JP5501604B2 - Organic thin film transistor - Google Patents

Description

  The present invention relates to an organic thin film transistor using an organic material for a semiconductor portion, and more particularly, to an organic thin film transistor having an electrode that is electrically connected to an organic semiconductor and has excellent adhesion.

  In recent years, so-called organic thin film transistors using a semiconductor made of an organic material have attracted attention with respect to inorganic semiconductors represented by silicon.

  In recent years, organic thin film transistors have also been reported to exhibit mobility equivalent to that of amorphous silicon thin film transistors (hereinafter a-Si TFTs). In addition, since it is possible to fabricate elements at a low process temperature of 200 ° C. or lower, it becomes possible to form transistor elements on plastic substrates with low heat resistance, etc., making use of the flexibility of plastic substrates. It is being studied as a technology for realizing a simple device.

  In addition, since an organic material can be manufactured by a printing method or the like depending on the type of material, it is also expected as a semiconductor element capable of reducing manufacturing costs and manufacturing a large area device by printing.

  In general, a thin film transistor is composed of a gate electrode, a gate insulating layer, a semiconductor layer, and a source electrode and a drain electrode, and the element structure mainly includes a source electrode and a drain electrode formed on the semiconductor layer. There are roughly two types: a top contact type and a bottom contact type in which a source electrode and a drain electrode are formed in the lower part of the semiconductor.

  For example, as shown in Patent Document 1, in the top contact type structure, the source electrode and the drain electrode used a general photolithography method, a lift-off method, and a shadow mask having an electrode-shaped opening. It is produced by a pattern film forming method or the like.

  In the case of the top contact type, since an electrode is directly formed on a semiconductor layer made of an organic material, there is a concern about damage to the organic semiconductor layer due to chemicals for photolithography or etching of the electrode material. For this reason, the source electrode and the drain electrode have been formed by the shadow mask, the ink jet printing technique, etc. with little damage to the semiconductor layer at the time of electrode formation.

  However, with these methods, it is difficult to reduce the channel length, which is the distance between the source electrode and the drain electrode, which affects the characteristics of the thin film transistor element. There are also problems in the dimensional stability and reproducibility of the electrodes formed.

  On the other hand, in the case of the bottom contact type, since the organic semiconductor layer is formed after forming the source electrode and the drain electrode, the organic semiconductor layer is not damaged unlike the top contact type. For this reason, it is possible to use a method for forming the source electrode and the drain electrode by the photolithography method or the lift-off method capable of forming the above-described channel length finely.

  As a material constituting the source electrode and the drain electrode for electrical connection with the organic semiconductor, for example, as shown in Patent Document 2, it is made of gold (Au) that can easily be electrically connected with the organic semiconductor. Are often used. Gold is a good conductor and is a metal that is generally used as an electrode material. On the other hand, gold has a problem of low adhesion to other materials. For this reason, when gold is used as the electrode material, measures such as forming an adhesion layer as disclosed in Patent Document 2 between the gold electrode and the substrate have been generally taken.

  However, according to Non-Patent Document 1, in the bottom contact type organic thin film transistor, the adhesion layer provided between the electrode used for improving the adhesion between the source electrode and the drain electrode and the substrate includes the source electrode and the substrate. It is shown that it is a cause of parasitic resistance generated between the drain electrode and the organic semiconductor layer.

  According to Non-Patent Document 1, in an organic thin film transistor having a bottom contact structure formed on a gate insulating layer superimposed on a gate electrode, a channel layer formed in an organic semiconductor by a gate voltage applied to the gate electrode is When the adhesion layer formed below the gold electrode is thicker than the channel layer, the adhesion layer is formed with a thickness of about several nanometers from the gate insulating layer / organic semiconductor layer interface. It will be in direct contact with the channel layer. For this reason, the gold electrode part constituting the source electrode and the drain electrode cannot be in direct contact with the channel layer, and a parasitic resistance is generated due to the gold electrode-adhesion layer-organic semiconductor series structure. It is said.

For such a problem of parasitic resistance, a self-assembled monolayer (SAM) having a film thickness of several nanometers is formed as a very thin adhesion layer in Non-Patent Document 1 and Patent Document 3. Thus, a method of suppressing parasitic resistance is disclosed.
JP 2004-288836 (released on October 14, 2004) JP 2005-175157 (released June 30, 2005) JP 2005-86147 (published March 31, 2005) N. Yoneya et al, Applied Physics Letters, 85, (2004) 4663-4665.

  However, the SAM film is an organic monomolecular film that can be formed by combining organic molecules having a functional group capable of chemically bonding to a specific surface. In the above method, a material capable of chemically bonding organic molecules constituting the SAM film needs to be formed on the substrate surface for forming the SAM film. For this reason, it has been difficult to form a SAM film as an adhesion layer on an arbitrary substrate surface.

  In addition, since the SAM film as the adhesion layer is basically formed of organic molecules that are insulators, in the structure described in Non-Patent Document 1, in the vicinity of the interface between the organic semiconductor and the gate insulating layer. The formed SAM film and the metal electrode formed on the SAM film are in contact with the formed channel layer. For this reason, there is a problem that the portion of the ultra-thin channel layer that is in contact with the SAM film does not contribute to the electrical connection between the source electrode and the drain electrode.

  The object of the present invention has been made in view of the above-mentioned problems, and the object thereof is a source electrode and a drain electrode that have good adhesion to the gate insulating layer and low parasitic resistance with the organic semiconductor layer. It is providing the organic thin-film transistor which has these.

  The present inventor has intensively studied to solve the above problems. As a result, it has not been used as a material for improving adhesion until now, and when this material is used for an organic transistor, a composition ratio that satisfies both element characteristics and adhesion to a substrate, particularly adhesion The above problem can be solved by providing an adhesion layer between the source electrode, the drain electrode, and the gate insulating layer of a gold alloy having a predetermined composition ratio, for which there is no example in which the composition ratio has been studied focusing on the improvement of As a result, the present invention has been completed.

  In order to solve the above problems, an organic thin film transistor of the present invention is an organic thin film transistor comprising a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer on an insulating substrate, An adhesion layer made of an alloy containing gold as a main component is provided between the source electrode and the insulating substrate or the gate insulating layer, and between the drain electrode and the insulating substrate or the gate insulating layer, respectively. The drain electrode is made of gold, and the adhesion layer is characterized in that the gold content is in the range of 67 atomic% to 97 atomic%.

  According to the above configuration, since the adhesion layer made of the gold alloy having a predetermined composition ratio is provided, the source electrode and the drain have good adhesion to the gate insulating layer and low parasitic resistance with the organic semiconductor layer. The organic thin-film transistor which has the outstanding characteristic provided with the electrode can be provided.

  In the organic thin film transistor of the present invention, the adhesion layer is at least selected from the group consisting of nickel (Ni), chromium (Cr), titanium (Ti), aluminum (Al), tantalum (Ta), and molybdenum (Mo). An alloy of one kind of metal and gold is preferable.

  According to the above configuration, an organic thin film transistor having excellent characteristics is provided, which has a source electrode and a drain electrode that have better adhesion to the gate insulating layer and lower parasitic resistance with the organic semiconductor layer. be able to.

  In the organic thin film transistor of the present invention, it is preferable that the adhesion layer has a gold content changing from the source electrode and the drain electrode toward the gate insulating layer.

  According to the above configuration, an organic thin film transistor having excellent characteristics is provided, which has a source electrode and a drain electrode that have better adhesion to the gate insulating layer and lower parasitic resistance with the organic semiconductor layer. be able to.

  In addition, for example, by changing the ratio of the metal material other than gold contained in the electrode so as to decrease in the film thickness direction, a metal thin film having an alloy portion with good adhesion and an Au portion serving as an electrode is integrated. It can be manufactured by a single process, and the manufacturing cost can be reduced.

  In the organic thin film transistor of the present invention, the thickness of the adhesion layer is preferably in the range of 1 nm to 3 nm.

  According to the above configuration, an organic thin film transistor having excellent characteristics is provided, which has a source electrode and a drain electrode that have better adhesion to the gate insulating layer and lower parasitic resistance with the organic semiconductor layer. be able to.

  The organic thin film transistor of the present invention includes a gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer in this order, and the transistor structure preferably has a bottom gate structure and a bottom contact structure.

  According to the above configuration, it is possible to provide an organic thin film transistor having a source electrode and a drain electrode that have good adhesion to the gate insulating layer and low parasitic resistance with the organic semiconductor layer.

  In the organic thin film transistor of the present invention, it is preferable that the adhesion layer has a gold content decreasing from the source electrode or the drain electrode toward the gate insulating layer.

  According to the above configuration, an organic thin film transistor having excellent characteristics is provided, which has a source electrode and a drain electrode that have better adhesion to the gate insulating layer and lower parasitic resistance with the organic semiconductor layer. be able to.

  In addition, by changing the ratio of the metal material other than gold contained in the electrode so as to decrease in the film thickness direction, a metal thin film having an alloy part with good adhesion and an Au part serving as an electrode is formed once. It can be manufactured by a process, and the manufacturing cost can be reduced.

  As described above, the organic thin film transistor of the present invention is an organic thin film transistor including a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer on an insulating substrate. An adhesion layer made of an alloy containing gold as a main component is provided between the insulating substrate or the gate insulating layer, and between the drain electrode and the insulating substrate or the gate insulating layer, respectively. It is made of gold, and the adhesion layer is characterized in that the gold content is in the range of 67 atomic% to 97 atomic%.

  For this reason, there is an effect that an organic thin film transistor having a source electrode and a drain electrode having good adhesion to the gate insulating layer and low parasitic resistance with the organic semiconductor layer can be provided.

  Embodiments of the present invention will be described in detail below with reference to the drawings. However, the present invention is not limited to these.

(1) Organic Thin Film Transistor FIG. 1 shows a main part configuration of an organic thin film transistor, where (a) is a top view and (b) is a cross-sectional view taken along line AA ′ in FIG.

  As shown in FIG. 1, the organic thin film transistor according to the present embodiment includes a gate insulating layer 3 on a gate electrode 2, a source electrode 4 and a drain electrode 5 on the gate insulating layer 3, and the source electrode 4 is an organic thin film transistor including an organic semiconductor layer 9 including a channel region 11 on 4 and a drain electrode 5.

  The organic thin film transistor includes an adhesion layer 7 between the source electrode 4 and the gate insulating layer 3 and between the drain electrode 5 and the gate insulating layer 3.

  The material which comprises the said gate electrode 2 is not specifically limited, A conventionally well-known material can be used. For example, Al, Ti, Mo, Ta, silicon (Si), silver (Ag), or an alloy thereof can be used as a constituent material of the gate electrode 2.

  The material constituting the gate insulating layer 3 is not particularly limited as long as it is insulative. For example, an inorganic insulating film such as silicon oxide, aluminum oxide or tantalum oxide, or an organic material such as polyimide or polyvinylphenol is adopted. be able to.

  The material constituting the source electrode 4 and the drain electrode 5 is gold, and the material constituting the adhesion layer 7 is an alloy containing gold as a main component.

  Although it does not specifically limit as metals other than gold | metal | money which comprises the said alloy, For example, Ni, Cr, Ti, Al, Ta, and Mo are mentioned.

  The gold content in the alloy constituting the adhesion layer 7 is in the range of 67 atomic percent to 97 atomic percent, and preferably in the range of 70 atomic percent to 97 atomic percent.

  If the gold content in the alloy is less than 67 atomic%, the field-effect mobility is reduced as compared with the case where the adhesion layer 7 is not provided. Further, when the gold content in the alloy is higher than 97 atomic%, the adhesion between the gate insulating layer 3 and the electrode becomes insufficient.

  Here, “atomic%” means the percentage of the number of target atoms with respect to the total number of atoms in the substance.

  The thickness of the adhesion layer 7 is preferably in the range of 1 nm to 3 nm. If the film thickness is within the range, the adhesion between the source electrode 4 and the drain electrode 5 and the gate insulating layer 3 can be improved without increasing the parasitic resistance.

  The organic semiconductor layer 9 is a layer containing an organic material as a main component. The material constituting the organic semiconductor layer 9 is not particularly limited as long as it is an organic semiconductor used in a conventionally known organic thin film transistor. For example, fullerene, polythiophene, pentacene and the like and derivatives thereof can be mentioned.

  In the organic thin film transistor according to this embodiment, since the adhesion layer 7 made of a gold alloy is provided between the source electrode 4 and the drain electrode 5 and the gate insulating layer 3, the source electrode 4 and the drain electrode 5 and the gate are provided. The insulating layer 3 can be satisfactorily adhered.

  Further, in the bottom gate type thin film transistor structure, when a voltage is applied to the gate electrode 2, the channel region 11 of the organic thin film transistor formed in the vicinity of the interface between the gate insulating layer 3 and the organic semiconductor layer 9 has a source electrode 4, the drain electrode 5, and the adhesion layer 7.

  In the present embodiment, a gold alloy having good electrical connectivity with the organic semiconductor layer 9 is used as the adhesion layer 7, so that the parasitic between the source electrode 4 and the drain electrode 5 and the organic semiconductor layer 9 is achieved. Resistance can be suppressed and an organic thin film transistor having excellent characteristics can be obtained.

(2) Manufacturing Method of Organic Thin Film Transistor The organic thin film transistor according to this embodiment can be manufactured as follows, for example. FIG. 2 is a cross-sectional view showing an example of the manufacturing process of the organic thin film transistor according to the present embodiment.

(A) Production of Gate Electrode As shown in FIG. 2A, first, the gate electrode 2 is formed on the substrate 1.

  In this embodiment, the case where the entire surface of the substrate 1 becomes the gate electrode 2 is described for the sake of simplification. However, the gate electrode 2 is patterned using a photolithography method, a mask film forming method, or the like. May be used.

  As the substrate 1, for example, a transparent substrate such as a glass substrate and a quartz substrate, a silicon substrate with an oxide film, polyethersulfone (PES), polyethylene naphthalate (PEN), and a plastic substrate made of a polymer such as polyimide are used. It may be used. Moreover, you may use what formed the insulating layer as needed on the surface of the said board | substrate.

(B) Production of Gate Insulating Layer Next, the gate insulating layer 3 is formed so as to overlap the gate electrode 2. For the production of the gate insulating layer 3, various methods such as normal vacuum deposition, sputtering film formation, spin coating method, and ink jet method can be used.

(C) Production of Adhesion Layer Subsequently, the source electrode 4 and the drain electrode 5 are produced on the gate insulating layer 3.

  As shown in FIG. 2B, a photoresist is applied on the gate insulating layer 3 formed on the substrate 1, and the region where the source electrode 4 and the drain electrode 5 are formed is formed using a photolithography technique. A photoresist film 6 having an opening is formed. At this time, the distance between the two opening portions facing each other corresponds to the channel length L of the organic thin film transistor shown in FIG. 1, and the length of the two opening portions facing each other corresponds to the channel width W.

  Next, as shown in FIG. 2C, a gold alloy to be the adhesion layer 7 is formed on the photoresist film 6 in which the opening is formed.

  The gold alloy can be formed by a general metal thin film forming method such as vacuum vapor deposition or sputtering. For example, a film formation material made of the above alloy having a gold content in the range of 67 atomic% or more and 97 atomic% or less may be formed in advance and film formation may be performed by the film formation method described above. In addition, a so-called co-evaporation method or co-sputtering method is used in which a metal film is formed on a substrate at the same time using a plurality of film formation sources including a gold film formation source and a metal film formation source other than gold. Such a film forming method may be used.

(D) Production of Source / Drain Electrode Subsequently, as shown in FIG. 2 (d), Au to be an electrode (source electrode and drain electrode) 8 is formed so as to overlap the adhesive layer 7. The electrode 8 made of Au may be produced by using a so-called physical vapor deposition method such as the above vapor deposition method or sputtering method, or may be produced by using an electroless gold plating method or the like using the adhesion layer 7 as a seed layer. Good.

  Next, by removing the photoresist film 6 from the substrate 1, the adhesion layer 7 and the electrode 8 formed in the opening shown in FIG. 2E are formed.

  Note that although a method for manufacturing a source electrode and a drain electrode by a lift-off method has been described as an example in this embodiment, the source electrode and the drain electrode may be manufactured by a method other than this. Specifically, it can be manufactured using a normal manufacturing process such as a photolithography method or a mask vapor deposition method. By adopting such a method, the distance (channel length) between the source electrode and the drain electrode, which affects the characteristics of the transistor element, can be finely processed according to the purpose, or simply produced by mask vapor deposition. Therefore, it is possible to improve element characteristics, improve dimensional stability, reduce manufacturing man-hours, and the like.

(E) Production of Organic Semiconductor Layer Finally, as shown in FIG. 2 (f), the organic semiconductor layer 9 is formed so as to overlap the source electrode 4 and the drain electrode 5.

  The organic semiconductor layer 9 can be manufactured using, for example, a vacuum evaporation method using resistance heating, and can be manufactured using a general method such as a coating method or a printing method as long as it is a soluble material. Is possible.

  The organic semiconductor layer 9 may be formed on the entire surface of the substrate 1, but is preferably patterned so as to overlap with the source electrode 4 and the drain electrode 5 from the viewpoint of parasitic capacitance and the like.

  There are various methods for forming the pattern of the organic semiconductor layer 9. In FIG. 2 (f), as an example, an evaporation mask 10 having an opening that matches the shape of the organic semiconductor layer 9 is used. The case where the semiconductor layer 9 is formed by a vapor deposition method is shown.

  Through the steps as described above, an organic thin film transistor having a bottom-gate type structure according to this embodiment is manufactured.

  In the above description, the case where the transistor has a bottom gate structure and a bottom contact structure has been described. However, the present invention is not limited to this. The transistor may have a top gate structure.

Moreover, the present invention described above can be paraphrased as follows. That is,
(1) In an organic thin film transistor comprising a gate electrode, a gate insulating film, a source / drain electrode, and a semiconductor layer made of an organic material on an insulating substrate, the source / drain electrode includes an electrode portion made of gold and An organic thin film transistor comprising an adhesion portion made of an alloy mainly composed of gold, wherein the alloy mainly composed of gold has a metal content other than gold of 3 atomic% to 30 atomic%. An organic thin film transistor, wherein

  (2) The organic thin film transistor according to (1), wherein the alloy mainly composed of gold is an alloy with any of Ni, Cr, Ti, Al, Ta, and Mo.

  (3) The organic thin film transistor according to (1) or (2), wherein the alloy mainly composed of gold in the contact portion has an alloy content changing in a film thickness direction.

  (4) The organic thin film transistor has a bottom gate structure and a bottom contact structure in which a gate electrode, a gate insulating film, a source / drain electrode, and an organic semiconductor layer are provided in this order on a substrate (1) )-(3) The organic thin-film transistor as described in any one.

  (5) The organic thin film transistor according to any one of (1) to (4), wherein the source / drain electrode is formed by stacking the contact portion and the electrode portion.

  (6) The organic thin film transistor according to (5), wherein a film thickness of a close contact portion of the stacked source / drain electrodes is 1 to 3 nm.

  (7) The source / drain electrodes are made of a gold alloy in which the content of materials other than gold decreases in the direction of increasing film thickness, according to any one of (1) to (4), Organic thin film transistor.

  Further, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. Embodiments are also included in the technical scope of the present invention.

  Hereinafter, the present invention will be specifically described by way of examples.

[Reference Example 1]
An adhesion layer made of an Au—Ni alloy and an electrode layer made of gold were formed on a silicon substrate with a silicon oxide (SiO ₂ ) simulating a gate insulating layer by a mask vapor deposition method, and the Ni content is a value shown in Table 1. The laminated body which each has the adhesion layer which is is produced.

  The source electrode and the drain electrode were prepared as rectangular electrodes of 0.4 mm × 1.4 mm, the adhesion layer was formed with a thickness of 3 nm, and the source electrode and the drain electrode were formed with a thickness of 25 nm.

  Next, after applying the mechanical vibration by ultrasonically washing each of the laminates for producing the electrodes in an acetone solution for 1 minute, the state of peeling of the electrodes is observed visually and with an optical microscope, The adhesion between the source and drain electrodes and the substrate was confirmed. The results of adhesion evaluation are shown in Table 1.

As shown in Table 1, when the adhesion layer is made of Au not containing Ni, and when the Ni content is 1 atomic%, the adhesion with the SiO ₂ that is the gate insulating layer is weak and the production is made. The source and drain electrodes thus peeled off from the SiO ₂ surface on the substrate.

When the Ni content is increased to about 3 atomic% (Au content is 97 atomic%), the source electrode and the drain electrode are not peeled off from the SiO ₂ surface on the substrate, and good adhesion is exhibited. It was confirmed.

  Further, in the evaluation of the adhesion, the Ni content in the adhesion layer is 10 atomic% (Au content is 90 atomic%), and the film thickness of the adhesion layer made of the Au—Ni alloy is set to the value shown in Table 2. The adhesiveness was evaluated by changing. The results are shown in Table 2.

  As shown in Table 2, it was confirmed that the adhesion was improved by setting the film thickness of the adhesion layer to 1 nm or more.

  In addition, even if the thickness of the adhesion layer is further increased, it is considered that the effect of improving the adhesion is obtained in the same manner. However, the electrical resistivity of the gold alloy as the adhesion layer is the resistivity of Au as the electrode portion. The parasitic resistance due to the adhesion layer increases as the film thickness increases, and it is expected that the element characteristics are decreased due to the increase in parasitic resistance as in the result of Reference Example 2 described later.

  When an experiment similar to the above was performed by changing Ni in the adhesion layer to Ti, Cr, Al, Ta and Mo, respectively, almost the same results were obtained.

  From these results, in the gold alloy mainly composed of gold as the adhesion layer, the content of the alloy material other than Au is 3 atomic% to 33 atomic% (the Au content is 67 atomic% to 97 atomic%). It was confirmed that an organic thin film transistor having good device characteristics can be produced by setting the thickness of the adhesion layer made of a gold alloy layer to about 1 nm to 3 nm.

[Reference Example 2]
As an organic thin film transistor having a structure as shown in FIG. 1, a SiO ₂ film having a thickness of 310 nm is formed as a gate insulating layer 3 on an n-type silicon substrate serving as both the substrate 1 and the gate electrode 2, and an adhesion layer 7 is formed thereon. As a result, an alloy film of Au and Ni was formed with a film thickness of 3 nm, and Au was further formed with a film thickness of 25 nm as the electrode 8, and the source electrode 4 and the drain electrode 5 were manufactured by a lift-off method.

To prepare a n-type organic thin film transistor by forming a film in a film thickness 100nm by mask deposition method fullerene C ₆₀ as the organic semiconductor layer 9 on this. A plurality of organic thin film transistors were manufactured by changing the Ni content in the adhesion layer 7 from 0 atomic% to 100 atomic%.

  Using the obtained transistor, the field effect mobility of the thin film transistor with respect to the Ni content was evaluated. The channel length L of the produced organic thin film transistor was 10 μm and the channel width W was 1 mm.

  FIG. 3 shows the relationship between the field effect mobility indicating the element characteristics of the organic thin film transistor and the composition ratio of the gold alloy as the adhesion layer.

  As shown in FIG. 3, when the content of Ni in the adhesion layer is about 33 atomic% (the content of Au is 67 atomic%), the case where the electrode is made of only Au not containing Ni (white circle) High field-effect mobility was almost the same. On the other hand, when the Ni content was increased to about 50 atomic% (Au content was 50 atomic%), a sharp decrease in field effect mobility was confirmed, and the device characteristics deteriorated. This is because the electrical parasitic resistance between the organic semiconductor layer 9 and the adhesion layer 7 increases due to an increase in the amount of Ni contained in the adhesion layer, resulting in the source electrode 4 and the drain. It is considered that the parasitic resistance between the electrode 5 and the organic semiconductor layer 9 is increased, and the field effect mobility indicating the characteristics of the organic thin film transistor is decreased.

Further, when the adhesion layer is made of only Au, or when the Ni content is 1 atomic%, the adhesion between SiO _{2 as} the gate insulating layer and the adhesion layer is weak, and the produced source electrode and drain electrode Peeled from the SiO ₂ surface on the substrate. When the Ni content in the adhesion layer is increased to about 3 atomic% (Au content is 97 atomic%), the source electrode and the drain electrode are not peeled off from the SiO ₂ surface on the substrate. Showed good adhesion.

[Example 1]
In Example 1, the organic thin film transistor shown in FIG. 4 was produced using an alloy of Au and Ni as the adhesion layer.

  First, as shown in FIG. 5A, a glass substrate (Corning Inc., trade name: Eagle 2000) was used as the substrate 12. And on the said board | substrate 12, the sputtering method was performed using the metal target which consists of TiSi alloy which added Si at 10 atomic% with respect to Ti, and the metal film which consists of TiSi was formed with the film thickness of 40 nm. The gate electrode 13 was formed by processing the metal film made of TiSi into a desired pattern using photolithography and etching.

Then, using the SiO ₂ target, by performing sputtering while supplying oxygen, and the SiO ₂ was formed to a thickness of 200nm as the gate insulating layer 14 on the gate electrode 13.

  Next, a 4 μm-thick resist film was formed by spin coating using a negative photoresist for lift-off process (trade name: ZPN1150, Nippon Zeon Co., Ltd.) as a photoresist. Thereafter, an exposure and development process is performed using a photolithography method, thereby forming a photoresist film 15 having openings for producing a source electrode and a drain electrode as shown in FIG. 5B.

Next, as shown in FIG. 5C, a mixed material of Au and Ni, which is adjusted so that the composition ratio of Ni in the adhesion layer is 3 atomic% (the content of Au is 97 atomic%), is used. Then, a metal film made of an Au—Ni alloy was formed by vacuum deposition with a film thickness of 2 nm and serving as the adhesion layer 16 of the source electrode and the drain electrode. Ultimate vacuum of a vacuum deposition apparatus at this time was 2 × 10- ⁵ Pa, substrate heating was not performed.

  Subsequently, as an electrode 17 shown in FIG. 5 (d), a metal film made of Au was formed in a film thickness of 40 nm by the same vacuum deposition method.

  After sequentially laminating the adhesion layer 16 and the electrode 17, in order to remove the photoresist film 15 on the gate insulating layer 14, a lift-off process is performed in which the obtained laminate is immersed in an organic solvent such as acetone. The film 15 and the unnecessary Au / Au—Ni laminated film laminated thereon were removed.

  At this time, the distance between the source electrode 19 and the drain electrode 20 corresponding to the channel length L of the thin film transistor was 10 μm, and the length corresponding to the channel width W was 1 mm.

Finally, using fullerene C ₆₀ which is an n-type organic semiconductor, vapor deposition is performed by a vacuum vapor deposition method through a mask (not shown) having a predetermined opening at a substrate temperature of 120 ° C. An organic semiconductor layer 21 having a thickness of 100 nm as shown in FIG.

FIG. 6 shows the gate voltage (Vg) -drain current (Id) characteristics of the n-type organic thin film transistor fabricated in Example 1. The mobility of the produced organic thin film transistor was about 2.2 cm ² / Vs.

  In the organic thin film transistor of Example 1, an organic semiconductor layer and a source electrode were used as the adhesion layer by using a gold alloy containing 3 atomic% of Ni having good adhesion and good electrical connectivity with the organic semiconductor. In addition, parasitic resistance between the first electrode and the drain electrode is suppressed, and good transistor characteristics can be obtained as shown in FIG.

  In addition, evaluation of the adhesiveness of the organic thin-film transistor was performed as follows.

[Adhesion evaluation method]
In the evaluation of adhesion, the peeling state of the source electrode and the drain electrode in the step of removing the resist was observed, and when the adhesion layer was not peeled off in the step of removing the resist, it was judged that the adhesion was good. . The same evaluation was made in the following examples.

[Example 2]
FIG. 7A shows a schematic cross-sectional view of the organic thin film transistor fabricated in Example 2. FIG.

  In Example 2, as in Example 1, a bottom gate / bottom contact type organic thin film transistor having a gate electrode 31, a gate insulating layer 32, a source electrode 37 and a drain electrode 38, and an organic semiconductor 39 on a substrate 30 is manufactured. did.

  The source electrode 37 and the drain electrode 38 of the organic transistor in Example 2 are each formed from one metal film as shown in FIG. 7B, but the ratio of the metal constituting the metal film is shown in FIG. It changes as shown in FIG. 7C with respect to the film thickness direction Z shown in FIG.

  In the production of the organic thin film transistor of Example 2, an alloy of Au and Cr was used as an adhesion layer in order to improve the adhesion between the source electrode 37 and the drain electrode 38.

  As shown in FIG. 7C, the metal layer 36 constituting the source electrode 37 and the drain electrode 38 includes about 20 atomic% of Cr (Au is about 80 atomic%) as an adhesion layer in a region close to the substrate side. As the film thickness increases, the Cr content decreases and a region finally functioning as an electrode portion made of Au is formed. As described above, the organic thin film transistor of Example 2 is different in the content ratio of Au and Cr in the metal film serving as the source electrode and the drain electrode in the thickness direction, thereby providing the source electrode including the adhesion layer and the electrode portion. It has a drain electrode.

  In the above configuration, the thickness of the adhesion layer was 2 nm, and the gold content in the adhesion layer was about 88 atomic%.

  Such an organic thin film transistor is manufactured as follows.

  Since the steps up to forming the gate electrode, the gate insulating layer, and the photoresist film for forming the source electrode and the drain electrode on the substrate are the same as those in Example 1, here, the following adhesion layer, electrode portion, The formation of the metal film made of will be described with reference to FIGS.

  A photoresist having a gate electrode 31 and a gate insulating layer 32 formed on the substrate 30 and having openings in the region where the source electrode and the drain electrode are formed, as shown in FIG. A film 33 was formed on the gate insulating layer 32.

  Next, a metal film for forming the source electrode 37 and the drain electrode 38 on the substrate 30 was produced.

  As shown in FIG. 8B, a so-called binary resistance heating vapor deposition apparatus capable of simultaneously vapor-depositing two kinds of metal materials by a vacuum vapor deposition method, and using two kinds of vapor deposition materials of Au and Cr A metal film was formed as described above.

First, the photoresist film 33 and the substrate 30 on which the opening is formed are introduced into a resistance heating vapor deposition apparatus (not shown) having an evaporation source 34 filled with Au and an evaporation source 35 filled with Cr. The inside of the apparatus was evacuated and evacuated. Ultimate pressure in the system at this time was ⁵ × 10- 5 Pa.

  As shown in FIG. 8B, an evaporation source 34 of Au and an evaporation source 35 of Cr are installed in the vapor deposition apparatus, and by heating the crucible filled with each material by current control or the like, It is possible to perform film formation while individually controlling the deposition rates of Au and Cr. A shutter is provided on each crucible of each evaporation source, and by opening and closing the shutter, the supply of metal vapor to the substrate is controlled, and the deposition of two types of metal films is individually turned on and off. It is possible to control.

  Next, in order to form an Au—Cr alloy film as an adhesion layer, the Au deposition source 34 and the Cr deposition source 35 heated to the deposition possible temperatures are simultaneously opened, so that Au and Cr are formed on the surface of the substrate 30. The supply of metal vapor was started simultaneously, and an adhesion layer made of an alloy of Au and Cr was formed on the gate insulating layer 32 and the photoresist film 33 on the surface of the substrate 30.

  The composition ratio of the formed Au—Cr alloy film was controlled by controlling the evaporation rate of each material and the amount of current for heating the evaporation source.

  When the composition of the produced Au—Cr alloy film was examined, the Cr content was about 20 atomic% (Au content was about 80 atomic%) in the region close to the substrate side. The film thickness of the Au—Cr adhesion layer is controlled while being monitored by a crystal resonator (not shown) provided in the vapor deposition apparatus, and when the film thickness reaches 2 nm, the shutter on the Cr vapor deposition source 35 side is closed. The supply of Cr vapor was cut off to control the film thickness of the adhesion layer made of Au—Cr alloy.

  At this time, as shown in FIG. 8C, Au vapor is continuously supplied from the Au vapor deposition source 34 to the surface of the substrate 30, so that only Au is formed on the Au—Cr alloy as the adhesion layer. The electrodes are continuously formed. The film thickness of the electrode made of Au was controlled while being monitored by a crystal resonator in the same manner as before, so that an electrode made of Au having a thickness of 40 nm was finally formed.

  In this way, as shown in FIGS. 7B and 7C, it includes an adhesion layer made of an Au—Cr alloy containing Cr and having an electrode made only of Au, the composition of which changed in the film thickness direction. A metal layer 36 was formed.

  According to the method of Example 2, it is possible to continuously form the Au—Cr alloy layer as the adhesion layer region and the Au layer as the electrode partial region in a vacuum, and form each region individually. Compared to the case, the manufacturing process can be simplified without the necessity of replacing the evaporation source or moving the substrate between the film forming apparatuses.

  Furthermore, it becomes possible to suppress the deterioration of the electrical characteristics due to the inclusion of foreign matters such as oxide layers and impurities between the adhesion layer and the electrode part, and the electrical characteristics of the source electrode and the drain electrode formed from this metal film can be reduced. Further improvement is possible.

  Subsequently, the photoresist film 33 on the surface of the substrate is peeled off, and the metal layer 36 on the photoresist other than the photoresist opening is removed to form an Au—Cr alloy as shown in FIG. An adhesion layer and a source electrode 37 and a drain electrode 38 made of Au were formed.

  The electrode spacing (channel length) between the fabricated source electrode and drain electrode was 5 μm, and the length of the electrodes facing each other (channel width) was 1 mm.

Subsequently, as shown in FIG. 8E, an organic thin film made of fullerene C _{60 is} deposited as the organic semiconductor layer 39 by a resistance heating vapor deposition method at a film thickness of 60 nm through a mask to complete an organic thin film transistor. It was. The film formation conditions for the C ₆₀ film at this time were an ultimate vacuum of 4 × 10 ⁵ Pa, a substrate temperature of 150 ° C., and a film formation rate of 1.2 nm / min. The mobility of the obtained organic thin film transistor was about 2.1 cm ² / Vs.

  In this embodiment, the composition of the metal film to be the source electrode and the drain electrode is controlled in the film thickness direction, so that Au is excellent in adhesion on the substrate side and has good electrical connectivity with the organic semiconductor. An adhesion layer made of an alloy of Cr and Cr was formed. Subsequently, a source electrode and a drain electrode made of Au, which have excellent electrical connectivity with the organic semiconductor by reducing the Cr component in the film, were prepared. As a result, an electrode having excellent electrical characteristics could be produced with fewer process steps.

  In this example, the adhesion layer and the electrode portion are formed continuously, but the portion made of a gold alloy whose gold content changes is the adhesion layer, and the portion made of gold is the source electrode and This is the drain electrode (see FIG. 7C).

Example 3
In Example 3 of the present invention, a source electrode and a drain electrode were prepared in the same manner as in Example 2, and then formed using pentacene, which is a p-type organic semiconductor layer, as an organic semiconductor layer, thereby forming a p-type organic thin film transistor. Produced. FIG. 9 shows the characteristics of the p-type organic thin film transistor fabricated in Example 3.

The mobility of the produced organic thin film transistor was about 0.4 cm ² / Vs. In addition, the organic thin film transistor thus produced has a good adhesion to the substrate and a good adhesion between the organic semiconductor and an adhesion layer made of an Au-Cr alloy, and a source electrode excellent in electrical connectivity between the organic semiconductor and pentacene. In addition, since it has a drain electrode, it has good characteristics with little influence of parasitic resistance.

Example 4
In Example 4 of the present invention, a complementary integrated element, a so-called CMOS (Complementary MOS) element, was constructed using the n-type and p-type organic thin film transistors fabricated in Examples 2 and 3 described above.

  FIG. 10 shows a schematic view and a cross-sectional view of the main part of the CMOS device of the fourth embodiment.

  10A and 10B, the CMOS device includes a gate electrode 41 of an n-type organic thin film transistor 52, a gate electrode 42 of a p-type organic thin film transistor 53, source and drain electrodes 45 to 47, and Are connected to each other, and as a basic element of various logic circuits, there is an advantage that the range of application is wide and power consumption is small.

  As shown in FIG. 11A, gate electrodes 41 and 42 of n-type and p-type transistors were formed on a substrate 40, respectively. In Example 4, a TiSi alloy in which a glass substrate (Corning, trade name: Eagle 2000) is used as the substrate 40 and Si is added at 10 atomic% to Ti as a metal film for forming the gate electrodes 41 and 42. A metal film made of TiSi was formed to a thickness of 40 nm by sputtering using a metal target made of Then, the gate electrodes 41 and 42 were produced by processing into a desired pattern using photolithography and an etching method.

  As shown in the top view of FIG. 10A, the gate electrodes 41 and 42 are the same electrically connected electrodes and function as a common gate electrode for both n-type and p-type transistors.

Next, as shown in FIG. 11B, a ZrSiO _x film formed by sputtering while supplying oxygen using an alloy target of Zr and Si as a gate insulating layer 43 on the gate electrodes 41 and 42 is formed. A gate insulating layer 43 was formed with a thickness of 100 nm.

  Subsequently, as shown in FIG. 11C, a photoresist film 44 having a predetermined opening was formed on the gate insulating layer 43 by a photolithography method in order to produce a source electrode and a drain electrode. Thereafter, as in Example 2 described above, a metal film was formed using a vacuum deposition apparatus (not shown) having two types of deposition sources of Au and Ti.

  The alloy portion of Au and Ti that becomes the adhesion layer is formed under the film forming conditions that the Ti content is about 30 atomic% (Au content is about 70 atomic%) and the adhesion layer has a thickness of 1 nm. Further, after the supply of Ti was stopped, an electrode portion made of Au was vapor-deposited to produce a metal film having a thickness of 40 nm as a whole.

  Subsequently, unnecessary photoresist film 44 was removed with a stripping solution or the like, so that source and drain electrodes 45 to 47 as shown in FIG.

Next, as shown in FIG. 11 (e), in order to form the organic semiconductor layer 48 of the n-type transistor, fullerene C ₆₀ is vacuum deposited using a deposition mask 49 having an opening in a predetermined region. went. The ultimate vacuum degree of the vacuum vapor deposition apparatus (not shown) at this time was 5 × 10 ⁻⁵ Pa, and the film thickness of fullerene C ₆₀ was 60 nm.

  Subsequently, as shown in FIG. 11 (f), in order to produce an organic semiconductor layer 50 made of pentacene in a region for producing a p-type transistor, a vacuum for pentacene is used using an evaporation mask 51 having an opening in this region. The organic semiconductor layer 50 was formed by vapor deposition. The thickness of the pentacene semiconductor film at this time was 40 nm.

As described above, as shown in FIG. 11G, the present embodiment is composed of the organic thin film transistor 52 in which fullerene C ₆₀ is an n-type organic semiconductor layer and the organic thin film transistor 53 in which pentacene is a p-type organic semiconductor. A CMOS device composed of 4 organic thin film transistors was fabricated.

  In the above-mentioned organic CMOS device, when manufacturing n-type and p-type organic thin film transistors, the source electrode and the drain electrode used for each transistor can be formed in the same process, and the process necessary for device manufacture It becomes possible to reduce the number of processes. In addition, it has both an adhesion layer that has good adhesion and low parasitic resistance with the organic semiconductor, and an electrode portion that has excellent electrical connectivity to both n-type and p-type semiconductor layers. Since the source and drain electrodes are used, the parasitic resistance between each organic semiconductor layer and the source and drain electrodes is reduced, so that the characteristics of the n-type and p-type organic transistors constituting the CMOS device are reduced. As a result, good CMOS device characteristics can be obtained.

Prepared n-type, the mobility of p-type organic thin film transistor were about 0.68cm ² /Vs,0.59cm ² / Vs. The low n-type mobility compared to Examples 1 and 2 is considered to be due to the effect of changing the gate insulating layer.

FIG. 12 shows the inverter operating characteristics of the organic CMOS circuit fabricated in the fourth embodiment. In the inverter circuit configured by using the CMOS element manufactured in the fourth embodiment, a good inversion output (V _out ) is obtained with respect to an input voltage (V _in ) of 0 to 5 V, which is caused by parasitic resistance or the like. It was confirmed that good inverter characteristics without deterioration of characteristics were obtained.

  The organic thin film transistor of the present invention has a source electrode and a drain electrode that have good adhesion to the gate insulating layer and low parasitic resistance with the organic semiconductor layer. For this reason, it can be used suitably for various electronic components.

The principal part structure of the organic thin-film transistor concerning embodiment of this invention is shown, (a) is a top view, (b) is A-A 'arrow sectional drawing in Fig.1 (a). It is sectional drawing which shows the process process of the manufacturing method of the organic thin-film transistor which concerns on embodiment of this invention. It is a graph which shows the correlation of the field effect mobility of the organic thin-film transistor which concerns on the reference example 2, and Ni content of the gold alloy used as the contact | glue layer of a source / drain electrode. 1 is a cross-sectional view illustrating a waist configuration of an organic thin film transistor according to Example 1. FIG. 6 is a cross-sectional view showing a manufacturing process of an organic thin film transistor according to Example 1. FIG. 4 is a graph showing a correlation of Vg-Id characteristics of an organic thin film transistor according to Example 1. FIG. 7A is a cross-sectional view illustrating the main configuration of the organic thin film transistor according to the second embodiment. FIG. 7B is an enlarged cross-sectional view showing the structure of the electrode portion surrounded by a dotted line in FIG. FIG. 7C is a graph showing a composition distribution diagram of the electrode material according to Example 2. 6 is a cross-sectional view showing process steps of a method for manufacturing an organic thin film transistor according to Example 2. FIG. 6 is a graph showing a correlation of Vg-Id characteristics of an organic thin film transistor according to Example 3. The principal part structure of the CMOS element which concerns on Example 4 is shown, (a) is a top view, (b) is C-C 'arrow sectional drawing in Fig.10 (a). 10 is a cross-sectional view showing process steps of a method for manufacturing a CMOS device according to Example 4. FIG. 6 is a graph showing operating characteristics of an inverter circuit using a CMOS element according to Example 4;

Explanation of symbols

1, 12, 30, 40 Substrate 2, 13, 31, 41, 42 Gate electrode 3, 14, 32, 43 Gate insulating layer 6, 15, 33, 44 Photoresist film 4, 19, 37, 45 Source electrode 5, 20, 38, 47 Drain electrode 46 Source / drain electrode 7, 16 Adhesion layer 8, 17 Electrode (source electrode, drain electrode)
9, 21, 39, 48, 50 Organic semiconductor layer 10, 49, 51 Evaporation mask 11 Channel region 34, 35 Evaporation source 36 Metal film 52 N-type organic thin film transistor 53 P-type organic thin film transistor

Claims (5)

An organic thin film transistor comprising a gate electrode, a gate insulating layer, a source electrode, a drain electrode, and an organic semiconductor layer on an insulating substrate,
Between the source electrode and the insulating substrate or the gate insulating layer, and between the drain electrode and the insulating substrate or the gate insulating layer, an adhesion layer made of an alloy mainly composed of gold is provided, respectively.
The source electrode and drain electrode are made of gold,
The adhesion layer, the content of gold state, and are within the following 97 atomic% 67 atomic% or more,
The adhesion layer includes at least one metal selected from the group consisting of nickel (Ni), chromium (Cr), titanium (Ti), aluminum (Al), tantalum (Ta), and molybdenum (Mo); and gold the organic thin film transistor according to claim Rukoto composed of an alloy of. In the adhesion layer, the gold content changes from the source electrode and the drain electrode toward the gate insulating layer ,
The organic thin film transistor according to claim 1, wherein the adhesion layer is provided between the source electrode and the gate insulating layer and between the drain electrode and the gate insulating layer .   2. The organic thin film transistor according to claim 1, wherein the thickness of the adhesion layer is in the range of 1 nm to 3 nm. A gate electrode, a gate insulating film, a source electrode and a drain electrode, and an organic semiconductor layer are provided in this order,
2. The organic thin film transistor according to claim 1, wherein the transistor has a bottom gate structure and a bottom contact structure. 3. The organic thin film transistor according to claim 2 , wherein the adhesion layer has a gold content decreasing from the source electrode or the drain electrode toward the gate insulating layer.

Images