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This paper presents a detailed RF study for source/drain Schottky-barrier (SB) MOSFETs. Using on-wafer S-parameters, high-frequency (HF) figures-of-merit (FoMs) and small-signal equivalent circuits (SSEC) are first extracted and discussed for a 120-nm-gate-length SB MOSFET. Then, using ac simulations, HF FoM's sensitivity along SB height and underlap length variations are subsequently presented. The whole study provides, for SB MOSFETs, a deep understanding of key ac-element (transconductances and capacitances) behavior as well as process-parameter optimization to achieve the best HF FoMs. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a systematic analysis on the impact of source–drain engineering using gate “non-overlapped” on the RF performance of nano-scaled fully depleted Double Gate SOI transistors, when used in the design of a typical two stage Operational Transconductance Amplifier (OTA). It is evident that for a gate length less than 40nm, the incorporation of optimal source–drain engineering requiring a spacer length, which may exceed the length of the gate, is particularly beneficial in analogue applications. Lengthening the spacer reduces gate capacitance in the weak/moderate inversion region more than transconductance, improving cut-off frequency f T. This improvement is particularly significant in a circuit application where an optimal spacer of 1.5 times the gate length is proposed. This gate under-lapped concept with extended spacer can also significantly enhance DC gain of the OTA, by increasing the Early Voltage, while maximising the transconductance to current ratio in the weak to moderate inversion, close to threshold voltage. With optimally designed devices, the sensitivity of OTA circuit performance to doping profile is shown to be relatively low. [Copyright &y& Elsevier]

Abstract: In this paper, the analogue performance of a 65nm node double gate SOI (DGSOI) is qualitatively investigated using MixedMode simulation. The intrinsic resistance of the device is optimised by evaluating the impact of the source/drain engineering using variation of spacers and doping profile on the RF key figures of merit such as f T, and f MAX. It is evident that longer spacers, which approach the length of the gate offer better RF performance irrespective of the profile as long as the doping gradient at the gate edge is <7nm/decade. Analytical expressions, which reflect the dependence of f T, and f MAX on extrinsic source, drain and gate resistances R S, R D and R G have been derived. While R D and R S have equal effect on f T, R D appears to be more influential than R S in reducing f MAX. The sensitivity of f MAX to R S and R D. has been shown to be greater than to R G. [Copyright &y& Elsevier]