An optical IR-source and CO/sub 2/-chamber system for CO/sub 2/ measurements

A new silicon IR source and CO/sub 2/-chamber system for measurement of CO/sub 2/ concentration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended across a KOH-etched cavity, is used to generate two switched "sample" and "reference" beams. The electrically modulated sources present a modulation time of 10 ms and a power consumption of 1 W. The CO/sub 2/ chambers, placed beneath the reference sources, are used to produce a reference beam for long term stability and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO/sub 2/ is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antireflective coating to optimize the filter's optical characteristics. Numerical simulations of the filters are presented and show good agreement with the measurements. The IR sources and the CO/sub 2/ filters are both fabricated at wafer level. Using the presented IR-sensor system, measurements with a 9-mm-wide test channel show high CO/sub 2/-sensitivity for CO/sub 2/ concentrations between 0 and 10% confirming that the stringent requirements for this respirator application can be fulfilled.