Low-Temperature Polycrystalline-Silicon Thin-Film Transistors Fabricated by Continuous-Wave Laser Lateral Crystallization and Metal/Hafnium Oxide Gate Stack on Nonalkaline Glass Substrate

Tatsuya MEGURO  Akito HARA  

Publication
IEICE TRANSACTIONS on Electronics   Vol.E100-C   No.1   pp.94-100
Publication Date: 2017/01/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.E100.C.94
Type of Manuscript: PAPER
Category: Semiconductor Materials and Devices
Keyword: 
poly-Si,  TFT,  high-k,  HfO2,  CMOS,  glass substrate,  

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Summary: 
Enhancing the performance of low-temperature (LT) polycrystalline-silicon (poly-Si) thin-film transistors (TFTs) requires high-quality poly-Si films. One of the authors (A.H.) has already demonstrated a continuous-wave (CW) laser lateral crystallization (CLC) method to improve the crystalline quality of thin poly-Si films, using a diode-pumped solid-state CW laser. Another candidate method to increase the on-current and decrease the subthreshold swing (s.s.) is the use of a high-k gate stack. In this paper, we discuss the performance of top-gate CLC LT poly-Si TFTs with sputtering metal/hafnium oxide (HfO2) gate stacks on nonalkaline glass substrates. A mobility of 180 cm2/Vs is obtained for n-ch TFTs, which is considerably higher than those of previously reported n-ch LT poly-Si TFTs with high-k gate stacks; it is, however, lower than the one obtained with a plasma enhanced chemical vapor deposited SiO2 gate stack. For p-ch TFTs, a mobility of 92 cm2/Vs and an s.s. of 98 mV/dec were obtained. This s.s. value is smaller than the ones of the previously reported p-ch LT poly-Si TFTs with high-k gate stacks. The evaluation of a fabricated complementary metal-oxide-semiconductor inverter showed a switching threshold voltage of 0.8 V and a gain of 38 at an input voltage of 2.0 V; moreover, full swing inverter operation was successfully confirmed at the low input voltage of 1.0 V. This shows the feasibility of CLC LT poly-Si TFTs with a sputtered HfO2 gate dielectric on nonalkaline glass substrates.