Thin film semiconductor devices have been investigated over the past twenty years for application in large area flat panel displays. The development of thin film transistors and diodes based on amorphous silicon (a-Si) alloy materials has made the application of these devices, to display technologies, very attractive. More recently, manufacturing techniques to produce high quality large area films of amorphous silicon alloys have been demonstrated for photovoltaic applications.
Most of the current research and development effort on active matrix liquid crystal displays (LCDs) has concentrated on a-Si alloy TFTs. The success of TFT based displays for large area flat panel displays has been limited so far, mainly due to the difficulty of obtaining a high quality gate dielectric by plasma deposition and due to the presence of crossing conductors on the same substrate, both increasing the probability of defects in the display. When a two terminal sandwich device is used, on the other hand, no gate dielectric is required, hence, a higher yield can be expected. Metal-insulator-metal and hydrogenated amorphous silicon alloy devices have been proposed for incorporation in LCDs. Performance requirements for a useful active matrix switching element and a comparison among the different a-Si alloy thin film devices used for this purpose will be reviewed.