Browsing by Author "Xu, NingSheng"

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Nitrogen-Doped Amorphous InZnSnO Thin Film Transistors With a Tandem Structure for High-Mobility and Reliable Operations
(2016-05)
Li, GongTan
;
Yang, Bo-Ru
;
Liu, Chuan
;
Lee, Chia-Yu
;
Wu, Yuan-Chun
The threshold voltage shift (Delta V-th) in amorphous InZnSnO thin-film transistors (a-IZTO TFTs) during negative gate-bias stress (NGBS) is significantly improved by nitrogen doping. Numerous N-In bonds eliminate donorlike subgap states near the Fermi level, which improve stability during stress but degrade electron mobility. We developed tandem TFTs with an a-IZTO:N layer on top of an a-IZTO layer, in which mobility reaches 31.76 +/- 0.81 cm(2)/Vs and the reliability is improved. Especially, Delta V-th in NGBS is reduced by 80% for pristine a-IZTO devices. This simple but an effective method achieves fast and reliable operation in the a-IZTO TFTs.
Positive gate bias instability alleviated by self-passivation effect in amorphous InGaZnO thin-film transistors
(2015-12-02)
Li, GongTan
;
Yang, Bo-Ru
;
Liu, Chuan
;
Lee, Chia-Yu
;
Tseng, Chih-Yuan
The threshold voltage shift (Delta Vth) under positive gate bias stress (PGBS), generally found in amorphous InGaZnO thin-film transistors (a-IGZO TFTs), has usually been suppressed by external passivation layers. We report it can also be alleviated by the self-passivation effect of the active layer, where moderately increasing the active layer thickness (d(s)) reduces Delta Vth by 82% in SiOx-passivated a-IGZO TFTs. Our experiments in conjunction with simulations show that the instability of V-th comes from ambient factors at the back channel. Larger d(s) results in lower carrier concentrations at the back channel (N-back), fewer diffusive ions affecting the front channel, and much more stable operations under PGBS. The optimal thickness of an IGZO film simultaneously obtaining a small Delta V-th, near-zero Vth, and sharp sub-threshold swing is about 80-90 nm, thicker than those usually adopted. The self-passivation effect combined with the externally deposited passivation layer can improve the overall device reliability.
Subgap State Engineering Using Nitrogen Incorporation to Improve Reliability of Amorphous InGaZnO Thin-Film Transistors in Various Stressing Conditions
(2016-11)
Li, GongTan
;
Zhan, Runze
;
Yang, Bo-Ru
;
Liu, Chuan
;
Dong, ChengYuan
Instability of amorphous InGaZnO thin-film transistors (a-IGZO TFTs) remains an obstacle for commercialization. Here, we systematically discuss the effect of nitrogen incorporation on a-IGZO TFT stability and developed Ar/O-2/N-2 atmosphere to improve the stability under stressing in different conditions. Based on X-ray photoelectron spectrometer results, it is revealed that the positive gate bias stress (PGBS) stability is significantly improved due to microscopically passivated metal-oxygen bonds. Yet, the negative gate bias and light stress (NBLS) stability is seriously deteriorated with heavily nitrogen incorporation probably due to the bandgap narrowing effect. By optimizing a mixed O-2/N-2 atmosphere, the subgap states are finely tuned to afford optimal performance and stability. The developed IGZO TFTs exhibit mobility (12.67 cm(2)/Vs), small shift of threshold voltage under PGBS (reduced by 64% as compared with the pristine a-IGZO TFTs), and good negative gate bias stability and with NBLS stability as well.