Browsing by Author "Sze, Simon"

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A Novel Structural Design Serving as a Stress Relief Layer for Flexible LTPS TFTs
(2019-01-01)
Wang, Yu-Xuan
;
Chang, Ting-Chang
;
Huang, Shin-Ping
;
Tai, Mao-Chou
;
Zheng, Yu-Zhe
In this work a novel device structure aiming to suppress the degradations under bending in flexible devices is demonstrated, named as a wing-shape TFT. Investigations of the electrical characteristics and reliabilities are supported by simulations, theoretical calculations, and structural discussions. First, through both electrical and mechanical stress simulation, the regions of degradation are confirmed to occur at the corner of the gate insulator. After long term mechanical stress, behaviors including an abnormal hump, serious threshold voltage (Vth) shifts, on-current increase, and off-current decrease are observed. By extending the active layer, also serving as a stress relief layer, removes the degradation regions away from the main channel. Therefore, the reliability of the devices is dramatically improved. The geometries of the wings in wing-shape TFTs are also in consideration. From results, with different wing lengths, a similar improvement of the reliability is shown, but the on current is enhanced when the wing length is extended. These phenomena are realized as a result of the difference in the effective width. The proposed wing-shape LTPS TFT has its potential and benefits for future flexible displays.
A Novel Structure to Reduce Degradation Under Mechanical Bending in Foldable Low Temperature Polysilicon TFTs Fabricated on Polyimide
(2020-05-01)
Wang, Yu-Xuan
;
Chang, Ting-Chang
;
Huang, Shin-Ping
;
Tai, Mao-Chou
;
Zheng, Yu-Zhe
In this study, a novel structural device, named as a wing-shaped TFT, is proposed and is demonstrated to prevent fast deterioration under mechanical bending in foldable devices. After long-term mechanical bending, standard low-temperature polysilicon TFTs exhibit instability behaviors such as sub-channel formation, serious threshold voltage shifts, an on-current (I-ON) increase, and an off-current (I-OFF) decrease. These phenomena are believed to be due to additional oxide traps along the channel-width edges of the gate insulator after bending. In order to suppress this degradation, a wing-shaped structure is proposed. By extending the active layer, degradation regions are shifted away from the main channel. Therefore, the reliability of the devices is enhanced. The transfer characteristics show enhanced electrical behavior after being held for 48 hours in a static bent condition, with an 88% drop in threshold voltage shift as well as a 55% decrease in subthreshold swing degradation, proving better durability of the foldable TFT to bending stress for devices with these wings. Time-dependent transfer characteristics, a COMSOL simulation, and device geometry are discussed to support our findings.