Effect of Bulk-Accumulation on Switching Speed of Dual-Gate a-IGZO TFT-Based Circuits

The effect of bulk accumulation on switching speed of dual-gate amorphous indium-gallium-zinc-oxide thin-film transistor (TFT)-based circuits is investigated. Given that bulk accumulation is achieved by synchronized driving of the top gate (TG) and bottom gate, it can be modulated by varying the length of the TG (L
_TG
) for fixed source-drain distance (L). It is confirmed from fabricated ring oscillators that switching speed increases with increasing L
_TG
for fixed L, verifying that bulk accumulation improves switching speed. However, switching speed drops dramatically when the TG overlaps the source/drain electrodes due to additional parasitic capacitance. TFT-circuits with the longest, but nonoverlapping TGs are demonstrated to exhibit the fastest switching speed; operation frequency exceeding 2.63 MHz for input voltage V
_DD
of 20 V, which is also the fastest among all inverted staggered amorphous-oxide-semiconductor TFT-based circuits.