Thin-Film Transistors
“A thin-film transistor (TFT) is a special kind of field-effect transistor made by depositing thin films of a semiconductor active layer as well as the dielectric layer and metallic contacts over a supporting substrate. A common substrate is glass, since the primary application of TFTs is in liquid crystal displays. This differs from the conventional transistor where the semiconductor material typically is the substrate,. (Wikipedia, Thin-Film Transistor, 4/8/2011)
"Thin film transistors (TFTs) are fundamental components in modern-age electronics, including, for example, sensors, image scanners, and electronic display devices. TFT circuits using current mainstream silicon technology may be too costly for some applications, particularly for large-area electronic devices such as backplane switching circuits for displays (e.g., active matrix liquid crystal monitors or televisions) where high switching speeds are not essential. The high costs of silicon-based TFT circuits are primarily due to the use of capital-intensive silicon manufacturing facilities as well as complex high-temperature, high-vacuum photolithographic fabrication processes under strictly controlled environments. It is generally desired to make TFTs which have not only much lower manufacturing costs, but also appealing mechanical properties such as being physically compact, lightweight, and flexible. Organic thin film transistors (OTFTs) may be suited for those applications not needing high switching speeds or high densities."
"The performance of a TFT can be measured by at least three properties: the mobility, current on/off ratio, and threshold voltage. The mobility is measured in units of cm.sup.2/Vsec; higher mobility is desired. A higher current on/off ratio is also desired. Threshold voltage relates to the bias voltage needed to be applied to the gate electrode in order to allow current to flow. Generally, a threshold voltage as close to zero (0) as possible is desired."
"Most high-performance organic semiconductors suffer from either (1) significant degradation of their electrical properties when exposed to air; or (2) poor solution processability. Some solution-processable, high-performance polythiophene semiconductors are known for electronic device applications. For example, described in U.S. Pat. Nos. 6,770,904; 7,132,500; 7,282,733; 7,250,625; and 7,141,644 (all of which are hereby fully incorporated by reference) is the use of a semiconducting polythiophene referred to as PQT-12:"
Recent US Patents
11/23/2010
7,837,903
Polythiophenes and electronic devices comprising the same
Lu, Wu and Yuning of Xerox, Connecticut, developed polythiophene copolymers which do not require the use of chlorinated solvents to achieve high solubility. These polythiophenes also have high mobility and good on/off ratio performance and are used for thin film transistors. (RDC 4/8/2011)