|Materials Technologies for Flat Panel Displays IV
In this issue we look at one of the key areas of materials technology in displays, namely the backplane of the display. The backplane is what drives the display, turning pixels on and off. The Flat Panel Display industry has used amorphous-Si for the backplane thin film transistors (TFTs) since the late 1980s with the commercial breakthrough starting in the mid to late 1990s. This material has disadvantages like low mobility and high leakage current. Currently, high performance small displays (e.g. “retina” displays) use LTPS (low temperature poysilicon) backplanes but it is relatively expensive and difficult to scale up for large displays, which partly relates to the presence of grain boundaries. The recent development has been the introduction of amorphous metal oxide TFTs, particularly Indium- Gallium- Zn- Oxide (IGZO), which was first protoyped as a TFT in 2004 by Professor Hosono’s group in Japan. They have high mobility, low leakage current (key for mobile displays to reduce power consumption), and allow low cost processing. Sharp is the current technology leader: their partner developed a special IGZO variant with a novel structure. This Newsletter looks at recent technical and commercial developments in backplane display technology. The technology is not only applicable to glass substrate LCDs and OLEDs but also flexible displays on polymer; metal oxide TFTs can be deposited at low temperature and there is active research on solution based processing.