With their relatively low process temperature, high field-effect mobility, low leakage current and high transparency, thin-film transistors (TFTs) based on metal oxide (MO), especially indium-gallium-zinc oxide (IGZO), are being intensively studied as the promising active device of next-generation flat-panel displays, as well as other logic circuit application. The resistivity of the IGZO film is related to the thermal processes it has gone through. When the annealing atmosphere is nitrogen, or the channel region is covered by the impermeable cover, the resistivity of the IGZO layer will drop down, leading to a negative shift of threshold voltage (V_th) for the annealed IGZO TFTs. By selectively modulating the channel, depletion mode (DM) and enhancement mode (EM) TFTs can be simultaneou...[ Read more ]

With their relatively low process temperature, high field-effect mobility, low leakage current and high transparency, thin-film transistors (TFTs) based on metal oxide (MO), especially indium-gallium-zinc oxide (IGZO), are being intensively studied as the promising active device of next-generation flat-panel displays, as well as other logic circuit application. The resistivity of the IGZO film is related to the thermal processes it has gone through. When the annealing atmosphere is nitrogen, or the channel region is covered by the impermeable cover, the resistivity of the IGZO layer will drop down, leading to a negative shift of threshold voltage (V_th) for the annealed IGZO TFTs. By selectively modulating the channel, depletion mode (DM) and enhancement mode (EM) TFTs can be simultaneously fabricated with an additional photolithography step. The inverter with EM and DM TFTs exhibit rail-to-rail performance along with high gain which is compatible to CMOS based inverter. With proper annealing step, the V_th variation between DM and EM TFTs are controllable, therefore resulting in good performance of such inverter with proper operation point. This integration method for IGZO TFTs with different driving modes can be used to produce the next generation logic circuit on flexible or transparent substrate with good electrical performance for applications like wearable circuits or system on panel application.