Design optimization of a CMOS-MEMS resonator for molecular adherence applications

Intensive research within the biomedical domain during the last decade has raised an increasing interest on the capabilities of disease diagnosis based on exhaled breath analysis. While human exhaled breath has been shown to contain more than 3.000 different Volatile Organic Compounds (VOC), only about 10 of such VOCs are distinctive of a clinical state, requiring high specificity for its identification, with the added difficulty of concentrations ranging from ppm to ppt. While complex laboratory techniques like gas chromatography or mass spectrometry (or both) can be used for such identification, these solutions require bulky laboratory instruments being nowadays costly and time-consuming. The advancement of the Moore's law archetype started with the integration of the first CMOS circuits, and the relatively new - More than Moore - scaling paradigm oriented to diversification of the elements integrated on a system, has brought the capability of fabricating powerful and portable systems capable of processing not only electrical parameters but environmental and biochemical ones with the advantage of operating on-line. In this Master Thesis we develop a specific fully integrated CMOS-MEMS structure conceived for the detection of VOCs. The work starts from previously designed resonant structures oriented to mass sensing (with a demonstrated sensitivity in the order of attograms/Hz). A comprehensive analysis for the development of specific resonant platforms oriented to efficient chemical functionalization is presented. The final goal is to obtain an integrated sensor capable of high VOC specificity together with high sensitivity to allow for small VOC concentration detection. The work comprises the conception of the resonant MEMS structures, the development of equivalent-circuit models derived from analytical formulae, numerical FEM simulation, fabrication and experimental measurement of the overall system response. These structures are fabricated on a commercial 0.35µm CMOS technology adding a final maskless wet processing step to release the mechanical structures.