Design and fabrication of high-temperature micro-hotplates for drop-coated gas sensors

This paper reports on the optimisation of micromachined hotplates for gas-sensing applications designed to stand high-temperature coating processes and modes of operation. Different thin film materials, geometry and dimensions have been investigated regarding their power consumption, temperature distribution over the sensing area and robustness when annealed at high temperature. In comparison with oxide films, the micro-hotplates made of nitride were the most robust. They withstood annealing temperatures of up to 700°C and a pulsed temperature mode of operation. Their robustness allowed the sensing area to be heated up to a high temperature (550–700°C). These micro-hotplates are therefore suitable for the annealing “on-chip” of the gas-sensitive materials deposited in a drop-coating procedure. Sensors coated with a Pd-doped tin oxide drop and annealed using the integrated heater have been tested under different concentrations of CO and CH4 in air.