Self-aligned amorphous-silicon TFTs on clear plastic substrates

We fabricated the first bottom-gate amorphous silicon (a-Si:H) thin-film transistors (TFTs) on a clear plastic substrate with source and drain self-aligned to the gate. The top source and drain are self-aligned to the bottom gate by backside exposure photolithography through the plastic substrate and the TFT tri-layer. The a-Si:H channel in the tri-layer is made only 30 nm thick to ensure high optical transparency at the exposure wavelength of 405 nm. The TFTs have a threshold voltage of /spl sim/3 V, subthreshold slope of /spl sim/0.5 V/dec, linear mobility of /spl sim/1 cm/sup 2/V/sup -1/ s/sup -1/, saturation mobility of /spl sim/0.8 cm/sup 2/V/sup -1/s/sup -1/, and on/off current ratio of >10/sup 6/. These results show that self-alignment by backside exposure provides a solution to the fundamental challenge of making electronics on plastics: overlay misalignment.