Leakage current mechanisms in Hydrogen-passivated fine-grain polycrystalline Silicon on insulator MOSFET's

In this paper we identify various sources of leakage current in thin-film silicon on insulator (SOI) MOSFET's made in hydrogen-passivated small-grain polycrystalline silicon. The action of a parasitic bipolar transistor that can amplify the leakage current due to the thermally generated carriers has been confirmed and characterized. A current gain (β) of more than 6 for the parasitic bipolar transistor has been experimentally measured in accumulation-mode devices, in spite of the presence of a large number of defects. This high gain is attributed to the presence of the vertical electric field, which separates the carriers, thus reducing the probability of recombination. The presence of field-enhanced generation is shown to be the cause of the observed increase in the leakage current with positive front- or back-gate bias for p-channel accumulation-mode devices. Reasonable agreement has been obtained between experimental data and theory based on field-enhanced generation due to Poole-Frenkel barrier lowering.