Amorphous Silicon Back-Plane Electronics for OLED Displays

This paper reviews design considerations along with measurement results pertinent to amorphous silicon (a-Si:H) thin-film transistor (TFT) drive circuits for active matrix organic light-emitting diode displays, and follows from work presented earlier (A. Nathan et al., 2002), (A. Nathan et al., 2003). We describe both pixel architectures and TFT circuit topologies that are amenable for vertically integrated, high aperture ratio pixels. Here, the organic light-emitting diode layer is integrated directly above the TFT circuit layer to provide an active pixel area that is at least 90% of the total pixel area with an aperture ratio that remains virtually independent of scaling. Both voltage-programmed and current-programmed drive circuits are considered. The latter provides compensation for shifts in device characteristics due to metastable shifts in the threshold voltage of the TFT. Integration of on-panel gate drivers is also discussed, where we present the architecture of an a-Si:H-based gate demultiplexer that is threshold voltage shift invariant. In addition, a programmable current mirror with good linearity and stability is presented. Programmable current sources are an essential requirement in the design of source driver output stages.