MEMS Doubly Clamped High Sensitivity Mass Detector

After reading the abstract on the resonanting cantilever mass detector, I think this paper might be of interest to some.  My colleagues and I wrote this for a MEMS device class we took Fall 2005 at Columbia University while I was an undergraduate.  It was a term design project.

Abstract – Micro-electromechanical systems (MEMS) often provide cost effective 

solutions with rapid response times to many macroscopic engineering enigmas. While MEMS devices offer micro-scale actuation and sensing, nano-electromechanical systems (NEMS) give even greater sensitivity, faster response times, and a larger breadth of applications. Nano-sized resonating beams, specifically, provide promise in ultra- sensitive mass detection and substance sensing. Detection is achieved through the coloration of resonant frequency shifts with the existence of specific environmental conditions. In an effort to increase sensitivity, we have designed a micro-scale comb drive electrostatic actuator.  Our MEMS device will have the versatility to load a 10 μm long, 80 nm wide, and 100 nm thick gold/palladium beam with tensile and compressive stresses. The structure is made using a combination of electron beam evaporation of gold and palladium, Reactive Ion Etching (RIE), and 5:1 BHF etchant on a Si-SiO2-Si wafer. A voltage applied to the comb drive will change the compression and tension of the beam. The beam will drive and the resonant frequency will be determined by a magnetomotive technique [13].   A DC voltage along with a sinusoidal current, which is out of phase with the resonating beam, will be applied to comb drive plates in order to keep the structure stable and apply the desired tensile or compressive loading. The device is packaged using an innovative leadless contact approach, which increases stability over time and environment.  Potential applications include gas and homeland security bioterrorism sensors.