Polythiophenes and electronic devices generated therefrom

Details Polythiophenes and electronic devices generated therefrom Polythiophenes and electronic devices generated therefrom

2002-01-11

2004-08-03

Kielin, Erik (Department: 2813)

Active solid-state devices (e.g., transistors, solid-state diode

Organic semiconductor material

C438S099000, C528S373000

Reexamination Certificate

active

06770904

ABSTRACT:

COPENDING APPLICATIONS
Illustrated in copending applications U.S. Ser. No. 10/042,342, U.S. Ser. No. 10/042,356, U.S. Ser. No. 10/042,357, U.S. Ser. No. 10/042,359, U.S. Ser. No. 10/042,360, the disclosures of which are totally incorporated herein by reference, and filed concurrently herewith, all titled “Polythiophenes and Devices Thereof” and all filed Jan. 11, 2002, are polythiophenes and devices thereof. The appropriate components, processes thereof and uses thereof illustrated in those copending applications may be selected for the present invention in embodiments thereof.
BACKGROUND
The present invention is generally directed to polythiophenes and uses thereof. More specifically, the present invention in embodiments is directed to a class of polythiophenes wherein certain repeating thienylene units possess side chains, such as alkyl, which are arranged in a regioregular manner on the polythiophene backbone, and which polythiophenes are, for example, useful as active semiconductive materials for thin film field-effect transistors (FETs).
Semiconductive polymers like certain polythiophenes, which are useful as active semiconductor materials in thin film transistors (TFTs), have been reported. A number of these polymers have some solubility in organic solvents and are thus able to be fabricated as semiconductor channel layers in TFTs by solution processes, such as spin coating, solution casting, dip coating, screen printing, stamp printing, jet printing and the like. Their ability to be fabricated via common solution processes would render their manufacturing simpler and cost effective as compared to the costly conventional photolithographic processes typical of silicon-based devices such as hydrogenated amorphous silicon TFTs. Moreover, desired are transistors fabricated with polymer materials, such as polythiophenes, referred to as polymer TFTs, with excellent mechanical durability and structural flexibility, which may be highly desirable for fabricating flexible TFTs on plastic substrates. Flexible TFTs would enable the design of electronic devices which usually require structural flexibility and mechanical durability characteristics. The use of plastic substrates together with organic or polymer transistor components can transform the traditionally rigid silicon TFT into a mechanically more durable and structurally flexible polymer TFT design. The latter is of particular value to large area devices such as large-area image sensors, electronic paper and other display media. Also, the selection of polymer TFTs for integrated circuit logic elements for low end microelectronics, such as smart cards, radio frequency identification (RFID) tags, and memory/storage devices, may also greatly enhance their mechanical durability, and thus their useful life span. Nonetheless, many of the semiconductor polythiophenes are not, it is believed, stable when exposed to air as they become oxidatively doped by ambient oxygen, resulting in increased conductivity. The result is larger off-current and thus lower current on/off ratio for the devices fabricated from these materials. Accordingly, with many of these materials, rigorous precautions have to be undertaken during materials processing and device fabrication to exclude environmental oxygen to avoid or minimize oxidative doping. These precautionary measures add to the cost of manufacturing therefore offsetting the appeal of certain polymer TFTs as an economical alternative to amorphous silicon technology, particularly for large area devices. These and other disadvantages are avoided or minimized in embodiments of the present invention.
REFERENCES
A number of organic semiconductor materials has been described for use in field-effect TFTs, which materials include organic small molecules such as pentacene, see for example D. J. Gundlach et al., “Pentacene organic thin film transistors—molecular ordering and mobility”,
IEEE Electron Device Lett
., Vol. 18, p. 87 (1997), to oligomers such as sexithiophenes or their variants, see for example reference F. Garnier et al., “Molecular engineering of organic semiconductors: Design of self-assembly properties in conjugated thiophene oligomers”,
Amer. Chem. Soc
., Vol. 115, p. 8716 (1993), and certain polythiophenes, such as poly(3-alkylthiophene), see for example reference Z. Bao et al., “Soluble and processable regioregular poly(3-hexylthiophene) for field-effect thin film transistor application with high mobility”,
Appl. Phys. Lett
. Vol. 69, p4108 (1996). Although organic material based TFTs generally provide lower performance characteristics than their conventional silicon counterparts, such as silicon crystal or polysilicon TFTs, they are nonetheless sufficiently useful for applications in areas where high mobility is not required. These include large area devices, such as image sensors, active matrix liquid crystal displays and low end microelectronics such as smart cards and RFID tags. TFTs fabricated from organic or polymer materials may be functionally and structurally more desirable than conventional silicon technology in the aforementioned areas in that they may offer mechanical durability, structural flexibility, and the potential of being able to be incorporated directly onto the active media of the devices, thus enhancing device compactness for transportability. However, most small molecule or oligomer-based devices rely on difficult vacuum deposition techniques for fabrication. Vacuum deposition is selected primarily because the small molecular materials are either insoluble or their solution processing by spin coating, solution casting, or stamp printing do not generally provide uniform thin films. In addition, vacuum deposition may also involve the difficulty of achieving consistent thin film quality for large area format. Polymer TFTs, such as those fabricated from regioregular polythiophenes of, for example, regioregular poly(3-alkylthiophene-2,5-diyl) by solution processes, while offering some mobility, suffer from their propensity towards oxidative doping in air. For practical low cost TFT design, it is therefore of value to have a semiconductor material that is both stable and solution processable, and where its performance is not adversely affected by ambient oxygen, for example, regioregular polythiophenes such as poly(3-alkylthiophene-2,5-diyl) are very sensitive to air. The TFTs fabricated from these materials in ambient conditions generally exhibit very large off-current, very low current on/off ratios, and their performance characteristics degrade rapidly.
References that may be of interest include U.S. Pat. Nos. 6,150,191; 6,107,117; 5,969,376; 5,619,357, and 5,777,070.
FIGURES
Illustrated in
FIGS. 1
to
4
are various representative embodiments of the present invention and wherein polythiophenes are selected as the channel materials in thin film transistor (TFT) configurations.
SUMMARY AND EMBODIMENTS
It is a feature of the present invention to provide semiconductor polymers such as polythiophenes, which are useful for microelectronic device applications, such as TFT devices.
It is another feature of the present invention to provide polythiophenes with a band gap of from about 1.5 eV to about 3 eV as determined from the absorption spectra of thin films thereof, and which polythiophenes are suitable for use as TFT semiconductor channel layer materials.
In yet a further feature of the present invention there are provided polythiophenes which are useful as microelectronic components, and which polythiophenes have reasonable solubility of, for example, at least about 0.1 percent by weight in common organic solvents, such as methylene chloride, tetrahydrofuran, toluene, xylene, mesitylene, chlorobenzene, and the like, and thus these components can be economically fabricated by solution processes such as spin coating, screen printing, stamp printing, dip coating, solution casting, jet printing, and the like.
Another feature of the present invention resides in providing electronic devices, such as TFTs with a polythiophene channel layer, and which layer has a conductivi

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