Complementary metal-oxide-semiconductor thin-film transistor circuits from a high-temperature polycrystalline silicon process on steel foil substrates

Abstract

We fabricated CMOS circuits from polycrystalline silicon films on steel foil substrates at process temperatures up to 950 C. The substrates were 0.2-mm thick steel foil coated with 0.5-m thick SiO 2 . We employed silicon crystallization times ranging from 6 h (600 C) to 20 s (950 C). Thin-film transistors (TFTs) were made in either self-aligned or nonself-aligned geometries. The gate dielectric was SiO 2 made by thermal oxidation or from deposited SiO 2 . The field-effect mobilities reach 64 cm 2 Vs for electrons and 22 cm 2 Vs for holes. Complementary metal-oxide-silicon (CMOS) circuits were fabricated with self-aligned TFT geometries, and exhibit ring oscillator frequencies of 1 MHz. These results lay the groundwork for polycrystalline silicon circuitry on flexible substrates for large-area electronic backplanes. Index Terms-Complementary metal-oxide-semiconductor devices (CMOS), thin-film circuits, thin-film transistors (TFTs).

Flexible AMOLED displays on stainless-steel foil

“…There have been a few reports on the fabrication of Si TFTs on stainless-steel foil. 1,[10][11][12][18][19][20] Theiss et al reported hydrogenated a-Si TFTs with an inverted-staggered structure on a stainless-steel substrate. 1 Although the typical ON/OFF-current ratio of 10 7 and OFF-current on the order of 10 -12 A were obtained, the channel mobility was quite low (0.5 cm 2 /V-sec) due to the amorphous nature of active Si film.…”

“…On the other hand, since stainless-steel foil has excellent thermal dimensional stability, it is possible to apply it to the conventional low-temperature poly-Si (LTPS) process. 1,[10][11][12] Furthermore, the stainless-steel foil itself is an excellent diffusion barrier against moisture and oxygen; thus, there is no permeation issue, which is a prerequisite for flexible AMOLED displays. These are the reasons why an AMOLED display on stainless-steel foil is promising for the next generation of mobile applications.…”

Effect of bias stress on mechanically strained low temperature polycrystalline silicon thin film transistor on stainless steel substrate

“…In addition, the polycrystalline-Si ͑poly-Si͒ TFTs has attracted much attention because of the higher field-effect mobility than any other kinds of TFTs. 2 Previous researchers have reported the effect of tensile strain on the mobility of poly-Si TFTs. 3 However, no further investigation was reported for the influence of bias stress on the mechanically strained poly-Si TFT devices.…”

High Performance of Ultralow Temperature Polycrystalline Silicon Thin Film Transistor on Flexible Metal Foil Substrate

“…5) Stainless steel foil substrates are also promising candidates for flexible and robust flat panels display applications. 6,7) Compared to plastic substrate, stainless steel foil substrate offers high thermal and chemical resistance, and lithography stability. As hard inorganic materials are mainly used in ultralow temperature poly-Si (ULTPS) processes, stainless steel foil is expected to reduce stress which originates from difference in coefficient of thermal expansion.…”