Air Force

Short-gate length, thin-film transistors

Method may be used to fabricate transistors with channels as small as a few nanometers


Thin-film electronics are particularly useful for large area electronics that can be made over non-planar and flexible substrates. Thin-film transistors (TFT) are the basic building blocks of large area electronic circuits such as those used in the backplanes of active matrix liquid crystal displays (AMLCD) of the type often used in flat panel monitors and televisions. In these applications, TFT based circuits are used to control the activation of pixels that make up the display. The speed of TFT relate directly to their gate length, which must be kept as short as possible to lower electron transport time between electrodes and improve high frequency response characteristics. Since current density is proportional to gate width and gate length, reduced gate length improves device current density capability. However, wavelength-related limitations of optical lithography make it suitable only for line widths larger than 1 micrometer. Advanced and costly lithography techniques involving electron beams, phase shift techniques, etc., are generally not compatible with large area electronics.

Air Force researchers have overcome the problems associated with the fabrication of short gate length metal oxide TFT using conventional photolithography techniques. The methodology relies on the fabrication of self-aligned contacts with controlled gap between them and is compatible with large area substrates. Further, the channel length dimension is controlled by process parameters and not by lithography resolution.

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