Microfabrication of a variable range and multi-directionally sensitive thermal flow sensor

This investigation reports the design, fabrication and characterization of a variable range and multi-directionally sensitive micromachined thermal flow sensor based on amorphous germanium thermistors. For measuring various flow ranges and flow directions with a single device, 12 thermistors are placed on an 2 mm × 2 mm supporting square shaped dielectric membrane made with silicon nitride. The thermistors are located at different optimized distances from a central micro-heater that is made with a bilayer of Ti/Pt and can be heated to 200 °C with about 580 mW applied power. The thermistors are laid as six pairs on the aforementioned substrate with three pairs located along the X-axis and another three pairs located along the Y-axis. The device was characterized in the presence of air flow velocities up to 20 m/s and at constant heating power modes of 500 mW and 250 mW in order to measure the achievable flow speed and direction. Characterization results were compared with simulation results and the errors in flow speed and angle measurement have been discussed.