Explicit approximation of surface potential for fully-depleted polysilicon thin-film transistors

A physical-based and explicit calculation of surface potential for fully-depleted polysilicon thin-film transistors is proposed in this paper. For fully-depleted devices, not only the surface potential in the channel, but also the potential at the back surface are solved analytically. An exponential density of defect states is taken into account. The proposed scheme to calculate the surface potential at both interfaces is derived by using the Lambert W function, which greatly improves computational efficiency and is critical in circuit simulation. The effects of trap state density and film thickness on surface potential was discussed. It is verified that the proposed scheme accurately reproduces the numerical results.