Evaluation of polycrystalline silicon thin film transistors with the charge pumping technique

Poly-Si TFT (thin-film transistor) characteristics are evaluated by using the charge pumping technique. The generation-recombination current at the grain boundary (GB) traps is measured as the charge pumping current. Therefore, the influence of the GB traps is directly evaluated. It is confirmed that a large number of donorlike and acceptorlike traps exist at the GBs in poly-Si TFTs. The trap density is derived from the pulse frequency and pulse risetime dependence of the charge pumping current. It is observed that there is a direct correlation between the field-effect mobility and the charge pumping current. The influence of device type and process temperature on trap properties is examined using the charge pumping technique. Furthermore, the device characteristic degradation after hot carrier stress is evaluated using this technique.<
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