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 S100ββ protein. Added masses down to a level of 9 pg were detected.

A hybrid microfluidic system for cancer diagnosis based on MEMS biosensors

“…10. This was in accordance with what was previously observed during characterization of large die devices, in which severe vibrational damping was present in devices tested at atmospheric pressure [6]. Moreover, a similar damping effect has been reported by Pandey et al [10].…”

“…The current die layout of 2mm x 2mm is better suited to PCB packaging than the 15mm x 5mm die previously presented and designed for dual in-line packaging [6]. The CDR device layout and diaphragm details are shown in Fig.…”

“…9b and 9c). This setup has been designed to achieve and withstand a partial vacuum which, as reported in [6], is highly desirable. Although an ultimate aim of the SmartHEALTH project is to develop an instrument, which achieves an electronic readout of the signal, the preliminary tests of the CDR biosensor have been carried out using electrical stimulation and optical detection.…”

“…Although an ultimate aim of the SmartHEALTH project is to develop an instrument, which achieves an electronic readout of the signal, the preliminary tests of the CDR biosensor have been carried out using electrical stimulation and optical detection. The laser Doppler vibrometry test station used has been described previously [6]. For the purpose of optical access, a window was incorporated into the development prototype cartridge.…”

The theory of a trapped degenerate mode resonator

“…To first order it can be shown that structures with cyclic symmetries of order p, which break this degeneracy are determined by the condition 2n=p ¼ 1; 2; 3; :::. 6 When mass or stiffness is added to p identical sectors of the resonator, then the degeneracy is broken and the single resonant frequency "splits" to yield two, close, resonant frequencies. This frequency split is used to record the added mass.…”