A silicon IR-source and CO2-chamber for Co2 measurements

For the first time a silicon IR-source and CO2-chamber system for measurement of CO2 concentration is presented. This new miniaturized infrared sensor is specially designed for the measurement of respiratory gases present in patient airways during anesthesia 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 CO2 chambers directly beneath the two reference sources. These chambers "pre-absorb" the reference beam at the CO2 wavelength band around 4.26 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 mu m deep cavity. The CO2-chambers with a length of 1 mm are fabricated by silicon fusion and anodic bonding at a chosen CO2 pressure for optimal filter characteristics. Test measurements of the infrared sensor system show high CO2-sensitivity meaning that the stringent requirements for this respirator application can be reached.