Microresonator-on-Membrane for Real-Time Mass Sensing in Liquid Phase

Microresonator-on-membrane (MRoM) is presented in this article as a new approach to address the performance deterioration of microscale resonators in contact with a liquid media. An MRoM is composed of a rectangular piezoelectricon-substrate resonator formed on top of an isolating membrane, which can operate in its length and width extensional (LE and WE) resonance modes. In the proposed scheme, the solution under a test is added into a microcavity on the back side of the MRoM chip. In this manner, the contact surface of the resonator to liquid is minimized to reduce mechanical losses caused by viscous damping, leading to a higher resonator quality factor (Q). Simultaneously, isolation caused by the membrane eliminates electrical interference of ionic solutions on a resonator performance. Despite enabling such advantages, the membrane underneath the resonator causes further anchoring losses, which reduces the Qs of MRoMs operating in air. To minimize such losses, in-plane primary and secondary circular acoustic reflectors are located around the resonator leading to higher Qs. Consequently, the MRoMs with secondary reflectors exhibit the Qs as high as 3500 for operation at both LE and WE resonance modes of 39 and 83 MHz, respectively, when operating in air, showing adequate suppression of anchoring loss caused by the presence of the membrane. Also, maximum liquid phase Qs up to 410 are achieved for the MRoMs, which operate in the WE mode. As mass sensors, the MRoMs demonstrate mass sensitivity of similar to 12 Hz.cm(2)/ng while operating at the same mode.