JP6365835B2 - Electrode formation method - Google Patents

Description

The present invention relates to a technique for forming an electrode pattern on an organic semiconductor substrate, and more particularly to a technique for forming a source electrode and a drain electrode of an organic semiconductor field effect transistor (OFET).

In recent years, in the electronic industry, so-called organic semiconductor transistors using organic materials have been developed from inorganic semiconductor transistors made of inorganic materials such as silicon. OFETs using this organic material can be easily manufactured electronically by means of printing, spin coating, dipping, etc., and can be manufactured at orders of magnitude less than conventional Si-based semiconductor devices. . OFETs can also be formed on plastics, and it is expected to realize devices such as flexible displays and flexible sensors that can be bent lightly and thinly.

As an OFET structure, a bottom-gate / top-contact transistor is taken as an example.
A gate insulating film is provided on the gate electrode formed on the substrate, and an organic semiconductor layer is formed thereon. Further, contact electrodes (source electrode and drain electrode) for carrier injection are formed on the organic semiconductor layer on the gate insulating film.

Examples of the material for the gate insulating film include oxide insulators such as SiO ₂ and Al ₂ O ₃ , polystyrene, polyimide, polyamideimide, polyvinylphenylene, polycarbonate (PC), and polymethyl methacrylate (PMMA). Examples include acrylic resins, fluorine resins such as polytetrafluoroethylene (PTFE), phenol resins such as polyvinylphenol or novolac resin, olefin resins such as polyethylene, polypropylene, polyisobutylene, and polybutene. One or two or more of them can be used in combination.

Examples of the organic semiconductor material include [1] benzothieno [3,2-b] [1] benzothiophene derivatives and 2,9-dialkyldinaphtho [2,3-b: 2 ′, 3′-f]. Thieno [3,2-b] thiophene derivatives, dinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2-b] thiophene derivatives, TIPS-pentacene, TES-ADT, and derivatives thereof, Monomolecular organic semiconductor materials such as perylene derivatives, TCNQ, F4-TCNQ, F4-TCNQ, rubrene, pentacene, p3HT, pBTTT, and pDA2T-C16, poly-N-vinylcarbazole, polyvinylpyrene, polyvinylanthracene, polythiophene, Polyhexylthiophene, poly (p-phenylene vinylene), polytinylene vinylene, polyarylamino High molecular organic semiconductor materials such as pyrene formaldehyde resin, ethylcarbazole formaldehyde resin, fluorene-bithiophene copolymer, fluorene-arylamine copolymer, or derivatives thereof, one or two of them A combination of the above can be used.

Such a conjugated molecular material has a unique electron cloud spread due to its high crystallinity, has high carrier mobility, and can be formed at low temperatures. It is expected that it can be formed on a plastic film. Furthermore, the material properties can be easily changed by changing the molecular structure, so there are a wide variety of materials, and it is possible to realize functions and elements that could not be achieved with inorganic semiconductor materials. .

One of the parameters indicating the characteristics of the transistor is a current _on / off ratio (I _on / I _off ). In order to increase the on-current, the field effect mobility is improved, the distance between the contact electrodes (source electrode and drain electrode) is reduced, and the contact resistance between the organic semiconductor layer and the contact electrode is reduced. Etc. are known to be effective.

However, the organic semiconductor layer generally has not only chemical resistance and heat resistance but also inferior weather resistance and water resistance, and has a defect that it is very easily deteriorated. Therefore, even in the case of an organic semiconductor material that provides high carrier mobility as described above, a method of forming a contact electrode by a vacuum deposition method is the mainstream in the production of an organic FET. However, if the vacuum vapor deposition method is used for forming the contact electrode, the processing is complicated and costly, so that the merit of the organic semiconductor that can be formed in the air is greatly impaired.

Therefore, in order to enable transistor formation in the atmosphere, an electrode forming technique using a metal paste or metal ink has been proposed (International Publication No. 2005/122233, International Publication No. 2007/015364). However, these electrode forming techniques have the problem that the contact resistance with the organic semiconductor layer is high as shown in the next paragraph, and the problem that the organic solvent contained dissolves the organic semiconductor layer.

That is, the contact resistance value between the contact electrode formed of a metal paste or metal ink that is generally reported and the organic semiconductor layer is about 100 to 1000 kΩcm, which is compared with the value of Si-MOSFET. 5 or 6 digits higher. In particular, the contact resistance between the organic semiconductor layer and the contact electrode is greatly influenced by the state of the junction interface, and a method for forming an electrode in contact with the organic semiconductor layer is important.

However, when a contact electrode is formed with a metal paste or metal ink composed of conductive particles, there is a limit to the refinement of the conductive particles used, and conductive particles having a particle size of several tens of nm or less have not been put into practical use. For this reason, the contact area at the bonding interface between the conductive particles of about several hundred nm and the organic semiconductor layer is reduced, and the contact resistance tends to be increased. Although it has been devised to perform the sintering at 100 ° C. or higher to reduce the contact resistance, the deterioration of the organic semiconductor due to the high temperature treatment becomes a problem. In general, since the metal paste and the metal ink contain an organic solvent, there is a problem that the organic semiconductor crystal is dissolved when the electrode is formed. Therefore, the contact resistance between the organic semiconductor layer and the contact electrode formed in the atmosphere remains a big problem.

Therefore, in order to solve the above-described problems, several types of electrode forming techniques using wet plating have been studied. In wet plating, metal ions in the plating solution can be deposited on the surface of the organic semiconductor at the atomic level as plating metal. Therefore, it was considered that the contact resistance between the organic semiconductor layer and the plated metal would be reduced if the plated metal could be formed in close contact with the desired location.

For example, in International Publication No. 2007/015364 (Patent Document 1 described later), after forming a protective layer on the channel portion on the organic semiconductor layer by photolithography, “a hydrochloric acid solution of palladium chloride (1% by mass of barium chloride, Using hydrochloric acid 10% by mass, isopropyl alcohol 20% by mass and polyvinyl alcohol 1% by mass aqueous solution ”(paragraph 165), followed by“ electroless gold plating bath (dicyanogold potassium 0.1 mol / liter, sodium oxalate 0.1 mol) (A uniform solution in which 0.1 mol / liter of sodium potassium tartrate and 0.1 mol / liter of sodium tartrate are dissolved) to form a source electrode and a drain electrode with a metal thin film M2 made of gold having a thickness of 110 nm "(paragraph 166).

However, the organic semiconductor material used in Patent Document 1 is a thiophene oligomer, and the general carrier mobility is about 10 ⁻² cm ² / Vs. For this reason, when the protective layer is not formed, the organic semiconductor layer seems to be damaged by the hydrochloric acid solution (hydrochloric acid 10% by mass) as the catalyst solution. However, since the carrier mobility is low, The damage to the semiconductor layer becomes relatively small, and it is difficult to confirm a change in the contact resistance between the organic semiconductor layer and the contact electrode. Further, in the method for forming a catalyst nucleus for plating described in Patent Document 1, since the process proceeds to an electroless plating process while holding a solution containing the catalyst nucleus on the organic semiconductor film, it is reduced at this catalyst nucleus site. As the metal atoms are replaced and the deposit grows, there is a problem that excess catalyst nuclei and the grown deposit are released into the electroless plating bath, causing a runaway reaction of the plating bath.

In general, organic semiconductor films are very sensitive to acids, alkaline aqueous solutions, and organic solvents. Therefore, contact with a strong acid or strong alkali pretreatment solution, plating solution, photoresist, or the like causes deterioration of the organic surface layer. . In particular, an organic semiconductor crystal with high crystallinity that boasts high mobility exceeding 1 cm ² / Vs causes a significant decrease in mobility.

In Japanese Patent Application Laid-Open No. 2008-192752 (Patent Document 2 described later), a self-assembled monolayer is formed on an inorganic insulating layer by a silane coupling reaction, and an organic layer is sequentially deposited thereon to form an organic semiconductor layer. Is forming. Furthermore, the surface terminal of the organic semiconductor layer is converted to an amino group, so that Pd ions that become a Pd catalyst for plating can be strongly adsorbed in the next step. Thereafter, source / drain electrodes are formed by an electroless gold plating solution containing L-ascorbic acid. And it is supposed that contact resistance was reduced by this.

However, in this method, since the process is complicated, it takes time and it is difficult to form an organic semiconductor layer with high crystallinity and high mobility. Furthermore, this method is a contact electrode forming method in which the surface terminal on the stacked organic semiconductor is converted to an amino group, and therefore, it is difficult to apply the present method to a method for manufacturing an organic transistor that operates at high speed. In the future, in order to drive organic transistors at high speed for the purpose of driving sophisticated electronic devices, the distance between the contact electrodes (source electrode, drain electrode) is reduced, and the contact resistance between the organic semiconductor layer and the contact electrode It is pointed out that it is necessary to lower the value.

On the other hand, application of an electroless plating method applied to an existing Si semiconductor or the like to an organic semiconductor layer is also considered. For example, in paragraph 34 of JP-A-2009-293082, “(S23) Next, after the substrate 11 is immersed in a palladium chloride solution for 1 to 3 minutes, it is washed with pure water and dried to obtain the catalyst metal 12b. Pd was applied to the organic molecular film 12a as a catalyst to form the adhesion layer 12. (S24) The substrate 11 was immersed in an electroless plating solution capable of depositing Ni-B, and Ni-B was deposited on the adhesion layer 12. At this time, the film thickness of the metal layer 13 was controlled so as to be about 200 nm depending on the immersion time in the electroless plating solution, and then the substrate 11 was washed with pure water after being immersed in the electroless plating solution. Then, the method of drying with dry N ₂ ”is described, and paragraph 35 discloses that the metal layer does not peel off even by the Si oxide film removal treatment and has good adhesion. Yes.

Japanese Patent Application Laid-Open No. 2005-146400 discloses “an electrode forming method for forming an electrode that contacts an organic layer mainly composed of an organic material, and a metal salt of the metal and a reducing agent for forming the electrode. An electrode forming method characterized in that the electrode is formed by electroless plating using a plating solution that contains substantially no alkali metal ions. When Pd is used as a catalyst, the Pd alloy is adsorbed on the surface of the substrate 2 by immersing the substrate 2 in a colloidal solution of a Pd alloy such as Sn—Pd, etc. Thereafter, an element that does not participate in the catalyst. Pd is exposed on the surface of the substrate 2 by removing "and" 112, 113 paragraphs "Next, the glass substrate is immersed in a Sn-Pd colloidal solution (25 ° C) for 60 seconds. . Thus, to allow adsorption of Sn-Pd on the surface of the glass substrate. Then, water was washed glass substrate using a. Then, in an aqueous solution (25 ° C.) containing a HBF ₄ and glucose, a glass substrate The glass substrate was immersed for 60 seconds, thereby removing Sn from the surface of the glass substrate to expose Pd on the surface of the glass substrate, and then cleaning the glass substrate with water. The glass substrate was immersed in the glass substrate at 60 ° C. and pH 8.5) for 60 seconds, whereby a Ni plating film having an average thickness of 100 nm was formed on the surface of the glass substrate.

Furthermore, paragraph 16 of Japanese Patent Application Laid-Open No. 2008-019457 states that “a polyester plate is immersed in a dark brown transparent palladium hydrosol containing a 1% -stearyltrimethylammonium chloride aqueous solution at 25 ° C. for 1 hour and then washed with water. Palladium is added to the solution, and then, in an electroless gold plating solution obtained by mixing a 20 mM aqueous solution of gold chloride (III) (1 ml) and a 0.5 M aqueous solution of hydrogen peroxide (1 ml) at 25 ° C., 5 ° C. It is described that the polyester plate was immersed for a minute to obtain a gold-colored polyester plate, and the polyester plate contained 0.7% gold and exhibited good conductivity.

However, in a highly crystalline organic semiconductor crystal that boasts high mobility, the crystal surface changes greatly due to acid, alkali, liquid temperature, etc., causing a significant decrease in mobility. That is, the surface of a general palladium chloride solution is affected by hydrochloric acid. In addition, the crystal surface changes greatly when Sn is completely removed from the adsorbed Sn-Pd colloid. Furthermore, even in an aqueous hydrogen peroxide solution, the surface is affected by oxygen during the nascent stage.

From the above, there has been a demand for a method of forming a contact electrode having a low contact resistance on an organic semiconductor layer without using a vacuum environment without altering the surface properties of the organic semiconductor layer boasting high carrier mobility. .

International Publication No. 2007/015364 JP 2008-192752 A

The present invention has been made against the background of the above circumstances, and does not alter the surface properties of the organic semiconductor layer during electroless plating, and the contact resistance between the organic semiconductor layer and the contact electrode is as low as vacuum deposition. An object of the present invention is to provide an electrode forming method for forming a contact electrode of a noble metal such as gold by electroless plating.

In particular, an object of the present invention is to provide a method of forming a contact electrode in the atmosphere that greatly reduces the contact resistance between the contact electrode of the OFET and the organic semiconductor. Another object of the present invention is to provide a method for forming a contact electrode in the atmosphere without deteriorating the characteristics of the organic semiconductor crystal. Another object of the present invention is to provide a method for forming an OFET contact electrode having a uniform thickness on an organic semiconductor layer having a large surface area. It is another object of the present invention to provide a method for forming an OFET contact electrode that can stably mass-produce a certain quality of a plated electrode even when electroless plating is repeatedly performed.

An electrode forming method for solving the problems of the present invention is a method for forming a contact electrode on an organic semiconductor layer, a pretreatment step for adsorbing noble metal nanoparticles on the organic semiconductor layer, and then a pH of 5 to 9 A plating metal is deposited on the noble metal nanoparticles in an electroless plating bath.

According to the electrode forming method of the present invention, a plated metal film that follows the shape of the surface of the organic semiconductor can be obtained without altering the surface of the organic semiconductor, and a low-resistance contact electrode can be formed.

According to the electrode forming method of the present invention, metal ions in the plating bath are reduced to zero-valent metal atoms in the electroless plating step, and an electrode is formed on the organic semiconductor. In the present invention, this reaction causes a catalytic reaction of the noble metal nanoparticles adsorbed on the organic semiconductor layer, so that electrodes are formed in a chain from the surface, and a plated metal film following the surface shape of the organic semiconductor can be obtained.

In addition, the conventional method for forming an electrode includes a reduction reaction in a strong acid or strong alkali. As a result, the properties of the organic semiconductor surface change, and the mobility of the organic semiconductor is greatly reduced, or the organic semiconductor film The contact resistance between the contact electrode and the contact electrode is increased. According to the electrode forming method of the present invention, the pH of the plating bath is set to a neutral region of 5 to 9, whereby an organic semiconductor crystal plane that is easily altered can be maintained. In the electrode forming method according to the present invention, the type of electroless plating solution in the subsequent step is not particularly limited, and an electroless plating solution containing components constituting the electrode can be adopted. Therefore, the plating bath was set to pH = 5-9.

In the method for forming an electrode circuit of the present invention, preferred embodiments are as follows.
The organic semiconductor layer is [1] benzothieno [3,2-b] [1] benzothiophene derivative, 2,9-dialkyldinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2 -B] thiophene derivative, dinaphtho [2,3-b: 2 ', 3'-f] thieno [3,2-b] thiophene derivative, dinaphtho [2,3-d: 2', 3'-d '] Benzo [1,2-b: 4,5-b ′] dithiophene derivatives, TIPS-pentacene, TES-ADT, and derivatives thereof, perylene derivatives, TCNQ, F4-TCNQ, F4-TCNQ, rubrene, pentacene, p3HT, pBTT , And a crystal of pDA2T-C16. This is because these semiconductor crystals can provide organic semiconductor crystals with high crystallinity that boast high mobility exceeding 1 cm ² / Vs.

Moreover, it is preferable that a noble metal nanoparticle is either gold | metal | money (Au), platinum (Pt), or palladium (Pd). In particular, gold (Au) or platinum (Pt) nanoparticles having a high density are preferable.

The plating solution is preferably a self-reducing electroless plating solution. This is because the high mobility organic semiconductor crystal surface is not adversely affected during the reduction. Specifically, an electroless plating solution of gold (Au), platinum (Pt), silver (Ag), palladium (Pd), nickel (Ni), copper (Cu), iron (Fe) or cobalt (Co). Preferably there is.

The average particle diameter of the noble metal nanoparticles is preferably 5 to 60 nm. The noble metal nanoparticles are generally preferably gold (Au), platinum (Pt), particularly gold (Au). This is because gold nanoparticles are less susceptible to chemical reaction and stably perform a reduction action on the surface of the organic semiconductor crystal in the metal plating bath.

The noble metal nanoparticles are preferably protected with a low molecular weight protective agent in order to avoid alteration before plating. In particular, the noble metal nanoparticles are preferably any one of gold (Au), platinum (Pt), and palladium (Pd) protected by a sugar alcohol. This is because by using sugar alcohol, the spherical shape of the nanoparticles can be maintained in pure water, and the reducing action can be stably performed on the organic semiconductor crystal surface. Further, gold (Au), platinum (Pt) or palladium (Pd) fine particles protected by a sugar alcohol are stable even in strong alkalis or strong acids, and have the property of not being affected by heat.

The sugar alcohol contains 0.01 to 200 g / L of at least one of tritol, tetritol, pentitol, hexitol, heptitol, octitol, inositol, quercitol, and pentaerythritol in total in the pretreatment liquid. It is preferable. This is because moderately spherical noble metal nanoparticles can be dispersed on the surface of the organic semiconductor crystal.

In the electrode forming method according to the present invention, a gold plating bath is particularly preferable when forming an electrode on a p-type organic semiconductor. In addition, when an electrode is formed on an n-type organic semiconductor, a silver plating bath is particularly preferable.

According to the present invention, an electrode can be stably formed on an organic semiconductor layer using a metal plating method. Moreover, the surface property of the organic semiconductor layer is not altered during electroless plating, the mobility of the organic semiconductor is not lowered, and the contact resistance between the organic semiconductor layer and the contact electrode can be reduced to the same level as vacuum deposition. . Further, according to the electrode forming method of the present invention, the contact electrode can be formed in the atmosphere without using a vacuum process, and the manufacturing cost of the contact electrode can be greatly reduced. Furthermore, according to the method for forming an electrode of the present invention, a contact electrode for OFET having a uniform nano-level thickness can be formed on an organic semiconductor layer having a large surface area. Further, according to the present invention, a plating electrode having a certain quality can be stably mass-produced even when electroless plating is repeatedly performed. Further, according to the method for forming an electrode circuit of the present invention, since the organic semiconductor layer and the source / drain electrodes are metal-plated via nanoparticles, a device having a low contact resistance and a stable long life can be obtained. .

Hereinafter, the present invention will be described in more detail with reference to examples.

[Example 1]
A bottom gate / top contact type OFET as shown in FIG. 1 was fabricated.
As the substrate, a silicon (Si) substrate on which silicon oxide (SiO ₂ ) having a thickness of 200 nm was formed by thermal oxidation was used, and silicon (Si) was used as a gate electrode and silicon oxide (SiO ₂ ) was used as an insulating layer. This substrate was immersed in acetone and degreased by ultrasonic cleaning, and then subjected to ultraviolet (UV) irradiation and ozone treatment to obtain a clean surface.

Next, an organic semiconductor layer was deposited by vacuum evaporation. As the organic semiconductor material, 2,9-didecyl-dinaphtho [2,3-b: 2 ', 3'-f] thieno [3,2-b] thiophene was used to obtain an organic semiconductor layer having an average thickness of 30 nm.

Next, gold (Au) nanoparticles were prepared. Specifically, first, sodium tetrachloroaurate (III) tetrahydrate was converted to gold (Au) equivalent concentration of 0.1 g / L and 10.0 g / L glycerin at 90 ° C. sodium hydroxide aqueous solution ( Dissolved in pH = 12). Thereafter, reduction with sodium citrate dihydrate gave an aqueous colloidal gold (Au) nanoparticle solution. The average particle diameter of the gold (Au) nanoparticles was 30 nm, and 95% or more was in the range of 20 to 40 nm (d = 30 ± 10 nm).

Next, adsorption processing of gold (Au) nanoparticles onto an organic semiconductor was performed.
The substrate formed up to the organic semiconductor layer was immersed in an aqueous 0.1% trimethylstearylammonium chloride solution for 30 seconds and washed with pure water for 5 minutes. Furthermore, after being immersed in the aqueous solution containing the above gold (Au) nanoparticles for 5 minutes, pure water was washed with running water for 5 minutes.

Next, a non-cyan self-reducing electroless gold plating bath (trade name: Precious Fab ACG 3000WX, gold (Au) concentration (2 g / L), pH = 7.5) manufactured by Nippon Electroplating Engineers Co., Ltd. Immersion was performed at 65 ° C. for 5 minutes to obtain a gold (Au) layer having an average film thickness of 50 nm.

Next, an electrode pattern was formed on the gold (Au) layer by photolithography. Thereafter, unnecessary portions of gold were removed with an iodine-based gold etching solution (trade name: Aurum manufactured by Kanto Chemical Co., Ltd.) to form an electrode pattern. As a result, an OFET having gold (Au) contact electrodes with a channel width of 1000 μm and channel lengths of 5, 10, 20, 50, and 100 μm as shown in FIG. 2 was obtained.

As an evaluation of the manufactured element, the carrier mobility as a transistor was measured and found to be about 2.0 cm ² / Vs. Further, as an evaluation of the contact resistance of the contact electrode, the contact resistance was estimated by the TML method (Transfer Line Method) and found to be 0.8 kΩcm.

[Standard example]
A vacuum deposition method was used instead of the plating method for forming the gold (Au) layer in Example 1. After the gold (Au) layer was formed, the same process as in Example 1 was performed to obtain an OFET. As a result of measuring the carrier movement as a transistor as an evaluation of the manufactured element, it was about 2.1 cm ² / Vs. The contact resistance of the contact electrode was 0.5 kΩcm.

That is, the carrier mobility of about 2.0 cm ² / Vs of the gold (Au) layer in Example 1 manufactured by the wet method is not comparable to the carrier mobility of about 2.1 cm ² / Vs of the vacuum deposition method. It can be seen that the contact resistance of the contact electrode is approximately equal to 0.8 kΩcm with respect to 0.5 kΩcm.

[Example 2]
A bottom gate / top contact type OFET as shown in FIG. 3 was fabricated. PEN (Theonex 125Q65HA TEIJIN Co., Ltd.) was used as the substrate. A gate electrode layer of Cr / Au / Cr = 3/5/3 nm was formed on this substrate by vacuum evaporation. Next, an alumina insulating layer (100 nm) was formed using the ALD method. Next, an organic semiconductor layer was deposited by vacuum evaporation. The organic semiconductor material uses 3,10-didecyl-dinaphtho [2,3-d: 2 ′, 3′-d ′] benzo [1,2-b: 4,5-b ′] dithiophene, and has an average thickness of 30 nm. An organic semiconductor layer was obtained.

Next, gold (Au) nanoparticles were prepared. Specifically, first, sodium tetrachloroaurate (III) tetrahydrate was added at a gold (Au) equivalent concentration of 0.1 g / L and xylitol: 1.0 g / L at 90 ° C. sodium hydroxide aqueous solution ( It was dissolved in pH = 12) and reduced with sodium citrate dihydrate to obtain a colloidal gold (Au) nanoparticle aqueous solution. The average particle diameter of the gold (Au) nanoparticles was 19 nm, and 90% or more was in the range of 14 to 24 nm (d = 19 ± 5 nm).

Next, adsorption processing of gold (Au) nanoparticles onto an organic semiconductor was performed.
That is, the substrate formed up to the organic semiconductor layer was immersed in a 0.1% trimethylstearylammonium chloride aqueous solution for 30 seconds and washed with pure water for 5 minutes. Furthermore, after being immersed in the aqueous solution containing the above gold (Au) nanoparticles for 5 minutes, pure water was washed with running water for 5 minutes. Next, a non-cyan self-reducing electroless gold plating bath (trade name: Precious Fab ACG 3000WX, gold (Au) concentration (2 g / L), pH = 7.5) manufactured by Nippon Electroplating Engineers Co., Ltd. Immersion was performed at 65 ° C. for 5 minutes to obtain a gold (Au) layer having an average film thickness of 50 nm.

Next, an electrode pattern was formed on the gold (Au) layer by photolithography. Thereafter, unnecessary portions of gold were removed with an iodine-based gold etching solution (Aurum Kanto Chemical Co., Ltd.) to form an electrode pattern. As a result, an OFET having gold (Au) contact electrodes with a channel width of 1000 μm and channel lengths of 5, 10, 20, 50, and 100 μm as shown in FIG. 2 was obtained.

As an evaluation of the manufactured element, the carrier mobility as a transistor was measured and found to be about 2.0 cm ² / Vs. The contact resistance of the contact electrode was estimated by the TML method to be 0.7 kΩcm.

Example 3
Similar to Example 1, a bottom gate / top contact type OFET as shown in FIG.
As the substrate, a Si substrate on which SiO ₂ (200 nm) was formed by thermal oxidation was used, Si being a gate electrode, and SiO ₂ being an insulating layer. After the substrate was immersed in acetone and degreased by ultrasonic cleaning, UV ozone treatment was performed to obtain a clean surface. Next, an organic semiconductor layer was deposited by vacuum evaporation. As the organic semiconductor material, 2,9-didecyl-dinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2-b] thiophene was used to obtain an organic semiconductor layer having an average thickness of 30 nm.

Next, platinum (Pt) nanoparticles were prepared. Specifically, first, hexahydroxoplatinum (IV) was dissolved in a platinum (Pt) equivalent concentration of 0.3 g / L and mannitol: 3.0 g / L in a 90 ° C. aqueous sodium hydroxide solution (pH = 12). Reduction with hydrazine gave a platinum (Pt) colloidal solution. The average particle diameter of the platinum (Pt) nanoparticles was 35 nm (d = 35 ± 20 nm).

Next, adsorption treatment of platinum (Pt) nanoparticles on the organic semiconductor was performed.
The substrate formed up to the organic semiconductor layer was immersed in the aqueous solution containing the platinum (Pt) nanoparticles for 5 minutes, and then washed with pure water for 5 minutes. Next, electroless platinum containing 1.0 g / L of hexahydroxoplatinum (IV) in terms of platinum (Pt), 50.0 g / L of ammonium sulfate, 5.0 g / L of boric acid, and 0.15 g / L of hydrazine It was immersed in a (Pt) plating solution (pH = 8.0) at 25 ° C. for 3 minutes to obtain a platinum (Pt) film having an average film thickness of 50 nm.

Next, unnecessary portions of platinum were removed by laser ablation, and an electrode pattern was formed. As a result, an OFET having a platinum (Pt) contact electrode with a channel width of 2000 μm and a channel length of 50, 100, 200, 5000 μm was obtained.

As an evaluation of the manufactured element, the carrier mobility as a transistor was measured and found to be about 0.9 cm ² / Vs. The contact resistance of the contact electrode was estimated to be 2.0 kΩcm.

[Comparative Example 1]
The same test as in Example 1 was performed except that the gold (Au) nanoparticles and the electroless gold plating solution in Example 1 were changed.
Specifically, first, sodium tetrachloroaurate (III) tetrahydrate is 0.1 g / L in terms of gold (Au), sodium citrate dihydrate: 0.6 g / L and hydrogen. An aqueous solution containing sodium borohydride: 0.1 g / L was heated at 90 ° C. for 30 minutes to obtain a colloidal gold (Au) nanoparticle aqueous solution. The average particle diameter of the gold (Au) nanoparticles was 3 ± 2 nm. Next, adsorption processing of gold (Au) nanoparticles onto an organic semiconductor was performed. The substrate formed up to the organic semiconductor layer was immersed in an aqueous 0.1% trimethylstearylammonium chloride solution for 30 seconds and washed with pure water for 5 minutes. Furthermore, after being immersed in the aqueous solution containing the above gold (Au) nanoparticles for 5 minutes, pure water was washed with running water for 5 minutes. Next, a strongly acidic electroless gold (Au) plating solution was prepared. Gold (Au) with an average film thickness of 50 nm is immersed in electroless gold plating (pH = 1) containing 10 mM sodium tetrachlorogold (III) tetrahydrate and 20 mM hydrogen peroxide at 25 ° C. for 2 minutes. A layer was obtained. Thereafter, the same treatment as in Example 1 was performed to obtain an OFET.

As a result of measuring the carrier movement as a transistor as an evaluation of the manufactured element, it was about 0.4 cm ² / Vs. The contact resistance of the contact electrode was 8.0 kΩcm. Compared with the reference example in which the electrode was formed by vacuum deposition, the carrier mobility was reduced by an order of magnitude, and the contact resistance was 10 times or more.

[Comparative Example 2]
The same test as in Example 3 was performed except that the electroless platinum plating solution of Example 3 was changed to a strong alkaline electroless gold plating solution. That is, an electroless platinum (Pt) plating solution containing 1.0 g / L of hexahydroxoplatinum (IV) in terms of platinum (Pt), 20 ml / L of aqueous ammonia and 0.15 g / L of hydrazine (pH = 13. 0) for 4 minutes at 50 ° C. to obtain a platinum (Pt) film having an average film thickness of 50 nm.

When the characteristics of the transistor were evaluated as an evaluation of the manufactured element, the characteristics as a transistor were not shown, and it was found that the organic semiconductor crystal was seriously damaged.

According to the present invention, an electrode made of a target metal can be reliably and stably formed on the surface of an organic semiconductor by electroless plating, thereby improving the production efficiency of an organic semiconductor field effect transistor. Is possible.

It is the schematic which shows the Example of the organic transistor of this invention. It is the schematic which shows the measuring method of the contact resistance of the organic transistor of this invention. It is the schematic which shows the other Example of the organic transistor of this invention.

1: Si wafer 2: SiO ₂ insulating layer 3: Organic semiconductor layer
4: Source / drain electrode 5: PEN substrate 6: Cr / Au / Cr gate electrode 7: Alumina insulating layer

Claims (6)

In the method for forming a contact electrode on an organic semiconductor layer , a noble metal nanoparticle that is one of gold (Au), platinum (Pt), and palladium (Pd) protected by a sugar alcohol is formed on the organic semiconductor layer. A method for forming an electrode, characterized by depositing a plating metal on the noble metal nanoparticles in an electroless plating bath having a pH of 5 to 9 after a pretreatment step for adsorption. The sugar alcohol contains 0.01 to 200 g / L of the total amount of at least one of tritol, tetritol, pentitol, hexitol, heptitol, octitol, inositol, quercitol, and pentaerythritol in the pretreatment liquid. The electrode forming method according to claim 1 . The organic semiconductor layer is [1] benzothieno [3,2-b] [1] benzothiophene derivative, 2,9-dialkyldinaphtho [2,3-b: 2 ′, 3′-f] thieno [3,2 -B] thiophene derivative, dinaphtho [2,3-b: 2 ', 3'-f] thieno [3,2-b] thiophene derivative, dinaphtho [2,3-d: 2', 3'-d '] Benzo [1,2-b: 4,5-b ′] dithiophene derivatives, TIPS-pentacene, TES-ADT, and derivatives thereof, perylene derivatives, TCNQ, F4-TCNQ, F4-TCNQ, rubrene, pentacene, p3HT, pBTT The electrode forming method according to claim 1, wherein the electrode is a crystal of pDA2T-C16. 2. The electrode forming method according to claim 1, wherein the plating bath is made of a self-reducing electroless plating solution and is an electroless plating solution of gold (Au), platinum (Pt), or palladium (Pd). . The electrode forming method according to claim 1, wherein the noble metal nanoparticles have an average particle diameter of 5 to 60 nm. The electrode forming method according to claim 1, wherein the noble metal nanoparticles are protected by a low molecular protective agent.

Images