The leakage currents of amorphous silicon thin-film transistors: injection currents, back channel currents and stress effects

Transient leakage currents in amorphous silicon thin-film transistors caused by injection at the drain contact are investigated using up to one hundred devices connected in parallel. Transients extend to many seconds and vary in characteristics with the gate off-voltage. Electron back channel conduction has the distinguishing feature of a transient current that increases in time. Hole injection instead shows a monotonic decay to the steady state. The dependence on the bias, temperature, and sample stress history for both mechanisms is studied. Light soaking/annealing cycles are used to probe the effect of the density of defects in the channel, while a high-temperature bias stress introduces charges in the gate insulator.