John Brewer

Why are High Mobility Metal Oxide TFTs So Difficult?

Silicon has been the workhorse semiconductor technology for display backplanes for over 30 years -first amorphous silicon, then laser-annealed polycrystalline silicon (LTPS) and LTPS-based low temperature polysilicon oxide (LTPO). However, the era of silicon-based backplanes has passed. Amorphous silicon TFTs are far too slow and produce too little current for premium-grade AMOLED image quality. While LTPS TFTs are fast and produce sufficient current, they are high-leakage devices requiring complex and capital-intensive fabrication processes. LTPS cannot support the sub-1Hz image refresh rates required for reducing mobile device power consumption. LTPO, while improving variable image refresh rate performance, increases G6 capital equipment cost by 25% while significantly reducing output capacity from a 30k substrate-per-month fabrication line.

The display industry today faces the fundamental challenge of moving to a more capable semiconductor for backplanes without further increasing capital expenses and manufacturing complexity. That semiconductor is amorphous metal oxide. It functions differently than amorphous or polycrystalline silicon, presenting TFT technology challenges that have stymied the display industry for over a decade.

This presentation looks at why high mobility amorphous metal oxide TFTs have frustrated the display industry, and what learnings can be taken from the 40-year history of compound semiconductors in communications semiconductors to overcome the sources of frustration.