transfer occurs between the HOMO (Highest Occupied Molecular Orbital) of the organic semiconductor in the organic semiconductor film <NUM> and the LUMO (Lowest Unoccupied Molecular Orbital) of the dopant constituting the dopant film <NUM>, so that carriers (holes in this example) move to the surface of the organic semiconductor film <NUM>, forming the doped layer <NUM>.

When the P type organic semiconductor is used as the organic semiconductor film <NUM>, the dopant constituting the dopant film <NUM> may be any dopant as long as it satisfies the following relationship that: the energy level (ELUMO) of the LUMO of the dopant is a value which is lower than the energy level (EHOMO) of the HOMO of the organic semiconductor in the organic semiconductor film <NUM> by about <NUM> eV (EHOMO - <NUM>) or more (ELUMO > EHOMO - <NUM>). When the N type organic semiconductor is used as the organic semiconductor film <NUM>, the dopant constituting the dopant film <NUM> may be any dopant as long as it satisfies the following relationship that: the energy level (E'HOMO) of the HOMO of the dopant is a value which is higher than the energy level (E'LUMO) of the LUMO of the organic semiconductor in the organic semiconductor film <NUM> by about <NUM> eV (E'LUMO + <NUM>) or less (E'HOMO < E'LUMO + <NUM>).

Examples of dopant materials for the P type organic semiconductor include the above-mentioned F<NUM>TCNQ, molybdenum tris-<NUM>-trifluoroacetyl-<NUM>-trifluoromethylethane-<NUM>,<NUM>-dithiol ene (Mo(tfd-COCF<NUM>)<NUM>), and nitrosonium hexafluoroantimonate (NO+SbF<NUM>-). Examples of dopant materials for the N type organic semiconductor include cobaltocene, decamethylcobaltocene, ruthenocene, ferrocene, and <NUM>,<NUM>-dimethyl-<NUM>-phenyl-<NUM>,<NUM>-dihydro-benzoimidazole. In these dopant materials, some are of a type that the material itself becomes anion or cation and functions as a dopant, and some are of a type that a part of the material is dissociated and functions as a dopant. For example, as shown in the formulae (<NUM>) and (<NUM>) below, F<NUM>TCNQ and Mo(tfd-COCF<NUM>)<NUM> are an example of the former, and, as shown in the formula (<NUM>) below, NO+SbF<NUM>- is an example of the latter. The formulae (<NUM>) to (<NUM>) show the case that the material functions as a dopant for the organic semiconductor film <NUM> formed from C8-DNBDT.

A procedure for producing the organic semiconductor element <NUM> is described below. The procedure described below is an example, and the procedure is not limited to this example. When the organic semiconductor element <NUM> is produced, the formation of the organic semiconductor film <NUM>, the formation of the electrodes <NUM>, <NUM>, and the formation of the dopant film <NUM> are successively conducted.

As shown in <FIG>, the organic semiconductor film <NUM> is formed by, for example, an edge casting method. In the edge casting method, a blade <NUM> is arranged above the substrate <NUM> so that the blade is substantially vertical with respect to the substrate <NUM>. In this instance, the position of the blade <NUM> is controlled in the vertical direction so that the gap between the substrate <NUM> and the lower end of the blade <NUM> becomes larger than the thickness of the organic semiconductor film <NUM> to be formed. While moving the substrate <NUM> in one direction (direction to the right in the example of <FIG>), a solution <NUM> is supplied to the position between the substrate <NUM> and the lower end of the blade <NUM>. In this instance, the solution <NUM> is supplied through a supply pipe <NUM> on the side upstream of the blade <NUM> as viewed in the moving direction of the substrate <NUM> (on the left side of the blade <NUM> in the example of <FIG>). The solution <NUM> is obtained by dissolving in a solvent an organic semiconductor which constitutes the organic semiconductor film <NUM>. As the solvent, for example, an aromatic compound (such as o-dichlorobenzene) can be used.

In the above-mentioned movement of the substrate <NUM> and supply of the solution <NUM>, the solvent of the solution <NUM> is evaporated wherein the solution <NUM> is present in the position which is away from the blade <NUM> and downstream of the blade <NUM> as viewed in the moving direction, so that the organic semiconductor is precipitated. Thus, a thin film of single crystal of the organic semiconductor, which constitutes the organic semiconductor film <NUM>, is formed. In this example, the substrate <NUM> is moved, but there is only a need that the substrate <NUM>, the blade <NUM>, and the supply pipe <NUM> be relatively moved, and therefore, for example, the blade <NUM> and the supply pipe <NUM> may be moved, instead of moving the substrate <NUM>.

With respect to the solution <NUM>, a solution having dissolved in a solvent a polymer material and an organic semiconductor which constitutes the organic semiconductor film <NUM> may be used. When using such a solution <NUM>, a polymer layer composed of the polymermaterial and a layer composed of the organic semiconductor, i.e., the organic semiconductor film <NUM> are separated from each other during the process in which the solvent is evaporated. Thus, the organic semiconductor film <NUM> in which the organic semiconductor is more advantageously oriented and crystallized is formed on the polymer layer.

Examples of the polymer materials include a polymethyl methacrylateresin,poly(<NUM>-methylstyrene),poly(triarylamine), polystyrene, polyacrylonitrile, polyethylene, and polyvinyl acetate. With respect to the solvent, there is no particular limitation as long as it can dissolve therein both an organic compound and a polymer, for example, a halogen aromatic solvent, such as chlorobenzene, <NUM>-chlorothiophene, or <NUM>-chloronaphthalene, a hydrocarbon solvent, such as hexane or heptane, or a non-halogen aromatic solvent, such as toluene, xylene, or tetralin, can be used.

After forming the organic semiconductor film <NUM>, the electrodes <NUM>, <NUM> are formed. The electrodes <NUM>, <NUM> as well as the lead wires <NUM>, <NUM> are formed by, for example, vapor deposition.

After forming the electrodes <NUM>, <NUM>, the dopant film <NUM> is formed. For example, as shown in <FIG>, together with the substrate <NUM>, the organic semiconductor film <NUM> is immersed in a solution <NUM> in a container <NUM>, and then the solvent is evaporated to form the dopant film <NUM> on the surface of the organic semiconductor film <NUM>. The solution <NUM> is obtained by dissolving a dopant material in a solvent. As the solvent, acetonitrile, butyl acetate, or the like can be used. The dopant film <NUM> is formed as mentioned above, so that the doped layer <NUM> is formed.

The method for forming the dopant film <NUM> is not limited to the above-mentioned method. For example, the dopant film <NUM> may be formed on the organic semiconductor film <NUM> by dropwise adding and spreading a solution having a dopant dissolved therein to the surface of the organic semiconductor film <NUM>, and then evaporating the solvent. Alternatively, the dopant film <NUM> may be formed by vapor deposition of a dopant on the surface of the organic semiconductor film <NUM>.

Elastic deformation of the substrate <NUM> causes the organic semiconductor element <NUM>, i.e., the organic semiconductor film <NUM> having the doped layer <NUM> to be compressed or stretched. In this example, the organic semiconductor element <NUM> is formed on the upper surface of the substrate <NUM>, and therefore, when the substrate <NUM> flexes so that another end of the substrate <NUM> moves downwardly, the organic semiconductor film <NUM> is stretched, and, when the substrate <NUM> flexes so that another end of the substrate <NUM> moves upwardly, the organic semiconductor film <NUM> is compressed. The organic semiconductor film <NUM> changes in the mobility of carriers according to the compression or stretching, i.e., strain. By detecting the change of the carrier mobility as a change of the resistance of the organic semiconductor element <NUM> through the electrodes <NUM>, <NUM>, an acceleration of the detection object can be detected.

The reason that the mobility of carriers in the organic semiconductor film <NUM> changes according to the strain is presumed as follows. As can be seen from the state of molecules of the organic semiconductor in the organic semiconductor film <NUM> diagrammatically shown in <FIG>, when the organic semiconductor film <NUM> is compressed so that a stress in compression acts on the organic semiconductor film <NUM>, strain is caused in the crystal and the molecules are close to each other, which makes it easier for carriers to move through the organic semiconductor, increasing the mobility of carriers. Further, when the molecules are close to each other, the molecular vibration becomes small, which makes it easier for carriers to move through the organic semiconductor film <NUM>, increasing the mobility of carriers. Conversely, when the organic semiconductor film <NUM> is stretched so that a stress in tension acts on the organic semiconductor film <NUM>, strain is caused in the crystal and the molecules are apart from each other, which makes it more difficult for carriers to move through the organic semiconductor, reducing the mobility of carriers. Further, when the molecules are apart from each other, the molecular vibration becomes large, which makes it more difficult for carriers to move through the organic semiconductor film <NUM>, reducing the mobility of carriers. As the stress in compression or the stress in tension is increased, the strain caused in the crystal of the organic semiconductor film <NUM> is increased, and hence a change of the carrier mobility is increased. The organic semiconductor film <NUM> formed from single crystal has properties such that a change of the mobility of carriers is increased as the strain applied to the film is increased.

The organic semiconductor film <NUM> formed from single crystal has such a high detection sensitivity that a change of the resistance of the organic semiconductor film <NUM> in accordance with the strain is well detected. Further, the organic semiconductor film <NUM> has such a high response property that the resistance changes with a short delay in accordance with the change of the acceleration of vibration. Therefore, the vibration sensor <NUM> is advantageous in that the resistance of the organic semiconductor film <NUM> changes following even a high-speed change of the acceleration, enabling detection of vibration at a high frequency, and thus is useful as a vibration sensor.

With respect to a polycrystalline organic semiconductor, the individual organic semiconductor films have different crystal structures, and therefore, even when the same strain is caused in the organic semiconductor films by applying the same stress, the same mobility of carriers cannot be obtained. In contrast, the organic semiconductor film <NUM> in this example is formed from single crystal, and the crystal structure is determined according to the molecules of the organic compound. Further, as mentioned above, only the surface of the organic semiconductor film <NUM> is doped, and therefore the crystal structure is not disordered. For this reason, the individual organic semiconductor films <NUM> have the same crystal structure, and, when the same strain is caused in the organic semiconductor films by applying the same stress, the same mobility of carriers can be obtained. Therefore, the individual organic semiconductor films <NUM> have identical properties.

Further, in the organic semiconductor film <NUM> in this example, the doped layer <NUM> is formed in the surface of the organic semiconductor film, and the doped layer <NUM> has a large electrical conductivity, as compared to the other portion of the organic semiconductor film <NUM>. For this reason, in the organic semiconductor element <NUM> in this example, a change of the resistance of the doped layer <NUM> is detected as a change of the resistance of the organic semiconductor film <NUM> between the electrodes <NUM>, <NUM>. With respect to the organic semiconductor film <NUM>, in the case where the doped layer <NUM> is not formed, that is, the organic semiconductor film is not doped, it is likely that the organic semiconductor film has such a high resistance that a satisfactory current (gage current) does not flow unless a high voltage is applied, but, by doing the organic semiconductor film, the resultant film is a resistance element through which a satisfactory gage current flows even at a low voltage. Further, by virtue of forming the doped layer <NUM>, there is no need to employ a three-terminal construction having a gate electrode formed on the surface of the organic semiconductor film <NUM>, and the organic semiconductor film <NUM> can be used as a resistance element having a simple construction such that the resistance is changed according to strain. In addition, the single crystal structure of the organic semiconductor film <NUM> is not disordered by the doped layer <NUM>, and hence deterioration of the properties of the organic semiconductor film <NUM> formed from single crystal does not occur.

When detecting vibration of an object to be detected (detection object) using the vibration sensor <NUM> having the above-described construction, the leg <NUM> is fixed to the detection object. A measuring apparatus is connected to the lead wires <NUM>, <NUM>.

When the detection object vibrates, the substrate <NUM> elastically deforms so that another end of the substrate moves in the vertical direction due to inertia force. The elastic deformation of the substrate <NUM> causes the organic semiconductor film <NUM> having the doped layer <NUM> to be compressed or stretched. As a result, the strain of the organic semiconductor film <NUM> is changed, so that the mobility of carriers of the doped layer <NUM> is changed, that is, the resistance of the organic semiconductor element <NUM> is changed. When the substrate <NUM> elastically deforms in such a direction that another end of the substrate <NUM> moves upwardly as viewed from one end, the organic semiconductor film <NUM> is compressed, and therefore the carrier mobility is increased and the resistance of the organic semiconductor element <NUM> is reduced. Meanwhile, when the substrate <NUM> elastically deforms in such a direction that another end of the substrate <NUM> moves downwardly as viewed from one end, the organic semiconductor film <NUM> is stretched, and therefore the carrier mobility is reduced and the resistance of the organic semiconductor element <NUM> is increased. According to the amount of deformation of the substrate <NUM>, the amount of compression or stretching of the organic semiconductor film <NUM> is changed, obtaining a resistance of the organic semiconductor film <NUM>, which is increased or reduced according to the change. Thus, the vibration is detected by the vibration sensor <NUM>.

The vibration sensor <NUM> in the above-mentioned example is of a cantilever structure, but may be of a both-end-fixed beam structure in which, as shown in <FIG>, both ends of the substrate <NUM> having the sensor portion S formed thereon are fixed with a pair of legs <NUM>.

The vibration sensor in the above-mentioned example is an example of the application of a vibration sensor using the organic semiconductor element. <FIG> shows an example of a diaphragm-type pressure sensor <NUM> using the organic semiconductor element <NUM>. The pressure sensor <NUM> has the substrate <NUM> having the sensor portion S formed thereon and a container <NUM>. The construction of the sensor portion S and that of the substrate <NUM> are similar to those in the above-mentioned example. The container <NUM> is in a hollow box form having an opening in one side, and the opening is airtightly closed using the substrate <NUM>. In the pressure sensor <NUM>, a difference between the pressure of a space <NUM> inside the container <NUM> and the pressure outside the container <NUM> causes the substrate <NUM> to suffer elastic deformation, so that the organic semiconductor element <NUM> is compressed or stretched according the deformation of the substrate. The outside pressure can be detected as a resistance of the organic semiconductor film <NUM>.

Alternatively, for example, a strain sensor may be constructed in which only a resin layer, such as polyparaxylene, constitutes the substrate <NUM> on which the sensor portion S is formed so that the substrate is in a film form which is deformable in bend or stretchable. In such a strain sensor, the substrate <NUM> of the sensor is fixed to the surface of a detection object by bonding or the like, enabling detection of strain of the surface of the detection object.

In each of the above-described examples, a single organic semiconductor element is formed between a pair of electrodes, but a construction may be employed such that, as shown in <FIG>, the electrodes <NUM>, <NUM> are individually formed in a shape like the teeth of a comb, and the organic semiconductor element <NUM> is formed between each electrode <NUM> and each electrode <NUM> to form one sensor portion S. In such a construction, it is possible to control a resistance of the element between the electrode <NUM> and the electrode <NUM>.

Next, an example of doping via ion exchange is described. Doping via ion exchange is a method in which an intermediate of the organic semiconductor in the organic semiconductor film <NUM> and a substance different from the intended dopant (hereinafter, referred to as "initiator dopant") is formed, and then the initiator dopant is replaced by an ultimate dopant (ion) via ion exchange to form a charge transfer complex of the organic semiconductor in the organic semiconductor film <NUM> and the ultimate dopant. In the doping made by this method, the doping amount can be considerably increased.

When the organic semiconductor in the organic semiconductor film <NUM> is taken as "A", the initiator dopant is taken as "B", an ion capable of forming a salt, together with the ultimate dopant (ion) (hereinafter, referred to as "spectator ion") is taken as "C", and the ultimate dopant (ion) (hereinafter, referred to as "alternative ion" in the case of this ion exchange) is taken as "D", doping via ion exchange can be represented by the following formula (<NUM>) in the case where the organic semiconductor is of a P type, and can be represented by the following formula (<NUM>) in the case where the organic semiconductor is of an N type.

In doping via ion exchange, a treatment liquid <NUM> (see <FIG>) is prepared by dissolving an initiator dopant having the same polarity (anion or cation) as that of the alternative ion in an ionic liquid which is a liquid of a salt composed of a spectator ion and an alternative ion. The salt composed of a spectator ion and an alternative ion need not be in a liquid state by itself, and may be dissolved in an organic solvent, such as acetonitrile or butyl acetate. The substrate <NUM> having the organic semiconductor film <NUM> formed thereon is immersed in the treatment liquid <NUM> for a predetermined period of time, and then the substrate <NUM> is removed from the treatment liquid <NUM>, and the surface of the substrate is dried by air blow or the like. As a result, the alternative ion adsorbs on the surface of the organic semiconductor film <NUM> to form the doped layer <NUM> in the surface (interface) of the organic semiconductor film <NUM>. In this instance, an extremely thin dopant film <NUM> composed of the alternative ion which has adsorbed is formed on the surface of the organic semiconductor film <NUM>.

The alternative ion is a first ion which serves as a dopant, and the initiator dopant (ion) is a second ion which oxidizes or reduces the organic semiconductor. When doping is conducted by ion exchange, for example, the treatment liquid <NUM> may be applied, dropwise added and spread to the surface of the organic semiconductor film <NUM> as long as a reaction can be caused as mentioned above by allowing the treatment liquid <NUM> to be in contact with the surface of the organic semiconductor film <NUM>.

As seen from the state of the organic semiconductor film being doped, diagrammatically shown in <FIG>, in the case where the organic semiconductor in the organic semiconductor film <NUM> is of a P type, when the organic semiconductor film <NUM> is immersed in the treatment liquid <NUM>, a redox reaction of the organic semiconductor and the initiator dopant represented by the formula (<NUM>) below is caused on the surface of the organic semiconductor film24 (<FIG>). Specifically, an intermediate ([A]+[B]-) composed of the organic semiconductor (cation [A]+) and the initiator dopant (anion [B]-) is formed, and, in this instance, charge transfer occurs between the organic semiconductor and the initiator dopant, so that carriers (holes in this example) are injected into the organic semiconductor film. <NUM>] <MAT>.

The redox reaction of the organic semiconductor and the initiator dopant represented by the formula (<NUM>) is reversible, and, after the reaction has reached a state of equilibrium, the amount of the intermediate formed is not increased. That is, doping of the organic semiconductor film <NUM> with the initiator dopant does not proceed after reaching a state of equilibrium. However, when the alternative ion (anion [D]-) which is more likely to chemically form a pair with the organic semiconductor than the initiator dopant (anion [B]-) is present in the system, as shown in the formula (<NUM>) below, the initiator dopant (anion [B]-) forming the intermediate is replaced (ion-exchanged) by the alternative ion (anion [D]) (<FIG>). This replacement causes a redox reaction of the organic semiconductor and the initiator dopant so as to maintain the state of equilibrium, and further the initiator dopant (anion, [B]-) in the intermediate formed by the redox reaction is replaced by the alternative ion (anion, [D]-). <NUM>] <MAT>.

When the organic semiconductor film <NUM> is C8-DNBDT which is a P type organic semiconductor, the initiator dopant is F<NUM>TCNQ, the alternative ion is TFSI-, and the spectator ion is EMMI+, the formulae (<NUM>) and (<NUM>) above are represented by the following formulae (<NUM>) and (<NUM>).

As a result of the above reactions, a state is formed in which the surface of the organic semiconductor film <NUM> is doped with the alternative ion. In the organic semiconductor film <NUM> which is doped as mentioned above, the doping amount is large, as compared to that in the case of doping made by immersing the film in a solution having dissolved only an initiator dopant. In addition, the above-mentioned reactions are caused on the surface of the organic semiconductor film <NUM>, and therefore doping can be advantageously made without causing the crystal structure of the organic semiconductor film <NUM> to be disordered. Further, it has been found that the organic semiconductor film <NUM> in the doped state has high stability to heat and high stability in air. With respect to the data showing the stability in air, <FIG> shows a change with time of the current flowing the organic semiconductor element <NUM> when applying a constant voltage to the organic semiconductor element. Similar data is obtained in the case where the organic semiconductor in the organic semiconductor film <NUM> is of an N type.

With respect to the P type organic semiconductor, there is used one which forms single crystal, and the HOMO level of which satisfies the predetermined requirement in respect of the LUMO level of the initiator dopant as mentioned below. With respect to the N type organic semiconductor, there is used one which forms single crystal, and the LUMO level of which satisfies the predetermined requirement in respect of the HOMO level of the initiator dopant as mentioned below. When the organic semiconductor film <NUM> is formed by the above-mentioned edge casting method, an organic semiconductor soluble in an organic solvent is used.

When using the P type organic semiconductor, as the initiator dopant, F<NUM>TCNQ is used. Further examples of such initiator dopants include <NUM>,<NUM>,<NUM>,<NUM>-tetracyanoxydimethane and Mo(tfd-COCF<NUM>)<NUM>.

When using the P type organic semiconductor, the requirement: "VH1 ≤ VL1 + <NUM> (eV)" is satisfied wherein the HOMO level of the organic semiconductor is VH1 (eV), and the LUMO level of the initiator dopant is VL1 (eV).

When using the P type organic semiconductor, as the alternative ion, an anion having a closed shell structure capable of forming a salt, together with the spectator ion, is used. Examples of such alternative ions include tetrafluoroborate (BF4), hexafluorophosphate (PF6), hexafluoroantimonate (SbF6), a carbonate ion, a sulfonate ion, a nitrate ion, a phosphate ion, a thiocyanate ion, a cyanate ion, a chloride ion, a bromide ion, an iodide ion, a triiodide ion, a fluoride ion, trifluoro[tri(pentafluoroethyl)]phosphate (FAP), bis(trifluoromethanesufonyl)imide (TFSI), bis(pentafluoroethanesufonyl)imide (TFESI), a bis (oxalato) borate ion (BOB), a bis (malonato) borate ion (MOB), a tetrakis(pentafluorophenyl)borate ion (PFPB), tetrakis(<NUM><NUM>-trifluoromethyl)phenylborate (TFPB), and an iron tetrachloride ion (FeCl<NUM>).

When using the P type organic semiconductor, the spectator ion is a cation having a closed shell structure capable of forming a salt, together with the alternative ion. Examples of spectator ions include metal ions and metal ions modified with a cyclic ether or the like, organic molecular ions and derivatives thereof, Li, Na, Cs, Mg, Ca, Cu, Ag, imidazolium, morpholinium, piperidinium, pyrridinium, ppyrolodinium, ammonium, and phosphonium.

When using the N type organic semiconductor, as the initiator dopant, cobaltocene is used. Examples of such initiator dopants include decamethylcobaltocene, ruthenocene, ferrocene, and <NUM>,<NUM>-dimethyl-<NUM>-phenyl-<NUM>,<NUM>-dihydro-benzoimidazole.

When using the N type organic semiconductor, the requirement: "VL2 ≥ VH2 - <NUM> (eV)" is satisfied wherein the LUMO level of the organic semiconductor is VL2 (eV), and the HOMO level of the initiator dopant is VH2 (eV).

When using the N type organic semiconductor, as the alternative ion, a cation having a closed shell structure capable of forming a salt, together with the spectator ion, is used. Examples of such alternative ions include metal ions and metal ions modified with a cyclic ether or the like, organic molecular ions and derivatives thereof, Li, Na, Cs, Mg, Ca, Cu, Ag, imidazolium, morpholinium, piperidinium, pyrridinium, ppyrolodinium, ammonium, and phosphonium.

The spectator ion of the N type is an anion having a closed shell structure capable of forming a salt, together with the alternative ion. Examples of spectator ions include tetrafluoroborate (BF4), hexafluorophosphate (PF6), hexafluoroantimonate (SbF6), a carbonate ion, a sulfonate ion, a nitrate ion, a phosphate ion, a thiocyanate ion, a cyanate ion, a chloride ion, a bromide ion, an iodide ion, a triiodide ion, a fluoride ion, FAP, TFSI, TFESI, BOB, MOB, PFPB, TFPB, and FeCl<NUM>.

For achieving a reaction in which the initiator dopant forming the intermediate is replaced by the alternative ion, the system is controlled so that the Gibbs energy of the system is stabilized by pairing of the initiator dopant and the spectator ion, or the Gibbs energy of the system is stabilized by pairing of the organic semiconductor and the alternative ion.

In Examples, using a sample having the sensor portion S formed on the substrate <NUM>, properties of the organic semiconductor element <NUM> were measured. In the sample, the organic semiconductor element <NUM> was formed in the middle of the substrate <NUM> as viewed in the longitudinal direction of the substrate, and the sample was curved at the middle of the substrate <NUM> in each measurement. The sensor portion S had a structure in which, as shown in <FIG>, the electrodes <NUM>, <NUM> are individually formed in a shape like the teeth of a comb, and the organic semiconductor element <NUM> is formed between each electrode <NUM> and each electrode <NUM>. Each sample has no leg <NUM>.

<FIG> shows the results of the measurement of a resistance change rate in relation to strain ε with respect to samples <NUM> to <NUM> prepared using different dopant films <NUM>. In the samples <NUM> to <NUM>, the organic semiconductor film <NUM> was formed from single crystal of C8-DNBDT. With respect to the dopant constituting the dopant film <NUM>, Mo(tfd-COCF<NUM>)<NUM>- was used in the sample <NUM> SbF<NUM>- was used in the sample <NUM>, and TFSI- was used in the sample <NUM>. In the sample <NUM>, Mo(tfd-COCF<NUM>)<NUM> was used as a dopant material, and, in the sample <NUM>, NO+SbF<NUM>- was used as a dopant material, and the dopant film <NUM> was formed by a method of immersing the organic semiconductor film <NUM> in a solution having each dopant material dissolved in a solvent. In the sample <NUM>, F<NUM>TCNQ was used as the initiator dopant, TFSI- was used as the alternative ion, EMMI+ was used as the spectator ion, and doping was conducted using the above-mentioned ion exchange method.

The strain ε was "positive" in the case that the organic semiconductor element <NUM> is stretched, and "negative" in the case that the organic semiconductor element <NUM> is compressed, and was determined from "ε = h/2r" wherein a thickness of the substrate <NUM> is taken as h, and a curvature radius of the organic semiconductor element <NUM> is taken as r. The resistance change rate was determined from "ΔR/R × <NUM> (%) " wherein a resistance of the organic semiconductor element <NUM> measured when the substrate <NUM> is not deformed is taken as R, and an increase of the resistance of the organic semiconductor element <NUM> measured when the substrate <NUM> is deformed is taken as ΔR. A change of the resistance of the organic semiconductor element <NUM> was determined from the output voltage of a bridge circuit to which the lead wires <NUM>, <NUM> were connected.

As can be seen from the graph of <FIG>, irrespective of the dopant and the method for doping, the relationship between the resistance change rate and the strain ε was almost the same. A gage rate k (= (ΔR/R)/ε) of the samples <NUM> to <NUM> in the compression direction was about <NUM>, which is about <NUM> times the value obtained when using a metal as a strain detecting element. The gage rate k of the organic semiconductor element <NUM> in the stretching direction was larger than that in the compression direction.

Further, <FIG> shows the results of the measurement of a resistance change rate in relation to very small strain ε with respect to a sample <NUM>. In the sample <NUM>, the organic semiconductor film <NUM> was formed from single crystal of C10-DNBDT, and the organic semiconductor element <NUM> was prepared by an ion exchange method using TFSI- as a dopant. As can be seen from the graph of <FIG>, the organic semiconductor element <NUM> can detect even a very small strain ε of <NUM>% or less with high sensitivity. The gage rate k of the organic semiconductor element <NUM> in the region of the very small strain measured was <NUM>, which indicates a result that the sensitivity is higher than the value obtained when using a metal as an element (K = <NUM>).

<FIG> shows the results of the measurement of an output voltage from the bridge circuit having connected thereto the sensor portion S with respect to the sample <NUM> when mechanically vibrating in the vertical direction the middle portion of the substrate <NUM>, both ends of which were fixed. In this measurement, the frequency of vibration was <NUM>,<NUM>, and the amplitude was <NUM>, and the measurement was made in respect of two types of input voltages, i.e., <NUM> V and <NUM> V. When the input voltage was <NUM> V, it is considered that an output voltage is generated by an effect of electromagnetic induction caused due to movement of the circuit of the sensor portion S at a high speed in the environmental magnetic field.

There is a large difference between the output voltage measured for the input voltage of <NUM> V and the output voltage measured for the input voltage of <NUM> V, and this shows that, with respect to the output voltage for the input voltage of <NUM> V, the organic semiconductor element <NUM> responds to the vibration at <NUM>,<NUM> to cause the output voltage to be changed. From the result, it is found that the organic semiconductor element <NUM> has a response speed of <NUM> or less. Further, it is apparent that the organic semiconductor element has such high sensitivity that an amplitude as very small as <NUM> can be detected.

Claim 1:
An organic semiconductor element (<NUM>) to be connected to a pair of electrodes (<NUM>, <NUM>), comprising:
an organic semiconductor film (<NUM>) formed from single crystal of an organic semiconductor;
a doped layer (<NUM>) formed in a surface of the organic semiconductor film (<NUM>); and
a dopant film (<NUM>), formed on the surface of the organic semiconductor film (<NUM>) for supplying carriers to the surface of the organic semiconductor film to form the doped layer (<NUM>),
characterized in that the organic semiconductor film (<NUM>) is a resistance element through which a gage current flows when a voltage is applied between the pair of electrodes (<NUM>, <NUM>) which are electrically connected through the doped layer (<NUM>), and the dopant film (<NUM>) is composed of an anion or a cation having a closed shell structure adsorbed on the surface of the organic semiconductor film (<NUM>).