MOXSens® Technology for Measuring Indoor Air Quality
MOXSens® Technology combines a CMOSens® platform with metal-oxide based sensing technology in the SGP gas sensor. The SGP gas sensors consists of a complete sensor system integrated into a very small 2.45 × 2.45 × 0.9 mm3 DFN package featuring an I2C interface and fully calibrated air quality output signals. Sensirion’s MOXSens® Technology enables highly sensitive and reliable measurements of typical indoor pollutants like volatile organic compounds or hydrogen as proxy for CO2, respectively. The SGP further combines multiple metal-oxide sensing elements on one chip to provide more detailed air quality signals.
Metal-Oxide Based Gas Sensing Principle
Metal-oxide based gas sensors consist of a conglomerate of metal-oxide particles between two electrodes, on top of a hotplate for heating purposes. Heating the metal-oxide to high temperatures yields negatively charged oxygen species absorbed at the metal-oxide surface, in combination with a positively charged depletion layer in the subsurface region. This depletion layer creates a potential barrier which determines the electrical resistivity of the metal-oxide compound between the two electrodes. Reaction of the surface oxygen with a broad range of ambient target gases affects the charge depletion layer on a microscopic scale within the metal-oxide. On a macroscopic scale, the measured electrical resistance between the electrodes thereby depends on the ambient gas concentration. Gas sensors with Sensirion’s MOXSens® technology measure the analog metal-oxide resistivities as function of target gas concentrations and provide preprocessed, calibrated and digitalized indoor air quality signals.
Advantages of Metal-Oxide Technology
The biggest advantage of a metal-oxide sensor is the high sensitivity to a variety of target gases, such as e.g. volatile organic compounds (VOC) and hydrogen. The limits of detection range around very small concentrations from a few parts per million (ppm) down to parts per billion (ppb). By integrating into small packages, CMOSens® metal-oxide sensors become a cost-effective and sensitive sensing technology, which is suitable for mass production.
SGP – A Gas Sensor System on a Chip
The multi-pixel gas sensor platform integrates four metal-oxide sensing elements – the pixels – into into a very small 2.45 × 2.45 × 0.9 mm3 DFN package. Using Sensirion’s CMOSens® Technology, the SGP offers a complete sensor system on a single chip featuring a digital I2C interface, which can be connected directly to any microprocessor system and thereby allows for time efficient and cost effective integration. A temperature-controlled micro-hotplate assures stable operation of the four individual sensing pixels. On-chip algorithms for baseline, temperature and humidity calibration transform the sensor pixel signals into preprocessed and calibrated digital signals, such as ambient VOC concentration and equivalent concentration of CO2. As the first metal-oxide gas sensor featuring multiple sensing elements on one chip, the SGP30 provides more detailed information about the indoor air quality.
Traditional metal-oxide gas sensors suffer from poor long-term stability caused through irreversible contamination by siloxanes. Typical symptoms are a significant loss of VOC sensitivity combined with retarded response times. Siloxane molecules are omnipresent in common indoor environments since they range amongst the most abundant VOC emitted by humans and are often contained in consumer products. Sensirion’s proprietary MOXSens® Technology provides the SGP gas sensors with an unmatched robustness against siloxanes, resulting in unique long-term stability and accuracy.