Gas Permeable Environmental Protection Caps for Wafer Level Capping of MEMS Gas and Pressure Sensors

This paper reports on novel porous environmental protection caps for wafer level capping of MEMS gas and pressure sensors. Permeable porous microstructures of several hundred micrometer thickness are formed inside 200 mm silicon (Si) wafers from loose aluminum oxide powder (Al<inf>2</inf>O<inf>3</inf>), solidified by atomic layer deposition (ALD) of an aluminum oxide layer throughout the structure.For the first time, we demonstrate the feasibility of the approach for potential wafer-level capping of MEMS and investigate the influence of this novel type of cap on the performance of MEMS humidity sensors.In addition, we demonstrate the ability to functionalize such caps with superhydrophobic thin films deposited by initiated chemical vapor deposition (iCVD).