Characteristics and Reliability of Thin Flm Transistors

• Main Authors: Chi-Hong Cheng, 鄭志宏
• Other Authors: Kuei-Shu Chang-Liao
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/40742870224510690731

碩士 === 國立清華大學 === 工程與系統科學系 === 94 === In this thesis, we designed and fabricated poly-Si TFTs with various design structures. Experiment results reveal that TFTs with multi-channel design can obtain better initial characteristics such as higher Ion current, lower threshold voltage, and smaller subthreshold swing. It is because that multi-channel structure can enhance gate control ability, and furthermore improve initial characteristics. Also the leakage current of TFT with multi-channel is eliminated compared with single channel due to more effective region passivation can performed. As for multi-gate TFTs, the improvement on initial characteristic is also observed. And multi-gate TFT exhibits higher Ion current, smaller threshold voltage, and smaller subthreshold swing. After hot carrier stress, TFTs with multi-channel and multi-gate design both show poor reliability than that with single gate one which may due to higher Ion impact ionization. LDD or GOLD design can be adopted to suppress severe impact ionization induced reliability instability. Then TFTs with plasma charging effects were investigated. The initial characteristics of area antenna and peripheral antenna show less dependence to plasma charging effect. After hot carrier stress, parameter degradation and variation change with stress time. TFTs with higher area ratio (AR) don’t show obvious reliability degradation by plasma charging damage. As for peripheral TFTs, the plasma charging induced damage become vivid. It is concluded that TFTs with larger peripheral length can collect more charges than shorter peripheral one. The plasma charging damage may induce more fixed oxide trap charges and contribute poorer interface such as more interface trap states. Strengthening the roughness of the gate dielectric is one of the strategies for reducing the damage induced by the plasma charging damage effects.