Suspended-Gate MEMS devices have application potential in the field of switches, memory, micro-machined gas sensors, ultra-sensitive bio-sensors, and accelerometers in the low-frequency range. Proper design of Suspended-Gate Field Effect Transistor (SGFET) can lead to a reduction in the sub-threshold swing (S) below the “Boltzmann Limit” of 60 mV/decade.

This work consists of the design and fabrication of the SGFET. A fixed-fixed beam serves as a suspended movable gate, replacing the metal in a conventional silicon MOSFET structure. The gate dielectric is a combination of SiO2 and air. The gap between the beam and the MOSFET is an important parameter of interest that serves as a design constraint in achieving the sub-threshold swing below the Boltzmann Limit. The device exhibits two stable states, one up state when the beam is up leading to a low off-state current and one down state when the beam is pulled down resulting in a high on-state current. Linear spring model equations of the beam coupled with MOSFET equations as suggested in literature is used to calculate some parameter of interest like the pull-in voltage and current values for the dimensions of the devices that are fabricated.

A two mask process flow is developed for a Poly-Si gate SGFET and fabricated. Process issues including problems regarding dry-release will be discussed. Subsequently, a five-mask gold gate SGFET process flow with Cr/Au as the source and drain contact was followed. DC characterization of the released devices was done using a manual probe station and Agilent B1500A semiconductor device parameter analyzer and the results will be presented. Finally, proposed changes for the improvement of some parameters of interest like the pull-in voltage and the threshold voltage for the sensitivity enhancement in sensor applications will be suggested.