High-Voltage a-IGZO Thin Film Transistor with the Symmetrical Stair Gate-Dielectric Structure

We fabricated the a-IGZO transistors with the symmetrical stair gate-dielectric structure. The electrical properties of the studied devices are examined in detail. Both the source and drain breakdown voltage (V
BD, GS
and V
BD, GD
) of over 60 V are obtained with the L
stair
of 3 μm. It is observed that the threshold voltage (V
th
) and subthreshold voltage have a negligible variation with the length of the stair region (L
stair
). The transconductance (g
m
) slightly decreases with the L
stair
because the gate capacitance is smaller in the device with the symmetrical stair structure. The distribution of the on-resistance (R
on
) of the stair region (M
stair
) is demonstrated. The simulation is performed to further understand the operation mechanism of the symmetrical stair structure a-IGZO TFTs.