An amorphous silicon TFT with annular-shaped channel and reduced gate-source capacitance

An amorphous silicon thin-film transistor (a-Si TFT) with an annular-shaped channel is presented. The annular-channel TFT (AC-TFT) is fabricated using standard design rules with 4 /spl mu/m minimum feature size which is common in large area applications such as active matrix LCD's. The AC-TFT has two times smaller gate-to-source capacitance of about 50 fF in the on-state as compared to a conventional rectangular-channel TFT (RC-TFT) which has the same on-current of more than 10 /spl mu/A at V/sub gs/=20 V and V/sub ds/=10 V. Its off-current under illumination from the gate side is about ten times lower than that of the RC-TFT.