Impact of elliptical cross-section on the propagation delay of multi-channel gate-all-around MOSFET based inverters

Abstract

Multi-channel (MC) gate-all-around (GAA) metal-oxide-semiconductor field-effect transistor (MOSFET) is one of the promising candidates for the next-generation high performance devices. However, due to fabrication imperfections the cross-section of GAA devices may be ellipse-shaped having different major (a) and minor (b) axes, instead of the theoretically ideal round shape. The aspect ratio (AR), defined as a/b, of such elliptical GAA devices can vary depending on a and b. This introduces variability in the effective diameter, which in turn affect the performance parameters of circuits based on elliptical GAA MOSFETs. In the present work we have investigated the impact of diameter variability on the transient response of MC elliptical GAA MOSFET based CMOS inverters with a novel perspective. We have modeled the spread in the effective diameter by a parameter, σ, the standard deviation (SD), which may be thought of as a quantitative measure of the amount of variability introduced in the device. We have elaborated the ‘ON-Resistance’ method for calculating the propagation delay of MC GAA MOSFET based CMOS inverters. Computations were carried out to show the dependence of the propagation delay of such inverters on some important device/circuit parameters. We have also shown that even long channel elliptical devices can offer significant reduction of circuit delay (comparable to short channel devices) by proper tuning the effective diameter and number of channels, provided the admissible small dimensional effects have been taken into account.