Influence of white light illumination on the performance of a-IGZO thin film transistor under positive gate-bias stress

a-IGZO thin films are prepared by pulsed laser deposition and fabricated into thin film transistors (TFTs) devices. In-situ X-ray photoelectron spectroscopy (XPS) illustrates that weakly bonded oxygen (O) atoms exist in a-IGZO thin films deposited under high O2 pressure, but can be eliminated by vacuum annealing. The threshold voltage (Vth) of the a-IGZO TFTs is shifted under positive gate bias, and the Vth shift is positively related with the deposition pressure. A temperature varying experiment in the range of 20-300 K demonstrates that an activation energy of 144 meV is required for the Vth shift, which is close to the activation energy for the migration of weakly bonded O atoms in a-IGZO thin films. Accordingly, the Vth shift is attributed to the acceptor-like states induced by the accumulation of weakly bonded O atoms at the a-IGZO/SiO2 interface under positive gate bias. The results provide insight into the mechanism for the Vth shift of the a-IGZO TFTs, and are helpful to the reliability design.

Section: Fabrication Of Tfts and Details Of The Electrical Measurementmentioning

confidence: 99%

Migration of weakly bonded oxygen atoms in a-IGZO thin films and the positive shift of threshold voltage in TFTs

Wang¹,

Lu²,

Li³

et al. 2022

“…7(a), under a gate voltage of 20 V, the transfer curve shows a negative shift as small as 0.95 V. Electron trapping in the gate oxide may also occur during PBS, but it results into positive shift of the transfer curve. [6,17,18] Thus, the degradation mechanism is proposed to be the drift and accumulation of the existing V 2+ o in the a-IGZO to the back-channel surface under the electric field. [4] As shown in Fig.…”

Section: Pbs and Pbis Degradationmentioning

confidence: 99%

“…[4] However, for PBIS, the transfer curve also shifts to the positive gate bias direction but the shift is less than that under PBS because the ionized oxygen vacancies (V 2+ o ) generated with the help of light move to the back channel and contribute a negative shift of the transfer curve. [5,6] The transfer curve of a-IGZO TFTs generally shifts to the negative gate bias direction under NBS due to the generation and accumulation of V 2+ o at the interface between the channel and the gate insulator. [7][8][9][10] The negative shift of the transfer curve under NBIS is more evident, where the mechanism is similar to that under NBS, but the density of V 2+ o is larger with the help of illumination.…”

Section: Introductionmentioning

confidence: 99%

Degradation and its fast recovery in a-IGZO thin-film transistors under negative gate bias stress*

Guo¹,

Zhang²,

Wang³

et al. 2021

A new type of degradation phenomena featured with increased subthreshold swing and threshold voltage after negative gate bias stress (NBS) is observed for amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs), which can recover in a short time. After comparing with the degradation phenomena under negative bias illumination stress (NBIS), positive bias stress (PBS), and positive bias illumination stress (PBIS), degradation mechanisms under NBS is proposed to be the generation of singly charged oxygen vacancies ( V o + ) in addition to the commonly reported doubly charged oxygen vacancies ( V o 2 + ). Furthermore, the NBS degradation phenomena can only be observed when the transfer curves after NBS are measured from the negative gate bias to the positive gate bias direction due to the fast recovery of V o + under positive gate bias. The proposed degradation mechanisms are verified by TCAD simulation.

“…[1] Amorphous indium-gallium-zinc oxide (a-IGZO) TFT, first reported by Nomura et al in 2004, [2] exhibits some superior properties, such as higher field-effect mobility (µ FET ) than that of a-Si TFT, low off-state current (I off ), low sub-threshold swing (SS), high on/off-current ratio, good uniformity, low temperature processing, and high transparency in the visible light range. [1][2][3][4][5][6][7][8][9] Recently, a new TFT structure named elevated-metal metal-oxide (EMMO) TFT (as shown in Fig. 1) was developed.…”

Section: Introductionmentioning

confidence: 99%

Positive gate bias stress-induced hump-effect in elevated-metal metal–oxide thin film transistors

Zhang

Wang

2017

Under the action of a positive gate bias stress, a hump in the subthreshold region of the transfer characteristic is observed for the amorphous indium-gallium-zinc oxide thin film transistor, which adopts an elevated-metal metal-oxide structure. As stress time goes by, both the on-state current and the hump shift towards the negative gate-voltage direction.The humps occur at almost the same current levels for devices with different channel widths, which is attributed to the parasitic transistors located at the channel width edges. Therefore, we propose that the positive charges trapped at the backchannel interface cause the negative shift, and the origin of the hump is considered as being due to more positive charges trapped at the edges along the channel width direction. On the other hand, the hump-effect becomes more significant in a short channel device (L = 2 µm). It is proposed that the diffusion of oxygen vacancies takes place from the high concentration source/drain region to the intrinsic channel region.