Oxygen-Adsorption-Induced Anomalous Capacitance Degradation in Amorphous Indium-Gallium-Zinc-Oxide Thin-Film-Transistors under Hot-Carrier Stress

Abstract

This paper investigates anomalous capacitance-voltage (C-V) degradation in amorphous indium-gallium-zinc-oxide (a-IGZO) thinfilm-transistors (TFTs) under hot carrier stress. In vacuum hot carrier stress, both the gate-to-drain capacitance (C GD ) and the gateto-source capacitance (C GS ) curves exhibited positive shifts due to electron trapping in the gate dielectric. In addition, an observed increase in capacitance value at a lower gate voltage in the C GD measurement only can be ascribed to interface state creation. However, when the hot carrier stress was performed in an oxygen-rich environment, the C GD -V G curve showed a significantly positive shift due to the electric-field-induced oxygen adsorption near the drain terminal. The degradation in the C GS -V G curve is due not only to the positive shift, but also the anomalous two step turn-on behavior. This phenomenon can be ascribed to the electron trapping in the gate dielectric and electric-field-induced oxygen adsorption on the channel layer, especially in the area adjacent to the drain terminal. The electron trapping increased the source energy barrier, with the electric-field-induced oxygen adsorption further raising the energy-band near the drain, resulting in a two-step turn-on behavior in the C GS -V G curve.

Effects of electron trapping and interface state generation on bias stress induced in indium–gallium–zinc oxide thin-film transistors

“…Transparent amorphous indium-gallium-zinc oxide thin-film transistors (a-IGZO TFTs) have been attracting considerable attention for their wide applications, such as in active-matrix liquid crystal displays (AMLCDs), active-matrix organic light emitting diodes (AMOLEDs), flexible displays, and transparent displays, owing to their advantages of high mobility, excellent on/off ratio, high transparency, and low processing temperature. [1][2][3][4][5] Although a-IGZO TFTs offer excellent performance, electrical instability issues, such as threshold voltage (V TH ) shift under gate bias temperature stress (BTS), negative effect of light exposure, and degradation by hot carriers in the operating mode, still remain. [6][7][8][9][10][11][12][13][14][15][16] The V TH shift under gate bias stress due to charge trapping and detrapping in the gate insulator or at the insulator/channel interface has been reported.…”

Hot carrier effects in InGaZnO thin-film transistor

“…5,8,13) In TAOS-TFTs, many researchers predicted the existence of hot carriers as one of the degradation models of device reliability from transfer characteristics and capacitancevoltage (C-V ) characteristics. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] However, it is a discussion point as to whether the generation of hot carriers is possible or not because TAOS such as IGZO have an amorphous structure and exhibit relatively low mobility of around 10 cm 2 V −1 s −1 compared with poly-Si or sc-Si. When hot carriers are generated in TAOS-TFTs, photon emission should be observed.…”

High-performance transparent, all-oxide nonvolatile charge trap memory transistor using In-Ga-Zn-O channel and ZnO trap layer

“…According to previous works, in bottom-gate TFTs, the threshold voltage (V TH ) may easily shift in the negative or positive direction due to the absorption or desorption of oxygen and/or water molecules at the back channel surface. [13][14][15][16][17] For our proposed Ox-CTMT, a 9-nm-thick Al 2 O 3 layer was deposited onto the IGZO channel as a protection layer. However, this thin Al 2 O 3 layer was found to be rather insufficient to completely protect against environmental influences.…”