Resonant piezoresistive amplifiers: Towards single element nano-mechanical RF front ends

This work presents measurement and scaling results for micro/nano-mechanical resonant piezoresistive amplifiers (RPA) showing the potential of such devices as single element receiver front-ends. It has been previously demonstrated that the formation of an internal electromechanical positive feedback within a suspended resonant piezoresistor leads to a negative (active) motional resistance. Such devices can simultaneously amplify and filter incoming electrical signals while maintaining a low noise figure. Basic scaling physics suggests that by reducing the dimensions into the deep submicron range, RPAs can maintain similar negative motional resistances (−r
m
), while consuming significantly less power and operating at higher frequencies. However, no empirical data has been shown to support this claim. In this work, RPAs with operating frequencies ranging from 5MHz to 162MHz have been fabricated and their performances have been compared. Measurements show a negative transconductance (g
m
) of −22mA/V (r
m
= −45Ω) with an effective quality factor of 2100 (in air) for a 162MHz RPA with DC bias power of only 530 μW. It is also shown that the figure of merit (FOM) for such devices (defined as g
m
/P
DC
) significantly improves by miniaturization of the resonant piezoresistor.