A suspended low power gas sensor with in-plane heater

An ultralow power suspended gas sensor with in-plane heater and nano gap sensor electrodes is presented. The heater and sensing electrodes, separated by 1-μm air gap, are processed using single lithography step with standard micro-fabrication techniques. Controlled electromigration is used to create a nanogap in the middle of the sensing electrode. The sol-gel grown ZnO is dispensed using a picoliter dispenser to bridge the nanogap electrode, created by electromigration, to get required metal oxide film as a sensing element. The gap between the electrode and heater is optimized by electrothermal simulation to obtain desired temperature profile on ZnO. The resulting device exhibits excellent sensing performance for hydrogen (~86% at 20 ppm) at 0.5 mW. A detailed characterization was carried out to analyze the performance of the device. This unique, in-plane structure is superior compared with the conventional out of plane structure in terms of the power efficiency and ease of processing.