Amorphous silicon driver circuits for organic light-emitting diode displays

This article presents design considerations pertinent to amorphous silicon (a-Si:H) pixel drive circuits for mobile display applications. We describe both pixel architectures and circuit topologies that are amenable for vertically stacked organic light-emitting diode (OLED) pixels in a-Si:H technology. Here, a dual-gate transistor structure is used to minimize the parasitic coupling between the OLED and the transistor layers. We consider both the two-transistor (2-T) voltage-programmed drive circuit and the five-transistor (5-T) current-programmed drive circuit. The latter provides compensation for shifts in device characteristics by virtue of metastable shifts in the threshold voltage of the thin-film transistor (TFT). Implementation of the 5-T drive circuit using dual-gate TFTs that enables high aperture ratio (∼100%), low leakage current, and surface emissive OLED pixels that are independent of scaling is also presented, along with simulation results of transfer characteristics.