Reliability of freestanding polysilicon microheaters to be used as igniters in solid propellant microthrusters

This paper presents the design, fabrication and characterisation of surface micromachined polysilicon microheaters to be used as microigniters for micropropulsion applications. The microigniters are heated up by Joule effect and the thermal losses through the substrate are minimised by suspending the microheaters above the substrate. The developed process was compatible with the integration of the nozzle part of the microthruster. The electrical, thermal and mechanical characteristics of the microheaters were studied with the aim of evaluating their reliability. Temperatures up to 470 °C could be reached with an electrical power of 45 mW/beam. The current-voltage relation followed a linear characteristic at low power; at high bias voltages, a drift of the electrical resistance was measured after a few I-V cycles at power higher than 40 mW/beam. The elastic and plastic deformation threshold of the microheaters in operation and their maximum deflection before rupture were measured. The microheaters could dissipate relatively high constant powers for a few minutes to hours. The fabricated microheaters are promising candidates for the ignition of solid propellant microthrusters.