Micro-Resonator-on-Membrane for Real-Time Biosensing

This work presents Micro-Resonator-on-Membrane (MRoM) as an effective approach to harness high mass sensitivity of MEMS resonators for real-time label-free biosensing. MRoMs are formed on SOI substrates and are comprised of a Thin-film Piezoelectric-on-Si (TPoS) micro-resonator separated by a thin oxide membrane from the backside cavity in which biological solutions are hosted. The isolating membrane reduces the liquid-resonator interaction and minimizes viscous losses to maintain relatively high resonator quality factor $(Q)$ in contact with liquid. The membrane also insulates the resonator electrical connections from the conductive biological solution eliminating undesirable interferences. In order to minimize the added anchor loss from the membrane connecting the resonator to the substrate, in-plane acoustic reflectors are carved into the device layer around the resonator. Membrane surface modification with antibody and detection of target analyte has been successfully demonstrated for MRoMs. Frequency shift of 90 kHz (805 ppm) has been measured for a 111 MHz 3rd length extensional (LE) mode of an MRoM due to adsorption of anti-mouse-IgG molecules tagged with 10 nm diameter gold nanoparticles with surface density of 1011/cm2. This translates to measured mass sensitivity of −88.9 Hz.cm2/ng