Reliability of Platinum Microheater Geometries for MEMS-Based Gas Sensors

We model the electromigration (EM)- and thermo-migration (TM)-induced stress build-up in MEMS microheaters based on platinum spiral geometries in order to study the impact of several design decisions, including the film thickness, the rounding of sharp corners, and the introduction of a heatspreading plate. We observed that the TM-induced stress is dominant and found that reducing the film thickness results in a direct increase in the EM stress; however, the TM stress did not vary significantly even though the temperature uniformity was degraded. Rounding the sharp corners in the spiral geometry was shown to be beneficial in reducing the stress, with a direct correlation between increasing corner radius and reducing the induced stress. Furthermore, many microheater designs include a heat-spreading plate in order to improve the temperature uniformity across the microheater. In this study, we show that, while the heat-spreading plate has the desired effect, it comes at a cost of a significant increase in the power consumption (+70%) and in the EM- and TM-induced stress (+100%).