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Near Zero Sub-threshold Swing Nano-Electro-Mechanical Field Effect Transistor with Suspended Ge/Si Core/Shell Nanowire Chanel

Abstract

The static power consumption became one of the key limiting factors on the shrinkage of feature size of VLSI circuit using CMOS technology. One major reason of high static power consumption is the off-state sub-threshold leakage current of the transistor. At room temperature, the possible steepest sub-threshold swing (SS) for turning off the transistor, is limited to 60 mV/decade due to a constant fundamental thermal dynamical limit (kBT/q) that is not scalable with reduced dimension. This limitation is inherent to CMOS because its off-state is governed by thermally activated diffusive current over a potential gate-controlled potential barrier. Completely different switching mechanism such as using the mechanical degree of freedom is necessary to break the SS limit. Previous studies using nano-electro-mechanical-system (NEMS) have shown suspended-gate MOSFET (SG-MOSFET) as logical switch, while we have previously proposed a suspended nanowire (NW) channel FET (NEMFET) with low pull-in voltage(Vpi) and high Ion/Ioff ratio due to the flexibility of nanowires. Here we report the first demonstration of a NEMFET device using suspended Ge/Si core/shell nanowire channel. The NEMFET channel is suspended over a local metal gate with the air gap thickness defined by the thickness of the supporting source/drain electrodes. DC transfer characteristics on multiple switching NEMFET demonstrates close-to-zero SS (<6mV) at room temperature with the slope only limited by measurement equipment resolution. Furthermore, we employed electrostatic actuation to study the AC mechanical response of the nanowire channel. Using the NEMFET as a signal mixer we characterized the resonant frequency and the speed of NEMFET device to be 125.9 MHz

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