Embedded LTPS flash cells with oxide-nitride-oxynitride stack structure for realization of multi-function mobile flat panel displays

In this paper, embedded flash (eFlash) cells were fabricated for realization of multi-functions, such as systems on panels (SOPs) and threshold voltage (V_TH) stabilization of flat panel displays (FPDs). Fabrication was via low temperature polycrystalline silicon (LTPS) thin film transistor (TFT) technology and an oxide-nitride-oxynitride (ONOn) stack structure on glass. Poly-silicon (poly-Si) on glass, which was annealed via an excimer laser, has a very rough surface. To fabricate LTPS eFlash cells on glass with a very rough poly-Si surface, plasma-assisted oxynitridation was performed; nitrous oxide (N₂O) served as a reactive gas. LTPS eFlash cells have excellent TFT electrical properties, such as V_TH, a high On/Off current ratio and a low sub-threshold swing (S). The results demonstrate that eFlash cells fabricated on glass with a rough silicon surface, via an ONOn stack structure, have switching characteristics suitable for data storage, such as a low operating voltage (<10 V) suitable for mobile FPDs, a threshold voltage window, ΔV_TH, which exceeds 2.3 V, between the programming and erasing (P/E) states, over a period of 10 years, and the capacity to retain the initial ΔV_TH over a period of 10 ⁵ P/E operations.