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.