Effect of nitrogen-doping on drain current modulation characteristics of an indium-gallium-zinc oxide thin-film transistor.

The effect of nitrogen-doping (N-doping) in an indium-gallium-zinc oxide (IGZO) channel layer on the analog, linear, and reversible drain current modulation in the thin-film transistors (TFTs) with Al-top-gate/SiOx/TaOx/IGZO stack is investigated for the potential application to artificial synaptic devices. The N-doped devices exhibit a more linear increase of drain current upon repeating positive gate biasing corresponding to synaptic potentiation, while the undoped device shows a highly non-linear and abrupt increase of drain current. Distinct from the increase of drain current at positive biasing for potentiation, the decrease of drain current for depression behavior at negative biasing is found to be the same. Whereas the increase of drain current becomes more linear, the channel conductance, magnitude of its change, and its changing speed are decreased by the N-doping. The partial replacement of oxygen with nitrogen having higher binding energy with metal-cations suppresses oxygen vacancy formation, then decreases the channel conductance. It also retards the migration of oxygen ions, then leads to a linear increase of drain current. These results reveal that the characteristics of tunable drain current such as its linearity, dynamic range, and speed could be controlled by altering internal state of IGZO channel, which is crucial for the application to artificial synapse for neuromorphic system.