Analytical modeling of short channel effects in double gate MOSFET

As CMOS scaling is approaching the limits imposed by oxide tunneling and voltage non-scaling, double-gate (DG) MOSFET has become a subject of intense VLSI research. In this dissertation, a predictive analytical model is developed for short channel effects (SCEs) in undoped (or lightly doped) double-gate (DG) MOSFETs. It has been implemented in SPICE for circuit modeling.; For the purpose of modeling the off current of undoped or lightly doped double-gate MOSFETs, we started from the 2-D Poisson's equation in subthreshold region with the inversion charge term neglected. By specifying the potential values at the source/drain edge, a 2-D boundary value problem is formulated. Using superposition, the solution for electrostatic potential is broken into three parts. Each part satisfies the Poisson's equation and boundary conditions at the one boundary, and vanishes at the other boundaries. The solution that satisfies boundary conditions at source/drain can be expressed as a series of orthogonal eigen-fuctions. By matching the dielectric boundary conditions at the two silicon-insulator interfaces, we obtain an eigen-value equation which has multiple solutions for scale length (eigenvalue). The dominant, lowest order terms can be evaluated analytically through the orthogonality relationship. After the 2-D potential function is solved, inversion charge density can be evaluated at every point in the channel. By assuming the current flows dominantly along the channel direction, analytical solution for subthreshold current is obtained from the current continuity equation. The analytical solutions of electrostatic potential and subthreshold current are validated by their agreement with 2D simulation results and published hardware data.; For circuit modeling purposes, simplifications of the analytical solutions are necessary for developing expressions of threshold voltage roll-off and subthreshold slope. It is shown that Taylor expansion method achieves simplification without losing accuracy of the analytical results.; This model is also directly extendable to high-k dielectric gate insulators and one-gate operation mode of DG MOSFET, which provides more design space for the circuit implementation of DG MOSFETs.