OLED display backplanes, part 2 of 7: amorphous silicon (a-Si)

This is the second article in our OLED display backplane series. In the first article, we introduced display backplanes and discussed the PMOLED display architecture. Here, we examine amorphous silicon and its limitations.

If one backplane technology made the flat-panel era possible, it is amorphous silicon. a-Si TFTs are deposited by plasma-enhanced chemical vapor deposition (PECVD) at low temperature, in a process that is mature, inexpensive and extraordinarily uniform across very large sheets of glass. That is why a-Si scales effortlessly to the biggest substrates in the industry, up to 10.5-Gen, and why it has been used (and still is) in TVs and monitors for decades.

The main weakness of a-Si is its low electron mobility: at roughly 0.5 to 1 cm²/V·s, a-Si is about a hundred times slower than the polysilicon (LTPS) we meet in the next article. For an LCD, that turns out not to matter much. For an OLED, it is one of two reasons the technology never made it to mass production.