New gas sensor chip paves the way to autonomous e-nose

According to researchers, the polymer-coated microbridges in high-density arrays can detect ppm-level concentrations of vapours using on-chip integrated read-out techniques. The technology is suitable for miniaturisation of electronic nose devices due to the low power consumption (<1 µW/bridge) and small form factor. The market for wireless sensor nodes that can chemically detect gaseous compounds ranges from food monitoring, healthcare and safety applications. One of the main gas sensing approaches in uncontrolled environments is the identification of vapours using multiple sensing elements known as receptors, in a system referred to as an 'electronic nose' or 'e-nose'. An accurate e-nose requires small, integrated, low power detectors with individually tuned chemical coatings. Current solutions, like chemi-resistors or quartz crystals are not scalable or power efficient enough to build low power small form factor e-noses. Imec and Holst Centre have developed a new generation of microbridges with embedded individual piezoelectric 'shakers' in a high density array with very high fabrication yield. The design is said to allow for rapid coating of a range of absorbents on individual microbridges using commercial inkjet printing technology. The suspended structures vibrate individually, and changes in their modes of vibration are monitored as an indication of vapour absorption in their coatings. Due to the very high length-to-thickness ratio of the microbridges, imec and Holst Centre's gas sensor chip has a high sensitivity to low concentration vapours and by implementing integrated piezoelectric read out schemes, researchers say ultra low power operation is possible. Current work is ongoing to integrate the structures with low power analogue readout circuits and to demonstrate simultaneous measurements from multiple structures. According to imec, this low power miniaturised implementation of an e-nose technology can be used in current applications such as wine and cheese monitoring, but could in the future also help sniff out human conditions such as asthma, lung cancer, and kidney diseases.