Effect of resonance-mode order on mass-sensing resolution of microcantilever sensors

The paper reports a systematic study of the resonance-mode effect on mass-sensing performance of resonant microcantilevers by both analytic and experimental methods. Firstly the research reveals that the in-air mass-sensing resolution of resonant microcantilevers is dominated by air-drag loss limited Q-factor. Using theoretic analysis and software simulation, we conclude that a higher order mode is with the resolution superior to a lower order mode and a torsion-mode is generally better than a flexure-mode. 4 types of cantilevers resonating in 4 practically realizable resonance-modes, i.e. the 1st, 2nd flexural modes and the 1st, 2nd torsional modes, are designed with identical length, thickness and the main-stem width. Micromachining techniques are used to fabricate the 4 silicon cantilevers with the actuating and signal-readout elements integrated. Biotin-avidin detecting experiment is performed, with the results well verifying the analytic conclusion for sensor optimal design guidance.