Operating Voltage Constraints in 45-nm SOI nMOSFETs and Cascode Cores

Abstract

We investigate the operating voltage constraints and hot carrier reliability (HCR) of 45-nm SOI RF nMOSFETs and cascode cores built from these devices. The devices were implemented with both “floating” body and “contacted” body schemes. It is shown through experimental results that floating-body (FB) devices have greater hot carrier degradation compared with body-contacted (BC) devices. Cascode cores designed with two FB devices (FB-FB), with one BC device and one FB device (BC-FB), and with two BC devices (BC-BC), were also investigated. The tradeoffs in the dc versus radio-frequency (RF) performance versus the HCR of these cascode cores were assessed. The cascode cores have a much longer reliability lifetime compared with a single device operating under similar stress conditions. The BC-BC cascode core is shown to have a much longer reliability lifetime compared with BC-FB and FB-FB cascode core topologies. The physical mechanisms behind the observed hot carrier degradation in these devices and cascode cores are explored using calibrated technology computer-aided design (TCAD) simulations. Taken together, these results suggest some important implications for realizing high-performance and high-reliability RF circuit designs using 45-nm CMOS-on-SOI technology.