Slide 2:
VOCs are volatile organic compounds which can have adverse effects on human health.
Detection is necessary to keep them under limiting levels.
MEMS based chemical sensors are used for VOCs detection.
Resonating cantilevers coated with polymers detect VOCs, undergo mass change which changes the resonant frequency.
Design and Fabrication :
Design and Fabrication Dimensions for cantilever beam
Length – 500 microns
Width – 200 microns
Fabrication process: 5 step process.
First 3 steps make electrical contacts and last two decide the geometry of cantilever for front face and back face etching of silicon with DRIE
Polymer coated is PEUT- Poly(etherurethane) by spray coating. PEUT has good affinity towards ethanol sensing.
Constraints :
Constraints Dynamic mode of sensing- applicable only to gas phase.
Modification in geometry has different implications in terms of noise.
Reducing the geometry increases the resonant frequency ( which reduces the noise) but can also lead to decrease in quality factor ( which increases the noise)
References :
References L Fadel, F Lochon, I Dufour and O Francais, J. Micromech. Microeng. 14 (2004) S23–S30.
Lavrik et al, Rev. Sci. Inst. 75,7,2229 (2004)
D.Lange, A.Koll, O.Brand and H.Baltes, Conference on Smart structures and Materials, Proceedings of SPIE, vol 3328, 1998, 233-243
MEMS, A practical guide to design analysis and applications, Jan G.Korvink, Oliver Paul.