An optical IR-source and CO2-chamber system for CO2 measurements

A new silicon IR-source and CO2-chamber system for measurement of CO2 conce ntration is presented. The micromachined IR-source, which consists of four groups of polysilicon filaments coated with silicon nitride suspended acros s a KOH-etched cavity, is used to generate two switched "sample" and "refer ence" beams. The electrically modulated sources present a modulation time o f 10 ms and a power consumption of 1 W. The CO2 chambers, placed beneath th e reference sources, are used to produce a reference beam for long term sta bility and compensation against cuvette window contamination. They consist of 1-mm-deep micromachined cavities in which CO2 is encapsulated during an overpressure anodic bonding procedure. Silicon dioxide is used as an antire flective coating to optimize the filter's optical characteristics. Numerica l simulations of the filters are presented and show good agreement with the measurements. The IR-sources and the CO2 filters are both fabricated at wa fer level. Using the presented IR-sensor system, measurements with a 9-mm-w ide test channel show high CO2-sensitivity for CO2 concentrations between 0 and 10% confirming that the stringent requirements for this respirator app lication can be fulfilled.