A silicon IR-source and CO/sub 2/-chamber for CO/sub 2/ measurements

For the first time a silicon IR-source and CO/sub 2/-chamber system for measurement of CO/sub 2/ concentration is presented. This new miniaturized infrared sensor is specially designed for the measurement of respiratory gases present in patient airways during anaesthesia or intensive care. The IR-sensor assembly consists of an IR-source chip with two pairs of diagonally arranged IR-sources for the generation of two switched "sample" and reference beams. The gas filter chip is arranged with two CO/sub 2/ chambers directly beneath the two reference sources. These chambers "pre-absorb" the reference beam at the CO/sub 2/ wavelength band around 4.26 /spl mu/m. The reference beam is needed for long term stability and for compensation against cuvette window contamination. The electrically modulated IR-sources consist of incandescent polysilicon filaments coated with silicon nitride across a 220 /spl mu/m deep cavity. The CO/sub 2/-chambers with a length of 1 mm are fabricated by silicon fusion and anodic bonding at a chosen CO/sub 2/ pressure for optimal filter characteristics. Test measurements of the infrared sensor system show high CO/sub 2/-sensitivity meaning that the stringent requirements for this respirator application can be reached.