Ultralow-frequency PiezoMEMS energy harvester using thin-film silicon and parylene substrates

Developing a self-sustained leadless pacemaker requires the development of an ultralow-frequency energy harvesting system that can fit within the required dimensions. This paper reports on the design and development of two types of PiezoMEMS energy harvesters that fit within the capsule dimensions and have a low resonant frequency between 20 to 30 Hz, which is required for the application. A bullet-shaped mass was designed to maximize the displacement and enhance power density of the devices. In addition, two types of devices were fabricated and compared (i) a silicon-based cantilever and (ii) a parylene-C-based cantilever with a thin aluminum nitride layer. The silicon device demonstrated higher peak power of 29.8 μW compared with the 6.4 μW for the parylene device. However, due to the low duty cycle of the heart rate and the damping factors of the two materials the average power was significantly higher for the parylene device (2.71 μW) compared with the silicon device (1.22 μW) per cantilever. The results demonstrate that a polymer-based energy harvester can increase the average power due to low damping for an impulse-based vibration application.