Quantitative understanding of inversion-layer capacitance in Si MOSFET's

Abstract

The inversion-layer capacitance (C/sub inv/) in n-channel Si MOSFET's is studied experimentally and theoretically with emphasis on the surface carrier concentration (N/sub s/) dependence of C/sub inv/, which is important in the quantitative description of the inversion-layer capacitance. Based on the experimental N/sub s/ and temperature dependencies, the physical origin of C/sub inv/ is discussed. It is shown that, at lower N/sub s/, C/sub inv/ is determined by the finite effective density of states, while, at higher N/sub s/ C/sub inv/ is determined quantum mechanically by the finite inversion-layer thickness. Also, the results of the surface orientation dependence of C/sub inv/ are presented as the first direct evidence for the fact that surface quantization plays a significant role in C/sub inv/ even at room temperature. The self-consistent Poisson-Schrodinger calculation of C/sub inv/ is performed and found to represent the experimental results accurately. The influence of C/sub inv/ on the gate capacitance is discussed in terms of the device scaling on basis of the experimental and calculated values of C/sub inv/.