Effect of MEMS-compatible thin film hard coatings on the erosion resistance of silicon micromachined atomizers

A comparison of five different MEMS-compatible, thin film, hard coatings has been performed using silicon (Si) micromachined atomizers as test devices. Single-crystal and polycrystalline silicon carbide, silicon nitride, silicon dioxide, and diamond-like carbon were either thermally grown or chemically vapor deposited onto the non-planar topography of the device. Eighteen-hour long, industry-standard erosion tests were performed to qualitatively evaluate the coatings for erosion resistance when exposed to an aggressively contaminated test fluid. No wear was measured on the majority of the swirl chamber floor for the five coatings, though varying degrees of erosive wear were observed at the edge of the exit orifice. The single-crystal silicon carbide demonstrated the best wear performance of all the coatings, exhibiting no noticeable changes of its surface morphology as a function of the erosion tests. The silicon nitride and diamond-like carbon coatings showed the most wear, exhibiting micro-cracking, chipping and flaking at the exit orifice edge.