Gated-four-probe TFT structure: A new technique to measure the intrinsic performance of a-Si:H TFT

A new technique to determine the intrinsic performance of hydrogenated amorphous silicon (a-Si:H) thin film transistor (TFT) without any influence from source/drain series resistances is proposed. This technique is based on a-Si:H gated-four-probe (GFP) TFT structure. In this method, two probes within the channel of a conventional inverted-staggered a-Si:H TFT are used to measured the voltage difference. By correlating this voltage difference with the drain-source current induced by applied gate bias, the intrinsic performance of a-Si:H TFT, such as mobility, threshold voltage and field-effect conductance activation energy, can be accurately determined without influence fi om the source/drain series resistances. The a-Si:H GFP TFT and conventional a-Si:H TFT structures are also analyzed and their properties are compared by using two-dimensional simulation based on finite element method. The influence of series resistances on a-Si:H TFT electrical performance is clearly described from the simulation results.