Air-spacers as analog-performance booster for 5 nm-node N-channel nanosheet transistor

Abstract

This work investigates the use of air-spacers as an analog-performance booster for nanosheet transistors (NSTs) at 5 nm node. The NSTs with air-spacers are evaluated across the design space for analog circuits. A fully calibrated three-dimensional technology computer-aided design platform was used for the device and mixed-mode circuit simulations. The use of air-spacers improves the output impedance (r o) from 974 kΩ to 1.32 MΩ, as well as the intrinsic gain (A v) from 90 to 118, for the NST with L g/W g = 240 nm/15 nm. The air-spacers also improve analog performance parameters such as the unit-gain frequency (f T) from 562 to 596 GHz; gain-frequency product from 4.76 to 5 THz; transconductance-frequency product from 2.11 to 2.22 THz; and the gain-transconductance-frequency product from 17.9 to 18.7 THz; for the NST with L g/W g value of 12 nm/15 nm. In addition, the discharge time (t d) also improves from 1.64 to 1.5 ns, for NST with L g/W g = 12 nm/120 nm. The oscillation frequency of a three-stage ring-oscillator is also reported to improve from 68.3 to 88.2 GHz by the use of air-spacers.