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This paper reports on a wafer-level thin film vacuum packaging technology for MEMS. It is based on the fabrication of freestanding porous anodic alumina membranes of a typical thickness of 2 to 3μm, featuring cylindrical nanopores that are a mere 15-20nm in diameter (aspect ratio >;100). The fabrication process involves in situ perforation of the thin AlOx barrier layer present at the bottom of the nanoporous membranes. For the present paper, a silicon oxide sacrificial layer and a vapor-phase HF release etch through the pores are utilized. The thin film packages are next sealed with a 4μm-thick PECVD nitride layer. Strong and “air-tight” thin film packages are obtained this way. Negligible impact on the RF transmission losses (up to 67GHz) is observed. A basic assessment of the package hermeticity based on the cap deflection method is also presented.