Transparent And Photo-stable Zno Thin-film Transistors To Drive An Active Matrix Organic-light-emitting-diode Display Panel

摘要

Photo and electrically stable transparent ZnO thin-film transistors for an active matrix organic light emitting diode (AM-OLED) panel are reported. Oxide semiconductor-based thin-film transistors (TFTs) have been extensively studied mainly to replace Si-based TFTs in electrical and optical devices. Therefore, there have been many reports on oxide-based TFTs: transparent oxide TFTs, amorphous oxide TFTs, polycrystalline oxide TFTs, and even photo-detecting oxide TFTs. In particular, transparent ZnO-TFTs have attracted much attention as display drivers that possess some evident advantages over opaque Si-based TFTs. Transparent TFTs (TTFTs) with a large energy bandgap channel of ～3.3 eV would transmit a visible light signal to increase the aperture ratio even in the bottom emission OLED display, which could not be anticipated from any conventional opaque TFTs. Well-designed TTFTs would result in important benefits such as longer life time and lower fabrication price of OLEDs or TFT-LCDs. However, since the ZnO-TFTs usually contain defects in the ZnO channel and deep level defects in the channel/dielectric interface that generate unwanted photo-current during light transmission and device operation, the very advantages of the transparent ZnO-TFTs have never been fully utilized or demonstrated for display panels, to the best of our limited knowledge. We recently developed an effective fabrication methodology to greatly reduce the number of defects in the channel and interfacial charge trap defects using a low temperature (200 ℃) atomic layer deposition (ALD) for a ZnO semiconductor channel and Al_2O_3 dielectric. We found that our transparent ZnO-TFTs with defect-controlled channel and channel/dielectric interface maintain good photo-stability during device operation without generating much detectable photo-current. Our ZnO-TFTs showed a good mobility of ～4cm~2 V~(-1) s~(-1) and an excellent high on/off ratio of ～10~7. The display back panels with our photo-stable and fully transparent ZnO-TFT array demonstrate a successful operation of a 2.5 inch-sized bottom emission AM-OLED panel under 15 V, which exhibited a high aperture ratio of ～60%.