Alleviating Electrical Degradation under Self-Heating Stress in LTPS TFTs by Structural Partitioning

Chih-Ying Lien^1*, Ting-Chang Chang¹, Hong-Chih Chen², Kuan-Ju Zhou¹, Li-Chuan Sun³

¹Department of Physics, National Sun Yat-Sen University, Kaohsiung, Taiwan
²Department of Photonics, National Cheng Kung University, Tainan, Taiwan
³Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan

* Presenter:Chih-Ying Lien, email:Debby0327@gmail.com

In this study, the electrical properties of a p-type low temperature poly silicon (LTPS) device under self-heating stress was thoroughly investigated. During high current operation, a large amount of heat was generated. Due to the inherent grain boundaries in LTPS, significant amounts of grain boundary traps and interface traps between the channel and the oxide were generated. With increasing stress time, more heat accumulates and negative bias temperature instability (NBTI) was clearly observed. Therefore, the I-V transfer curves in the linear region exhibit significant degradation. Devices with different partition widths were investigated, and results showed that heat can be effectively dissipated in the most partitioned structure, effectively alleviating electrical degradation. A threshold voltage (Input subscript of V:_th) left shift and subthreshold swing (S.S.) collapse were also improved. After identifying the degradation mechanism, COMSOL simulation was used to verify the heat dissipation, confirming that the width partition structure can improve reliability.

Keywords: LTPS, Self-heating stress, Grain boundaries, NBTI, Width partition