JP2005072495A - Organic field effect transistor, and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic FET and the manufacturing method thereof wherein the bonding quality of both its source and drain electrodes to its organic semiconductor layer is sufficiently improved, and the deterioration of its organic semiconductor layer with the passage of time is made small. <P>SOLUTION: The organic FET 1 has a gate electrode 2 formed on one side of a gate insulation film 4, an organic semiconductor layer 6 formed on the other side of the gate insulation film 4, source and drain electrodes 10, 12 formed above the layer 6 and disposed with a constant space between them, and a buffer layer 8 formed between both the electrodes 10, 12 and the organic semiconductor layer 6. This buffer layer 8 is so constituted out of a metal complex as to be able to improve the bonding quality of both the electrodes 10, 12 to the organic semiconductor layer 6. Consequently, the contacting resistances of both the electrodes 10, 12 with the organic semiconductor layer 6 are made very low in the organic FET 1 having this buffer layer 8. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an organic field effect transistor (organic FET) and a method for manufacturing the same.

  In general, thin-film organic FETs using organic semiconductors are manufactured at a much lower cost than FETs using inorganic semiconductors, since the semiconductor layer can be formed by a simple process such as printing, spraying, and ink-jet methods. be able to. In addition, there is a possibility that a light-weight and thin integrated circuit having a large area can be easily produced, and application to liquid crystal displays, organic EL displays, IC cards, and the like is expected.

  In recent years, the carrier mobility of organic semiconductors has been improved, and it has been found that the mobility that is comparable to that of amorphous silicon can be expressed. For practical application of FETs using organic semiconductors having these high mobility. Research towards this is actively underway. Specifically, pentacene, polyalkylthiophene, and the like have been obtained as organic materials that exhibit such high mobility, and great progress has been made in the development of organic FETs.

  However, in these organic FETs, since the source electrode and the drain electrode are usually made of an inorganic material such as a metal, the bonding state between these electrodes and the organic semiconductor layer that is an organic material tends to be poor. When these junction states are poor in the organic FET, the contact resistance between the electrode and the organic semiconductor layer increases, and a loss of the applied gate voltage occurs. For this reason, conventional organic FETs often require an excessive gate voltage in order to obtain a current value equivalent to that of an FET using an inorganic semiconductor, and the high mobility inherent in organic semiconductors. Nevertheless, it was difficult to use in a practical voltage range.

Therefore, in order to improve the bondability between the source and drain electrodes and the organic semiconductor layer and to reduce the contact resistance between them, a dopant having a property of being paired with the organic semiconductor is applied to the region in contact with the source and drain electrodes in the semiconductor layer. Only an organic FET doped with only one is known (for example, see Patent Document 1). In such an organic FET, a dopant is doped in the region of the organic semiconductor layer near the source and drain electrodes, thereby forming a charge transfer complex in the organic semiconductor layer, thereby increasing the carrier density, thereby increasing both the electrode and the organic semiconductor. The contact resistance with the layer is reduced.
JP 2002-204012 A

  However, even with the organic FET described in Patent Document 1, the effect of improving the bondability between the source and drain electrodes and the organic semiconductor layer has not been sufficiently obtained. An improvement was needed.

  Further, in this so-called top contact type organic FET in which the source electrode and the drain electrode are formed on the organic semiconductor layer as in this organic FET, these electrodes are often formed by vapor deposition or the like. However, the organic FET manufactured in this way is subject to thermal damage due to the high temperature at the time of electrode formation, so that the organic semiconductor layer is deteriorated in the vicinity of the junction with each electrode. was there. Such deterioration of the organic semiconductor layer has also contributed to the deterioration of the bonding property between the electrode and the organic semiconductor layer.

  Furthermore, when this organic FET is exposed to the atmosphere for a long time or the number of times of use increases, the organic semiconductor layer deteriorates with time, and a considerable amount of current flows even when no gate voltage is applied. There was a case where it became like this. In this case, the organic FET has a small difference in current value during on / off, and is not suitable for use as a transistor.

  The present invention has been made in view of such circumstances, and an organic FET in which the bondability between the source and drain electrodes and the organic semiconductor layer is sufficiently improved and the deterioration of the organic semiconductor layer with time is small, and the production thereof. It aims to provide a method.

  According to detailed studies by the present inventors, it has been found that the organic FET described in Patent Document 1 does not have a sufficient improvement in bonding properties due to the following causes. That is, in this organic FET, by increasing the carrier density in the vicinity of the source and drain electrodes in the organic semiconductor layer, an electrical interaction between the electrode and the organic semiconductor layer is easily caused by the movement of carriers. However, such a technique does not essentially improve the bondability between the source and drain electrodes and the organic semiconductor layer, and for this reason, the effect of improving the bondability to some extent has not been obtained.

  Further, the organic FET described in Patent Document 1 is doped with a dopant only in the organic semiconductor layer in the vicinity of the source and drain electrodes, so that a charge transfer complex is not formed in the entire organic semiconductor layer. Is prevented from becoming undesirably large. However, the present inventors have found that even when such a configuration is adopted, diffusion of dopant over time, migration during voltage application, etc. cannot be avoided. And this presumed that the organic semiconductor layer caused deterioration with time.

  Based on such knowledge, the present inventors do not introduce other substances into the organic semiconductor layer to improve its characteristics, but provide a specific layer between the source and drain electrodes and the organic semiconductor layer. Introducing the present invention has led to the improvement of the bonding properties between the two and the discovery of a highly stable organic semiconductor layer, leading to the present invention.

  That is, the organic FET of the present invention includes a source electrode and a drain electrode, an organic semiconductor layer that becomes a channel between the source electrode and the drain electrode, a gate electrode for controlling the amount of current passing through the channel, and an organic semiconductor layer And a buffer layer including a metal complex, and is formed between at least one of the source electrode and the drain electrode.

  When the buffer layer made of the metal complex is formed between the organic semiconductor layer and the source electrode or the drain electrode in this way, the electric layer is electrically connected through the two interfaces between the electrode-buffer layer and the buffer layer-organic semiconductor layer. The action comes to occur. The metal element contained in the metal complex constituting the buffer layer is considered to be able to reduce the potential barrier generated at the interface between these two, particularly the potential barrier generated by the contact between the buffer layer and the organic semiconductor layer. As a result, an electrical action at the two interfaces is very likely to occur. As a result of the improved bondability of the two interfaces existing between the source and drain electrodes and the organic semiconductor layer, both the electrodes and the organic semiconductor layer are compared with the conventional organic FET in which both electrodes are directly bonded. It is presumed that the resistance caused by the contact is greatly reduced.

  Moreover, the metal complex which comprises the buffer layer has the ligand with favorable affinity with an organic compound around a metal element normally. For this reason, by interposing a buffer layer made of a metal complex between the source and drain electrodes and the organic semiconductor layer, the metal element of the metal complex and the metal of the source and drain electrodes, and the ligand of the metal complex and It is thought that two affinity improvement effects are produced by the action of organic substances with the organic semiconductor layer. However, the action is not limited to these.

  Furthermore, when manufacturing an organic FET having a source or drain electrode on an organic semiconductor layer as in the top contact type described above, according to the organic FET of the present invention, the source or drain electrode is connected to the organic semiconductor via the buffer layer. Formed on the layer. In addition, the metal complex composing the buffer layer can be deposited at a temperature significantly lower than that of metal, etc., and the influence of heat on the organic semiconductor layer when the buffer layer is formed on the organic semiconductor layer. Is extremely small. For this reason, the organic FET of the present invention is significantly less deteriorated when forming these electrodes than the conventional organic FET in which the source or drain electrode is formed directly on the organic semiconductor layer. Will be reduced.

  Furthermore, according to the organic FET of the present invention, even an organic semiconductor layer substantially composed of a single organic semiconductor has good bonding properties with the source or drain electrode. Accordingly, since it is not necessary to introduce a dopant or the like into the organic semiconductor layer as in the conventional organic FET, the deterioration of the organic semiconductor layer over time due to the diffusion or the like cannot occur.

  More specifically, the organic FET of the present invention has an insulating layer formed between a source electrode, a drain electrode, and a gate electrode, and the organic semiconductor layer has a source electrode and an insulating layer with respect to the insulating layer. Preferably, the drain electrode is formed on the side where the drain electrode is located.

  Here, in order to further reduce the potential barrier between the buffer layer and the organic semiconductor layer, the organic semiconductor that constitutes the organic semiconductor layer is a p-type semiconductor, and the metal element that the metal complex that constitutes the buffer layer has is more than the organic semiconductor. It is desirable to have a large work function. Specifically, the work function of the metal element in this case is preferably 4.6 eV or more. According to the organic FET having such a configuration, a current value substantially proportional to the applied voltage can be obtained, and driving in a more realistic voltage range is possible as compared with the conventional organic FET. .

  The reason why the above-described effect can be obtained by combining the organic semiconductor layer and the metal complex contained in the buffer layer is not clear at present. However, for example, the following reasons are assumed. That is, in the organic FET of the present invention, the buffer layer has a thin film shape. When the metal complex is formed in such a thin film shape, the metal element and the ligand are separated in the thin film, and the metal element existing near the surface of the buffer layer may come into contact with the organic semiconductor layer. Here, since the organic semiconductor layer is made of a p-type semiconductor and the metal element has the predetermined work function described above, these contacts are so-called non-rectifying contacts (ohmic contacts) in which no potential barrier is generated. ) State. In this case, it is considered that the potential barrier at the contact between the entire buffer layer and the organic semiconductor layer is significantly reduced. Thus, it is presumed that the above-described effects are exhibited.

  From the same viewpoint, when the organic semiconductor layer is an n-type semiconductor, it is desirable that the metal element included in the metal complex constituting the buffer layer has a work function smaller than that of the organic semiconductor. Specifically, the work function of the metal element in this case is more preferably 5.2 eV or less.

  These buffer layers are more preferably composed of a metal complex whose metal element is a noble metal element. Such a buffer layer has a characteristic that it has excellent bonding properties with the source and drain electrodes and the organic semiconductor layer. Further, since the noble metal element usually has a high work function, such a buffer layer can be applied particularly preferably when the organic semiconductor is a p-type semiconductor.

  The metal complex contained in the buffer layer is more preferably a nonionic metal complex. When the metal complex is an ionic complex, the counter ion may move to the organic semiconductor layer and cause a decrease in stability.

  Furthermore, in the organic FET of the present invention, the thickness of the buffer layer is preferably 0.5 to 10 nm. If the buffer layer is too thick, the resistance of the buffer layer itself becomes so large that it cannot be ignored, and an excessive voltage may be required to obtain a desired current value. On the other hand, if it is too thin, it is difficult to form a uniform film, and a sufficient bonding property improving effect tends not to be obtained due to variations in thickness.

  Further, the organic FET manufacturing method according to the present invention is a method for easily manufacturing the organic FET of the present invention, and is an organic material serving as a channel between the source electrode and the drain electrode and between the source electrode and the drain electrode. A method of manufacturing an organic field effect transistor comprising a semiconductor layer and a gate electrode for controlling the amount of current passing through a channel, the method comprising: at least one of a source electrode and a drain electrode; and an organic semiconductor layer And a step of forming a buffer layer containing a metal complex.

  More specifically, a step of forming a stacked body including a gate electrode and an insulating layer, a step of forming an organic semiconductor layer on the side of the stacked body where the insulating layer is formed, and a side of the stacked body where the organic semiconductor layer is formed And a step of forming a source electrode and a drain electrode on the side where the buffer layer is formed in the laminate so that at least one of the electrodes is positioned on the buffer layer. Is preferred. By such a manufacturing method, a top contact type organic FET in which at least one of the source electrode and the drain electrode is bonded to the organic semiconductor layer with the buffer layer interposed therebetween is manufactured.

  The method for manufacturing an organic FET according to the present invention also provides a method for easily manufacturing a bottom contact type organic FET having a source and a gate electrode below an organic semiconductor layer. Such a method includes a step of forming a stacked body including a gate electrode and an insulating layer, a step of forming a source electrode and a drain electrode on the side of the stacked body where the insulating layer is formed, and at least one of the source electrode and the drain electrode. Forming a buffer layer, and forming an organic semiconductor layer so that the buffer layer is sandwiched between at least one of the source electrode and the drain electrode.

  ADVANTAGE OF THE INVENTION According to this invention, the organic field effect transistor which is excellent in the adhesiveness of a source electrode and a drain electrode, and an organic-semiconductor layer, and has little deterioration with time of an organic-semiconductor layer, and its manufacturing method can be provided.

  DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted. Also, the positional relationship such as up / down / left / right is based on the positional relationship of the drawings.

  FIG. 1 is a cross-sectional view schematically showing a main part of the organic FET according to the first embodiment of the present invention. The organic FET 1 includes a gate electrode 2 provided on one side (lower side in the figure) of the gate insulating film 4 (insulating layer), an organic semiconductor layer 6 provided on the other side (upper side in the figure), and a gate. On the other side of the insulating film 4 (upper side in the figure), between the source electrode 10 and the drain electrode 12 provided on the organic semiconductor layer 6, and between the organic semiconductor layer 6 and the source electrode 10 and drain electrode 12. Each of them has a buffer layer 8 provided, and is an organic FET having a so-called top contact type configuration.

  The gate electrode 2 in the organic FET 1 having such a configuration has a function of controlling the amount of drain current passing through the organic semiconductor layer 6 described later functioning as a channel. The gate electrode 2 is made of a conductive member such as polysilicon, doped Si, metal, or conductive polymer, and also serves as a substrate. Note that an insulating substrate such as a glass material, a ceramic material, or a plastic material can be separately provided as the substrate. In this case, the gate electrode 2 is formed on these substrates.

The gate insulating film 4 formed on the gate electrode 2 is made of a material that can exhibit appropriate dielectric properties. Specifically, for example, SiO ₂ , Al ₂ O ₃ , Si ₃ N ₄ , TiO _2, etc. Inorganic dielectrics, and organic polymers such as polyimide, mylar, polyvinylidene fluoride, and polymethyl methacrylate. When the gate electrode 2 is made of a material that is oxidized to exhibit dielectric properties, the gate insulating film 4 can be an oxide film formed by oxidizing the surface of the gate electrode 2. Examples of the gate electrode 2 and the gate insulating film 4 include Si and SiO ₂ .

The organic semiconductor layer 6 formed on the gate insulating film 4 has a function as a so-called channel that becomes a current path between a source electrode 10 and a drain electrode 12 described later. The organic semiconductor layer 6 can be applied without distinction between p-type and n-type as long as it is an organic substance having such semiconductor characteristics as to realize this channel structure. For example, the p-type semiconductor is arranged in series such as pentacene and tetracene. Examples thereof include polycycles (acene) composed of 4 or 5 or more ortho-fused benzene rings, polyalkylthiophenes, thiophene oligomers, etc., and n-type semiconductors include C ₆₀ , fluorinated phthalocyanines and the like.

  The buffer layer 8 is formed between the organic semiconductor layer 6 and the source electrode 10 and the drain electrode 12 so as not to contact each other. The buffer layer 8 is mainly composed of a metal complex. The metal complex constituting the buffer layer 8 is preferably one that can form a film stably and has excellent stability after film formation.

  As such a metal complex, for example, when the organic semiconductor layer 6 is composed of a p-type semiconductor, the metal element contained in the metal complex has a larger work function than the organic semiconductor layer 6. Those are preferred. Specifically, the work function of the metal element in this case is preferably 4.6 eV or more, and examples of metals that satisfy this condition include Au, Cu, Pt, Ni, Pd, Ir, Rh, and Co. Etc.

  On the other hand, when the organic semiconductor layer 6 is composed of an n-type semiconductor, a metal complex in which the metal element has a work function smaller than that of the organic semiconductor layer 6 is preferable. In this case, specifically, the work function of the metal element is preferably 5.2 eV or less. Examples of the metal element having such a work function include Al, Ag, Mg, Ca, and Li.

  The metal elements in these metal complexes are more preferably metal elements such as Au, Ag, and Pt, which are generally classified as noble metals, and can be appropriately selected according to the type of semiconductor forming the organic semiconductor layer 6. Use it. Since most precious metal elements have a large work function, they are often suitable in combination with the organic semiconductor layer 6 made of a p-type semiconductor.

  The metal complex is more preferably a nonionic complex that is not ionic and has no structure such as a salt, that is, a molecular complex. Therefore, the combination of the metal element and the ligand may be selected so that the sum of their valences becomes zero. When the metal complex contained in the buffer layer 8 is an ionic complex, the counter ion is diffused or the like and taken into the organic semiconductor layer 6, which reduces the stability in the atmosphere, and the organic semiconductor layer 6 is timed. May cause general deterioration.

The ligand that coordinates to these metal elements is not particularly limited, and examples thereof include 0 to divalent ligands. Specific examples include zero-valent ligands having structures represented by the following formulas (1a) to (1d). In the following formulae, R represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group.

Examples of the monovalent ligand include the following formulas (2a) to (2j). In the following formulae, R is as defined above.

Further, examples of the divalent ligand include those represented by the following formulas (3a) to (3e). In the following formulae, R is as defined above.

  Among these ligands, acetylacetonate (ligand represented by the above formula (2g)), phenylpyridine (ligand represented by the above formula (2f)), phthalocyanine (the above formula (3a) ) And porphyrins (ligands represented by the above formula (3b)) are excellent in bonding property improving effect, and are relatively available. It is preferable because it is easy.

Preferred examples of the metal complex having the metal element and ligand described above include platinum (II) octaethylporphyrin (a compound represented by the following formula (4a)), platinum (II) acetylacetone (the following formula (4b)) Examples thereof include iridium (III) phenylpyridine (compound represented by the following formula (4c)), copper (II) phthalocyanine (compound represented by the following formula (4d)), and the like. In formula (4a), R ¹ represents an ethyl group.

  The buffer layer 8 mainly composed of these metal complexes can have a thickness of about 0.0005 to 0.1 times the thickness of the organic semiconductor layer 6. The size of the organic FET is preferably 0.5 to 10 nm.

  Further, the source electrode 10 and the drain electrode 12 formed on the buffer layer 8 are made of a known conductive material, and at least one of the electrodes 10 and 12 is made of a metal material. It is preferable to become. As the metal material, those usually used as materials for electrodes, such as Au, Ag, Cu, and Pt, can be applied without particular limitation.

Next, an example of a procedure for manufacturing the organic FET 1 configured as described above will be described. First, a gate electrode 2 made of n-type silicon or the like and serving as a substrate is prepared. In the case of forming the gate electrode 2 on another substrate, after preparing the substrate separately, the gate electrode 2 is formed on the substrate by a known method. The gate electrode 2 is appropriately heat-treated to form a gate insulating film 4 made of a thermal oxide film (SiO ₂ film) having a thickness of about 30 to 500 nm.

  Next, the material of the organic semiconductor layer 6 described above is formed on the gate insulating film 4 so as to have a thickness of about 10 to 100 nm by vapor deposition or the like, and the gate electrode 2, the gate insulating film 4, and the organic semiconductor layer 6 are formed. The laminated body comprised from these is formed.

  Next, a buffer layer 8 having a thickness of preferably 0.5 to 10 nm is formed on the organic semiconductor layer 6 in the stacked body. The buffer layer 8 is formed at a position on the organic semiconductor layer 6 corresponding to a position where the source electrode 10 and the drain electrode 12 are formed in a later step. As a method for forming the buffer layer 8, a method such as vapor deposition or sputtering, or a method in which a material constituting the buffer layer 8 such as a metal complex is dissolved in a solvent, applied onto the organic semiconductor layer 6, and then dried. Among them, the vapor deposition method is preferable because workability is good. When the buffer layer 8 is formed by vapor deposition, the buffer layer 8 is formed at a desired position as described above by performing vapor deposition through a shadow mask having an opening at a portion where the buffer layer 8 is formed. Let

  Further, by depositing an electrode material made of a metal such as Au on the buffer layer 8 formed in this manner, the source electrode 10 and the drain electrode 12 each having a thickness of about 50 to 200 nm are formed, and the organic FET 1 is formed. obtain. In this case, the channel length is preferably about 0.7 to 100 μm, and the channel width is preferably about 0.1 to 10 mm.

  In the organic FET 1 configured as described above, the source electrode 10 and the drain electrode 12 are attached to the organic semiconductor layer 6 with the buffer layer 8 interposed therebetween. The buffer layer 8 is mainly composed of a metal complex. The metal element contained in the metal complex can lower the potential barrier between the electrodes 10 and 12 and the buffer layer 8 and the potential barrier between the buffer layer 8 and the organic semiconductor layer 6. It is considered that the ligand possessed can improve the affinity between the buffer layer 8 and the organic semiconductor layer 6. In the organic FET 1 including the buffer layer 8 having such an action, the contact resistance between the source electrode 10 and the drain electrode 12 and the organic semiconductor layer 6 is extremely low.

  In addition, since the source electrode 10 and the drain electrode 12 are thus deposited on the organic semiconductor layer 6 via the buffer layer, the organic semiconductor layer 6 can be used when the electrodes 10 and 12 are deposited. Less susceptible to heat For this reason, the deterioration of the organic semiconductor layer 6 at the time of manufacture, which has been a problem in the conventional organic FET, becomes extremely small.

  Further, when the organic semiconductor layer 6 in the organic FET 1 is made of a p-type semiconductor, if the metal element included in the metal complex constituting the buffer layer 8 has a work function larger than that of the organic semiconductor layer 6, the buffer Contact between the metal element near the surface of the layer 8 and the organic semiconductor layer 6 can be almost ohmic. In this case, the potential barrier due to the contact between the source electrode 10 and the drain electrode 12 and the organic semiconductor layer 6 is considered to be extremely small, and the driving in a more realistic voltage range is possible as compared with the conventional organic FET. . The same effect is also achieved when the organic semiconductor layer 6 is n-type and the work function of the metal element of the metal complex constituting the buffer layer 8 is smaller than that of the organic semiconductor layer 6.

  The first embodiment of the organic FET of the present invention has been described above. However, the present invention is not necessarily limited to the above-described configuration, and various modifications can be made without departing from the spirit of the present invention.

  For example, the buffer layer 8 is not necessarily formed between both the source electrode 10 and the drain electrode 12 and the organic semiconductor layer 6, and at least one of the electrodes 10 and 12 and the organic semiconductor layer 6 If it is formed in between, the effect of improving the bonding property can be exhibited. When only one of the electrodes 10 and 12 is made of a metal material, it is desirable that the buffer layer 8 be formed on the side of the electrode made of metal.

  Moreover, the buffer layer 8 should just be provided so that the source electrode 10 and the drain electrode 12 and the organic-semiconductor layer 6 may not contact at least, for example, the buffer layer 8 of the buffer layer 8 rather than the electrodes 10 and 12 formed in the upper part. The size may be large.

  Next, a second embodiment of the organic FET of the present invention will be described. FIG. 2 is a cross-sectional view schematically showing a main part of an organic FET according to the second embodiment of the present invention. The organic FET 11 is an organic FET having a so-called bottom contact type configuration. In the organic FET 11, a gate electrode 2 for controlling the amount of current passing through the channel is formed on one side of the gate insulating film 4 (insulating layer), and a constant interval is formed on the other side of the gate insulating film 4. The source electrode 10 and the drain electrode 12 are disposed. Further, a buffer layer 18 mainly composed of a metal complex is formed on the other side of the gate insulating film 4 and on the source electrode 10 and the drain electrode 12, and above and between these buffer layers 18. An organic semiconductor layer 6 that becomes a channel between the source electrode 10 and the drain electrode 12 is formed. The organic FET 11 having such a configuration is formed from the same material as the organic FET 1 described above.

  This organic FET 11 can be manufactured as follows. First, a gate electrode 2 is prepared, and a gate insulating film 4 is formed thereon by a method similar to that of the organic FET 1 to obtain a stacked body, and then disposed on the gate insulating film 4 of the stacked body at a predetermined interval. The source electrode 10 and the drain electrode 12 are formed. In this case, the formation method of both the electrodes 10 and 12 is not particularly limited. For example, after forming the electrode material on the gate insulating film 4 by sputtering, patterning can be performed by photolithography or the like.

  Next, the buffer layer 18 is formed on the source electrode 10 and the drain electrode 12 by vapor deposition or the like. The buffer layer 18 is desirably formed so as to cover both the electrodes 10 and 12 so as not to cause contact between the both electrodes 10 and 12 and the organic semiconductor layer 6 formed thereon.

  After the buffer layer 18 is formed on the source electrode 10 and the drain electrode 12 in this way, the organic semiconductor layer 6 is formed above and between the buffer layers 18 so as to provide current paths for the source electrode 10 and the drain electrode 12. Thus, the organic FET 11 is obtained. As a method for forming the organic semiconductor layer 6, a vapor deposition method is preferable.

  The organic FET 11 can be variously modified similarly to the organic FET 1 described above. For example, the buffer layer 18 does not necessarily have to be formed on both the source electrode 10 and the drain electrode 12, and if it is formed on one of them, the effect of improving the bonding property can be exhibited.

  In the organic FET 11 configured as described above, the organic semiconductor layer 6 and the source electrode 10 and the drain electrode 12 are in contact with each other with a buffer layer 18 made of a metal complex interposed therebetween. For this reason, as in the case of the organic FET 1, the contact resistance between the electrodes 10, 12 and the organic semiconductor layer 6 becomes extremely small due to the buffer layer 18.

  The organic FET of the present invention is not necessarily limited to the organic FET having the top contact type and bottom contact type structures described above. Specifically, for example, a top-and-bottom contact type organic FET in which one of a source electrode and a drain electrode is formed on one side of the organic semiconductor layer and the other electrode is formed on the other side, or a source electrode A vertical organic FET in which a gate electrode is formed between the gate electrode and the drain electrode and an organic semiconductor layer serving as a channel between the source electrode and the drain electrode is formed around the gate electrode is also an organic FET of the present invention. included. In any organic FET, a buffer layer mainly composed of a metal complex is formed between at least one of the source electrode and the drain electrode and the organic semiconductor layer, whereby the source electrode or the drain electrode And the organic semiconductor layer have good bonding properties.

  EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these.

[Manufacture of organic FET]
(Example 1)
First, a highly doped n-type silicon substrate (bulk resistivity: 1 Ωcm) also serving as a gate electrode on which a thermal oxide film of about 200 nm was formed as a gate insulating film was prepared, and this was cut out into a 9 × 25 mm rectangular plate shape. . Next, pentacene was vacuum-deposited on the gate insulating film of the substrate to form an organic semiconductor layer having a thickness of about 50 nm.

  On this organic semiconductor layer, platinum (II) octaethylporphyrin was vacuum-deposited through a shadow mask in which a portion to be a channel portion was separated to form a buffer layer having a thickness of about 2 nm. Further, a gold film having a thickness of about 80 nm was vacuum deposited on the buffer layer to form a source electrode and a drain electrode, thereby obtaining an organic FET. The channel length was 20 μm and the channel width was 5 mm.

(Example 2)
An organic FET was obtained in the same manner as in Example 1 except that iridium (III) phenylpyridine was used instead of platinum (II) octaethylporphyrin.

(Example 3)
An organic FET was obtained in the same manner as in Example 1 except that platinum (II) acetylacetone was used instead of platinum (II) octaethylporphyrin.

Example 4
An organic FET was obtained in the same manner as in Example 1 except that copper (II) phthalocyanine was used instead of platinum (II) octaethylporphyrin.

(Comparative Example 1)
Organic FET was obtained like Example 1 except not having provided the buffer layer.

[Characteristic evaluation]
First, for the organic FETs obtained in Examples 1 to 4 and Comparative Example 1, the change in drain current with respect to the gate voltage was measured. The change in the drain current with respect to the gate voltage is measured using a semiconductor parameter analyzer (4155C, manufactured by Agilent Technologies), and the gate / voltage is measured with respect to various values of drain-source voltage (drain voltage). This was performed by monitoring the value of the current (drain current) flowing between the source electrode and the drain electrode when the voltage between the source electrodes (gate voltage) was continuously changed. Each organic FET has a typical p-type transistor because the drain current value increases when a voltage is applied so that the drain electrode and the gate electrode are negative with respect to the potential of the source electrode. It was found to exhibit characteristics.

  Next, the field effect mobility and the gate voltage threshold value (Vth) in the FET structure were calculated from the plot of the change in drain current against the obtained gate voltage. Specifically, the square root of the drain current value versus the gate voltage value when the drain voltage is set to −100 V is plotted. The mobility was calculated from the slope of the tangent line at a gate voltage of −50 V, which is a condition for obtaining a sufficiently saturated region in this plot. Vth was derived by reading the X-axis intercept at this tangent. The obtained mobility and Vth results are shown in Table 1.

表１より、金属錯体からなるバッファ層を設けた実施例１〜４の有機ＦＥＴは、バッファ層を設けなかった比較例１の有機ＦＥＴに比して、移動度が有意に高く、またＶｔｈの値がより０に近いことが判明した。

From Table 1, the organic FETs of Examples 1 to 4 provided with a buffer layer made of a metal complex have a significantly higher mobility and a Vth of Vth compared to the organic FET of Comparative Example 1 provided with no buffer layer. The value was found to be closer to zero.

It is sectional drawing which shows typically the principal part of organic FET which concerns on 1st Embodiment of this invention. It is sectional drawing which shows typically the principal part of organic FET which concerns on 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Organic FET, 2 ... Gate electrode, 4 ... Gate insulating film, 6 ... Organic-semiconductor layer, 8 ... Buffer layer, 10 ... Source electrode, 11 ... Organic FET, 12 ... Drain electrode, 18 ... Buffer layer.

Claims (12)

A source electrode and a drain electrode;
An organic semiconductor layer serving as a channel between the source electrode and the drain electrode;
A gate electrode for controlling the amount of current through the channel;
A buffer layer formed between the organic semiconductor layer and at least one of the source electrode and the drain electrode, and containing a metal complex;
An organic field effect transistor comprising: An insulating layer formed between the source and drain electrodes and the gate electrode;
The organic field effect transistor according to claim 1, wherein the organic semiconductor layer is formed on a side where the source electrode and the drain electrode are located with respect to the insulating layer.   The organic field effect according to claim 1 or 2, wherein the organic semiconductor constituting the organic semiconductor layer is a p-type semiconductor, and the metal element of the metal complex has a work function larger than that of the organic semiconductor. Transistor.   The organic field effect transistor according to claim 3, wherein a work function of a metal element of the metal complex is 4.6 eV or more.   The organic field effect according to claim 1 or 2, wherein the organic semiconductor constituting the organic semiconductor layer is an n-type semiconductor, and the metal element of the metal complex has a work function smaller than that of the organic semiconductor. Transistor.   The organic field effect transistor according to claim 5, wherein a work function of a metal element of the metal complex is 5.2 eV or less.   The organic field effect transistor according to claim 1 or 2, wherein the metal element of the metal complex constituting the buffer layer is a noble metal element.   The organic field effect transistor according to any one of claims 1 to 7, wherein the metal complex is a nonionic complex.   The organic field effect transistor according to any one of claims 1 to 8, wherein the buffer layer has a thickness of 0.5 to 10 nm. An organic field effect transistor comprising a source electrode and a drain electrode, an organic semiconductor layer serving as a channel between the source electrode and the drain electrode, and a gate electrode for controlling the amount of current passing through the channel is manufactured. A method,
The manufacturing method of the organic field effect transistor which has the process of forming the buffer layer containing a metal complex between at least one electrode of the said source electrode and the said drain electrode, and the said organic-semiconductor layer. Forming a laminate including the gate electrode and an insulating layer;
Forming the organic semiconductor layer on the side of the laminate on which the insulating layer is formed;
Forming the buffer layer on the side of the laminate on which the organic semiconductor layer is formed;
Forming the source electrode and the drain electrode on the side of the stacked body where the buffer layer is formed so that at least one of the electrodes is positioned on the buffer layer;
The manufacturing method of the organic field effect transistor of Claim 10 which has these. Forming a laminate including the gate electrode and an insulating layer;
Forming the source electrode and the drain electrode on the side of the laminate on which the insulating layer is formed;
Forming the buffer layer on at least one of the source electrode and the drain electrode;
Forming the organic semiconductor layer so as to sandwich the buffer layer between at least one of the source electrode and the drain electrode;
The manufacturing method of the organic field effect transistor of Claim 10 which has these.

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