Mass sensor utilising the mode-localisation effect in an electrostatically-coupled MEMS resonator pair fabricated using an SOI process

• Pair of electrostatically coupled resonators driven into in-phase resonant mode
• Novel design of resonators that utilises stiction-free SOI fabrication process
• A focused ion beam has been used to decrease the mass of one resonator.
• Amplitude ratio of resonators at the in-phase mode responds to mass change.
• Mass sensitivity of amplitude ratio response is 5.4 × greater than state-of-the-art.

The change in the mass, achieved with focused ion beam (FIB) milling, of one of a pair of electrostatically-coupled microelectromechanical systems (MEMS) resonators has been detected utilising the mode-localisation effect. It has been demonstrated that the shift in the amplitude ratio of the coupled-resonators at the in-phase mode-frequency, in response to a mass change, is five orders of magnitude greater than the equivalent resonant frequency shift of a single resonator device. The device has been fabricated using a silicon-on-insulator (SOI) based process, which allows for high-yield and stiction-free fabrication. In addition, the design of the resonators has been created to have a larger surface area than previously reported designs, in order to facilitate future biological functionalisation. The mass sensitivity has been compared to current state-of-the-art mode-localised mass sensors and a 5.4 times increase in the amplitude ratio response to a given mass change has been demonstrated for the device in this work.

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