CMUT for high sensitivity greenhouse gas sensing

In our work we address creation of reliable and cross-selective platform of greenhouse gas sensing for environmental monitoring and safety purposes based on capacitive micromachined ultrasound transducers (CMUT) technology. We emphasize the need of cross-selectivity between CO₂, CH₄ and H₂S since mixture of these gases is common in anthropogenic and natural gas emissions, and their impact to the greenhouse effect remains underexplored. CMUT sensors containing five elements with resonance frequencies from 15 to 35 MHz were designed and fabricated by fully CMOS compatible surface micromachining technology. Two parallel measurement channels, one reference and one sensing were arranged to measure the mass loading of the CMUT structure and eliminate the non-informative changes of the working environment as temperature, pressure and humidity. CO₂ sensing experiments show that present sensing setup, when CMUT structure is functionalized by thin polyethyleneimine film, has the 4 Hz/ppm sensitivity.