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

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