The fabrication, characterization and testing of a MEMS circular diaphragm mass sensor

Abstract

This paper presents a discussion on the fabrication, characterization and testing of a degenerate mode resonant mass sensor which takes the form of a crystalline silicon MEMS circular diaphragm. The device is fabricated from the device layer of a SOI wafer which is bonded anodically to a Pyrex substrate. The efficacy of the fabrication process is assessed. Characterization of the diaphragm is performed by actuating the diaphragm electrostatically and measuring its response using optical surface profilometry and laser Doppler vibrometry. The temperature stability of the degenerate modes of vibration is investigated and it is shown that the initial frequency split in the resonant frequencies of these modes does not change significantly with temperature. Structures which present a symmetric surface profile after processing show remarkable temperature stability. The performance of the device as a mass sensor has been evaluated by functionalizing specific sectors of the diaphragm to provide bonding sites for a S100ßß protein. Added masses down to a level of 9 pg were detected.