MOSFET Replacement Devices for Energy-Efficient Digital Integrated Circuits

摘要

Increasing power density is a daunting challenge for continued MOSFET scaling due to non-scalability of the thermal voltage kBT/q. To circumvent this CMOS power crisis and to allow for aggressive supply voltage reduction alternative switching device designs have been proposed and demonstrated to achieve steeper than 60mV/dec subthreshold swing (S). This dissertation begins with a general overview of the physics and operation of these MOSFET-replacement devices. It then applies circuit-level metrics to establish evaluation guidelines for assessing the promise of these alternative transistor designs. This dissertation then investigates the abrupt 'pull-in' effect of an electrostatically actuated beam to achieve abrupt switching behavior in the nanoelectro-mechanical field effect transistor (NEMFET). To facilitate low-voltage NEMFET design, the Euler-Bernoulli beam equation is solved simultaneously with the Poisson equation in order to accurately model the switching behavior of a NEMFET. The impact of various transistor design parameters on the gate pull-in voltage and release voltage are examined. A unified pull-in/release voltage model is developed. Finally, this dissertation proposes the use of micro-relays for zero-standby-power digital logic applications. To mitigate the contact reliability issue, it is demonstrated that since relatively high on-state resistance can be tolerated while extremely high endurance is a necessity, hard contacting electrode materials and operation with low contact force are preferred for reliable circuit operation. Using this contact design approach, a reliable relay technology that employs titanium dioxide (TiO2) coated tungsten (W) electrodes is developed for digital logic applications.