WIRING AND ORGANIC TRANSISTOR, AND MANUFACTURING METHOD THEREOF

Abstract
If an organic transistor is formed by printing with a low cost, there are problems in that an inexpensive electrode material has a high contact resistance with a semiconductor, and an expensive electrode material has a low contact resistance. To solve the problems, the present invention provides an organic transistor and a method of forming the same, the organic transistor being formed with a low material cost and low manufacturing cost and providing a low contact resistance with a semiconductor and high performance.
Description

BRIEF DESCRIPTION OF THE DRAWINGS


FIG. 1A is a view showing a particle of an alloy in which copper atoms 11 and gold atoms 12 are randomly scattered, the particle being covered with an organic material 16 so as to allow the particle to be dissolved in a solvent;



FIG. 1B is a view showing a state after metal ink of the particles of the alloy is printed on a substrate and the solvent is evaporated;



FIG. 2A is a cross sectional view showing a state where a structure shown in FIG. 1B is subjected to a heat treatment for about one hour at a predetermined temperature ranging from 50° C. to 300° C. so that organic molecules are burned and removed to leave only the metal;



FIG. 2B is a cross sectional view showing a state where the gold atoms are segregated by a heat treatment at a relatively higher temperature than the temperature during the heat treatment shown in FIG. 2A so that the surface of the copper atoms 11 is covered with one atom layer of the gold atoms 12;



FIG. 2C is a cross sectional view showing a structure in which a pentacene crystal is formed on an electrode having a thin gold film as shown in FIG. 2B;



FIG. 3A is a cross sectional view showing a state where a source electrode and a drain electrode for a FET structure are formed by printing with the alloy;



FIG. 3B is a cross sectional view showing a state where gold atoms in the source electrode and the drain electrode are segregated on the surface of the copper atoms by a heat treatment;



FIG. 3C is a cross sectional view showing the complete FET structure in which an organic semiconductor is formed;



FIG. 4A is a diagram showing a state where a gate electrode pattern is formed on the substrate in order to form a driving circuit for a liquid crystal display using the FET structure according to the present invention;



FIG. 4B is a diagram showing a state where the source electrode and the drain electrode are formed using the pattern as shown in FIG. 4A;



FIG. 4C is a diagram showing a state where pentacene is printed and crystallized at a portion used to form the FET structure;



FIG. 5A is a view showing ink of a particle including gold atoms;



FIG. 5B is a view showing ink of a particle including copper atoms;



FIG. 5C is a cross sectional view showing a state after the ink of the particles including the gold atoms and the ink of the particles including the copper atoms are mixed and printed, and a solvent is evaporated;



FIG. 6A is a cross sectional view showing an electrode in which gold atoms and copper atoms are mixed;



FIG. 6B is a cross sectional view showing a state where a monolayer is adsorbed and the gold atoms are segregated on the surface by performing a heat treatment;



FIG. 6C is a cross sectional view showing a structure in which the organic semiconductor is formed on the monolayer;



FIG. 7A is a cross sectional view showing an electrode formed of copper atoms on the substrate;



FIG. 7B is a cross sectional view showing a state where the ink of a particle including gold atoms is printed on the electrode formed of the copper atoms and the solvent is evaporated;



FIG. 7C is a cross sectional view showing a state where a thin film of the gold atoms is formed on the surface of the electrode formed of the copper atoms by a heat treatment;



FIG. 8A is a cross sectional view showing a state where the ink of the particles including copper atoms is printed on the substrate and the solvent is evaporated;



FIG. 8B is a cross sectional view showing a state where the ink of the particles including gold atoms is further printed and the solvent is evaporated; and



FIG. 8C is a cross sectional view showing a state where the electrode of the copper atoms and a thin film of the gold atoms on the electrode surface are formed by a heat treatment.





DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment

A description will be made of a method of manufacturing an organic transistor with high performance and a low cost. Such an organic transistor can be achieved by using pentacene as an organic semiconductor and forming an electrode of an alloy of gold and copper in a first embodiment of the present invention.


Gold has a relatively low contact resistance with pentacene. Also, gold is most excellent in performance as an electrode material with respect to a combination with pentacene. There is a problem, however, in that gold is expensive. On the other hand, copper has a relatively high contact resistance with pentacene. This characteristic of copper is not preferable. However, copper has advantages in that it is much more inexpensive than gold and has been used as a material for wiring and electrodes formed in silicon devices. From the view point of stability and corrosion resistance of a device structure in the air, copper is not so unstable. However, gold is excellent in chemical reaction resistance and stability. To use only the advantages of both gold and copper, a structure is formed in which wiring and electrodes formed mainly of copper (first metal) are covered with a thin film of gold (second metal). In order to form the above structure at a low cost, using an alloy formed by mixing gold and copper, an electrode is formed by printing. Then, the printed electrode is subjected to a heat treatment at an appropriate temperature so that gold atoms are segregated on the electrode surface.



FIG. 1A is a view showing a particle of an alloy in which copper atoms 11 and gold atoms 12 are randomly scattered, the particle being covered with an organic material 16 so as to allow the particle to be dissolved in a solvent. A method of covering fine metal particles with an organic material to increase solubility is typically used to form metal ink or paste. The ratio of the number of the gold atoms 12 to the number of the copper atoms 11 ranges from about 0.2 to about 0.01.


The smaller the ratio of the number of the gold atoms 12 to the number of the copper atoms 11 is, the more the material cost is reduced. If the ratio is too small, the density of the gold atoms 12 is not sufficient on the surface even if the gold atoms are segregated on the surface of the copper atoms 11 after formation of the electrode, so that a reduction in contact resistance and improvement in corrosion resistance cannot be sufficiently obtained. Therefore, it is ideal that the ratio of the number of the gold atoms 12 to the number of the copper atoms 11 is reduced in a range in which sufficient performance is obtained. The optimum ratio depends on the relationship between a volume and a surface area of the electrode. The volume of the electrode is proportional to the number n of atoms to the third power, whereas the surface area of the electrode is proportional to the number n of atoms to the second power. Hence, the smaller the volume of the electrode is, the larger the ratio of the number of the gold atoms 12 (to the number of the copper atoms 11) required for covering the surface is. However, the above proportional expressions are not accurately established since it is not ensured that all the gold atoms 12 included in the alloy can be segregated on the surface of the copper atoms 11. Therefore, the optimum ratio varies depending on the detailed structure and size of the organic FET.



FIG. 1B is a view showing a state after metal ink of the particles of the alloy is printed on a substrate 20 of glass, polyimide, or the like, and a solvent is evaporated. Since the particles are covered with the organic material, the entire deposited materials formed on the substrate 20 are not in a metallic state.



FIG. 2A is a cross sectional view showing a state where a structure shown in FIG. 1B is subjected to a heat treatment for about one hour at a predetermined temperature ranging from 50° C. to 300° C. so that organic molecules are burned and removed to leave only the metal. The copper atoms 11 and the gold atoms 12 are randomly scattered. In FIG. 2A, it is assumed that only organic materials 16 are removed and the gold atoms 12 are not segregated on the surface (the surface segregation will be described later). When the above two processes (removal and surface segregation) are simultaneously performed by a single heat treatment, the structure shown in FIG. 2A may not be formed.



FIG. 2B is a cross sectional view showing a state where the gold atoms are segregated by a heat treatment at a relatively higher temperature than the temperature during the heat treatment shown in FIG. 2A so that the surface is covered with one atom layer of the gold atoms 12. When some of the gold atoms 12 are left with one atom layer being formed on the surface, the left gold atoms 12 may be randomly scattered in an area of the copper atoms or may be partially accumulated under the one atom layer, as shown in FIG. 2B. The arrangement varies depending on the combination of types of the first metal and the second metal.


When all the atoms in a top most layer of the surface of copper are replaced with gold atoms, the thickness of a thin film of gold to be formed on the surface is regarded as one atom layer. A thickness of 0.5 to 5 atom layers suffices for such a thin film of gold. In order to reduce a contact resistance caused by a Schottky barrier of the copper electrode, it is necessary that the Fermi level of the surface of the electrode is close to that of bulk gold. For this reason, the gold atom layer placed near a boundary with pentacene is required to have a Fermi level close to bulk gold. Preferably, the thin gold film has a thickness to a certain extent. For the reason of short screening length in the electronic state of the metal or other reasons, the thickness of the thin gold film desirably has about five atom layers. The thickness less than five atom layers can also provide the effect of reducing the contact resistance.


The thin gold film, when formed on the surface using the surface segregation, can be easily formed with one atom layer. Whether or not a thin film having a thickness larger than one atom layer can be formed, however, depends on the combination of two types of metal. From the view point of the cost, it is preferable to use a thin film with a thickness reduced to a minimum thickness in which sufficient performance can be provided. The thickness of 0.5 atom layers (which means that the number of gold atoms is the same as the number of copper atoms in the first atom layer) can be expected to improve the performance (to reduce the contact resistance). Therefore, the above thickness is about the minimum level of the thickness of the thin gold film to be formed.


If a temperature during a heat treatment for removing organic molecules placed around fine metal particles of metal ink is lower than a temperature during a heat treatment for promoting the surface segregation, the organic molecules are first removed to obtain the state as shown in FIG. 2A or a similar state thereto. After that, the gold atoms 12 are segregated on the surface of the copper atoms 11 so that the abovementioned state is changed to the state as shown in FIG. 2B or a similar state thereto. If the temperature during the heat treatment for removing organic molecules is higher than the temperature during the heat treatment for promoting the surface segregation, the removal of organic molecules and the surface segregation simultaneously occur so as to obtain the state as shown in FIG. 2B or a similar state thereto without shifting to the state as shown in FIG. 2A or a similar state thereto. It is not necessary that the state as shown in FIG. 2A be obtained. Thus, irrespective of which temperature is higher than the other between the two heat treatments, if a heat treatment performed at a higher temperature is conducted, it is not necessary that the heat treatment be performed twice.



FIG. 2C is a cross sectional view showing a structure in which a pentacene crystal 30 is formed on the electrode having the thin gold film formed thereon, as described above. This structure has the pentacene crystal 30 formed on the thin gold film covering the copper electrode. Since the pentacene crystal 30 contacts the thin gold film, the contact resistance is lower than that in the case of a copper electrode not having a thin gold film formed thereon.



FIGS. 3A to 3C show a process of forming a FET structure in detail. As shown in FIG. 3A, a gate electrode 13 is formed on the substrate 20, and an insulating layer 21 is formed so as to cover the gate electrode 13. The gate electrode 13 is not in direct contact with a semiconductor. Thus, it is not necessary that the method for reducing the contact resistance according to the present invention be applied to the gate electrode 13. It should be noted that the gate electrode 13 may be formed by the method according to the present invention since the method allows the corrosion resistance to be improved with low material cost.


Next, metal ink of the particles of the alloy, in which the copper atoms 11 and the gold atoms 12 are randomly scattered, is printed on the insulating layer 21 so as to form a source electrode 14 and a drain electrode 15, as shown in FIG. 2A. The particles of the alloy are covered with the organic material 16. In the source electrode 14 and the drain electrode 15, the copper atoms 11 and the gold atoms 12 are randomly scattered.


Next, the gold atoms 12 are segregated on the surface of the copper atoms 11 by a heat treatment. As shown in FIG. 3B, the gold atoms 12 cover the surfaces of the source electrode 14 and the drain electrode 15. In such a structure, the source electrode 14 and the drain electrode 15 are formed upward to provide convex shapes. The gold atoms 12 are segregated so as to cover the entire surface. If the metal ink of the coated alloy is subjected to a heat treatment, it is not required that the structure shown in FIG. 3A be formed when the removal of organic molecules covered with the particles of the alloy and the surface segregation of the gold atoms 12 occur simultaneously.


Lastly, pentacene 30 is printed, and a solvent is evaporated to crystallize the pentacene 30. As shown in FIG. 3C, the FET structure is completed. A part of wiring not having the FET structure is not covered with the pentacene 30 (organic semiconductor). In this case, if such an exposed wiring portion is formed by the method according to the present invention, the surface of the exposed wiring portion is covered with gold, resulting in good corrosion resistance.



FIGS. 4A to 4C are plan views showing an example of forming a driving circuit for a liquid crystal display by use of the FET structure according of the present invention. As shown in FIG. 4A, a pattern of the gate electrodes 13 is formed on the substrate. Then, the insulating layer is printed so as to cover the entire pattern. In FIGS. 4A to 4C, the insulating layer is not illustrated for simplicity. The state as shown in FIG. 4A corresponds to the state shown in FIG. 3A after the substrate 20, the gate electrode 13, and the insulating layer 21 are formed. In FIG. 4A, a pixel 18, is composed of three elements of R (red), G (green), and B (blue). The gate electrodes 13 include gate electrodes 131R, 131G, and 131B, corresponding to the pixel 18. Each of the gate electrodes 131R, 131G, and 131B is connected with a line 171. A pixel 182 has a similar structure to the pixel 181. In the pixel 182, only reference numerals of a line 172 and a gate electrode 132 are shown to avoid complexity in the figure.


Next, the metal ink is printed and is subjected to a heat treatment so as to form source electrodes 14R, 14G, 14B and drain electrodes 15R, 15G, 15B on a pattern as shown in FIG. 4B. In this case, each of the source electrodes 14R, 14G, 14B is provided in common with the pixels 181, 182 . . . and each of the drain electrodes 15R, 15G, 15B is provided independently of the pixels 181, 182 . . . . This state corresponds to the state as shown in FIG. 3B.


Lastly, as shown in FIG. 4C, the pentacene 30 is printed and crystallized on a portion to be formed of the FET structure. The pentacene 30 is disposed so as to connect each of the source electrodes 14R, 14G, 14B (in common with each of the pixels), each of the drain electrodes 15R, 15G, 15B (independent of each of the pixels), and each of the gate electrodes 131R, 131G, 131B (independent of each of the pixels), respectively. Also, the pentacene 30 crosses each of the source electrodes 14R, 14G, 14B, each of the drain electrodes 15R, 15G, 15B, and each of the gate electrodes 131R, 131G, 131B, respectively. The cross sectional structure of the portion covered with the pentacene 30 corresponds to that of FIG. 3C.


Furthermore, a liquid crystal layer and a transparent electrode are laminated on the pattern shown in FIG. 4C.


A voltage is successively applied to each of the gate electrodes 131R, 131G, 131B, at a predetermined frequency through the lines 171, 172 . . . used as scanning lines so as to successively activate each of the pixels 181, 182 . . . . Also, a voltage associated with the scanning line is applied to each of the source electrodes 14R, 14G, 14B, which are in common with the pixels. Charges accumulated in a square area of each of the gate electrodes 13 are controlled so as to control to turn on and off the pixels of the liquid crystal display.


Second Embodiment

In a second embodiment, first metal ink and second metal ink are prepared, instead of using ink of particles of an alloy to form an electrode. The two types of ink are mixed and printed so as to form an electrode structure similar to that in the case of using the ink of an alloy. Similarly to the first embodiment, a description will be made of gold atoms 12 and copper atoms 11 as an example.



FIG. 5A is a view schematically showing a particle including gold atoms 12 covered with an organic material 16. FIG. 5B is a view schematically showing a particle including copper atoms 11 covered with the organic material 16. The particles formed by covering gold atoms 12 with the organic material 16 are dissolved in a solvent so as to form gold ink. The particles formed by covering copper atoms 11 with the organic material 16 are dissolved in a solvent so as to form copper ink. The gold ink and the copper ink are mixed. In this example, the organic material 16 covering the gold atoms 12 and the organic material 16 covering the copper atoms 11 are the same. The organic materials 16, however, may be different from each other. In this case, the organic materials 16 require a common solvent capable of dissolving both types of the particles. In addition, when the two types of ink are mixed, they must scatter to a certain extent without being phase-separated. It is easy to adjust an amount of each type of ink. The percentages of the metal materials required for the final electrode structure may be determined when mixing the two types of metal ink.



FIG. 5C is a view showing a state where the abovementioned mixed ink is printed on the substrate 20 and the solvent is evaporated. As understood from the comparison with FIG. 1B, there are only two types of a particle formed only of gold atoms 12 and a particle formed only of copper atoms 11 in the second embodiment, whereas each particle includes gold atoms 12 and copper atoms 11 in the first embodiment. In the second embodiment, each amount of the two types of metal ink is adjusted to determine the percentages of the metal materials required for the electrode structure when the two types of metal ink are mixed.


During a heat treatment for removing organic molecules, it is expected that gold atoms are sufficiently diffused and mixed. In the heat treatment, a structure similar to that of FIG. 2A or FIG. 2B can be thus achieved. Subsequently, an organic transistor is formed by a method similar to that in the first embodiment.


Third Embodiment

In a third embodiment, a third material is adsorbed on the electrode surface in addition to the heat treatment, in order to promote the surface segregation of the second metal in the electrode in which the first metal and the second metal are mixed. This allows the surface segregation to be more effective.



FIG. 6A shows the same state as that shown in FIG. 2A. FIG. 6A, however, is a cross sectional view showing an electrode in which the surface segregation of the second metal cannot be effected only through the heat treatment for removing organic molecules of the metal ink, and the first metal and the second metal are randomly scattered.



FIG. 6B a cross sectional view showing an electrode in which the third material 40 is adsorbed on the surface of the electrode shown in FIG. 6A. If a foreign material is adsorbed on the surface, the electronic state on the surface may be changed so that the atom arrangement may be changed or that a force applied to the atoms arranged on the surface may be changed. The change differs depending on the combination of the electrode materials (first metal and second metal) with the third material 40 that has been adsorbed, and on the structure of the surface (crystal orientation and the like).


The third material 40 is required to have a property of being adsorbed on a target electrode surface so as to promote the surface segregation of the second metal. The atom arrangement and the electronic state in the vicinity of the surface may be changed due to the adsorption of the third material 40 on the surface. The changes may promote the surface segregation of the second metal or may produce the opposite effect. As an example of promoting surface segregation, Physical Review Letters (Vol. 90, page 156101) introduces that it has been observed that dopant atoms in a semiconductor are segregated on the surface due to hydrogen adsorption. Like the above example, an adsorptive material capable of promoting a surface segregation effect is not rare.


In addition, it is important that the third material 40 have another property of being easily removable from the surface after the surface segregation of the second metal is completed. Alternatively, the property is to avoid increasing the contact resistance even if the third material 40 is not removed and is present at the boundary between the organic semiconductor and the electrode. Hydrogen atoms or halogen atoms, for example, can be removed from the surface through a heat treatment to some extent after the surface segregation is promoted. Those atoms can be thus used for such a purpose. When the third material 40 is present on the surface without being removed, it preferably has a property to avoid increasing the contact resistance and actively reduce the contact resistance.


Furthermore, the third material 40 is desirably inexpensive. Also, it is desirable that processes for using the third material 40 be as simple as conceivably possible, and that the manufacturing cost be not significantly increased.


As a material which satisfies the above requirements, there is a self-assembled monolayer formed of a molecular material. When molecular materials are dissolved in a solvent and printed, the molecules are adsorbed on an electrode surface and are self-assembled to produce an array with a certain surface density. This can be implemented for a printing process in a series of processes for forming an organic transistor by printing. Also, there is no need for controlling an alignment, and the material cost is not high. In addition, Physical Review B (Vol. 54, page 14321) discloses that some molecular materials can exhibit properties of reducing a Schottky barrier between an electrode and an organic semiconductor and hence reducing the contact resistance. As molecules forming a material for a self-assembled monolayer film, alkylthiols such as ethanethiol, propanethiol, and butanethiol can be regarded, for example.



FIG. 6B is a cross sectional view showing a state where a monomolecular film 40 is formed by printing on the electrode of the alloy formed on the substrate, as shown in FIG. 6A, and the second metal is segregated on the electrode surface by a heat treatment at an appropriate temperature (50 to 200° C.). This method makes it possible to more easily promote the surface segregation than in the case where the monomolecular film is not added. A molecular material forming the monomolecular film 40 is selected in advance so that it has a property of reducing a Schottky barrier at the boundary between the electrode and the organic semiconductor and a property of promoting the surface segregation of the second metal.



FIG. 6C is a cross sectional view showing a state where an organic semiconductor 30 is formed on the monomolecular film 40 which is not removed. In this structure, the contact resistance between the electrode and the organic semiconductor is reduced due to both the thin film of the second metal and the monomolecular film.


With such a structure of the boundary between the electrode and the organic semiconductor, the organic transistor is formed by the subsequent processes similar to those of the first embodiment.


Fourth Embodiment

In a fourth embodiment, the electrode is formed of the first metal, and the thin film of the second metal is formed after the formation of the electrode, without forming a thin metal film covering the electrode surface by surface segregation. Similarly to the first to third embodiments, the copper atoms 11 and the gold atoms 12 will be described below as an example.



FIG. 7A is a cross sectional view of a structure in which an electrode is formed only of the copper atoms 11 on the substrate 20. Although the method of forming this structure is not limited, the method of printing copper ink formed only of the copper atoms 11 and performing a heat treatment is inexpensive and effective.



FIG. 7B is a cross sectional view of a structure in which ink formed only of the gold atoms 12 is printed on the electrode formed only of the copper atoms 11. In this state, a heat treatment is subsequently performed so as to remove the organic material 16 around the particles of the gold atoms 12.


The gold atoms 12 undergo diffusive motion during the heat treatment. Thus, the gold atoms 12 may be mixed with the copper atoms 11 to a certain extent. However, since the gold atoms 12 are stable on the electrode surface, not all the gold atoms 12 that are placed on the electrode surface before the heat treatment are diffused into the copper electrode. A certain amount of the gold atoms 12 are left on the electrode surface so as to form the thin metal film. During the heat treatment, the gold atoms 12, which have formed particles, are diffused so as to thinly spread on the surface. Thus, the thin film of the gold atoms 12 can be formed.



FIG. 7C is a cross sectional view showing the final structure of the thin metal film covering the electrode surface, according to the fourth embodiment.


In the procedures of the method of the fourth embodiment, after the electrode is formed, the process of forming the thin metal film is required. Thus, the number of processes is increased. However, the heat treatment starts in the state where the gold atoms 12 are placed on the surface of the copper atoms 11 in the fourth embodiment, instead of starting the heat treatment in the state of the alloy in which the gold atoms 12 and the copper atoms 11 are uniformly scattered so as to cause the surface segregation. Thus, distances of movements of the gold atoms 12 are shorter, and the thin metal film can be more effectively formed, as compared with the latter.


Furthermore, in the case of a combination of two types of metal atoms other than gold atoms and copper atoms, even if the second metal are not easily segregated on the surface due to the combination of the two types of the metal atoms, the second metal is first arranged on the first metal, and the electrode can be formed. Thus, there is an advantage in that the thin film formed of the second metal atoms can cover the electrode surface using such a combination of two types of metal atoms. In the case of such a combination of two types of metal, however, it is necessary to pay attention to a temperature and time of the heat treatment so as not to cause excessive diffusion of the metal atoms.


With such a method of forming the electrode, the organic transistor is formed by the subsequent processes similar to those of the first embodiment.


Fifth Embodiment

In a fifth embodiment, the second metal used as a thin film is printed on an electrode formed of the first metal. After that, a heat treatment is performed. Similarly to the first to fourth embodiments, a description will be made of the copper atoms 11 and the gold atoms 12 as an example.



FIG. 8A is a view showing a state where ink containing the particles of the copper atoms 11 is printed and a solvent is evaporated.



FIG. 8B is a view showing a state where ink containing the particles of the gold atoms 12 is printed on a layer formed of the particles of the copper atoms 11, and the solvent is evaporated. In this case, it is necessary that the ratio of an amount of the ink containing the particles of the copper atoms 11 to an amount of the ink containing the particles of the gold atoms 12 be approximately proportional to the ratio of an amount of copper to an amount of gold, the copper and the gold both being required for the final electrode structure, as described in the second embodiment. After the printing, a heat treatment is performed so as to remove the organic material 16 around the particles of the copper atoms 11 and the organic material 16 around the particles of the gold atoms 12.



FIG. 8C is a view showing an electrode structure formed in the fifth embodiment.


In the fifth embodiment, since the heat treatment is performed once, the number of the processes is reduced, as compared with the following method as described in the fourth embodiment: the heat treatment is performed so as to form the copper electrode, the gold is subsequently printed, and the heat treatment is lastly performed once again. Furthermore, as compared with the method in which the metal ink is completely mixed with the copper ink and the mixed ink is printed, the method in the fifth embodiment is more complicated since two printing processes are required. Before the diffusion occurs due to the heat treatment, however, the copper atoms 11 and the gold atoms 12 are close to the final positions to be reached. Thus, the final electrode structure can be efficiently formed because of the distances to the final positions. In addition, in the case where the thin film of the second metal is only required to cover the electrode surface and not required to cover the entire wiring, the ink of the second metal can be printed only on the electrode surface. This saves the expensive material.


In addition, even when the second metal is not segregated on the surface due to the combination of the first metal and the second metal, since the heat treatment is performed after the second metal is arranged near the surface, the electrode can be formed with the second metal being formed thereon. In such a case where no surface segregation occurs, however, the two types of metal are highly mixed as compared with the case of the fourth embodiment. This results in a decrease in the efficiency of forming the electrode.


With such a method of forming the electrode, the organic transistor is formed by the subsequent processes similar to those of the first embodiment.


Reference numerals shown in the drawings attached hereto are explained as follows:

  • 11 . . . Copper atom
  • 12 . . . Gold atom
  • 16 . . . Organic material used to improve solubility
  • 20 . . . Substrate
  • 30 . . . Organic semiconductor
  • 13 . . . Gate electrode
  • 14 . . . Source electrode
  • 15 . . . Drain electrode
  • 21 . . . insulating material
  • 40 . . . Monomolecular film

Claims
  • 1. Electrical wiring disposed on an insulating layer, wherein the body of the electrical wiring is formed of a first metal; andthe surface of the first metal is covered with a thin film formed of a second metal having a thickness of 0.5 to 5 atom layers.
  • 2. The electrical wiring according to claim 1, wherein the first metal is any one of Ag, Cu, Fe, Al, or Ni;the second metal is any one of Au, W, Pb, Pt, Rh, Pd, Ir, Ru, Os, or Mo; andthe second metal is segregated on the surface of the first metal in the combination of the first metal with the second metal.
  • 3. An organic transistor comprising: a substrate;a gate electrode disposed on the substrate;an insulating layer disposed so as to cover the gate electrode;a source electrode and a drain electrode that are disposed on the insulating layer so as to sandwich the gate electrode; andan organic semiconductor disposed so as to cover the source electrode and the drain electrode;wherein the bodies of the source electrode and the drain electrode are each formed of the first metal; andwherein the surfaces of the bodies of the source electrode and the drain electrode are each covered with a thin film of a second metal having a thickness of 0.5 to 5 atom layers.
  • 4. The organic transistor according to claim 3, wherein the first metal is any one of Ag, Cu, Fe, Al, or Ni;the second metal is any one of Au, W, Pb, Pt, Rh, Pd, Ir, Ru, Os, or Mo; andthe second metal is segregated on the surface of the first metal in the combination of the first metal with the second metal.
  • 5. The organic transistor according to claim 3, wherein the bodies of the source electrode and the drain electrode are formed of the first metal;the surfaces of the bodies of the source electrode and the drain electrode are each covered with the thin film of the second metal having a thickness of 0.5 to 5 atom layers; anda self-assembled monolayer film is interposed at a contact portion between the outer surface of the source electrode and the organic semiconductor and at a contact portion between the outer surface of the drain electrode and the organic semiconductor.
  • 6. A method of forming an organic transistor, the method comprising the steps of: preparing a substrate;forming a gate electrode on the substrate;forming an insulating layer so as to cover the gate electrode;forming a source electrode and a drain electrode so as to be disposed on the insulating layer and to sandwich the gate electrode; andforming an organic semiconductor so as to cover the source electrode and the drain electrode;wherein the method further comprises the steps of:printing, on a portion forming the source electrode and a portion forming the drain electrode, ink of particles that include a predetermined percentage of atoms of the first metal and a predetermined percentage of atoms of the second metal and that are formed using a predetermined organic material; andperforming a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the particles and to segregate the atoms of the second metal and to form a thin film of the second metal with a thickness of 0.5 to 5 atom layers on the surface of the atoms of the first metal at the same time of the removal of the organic material.
  • 7. The method of forming an organic transistor according to claim 6, instead of including the printing step and the heat treatment step, the method comprising the steps of: printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the first metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the ink of the particles composed of the atoms of the first metal;after the removal of the organic material, printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the second metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the ink of the particles composed of the atoms of the second metal and to form a thin film of the atoms of the second metal on the surface of the atoms of the first metal at the same time of the removal of the organic material.
  • 8. The method of forming an organic transistor according to claim 6, instead of including the printing step and heat treatment step, the method comprising the steps of: printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the first metal and that are formed using a predetermined organic material;printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the second metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove each of the organic materials from the ink of the first metal and from the ink of the second metal and to form a thin film of the atoms of the second metal on the surface of the first metal at the same time of the removal of each of the organic materials.
  • 9. A method of forming an organic transistor, the method comprising the steps of: preparing a substrate;forming a gate electrode on the substrate;forming an insulating layer so as to cover the gate electrode;forming a source electrode and a drain electrode so as to be disposed on the insulating layer and to sandwich the gate electrode;forming a self-assembled monolayer film on the outer surfaces of the source electrode and the drain electrode; andforming an organic semiconductor so as to cover a portion corresponding to the source electrode covered with the a self-assembled monolayer film and a portion corresponding to the drain electrode covered with the self-assembled monolayer film;wherein the method further comprises the steps of:printing, on a portion forming the source electrode and a portion forming the drain electrode, ink of particles that include a predetermined percentage of atoms of the first metal and a predetermined percentage of atoms of the second metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the particles;after the heat treatment, forming a self-assembled monolayer film by printing on the surfaces of the source electrode and the drain electrode; andperforming a heat treatment at a predetermined temperature ranging from 50° C. to 200° C. on the self-assembled monolayer film formed on the surfaces of the source electrode and the drain electrode so as to segregate the atoms of the second metal and to form a thin film of the second metal with a thickness of 0.5 to 5 atom layers on the surface of the atoms of the first metal.
  • 10. The method of forming an organic transistor according to claim 9, instead of including the printing step of the ink of the particles that are composed of the first metal and the second metal and the heat treatment steps immediately after that printing step, the method comprising the steps of: printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the first metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the ink of the particles composed of the atoms of the first metal;after removal of the organic material, printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of the second metal and that are formed using a predetermined organic material; andperforming a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove the organic material from the ink of the particles composed of the atoms of the second metal and to form a thin film of the atoms of the second metal on the surface of the atoms of the first metal at the same time of the removal of the organic material.
  • 11. The method of forming an organic transistor according to claim 9, instead of including the printing step of the ink of the particles that are composed of the first metal and the second metal and the heat treatment steps immediately after that printing step, the method comprising the steps of: printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of first metal and that are formed using a predetermined organic material;printing, on the portion forming the source electrode and the portion forming the drain electrode, ink of particles that are composed of the atoms of second metal and that are formed using a predetermined organic material;performing a heat treatment at a predetermined temperature ranging from 50° C. to 300° C. on the portion forming the source electrode and the portion forming the drain electrode so as to remove each of the organic materials from the ink of the first metal and from the ink of the second metal and to form a thin film of the atoms of the second metal on the surface of the first metal.
Priority Claims (1)
Number Date Country Kind
2006-133585 May 2006 JP national