This report describes miniature gas-filled plasma-discharge cavities fabricated using combined surface and subsurface micromachining. Starting with a bare silicon substrate, successive layers of polycrystalline silicon, low-stress silicon nitride, and low-temperature oxide layers were deposited to form the micro cavities. Polysilicon electrodes were patterned to serve as electrical connections to the gas. Low-stress silicon nitride formed the insulating layer and the cavity wall which confined neon at atmospheric pressure. Low-temperature oxide served as the sacrificial layer which defined the dimensions of the cavity before the silicon nitride walls were deposited.
Test structures were made to characterize the discharge characteristics of polysilicon electrodes in various gasses including air, argon, and neon. These experiments were done under atmospheric pressure to match the conditions in the final devices. Very high sputtering rates for the polysilicon electrodes were found in nitrogen and argon plasmas.
Processing techniques to seal the desired gasses into the cavity are described in this report. These include die-level sealing as well as wafer-level sealing using spin-on glass, optically transparent epoxy, low-temperature oxide, and paraffin wax.