JP4443944B2 - Transistor and manufacturing method thereof - Google Patents

Description

The present invention includes a transistor motor, a manufacturing method thereof.

In recent years, an organic transistor using an organic semiconductor material composed of an organic polymer or an organic low molecule in a channel region has been actively studied. This is because it is considered that lighter, more flexible and flexible flexible displays and electronic paper will be needed in the near future as the display of organic EL (Electro Luminescent Display) is becoming thinner. . As the display becomes more flexible, not only the display part but also the drive circuit part must be made flexible. Thin film transistors (Thin Film)
Transistor (abbreviated as TFT) uses a silicon-based inorganic material, but if bent, a crack occurs in the TFT channel region, that is, the semiconductor layer, which is not suitable for manufacturing a flexible device. Therefore, there is an increasing expectation for an organic transistor using a flexible and lightweight organic semiconductor material.

  For example, Patent Documents 1 to 5 disclose an organic transistor manufactured using an organic semiconductor material made of an organic polymer or an organic low molecule. Patent Document 1 discloses an organic thin film transistor in which an electron-donating acceptor molecule or an electron-donating donor molecule is used as a dopant and introduced into a condensed polycyclic aromatic compound thin film, for example, a pentacene thin film. Patent Document 2 discloses an organic electronic device in which a non-linear element that supplies current to an organic light emitting diode LED element has a structure in which a metal layer is sandwiched between two organic layers. Patent Document 3 discloses an organic transistor in which a charge transfer complex is generated by diffusing acceptor or donor introduced molecules in an organic semiconductor material. Patent Document 4 discloses an organic transistor having an active channel including a layer of organic molecules having conjugated multiple bonds. Patent Document 5 discloses a charge injection type organic transistor device having an organic semiconductor material.

  Replacing the current inorganic TFT with an organic TFT also has manufacturing advantages. This is because if a coatable organic polymer material is used, each electrode such as a source, drain, and gate, and each main structure of a transistor such as a semiconductor layer and an insulating layer can be manufactured by a printing or coating process. In the current inorganic TFT manufacturing process, it is necessary to perform many complicated processes such as vacuum deposition, patterning by photolithography, and etching, resulting in high process costs. If all of these can be carried out by printing or coating processes at room temperature and normal pressure, and can be continuously flowed as a line, a significant cost reduction is expected. Therefore, for example, Non-Patent Document 1 discloses that an organic transistor is formed by forming a source electrode, a drain electrode, a gate electrode, a semiconductor layer, and an insulating layer using an organic polymer material by an ink jet method and a spin coating method. It has been demonstrated that can be made.

The carrier mobility of the organic semiconductor layer in these organic transistors of the above-described prior art is about 1 cm ² / V · sec, even if it is a single crystal of pentacene, which is said to have the highest mobility at present, and is at most about amorphous silicon. Only mobility of is achieved. Therefore, the mobility of polysilicon and silicon crystals is not far, and even if organic transistors are used in the drive circuit parts such as flexible displays and electronic paper, the operating frequency is insufficient at present and it is difficult to achieve sufficient performance. It is.

JP-A-5-55568 JP 2002-208486 A JP 2002-204012 A JP 2003-31816 A JP 2003-101104 A T. Kawase et al. Tech Digest of IEDM, “All-Polymer Thin Film Transistors Fabricated by High-Resolution Ink-jet Printing” pp.25.5.1-25.5.4 623 (2000) (c) 2000 IEEE

  When a flexible device such as a flexible display or electronic paper is manufactured, this drawback hinders high-speed operation of a drive circuit portion, particularly a control circuit portion for addressing, and it is difficult to exhibit sufficient image display performance. Specifically, the transistor operating frequency required for a control circuit portion such as a display device is about several tens of MHz, but the current maximum operating frequency of an organic transistor is about several tens of kHz. There is a problem that display is difficult.

An object of the present invention is to provide a transistor having a semiconductor layer having flexibility and high carrier mobility, and a manufacturing method thereof.

The present invention uses a semiconductor layer made of gel composition comprising at least carbon nanotubes and an ionic liquid in the channel region,
The ionic liquids are 1-butyl-3-methylimidazolium tetrafluoro - a transistor, which is a Roboreto (1-Butyl-3-methylimidazolium tetrafluo-roborate).

Further, the present invention is characterized in that the semiconductor layer is formed on a flexible base material.
In the present invention, a semiconductor layer made of a gel-like composition containing carbon nanotubes and an ionic liquid is used for a channel region, and is printed or applied on a flexible substrate. The ionic liquid is 1-butyl A method for producing a transistor , characterized in that it is -3-methylimidazolium tetrafluoro-borate .

According to the present invention, due to the excellent material properties of the carbon nanotube, such as high electron velocity and high current density, it is possible to realize a semiconductor layer with high mobility exceeding, for example, 100 cm ² / V · sec, thereby exceeding, for example, several tens of MHz. A semiconductor element such as a transistor can be operated at a high frequency. In addition, since the carbon nanotube itself is highly flexible and has a tensile strength of, for example, several tens GPa and is a strong thin thread-like material, it is possible to form a highly flexible semiconductor layer optimal for a flexible device.

  Since carbon nanotubes are mixed with an ionic liquid and exist in a gel state, a semiconductor layer can be formed in an arbitrary shape. Moreover, since the handling property is good, mass production by continuous line production becomes easy.

  The said semiconductor layer can be produced by the application | coating to a base material, or printing using the handleability of the said gel-like composition. In this way, by using a coating or printing process for forming the semiconductor layer, a large-scale film forming apparatus and a vacuum apparatus that are used at the time of manufacturing a transistor in the conventional technique are not necessary, and the apparatus cost can be reduced. In addition, continuous line production at normal temperature and normal pressure can be realized, so that mass production and cost reduction of devices can be achieved.

  The method for forming the carbon nanotube gel semiconductor layer is a normal printing method utilizing the handling properties of the carbon nanotube gel, such as screen printing, offset printing, letterpress printing, intaglio printing, stencil printing, ink jet method, spin coating method, etc. Can be easily formed by a printing or coating process.

  In the present invention, an electrically insulating substrate, for example, a flexible film-like or sheet-like flexible substrate can be used, and includes a carbon nanotube produced by a printing or coating process as a semiconductor layer formed thereon. By using the gel composition, a transistor having high flexibility and capable of high-frequency operation can be manufactured in a continuous line process under normal temperature and normal pressure. This makes it possible to provide a high-performance flexible transistor at a low cost.

  The material of the electrically insulating substrate and the material of the insulating film for a field effect transistor (abbreviated as FET), which will be described later, are not particularly limited, but as a flexible substrate material, functional norbornene resin, acrylic resin, polyester Examples include resins, polycarbonate resins, styrene resins, vinyl chloride resins, epoxy resins, fluororesins, olefin resins, polyimide resins, and cellulose resins. Moreover, the copolymer which added these resins or other than that may be sufficient. Further, as the base material, a thermally oxidized silicon thin film obtained by thermally oxidizing the surface of a silicon substrate, an inorganic thin film produced by an inorganic material such as silicon nitride using a film forming apparatus, or a mixed material of an organic material and an inorganic material It is also possible to use organic-inorganic composite materials.

  The base material or the insulating film may be subjected to processing such as rubbing treatment, or two or more layers may be laminated. As a result, the carbon nanotubes are aligned and higher electron mobility is obtained.

  The electrode material is not particularly limited, but a metal material such as gold, aluminum, or copper may be used, and a semiconductor material having high electrical conductivity such as GaAs may be used. Two or more layers may be laminated to improve the characteristics.

  In the present invention, the carbon nanotube is 0.01 to 10.0% by weight of the gel composition.

The present invention, the semiconductor layer, you being a thickness 10 to 200 nm.

  According to the present invention, the carbon nanotubes are 0.01 to 10.0% by weight of the gel composition constituting the semiconductor layer. If it is less than 0.01% by weight, the semiconductor properties of the gel composition, particularly the electrical conductivity, will be insufficient. When the content exceeds 10.0% by weight, the carbon nanotubes are not uniformly dispersed in the ionic liquid and are aggregated, and as a result, a gel state is not achieved.

  The ionic liquid used in the present invention is not particularly limited, and various conventionally known ionic liquids can be used. However, the ionic liquid exhibits a liquid at room temperature or as close to room temperature as possible, and is stable. Is preferable. Moreover, the ionic liquid which consists of a cation represented by the following general formula (I)-(IV) and an anion (X-) is especially preferable.

[NR _X H _4-X ] ⁺ (III)
[PR _X H _4-X ] ⁺ (IV)

  In the above formulas (I) to (IV), R represents an alkyl group having 10 or less carbon atoms or an ether bond, and an alkyl group having a total number of carbon and oxygen of 10 or less. In the formula (I), R1 represents an alkyl group having 1 to 4 carbon atoms or a hydrogen atom, and a methyl group having 1 carbon atom is more preferable. In the formula (I), R and R1 are preferably not the same. In the formulas (III) and (IV), X is an integer of 1 to 4.

  Anions (X-) include tetrafluoroboric acid, hexafluorophosphoric acid, bis (trifluoromethylsulfonyl) imidic acid, perchloric acid, tris (trifluoromethylsulfonyl) carbonic acid, trifluoromethanesulfonic acid, dicyanamide , Trifluoroacetic acid, organic carboxylic acid, or halogen ion. Only one kind of these may be used, or a plurality of ionic liquids may be used.

  When the thickness of the semiconductor layer made of the gel composition is 10 nm or more, the above-described high performance of a semiconductor element such as a transistor can be achieved, and 200 nm or less is preferable from the viewpoint of productivity.

According to the transistor using the carbon nanotube of the present invention, the gel composition containing the carbon nanotube can be operated at a high frequency with a highly mobile and flexible semiconductor layer by a simple method such as printing or coating. the such transistor data can be produced. By using the semiconductor layer in a gel state, flexibility is obtained and adverse effects such as generation of cracks due to external force or deformation can be reduced. Further, by using a flexible substrate, it is possible to obtain a deformable transistor data, for example, the number of transistors data is formed films, the curved surface of a support such as housing of the electronic device, using paste It is also possible.

  The carbon nanotube has a structure like a graphene sheet wound, and a sheet having a π electron orbit is wound at a fine interval (for example, about 1 nm in diameter), so the overlap of the π electron orbit becomes large, It becomes easier to move the electrons. In gels containing carbon nanotubes, the electron transfer is defined by the slight hopping conduction between the carbon nanotubes and the rapid electron transfer in the carbon nanotubes. Operation is possible.

  In addition, since the semiconductor layer can be formed by a simple method such as printing or coating, the manufacturing cost can be reduced. Therefore, it is possible to achieve both high-speed operation and mass production / cost reduction, and it is possible to provide a flexible device such as a flexible display or electronic paper that requires a high frequency at a low cost.

  FIG. 1 is a cross-sectional view showing a so-called bottom gate type lateral transistor 11 according to an embodiment of the present invention. First, gold is vapor-deposited on a substrate 1 of a PET (polyethylene terephthalate) film to produce a gate electrode 2.

  Next, an insulating layer 3 made of polyimide resin is formed on the region of the substrate 2 not covered with the electrode 2 by spin coating. After the polyimide resin precursor is formed on the substrate 1 by spin coating, it is immediately dried and imidized.

  Next, the source electrode 4 and the drain electrode 5 are produced on the produced insulating layer 3 by vapor deposition of gold. A semiconductor layer 6 made of a gel-like composition containing carbon nanotubes is formed on the electrodes 4 and 5 and on the exposed region of the insulating material 3 where the electrodes 4 and 5 are not formed by an inkjet method.

  A gel-like composition containing carbon nanotubes was obtained by adding 1 mg of single-wall carbon nanotube powder having a diameter of about 1 μm and a length of about 1 μm in 1000 mg of 1-butyl-3-methylimidazolium tetrafluoro-borate, which is an ionic liquid, Prepare by stirring in a mortar. In this way, a field effect transistor which is a bottom gate type carbon nanotube gel lateral transistor is manufactured. Before the semiconductor layer 6 is provided, the insulating film 3 is rubbed, and the semiconductor layers 6 made of the electrodes 4 and 5 and the gel composition are formed on the insulating film 3 thus rubbed. preferable. Each electrode 2, 4, 5 has a thickness of 20 nm, for example, and insulating film 3 may have a thickness of, for example, 1-100 nm, preferably 30 nm. The thickness of the semiconductor layer 6 is 10 to 200 nm, preferably 20 to 100 nm.

  FIG. 2 is a graph showing characteristics of the semiconductor layer 6 shown in FIG. The present inventor dispersed 1 mg of single-wall carbon nanotube powder having a diameter of about 1 nm and a length of about 1 μm in 1000 mg of 1-butyl-3-methylimidazolium tetrafluoro-roborate, which is an ionic liquid, by dispersing in a mortar. The gel composition was prepared as described above, and the temperature dependence of the electrical resistance was measured. The measurement result is shown in FIG. As shown in FIG. 2, it was discovered that the gel-like composition containing carbon nanotubes exhibits the behavior of a semiconductor, which is an electrical property in which the electrical resistance decreases with decreasing temperature.

  In this experiment, the electrical resistance is measured by using a glass substrate on which a terminal made of gold is previously formed on a substrate, and applying a gel-like composition containing carbon nanotubes on the glass substrate on which the terminal is formed. A sample was made. The electrical resistance was measured by the 4-terminal method. The measurement was performed while cooling the sample by sealing in a liquid helium gas atmosphere. A bottom-gate lateral transistor using the gel-like composition containing the carbon nanotube as a semiconductor layer was fabricated as described above with reference to FIG. 1 and the current-voltage characteristics were evaluated. It has been found that the semiconductor layer 6 made of a gel-like composition containing carbon nanotubes operates as a transistor having a high electrical resistance ratio in the state.

  FIG. 3 is a cross-sectional view of a so-called top-and-gate lateral transistor 12 according to another embodiment of the present invention. This embodiment is similar to the above-described embodiment, and corresponding portions are denoted by the same reference numerals. First, a source electrode 4 and a drain electrode 5 are formed on a PET film substrate 1 by patterning gold by vapor deposition. Next, on these electrodes 4 and 5 and on the exposed region where the electrodes 4 and 5 of the substrate 1 are not formed, a gel containing carbon nanotubes is applied by the coating process such as the ink jet method as in the above-described embodiment. A composition is formed as the semiconductor layer 6. Furthermore, the polyimide thin film is apply | coated by the application | coating processes, such as a spin coat method, and the insulating layer 3 which consists of a polyimide resin is formed by drying and imidizing immediately. Finally, gold is deposited as a gate electrode 2 on the polyimide insulating layer to complete a top gate type transistor. Other configurations in the embodiment shown in FIG. 3 are the same as those in the above-described embodiment.

FIG. 4 shows a so-called SIT (Static Induction) according to still another embodiment of the present invention.
1 is a cross-sectional view showing a vertical transistor 13 of a transistor (electrostatic induction transistor) type. The embodiment shown in FIG. 4 is similar to each of the embodiments shown in FIGS. 1 to 3 described above, and corresponding portions are denoted by the same reference numerals. First, gold is vapor-deposited on a PET film substrate 1 to form one of the source and drain electrodes 4. On the electrode 4, a gel-like composition containing carbon nanotubes is applied by the inkjet method or the like as in the above-described embodiment. Gold is deposited thereon and inserted as the gate electrode 2. A gel-like composition containing carbon nanotubes is again applied on the gate electrode 2 by an ink jet method or the like to form the semiconductor layer 6. Thus, the gate electrode 2 is embedded in the semiconductor layer 6. Further, gold is deposited on the semiconductor layer 6 to form the other source or drain electrode 5. A vertical transistor is thus completed. The electrodes 4 and 5 have the same shape, the semiconductor layer 6 is sandwiched between the electrodes 4 and 5, and a plurality of (for example, 4 in this embodiment) gate electrodes 2 are embedded in the semiconductor layer 6.

  FIG. 5 is a cross-sectional view of a so-called top-and-bottom transistor 14 according to still another embodiment of the present invention. This embodiment is similar to each of the above-described embodiments, and corresponding portions are denoted by the same reference numerals. A source electrode 4 is formed on a PET film substrate 1 by vapor deposition, and a semiconductor layer 6 made of a gel-like composition containing carbon nanotubes is formed by a coating process such as an inkjet method, as in the above-described embodiments. Apply. Thereafter, gold is deposited to form the drain electrode 5. An insulating layer 3 made of polyimide resin is formed thereon by spin coating, and gold is further deposited to form the gate electrode 2. Here, the upper and lower positions of the source electrode 4 and the drain electrode 5 may be interchanged. The material of the substrate 1, the material of the insulating layer 3, and the materials of the electrodes 2, 4, 5 used in each embodiment described above can be appropriately selected from the materials described above.

  Each of the above embodiments is a field effect transistor 11-14, but in yet another embodiment of the present invention, a p-type semiconductor can be obtained by changing the type of ions that serve as dopants for the ionic liquid. It is also possible to form a bipolar transistor of the pnp conductivity type or the npn conductivity type, for example, by forming a layer and an n-type semiconductor layer, respectively. According to the present invention, not only a transistor but also other types of semiconductor elements can be realized.

Therefore the transistor data containing such carbon nanotubes, a semiconductor layer having a soft and high carrier mobility can be manufactured by a simple method such as, for example printing or coating. Therefore, it is possible to realize a flexible device that requires high flexibility such as a flexible display and electronic paper and high frequency drive performance. Furthermore, mass production and cost reduction of the flexible device are possible.

1 is a cross-sectional view showing a so-called bottom-gate lateral transistor 11 according to an embodiment of the present invention. It is a graph which shows the characteristic by experiment of this inventor of the semiconductor layer 6 shown by FIG. It is sectional drawing of what is called a top gate type horizontal transistor of other embodiment of this invention. It is sectional drawing which shows what is called a SIT type | mold vertical transistor 13 of the further another form of implementation of this invention. FIG. 5 is a cross-sectional view of a so-called top and bottom contact (abbreviated as TBC) transistor 14 according to still another embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 2 Gate electrode 3 Insulating layer 4 Source electrode 5 Drain electrode 6 Semiconductor layer 11, 12, 13, 14 Transistor

Claims (5)

The semiconductor layer composed of a gel composition used in the channel region including at least carbon nanotubes and an ionic liquid,
Transistor, which is a Roboreto - the ionic liquid 1-butyl-3-methylimidazolium tetrafluoro. 2. The transistor according to claim 1, wherein the semiconductor layer is formed on a flexible base material. Carbon nanotubes transistor according to claim 1 or 2, wherein it is 0.01 to 10.0% by weight of the gel composition. The transistor according to claim 1 , wherein the semiconductor layer has a thickness of 10 to 200 nm. Using a semiconductor layer made of gel composition containing carbon nanotube and an ionic liquid in the channel region, printed or coated on a flexible substrate, wherein the ionic liquid 1-butyl-3-methylimidazolium A process for producing a transistor , characterized in that it is lithium tetrafluoro-borate .

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