Five-terminal amorphous silicon thin-film transistor structure

Hydrogenated amorphous silicon (a-Si:H) thin-film transistors (TFTs) are widely used in large area electronics applications like active-matrix liquid-crystal displays (AMLCDs) or in or X-ray and optical sensors. TFTs often suffer from source and drain series resistances that perturbate the intrinsic channel performance, especially in the cases of poor source and drain contacts or high density of states present in the a-Si:H electronic gap. To accurately evaluate the TFT intrinsic properties without the influence of the parasitic series resistances, we have previously introduced the five-terminal TFT (FT TFT), or gated-four probe TFT (GFP TFT) structure (Chen and Kanicki, 1997 and 1998). This device has two additional electrodes fabricated between the source and drain contacts. Such a structure is expected to allow for evaluation of the potential difference along the conduction channel, assuming that the potential difference is the same at the conduction channel interface (a-Si:H/a-SiN/sub x/:H) and at the back interface (substrate/a-Si:H). We show in this paper that, indeed, FT TFTs can be used to accurately study TFT conduction channel intrinsic properties.