Mechanism Analysis of Current--Voltage Characteristic in a Lightly Doped Drain Polycrystalline Silicon Thin-Film Transistor Using Activation Energy

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We have analyzed the mechanism of the current--voltage characteristic in a lightly doped drain (LDD) polycrystalline silicon (poly-Si) thin-film transistor (TFT) by investigating the activation energy (E_{\text{a}}) in an experiment and the energy band calculated using device simulation. In the off state, E_{\text{a}} decreases as the gate voltage (V_{\text{gs}}) and drain voltage (V_{\text{ds}}) increase, which suggests that the off-leakage current is subject to phonon-assisted tunneling with the Poole--Frenkel effect at the junction between the LDD and drain regions. In the subthreshold state, E_{\text{a}} sharply decreases as V_{\text{gs}} increases, which suggests that the subthreshold-transition current is subject to the potential barriers at the junctions between the source, LDD, and channel regions. In the on state, E_{\text{a}} gradually decreases as V_{\text{ds}} increases, which suggests that the on current is subject to the potential barriers at the grain boundaries.
2012-03-25