Wafer-Level Vacuum-Packaged Piezoelectric Energy Harvesters Utilizing Two-Step Three-Wafer Bonding

This paper reports on the successful implementation of a wafer-level vacuum-packaged, CMOS-compatible aluminum nitride (AlN) based microelectromechanical system (MEMS) energy harvester (EH). The reported EH features high Q-factor (709.3) and high-g survivability (harmonic at 20g), achieved through wafer-level vacuum-package scheme which reduces the air damping effect and increases the Q-factor, overcoming the tradeoff between vibration amplitude and output power density for EHs operated in air. A power of 468.77µW, bandwidth of 71Hz (3.66%) is delivered by a ~0.119cm3 footprint (1×0.7×0.1705cm3) EH at 20g sinusoidal input vibration, equates to a record power density of ~3.93mW/cm3. This novel packaging and design scheme, which utilizes two-step three-wafer wafer level eutectic bonding, allows size reduction and shock-resilience improvement of future EH. The ability to harvest broad spectrum mechanical vibration energy with small footprint and high-g survivability, makes the reported EH one step closer towards powering the next generation battery-less Smart Tire Pressure Monitoring System (TPMS). Furthermore, the whole integration process, including the wafer-level vacuum-packaging process, is CMOS compatible, making the reported EH viable for mass production with low fabrication cost.