Fabrication of a fully integrated electrospray array with applications to space propulsion

A fully integrated MEMS planar electrospray array intended for space propulsion applications is reported. An extractor electrode, electrical insulation, liquid barriers and assembly clips are integrated into a single silicon and Pyrex component, fabricated with deep reactive ion etching (DRIE), laser micromachining and wafer bonding technology. An electrospray emitter head assembles by hand to the clips using a reversible high-precision hand-assembly method, allowing many emitters types to be tested with minimal fabrication effort. Externally-wetted emitters were formed using an alternation of DRIE and isotropic SF₆ plasma etching. A simple model is reported allowing the prediction of emitter geometry from mask geometry and etching steps. The fabricated thruster weighing 5 g was successfully fired with a 502 emitters array, and was shown to operate in the pure ion emission regime using the ionic liquid EMI-BF₄. Starting voltages as low as 500 V were observed, though the device was tested up to 5 kV without damage.