MOde-localized mass Sensors with Thermal Actuation and Piezoresistive DEtection (MOSTAPDE)

Micro/nano-electromechanical system (M/NEMS) resonant mass sensors have attracted utmost interest over the past two decades. This is due to their wide range of applications, especially in biochemistry, for instance weighing single molecules, nanoparticles, and even monitoring the growth of living cells. However, their performance is significantly decreased when operated at ambient air and measurements take a considerable time. Therefore, there are two main challenges for MEMS resonant mass sensors: (i) the improvement of the quality factor at ambient atmospheric pressure; (ii) the realization of real-time monitoring with a closed-loop control and interface circuit system. Additionally, higher sensitivity is always a desirable property to further increase the performance of mass sensors.
    In this project, entitled “MOde-localized mass Sensors with Thermal Actuation and Piezoresistive DEtection (MOSTAPDE)”, I aim addressing aforementioned challenges by combing thermal actuation and piezoresistive detection for MEMS resonators. With this approach a quality factor of several thousand at ambient pressure can be achieved. As a further novel approach, it is proposed to weakly couple two resonators and exploit the phenomenon of mode localization; by using the amplitude ratio as readout metric compared to the commonly used frequency modulation method; in this way the sensitivity can be enhanced by 2-3 orders of magnitude. Furthermore, the inherent common mode rejection property of mode-localized sensors can be exploited for higher robustness. Finally, particle contamination and blockage are avoided as the proposed sensors do not require small electrode-gaps as conventional capacitive sensors. For the microfabricated sensors, a closed-loop control circuit will be constructed to enable real time monitoring. We plan to demonstrate the concepts for measuring particulate matter, which is a major air pollutant, as a practical application of mass sensing.