Micromachined CMOS calorimetric chemical sensor with on-chip low noise amplifier

We report on a micromachined calorimetric chemical sensor for volatile organic compounds in air fabricated in industrial CMOS technology. The sensor measures enthalpy changes during absorption and desorption of a gaseous analyte into a chemically selective polymer. The enthalpy changes cause temperature variations of a thermally insulated micromachined membrane. The temperature variations are detected using thermopiles integrated on the membrane. The microsystem consists of a polymer coated sensor structure, an uncoated reference structure, and a low noise differential amplifier amplifying the difference of the two thermovoltages. The system provides a sensitivity of 51-1 mV//spl mu/W, resolving enthalpy changes of the order of /spl mu/J at sampling intervals down to 45 ms. To demonstrate the sensitivity and selectivity of the calorimetric chemical microsystem, we present results of different volatile organic compounds (VOCs).