In this paper we describe the design and operation of two novel types of amorphous silicon thin-film transistors and outline their application in large-area microelectronics. We first consider a high voltage transistor that can modulate a source-drain voltage in excess of 400 volts by applying low voltages to a controlling electrode covering a small portion of the channel near to the source. Secondly, for high-current output and moderately high voltage applications, we have fabricated vertical amorphous silicon transistors with channel lengths much smaller than the lithographic minimum feature size used in their fabrication. We show the design of both these new transistors together with their physics of operation and give results of output characteristics.
The integration of low and high voltage transistors into large-area circuits has enabled us to develop new applications for amorphous silicon in printing, input scanning and electronic copying. Page-wide arrays of both ionographic and electrographic printers have been fabricated. By combining amorphous silicon photodiodes with transistor arrays, we have made high resolution document scanners and copiers with directly coupled print and sensor elements. The ability to fabricate short channel vertical transistors offers the potential to further increase the speed and resolution of these large-area circuits.