Piezoresistive 6-MNA coated microcantilevers with signal conditioning circuits for electronic nose

This paper presents a micro cantilever based piezo-resistive sensor and its fabrication process along with two different techniques for signal conditioning of sensor output aimed for artificial nose applications. The proposed micro-cantilevers feature a special coating of 6-Marcaptonicotonic acid (6-MNA) on one side of the cantilever which leads to a selective reaction of the target analyte molecules with the functionalized cantilever surface. Two signal conditioning schemes, a novel current excitation method and a resistance to frequency conversion (RFC) method using a new proposed circuit are implemented to precisely read the piezo-resistance changes. Current excitation method is implemented using commercial ICs while RFC method is implemented using a low-power test chip constituting of instrumentation amplifier, buffer and comparator in 180nm mixed-mode CMOS technology. It is shown that the implemented RFC method provides a resolution of 5ppm and is useful for low-cost on-chip measurements involving the piezo-resistive sensors. Implemented current excitation method provides measurement resolution of 40 parts per billion with minimum SNR value of 5 dB which is better than previously-reported values.