A Self‐aligned, Trilayer, a‐Si:H Thin Film Transistor Prepared from Two Photomasks

A new self‐aligned TFT structure that requires two photomasks is described in this paper. Three process steps, i.e. , the backlight lithography, the top dielectric etch, and the n + etch, have been studied in detail. The finished TFT has transfer characteristics and I d ‐ V d curves similar to those of a TFT prepared from a more complicated conventional process. TFT structure parameters, such as the channel length, the a‐Si:H thickness, the source/drain via size, and the contact resistance, affect the field effect mobility and the I on / I off ratio. These relations were examined. Including a Ta 2 O 5 thin layer in the gate dielectric structure changes the device characteristics. The relation between the Ta 2 O 5 process and the device has been studied.