Gate bias instability in hydrogenated polycrystalline silicon thin-film transistors

The instability of n-channel hydrogenated polycrystalline silicon thin-film transistors has been investigated with respect to gate biasing. The hydrogenation was performed by hydrogen ion implantation through the gate oxide. The conduction mechanism in the gate oxide was studied for positive and negative gate bias, showing that the electron tunneling is much higher for positive gate bias. The oxide conduction follows the Fowler–Nordheim (FN) tunneling mechanism for electron tunneling from the channel and Poole–Frenkel for electron tunneling from the gate polysilicon. After constant FN stressing for short duration (<10 min), the evolution of the transfer characteristics with stress time indicate passivation of the grain boundary dangling bonds by the H+ positive ions introduced into the gate during hydrogenation with simultaneous electron injection into the gate oxide and interface states generation. For longer FN stress duration, the transfer characteristics are degraded due to enhancement of the donor-like interface states generation.