OLED display backplanes, part 3 of 7: polycrystalline silicon (LTPS)

This is the third article in our OLED display backplane series. In the first article, we introduced display backplanes and discussed the PMOLED display architecture, and then in the second article we discussed amorphous silicon (a-Si). 

In this article, we examine polycrystalline silicon, understand how it gave OLED the mobility and stability it needed to become the AMOLED backplane of choice - and also look at its scalability limitations.

From amorphous to polycrystalline

LTPS, or Low-Temperature Polycrystalline Silicon, starts from the same amorphous silicon we met in the previous article, then crystallizes it into polysilicon, which is silicon arranged into ordered crystalline grains rather than a disordered film. The "low temperature" matters because the whole thing has to happen on display glass substrate, and stay below roughly 600°C. Normally classic polysilicon requires much higher temperatures.