JP2008060312A - Field effect transistor and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a functional device, such as field effect transistors which hardly have disconnections or short circuits of electrodes, and has high reliability and small parasitic capacitance and has superior frequency characteristics. <P>SOLUTION: The field effect transistor comprises an insulating substrate, a first electrode which has a convex portion and is formed on the substrate, an insulating film which covers the top and side faces of the convex portion, second and third electrodes formed on the substrate surface on the side of one side face of the convex portion, a fourth electrode formed on the top face of the convex portion via the insulting film, and a semiconductor layer which is in contact with the second, third, and fourth electrodes but is separated from the first electrode by the insulating film. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a field effect transistor and the like and a manufacturing method thereof.

  In recent years, with the advanced development of information technology, there is an increasing demand for information processing devices, display devices, and storage devices that are ultra-thin and easy to carry. In addition, developments for practical application of prepaid electronic payment systems, postpaid electronic payment systems, immediate payment electronic payment systems, information distribution systems, information exchange systems, and the like using these are underway.

  As a technology for providing an ultra-thin information processing apparatus, functional devices such as field effect transistors, diodes, and capacitors using organic semiconductor thin films have attracted a great deal of attention. A functional device using an organic semiconductor thin film is manufactured at a lower temperature process than a functional device using an inorganic semiconductor thin film. Therefore, a plastic substrate or a film substrate having excellent flexibility can be used as a substrate. It is possible to manufacture a device that is light and hard to break. In addition, devices can be manufactured using methods such as application, spraying, and printing of a solution containing an organic semiconductor material, and a large number of devices can be quickly manufactured at low cost.

  As a functional device using such an organic semiconductor thin film, a field effect transistor in which a short gate length can be obtained with high precision and easily, and a gate electrode and a source / drain electrode are formed in a self-aligned manner. (FET) is disclosed (see Patent Document 1). Specifically, as shown in FIG. 6, the cross-sectional shape formed on the substrate is a quadrilateral gate electrode 102, the top surface of the gate electrode 102 and the insulating film 103 formed on both side surfaces, and the top surface of the gate electrode 102. The first source / drain electrode 106 formed above the first source / drain electrode 104, the second source / drain electrode 104 formed on both sides of the surface of the substrate divided by the gate electrode 102, and the third source / drain electrode 105 respectively. , And a semiconductor layer 107 formed on the first to third source / drain electrodes. Therefore, a channel region is formed between the first electrode 106 and the second electrode 104, or between the first electrode 106 and the third electrode 105, and a channel length as short as the thickness of the gate electrode 102 can be obtained. .

Further, in Patent Document 2, in addition to the above-described configuration, as shown in FIG. 7, the electrode on the top surface and the electrode on one substrate are connected to form a third electrode 205, and only the semiconductor layer 207 on the opposite side is connected. A configuration having a channel region is disclosed. With such a configuration, when the second electrode 204 and the third electrode 205 are formed, the material is deposited from the oblique direction with respect to the substrate surface, and the material is caused by the wraparound to the opposite convex side surface. Adhesion can be avoided, the reliability of the field effect transistor can be increased, and the number of steps in the manufacturing process can be reduced to improve the yield.
JP 2004-349292 A JP 2005-19446 A

  However, as illustrated in FIG. 7, in the conventional transistor disclosed in Patent Document 2 or the like, the first electrode 202 which is a gate electrode and the third electrode 205 which is a source electrode are interposed through an insulating film 203. Since they are stacked, there is a problem that the two electrodes act as a capacitor, the parasitic capacitance increases, and the frequency characteristics deteriorate.

  For example, in the case of use of a wireless IC tag as an example of communication equipment using a functional device such as a field effect transistor, the following bands can be exemplified as the main carrier frequency used in the communication circuit.

  (1) 125 kHz to 135 kHz, (2) 13 MHz to 14 MHz, (3) 860 MHz to 950 MHz, (4) 2.4 GHz to 2.5 GHz. In particular, for the 860 MHz to 950 MHz band, frequency allocation is made by region, and the 860 MHz band in Europe, the 915 MHz band in the United States, and the 950 MHz band in Japan are particularly preferably used. In addition, in the application of Bluetooth communication, the 2.4 GHz band is particularly preferably used.

  Moreover, in the application of UWB (Ultra Wideband) communication, the microwave band (3.1 to 10.6 GHz band) is particularly preferably used. For mobile communication, wireless LAN communication, and NWA (Nomadic Wireless Access) communication, in addition to the microwave band (1.7 GHz band, 2.5 GHz band, 4 GHz to 5 GHz band), a quasi-millimeter wave band of about 20 GHz, A millimeter wave band of 59 to 66 GHz is particularly preferably used. In the application of ITS communication, the 5.8 GHz band is particularly preferably used.

  As described above, there has been a demand for higher frequency communication equipment, and it is necessary to improve the frequency characteristics of functional devices such as field effect transistors in order to cope with the demand.

  An object of the present invention is to provide a functional device such as a field effect transistor that is less likely to cause disconnection or short-circuiting of electrodes, has high reliability, and has small parasitic capacitance and excellent frequency characteristics.

  In order to solve the conventional problems, a field effect transistor according to the present invention covers an insulating substrate, a first electrode provided on the substrate and having a convex portion, and an upper surface and side surfaces of the convex portion. An insulating film; second and third electrodes provided on the substrate surface on one side of the convex portion; a fourth electrode provided on the upper surface of the convex portion via the insulating film; and And a semiconductor layer in contact with the third electrode and the fourth electrode, and separated from the first electrode by the insulating film.

  According to the above configuration, the channel length between the second electrode and the fourth electrode, and the channel length between the third electrode and the fourth electrode can be shortened, and the possibility of short-circuiting or cutting between the electrodes is small and the reliability is high. A high field effect transistor can be provided. In addition, since the overlap between the first electrode and the second electrode or between the first electrode and the third electrode becomes minute, the two electrodes hardly act as a capacitor, and the parasitic capacitance is reduced. Is done. Further, when the transistor is OFF, the fourth electrode is in an electrically isolated state. Therefore, a parasitic effect is not generated between the fourth electrode and the first electrode, and a field effect transistor having high frequency characteristics is obtained. Can be provided.

  The first electrode potential can be switched between an electrically conductive state and an electrically non-conductive state between the second electrode and the third electrode.

  Thereby, the amount of current between the second electrode and the third electrode can be controlled using the first electrode as a gate electrode.

Furthermore, the semiconductor layer is made of an organic semiconductor material. Accordingly, the organic semiconductor layer can be formed by a low-cost process such as coating or printing, and a plastic substrate or a film substrate having excellent flexibility can be used as the insulating substrate.
The field effect transistor manufacturing method of the present invention includes a step of forming a first electrode having a convex portion on an insulating substrate, a step of forming an insulating film so as to cover an upper surface and a side surface of the convex portion, Forming a second electrode and a third electrode on the substrate surface on one side of the convex portion, forming a fourth electrode on the upper surface of the convex portion via the insulating film, and the second Forming a semiconductor layer on the first electrode with the insulating film interposed therebetween, and forming the semiconductor layer on the first electrode with the insulating film interposed therebetween.

  According to the above manufacturing method, the semiconductor layer is formed after forming the electrode and the dielectric layer in a predetermined shape. Therefore, when the semiconductor layer is made of an organic material, the electrode or the dielectric layer is formed or processed. It is possible to effectively avoid the damage caused by heat, light, chemical substances, etc., and to easily form a field effect transistor with a small parasitic capacitance.

  Further, the second, third and fourth electrodes are formed in the same film forming process.

  Thereby, an electrode can be formed with a more simplified manufacturing process.

  According to the present invention, in a high-performance field effect transistor with a short channel length, it is possible to obtain high reliability by suppressing the occurrence of disconnection and short-circuiting of electrodes while being a simple manufacturing process, and to achieve parasitic capacitance. And the frequency characteristics can be improved.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

<Structure of field effect transistor>
FIG. 1 is a perspective view (a), a sectional view (b), and a top view (c) showing an example of a field effect transistor according to an embodiment of the present invention. In this field effect transistor, a first electrode 2 is formed on a substrate 1 made of an insulating material so as to form a convex portion. An insulating film 3 is formed to have a substantially uniform thickness so as to cover the upper surface and side surfaces of the first electrode 2. As shown in FIG. 1, the second electrode 4 and the third electrode 5 are formed on the surface of the substrate on the one side surface of the convex portion in a band shape from the vicinity of the side surface of the convex portion at a predetermined interval. A fourth electrode 6 is formed on the surface of the insulating film 3 formed on the upper surface of the convex portion. As shown in FIG. 1, the fourth electrode 6 is formed so as to include the position of the upper surface of the convex portion corresponding to the second electrode 4 and the third electrode 5. Further, a semiconductor layer 7 is formed so as to be in contact with the second electrode 4, the third electrode 5, and the fourth electrode 6 and to be laminated with the first electrode 2 through the insulating film 3.

  In the field effect transistor of this embodiment, the first electrode 2 is a gate electrode, the insulating film 3 is a gate insulating film, the second electrode 4 is a drain electrode (or source electrode), and the third electrode 5 is a source electrode. (Or drain electrode), the semiconductor layer 7 functions as an active layer.

  Therefore, the semiconductor layer 7 between the second electrode 4 (for example, the drain electrode) and the fourth electrode 6 and the semiconductor layer 7 between the third electrode 5 (for example, the source electrode) and the fourth electrode 6 are included in the present invention. Since it becomes an active layer in the field effect transistor, the amount of current between the second electrode 4 and the third electrode 5 is controlled by the voltage applied to the first electrode 2 (gate electrode). The fourth electrode functions as a wiring connecting the active layer on the second electrode side and the active layer on the third electrode side when the gate is ON, and is electrically isolated when the gate is OFF It becomes.

  The height of the convex portion in the first electrode 2 is preferably in the range of 10 nanometers to 10 micrometers in order to define the channel length of the field effect transistor. Furthermore, the range of 0.1 μm to 1.5 μm is particularly preferable from the viewpoint of improving the operation speed and suppressing the leakage current.

In addition, the narrower the width of the convex portion in the first electrode 2 is, the better the degree of integration of the field effect transistors is. However, if the width is too small, the wiring resistance increases. Problems arise in formation and the like. Therefore, the width of the convex portion is preferably in the range of 0.1 μm to 100 μm, and more preferably in the range of 1 μm to 50 μm.
Moreover, it is preferable that the semiconductor layer 7 is formed at intervals between the second electrode 4 and the fourth electrode 6 and between the third electrode 5 and the fourth electrode 6. As a result, it is possible to prevent the second electrode 4 and the third electrode 5 from being directly electrically connected via the semiconductor layer 7 therebetween without using the fourth electrode 6.
Further, the fourth electrode 6 is partly arranged such that a gap is formed between a part connected to the semiconductor layer 7 on the second electrode 4 side and a part connected to the semiconductor layer 7 on the third electrode 5 side. It is preferable to have a shape with a notch. As a result, when the electrodes are formed, the vapor deposition position is shifted, the second electrode 4 and the third electrode 5 are formed to be connected, and the electrodes are short-circuited without the semiconductor layer 7 interposed therebetween. Thus, it can be prevented that the transistor does not function as a transistor.
As an example, the dimension about the width | variety etc. of each electrode of this embodiment is shown in FIG. The width (Wg) of the first electrode 2 is 10 μm, the widths (Ws, Wd) of the second electrode 4 and the third electrode 5 are 50 μm, and the distance between the second electrode 4 and the third electrode 5 is 25 μm. The width of the narrow portion OLE_LINK2 of the fourth electrode 6 was 8 μm. The end of the narrow portion of the fourth electrode 6 is 1 μm away from the end of the first electrode 2.

  The angle formed between the side surface of the convex portion and the surface of the substrate in the first electrode 2 will be described later. Since it becomes difficult to control adhesion, it is preferable to be within ± 30 degrees with respect to 90 degrees. Furthermore, it is preferable that the angle is within ± 20 degrees with respect to 90 degrees.

<Construction material of field effect transistor>
The material constituting the semiconductor layer 7 is Si, III-V group (mainly GaAs, other InP, GaAlAs, etc.), II-VI (CdS / CdTe, Cu2S, ZnS, ZnSe, etc.), I- There is no particular limitation such as III-VI group or organic semiconductor. However, the organic semiconductor is generally less resistant to heat, light, chemical substances, and the like during electrode formation and processing as compared with inorganic semiconductors, and thus is easily damaged.

  Since the field effect transistor of this embodiment has a structure in which the semiconductor layer is formed after electrode formation and processing, the semiconductor layer is not damaged. That is, the field effect transistor of this embodiment is particularly effective in that an organic semiconductor can be used without being damaged.

  As the organic semiconductor material constituting the semiconductor layer 7, both a material having an electron accepting function and a material having an electron donating function can be used. For example, materials exemplified below are used. The

  Examples of the material having an electron-accepting function include oligomers and polymers having pyridine and derivatives thereof as skeletons, oligomers and polymers having quinoline and derivatives thereof as skeletons, ladder polymers using benzophenanthrolines and derivatives thereof, cyano -Polymers such as polyphenylene vinylene, fluorinated metal-free phthalocyanines, fluorinated metal phthalocyanines and derivatives thereof, perylene and derivatives thereof (gold CDA, gold CDI etc.), naphthalene derivatives (NTCDA, NTCDI etc.), bathocuproin and derivatives thereof, etc. Of low molecular weight organic compounds.

  In addition, as materials having an electron donating function, oligomers and polymers having thiophene and its derivatives in the skeleton, oligomers and polymers having phenylene-vinylene and its derivatives in the skeleton, oligomers and polymers having fluorene and its derivatives in the skeleton, Oligomers and polymers having benzofuran and its derivatives in the backbone, oligomers and polymers having thienylene-vinylene and its derivatives in the backbone, aromatic tertiary amines such as triphenylamine and their derivatives, carbazole and polymers Oligomers and polymers having their derivatives in the backbone, oligomers and polymers having the backbone of vinylcarbazole and its derivatives, oligomers and polymers having the backbone of pyrrole and its derivatives, acetylene and derivatives thereof Oligomers and polymers having skeletons, oligomers and polymers having skeletons of isothiaphene and its derivatives, polymers such as oligomers and polymers having skeletons of heptadiene and its derivatives, metal-free phthalocyanines, metal phthalocyanines and their derivatives Diamines, phenyldiamines and derivatives thereof, acenes such as pentacene and derivatives thereof, porphyrin, tetramethylporphyrin, tetraphenylporphyrin, tetrabenzporphyrin, monoazotetrabenzporphyrin, diazotetrabenzporphine, triazotetrabenzporphyrin , No metal such as octaethylporphyrin, octaalkylthioporphyrazine, octaalkylaminoporphyrazine, hemiporphyrazine, chlorophyll Porphyrin or metalloporphyrin and their derivatives, cyanine dyes, merocyanine dyes, squarylium dyes, quinacridone dyes, azo dyes, anthraquinone, benzoquinone, low molecular organic compounds such as quinone-based dyes naphthoquinone is used. As metal phthalocyanine and metal porphyrin central metals, magnesium, zinc, copper, silver, aluminum, silicon, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, tin, gold, lead and other metals, metal oxides, A metal halide or the like is used.

  As the semiconductor layer 7, the above material may be used alone, or a material in which the above material is dispersed and mixed in an appropriate binder material may be used. Moreover, you may use the material which incorporated the said low molecular weight organic compound in the principal chain or side chain of a suitable high molecular organic compound. Examples of the binder organic material or the high molecular organic compound serving as the main chain include polycarbonate resin, polyvinyl acetal resin, polyester resin, modified ether-type polyester resin, polyarylate resin, phenoxy resin, polyvinyl chloride resin, polyvinyl acetate resin, Polyvinylidene chloride resin Polystyrene resin, acrylic resin, methacrylic resin, cellulose resin, urea resin, polyurethane resin, silicon resin, epoxy resin, polyamide resin, polyacrylamide resin, polyvinyl alcohol resin, etc., copolymers thereof, or polyvinyl Photoconductive polymers such as carbazole and polysilane are used.

  The material of the substrate 1 or the substrate 1 is not particularly limited as long as it stably holds the material formed thereon. Examples thereof include metals such as stainless steel and alloys, glass, resin, paper, and cloth.

  The material of the insulating film 3 is, for example, a polycarbonate resin, a polyvinyl acetal resin, a polyester resin, a modified ether type polyester resin, a polyarylate resin, in addition to inorganic materials such as a silicon oxide film, a silicon nitride film, and a mixed film thereof. Phenoxy resin, polyvinyl chloride resin, polyvinyl acetate resin, polyvinylidene chloride resin polystyrene resin, acrylic resin, methacrylic resin, cellulose resin, urea resin, polyurethane resin, silicon resin, epoxy resin, polyamide resin, polyacrylamide resin and polyvinyl alcohol Organic materials such as resins and copolymers thereof are used.

  Examples of the material of the first electrode 2, the second electrode 4, the third electrode 5, and the fourth electrode 6 include metals such as gold, aluminum, copper, tantalum, and titanium, alloys, and low materials such as highly doped silicon. Examples include alloys such as resistance semiconductors and metal silicides. Moreover, when forming in a transparent electrode, metal oxides, such as indium tin oxide (ITO), fluorine-doped tin oxide, zinc oxide, and tin oxide, are used, for example. Alternatively, a conductive high molecular organic compound such as polyacetylene, polypyrrole, or polythiazyl may be used. The electrode material is also selected depending on the electrical properties (ohmic properties, Schottky properties, etc.) with the semiconductor layer 7.

<Method of manufacturing field effect transistor>
Hereinafter, the manufacturing method of the field effect transistor of this embodiment will be described with reference to FIGS.

  First, the first electrode 2 is formed on the substrate 1. First, a film of a predetermined thickness made of a conductive material is formed, and this film is processed using a known photolithography technique so that the cross section shown in FIG. 4B is rectangular. . Specifically, an aluminum (Al) film having a thickness of about 1 μm is formed on a glass plate as the substrate 1 by a sputtering method, and then the aluminum film is processed by a photolithography method and a reactive ion etching method. Then, the first electrode 2 is formed.

  Next, an insulating film 3 that covers the first electrode 2 is formed. When the insulating film 3 is formed of an inorganic material such as silicon oxide or silicon nitride, or a polymer such as polyparaxylylene, it is preferable to use a CVD method such as plasma CVD. Further, when the first electrode 2 is formed of a material that forms an insulating oxide film such as aluminum or tantalum, the surface of the first electrode 2 is oxidized, thereby insulating the first electrode 2. The film 3 may be formed. As this oxidation method, known methods such as thermal oxidation, oxidation using a solution of an oxidizing agent, and anodic oxidation are used. Further, when the insulating film 3 is formed of an organic material, the organic material solution may be applied by a method such as spin coating. In this embodiment, as shown in FIG. 4C, the insulating film 3 made of silicon nitride having a thickness of about 200 nm is formed by plasma CVD.

  Next, as shown in FIG. 4D, the second electrode 4, the third electrode 5 and the fourth electrode 6 are formed on the insulating film 3. Here, when a film forming method with a high directivity of the material, such as a vapor deposition method, is used, the material adheres to a surface perpendicular to the direction having the directivity. The material hardly adheres to the substantially parallel surface. Utilizing this characteristic, the second electrode 4, the third electrode 5 and the fourth electrode 6 are simultaneously formed by vapor deposition from an oblique direction with respect to the substrate.

  Specifically, as shown in FIG. 5A, the material beam 9 is irradiated from a larger angle θ than the angle θ formed between the side surface of the first electrode 2 constituting the convex portion and the substrate normal line. By forming the film, it is possible to prevent the material from adhering to the side surface of the convex portion, and it is possible to cut between the second electrode 4 and the fourth electrode 6 and between the third electrode 5 and the fourth electrode 6. On the other hand, as shown in FIG. 5B, when the film is formed by irradiating the material beam 9 from an angle smaller than the angle θ formed between the side surface of the first electrode 2 constituting the convex portion and the substrate normal. Then, the material on the side surface of the convex portion adheres, and the second electrode 4 and the fourth electrode 6 and the third electrode 5 and the fourth electrode 6 are connected, and the semiconductor layer 7 is electrically connected. Short-circuited and no longer functions as a transistor.

  Note that, when the angle of the substrate with respect to the vapor deposition direction is increased during oblique vapor deposition, the effect of preventing film formation on the side surface of the first electrode 2 due to the wraparound of the vapor deposition material increases, but on the other hand, the second electrode 4 The edge of the third electrode 5 on the first electrode 2 side is too far from the side surface of the first electrode 2, so that the controllability by the first electrode 2 that is the gate electrode is reduced, or the channel length is long. The characteristics of the TFT may be degraded. Therefore, the larger the angle of the material beam 9 is, the better. It is necessary to moderate the angle appropriately. The angle of the material beam 9 is preferably about θ to θ + 10 degrees. Moreover, in order to make the separation of the electrodes more reliable, short-time etching for the entire electrode may be used in combination after oblique deposition and patterning.

  As a method of making the second electrode 4, the third electrode 5 and the fourth electrode 6 into a predetermined shape in a plane as shown in FIG. 1A or 1C, a resist mask or a metal is used. Known methods such as a method using a mask and a method of processing by a photolithography method after forming a film once can be used.

  In the present embodiment, the second electrode 4 made of gold (Au) having a thickness of about 150 nm is formed by an evaporation method from an oblique direction (an angle between the material beam 9 and the substrate normal: 10 degrees) using a metal mask. Three electrodes 5 and a fourth electrode 6 were formed simultaneously.

  Next, as shown in FIG. 4E, a semiconductor layer 7 is formed on the second electrode 4, the third electrode 5, and the fourth electrode 6. The semiconductor layer 7 is in contact with the second electrode 4, the third electrode 5, and the fourth electrode 6, while being separated from the first electrode 2 by the insulating film 3. The material for forming the semiconductor layer 7 is formed by a known method such as a vapor deposition method, a sputtering method, a coating method, a spin coating method, or an ink jet printing method.

  When the semiconductor layer 7 is formed using a method having a high directivity for depositing a material such as a vapor deposition method, the film may be interrupted at the step of the first electrode 2. Therefore, it is desirable to perform evaporation from an oblique direction in view of making the semiconductor portion less likely to break. In this embodiment, specifically, pentacene was deposited from an angle of 45 degrees with respect to the normal direction of the substrate 1 to form the semiconductor layer 7 having a thickness of about 50 nm.

  The field effect transistor of this embodiment is completed through the above steps.

  Furthermore, in order to improve the reliability, the semiconductor layer 7 may be covered with a protective film 8 as shown in FIG. By doing so, when the semiconductor layer 7 is formed of an organic material or the like, deterioration due to outside air can be suppressed. For example, an inorganic material such as silicon oxide or silicon nitride may be used as the material of the protective film 8, and a material such as polyimide or polyparaxylylene may be used as the organic material.

<Load capacity of field effect transistor>
The effect of reducing the load capacitance of the signal line by reducing the parasitic capacitance in the field effect transistor of this embodiment will be described below in comparison with the conventional example shown in FIG.

  The main difference from the conventional example is that the electrode overlapping the first electrode 2 or 202 is the third electrode 205 or the fourth electrode 6. The capacitance formed by the overlap of the third electrode 205 and the first electrode 202 in one transistor is Cs, and the capacitance formed by the overlap of the fourth electrode 6 and the first electrode 2 in one transistor. Let the capacitance to be Ca be Ca.

  In the case of the present invention, since the fourth electrode 6 is not electrically connected to the signal line when the transistor is OFF, the capacitance Ca does not give a load capacitance to the signal line. The load capacitance is given to the signal line when the transistor is ON.

  Considering an active matrix type thin film transistor display panel, if the number of transistors connected to one signal line is n, one transistor is ON and the other n-1 transistors are OFF. ing.

Therefore, in the present invention, the load capacity per signal line is expressed by the following equation.

Csig1 = Ca + Cb
= Ε0 · ε · Sa / d + Cb (Formula 1)

(Ca: capacitance per transistor formed by overlapping the upper part of the first electrode 2 and the fourth electrode 6 of the transistor, Cb: signal line 1 formed by crossing with other wiring in a portion other than the transistor. Capacity per book, Sa: area where the fourth electrode 6 overlaps the first electrode 2 (per transistor), ε0: dielectric constant of vacuum (F / m), ε: relative dielectric constant of insulating film , D: thickness of insulating film (m))

In the case of the conventional example shown in FIG. 7, the capacitance Cs gives a load capacitance to the signal line regardless of the ON-OFF state of the transistor.
Therefore, in the conventional example, the load capacity per signal line is expressed by the following equation.

Csig2 = n ・ Cs + Cb
= N ・ ε0 ・ ε ・ Ss / d + Cb
= N · ε0 · ε · Ws · Wg / d + Cb (Formula 2)

(Ss: area where the third electrode 205 overlaps the first electrode 202, Ws: width (m) of the third electrode 205, Wg: width (m) of the first electrode 202)

An expression representing the difference ΔCsig in load capacity between the present invention and the reference example is as follows.

ΔCsig = Csig2−Csig1
= Ε0 · ε · (n · Ws · Wg−Sa) / d (Equation 3)

Since the potential of the signal line is switched most frequently, the reduction of the load capacity of the signal line is very effective for high speed operation.

When the transistor shown in FIGS. 1 and 2 is used as, for example, a QCIF ((176 × 144) pixel) active matrix thin film transistor display panel as the field effect transistor of the present invention, it is connected to one signal line. Since there are 144 transistors, the load on the signal line is improved by about 22 pF from the case of using the conventional field effect transistor shown in FIG. 3 and FIG. 7 from (Equation 3).
(Where ε0 = 8.854E ⁻¹² (F / m), ε = 7, n = 144, Ws = 5E ⁻⁵ (m), Wg = 1E ⁻⁵ (m), d = 2E ⁻⁷ (m ), Sa = 1.1E ^-9 (m ² ).

  In the field effect transistor of this embodiment, the channel length is defined by the height of the convex portion of the first electrode 2 formed on the substrate 1. The height of the convex portion is determined by the thickness of the film forming the first electrode 2. Therefore, the height of the convex portion is extremely small and precisely controlled as compared with the horizontal dimension. Therefore, the field effect transistor of the present embodiment can easily realize a transistor that can shorten the channel length and can operate at high speed.

  Since an organic material is used for the semiconductor layer 7, each electrode, and the insulating film 3, basically, film formation or processing is performed by a normal temperature process, so that energy consumption during manufacturing can be suppressed.

  Further, since an organic material is used, the element is manufactured by a simple and low-cost process such as coating or printing. In addition, since organic materials are generally highly flexible, it is possible to produce a flexible element.

  According to the manufacturing method of the field effect transistor of the present embodiment, the first electrode 2 corresponding to the gate electrode, the insulating film 3 corresponding to the gate insulating film, the second electrode 4 corresponding to the drain electrode or the source electrode, and the source After the third electrode 5 corresponding to the electrode or drain electrode is formed in a predetermined shape, the semiconductor layer 7 is formed. That is, in order to form the semiconductor layer 7 in a process after forming all the electrodes, when the semiconductor layer 7 is made of an organic material, heat and light during the formation and processing of each electrode and the insulating film 3 are used. In addition, it is possible to effectively avoid damage caused by chemical substances. In addition, since the organic material is generally difficult to process, the manufacturing method of the present embodiment in which processing is not performed after the semiconductor layer 7 is stacked is particularly effective.

  Further, according to the field effect transistor of the present embodiment, the second electrode 4, the third electrode 5, and the fourth electrode 6 can be formed in one step, so that the second electrode and the third electrode The process is simplified as compared with the conventional vertical transistor in which the electrodes are formed in a separate process.

As described above, a field effect transistor with high reliability, reduced parasitic capacitance, and excellent frequency characteristics is provided by a simplified manufacturing process.

As described above, the field effect transistor according to the present invention is used in various electronic devices such as IC cards, information processing devices, display devices, storage devices, and the like.

1 is a schematic perspective view, cross-sectional view, and top view showing a field effect transistor according to an embodiment of the present invention. It is a figure which shows the electrode dimension of the field effect transistor of embodiment of this invention. It is a figure which shows the electrode dimension of the conventional field effect transistor. It is a figure which shows the manufacturing process of the field effect transistor of embodiment of this invention. It is a figure which shows the diagonal vapor deposition in the electrode manufacturing process of the field effect transistor of embodiment of this invention. It is a schematic sectional drawing which shows the conventional field effect transistor. It is a schematic sectional drawing which shows the conventional field effect transistor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Substrate 2,102,202 ... 1st electrode, gate electrode 3,103,203 ... Insulating film 4,104,204 ... 2nd electrode, 2nd source / drain electrode 5,105,205 ... 3rd Electrode, third source / drain electrode 6, 106... Fourth electrode, first source / drain electrode 7, 107, 207... Semiconductor layer 8. Protective film 9.

Claims (5)

An insulating substrate;
A first electrode provided on the substrate and having a convex portion;
An insulating film covering an upper surface and a side surface of the convex portion;
Second and third electrodes provided on the substrate surface on one side surface of the convex portion;
A fourth electrode provided on the upper surface of the convex portion via the insulating film;
A semiconductor layer in contact with the second electrode, the third electrode, and the fourth electrode, and separated from the first electrode by the insulating film;
A field effect transistor comprising: The electrical conduction state or the electrical non-passage state between the second electrode and the third electrode can be switched by the potential of the first electrode. Field effect transistor. The field effect transistor according to claim 1, wherein the semiconductor layer is made of an organic semiconductor material. Forming a first electrode having a protrusion on an insulating substrate;
Forming an insulating film so as to cover an upper surface and a side surface of the convex portion;
Forming second and third electrodes on the substrate surface on one side of the convex portion;
Forming a fourth electrode on the upper surface of the convex portion via the insulating film;
Forming in contact with the second electrode, the third electrode, and the fourth electrode, and forming a semiconductor layer on the first electrode through the insulating film;
A method of manufacturing a field effect transistor comprising: 5. The method of manufacturing a field effect transistor according to claim 4, wherein the second, third and fourth electrodes are formed in the same film forming step.

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