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

Abstract

In this paper, embedded flash (eFlash) cells were fabricated for realization of multi-functions, such as systems on panels (SOPs) and threshold voltage (VTH) 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 VTH, 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, ΔVTH, 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 ΔVTH over a period of 10 5 P/E operations. © 2008 IOP Publishing Ltd.