Piezoelectric P(VDF-TrFE) micro cantilevers and beams for low frequency vibration sensors and energy harvesters

Piezoelectric P(VDF-TrFE) micro-cantilevers and beams have been developed with a novel micro-electromechanical systems process very useful for low frequency vibration sensors and energy harvesters. The devices were designed and simulated using COMSOL Multiphysics simulation software to determine the resonant frequency, voltage and power output for various dimensions with length in the range 200 μm to 2000 μm, width in the range 100 μm to 400 μm and thickness 2.5 μm in all cases. Devices were fabricated on <110> silicon wafers using a novel bulk micromachining process by suspending them using critical process steps which include: micromachining of silicon substrate from the backside using anisotropic wet etchant TMAH to define the device suspension regions with thin SiO₂ diaphragm, and release of micro-cantilevers and beams by etching the SiO₂ diaphragm from backside with CHF₃/O₂ based plasma etching. All the devices were fabricated with 2.5 μm P(VDF-TrFE) spin coated on SiO₂. Laser Doppler Vibrometer was used to measure resonant frequency, voltage and power output of the devices which were operated in longitudinal mode with thermally evaporated Cr-Au interdigitated electrodes for power extraction. The experimental results obtained on fabricated devices for the first time using this process were in good agreement with those derived from simulation.