U.S. patent application number 10/835493 was filed with the patent office on 2004-10-14 for organic thin-film semiconductor element and manufacturing method for the same.
This patent application is currently assigned to KONICA CORPORATION. Invention is credited to Eguchi, Toshiya, Funayama, Satoshi, Hirai, Katsura, Yamamoto, Naoto.
Application Number | 20040201064 10/835493 |
Document ID | / |
Family ID | 19094961 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040201064 |
Kind Code |
A1 |
Hirai, Katsura ; et
al. |
October 14, 2004 |
Organic thin-film semiconductor element and manufacturing method
for the same
Abstract
There is described an organic thin-film transistor including an
active layer made of organic semiconductor and a manufacturing
method for the organic thin-film transistor. In particular, the
invention concerns an organic thin-film transistor capable of being
formed on a flexible base board made of a polymer material and a
manufacturing method for the same. The organic semiconductor
device, includes a drain electrode; a source electrode; a gate
electrode; a channel that is made of an organic semiconductor
material and is disposed between the drain electrode and the source
electrode; and an insulation film that is disposed between the gate
electrode and the channel; wherein the insulation film is formed
under an atmospheric pressure environment by employing a plasma
processing.
Inventors: |
Hirai, Katsura; (Tokyo,
JP) ; Funayama, Satoshi; (Tokyo, JP) ; Eguchi,
Toshiya; (Tokyo, JP) ; Yamamoto, Naoto;
(Tokyo, JP) |
Correspondence
Address: |
FRISHAUF, HOLTZ, GOODMAN & CHICK, PC
767 THIRD AVENUE
25TH FLOOR
NEW YORK
NY
10017-2023
US
|
Assignee: |
KONICA CORPORATION
Tokyo
JP
|
Family ID: |
19094961 |
Appl. No.: |
10/835493 |
Filed: |
April 28, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10835493 |
Apr 28, 2004 |
|
|
|
10230791 |
Aug 29, 2002 |
|
|
|
Current U.S.
Class: |
257/347 ; 257/40;
257/E21.279; 438/149 |
Current CPC
Class: |
C23C 16/545 20130101;
H01L 51/0545 20130101; C23C 16/509 20130101; H01L 21/31612
20130101; H01L 51/0541 20130101; H01L 27/3244 20130101; H01L
27/3274 20130101; H01L 51/0036 20130101; H01L 21/02164
20130101 |
Class at
Publication: |
257/347 ;
438/149; 257/040 |
International
Class: |
H01L 021/84; H01L
031/0392 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 5, 2001 |
JP |
269082/2001 |
Claims
What is claimed is:
1. An organic semiconductor device, comprising: a drain electrode;
a source electrode; a gate electrode; a channel that is made of an
organic semiconductor material and is disposed between said drain
electrode and said source electrode; and an insulation film that is
disposed between said gate electrode and said channel; wherein said
insulation film is formed under an atmospheric pressure environment
by employing a plasma processing.
2. The organic semiconductor device of claim 1, wherein said
insulation film comprises either oxide compounds or nitride
compounds.
3. The organic semiconductor device of claim 2, wherein said
insulation film comprises anyone of silicon oxide, aluminum oxide,
tantalum oxide and titanium oxide.
4. The organic semiconductor device of claim 2, wherein said
insulation film comprises silicon nitride.
5. The organic semiconductor device of claim 1, wherein said
organic semiconductor material is .pi.-conjugated polymers.
6. The organic semiconductor device of claim 1, wherein said
organic semiconductor device is fabricated on a supporting
substrate; and wherein said supporting substrate is a sheet made of
a resin material.
7. The organic semiconductor device of claim 6, wherein said sheet
is a plastic film.
8. The organic semiconductor device of claim 1, wherein said
organic semiconductor device is fabricated on a supporting
substrate; and wherein said supporting substrate is made of
polymers.
9. The organic semiconductor device of claim 1, wherein said
organic semiconductor device is fabricated on a supporting
substrate; and wherein sections of said organic semiconductor
device are formed in an order of said channel, said insulation film
and said gate electrode.
10. The organic semiconductor device of claim 1, wherein said
organic semiconductor device is a transistor.
11. A display panel for displaying an image, comprising: a
supporting substrate; and a plurality of organic semiconductor
devices formed on said supporting substrate; wherein each of said
plurality of organic semiconductor devices comprises: a drain
electrode; a source electrode; a gate electrode; a channel that is
made of an organic semiconductor material and is disposed between
said drain electrode and said source electrode; and an insulation
film that is disposed between said gate electrode and said channel;
wherein said insulation film is formed under an atmospheric
pressure environment by employing a plasma processing.
Description
[0001] This application is a Divisional Application of application
Ser. No. 10/230,791 filed Aug. 29, 2002 (now allowed).
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an organic thin-film
transistor including an active layer made of organic semiconductor
and to a manufacturing method for the organic thin-film transistor.
In particular, the invention relates to an organic thin-film
transistor capable of being formed on a flexible base board made of
a polymer material and a manufacturing method for the same.
[0003] With the spread of information terminals, there are
increasing demands for a flat panel display that serves as a
display for a computer. Further, with development of the
information technology, there has been increased a chance for
information offered in a form of a sheet of paper medium in the
past to be offered in an electronic form. An electronic paper or a
digital paper is demanded increasingly as a display medium for a
mobile that is thin, lightweight and handy.
[0004] In the case of a display device of a flat sheet type, a
display medium is generally formed by using an element that employs
a liquid crystal, organic EL or electrophoretic method. In the
display medium of this kind, a technology for using an active
driving element (TFT element), serving as an image displaying
element, is the main current for ensuring uniformity of screen
brightness and a screen rewriting speed. For example, in the case
of an ordinary computer display, a TFT element is formed on a glass
base board, and a liquid crystal or organic EL is sealed.
[0005] In this case, a semiconductor such as a-Si (amorphous
silicone) or p-Si (poly-silicone) can mainly be used for the TFT
element, and these Si semiconductors (including also a metal film
if necessary) are multi-layered, and source, drain and gate
electrodes are formed on the base board in succession to
manufacture the TFT element. The manufacture of the TFT element of
this kind usually requires a process of sputtering and other
manufacture process of a vacuum system.
[0006] On the other hand, recently, organic materials are studied
to be used as an active semi-conductive layer in a thin-film
transistor (TFT). Since the organic materials can be easily
processed, and they have high affinity with a plastic base board on
which TFT is formed generally, they are expected to be used as an
active semi-conductive layer in a thin-film transistor. Therefore,
they are studied as a low cost device having a large area,
especially as an active driving element for a display, and there
have been disclosed technologies in, for example, TOKKAIHEI No.
10-190001 and TOKKAI No. 2000-307172. In order for the organic
semiconductor to be used as an active semiconductive layer in a
thin-film TFT, conditions such as an ON/OFF ratio, leakage current,
driving voltage of a gate of a device and insulation durability of
the gate insulation layer, obtained as final result, need to be
satisfied sufficiently.
[0007] However, in the manufacture of the TFT element of this kind,
a manufacturing process of a vacuum system including a vacuum
chamber needs to be repeated time after time to form various
layers, resulting in a large amount of money in facility cost and
running cost. For example, in the case of the TFT element shown in
FIG. 9, steps of vacuum deposition, doping, photolithography and
development need to be repeated time after time for forming various
layers, and an element is formed on the base board through several
tens of steps. Even for the semiconductor portions representing a
vital point of switching operations, semiconductor layers in plural
types such as a p-type and an n-type are laminated.
[0008] In the conventional manufacturing method employing a
Si-semiconductor, drastic design changes in manufacturing apparatus
such as vacuum chambers are required for the needs of large-sized
display screens, and changes in apparatus are not easy.
[0009] Even in the case of a gate-insulating film of a transistor,
it has been formed generally with a film of silicone oxide obtained
through thermal oxidation of a silicone base board, or with a thin
film of oxide obtained through a dry process such as a sputtering
method, thus, formation of an insulating film had to rely on the
conventional method even when using organic materials as an active
semiconductor layer in TFT.
[0010] However, in order for the organic semiconductor to be used
as an active semi-conductive layer in a thin-film TFT, conditions
such as an ON/OFF ratio, leakage current and driving voltage of a
gate of a device obtained finally need to be satisfied
sufficiently. A practical method for realizing the aforementioned
characteristics has not been found sufficiently.
SUMMARY OF THE INVENTION
[0011] To overcome the abovementioned drawbacks in conventional
organic semiconductor devices, it is an object of the present
invention to improve characteristics of organic semiconductor
devices and thereby to realize reduction of manufacturing cost and
simplification of manufacturing process.
[0012] Accordingly, to overcome the cited shortcomings, the
abovementioned object of the present invention can be attained by
organic semiconductor devices and methods described as follow.
[0013] (1) An organic semiconductor device, comprising: a drain
electrode; a source electrode; a gate electrode; a channel that is
made of an organic semiconductor material and is disposed between
the drain electrode and the source electrode; and an insulation
film that is disposed between the gate electrode and the channel;
wherein the insulation film is formed under an atmospheric pressure
environment by employing a plasma processing.
[0014] (2) The organic semiconductor device of item 1, wherein the
insulation film comprises either oxide compounds or nitride
compounds.
[0015] (3) The organic semiconductor device of item 2, wherein the
insulation film comprises anyone of silicon oxide, aluminum oxide,
tantalum oxide and titanium oxide.
[0016] (4) The organic semiconductor device of item 2, wherein the
insulation film comprises silicon nitride.
[0017] (5) The organic semiconductor device of item 1, wherein the
organic semiconductor material is .pi.-conjugated polymers.
[0018] (6) The organic semiconductor device of item 1, wherein the
organic semiconductor device is fabricated on a supporting
substrate; and wherein the supporting substrate is a sheet made of
a resin material.
[0019] (7) The organic semiconductor device of item 6, wherein the
sheet is a plastic film.
[0020] (8) The organic semiconductor device of item 1, wherein the
organic semiconductor device is fabricated on a supporting
substrate; and wherein the supporting substrate is made of
polymers.
[0021] (9) The organic semiconductor device of item 1, wherein the
organic semiconductor device is fabricated on a supporting
substrate; and wherein sections of the organic semiconductor device
are formed in an order of the channel, the insulation film and the
gate electrode.
[0022] (10) The organic semiconductor device of item 1, wherein the
organic semiconductor device is a transistor.
[0023] (11) A method for manufacturing an organic semiconductor
device, which includes a drain electrode, a source electrode and a
gate electrode, comprising the steps of: forming a channel between
the drain electrode and-the source electrode with an organic
semiconductor material; and forming an insulation film, disposed
between a gate and the channel, under an atmospheric pressure
environment by employing a plasma processing.
[0024] (12) The method of item 11, wherein a reactive gas is exited
into plasma by a discharging operation under a pressure equivalent
or nearly equivalent to an atmospheric pressure to form the
insulation film.
[0025] (13) The method of item 11, wherein the organic
semiconductor device is fabricated on a supporting substrate; and
wherein, after the source electrode and the drain electrode are
formed on the supporting substrate, a field-effect active layer,
made of the organic semiconductor material, is fabricated between
them as the channel, and then, the insulation film and the gate
electrode are successively formed on the field-effect active
layer.
[0026] (14) The method of item 11, wherein the organic
semiconductor device is fabricated on a supporting substrate; and
wherein, after the gate electrode is formed on the supporting
substrate, the insulation film is formed so as to cover the gate
electrode, and then, the source electrode, the drain electrode and
a field-effect active layer, serving as the channel and made of the
organic semiconductor material, are successively formed on the
insulation film.
[0027] (15) The method of item 11, wherein the insulation film
comprises either oxide compounds or nitride compounds.
[0028] (16) The method of item 15, wherein the insulation film
comprises anyone of silicon oxide, aluminum oxide, tantalum oxide
and titanium oxide.
[0029] (17) The method of item 15, wherein the insulation film
comprises silicon nitride.
[0030] (18) The method of item 11, wherein the organic
semiconductor material is .pi.-conjugated polymers.
[0031] (19) The method of item 11, wherein the organic
semiconductor device is fabricated on a supporting substrate; and
wherein the supporting substrate is a sheet made of a resin
material.
[0032] (20) The method of item 19, wherein the sheet is a plastic
film.
[0033] (21) The method of item 11, wherein the organic
semiconductor device is fabricated on a supporting substrate; and
wherein the supporting substrate is made of polymers.
[0034] (22) The method of item 11, wherein the organic
semiconductor device is fabricated on a supporting substrate; and
further comprising the steps of: forming the source electrode and
the drain electrode on the supporting substrate forming the gate
electrode on the insulation film.
[0035] (23) The method of item 11, wherein the organic
semiconductor device is a transistor.
[0036] (24) A display panel for displaying an image, comprising: a
supporting substrate; and a plurality of organic semiconductor
devices formed on the supporting substrate; wherein each of the
plurality of organic semiconductor devices comprises: a drain
electrode; a source electrode; a gate electrode; a channel that is
made of an organic semiconductor material and is disposed between
the drain electrode and the source electrode; and an insulation
film that is disposed between the gate electrode and the channel;
wherein the insulation film is formed under an atmospheric pressure
environment by employing a plasma processing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Other objects and advantages of the present invention will
become apparent upon reading the following detailed description and
upon reference to the drawings in which:
[0038] FIG. 1(a), FIG. 1(b), FIG. 1(c), FIG. 1(d), FIG. 1(e) and
FIG. 1(f) show exemplified structures of the organic semiconductor
devices in each of which the gate electrode is arranged to be above
the organic semiconductor layer on the supporting substrate;
[0039] FIG. 2 is a block diagram showing the overall structure of a
display panel of the invention;
[0040] FIG. 3 is a schematic diagram showing a sectional view of
each pixel in FIG. 2;
[0041] FIG. 4 is a diagram showing an equivalent circuit of each
pixel;
[0042] FIG. 5 is a diagram for showing practical arrangement of
each member in the invention, and it is a diagram corresponding to
a sectional view on line X in FIG. 2;
[0043] FIG. 6 is a diagram showing a capacitor structure in each
pixel of the invention;
[0044] FIG. 7(A), FIG. 7(B), FIG. 7(C) and FIG. 7(D) are diagrams
showing patterning processes of each element material in the first
embodiment of the invention;
[0045] FIG. 8(A) and FIG. 8(B) are diagrams showing occasions where
display materials are sealed in the third embodiment of the
invention;
[0046] FIG. 9 is a diagram showing how conventional TFT elements
each using Si semiconductor are formed on the display panel base
board;
[0047] FIG. 10 is a diagram showing a system for evaluating
transistor characteristics; and
[0048] FIG. 11 is a diagram showing an apparatus conducting plasma
film forming processing.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0049] An embodiment of the invention will be explained in detail
as follows.
[0050] On a Si-semiconductor material used for an ordinary
switching element, there is formed a channel by combining a gate
electrode with a source section and a drain section, and ON and OFF
of an electric current is controlled between the source section and
the drain section. However, the ordinary semiconductor material
mentioned above requires facilities for sputtering or vacuum
deposition.
[0051] On the other hand, elements of the invention are arranged as
shown in FIG. 1, for example. Namely, the elements are composed of
gate electrode G, gate insulating film I, active layer by an
organic semiconductor P, source electrode S and drain electrode D.
Each of FIGS. 1(a), 1(b) and 1(c) is an example wherein the gate
electrode is arranged to be above the organic semiconductor layer
on the supporting substrate (hereinafter referred to as "the
support" for simplicity), and FIG. 1(a) represents an example
wherein the organic semiconductor layer is arranged between the
source electrode and the drain electrode to connect them, FIG. 1(b)
represents an example wherein the organic semiconductor layer is
arranged to stretch over the source electrode and the drain
electrode to cover them and FIG. 1(c) represents an example wherein
the organic semiconductor layer is arranged to stretch under the
source electrode and the drain electrode to connect them.
[0052] Each of FIGS. 1(d), 1(e) and 1(f) is an example wherein the
organic semiconductor layer is arranged to be above the gate
electrode on the support. Arrangements of FIGS. 1(d), 1(e) and 1(f)
in arrangements of the organic semiconductor layer for the source
electrode and the drain electrode correspond to the aforesaid
arrangements of FIGS. 1(a), 1(b) and 1(c), and FIG. 1(a) represents
an example wherein the organic semiconductor layer is arranged
between the source electrode and the drain electrode to connect
them, FIG. 1(b) represents an example wherein the organic
semiconductor layer is arranged to stretch over the source
electrode and the drain electrode to cover them and FIG. 1(c)
represents an example wherein the organic semiconductor layer is
arranged to stretch under the source electrode and the drain
electrode to connect them.
[0053] On the other hand, in organic materials, especially in
organic semiconductor materials, there have been found some which
exhibit specific behavior, but the same arrangement can be taken as
arrangement of elements.
[0054] For the mounting of elements appropriate to materials for
the elements whose materials are organic semiconductor materials,
or for application to a display panel, it is difficult to mention
at this stage that a sufficient mounting method is established.
[0055] Structures, materials and processes for each member will be
explained as follows.
[0056] <Organic Semiconductor Layer>
[0057] Preferably employed as organic semiconductors are
.pi.-conjugated polymers. For example, employed may be polypyrroles
such as polypyrrole, poly(N-substituted pyrrole),
poly(3-substituted pyrrole), and poly(3,4-disubstituted pyrrole);
polythiophenes such as polythiophene, poly(3-substituted
thiophene), poly(3,4-disubstituted thiophene), and
polybenzothiophene; polyisothianaphthenes such as
polyisothianaphthene; polythienylenevinylenes such as
polythienylenevinylene; poly(p-phenylenevinylenes) such as
poly(p-phenylenevinylene); polyanilines such as polyaniline,
poly(N-substituted aniline), poly(3-substituted aniline), and
poly(2,3-substituted aniline); polyacetylnenes such as
polyacetylene; polydiacetylens such as polydiacetylene;
polyazulenes such as polyazulene; polypyrenes such as polypyrene;
polycarbazoles such as polycarbazole and poly(N-substituted
carbazole), polyselenophenes such as polyselenophene; polyfurans
such as polyfuran and polybenzofuran; poly(p-phenylens) such as
poly(p-phenylene); polyindoles such as polyindole; polypyridazines
such as polypyridazine; polyacenes such as naphthacene, pentacene,
hexacene, heptacene, dibenzopentacene, tertabenzopentacene, pyrene,
dibenzopyrene, chrysene, perylene, coronene, Terylene, ovalene,
quoterylene, and circumanthracene; derivatives (such as
triphenodioxazine, triphenodithiazine, hexacene-6,15-quinone) which
are prepared by substituting some of carbon atoms of polyacens with
atoms such as N, S, and O, or a functional group such as a carbonyl
group; polymers such as polyvinylcarbazoles, polyphenylenesulfide,
and polyvinylenesulfide; and polycyclic condensation products
described in Japanese Patent Publication Open to Public Inspection
No. 11-195790. Further preferably employed may be oligomers having
the same repeating units as said polymers such as thiophene
hexamers including .alpha.-sexithiophene .alpha.,
.omega.-dihexyl-.alpha.-sexithiophene, .alpha.,
.omega.-dihexyl-.alpha.-q- uiinquethiophene, .alpha.,
.omega.-bis(3-butoxypropyl)-.alpha.-sexithiophe- ne, and
styrylbenzene derivatives. Further, listed are metal
phthalocyanines such as copper phthalocyanine, and
fluorine-substituted copper phthalocyanines, described in Japanese
Patent Publication Open to Public Inspection No. 11-251601;
condensed cyclic tetracarboxylic acid diimides including
naphthalenetetracarboxylic acid imides such as
1,4,5,8-teracarboxylic acid diimide,
N,N'-bis(4-trifluoromethylbenzyl)nap-
hthalene-1,4,5,8-tretracarboxylic acid diimide, as well as
naphthalenetetracarboxylic acid diimides such as
N,N'-bis(1H,1H-perfluoro- ctyl), N,N'-bis(1H,1H-perfluorobutyl) and
N,N'-dioctylnaphthalenel,4,5,8-t- etracarboxylic acid diimide
derivatives, naphthalenetetracarboxylic acid diimides such as
naphthalene-2,3,6,7-tetracarboxylic acid diimides;
anthracenetetracarbocylic acid diimides such as
anthracene-2,3,6,7-tetrac- arboxylic acid diimides; fullerenes such
as C.sub.60, C.sub.70, C.sub.76, C.sub.78, and C.sub.84; carbon
nanotube such as SWNT; and dyes such as merocyanines and
hemicyanines.
[0058] Of said .pi. conjugated compounds, preferably employed is at
least one selected from the group consisting of thiophene,
vinylene, thienylenevinylene, phenylenevinylene, p-phenylene,
substitution products thereof, oligomers which have at least two of
these as a repeating unit and have the number n of repeating units
of 4 to 10 or polymers which have the number n of said repeating
units of at least 20, condensed polycyclic aromatic compounds such
as pentacene, fullerenes, condensed cyclic tetracarboxylic acid
diimides, and metal phthalocyanines.
[0059] Further, employed as other organic semiconductors may be
organic molecular complexes such as a tetrathiafulvalene
(TTF)-tetracyanoquinodim- ethane (TCNQ) complex, a
bisethylenetetrathiafulvalene (BEDTTTF)-perchloric acid complex, a
BEDTTTF-iodine complex, and a TCNQ-iodine complex. Still further,
employed may be .sigma. conjugated system polymers such as
polysilane and polygermane, as well as organic-inorganic composite
materials described in Japanese Patent Publication Open to Public
Inspection No. 2000-260999.
[0060] In the present invention, the organic semiconductor layer
may be subjected to a so-called doping treatment by incorporating
in said layer, for example, acrylic acid, acetamide, materials
having a functional group such as a dimethylamino group, a cyano
group, a carboxyl group and a nitro group, materials such as
benzoquinone derivatives, and tetracyanoethylene as well as
tetracyanoquinodimethane, and derivatives thereof, which work as an
acceptor which accepts electrons, or, for example, materials having
a functional group such as an amino group, a triphenyl group, an
alkyl group, a hydroxyl group, an alkoxy group, and a phenyl group;
substituted amines such as phenylenediamine; anthracene,
benzoanthracene, substituted benzoanthracenes, pyrene, substituted
pyrene, carbazole and derivatives thereof, and tetrathiafulvalene
and derivatives thereof, which work as a donor which is an electron
donor.
[0061] The doping, as described herein, means that electron
accepting molecules (acceptors) or electron donating molecules
(donors) are incorporated in said thin film employing doping.
Accordingly, the thin film, which has been subjected to said
doping, is one which comprises said condensed polycyclic aromatic
compounds as well as dopants. Employed as dopants used in the
present invention may be either acceptors or donors. Listed as said
acceptors may be halogens such as Cl.sub.2, Br.sub.2, I.sub.2, ICl,
ICl.sub.3, IBr, and IF; Lewis acids such as PF.sub.5, AsF.sub.5,
SbF.sub.5, BF.sub.3, BCl.sub.3, BBr.sub.3, and SO.sub.3; protonic
acids such as HF, HCl, HNO.sub.3, H.sub.2SO.sub.4, HCIO.sub.4,
FSO.sub.3H, ClSO.sub.3H, and CF.sub.3SO.sub.3H; organic acids such
as acetic acid, formic acid, and amino acid; transition metal
compounds such as FeCl.sub.3, FeOCl, TiCl.sub.4, ZrCl.sub.4,
HfCl.sub.4, NbF.sub.5, NbF.sub.5, NbCl.sub.5, TaCl.sub.5,
MoCl.sub.5, WF.sub.5, WCl.sub.5, UF.sub.6, LnCl.sub.3
(Ln=lanthanoid such as La, Ce, Nd, and Pr, and Y), and electrolyte
anions such as Cl.sup.-, Br.sup.-, I.sup.-, ClO.sup.4-, PF.sup.6-,
AsF.sup.5-, SbF.sup.6-, BF.sup.4-, and a sulfonate anion. Further,
listed as donors may be alkaline metals such as Li, Na, K, Rb, and
Cs; alkaline earth metals such as Ca, Sr, and Ba; rare earth metals
such as Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, and Yb; an
ammonium ion; R.sub.4P.sup.+, R.sub.4AS.sup.+, and R.sub.3S.sup.+;
and acetylcholine. Doping these dopants may be carried out
employing either a method in which a thin organic semiconductor
film is prepared and subsequently, said dopants are incorporated,
or a method in which dopants are incorporated during preparation of
a thin semiconductor film. Listed as former methods may be a gas
phase doping in which gaseous dopants are employed, and a liquid
phase doping in which doping is carried out while said thin film
comes into contact with a dopant solution or liquid dopants.
Further, in said liquid phase doping, it is possible to adjust the
doping efficiency utilizing electrolysis. In the latter methods,
either a solution or a dispersion, consisting of organic
semiconductors and dopants, may be coated and subsequently dried.
For instance, when a vacuum deposition method is used, dopants may
be incorporated by achieving co-deposition of semiconductor
compounds together with dopants. Further, when a thin film is
prepared employing a sputtering method, dopants may be incorporated
in said thin film through sputtering, utilizing the two-dimensional
target of said organic semiconductors and said dopants. Still
further, as other methods, it is possible to use any of the
chemical doping such as electrochemical doping or photoinitiation
doping, or the physical doping such as an ion injection method
shown in, for example, a publication "Kogyo Jairyo (Industrial
Materials)", Volume 34, No. 4, page 55 (1986).
[0062] Listed as methods for preparing said thin organic films are
a vacuum deposition method, a molecular beam epitaxial growth
method, an ion cluster beam method, a low energy ion beam method,
an ion plating method, a CVD method, a sputtering method, a plasma
polymerization method, an electrolytic polymerization method, a
chemical polymerization method, a spray coating method, a spin
coating method, a blade coating method, a dip coating method, a
casting method, a roll coating method, an bar coating method, a die
coating method, and an LB method, which may be employed based on
materials. However, of these, from the viewpoint of productivity, a
spin coating method, a blade coating method, a dip coating method,
a roll coating method, a bar coating method, and a die coating
method are preferred which can simply and accurately form a thin
film employing an organic semiconductor solution. The thickness of
the thin film comprised of said organic semiconductors is not
particularly limited. However, since the characteristics of the
resultant transistors often vary depending on the thickness of the
active layer comprised of organic semiconductors, the thickness
varies depending on the organic semiconductors, but is commonly at
most 1 .mu.m, and is preferably from 10 to 300 nm.
[0063] <Electrodes (Source, Drain, and Gate Electrodes)>
[0064] Materials for constituting the gate, source, and drain
electrodes are not particularly restricted as long as they are
electrically conductive materials. Employed as materials are
platinum, gold, silver, nickel, chromium, copper, iron, tin,
antimony, lead, tantalum, indium, palladium, tellurium, rhenium,
iridium, aluminum, ruthenium, germanium, molybdenum, tungsten, tin
oxide-antimony, indium oxide-tin (ITO), fluorine-doped zinc oxide,
zinc, carbon, graphite, glassy carbon, silver paste as well as
carbon paste, lithium, beryllium, sodium, magnesium, potassium,
calcium, scandium, titanium, manganese, zirconium, gallium,
niobium, sodium, sodium-potassium alloy, magnesium, lithium,
aluminum magnesium/copper mixtures, magnesium/silver mixtures,
magnesium/aluminum mixtures, magnesium/indium mixtures,
aluminum/aluminum oxide mixtures, and lithium/aluminum mixtures. Of
theses, specifically preferred are platinum, gold, silver, copper,
aluminum, indium, ITO, and carbon. Alternatively, suitably employed
are electrically conductive polymers, known in the art, such as
electrically conductive polyaniline, electrically conductive
polypyrrole, electrically conductive polythiophene, and complexes
of polyethylenedioxythiophene and polystyrnesulfonic acid which
increase electrical conductivity upon being doped.
[0065] Methods for forming electrodes include a method in which an
electrode is prepared in such a manner that a photolithographic
method or a lift-off method, known in the art, is applied to
electrically conductive layer, which has been formed employing a
vacuum evaporation or sputtering method while employing the
aforesaid compounds as a raw material, and a method in which
etching is conducted employing a resist which has been prepared
employing thermal transfer or ink jet printing onto a foil of metal
such as aluminum or copper. Further, an electrically conductive
polymer solution or dispersion, or a minute electrically conductive
particle dispersion may be subjected directly to patterning,
employing ink jet printing. Said electrode may also be formed in
such a manner that a coated layer is subjected to lithograph or
laser ablation. In addition, a method may also be employed in which
ink comprising either an electrically conductive polymer or minute
electrically conductive particles, or electrically conductive paste
is subjected to patterning, employing any of the printing methods
such as letter press, intaglio printing, lithography, or screen
printing.
[0066] An electrode is employed which is formed by thermally fusing
minute metal particles, having a diameter of 1 to 50 nm, and
preferably having a diameter of 1 to 10 nm. Employed as metals may
be platinum, gold, silver, nickel, chromium, copper, iron, tin,
tantalum, indium, cobalt, palladium, tellurium, rhenium, iridium,
aluminum, ruthenium, germanium, molybdenum, tungsten, and zinc. Of
these, particularly preferred are platinum, gold, silver, copper,
cobalt, chromium, iridium, nickel, palladium, molybdenum, and
tungsten, which have a work function of at least 4.5 eV.
[0067] Listed as said minute electrically conductive particles,
having a diameter of 1 to 50 nm and preferably having from 1 to 10
nm, are minute particles of metals such as platinum, gold, silver,
copper, cobalt, chromium, iridium, nickel, palladium, molybdenum,
and tungsten. Cited as production methods of such minute metal
particle suspension are physical preparation methods such as an
in-gas evaporation method, a sputtering method, and a metal vapor
synthesis method, and chemical preparation methods such as a
colloid method and a coprecipitation method in which metal ions are
reduced in a liquid phase so that minute metal particles are
formed. Of these, preferred are dispersions which are prepared
using the colloid methods described in Japanese Patent Publication
Open to Public Inspection Nos. 11-76800, 11-80647, 319538, and
2000-239853 and the in-gas evaporation method described in Japanese
Patent Publication Open to Public Inspection Nos. 2001-254185,
2001-53028, 2001-35814, 2001-35255, 2000-124157, and 2000-123634.
After coating these dispersions and molding the resultant coating
to an electrode-patterned shape, solvents are vaporized. The
resultant is further subjected to a thermal treatment at 100 to
300.degree. C. and preferably at 150 to 200.degree. C., whereby an
electrode is formed by thermally fusing said minute metal
particles.
[0068] Incidentally, the gate line as well as the source line may
be formed in the same manner as said electrode.
[0069] <Gate Insulation Layer>
[0070] Various insulation layers may be employed. Of these, layers,
which are comprised of silicon-oxide, silicon nitride, aluminum
oxide, tantalum oxide, or titanium oxide, are particularly
preferred. In the present invention, said insulation layer is
specifically formed under an atmospheric pressure, employing a
plasma layer forming process.
[0071] i) Plasma Film Forming Processing Under the Atmospheric
Pressure
[0072] A forming method of an insulating film (for example, oxide:
SiO.sub.2, TiO.sub.2 etc./nitride: Si.sub.3N.sub.4 etc.) by Plasma
film forming processing under the atmospheric pressure is explained
as follows.
[0073] The plasma film forming processing under the atmospheric
pressure means a processing wherein a reactive gas is
plasma-excited by discharge conducted under the atmospheric
pressure or the pressure near the atmospheric pressure and a thin
film is formed on the element b material, and its method is
described in TOKKAIHEI No. 11-133205, TOKKAI No. 2000-185362,
TOKKAIHEI No. 11-61406 and TOKKAI Nos. 2000-147209 and 2000-121804
(hereinafter referred to also as an atmospheric pressure plasma
method). Owing to this, it is possible to form thin films with high
functions in the high productivity.
[0074] FIG. 11 is a diagram showing an apparatus conducting plasma
film forming processing. In FIG. 11, there are arranged plasma
discharge processing container 31, gas generating device 51, power
supply 41, and electrode cooling unit 60, as the constitution of
the apparatus. As a cooling agent for the electrode cooling unit
60, insulating materials such as distilled water and oil are
used.
[0075] In the plasma discharge processing container 31, roll
electrode 25 and fixed electrode 36 are arranged at prescribed
positions, and a mixed gas generated by the gas generating device
51 is controlled in terms of a flow rate to be put in the plasma
discharge processing container 31 from air inlet 52, and a mixed
gas to be used for plasma processing is filled in the plasma
discharge processing container 31, to be exhausted from air outlet
53. Next, voltage is impressed on the electrode 36 by power supply
41, and the roll electrode 25 is grounded on the ground to generate
discharge plasma. In this case, base material F is supplied by
roll-shaped mater roll base-material 61, and base material F wound
around the roll electrode 25 through guide roller 64 is pressed by
nip rollers 65 and 66 and is conveyed through the gap between both
electrodes in the plasma discharge processing container 31 under
the state of one-sided contact (contacting roll electrode 25),
thus, the surface of the base material F is discharge-processed by
discharge plasma, and after that, it is conveyed to the next
process through guide roller 67. In this case, the surface of the
base material F that does not contact the electrode 25 only is
discharge-processed.
[0076] Further, partitioning plate 54 is arranged to be close to
the nip rollers 65 and 66, and it controls approach of air that
enters the plasma discharge processing container 31.
[0077] Roll electrode 25, serving as a ground electrode, is
composed of a combination wherein ceramic sealing processed
dielectric made by sealing conductive base material such as metal
by using inorganic material after injecting melted ceramic. Or, it
may also be a combination wherein lining processed dielectric, in
which inorganic material is provided on conductive base material by
lining, is covered. As a lining material, there are preferably used
silicate type glass, borate type glass, phosphate type:glass,
germanate type glass, tellurite type glass, aluminate type glass
and vanadate type glass, and among these, borate type glass is used
more preferably because it is easy to be processed. As a conductive
base material such as metal, there are given metals such as silver,
platinum, stainless steel, aluminum and iron, and stainless steel
is preferable from the viewpoint of processing. As a ceramic
material used for the melted ceramic injection process, alumina,
silicon nitride, etc. are preferably used, and among these, alumina
is used more preferably because processing is easy. As base
material of roll electrode, it is possible to use a base material
of jacket roll that made of stainless steel and has a cooling means
by cooled water (not shown in the drawings).
[0078] As power supply 41 applying voltage on impression electrode
36, the high frequency power supply made by Pearl Industry (200
kHz), the high frequency power supply made by Pearl Industry (800
kHz), the high frequency power supply made by Nihon Denshi (13.56
MHz) and high frequency power supply made by Pearl Industry (150
MHz), etc. can be employed for this purpose, though there is no
limitation for that in particular.
[0079] A distance between the impression electrodes mentioned above
is determined by considering a thickness of solid-state dielectric
provided on the base material of the electrode, an amplitude of the
voltage to be applied, an object for employing plasma, etc. As a
shortest distance between the solid dielectric on the occasion
where the solid dielectric is provided on one of the electrodes and
the electrode and a distance between solid dielectrics in the case
of arranging the solid dielectrics both of the aforesaid
electrodes, it is preferable that both of them are 0.5-20 mm from
the viewpoint of conducting even discharging, and especially
preferably is 1 mm.+-.0.5 mm.
[0080] To the electrodes facing each other, there are given powers
of 1W/cm2 or more at the high frequency wave voltage exceeding 100
kHz, and plasma is generated by exiting reactive gas. By applying
the electric field of such high power, it is possible to obtain a
densely thin-film which has high uniformity of film thickness and
has high functional properties, at high productivity.
[0081] An upper limit value of the frequency of the high frequency
voltage to be applied onto the space between both electrodes is
preferably 150 MHz or less. A lower limit value of the frequency of
the high frequency voltage is preferably 200 kHz or more, and more
preferable is 800 kHz or more.
[0082] A lower limit value of power to be supplied between the
electrodes is preferably 1.2 W/cm2 or more, and an upper limit
value is preferably 50 W/cm2 or less, and more preferable is 20
W/cm2 kHz or less. Incidentally, an area (/cm2) for impression of
voltage on the electrode means an area of a range where electric
discharge occurs.
[0083] A value of voltage to be applied onto electrode 36 fixed by
power supply 41 is determined appropriately. Incidentally, with
regard to a method of impression of power supply, it is possible to
employ any of the continuous oscillation mode in the continuous
sine wave form that is called a continuous mode, and the
intermittent oscillation mode conducting ON/OFF intermittently that
is called a pulse mode, but a densely film having excellent quality
can be obtained by the continuous mode.
[0084] To control an influence of plasma processing on the base
material to be minimum, it is preferable to control the temperature
of the base material to be in the range from ordinary temperature
(15.degree. C.-25.degree. C.)-200.degree. C., and the more
preferable is to control from ordinary temperature -100.degree. C.
For the adjustment to the aforeasaid temperature range, discharge
plasma processing is conducted while the electrode and the base
material are cooled by the cooling means when necessary.
[0085] The discharge plasma processing is conducted under the
atmospheric pressure or under the pressure in the vicinity of
atmospheric pressure, and the pressure in the vicinity of the
atmospheric pressure indicates the pressure of 20 kPa-110 kPa, and
the preferable is 93 kPa-104 kPa.
[0086] In the electrode for discharging relating to the forming
method of thin-film, it is preferable that the maximum height
(Rmax) of the surface roughness stipulated by JIS B 0601 is
adjusted to be 10 .mu.m, and more preferable is that the maximum
value of the surface roughness is 8 .mu.m or less, and an
especially preferable value is 7 .mu.m or less.
[0087] Average center surface roughness stipulated by JIS B (Ra)
0.5 .mu.m or less, and more preferable is 0.1 .mu.m or less.
[0088] Mixed gases will now be described. When said thin film
forming method is practiced, gases to be used vary depending on the
kind of films provided on the substrate. However, fundamentally,
said gas is a mixture consisting of inert gases and reactive gases
which are used to form said thin layer. The content ratio of said
reactive gases is preferably from 0.01 to 10.00 percent by volume
of the mixed gas.
[0089] Listed as specific examples of said inert gases are elements
of group 18 of the Periodic Table, specifically including helium,
neon, argon, krypton, xenon and radon. Of these, helium as well as
argon is preferably employed.
[0090] For example, it is possible to form an electrically
conductive layer, an antistatic layer, or the intermediate
refractive index layer of a reflection minimizing layer by
employing reactive gases comprising at least one organic metal
compound selected from the group consisting of zinc acetyl acetate,
triethylindium, trimethylindium, diethylzinc, dimethylzinc,
tetraethyltin, tetramethyltin, diacetic acid di-n-butyltin,
tetrabutyltin, and tetraoctyltin.
[0091] Further, by employing gases comprised of fluorine containing
compounds, it is possible to form a water repellent layer in such a
manner that fluorine-containing groups are formed on the surface of
a substrate so as to decrease surface energy. Listed as
fluorine-containing compounds are fluorine-carbon compounds such as
hexafluorinated propylene (CF.sub.3CFCF.sub.2) and octafluorinated
butane (C.sub.4F.sub.8). From the viewpoint of safety, are employed
hexafluorinated propylene and octafluorinated butane which do not
from hazardous hydrogen fluoride gas.
[0092] Still further, it is possible to accumulate a hydrophilic
polymerization layer by carrying out a treatment under an
atmosphere of monomers having a hydrophilic group as well as
polymerizable unsaturated bonds in the molecules. Listed as said
hydrophilic groups are a hydroxyl group, a sulfonic acid group, a
sulfonic acid salt group, a primary, secondary, or tertiary amino
group, an amido group, a quaternary ammonium salt group, a
carboxylic acid group, and a carboxylic acid salt group. It is also
possible to accumulate said hydrophilic polymerization layer in the
same manner as above by using monomers having polyethylene glycol
chains.
[0093] Listed as said monomers are acrylic acid, methacrylic acid,
acrylamide, methacrylamide, N,N-dimethylacrylamide, sodium
acrylate, sodium methacrylate, potassium acrylate, potassium
methacrylate, sodium styrenesulfonate, allylalcohol, allylamine,
polyethylene glycol dimethacrylic acid esters, and polyethylene
glycol diacrylic acid esters. It is possible to use at least one of
these.
[0094] Further, it is possible to provide a low refractive index
layer or a high refractive index layer by employing reactive gases
comprising organic fluorine compounds, silicon compounds, or
titanium compounds.
[0095] Preferably employed as organic fluorine compounds are
fluorinated carbon gases and fluorinated hydrocarbon gases. Listed
as fluorinated carbon gases are tetrafluorinated carbon and
hexafluorinated carbon, specifically including tetrafluorinated
methane, tetrafluorinated ethylene, hexafluorinated propylene, and
octafluorinated cyclobutane.
[0096] Further, employed may be halides of fluorinated hydrocarbons
such as monochlorinated trifluorinated methane, monochlorinated
difluorinated methane, and dichlorinated teterafluorinated butane,
and fluorine substitution compounds of alcohols, acids and ketones.
However, the present invention is not limited to these. Further,
these compounds may have ethylenic unsaturated bonds in the
molecules. Said compounds may be employed individually or in
combination.
[0097] When the aforesaid organic fluorine compounds are employed
in mixed gases, from the viewpoint of uniformly forming a thin
layer on a substrate, employing a discharge plasma process, the
content ratio of said organic fluorine compounds in said mixed
gases is preferably from 0.1 to 10.0 percent by volume, and is more
preferably from 0.1 to 5.0 percent by volume.
[0098] Further, when said organic fluorine compounds are in the
form of gas at normal temperature and normal pressure, they may be
employed as a component of said mixed gas without any modification.
As a result, they may be readily employed. On the other hand, when
said organic fluorine compounds are in the form of liquid or solid
at normal temperature and normal pressure, they may be employed
upon being gasified employing methods such as heating and pressure
reduction. Further, they may be employed upon being dissolved in
suitable solvents.
[0099] When the aforesaid titanium compounds are employed in mixed
gases, from the viewpoint of uniformly forming a thin layer on a
substrate, employing a discharge plasma process, the content ratio
of said titanium compounds in said mixed gases is preferably from
0.1 to 10.0 percent by volume, and is more preferably from 0.1 to
5.0 percent by volume.
[0100] Further, by incorporating hydrogen gas in the aforesaid
mixed gases in an amount of 0.1 to 10.0 percent by volume, it is
possible to markedly enhance the hardness of said thin layer.
[0101] Still further, by incorporating components selected from the
group consisting of oxygen, ozone, hydrogen peroxide, carbon
dioxide, carbon monoxide, hydrogen, and nitrogen in the aforesaid
mixed gases in an amount of 0.01 to 5.00 percent by volume, it is
possible to enhance the reaction rate and to form the desired thin
layer.
[0102] From the viewpoint of handling, preferred as the aforesaid
silicon compounds as well as titanium compounds are metal hydrogen
compounds and metal alkoxides. Of these, metal alkoxides are more
preferably employed, since they are not corrosive, do not generate
hazardous gases and result in minimal staining during
processing.
[0103] Further, introduction of the aforesaid silicon compounds as
well as titanium compounds into the space between electrodes, which
is employed as a discharge space, may be carried out irrespective
of their states such as gas, liquid, or solid. When they are in the
form of gas, it is possible to introduce into said discharge space
without any modification. However, when they are in the form of
liquid or solid, they are used upon being gasified employing
methods such as heating, pressure reduction, and ultrasonic wave
application. When silicon compounds as well as titanium compounds,
such as tetraethoxysilane and tetraisopropoxytitanium, are employed
upon being gasified, metal alkoxides are suitably employed which
are in the form of liquid at normal temperature, having a boiling
pint of less than or equal to 200.degree. C. Said metal alkoxides
may be employed upon being diluted by solvents. Employed as said
solvents may be organic solvents such as methanol, ethanol, and
n-hexane, and mixtures thereof. Incidentally, since said dilution
solvents are decomposed into their molecular state and atomic state
during said plasma discharge process, it is possible to neglect any
of their effects against thin layer formation on the substrate, and
compositions of said thin layer.
[0104] Preferably employed as said silicon compounds are, for
example, organic metal compounds such as dimethylsilane and
tetramethylsilane, metal hydrogen compounds such as monosilane and
disilane, metal halogen compounds such as dichlorinated silane and
trichlorinated silane, alkoxysilanes such as tetramethoxysilane,
tetraethoxysilane, and dimethylethoxysilane, and organosilanes.
However, the present invention is not limited to these. Further,
these may be suitably employed in combination.
[0105] When the aforesaid silicon compounds are employed in mixed
gases, from the viewpoint of uniformly forming a thin film on the
substrate, employing a discharge plasma process, the content ratio
of said silicon compounds in said mixed gases is preferably from
0.1 to 10.0 percent by volume, and is more preferably from 0.1 to
5.0 percent by volume.
[0106] Preferably employed as said titanium compounds are organic
metal compounds such as tetradimethylaminotitanium, metal hydrogen
compounds such as monotitanium and dititanium, metal halogen
compounds such as titanium dichloride, titanium trichloride, and
titanium tetrachloride, and metal alkoxides such as
tetraethoxytitanium, tertaisopropoxytitanium, tetrabutoxytitanium.
However, the present invention is not limited to these.
[0107] <Supports>
[0108] Supports are comprised of glass or flexible resinous sheets.
For example, plastic films may be employed as a sheet. Listed as
said plastic films are those which are comprised of, for example,
polyethylene terephthalate (PET), polyethylene naphthalate (PEN),
polyethersulfone (PES), polyetherimide, polyetherketone,
polyphenylenesulfide, polyallylate, polyimide, polycarbonate (PC),
cellulose triacetate (TAC), and cellulose acetate propionate (CAP).
These films may be subjected to a surface treatment and surface
coating which are known in the art. For example, a vacuum
evaporation film formed by employing silicon oxide together with
aluminum oxide, a film comprised of metal oxides such as silicon
oxide and aluminum oxide, which is prepared employing an
atmospheric pressure plasma method, or a multilayered composite
film may be formed as a gas barrier layer. Further, a composite
film may be employed which is prepared by laminating films
vacuum-deposited with a thin layer comprised of metals such as
aluminum, or minute metal oxide particles may be incorporated in
said film. As mentioned above, by employing said plastic film, it
is possible to decrease weight, to enhance portability, and to
enhance durability against impact, compared to the case in which
glass substrates are employed.
[0109] <Protective Film>
[0110] In order to minimize a decease in working life due to oxygen
and moisture in atmosphere, it is preferable that said organic
semiconductor layer is separated from atmosphere by the use of a
protective film. Employed as said protective film are gas barrier
films comprised of PVA and ethylene-vinyl alcohol copolymers, and
metal oxides and metal nitrides, known in the art.
[0111] Suitably employed as said metal oxides and metal nitrides
may be silicon oxide, aluminum oxide, tantalum oxide, titanium
oxide, silicon nitride, and aluminum nitride.
[0112] Listed as methods for forming said protective film are those
using dry processes such as a vacuum deposition method, a molecular
beam epitaxial growth method, an ion cluster beam method, a low
energy ion beam method, an ion plating method, a CVD method, a
sputtering method, and an atmospheric pressure plasma method, and
wet processes using coating methods such as a spray coating method,
a spin coating method, a blade coating method, a dip coating
method, a casting method, a roll coating method, an bar coating
method, as well as methods employing patterning such as printing
and ink jet printing. It is possible to employ any of these methods
based on materials. Of these, the aforesaid atmospheric pressure
plasma method is preferred.
[0113] It is possible to employ an inorganic oxide film and an
organic oxide film while laminating these. The thickness of these
insulation films is commonly from 50 nm to 3 .mu.m, and is
preferably from 100 nm to 1 .mu.m.
[0114] [Display Panel]
[0115] Applied examples in which a display element is formed by
utilizing the characteristics of the organized semiconductor
materials will be explained as follows.
[0116] FIG. 2 is a block diagram showing the overall structure of
the display panel.
[0117] Each pixel arranged in a matrix form on display panel 100 of
display device has a flat plate electrode 1 (display image section
in the drawing) that accumulates electric charges and gives an
electric field to a liquid crystal. A transistor section (TFT drive
section 2) that switches ON and OFF of the electric current to the
flat plate electrode and capacitor 3 are arranged for each flat
plate electrode. The capacitor 3 accumulates electric charges and
keeps them at the prescribed timing to maintain the electric field
for the corresponding flat plate electrode 1. Driving control of
liquid crystal by these flat plate electrodes is executed by the
aforesaid TFT driving section 2, and this is controlled by power
supply line (source line 4) corresponding to the pixel controlled
by vertical drive circuit 6 and by control signal line (gate line
5) corresponding to the pixel controlled by horizontal drive
circuit 7.
[0118] On the panel 100, plural source lines 4 which are in
parallel each other and plural gate lines 5 which are in parallel
each other are arranged to intersect.
[0119] The aforesaid horizontal driving circuit 7 and the aforesaid
vertical driving circuit 6 are controlled by control circuit 8 in
accordance with the required image signals. Memory 9 is a buffer
memory for holding image data for one image plane, for example, and
the control circuit 8 reads required image signals from the memory
9.
[0120] As shown in FIG. 3, display material 11 such as liquid
crystal is sealed to be sandwiched by the flat plate electrode 1
and surface electrode 10 arranged above the flat plate electrode 1.
For the display material 11, organic EL and an element using
electrophoresis in addition to liquid crystal can be used. Then,
electric field is applied on display material 11 of display pixel
section, responding to the control of the TFT driving section 2,
and display is controlled at a unit of pixel.
[0121] Incidentally, in this case, for the purpose of satisfying
functions as display, the aforementioned surface electrode 10 has
light transmission property, and a transparent conductive film is
used as a practical example. The transparent conductive film is
formed by using conductive transparent material such as, for
example, indiumtinoxide (ITO),SnO2, or ZnO. For forming the
transparent electrode film, a thin film can be formed by employing
a method of evaporation deposition or a method of sputtering. It is
preferable for the transparent conductive film that its
transmission factor is greater than 10%, and sheet resistance is
several hundreds .OMEGA./or less. Coating thickness is formed to be
a thickness of 10 nm or more, though it depends a material. The
reason for the foregoing is that when the coating thickness is
thin, transparent electrodes become a shape of islands.
[0122] The transparent conductive film can be applied of forming of
the flat plate electrode 1, and in this case, a desired form
pattern may be formed through a photolithography method, or a
pattern may be formed through a desired form mask in the case of
evaporation deposition or sputtering of the aforesaid electrode
substances.
[0123] It is also possible to provide the prescribed transparent
protective layer on the upper position of the surface electrode 10,
and for example, it is possible to form the functional film such as
a reflection prevention layer.
[0124] An equivalent circuit of each pixel in FIG. 2 is the same as
that in FIG. 4. "S" represents a source electrode, "D" represents a
drain electrode, "G" means a gate electrode, and S, D and G
constitute TFT driving section 2. Cs represents a capacitor for
holding an electric field to be applied onto liquid crystal or
other display medium. Incidentally, source voltage Vs is applied
onto the source electrode S, and gate voltage Vg is applied onto
the gate electrode G.
[0125] [Layout of Each Member]
[0126] Next, concrete layout of each member in the invention will
be explained. When each pixel is viewed, its constituting members
are arranged as shown in FIG. 5. FIG. 5 mostly corresponds to a
sectional view on line X in FIG. 2.
[0127] Each of said plate electrodes (1, 1', and 1") is arranged on
first support 12 at even intervals. Said first support 12 is
comprised of a flexible resinous sheet. For example, it is possible
to use a plastic film as said sheet. Listed as said plastic films
are films comprised of, for examples, polyethylene terephthalate
(PET), polyethylene naphthalate (PEN), polyethersulfone (PES),
polyetherimide, polyether ether ketone, polyphenylenesulfide,
polyallylate, polyimide, polycarbonate (PC), cellulose triacetate
(TAC), and cellulose acetate propionate (CAP) . As mentioned above,
by employing said plastic film, it is possible to decrease weight,
to enhance portability, and to enhance durability against impact,
compared to the case in which glass substrates are employed.
[0128] Further, plasticizers such as trioctyl phosphate and dibutyl
phthalate may be incorporated in these plastic films and
benzotriazole based or benzophenone based UV absorbers, known in
the art, may also be incorporated in the same. Further, it is
possible to employ as raw material resins which have been prepared
employing a so-called organic-inorganic polymer hybrid method in
which molecular weight is increased by providing chemical catalysts
or energy such as heat and radiation while inorganic polymers such
as teraethoxysilane are added as a raw material.
EXAMPLES
[0129] Several embodiments based on the foregoing will now be
described. The formation of the insulation film, employing the
atmospheric pressure plasma method, is detailed below.
[0130] Each flat plate electrode (1, 1', 1") and each source line
(4, 4', 4") are arranged side by side while keeping the prescribed
interval. Then, organic semiconductor section (13, 13', 13") are
arrange to bridge flat plate electrode ends and corresponding
source lines (4, 4', 4") (the same as FIGS. 1(a) and 1(b)).
[0131] Above the organic semiconductor section (13, 13', 13"),
there is further arranged an insulating layer 14 (insulating film).
For the insulating layer 14, insulating film of SiO.sub.2 or
TiO.sub.2 can be used.
[0132] For example, when forming an insulating layer with SiO.sub.2
or TiO.sub.2, it is possible to form a film by plasma processing
under the aspheric pressure. In this method, it is possible to form
insulating film, which is extremely uniform, and it is also
effective for controlling the organic semiconductor section (13,
13', 13").
[0133] The insulating layers 14 are formed at the positions to
insulate source for a current path from the source lines (4, 4',
4") to the flat plate electrodes (1, 1', 1") on the pattern of the
organic semiconductor section (13, 13', 13") and for the gate line
5 to be arranged in the next step.
[0134] When forming insulating layers 14 in the aforesaid method,
on the entire surface of the first support 12, it is not necessary
to control the positions of formation of insulating layers
depending on the organic semiconductor section (13, 13', 13") or
the intersecting sections between gate line 5 and source lines (4,
4', 4"). Further, because of the improvement of the line speed in
manufacturing process, an insulating layer can be formed in a short
time even a panel is large in area.
[0135] On the other hand, it is also possible to form insulating
layer 14 for each pixel for the organic semiconductor section (13,
13', 13") or the intersecting sections between gate line 5 and
source lines (4, 4', 4"). An ink jet method can be used as a
forming method. In the patterning in the invention, insulating film
14 can be coated broadly to cover both the organic semiconductor
section (13, 13', 13") and the intersecting sections between gate
line 5 and source lines (4, 4', 4"). In this case, it is possible
to reduce raw material cost by securing switching operations even
for patterning with low accuracy though processing speed is
restricted, rather than making insulating film on the entire
surface of the support.
[0136] When providing insulating layer 14 on the entire surface of
the first support 12, or when providing partially, in any case, if
the same insulating layer 14 covers the organic semiconductor
section (13, 13', 13") and the intersecting sections between gate
line 5 and source lines (4, 4', 4"), it is possible to simplify the
forming process of insulating layers.
[0137] Above the insulating layer 14, the gate line 5 intersects
with the source lines (4, 4', 4") at right angles, and is arranged
to be positioned above the organic semiconductor section (13, 13',
13") (described later, referring to FIG. 7). The second support is
arranged above the gate line 5 of the corresponding pixel through
display material 11 (liquid crystal, etc.). This second support has
conductivity and it becomes a facing electrode for the flat plate
electrodes (1, 1', 1") of each pixel. In this case, the conductive
film 10 (transparent conductive film is preferable) is formed on
the surface on one side of the second support. This conductive film
10 can be provided at least the position corresponding to the flat
plate electrodes (1, 1', 1") of each pixel, and it is possible to
make facing electrode easily by covering the entire surface of the
second support with conductive film and by grounding them.
[0138] [Capacitor Structure]
[0139] When the distance between the flat electrode 1 on the first
support 12 mentioned above and the conductive thin-layer 16 facing
the flat electrode 1 is sufficiently small, by controlling the
dielectric constant of the display material to be sealded, a
capacitor structure can be formed between the flat electrode 1 and
the facing electrode and makes it possible to maintain the
electronic field.
[0140] On the other hand, when the distance between the flat
electrode 1 on the first support 12 mentioned above and the
conductive thin-layer 16 facing the flat electrode 1 is
sufficiently large, it is desirable that the following processing
are applied before the flat electrode 1 is provided on the first
support 12 for every pixels as shown in FIG. 6(A).
[0141] (1) The conductive thin-layer 16 is formed on the entire
surface of the first support 12. This formation is possible by
uniformly vapor-depositing the metal material on it by means of the
spattering method, etc.
[0142] (2) Then, the insulating layer 17 is covered on the entire
surface of the conductive thin-layer 16 formed by the above
process. For this purpose, either an applying process at the normal
pressure or the aforementioned plasma processing can be applied,
and it is also possible to form the insulating layer 17 while
controlling the layer thickness in a unit of micron order (or
sub-micron order).
[0143] According to the abovementioned processing, it becomes
possible to constitute a capacitor structure between the conductive
thin-layer 16, formed in advance when the flat electrode 1 is
formed on the first support 12 after the above process, and the
flat electrode 1, and to strongly maintain the electronic field
(namely, it is possible to intensify the strength of the electronic
field applied to the display material 11). Incidentally, in this
example, the conductive thin-layer 16 mentioned above is grounded
(refer to FIG. 6(B)).
[0144] Incidentally, although the conductive thin-layer 16 is
formed on the entire surface of the first support 12 in the above
example, by arranging a plurality of conductive earth-lines so as
to face the flat electrode 1, it is also possible to form a
capacitor structure between the plurality of conductive earth-lines
and the flat electrode 1. In this case, the plurality of conductive
earth-lines are grounded as well as the conductive thin-layer 16
mentioned above.
[0145] Even if the spattering method is employed in a part of the
forming process of the conductive thin-layer 16, a patterning
process, such as a photolithography, a developing process, etc., is
not necessary. Therefore, it becomes possible to form the
abovementioned capacitor structure with relatively low
manufacturing cost.
[0146] [Process of Patterning]
[0147] FIGS. 7(A)-7(D) show a schematic diagram of a formation
process of materials onto the, first support 12. In the following,
the formation process with respect to one pixel will be
detailed.
[0148] Initially, a plurality of source lines and a plurality of
flat electrodes are formed on the first support 12 in advance
(refer to FIG. 7(A)). Although anyone of the well-known methods for
forming the metallic thin layer (such as the spattering method, the
method of transferring the conductive material, etc.) can be
employed for this purpose, the spattering method is employed for
forming source lines 4 and flat electrodes 1 in the this
example.
[0149] Then, a solution or a dispersed-liquid of the organic
semiconductor material is employed for the patterning process, so
that the organic material dispersed-liquid overlaps both each of
source lines 4 and each of flat electrodes 1 (refer to FIG. 7(B)).
Since the organic material dispersed-liquid, employed for the
patterning process, exhibits a high fluidity, the dot formation by
means of the ink-jetting method is employed for the patterning
process. Pattern 13 of the organic semiconductor material could be
an arbitral shape, though pattern 13 is conceptually illustrated.
Of cause, this patterning process also can be achieved by
application and drying process after the masking process, for which
conventional well-known methods, such as the electro-photographic
method, etc., can be employed. According to the abovementioned
patterning method, it becomes possible to form the semiconductor
layer in an environment of normal pressure without repeating
vapor-depositing processes and etching processes as performed in
the conventional Si-semiconductor process.
[0150] The organic semiconductor section 13, formed by the
abovementioned process, is arranged so as to connect a part of flat
electrodes 1 with source line 4. In this example, the organic
semiconductor is formed as a dot so as to cover both an end portion
of flat electrode 1 and a part of source line 4. In other words, a
part of flat electrode 1 is continuously coupled to source line 4
only by a single semiconductor material. Alternatively, instead of
directly connecting, it is also possible that an arbitral electrode
is inserted between the organic semiconductor section 13 and the
flat electrode 1 or between the organic semiconductor section 13
and the source line 4, in order to support the electronic
connection.
[0151] Next, the insulating layer 14 of SiO.sub.2 is formed on the
pattern of the abovementioned organic semiconductor section 13,
formed in the process shown in FIG. 7(B), (refer to FIG. 7(C). The
insulating layer 14 covers the entire surface of the panel 100, and
also covers both the electronic current path from the source line 4
to the flat electrode 1 on the -organic semiconductor pattern and a
position at which the source line 4 is insulated from the gate line
5 to be arranged in the next process (a position at which the
source line 4 and the gate line 5 crosses each other).
[0152] The insulating layer 14 mentioned above is formed by the
plasma film formation processing under the atmospheric pressure,
and by employing the mixed gas for forming the SiO.sub.2 layer.
Since the insulating layer 14 is formed over the entire surface of
the first support 12 as aforementioned, it is not necessary to
control the forming position of the insulating layer 14 in response
to the intersecting position of gate line 5 and source line 4.
Since the processing can be performed under the atmospheric
pressure, it becomes possible to introduce the conveyer method into
the manufacturing line, and therefore, it becomes possible to
shorten the formation time for the insulating layer 14 by improving
the conveyer speed of the manufacturing line, even if the
large-sized panel is manufactured in the line.
[0153] As shown in FIG. 7(D), next, the gate line 5 is formed on
the insulating layer 14 in such a manner that the gate line 5
crosses the source line 4 (in this example, the gate line 5 is
orthogonal to the source line 4) and covers the organic
semiconductor section 13. This pattern can be formed by the method
of applying or transferring the conductive material, or by the
method of continuously forming ink-jetting dots. As shown in the
drawing, in this example, the gate line 5 is a signal line, which
also works as a gate electrode crossing the organic semiconductor
section 13 and directly affecting to the organic semiconductor
section 13 as it is without diverging.
[0154] Although the insulating layer 14 is made of SiO.sub.2 in the
abovementioned patterning process, TiO.sub.2 also can be employed
for forming the insulating layer 14 (in the process shown in FIG.
7(C)). In the embodiment employing TiO.sub.2, the insulating layer
14 is formed by the plasma film formation processing under the
atmospheric pressure, and by employing the mixed gas for forming
the TiO.sub.2 layer. The structure other than the abovementioned
insulating layer 14 is the same as that in the foregoing.
Accordingly, the insulating layer 14 made of TiO.sub.2 covers the
entire surface of the panel 100, and also covers both the
electronic current path from the source line 4 to the flat
electrode 1 on the organic semiconductor pattern and a position at
which the source line 4 is insulated from the gate line 5 to be
arranged in the next process (a position at which the source line 4
and the gate line 5 crosses each other).
[0155] Incidentally, when display material 11 (liquid crystal,
etc.) is sealed, the following process will be applied.
[0156] The opposing electrode is formed on the second support, and
conductivity is added to the surface of the opposing electrode. For
this purpose, it is applicable that the conductive thin-layer 16 is
formed at at-least a position facing to the plurality of flat
electrodes on the first support 12. In this example, a transparent
conductive thin-layer 16 is formed over the entire surface of the
second support. Although it is possible that the second support, on
which conductive thin-layer 16 is formed, is arranged at a third
support side in respect to the first support 12 (refer to FIG.
8(A)), it is also possible that the second support is arranged
opposite the third support in respect to the first support 12
(refer to FIG. 8(B)).
[0157] In the former case, the display material 11 is injected into
the space, maintaining a predetermined gap, between the third
support and the second support, and is sealed in it. While, in the
latter case, the display material 11 is injected into the space,
maintaining a predetermined gap, between the first support 12 and
the second support, and is sealed in it.
EXAMPLES
[0158] Several embodiments based on the foregoing will now be
described. The formation of the insulation film, employing the
atmospheric pressure plasma method, is detailed below.
Process Example
[0159] <<Reactive Gas>>
[0160] The composition of the mixed gas (being the reactive gas),
which is employed for the plasma process, will now be described
below.
[0161] (For forming an SiO.sub.2 layer)
[0162] Inert gas: argon 98.25 percent by volume
[0163] Reactive gas 1: hydrogen gas 1.5 percent by volume
[0164] Reactive gas 2: tetramethoxysilane vapor (bubbled employing
argon gas) 0.25 percent by volume
[0165] (For forming a TiO.sub.2 layer)
[0166] Inert gas: argon 98.9 percent by volume
[0167] Reactive gas 1: hydrogen gas 0.8 percent by volume
[0168] Reactive gas 2: tetraisopropoxytitanium vapor (liquid heated
at 150.degree. C. was bubbled with argon gas) 0.3 percent by
volume
[0169] The atmospheric pressure plasma process is continuously
carried out onto the hard coat layer of substrate film 8 under said
discharge conditions employing said reactive gases, whereby a 100
nm thin film is provided.
[0170] <<Discharge Conditions>>
[0171] Discharge output should be set at 10 W/cm.sup.2.
[0172] <<Electrode Conditions>>
[0173] A roll electrode comprising a dielectric (having a relative
dielectric constant of 10), which is grounded, is prepared as
follows. A mother stainless steel jacket roll, having a cooling
means employing cooling water, is covered with 1 mm thick alumina,
employing ceramic spraying. Thereafter, a solution prepared by
diluting tetramethoxysilane with ethyl acetate is applied and
subsequently dried. Subsequently, the resultant coating is hardened
while exposed to ultraviolet rays so that pores are sealed. The
resultant surface is then smoothed so as to be Rma.times.5 .mu.m.
On the other hand, an applied electrode is prepared by covering a
hollow square-shaped stainless steel pipe with the same dielectric
as above under the same conditions.
[0174] A prepared organic thin film transistor element will now be
described below.
Example A
[0175] The organic thin film transistor element, shown in FIG.
1(a), was prepared as described below.
[0176] A thin 500 .ANG. thick Au film was vacuum-deposited on a 150
.mu.m thick polyimide film, and each of a source electrode and a
drain electrode was formed employing a photolithographic method.
The channel length was determined to be 20 .mu.m. Further, a
chloroform solution of regioregular-poly(3-hexylthiophene),
purified as desired, was ejected employing piezoelectric system ink
jet and the portion between said source electrode and said drain
electrode was filled with said solution. By removing chloroform as
a solvent through drying, the resultant was heated at 100.degree.
C. for 5 minutes and was set aside at vacuum for 24 hours. The
resultant thickness of said regioregular-poly(3-hexylthiophene- )
film was approximately 50 nm. After being exposed to an atmosphere
of ammonia gas at room temperature for 5 hours, a 200 nm thick
silicon oxide film was formed on said source electrode, said drain
electrode, and said regioregular-poly (3-hexylthiphene), employing
the aforesaid atmospheric pressure plasma method. A desired film,
which exhibited excellent adhesion onto said regioregular-poly
(3-hexylthiphene) film, was obtained. Next, a 30 .mu.m wide gate
electrode was formed by employing an Ag paste available in the
conventional market, and as a result, the organic thin-film
transistor element, shown in the structural example A, is
obtained.
Comparative Example 1
[0177] An element was prepared in the same manner as Example A,
except that the silicon oxide film was formed employing a
conventional sputtering method.
Comparative Results
[0178] By employing the system for evaluating transistor
characteristics shown in FIG. 10, characteristics of both
transistors were measured. As a result, both exhibits good
operational characteristics as a p-channel FET transistor and the
following results were obtained. The leak electric current refers
to the leak current value at the gate insulation layer when the
voltage between the source and the gate is -30 V, and the breakdown
voltage refers to a voltage value at which dielectric breakdown of
the gate insulation layer occurs, while the on/off ratio refers to
the electric current ratio when the gate voltage is set at -30 V
and +30 V, while setting the voltage between the source and the
drain at -30 V.
1 Leak Electric Breakdown Current Voltage On/Off Ratio Example 1
-0.2 nA -150 V 10000 Comp. Example 1 -10 nA -80 V 5000 Example 2
-0.1 nA -170 V 15000
[0179] Incidentally, the organic thin-film transistor element of
Example 2 is made and evaluated in the entirely same process as
that of Example 1, except that the silicon oxide film of the gate
insulation layer is change to the titanium oxide, thickness of
which is 200 nm.
Example B
[0180] The thin organic film transistor element, shown in FIG.
1(b), was prepared as described below.
[0181] A vacuum-deposited Al film was formed on a 150 .mu.m thick
PET film, and subsequently, a 30 .mu. wide gate electrode was
formed employing a photolithographic method. A 200 nm thick silicon
oxide film was formed on the resultant gate electrode in the same
manner as Example 1. Further, a thin 300 .ANG. thick Cr film and a
thin 500 .ANG. thick Au film were vacuum-deposited one by one, and
each of a source electrode and a drain electrode was formed
employing a photolithographic method. The channel length was
determined to be 20 .mu.m. Further, a chloroform solution of
regioregular-poly(3-hexylthiophene), purified as desired, was
ejected employing piezoelectric system ink jet and the portion
between said source electrode and said drain electrode was filled
with said solution. By removing chloroform as a solvent through
drying, the resultant was heated at 100.degree. C. for 5 minutes
and was set aside at vacuum for 24 hours. The resultant thickness
of said regioregular-poly(3-hexylthiophene) film was approximately
100 nm. After being exposed to an ammonia gas atmosphere at room
temperature for 5 hours, the transistor element was sealed by
forming a silicon oxide film having 500 nm thickness through the
deposition process. Then, the transistor characteristics were
measured in the same process as that of Example 1.
Comparative Example 2
[0182] An element was prepared in the same manner as Example 3,
except that a silicon oxide film was formed employing a
conventional sputtering method.
Comparative Results
[0183] As well as Example A, by employing the system for evaluating
transistor characteristics shown in FIG. 10, characteristics of
both transistors were measured. The leak electric current refers to
the leak current value at the gate insulation layer when the
voltage between the source and the gate is -30 V, and the breakdown
voltage refers to a voltage value at which dielectric breakdown of
the gate insulation layer occurs, while the on/off ratio refers to
the electric current ratio when the gate voltage is set at -30 V
and +30 V, while setting the voltage between the source and the
drain at -30 V.
2 Leak Electric Breakdown Current Voltage On/Off Ratio Example 3
-0.3 nA -140 V 20000 Comp. Example 1 -50 nA -70 V 3000 Example 4
-0.1 nA -150 V 30000
[0184] Incidentally, the organic thin-film transistor element of
Example 4 is made and evaluated in the entirely same process as
that of Example 1, except that the silicon oxide film of the gate
insulation layer is change to the titanium oxide, thickness of
which is 200 nm.
[0185] As described in the foregoing, the insulation film, formed
in the atmospheric pressure plasma method, is close and has little
defects and exhibits a good electronic-field effect. Accordingly,
it becomes possible to reduce the leak current of the gate
insulation layer and the gate voltage, and to improve the on/off
ratio, resulting in realization of the good performances of the
thin-film transistor and improvement of the insulation
durability.
[0186] Further, according to the present invention, it is revealed
that the new combination of the insulation film, formed in the
atmospheric pressure plasma method, and the organic semiconductor
material exhibits superior effects, compared to the combination of
the conventional insulation film and the organic semiconductor
material. Since the film formation under the atmospheric pressure
environment is possible, the present invention is suitable for
processing the flexible base, such as polymer support member, etc.,
and it is possible to drastically reduce the manufacturing cost of
the organic FET.
[0187] As described in the foregoing, according to the present
invention, it is possible to improve the characteristics of the
device, such as the on/off ratio, the leak current, etc., when the
organic semiconductor is employed as the active semiconductor layer
in the thin-film TFT of the device. Further, since the formation
process of the insulation film does not require a vacuum
processing, it becomes possible to reduce the manufacturing cost
and to simplify the manufacturing process, resulting in the drastic
reduction of the total manufacturing cost.
[0188] Disclosed embodiment can be varied by a skilled person
without departing from the spirit and scope of the invention.
* * * * *