Fabrications of High-dielectric Plate Having Deep Trenches and its Application to Electrostatic Generator for Vibration Energy Harvesting

We propose two fabrication method of dielectric plate having trenches: One is a dicing method in which trenches are formed on a surface of Pr(Zr, Ti)O₃ plate by a dicing saw, and the other is a casting method in which a composite material of nano-BaTiO₃ particles and epoxy-resin is casted into a mold of patterned thick photosensitive dry film. An advantage in using the dicing method is that it can forms trenches with high aspect in a high dielectric constant plate even if it is hardly etched by a plasma etching. However, it can not fabricate curved trenches. On the other hand, the casting method for nano composite material of BaTiO₃ and epoxy-resin is compatible to MEMS process, i.e., the size and pattern of trenches are flexibly designed as far as photolithographic resolution admits. But dielectric constant of the BaTiO₃/epoxy composite is smaller than those of bulk BaTiO₃ and Pr(Zr, Ti)O₃. We applied those to electret energy harvesting devices which are based on fringe electrical field change inside the trenched high dielectric constant plate. The maximum experimental output power of 80 nW was achieved for 80 Hz/80 μm forced vibration.