Active solid-state devices (e.g. – transistors – solid-state diode – Organic semiconductor material
Reexamination Certificate
1996-01-29
2001-12-04
Thomas, Tom (Department: 2814)
Active solid-state devices (e.g., transistors, solid-state diode
Organic semiconductor material
Reexamination Certificate
active
06326640
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to an organic thin film transistor (TFT) and more specifically to TFTs with enhanced carrier mobility.
BACKGROUND OF THE INVENTION
Organic TFTs are generally composed of in sequence a conductive gate electrode, a layer of gate insulator, a thin (less than 1 micron in thickness) layer of active (semiconductive) organic material and two laterally-spaced conductive strips as source and drain electrodes. The transistor can operate either in the enhancement or in the depletion mode depending on the polarity of the voltage applied to the gate electrode.
The first examples of organic TFTs were based on two organic conjugated polymers, polyacetylene (for example, F. Ebisawa et. al. J. Appl. phys. 54, 3255 (1983)) and polythiophene (for example, A. Assadi et. al. Appl. Phys. Lett. 53, 195 (1988)). Organic TFTs have also been fabricated with organic molecular semiconductors, such as metallophthalocyanines (for example, G. Guillaud et. al. Chem. Phys. Lett. 167, 503 (1990)) and &agr;-sexithienyl (for example, X. Peng et. al. Appl. Phys. Lett. 57, 2013 (1990)).
In addition to low cost, abundance of raw materials, and the possibility of large-area applications by using the simple techniques of spin coating and vacuum evaporation, organic TFTs have the advantage of low process temperature, typically less then 200° C., as compared to conventional polycrystalline or amorphous silicon based thin film transistors, which generally require a process temperature above 350° C. The low process temperature allows organic TFTs to be fabricated on plastic substrates, which are generally vulnerable to high temperature. Organic TFTs on plastic substrates are attractive for portable, thin, light-weight, flexible active-matrix display applications such as plastic liquid crystal displays, plastic organic and inorganic electroluminescence displays.
Up to now, the development of organic TFTs has been hindered by the poor semiconducting properties of the organic materials used, exemplified by their carrier mobility value I as low as 10
−4
to 10
−5
cm
2
V
−1
s
−1
. One of the best organic TFTs is based on &agr;-sexithienyl reported by Garnier and co-worker with carrier mobility of 4.6×10
−1
cm
2
V
−1
s
−1
by manipulation of the gate insulator (Adv. Mater. 2, 592 (1990)). The result is comparable to those of hydrogenated amorphous silicon in a conventional MISFET, but the device is far from practical due to the hygroscopic property of the gate insulator used.
It is a purpose of this invention to disclose a new organic TFT structure that provides an organic TFT with enhanced carrier mobility.
It is another purpose of this invention to provide an organic TFT on plastic substrate for flexible, light-weight, large-area, display applications.
SUMMARY OF THE INVENTION
The above described problems and others are substantially solved and the above purposes and others are realized in an organic thin film transistor including a gate electrode, a layer of gate insulator material, a source electrode, a drain electrode and a layer of uniaxially aligned organic semiconductor material positioned between or underneath the source and drain electrodes in the direction from the source to the drain electrodes, wherein the alignment of the organic semiconductor is achieved by a layer of an orientation film positioned adjacent the organic semiconductor.
In the above organic TFTs, the alignment of organic semiconductor material between the source and the drain electrodes by the means of the orientation film enhances the carrier mobility from the source to the drain as compared to the un-aligned (random oriented) organic semiconductor.
REFERENCES:
patent: 4106951 (1978-08-01), Masi
patent: 5468519 (1995-11-01), Akiyama et al.
patent: 5500537 (1996-03-01), Tsumura et al.
patent: 418504A2 (1991-03-01), None
Lee Hsing-Chung
Shi Song Q.
Shieh Chan-Long
Koch William E.
Motorola Inc.
Parsons Eugene A.
Thomas Tom
Weiss Howard
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