An analytic threshold-voltage model for short-channel enhancement mode n-channel MOSFETs with double boron channel implantation

Abstract

This paper presents an analytic threshold-voltage model for n-channel MOSFETs with double boron channel implantation, in which the implanted boron profile in the substrate is approximated by a triple-step profile. The surface potential at strong inversion has been calculated from the condition of equal rate change of depletion layer charge density and inversion layer charge density with respect to the surface potential. The built-in voltage of the high-low junction in a triple-step profile has been correctly included in calculating the surface potential and maximum depletion width at strong inversion. This consideration removes the discontinuities of the threshold voltage with respect to the applied back-gate bias as the maximum depletion width passes through the high-low junction. Based on the above considerations, an analytic threshold-voltage model for short-channel MOSFETs with a triple-step profile in the substrate has been developed by using the modified charge sharing scheme. The geometric factors of the charge sharing scheme have been incorporated into the developed threshold-voltage model by means of the depletion charge superposition which also guarantees continuous threshold voltage change as the back-gate bias is continuously applied. Moreover, the developed threshold-voltage model has been compared with the experimental results of fabricated devices. Satisfactory agreement between these comparisons has been obtained for wide ranges of effective channel lengths and back-gate biases.