JPH06291312A - Field-effect transistor and liquid crystal display device using same - Google Patents

Abstract

PURPOSE:To provide field effect transistors which can uniformly fabricated at the same time on a substrate having a large area, wherein the source-drain current can largely be modulated by a voltage applied to the gate, the operation is stable, and the elements have a long life. CONSTITUTION:In a field effect transistor in which the conductivity of a semiconductor layer 8 as the current passage between a source electrode 4 and a drain electrode 5 is controlled by a gate electrode 2 provided through an insulation layer 3, a field effect transistor in which the semiconductor layer 8 is formed of a polymacrocyclic azannulene inorganic compound represented by azaphthalocyanine, phthalocyanine and naphthalocyanine derivatives.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field effect transistor, and more particularly to a field effect transistor whose active layer is an organic compound and a liquid crystal display device using the same.

[0002]

2. Description of the Related Art Conventional field effect transistors (hereinafter referred to as
FET element) is a semiconductor layer made of silicon or Ga.
Those using As single crystals are known. However, because they are expensive, cheaper organic semiconductors, such as
A FET device using polyacetylene has been reported (Ebisawa et al., Journal of Applied Physics, Volume 54, No. 6, 3255-3269).
Pp. F. Ebisawa et al. : Journal of Applied
Physics, Vol. 54, No. 6, pp3255-3269).

However, in an FET device using the above compound, when left in the air, polyacetylene having a large amount of unsaturated bonds is easily attacked by oxygen or water and deteriorates. Therefore, the FET element is poor in stability and inferior in electrical characteristics,
Moreover, there is a problem that the life is short. As a remedy for this, a conductive polymer represented by the following general formula [2] has been proposed (JP-A-62-31174 and JP-A-62-85224).
Issue).

[0004]

[Chemical 3]

(However, X ⁵ is S or O, and R ¹ and R ² are hydrogen atom, methyl group, ethyl group, methoxy group or ethoxy group.) The organic semiconductor having such a 5-membered heterocyclic ring is It can be synthesized by an electrolytic polymerization method, is relatively inexpensive, and has a long life. However, since the formation of the film as the organic semiconductor is performed by the electrolytic polymerization method, there is a problem that the electrode structure and the device configuration are significantly restricted.

Further, conventionally, FET elements made of inorganic materials (Si, Ge) have a drawback that they are limited by the size of the wafer made of these materials. On the other hand, a field effect transistor in which an amorphous silicon film or a polysilicon film is formed on a glass substrate is known.

Amorphous silicon film is plasma CVD
In addition, the polysilicon film is generally formed by a low pressure CVD method. It is difficult to manufacture a driving element such as a field-effect transistor in a uniform and large area by the plasma CVD method because of restrictions of a manufacturing apparatus and difficulty of plasma control. Furthermore, the film formation must be performed in a high vacuum, which is one of the causes of the decrease in throughput.

Further, the low pressure CVD method requires an expensive glass substrate having high heat resistance because the raw material gas at the time of film formation must be decomposed at a high temperature of 450 to 600 ° C.

In response to the above, a technique using an organic polymer as a semiconductor has been proposed (for example, Japanese Patent Laid-Open No. 58-114465).
However, the manufacturing method is a method of applying a catalyst to a large-area substrate and then introducing a source gas onto the substrate. However, it is difficult to uniformly apply the catalyst to a large area substrate, and it is not easy to uniformly introduce the source gas onto the large area substrate.

In addition, the use of metal phthalocyanines has been reported [Chemical Physics Letters (Chem. Phy.
s. Lett. 142, 103, 1987], but since metal phthalocyanine is produced by a vacuum evaporation method, it is not possible to produce a large number of FET devices simultaneously and uniformly.

Therefore, recently, a polythienylene derivative obtained by a method in which a precursor soluble in a solvent is converted is attracting attention as a stable π-conjugated polymer having excellent processability (Japanese Patent Laid-Open No. 4-69971). issue). However, since this is also synthesized by a condensation reaction under alkaline or acidic conditions, it may damage the electrodes (source, drain). Therefore, like an inverted stagger type semiconductor device to which this can be applied,
There is a problem that it is subject to structural restrictions.

[0012]

With the π-conjugated polymer obtained by the conventional electrolytic polymerization method and the organic compound obtained by the vacuum deposition method, it is difficult to simultaneously and uniformly produce FET devices on a large-area substrate. There are practical problems.

A relatively large current flows between the source and drain electrodes even when the gate voltage is not applied, that is, even when the FET element is in the off state. As a result, the ratio of the on-current to the off-current, that is, the switching ratio. Becomes smaller, and there is a problem when these elements are used as switching elements or the like. Furthermore, there are various problems such as the structural limitation of the semiconductor device.

An object of the present invention is to solve the above problems, and it is possible to form them uniformly on a large-area substrate at the same time, and to greatly modulate the source-drain current by the voltage applied to the gate. Another object of the present invention is to provide a FET device that has a long life and is easy to manufacture.

Another object of the present invention is to provide a liquid crystal display device using the above FET element.

[0016]

Means for Solving the Problems The gist of the present invention capable of solving the above problems is as follows.

(1) In a field effect transistor in which the conductivity of a semiconductor layer, which is a current path between a source electrode and a drain electrode, is controlled by a gate electrode provided via an insulating layer, the semiconductor layer is a poly-macrocyclic azaannulene. A field-effect transistor formed of an organic compound.

(2) The field effect transistor according to (1), wherein the insulating layer is made of a polymer material having a dielectric constant of 9 or less within an operating temperature range.

FIG. 1 is a schematic sectional view showing an example of the FET element of the present invention. A gate insulating film 3 is formed on a substrate 1 having a gate electrode 2 made of transparent ITO,
A source electrode 4 and a drain electrode 5 made of gold or the like are formed thereon by using a usual vacuum deposition method, a photolithography technique and an etching technique.

An organic semiconductor layer 8 represented by the above formula [1] is formed on the source electrode 4 and the drain electrode 5.

As the substrate 1, for example, an inorganic material such as glass or alumina sinter, or an organic material such as polyimide, polyester, polyethylene, polyphenylene sulfide, polyparaxylene or the like can be used.

As the gate electrode 2, metal such as gold, platinum, chromium, palladium, aluminum, indium, molybdenum, low resistance polysilicon, low resistance amorphous silicon, tin oxide, indium oxide, indium tin oxide film (ITO) is used. ) Etc. can be used. Two or more of these materials may be used in combination without any problem.

The gate electrode is formed by vapor deposition, sputtering,
It can be formed by plating, various types of CVD growth, or the like.

Further, as the source electrode 4 and the drain electrode 5, metals such as gold, silver, copper, aluminum, indium, chromium and molybdenum, platinum silicide, indium silicide, low resistance polysilicon, low resistance amorphous silicon, tin are used. Oxides, indium oxide, indium tin oxide (ITO), etc. can be used. These source electrode and drain electrode are formed by sputtering, plating, C
It can be formed by VD, vapor deposition, cluster ion beam vapor deposition, or the like.

The organic semiconductor layer 8 which is the point of the present invention has a chemical structure capable of ensuring a π electron system, and
It is a compound that can maintain rigidity. In particular, a poly macrocyclic azaannulene-based organic compound having the following chemical structural formula [3]
[5] is preferred. The long side of the compound is the long axis,
When the short side is the minor axis, the major axis / uniaxial ratio is preferably 2 or more. These may be used as a mixture of two or more.

[0026]

[Chemical 4]

[0027]

[Chemical 5]

[0028]

[Chemical 6]

The above-mentioned typical thin films of azaphthalocyanine, phthalocyanine, and naphthalocyanine derivatives are dissolved in a solvent to form a solution, which is formed on a predetermined substrate by a dipping method, a printing transfer method, a spin coating method, etc. Obtained by removing.

The solution concentration at that time is 0.1 to 10% by weight, preferably 0.1 to 5% by weight. For example, a 0.1 to 5% by weight solution of the above derivative is added to 1,000 to 5.0
00r. p. After being dropped on a substrate rotated at m, a film is formed and then the solvent is removed to form a film having a thickness of 10 to 200 nm.

If the solution concentration is too low when forming the organic semiconductor layer, the viscosity may be improved by dispersing polymer particles in the solution. Examples of the polymer include polyvinyl indene, polyethylene, polyvinyl carbazole and isopropyl carbazole.

Specific examples of the material used for the insulating layer (gate insulating film) 3 include polychloropyrene, polyethylene terephthalate, polyoxymethylene, polyvinyl acetate, polyvinyl chloride and polyvinylidene fluoride.

The dielectric constant of the insulating layer is FET
Within the operating temperature range of the device, 9 or less is desirable. If the dielectric constant exceeds 9, it is not preferable because it is strongly dependent on the temperature and the characteristics change easily.

It is also possible to use an organic polymer material containing ceramic powder as the insulating layer. Specifically, a filler of Al ₂ O ₃ can be used by mixing it with polyethylene, polystyrene or the like.

The insulating layer can be formed by printing, spin coating, dipping or the like as in the formation of the organic semiconductor layer.

FIG. 2 is a schematic sectional view showing an example of a liquid crystal display device using the FET element of the present invention.

In a matrix display type liquid crystal display device comprising a plurality of address lines and a plurality of signal lines, the FET element of the present invention is formed at intersections of matrix wirings. A matrix display is performed by driving the liquid crystal layer 11 sandwiched by the pixel electrode connected to the signal line via the FET element and the counter electrode 13 facing the pixel electrode. At this time, the conductivity of the organic semiconductor layer 8 which is a current path between the source electrode 6 and the drain electrode 7 of the FET element is controlled by the gate electrode 2 provided via the insulating layer 3 to drive the liquid crystal 10. is there.

According to the present invention, an FET element can be simultaneously formed on a large-area substrate like a liquid crystal display device. The source-drain current can be largely modulated by the voltage applied to the gate, and its operation is stable, so that an excellent matrix type liquid crystal display device can be provided.

[0039]

The reason why the FET element according to the present invention exhibits excellent characteristics is presumed as follows.

So far, compounds in which the overlapping of π electron clouds are regularly repeated have been used. In other words, we have emphasized the spread of the π-electron system based on the band theory that an energy band structure is formed throughout the solid.

On the other hand, the organic semiconductor layer of the present invention is
It has a part with a spread of π electrons and a part where π electron overlapping occurs to form a cluster,
It is considered that one unit of the cluster is one site and hopping is performed between them.

In order to explain the above, FIG. 3 shows a schematic view of the organic semiconductor portion. FIG. 3 (a) is a schematic diagram showing the state of a thin film of the compound, and FIG. 3 (b) is one cluster thereof,
It is a schematic diagram which shows the state of cluster formation by the overlapping of (pi) electron. Then, FIG. 3C is a schematic diagram showing a state in which a plurality of clusters are alternately stacked and a hopping state.

As described above, the organic semiconductor is formed of cluster units that conduct on π electrons, and depending on the degree of overlapping of molecules, a portion in which overlapping of π electrons alternates between molecules is also formed. Therefore, it is considered that the conduction mechanism due to the overlap of π electron orbits and the conduction mechanism that proceeds by hopping between the clusters coexist.

At this time, since the chemical structure of one cluster unit is small, it is presumed that the trapping of carriers due to structural defects such as π-conjugated polymer can be prevented.

[0045]

EXAMPLES The present invention will be specifically described below with reference to examples.

Example 1 An FET element of the present invention as shown in the schematic sectional view of FIG. 1 was produced. On a glass substrate 1 having a gate electrode 2 made of transparent ITO, a thickness of 55n
An m-polyvinylidene fluoride film was formed by a spin coating method and used as a gate insulating film 3.

Next, the gold source electrode 4 is formed by using the usual vacuum deposition method, photolithography technique and etching technique.
And the drain electrode 5 was formed. The width (channel width) of both electrodes 4 and 5 was 2 mm, and the interval (channel length) between both electrodes was 6 μm.

Next, a known method (Bailar, Jr., J.
C., Drinkard, Jr., W.A. C., and Judd, M .;
L., WADC Technical Report 57-391, A
STIA Document No. AD 131100, PB 1315
17, September, 1957) and the above formula [3]
Was dissolved in dimethylformamide to prepare a 2% by weight solution. The solution was dropped on the substrate to form a thin film having a film thickness of 50 nm by spin coating. 90 this
The organic semiconductor layer 8 was formed by allowing the organic semiconductor layer 8 to stand in a constant temperature bath at 1 ° C. for 1 hour to remove the solvent.

Next, as shown in FIG.
Source-drain current (I _S ) / source-drain voltage (V _DS ) characteristics when the gate voltage V _{G of the} device was changed were measured. The result is shown in FIG.

As can be seen from FIG. 4, when the gate voltage (V _G ) is zero V, I _S hardly flows even if V _DS becomes large, but when negative V _G is applied, large I _S flows. , I _S can be largely modulated by the applied V _G.

[Embodiment 2] Transparent IT as in Embodiment 1
A polyvinylidene fluoride film having a thickness of 56 nm is formed on the glass substrate with an O electrode by a spin coating method to form a gate insulating film 3, on which a gold source electrode 4 and a drain electrode 5 are formed.
Was formed. The channel width of both electrodes was 2 mm, and the channel length was 6 μm. Then, the compound of the above formula [5] was synthesized in the same manner as in Example 1 and dissolved with carbon tetrachloride to obtain a 3.2 wt% solution. The solution was dropped on the substrate to form a thin film having a film thickness of 62 nm by spin coating. It was left in a constant temperature bath at 90 ° C. for 1 hour to remove the solvent, and an FET element having the organic semiconductor layer 8 was produced.

The I _S / V _DS characteristics of this thin film when V _G was changed were measured and shown in FIG.

In FIG. 5, when V _G is zero V, V _DS
Although I _S hardly flows even when V _G becomes large, a large I _S flows when negative V _G is applied, and I _S could be largely modulated by the applied V _G.

Comparative Example 1 A 55 nm thick polyvinylidene fluoride film was spin-coated on a glass substrate with an ITO transparent electrode to form a gate insulating film. Next, the gold source /
A drain electrode was formed. The channel width of these electrodes is 2
mm, and the channel length was 6 μm.

Then, a known method (Clarisse, C., R
iou, M.-T., Brevet Francais 84.01164.), lithium phthalocyanine was vacuum-deposited on a substrate to form a thin film. I _S / when V _G of the thin film is changed
V _DS characteristics were measured. The result is shown in FIG.

[0056] In the FET device of the first embodiment, it is possible to reduce the I _S when not applied V _G, the I _S that can be modulated by V _G whereas reaches 5 or more orders of magnitude, in Comparative Example 1 In the fabricated FET element, I _S can be modulated by V _G
Was about two digits. Also, a good ON / OFF ratio could not be obtained with a monomolecular phthalocyanine with n = 1.

Example 3 Polystyrene containing SiO ₂ filler manufactured by Denki Kagaku Co., Ltd. (trade name FB30X) as a gate insulating film on a glass substrate with an ITO transparent electrode was dissolved in 1,2-dichloroethane at 3% by weight, A film was formed by spin coating. Next, a gold source electrode and a drain electrode were formed in the same manner as in Example 1. The channel width of these electrodes was 2 mm and the channel length was 6 μm.

Then, in the same manner as in Example 1, a solution of the compound of the above formula [3] was dropped on the substrate and spin-coated to form a thin film having a thickness of 50 nm. This was left in a constant temperature bath at 90 ° C. for 1 hour to remove the solvent and form the organic semiconductor layer 8. FIG. 7 shows the I _S / V _DS characteristics when V _G of this thin film was changed.

In FIG. 7, when V _G is zero V, V _DS
Although I _S hardly flows even when becomes larger, a large I _S flows when a negative V _G is applied. Moreover, a typical enhanced field effect transistor in which I _S is saturated in a region where V _DS is large was obtained. Also, the applied V _G
Was able to greatly modulate I _S.

Comparative Example 2 A SiO ₂ filler (FB30) was used as a gate insulating film on a glass substrate with an ITO transparent electrode.
X, manufactured by Electrochemical KK) was dissolved in 1,2-dichloroethane in an amount of 3% by weight and spin-coated to form a film. Next, gold source / drain electrodes were formed in the same manner as in Comparative Example 1. Channel width of these electrodes is 2m
m and the channel length was 6 μm.

Next, using the lithium phthalocyanine of Comparative Example 1, vacuum deposition was similarly performed to form a thin film. The Is / V _DS characteristics when V _G of the thin film was changed were measured. The measurement result is shown in FIG. 7.

[0062] In the FET device of Example 3, it is possible to reduce the I _S when not applied V _G, the I _S that can be modulated by V _G whereas reaches 5 or more digits, in Comparative Example 2 In the FET element, I _S that can be modulated by V _G was about two digits.

Comparative Example 3 A 300 nm thick SiO ₂ film was provided on a glass substrate with an ITO transparent electrode. next,
A gold source electrode and a drain electrode were formed in the same manner as in Comparative Example 1. The channel width of these electrodes was 2 mm and the channel length was 6 μm.

Next, using the lithium phthalocyanine of Comparative Example 1, vacuum deposition was performed in the same manner to form a thin film. The Is / V _DS characteristics when V _G of the thin film was changed were measured. The measurement result is shown in FIG.

[0065] In the FET device of Example 1, it is possible to reduce the I _S when not applied V _G, the I _S that can be modulated by V _G whereas reaches 5 or more digits, in Comparative Example 2 In the FET element, I _S that can be modulated by V _G was about one digit. A good ON / OFF ratio was not obtained with a monomolecular phthalocyanine of n = 1.

[0066]

INDUSTRIAL APPLICABILITY The present invention uses a polymacrocyclic azaannulene-based compound represented by azaphthalocyanine, phthalocyanine, or naphthalocyanine derivative, which is excellent in stability in air, as an organic semiconductor thin film of a FET device, and uses it as a gate insulating film. By using an insulating polymer having a relatively large dielectric constant, a FET element that is stable, has a long life, has high carrier mobility, and has excellent electrical characteristics can be obtained.

Further, since a large number of the above-mentioned organic semiconductor thin films can be uniformly formed on a large-area substrate, FE
It is possible to provide a matrix type liquid crystal display device having a T element.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a field effect transistor according to an embodiment of the present invention.

FIG. 2 is a schematic cross-sectional view of a liquid crystal display device having a field effect transistor according to an embodiment of the present invention.

FIG. 3 is an explanatory diagram illustrating a conduction mechanism of an organic semiconductor layer of the present invention.

FIG. 4 is a graph showing the relationship between the source-drain voltage (V _DS ) and the source-drain current (I _S ) of the FET element of Example 1.

FIG. 5 is a graph showing the relationship between the source-drain voltage (V _DS ) and the source-drain current (I _S ) of the FET device of Example 2.

[6] the gate of FET devices of Example 1 and Comparative Example 1 - G Voltage (V _G) and source - is a graph showing the relationship between the scan-to-drain current (I _S).

FIG. 7 is a graph showing the relationship between the gate voltage (V _G ) and the source-drain current (I _S ) of the FET devices of Example 3 and Comparative Example 2.

8 is a graph showing the relationship between the gate voltage (V _G ) and the source-drain current (I _S ) of the FET devices of Example 1 and Comparative Example 3. FIG.

[Explanation of symbols]

1, 14 ... Substrate, 2 ... Gate electrode, 3 ... Insulating layer, 4, 6 ...
Source electrode, 5, 7 ... Drain electrode, 8 ... Organic semiconductor layer, 9, 12 ... Alignment film, 10 ... Liquid crystal molecule, 11 ... Liquid crystal layer, 13 ... Counter electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshiki Kaneko 7-1-1, Omika-cho, Ibaraki Prefecture Hitachi Research Laboratory, Hitachi Ltd.

Claims (8)

[Claims] 1. A field-effect transistor in which the conductivity of a semiconductor layer, which is a current path between a source electrode and a drain electrode, is controlled by a gate electrode provided via an insulating layer, wherein the semiconductor layer is a poly-macrocyclic azaannulene series A field effect transistor formed of an organic compound. 2. A field effect transistor in which the conductivity of a semiconductor layer, which is a current path between a source electrode and a drain electrode, is controlled by a gate electrode provided via an insulating layer, wherein the semiconductor layer has a long axis of a compound / A field-effect transistor, which is formed of an organic compound having a minor axis length ratio of 2 or more. 3. In a field effect transistor in which the conductivity of a semiconductor layer, which is a current path between a source electrode and a drain electrode, is controlled by a gate electrode provided via an insulating layer, the semiconductor layer has a general formula [1. ] [Chemical 1] [Wherein M represents a transition metal or a metal unsubstituted, Z
¹ , Z ² , Z ³ and Z ⁴ represent a benzene ring or a naphthalene ring which is unsubstituted or has one or more monovalent substituents X ¹ , X ² , X ³ and X ⁴ , and the substituents X ¹ , X ² , X ³ and X ^{4 each} represent an alkyl group having 1 to 20 carbon atoms, an alkenyl group, a carboxy group, an alkylthio group, an aromatic hydrocarbon group, an acyl group or a tri-substituted silyl group. n is an integer of 2 or more and m is an integer smaller than n. ] It is formed with the organic compound represented by these, The field effect transistor characterized by the above-mentioned. 4. The field effect transistor according to claim 1, wherein the insulating layer is formed of a polymer material having a dielectric constant of 9 or less within an operating temperature range. 5. The field effect transistor according to claim 1, wherein the insulating layer is made of a polymer material containing ceramic powder. 6. A plurality of address lines and a plurality of signal lines are provided in a matrix form so as to face each other on a pair of opposing substrates, and a field effect transistor arranged at an intersection of the matrix wirings, An active matrix type liquid crystal display device in which a liquid crystal layer is sandwiched by a pixel electrode connected to the signal line via a field effect transistor and a counter electrode facing the pixel electrode and connected to the address line. The semiconductor layer, which is a current path between the source electrode and the drain electrode of the field effect transistor, is formed of a polymacrocyclic azaannulene organic compound, and its conductivity is controlled by a gate electrode provided through an insulating layer. A liquid crystal display device comprising: 7. The semiconductor layer has the general formula [1]: [Wherein M represents a transition metal or a metal unsubstituted, Z
¹ , Z ² , Z ³ and Z ^{4 each} represent a benzene ring or a naphthalene ring which is unsubstituted or has one or more monovalent substituents X ¹ , X ² , X ³ and X ⁴ , and the substituents X ¹ , X 3 ² , X ³ and X ^{4 each} represent an alkyl group having 1 to 20 carbon atoms, an alkenyl group, a carboxy group, an alkylthio group, an aromatic hydrocarbon group, an acyl group or a tri-substituted silyl group. n is an integer of 2 or more and m is an integer smaller than n. ] The liquid crystal display device of Claim 6 formed with the organic compound represented by these. 8. The insulating layer is formed of a polymer material having a dielectric constant of 9 or less within an operating temperature range.
The liquid crystal display device according to item 1.