Thin-film Transistor Device Characteristics

Thin-film Transistor Device Characteristics 11.3.3.1 a-Si H TFTs 

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Figure 10.13. (a) SEM image of ZnO nanorods coated with octylamine. Scale bar, 200 nm. (b) Uniform nanorod film fabricated by spin coating of ZnO nanorods. Scale bar, 500 nm. The nanorods assemble into domains with nematic ordering, (c) Saturated transfer characteristics for a thin-film transistor fabricated by spin coating of ZnO nanorods with different ligands octylamine (solid line), butylamine (dashed line). Vi = 60V. (d) Output characteristics of a spin-coated device made from octylamine-stabilized ZnO nanorods.The device structure is shown in the inset in (c). Reproduced from Ref. 83, Copyright 2006, with permission from the American Chemical Society. 

Y.-Y. Lin, D. J. Gundlach, S. F. Nelson, T. N. Jackson, Stacked pentacene layer organic thin-film transistors with improved characteristics, IEEE Electr. Device L. 1997, 18, 606-608. 

Francis Gamier [3, and references given therein] fabricated the first transistor using molecules of sexithiophene. The transistor could be twisted, bent or rolled without degrading its characteristics. Computers fabricated using these devices will work at less than one thousandth of the speed of those made with amorphous Si transistors. They would be useful in video displays and liquid-crystal displays. In active matrix displays, each pixel is controlled individually by a thin film transistor. A 50 cm full color display contains more than two million pixels. Organic transistors, considerably cheaper than the amorphous Si transistors being used at present, will be a boon to the manufacturers. 

Unlike thin film transistors, electroluminescence devices operate in a high electric field, and therefore homogeneity and low defect density of the thin films are more important than the carrier transport characteristics. In this sense, the approach to the use of nematic semiconductors by Kelly and O Neill should be reasonable. 

Polycrystalline silicon thin film transistors have also been employed for the detection of DNA hybridization [16]. A mixed self-assembled monolayer of thiolated DNA probes and mercapto-hexanol was immobilized onto the gold gate of an extended gate poly-Si TFT. A shift of the I-V characteristics on the order of 300 mV was obtained upon hybridization of the immobilized probe with a fully complementary strand. The shift is independent of electrode area, so microarrays can be constructed where a known DNA probe is immobilized on each FET. The inherent miniaturization and compatibility with microfabrication technologies make the technique highly promising for the development of low-cost portable devices. 

Prior to the development of thin film transistors (TFT) and active matrix technology for liquid crystal displays, the maximum number of hnes or rows in any display with an acceptable contrast was severely limited by the shallow voltage-transmission characteristics of, for instance, the twisted nematic mode. This inspired work to develop a liquid crystal device that could remain in either of two states (ideally black and white) after the removal of the electric field used to switch the liquid crystal into the selected state. With a memory in the liquid crystal an unlimited number of hnes can be displayed using a simple passive matrix and the constraints are instead in the refreshment requirements. 

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