Transparent-oxide-semiconductor-based self-alignment thin-film transistors (TFTs) fabricated by a back-surface exposure method were investigated. The alignment margin of the source and drain electrodes against a gate electrode was minimized. The length of the overlapping region between the gate-source and gate-drain electrodes was as small as 0.9 μm. The field-effect mobility, on-off ratio, threshold voltage, mutual conductance, and subthreshold slope were 4.3 cm2/Vs, 108, +0.5 V, 2.93 mS/mm, and 0.25 V/decade, respectively. Combined with the mutual conductance 0.88 mS and capacitance 2 pF, the estimated cutoff frequency was 70 MHz. A level-shift inverter with a super-buffer configuration, where a wide voltage margin and fast switching were expected, was fabricated. The obtained gain and logic swing was 1.8 and 2.5 V, respectively.
