Analytic Solution for Symmetric DG MOSFETs with Gate-Oxide-Thickness Asymmetry

An analytic solution for undoped (or lightly doped) symmetric DG (SDG) MOSFETs with small gate-oxide-thickness asymmetry is presented using Poisson's equation considering only the mobile charge term and Taylor series expansion. The existing analytic models for symmetric DG MOSFETs have been derived assuming the two gates are perfectly symmetric. In reality, the thicknesses of the two gate oxides are most likely slightly different due to process variations and uncertainties which can affect surface potential and other parameters of SDG MOSFETs. Therefore, it is very much essential to provide a model for estimating the severity of this gate-oxide-thickness deviation in the performance of SDG MOSFETs. The effects on the gate capacitance of SDG MOSFET performance caused by small asymmetric oxide thickness due to process variations and uncertainties is studied. The model can more accurately detect the errors on the performance of the SDG MOSFET with small gate-oxide-thickness asymmetry than as reported by Chang et al.