JP2007158118A - Method and device for applying nanowire solution - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To arrange a nanowire at a predetermined position on a substrate in a desired direction of orientation discharging a nanowire solution from a nozzle. <P>SOLUTION: A device for applying a nanowire solution includes the nozzle 1a which discharges the nanowire solution 2 which is obtained by distributing the nanowire 2a in a solvent, and a means 5 which applies a field to the nanowire solution 2 which passes through inside of the nozzle. In a process of sticking the nanowire solution 2 to the surface of the substrate 6, before the nanowire solution 2 reaches the substrate 6, the field is impressed to the nanowire solution 2 by the field application means 5 to orientate the nanowire 2a. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method and apparatus for applying a solution containing nanowires to a substrate.

  TFT technologies known as switching elements for various electronic devices include silicon transistors (single crystal, polycrystalline, amorphous), compound semiconductor transistors (III-V, II-VI, IV-IV), organic transistors (low Molecule, polymer) and the like are known.

A silicon-based transistor is a transistor using silicon as a semiconductor layer. This technology has the characteristics that silicon as a material is inexhaustible on the ground surface, p-type / n-type structure can be obtained by doping, and SiO ₂ which is an oxide of silicon can be used as a high-quality insulating film. . Furthermore, this technology can achieve excellent transistor performance due to high carrier mobility (single crystal: ~ 10 ³ cm ² / Vs, polycrystal: ~ 10 ² cm ² / Vs, amorphous: ~ ¹ cm ² / Vs). It has the characteristics of being able to. However, in the element formation process, a complicated process such as exposure and transfer is required in a large-scale manufacturing facility such as a clean room, and there is a problem of cost reduction and process simplification.

  A compound semiconductor transistor is a transistor using a compound (GaAs, SiC, etc.) composed of a plurality of elements in a semiconductor layer. This technology has much higher carrier mobility than silicon-based materials, and exhibits various characteristics such as low power driving at high frequencies, photoreactivity, and microwave emission depending on the type of compound. However, not only is the material expensive, but a large-scale and complicated process similar to that of a silicon transistor is required for element formation, so that its application is limited.

An organic transistor is a transistor using an organic substance (such as pentacene for a low molecular weight or PEDOT for a high molecular weight) as a semiconductor layer. Since this technique enables coating film formation particularly in a polymer system, it is possible to form a simple, large-scale, and low-cost element by an ink jet method or a roll-to-roll method. However, the carrier mobility that determines transistor performance is lower than that of silicon (up to 0.1cm ² / Vs), and it requires rapid development in terms of materials and manufacturing processes to be applied to various electronic devices. The

  In view of these points, it is desired to develop TFT technology that has high transistor performance and can be mass-produced by a simple and low-cost element formation process.

  As such next-generation TFT technology, silicon nanowire TFTs are attracting attention. The silicon nanowire TFT has a structure in which a plurality of silicon nanowires (diameter: 5 to 30 nm, wire length: 200 μm) are used for a semiconductor layer of a transistor. For example, the following method is known as a method for synthesizing silicon nanowires. That is, by depositing gold on the surface of the single crystal silicon substrate and heating in a silane gas atmosphere, a molten compound alloy of silicon and gold is formed on the surface of the silicon substrate. Silane gas is decomposed using this as a catalyst, and silicon nanowires grow between the catalyst and the silicon substrate (see, for example, Patent Document 1).

The silicon nanowires thus obtained have a very excellent crystallinity in the axial direction and have a structure in which the surface is covered with a natural oxide film SiO ₂ insulating layer (thickness of about 30 nm). For this reason, when used as a semiconductor layer of a TFT, the transistor performance is as high as that of polycrystalline silicon to single crystal silicon (see, for example, Patent Document 2). In element formation, coating can be formed on a substrate, and it has advantages in terms of process such as simple, low cost, and mass production.

  From these characteristics, the silicon nanowire TFT has both the high performance of the silicon-based TFT and the advantage of a simple formation process of the organic TFT, and is expected to have performance and new applications beyond the conventional TFT element.

  One example of application is the formation of TFTs on flexible substrates. The silicon nanowire TFT has not only excellent TFT performance as described above, but also has a feature that a driver circuit can be formed at the same time, it has excellent bending resistance, and can be molded by a complete solution process. Therefore, forming a nanowire TFT on a plastic substrate is expected to form a flexible electronic device having both high TFT performance and a simple formation process that could not be achieved by conventional TFT technology. For example, by combining a silicon nanowire TFT technology with a flat panel display technology such as a liquid crystal display or an organic EL display, it is possible to realize a flexible display that can be driven with high brightness, high image quality, and low power, which has not been conventionally available. Other TFTs may be applied to various fields such as phase control antennas.

  In order to form a high-performance silicon nanowire TFT, there are two points: structure control of the nanowire itself (crystallinity, diameter / size, core-shell structure) and deposition of a nanowire layer with excellent orientation and alignment Is important. For the former, the diameter, size, shell thickness, etc. can be controlled by the reaction conditions during nanowire synthesis.

  On the other hand, with respect to the latter, a technique for orientation / alignment by flowing a nanowire solution through a channel provided on a substrate has been reported (see, for example, Patent Document 3), but there are almost no other reports. The characteristics of the nanowire TFT depend on the orientation / alignment of the nanowire layer that connects the source and drain electrodes, and thus a simple process for forming a nanowire layer that is more excellent in orientation / alignment is required. Yes.

  As a channel material of a field effect transistor having a nanowire as a channel that is currently being developed, carbon nanotubes, Si nanowires, and Ge nanowires can be cited. Other materials for the nanowire include semiconductor materials such as III-V group compounds such as GaAs and InP, and II-VI group compound semiconductors such as CdS. In the present specification, nano-sized, needle-like or rod-like substances including these are collectively referred to as nanowires.

  As described above, nanowires are expected to be used in various applications in the future because they do not require a vacuum technique such as lithography and can produce a fine structure by a coating technique.

As described above, for example, in order to form a plurality of TFTs on a flexible substrate, a technique for aligning and arranging nanowires in a pattern region is very important. For example, in the case of a display, it is necessary to align nanowires in each TFT corresponding to about 10 ⁴ -10 ⁷ pixels. The orientation here refers to the directionality of the long axis of the nanowire on the substrate, and the array indicates the two-dimensional arrangement position of the nanowire on the substrate. However, the current situation is that these technologies have not been fully studied.

The following have been reported as conventional alignment techniques. That is, as described above, a technique for aligning and aligning a nanowire solution by flowing it through a channel provided on a substrate has been reported (for example, see Patent Document 3). This technology is effective for the orientation and arrangement of nanowires at specific positions, but if a large number of TFTs are to be produced at one time, it is necessary to take a complicated flow path configuration. The device becomes very large. In addition, an inkjet method has been reported as one method for applying nanowires (see, for example, Non-Patent Document 1). This technique is effective for arranging the nanowires at specific positions, but does not have a specific means for orienting the nanowires. Patent Document 4 introduces an example in which an alternating voltage is applied between two electrodes constituting a TFT in order to align carbon nanotubes. Although this method is an effective method, in this case, a voltage is applied to the gap between the electrode end and the electrode end, but a sufficient voltage is not applied to the electrode surface. For this reason, it is difficult to control the orientation of the nanotubes arranged on the electrode surface. Also, it is difficult to control the orientation of bent or entangled nanotubes by straightening them between very narrow electrodes. In addition, since the electric field concentrates at the end of the electrode, the end of the nanowire tends to be disposed at the end of the electrode, making it difficult to make electrical contact between the nanowire and the electrode.
JP-A-10-106960 U.S. Pat. U.S. Pat. No. 6,872,645 JP 2004-71654 A Nature Vol.425 18.Sep. P.274 (2003)

  An object of the present invention is to solve the problems of the prior art as described above and provide means capable of easily aligning nanowires in a desired direction and pattern. In particular, the present invention provides a method and an apparatus capable of easily arranging nanowires with a desired orientation direction when nanowires dispersed in the solution are aligned at predetermined positions on a substrate by discharging the nanowire solution from a nozzle. There is to do.

According to the present invention, the above object is achieved as follows:
A method of applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
In the process of adhering the nanowire solution to the surface of the substrate, the nanowire solution is applied by applying an electric field to the nanowire solution before the nanowire solution reaches the substrate. Method,
Is provided.

  In one aspect of the present invention, even after the nanowire solution reaches the substrate, an electric field is applied to the nanowire solution to orient the nanowires.

In addition, according to the present invention, the above-mentioned object is achieved as follows:
An apparatus for applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
A nozzle for discharging the nanowire solution;
Means for applying an electric field to the nanowire solution disposed in the nozzle and passing through the nozzle;
An apparatus for applying a nanowire solution, comprising:
Is provided.

  In one aspect of the present invention, the means for applying the electric field applies an electric field in a direction along the direction in which the nanowire solution passes through the nozzle. In one aspect of the present invention, the means for applying the electric field applies an electric field in a direction along a direction orthogonal to the direction in which the nanowire solution passes through the nozzle. In one aspect of the present invention, it further comprises means for applying an electric field to the nanowire solution by applying a voltage between the nozzle and the substrate.

In addition, according to the present invention, the above-mentioned object is achieved as follows:
An apparatus for applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
A nozzle for discharging the nanowire solution;
Means for applying an electric field to the nanowire solution by applying a voltage between the nozzle and the substrate;
An apparatus for applying a nanowire solution, comprising:
Is provided.

  In one embodiment of the present invention as described above, a plurality of the nozzles arranged in a row are provided.

  According to the present invention as described above, when a nanowire solution is ejected from a nozzle and the nanowires dispersed in the solution are aligned at predetermined positions on the substrate, the nanowires can be easily arranged with a desired orientation direction. Can do.

  Hereinafter, embodiments of a nanowire solution coating method and a nanowire coating apparatus according to the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

Nanowire is a needle-like or rod-like material of nano-sized as described above, in particular several nm~ several hundred nm in diameter, with a length of several μm~ hundred [mu] m, an aspect ratio of 10 to 10 ⁴ wire Those having a shape are typical. However, in the present invention, the nanowire includes not only a wire shape but also a tube shape such as a carbon nanotube, and the present invention can also be applied to this.

Specifically, nanowire semiconductor materials include group IV semiconductors (C, Si, Ge, Sn) and combinations thereof, group III-V semiconductors (Al, Ga, In) (N, P, As, Sb), II-VI semiconductors (Be, Mg, Zn, Cd, Hg) (O, S, Se, Te) are possible. Other semiconductors (Ge, Sn, Pb) (S, Se, Te), (Cu, Ag) (F, Cl, Br, I), (Cu, Ag) (Al, Ga, In, Tl, Fe ) (S, Se, Te) ₂ and (Al, Ga, In) ₂ (S, Se, Te) ₃ are possible. Furthermore, it is possible _{BeSiN 2, CaCN 2, ZnGeP 2} , CdSnAs 2, ZnSnSb 2, CuGeP 3, CuSi 2 P 3, Si 3 N 4, Ge 3 N 4, Al 2 O 3, Al 2 CO and the like. A combination of these is also possible. Here, the elements in parentheses () collectively represent all of one kind of materials or materials composed of a mixture of plural kinds of materials. Furthermore, a dopant may be added as appropriate for forming a p-type semiconductor and an n-type semiconductor.

  These nanowires are synthesized by various synthesis methods such as a gas phase method and a liquid phase method, and are dispersed in a solvent that can be uniformly dispersed. As examples of the solvent, in addition to ketones such as acetone, liquids such as diethyl ether, various alcohols such as water, ethanol, and ethylene glycol, toluene, chlorobenzene, and dichlorobenzene can be used. In order to make these dispersions uniform, sonication is also a good method.

  In addition, various types of nanowires such as carbon nanotubes and silicon nanowires can be selected from various types of conductivity depending on the composition and manufacturing method.

  The substrate to which the nanowire solution is applied is not particularly limited as long as the substrate is not affected by the nanowire solution and can be selected from a wide range of substrates such as a glass substrate and a plastic substrate. Further, the substrate may have a surface on which an electrical functional element such as an electrode or an insulating layer is formed.

<Embodiment 1>
FIG. 1 is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. FIG. 2 is a schematic diagram of the vicinity of the nozzle of the solution coating apparatus of the present embodiment, and FIG. 3 is a schematic diagram of the coated substrate viewed from above. FIG. 4 is a schematic view of still another coated substrate as viewed from above.

  As shown in FIG. 1, a nanowire solution (hereinafter simply referred to as “solution”) 2 in which nanowires 2a are dispersed in a solvent is specifically expressed by solution delivery means (not shown) 4 (for example, by applying air pressure), A predetermined amount is poured from the upper part into the container 1 at a predetermined timing. A nozzle 1a is provided at the lower portion of the container 1, and the solution 2 is discharged from the nozzle 1a downward by the predetermined amount. A substrate (coating substrate) 6 to be coated is disposed below the nozzle 1a in the vicinity thereof.

  An example of the substrate 6 is a substrate for producing a nanowire TFT. A pair of source / drain electrodes 7 are formed on the surface of the substrate 6, and a distance shorter than the length of the nanowire is provided between the source electrode and the drain electrode. The substrate 6 is conveyed leftward relative to the nozzle 1a in FIG.

  The nozzle 1a is provided with an electrode 3 for applying an electric field to the solution. Specifically, as shown in FIG. 2, electrodes 3a and 3b are arranged on the wall surface of the nozzle 1a at a distance along the moving direction (vertical direction) of the solution in the nozzle. For example, an AC voltage is applied between the electrodes 3a and 3b by the voltage applying means 5 as necessary. By making the nozzle length longer than the inner diameter of the nozzle, the direction of the electric field in the nozzle 1a can be made substantially parallel to the solution movement direction in the nozzle. Thereby, in the nozzle, the nanowires in the solution are linearly aligned along the solution moving direction by the electric field. The ratio of the nozzle length to the inner diameter of the nozzle is, for example, 2 or more, preferably 3 or more, more preferably 5 or more.

  In the drawing, an example in which a pair of electrodes is installed inside the nozzle has been described, but the present invention is not limited to this. If a plurality of stages of electrodes are provided to increase the distance to which a voltage can be applied, the orientation control of the nanowires in the solution can be made more reliable, and the voltage applied between each pair of electrodes can be reduced.

  A predetermined amount of the solution discharged downward from the nozzle 1a at a predetermined timing by the solution sending means 4 is applied onto the source / drain electrodes 7 of the substrate 6 disposed in proximity. At that time, the nanowires 2a in the solution oriented in the nozzle are applied in a state of being oriented in the substrate transport direction as shown in FIG. 3 because the substrate 6 is transported. Thus, the nanowires 2a are arranged so as to cross the distance between the source electrode and the drain electrode.

  Here, an example is shown in which air pressure is used as the driving force for discharging the solution from the nozzle, but the present invention is not limited to this. Oil pressure may be used, or a solution delivery / discharge means may be provided for each nozzle by using a piezo-type or bubble jet (registered trademark) -type ink jet technique.

  Further, a method for aligning the tip positions of the nanowires oriented on the substrate 6 will be described. In FIG. 1, when a voltage is applied to the electrode 3 in the nozzle 1a, the application / non-application of the voltage by the voltage application means 5 is controlled in accordance with the discharge / non-discharge timing of the solution from the nozzle 1a. As a result, as shown in FIG. 4, the phases of the nanowires in the length direction of the electrodes 7 on the substrate 6 can be aligned, and the nanowires can be arranged between the source / drain electrodes 7 without waste. Specifically, before discharging the solution from the nozzle 1a, a voltage is applied to the electrode 3 in the nozzle 1a to orient the nanowires in the solution, and then the solution is discharged to discharge the solution. The tip positions of the nanowires in the solution can be aligned. As a result, the nanowires in the applied solution extend across the distance between the source electrode and the drain electrode on the substrate, and one end is positioned on the source electrode and the other end is positioned on the drain electrode. They are all arranged. Thus, alignment and alignment by voltage can be performed efficiently.

<Embodiment 2>
FIG. 5 is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. FIG. 6 is a schematic view of the coated substrate as viewed from above. In these drawings, members having the same functions as those in the first embodiment are denoted by the same reference numerals.

  In the present embodiment, as shown in FIG. 5, an AC voltage is applied between the electrode 3 at the lowest position of the nozzle and the electrode 7 of the substrate 6 by the voltage applying means 5b. As a result, the nanowires in the solution discharged from the nozzle are aligned in the solution substantially along the discharge direction before being applied to the substrate, and are stably aligned on the substrate. In addition, since a voltage is applied between the nozzle and the substrate also on the electrode 7 of the substrate 6, a force for orienting the nanowires also acts on the electrode 7. For this reason, it is possible to efficiently orient the nanowire not only over the electrode end but over the entire surface of the electrode. As shown in FIG. 6, in order to align the nanowires between the two electrodes 7, it is effective to apply a voltage between the leading electrode and the nozzle in the substrate transport direction.

  The application of the electric field to the solution by the voltage application means 5b can be used in combination with the application of the electric field to the solution inside the nozzle 1a by the voltage application means 5a. Thereby, since the nanowire can be oriented before discharging from the nozzle, the effect is further enhanced.

<Embodiment 3>
FIG. 7 is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. FIG. 8 is a schematic diagram of the vicinity of the nozzle of the solution coating apparatus of the present embodiment, and FIG. 9 is a schematic diagram of the coated substrate as viewed from above. In these drawings, members having the same functions as those in the drawings of the first and second embodiments are denoted by the same reference numerals.

  In this embodiment, the structure of the nozzle 1a is different from that of the above embodiment. That is, FIG. 8 shows the nozzle as viewed from above (corresponding to a horizontal sectional view). In this cross section, the shape of the solution flow passage is elongated in a direction orthogonal to the substrate transport direction. The paired electrodes 3a and 3b are separated from each other in a direction orthogonal to the substrate transport direction, and are disposed at both ends of the elongated solution flow path in FIG.

  On the other hand, as shown in FIG. 9, the source / drain electrodes 7 are arranged on the substrate 6 at intervals in a direction orthogonal to the substrate transport direction.

  An AC voltage is applied between the electrodes 3a and 3b as necessary by the voltage applying means 5, and the nanowires 2a in the solution are oriented in the nozzle so as to be orthogonal to the solution movement direction by the voltage.

  A predetermined amount of the solution discharged downward from the nozzle 1a at a predetermined timing by the solution sending means 4 is applied onto the source / drain electrodes 7 of the substrate 6 disposed in proximity. At that time, the nanowires 2a in the solution are applied in a state of being oriented in a direction orthogonal to the substrate transport direction as shown in FIG. Thus, the nanowires 2a are arranged so as to cross the distance between the source electrode and the drain electrode.

  This embodiment is suitable when both the electrodes 7 of the substrate 6 are narrow and the counter electrode width is long, and the nozzle shape can be easily designed and the nanowire solution can be applied efficiently.

<Embodiment 4>
FIG. 10 is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. FIG. 11 is a schematic view of the vicinity of the nozzle of the solution coating apparatus of the present embodiment. In these drawings, members having the same functions as those in the drawings of Embodiments 1 to 3 are denoted by the same reference numerals.

  In the present embodiment, the container 1 is provided with a plurality of nozzles 1 a arranged in a line. The structure of each nozzle may be the same as that of the first or second embodiment as shown in FIG. 11, or may be the same as that of the third embodiment. By arranging a plurality of nozzles in this way, the nanowire solution can be efficiently applied to the plurality of source / drain electrodes on the substrate at once in a pattern.

  Further, by providing means for sending and discharging the solution to each nozzle as in the ink jet method, the solution can be discharged only from a predetermined nozzle.

  In the above embodiment, the nanowire solution application for forming the channel portion by the semiconductor nanowire between the source electrode and the drain electrode at the time of TFT fabrication has been described. However, the present invention provides the manufacture of an electric device having other nanowires. Can also be used. Examples of such an electric element include a resistor, a capacitor, an electroluminescent element, and a photoelectric conversion element.

It is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. FIG. 2 is a schematic diagram of the vicinity of a nozzle of the solution coating apparatus of FIG. 1. It is the schematic diagram which looked at the application substrate from the top. It is the schematic diagram which looked at the application substrate from the top. It is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. It is the schematic diagram which looked at the application substrate from the top. It is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. It is a schematic diagram near the nozzle of the solution coating apparatus of FIG. It is the schematic diagram which looked at the application substrate from the top. It is a schematic diagram showing an embodiment of a nanowire solution coating method and a nanowire solution coating apparatus according to the present invention. It is a schematic diagram near the nozzle of the solution coating apparatus of FIG.

Explanation of symbols

1: Container 1a: Nozzle 2: Solution 2a: Nanowires 3, 3a, 3b: Electrode 4: Solution sending means 5, 5a, 5b: Voltage applying means 6: Substrate 7: Source / drain electrodes

Claims (8)

A method of applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
In the process of adhering the nanowire solution to the surface of the substrate, the nanowire solution is applied by applying an electric field to the nanowire solution before the nanowire solution reaches the substrate. Method. 2. The nanowire solution coating method according to claim 1, wherein an electric field is applied to the nanowire solution even after the nanowire solution reaches the substrate to align the nanowire. 3. An apparatus for applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
A nozzle for discharging the nanowire solution;
Means for applying an electric field to the nanowire solution disposed in the nozzle and passing through the nozzle;
An apparatus for applying a nanowire solution, comprising: 4. The nanowire solution coating apparatus according to claim 3, wherein the means for applying the electric field applies an electric field in a direction along a direction in which the nanowire solution passes through the nozzle. The nanowire solution according to claim 3, wherein the means for applying the electric field applies an electric field in a direction along a direction orthogonal to a direction in which the nanowire solution passes through the nozzle. Coating device. The nanowire solution coating apparatus according to claim 3, further comprising means for applying an electric field to the nanowire solution by applying a voltage between the nozzle and the substrate. An apparatus for applying a nanowire solution obtained by dispersing nanowires in a solvent to a substrate,
A nozzle for discharging the nanowire solution;
Means for applying an electric field to the nanowire solution by applying a voltage between the nozzle and the substrate;
An apparatus for applying a nanowire solution, comprising: The nanowire solution coating apparatus according to claim 3, comprising a plurality of the nozzles arranged in a line.