A Submillimeter Package for Microsystems in High-Pressure and High-Salinity Downhole Environments

This paper describes a submillimeter-scale package intended for microsystem components in high-pressure and high-salinity environments, such as downhole environments in oil wells. The outer dimensions of the package are 0.8 x 0.8 x 0.8 mm³, whereas the interior cavity is 0.4 x 0.4 x 0.45 mm³. The package consists of a stainless steel 17-4 PH metal can and a borosilicate glass lid, and is hermetically sealed by an Au-In bond. The measured bond strength is ≈13 MPa. A component integration strategy is demonstrated: test silicon chips are assembled into a stack using a folded flexible polyimide cable that provides electrical interconnections among the chips. The packages coated with thin-film alumina by atomic layer deposition and Parylene-C survive >48 h in the American Petroleum Institute standard brine (with 8 wt% NaCl and 2 wt% CaCl₂ in deionized water) at 80 °C, and subsequently, in 50-MPa (≈7250 psi) hydraulic pressure.