Delay time studies and electron mobility measurement in a-Si:H TFT

The time delay in the drain current response to a step in the effective drive voltage was studied as one of the key parameters in characterizing the dynamic response of an a-Si:H thin-film transistor (TFT). It was determined that the a-Si:H delay time shows a similar behavior to that observed in a Si-MOSFET, i.e. it is directly proportional to the square of the channel length and inversely proportional to the effective drive voltage. A unique value of the channel field-effect electron mobility was measured by using the delay time results in the transmission line model. In amorphous semiconductors, the conventional methods of measuring mobility are inconvenient and complicated, whereas in this method the channel mobility is obtained by measuring only the delay time and the threshold voltage. Both of these parameters are obtained through electrical measurements on TFTs and hence require no special device structures