Abstract
In this paper, the gate oxide thickness, and the channel length and width of
low-temperature poly-Si thin-film transistors (LTPS-TFTs) have been comprehensively
studied. The scaling down of gate oxide thickness from 50 to 20 nm significantly
improves the subthreshold swing (S.S.) of LTPS-TFTs from 1.797 V/decade to 0.780
V/decade and the threshold voltage V<sub>TH</sub> from 10.87 V to 5.00 V. Moreover, the
threshold voltage V<sub>TH</sub> roll-off is also improved with the scaling down of gate
oxide thickness due to gate capacitance density enhancement. The channel length scaling
down also shows significant subthreshold swing S.S. improvement due to a decreasing of
the channel grain boundary trap density N<sub>t</sub>. However, the scaling down of channel
length also increases the series resistance effect, resulting in the degradation of the
field-effect mobility μ<sub>FE</sub>. Therefore, the channel length dependence of
field-effect mobility μ<sub>FE</sub> is slightly different with different channel width
due to the competition of channel grain boundary trap density effect and series
resistance effect.
© 2011 IEEE
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