Drop-coated sensing layers on ultra low power hotplates for an RFID flexible tag microlab

We report on the coating of a 4-element integrated array of ultra low power hotplate (ULPH) gas sensors with different metal oxide layers. The sensors are designed to be onboard of a radio frequency identification (RFID) flexible tag aimed at monitoring climacteric fruit during transport and vending. The architecture of these microsensors is briefly discussed, the method for coating the ULPH membranes is described and the functionality of the sensors for the application sought is shown. It is shown that a 4-element ULPH coated with tin oxide and tungsten oxide sensors is highly sensitive to the gases relevant for the application. The microarray allows for discriminating among ethylene, acetaldehyde, ethanol and ammonia using simple discriminant factor analysis. Power consumption is low (7 mW per microsensor @ 350 °C) and sensor characteristics are shown to remain stable over a three-month period.