Modeling of anomalous charge-pumping current in polycrystalline silicon thin film transistors = 다결정 실리콘 박막 트랜지스터에서의 전하 펌프 전류 모델링

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In this dissertation, anomalous charge pumping current of polycrystalline silicon thin film transistors (poly-Si TFTs) is analyzed and modeled. In contrast with the conventional MOSFETs, large substrate resistance of poly-Si TFTs can suppress the carrier supply from the body and source/drain regions, which distorts the charge pumping current especially at high frequency range. The model can describe well the anomalous frequency characteristics that the charge pumping current starts to decrease with frequency above a critical frequency. The critical frequencies for several devices with different sizes were calculated and these were in good agreement with those of experiment. The model suggests frequency range and size of devices should be chosen carefully for the correct evaluation of trap state density. Based on the model, process influence on traps and electrical characteristics were examined for two kinds of devices: one with a gate oxide by electron cyclotron resonance (ECR) $O_2$ plasma oxidation and the other with a chemical vapor deposition (CVD) oxide. Hole capture cross section was extracted to be $1.0\times10^{-17}cm^{-2}$ for both groups, but the ECR group shows much larger substrate resistance and lower trap density which is thought to be caused by an $O_2$ passivation effect. The trap characteristics of the ECR group are related with excellent electrical characteristics such as higher mobility, lower subthreshold slope and leakage current. We also showed by calculations and verified by experiments that the substrate resistance of poly-Si TFTs causes the large geometric component especially when the gate pulse transition time is short. We proposed a model for the geometric component explaining the rising/falling time dependence of the charge pumping current in poly-Si TFTs, which is helpful to decide the proper range of gate pulse transition times for extracting the energy distribution of traps. The proposed model is confirmed by the experimental ...
Han, Chul-Hiresearcher한철희researcher
한국과학기술원 : 전기및전자공학과,
Issue Date
156191/325007 / 000965261

학위논문(박사) - 한국과학기술원 : 전기및전자공학과, 1999.8, [ vi, 154 p. ]


Polysilcon; Charge-pumping; TFT; 박막트랜지스터; 다결정실리콘; 전하펌프

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