OLED display backplanes, part 4 of 7: Oxide TFT (IGZO)

This is the fourth article in our OLED display backplane series. In the previous article, we examined LTPS, the laser-crystallized silicon that finally drove OLED displays. Here, we look at oxide TFTs (IGZO) - a transparent metal-oxide semiconductor with ultra-low leakage and large-area uniformity, the backplane behind big OLED TVs and the new wave of high-resolution IT panels.

Oxide TFTs broke the old choice between cheap-but-slow a-Si and fast-but-unscalable LTPS by using a different kind of material entirely: an amorphous metal-oxide semiconductor. The most famous is IGZO - indium gallium zinc oxide. IGZO itself was first synthesized as a crystalline ceramic material in 1985 by Dr. Noboru Kimizuka from the Tokyo Institute of Technology. In 2004, a team led by Hideo Hosono at the Tokyo Institute of Technology invented the first amorphous IGZO TFTs.

IGZO's mobility, around 10 to 15 cm²/V·s, sits neatly between a-Si's ~1 and LTPS's ~100. That is comfortably enough to drive displays a-Si never could, and it comes packaged with two properties that turned out to be transformative.