p-Channel TFT's using magnetron-sputtered Ta2O5films as gate insulators

Metal-gate thin-film transistors (TFT's) have been fabricated in layers of laser-recrystallized polycrystalline silicon on fused quartz substrates at processing temperatures below 625°C. Tantalum pentoxide (Ta
2
O
5
) was used as a gate insulator instead of a conventional thermally grown silicon dioxide (SiO
2
). Ta
2
O
5
gate insulator was deposited onto the recrystallized silicon layer at room temperature, using an RF-magnetron sputtering system. The reactive ion etching method, using CF
4
as a reactive gas, was employed in patterning deposited Ta
2
O
5
. These TFT's have exhibited p-channel depletion-mode characteristics with a threshold voltage of 2.5 V and a transconductance of 70 µS at V
g
= - 2 V. An on-off current ratio exceeding 10
⁵
has been obtained.