Interface circuitry for CMOS-based monolithic gas sensor arrays

Interface circuitry for single-chip gas sensor arrays fabricated in industrial CMOS technology combined with post-CMOS micromachining is presented. Two exemplary designs are detailed. The first one includes three polymer-based transducers and their read-out circuitry: a mass-sensitive resonant beam oscillator, a capacitive sensor incorporated into a second-order MA-modulator, and a calorimetric sensor with low-noise signal conditioning circuitry. Furthermore, the preprocessed sensor signals are converted to the digital domain already on chip. An additional integrated controller sets the sensor parameters and transmits the sensor values to an off-chip data recording unit via a standard serial interface. The second chip demonstrates monolithic integration of metal-oxide (SnO2)-covered micro-hotplates along with the necessary driving and signal-conditioning circuitry. The on-chip temperature controller regulates the temperature of the membrane up to 350(i)C and a logarithmic converter was included to measure the SnO2 resistance change upon gas exposure.