AlN wideband energy harvesters with wafer-level vacuum packaging utilizing three-wafer bonding

Abstract

This paper experimentally demonstrates an aluminum nitride (AlN) based piezoelectric MEMS energy harvester (EH) with an operation bandwidth of 64.6Hz (859.9Hz-924.5Hz, 7.24%), peak output open-circuit voltage of 4.43V, and an output power of 82.24μW that yields a high power density of 0.734mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> with its size of 0.8×0.8×0.175cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The in-house microfabricated wideband EH is packaged using a novel wafer-level vacuum packaging scheme which employs two times of eutectic AlGe bonding to bond the device wafer to both the top cap wafer and the bottom cap wafer. In addition, Ti is employed as the getter material to enhance the vacuum level inside the cavity, hence reducing the air damping experienced by the cantilevers and increasing the quality factor (Q-factor) and output voltage. The reported EH is a promising candidate in the application of Internet of Things (IoT) to for powering various wireless sensor nodes (WSN) which are located in environment with a wide range of vibration frequencies.