Nanostructured Membranes for MEMS Energy Harvester

Abstract

The development of embedded systems and autonomous microsystems requires significant progress in the research of MEMS energy converters. Converting mechanical vibrations into electricity is an efficient way to collect environmental energy by using MEMS. Our contribution to this hot topic is based on the study of piezoelectric converters on silicon membranes. Due to the nature of the energy sources such as motorized machines, miniaturized devices working at low frequencies (few hundred hertz) with efficient coupling coefficient are needed and make essential the emergence of innovative solutions. In this work we propose an improved approach based on the insertion of nanostructured porous zones in circular monocrystalline silicon membranes used as resonating structures of piezoelectric converters. We have shown (in previous work) that nanostructured porous silicon exhibits an unexpected low rigidity due to the disordered interconnections of the crystallites in the porous zones (the Young modulus is divided by a factor of 10 for porosities around 50%). Using such porous silicon properties, ring-shaped nanostructured zones allowing the creation of low rigidity membranes combined with central seismic masses were realized and tested. Interesting potentialities for the development of high quality factor devices at low resonant frequencies have been then demonstrated. The effect of the position, the shape and the size of the nanostructured zones on the resonant frequency and the quality factor of the membrane were experimentally investigated. Complementary numerical simulations were performed using ANSYS software on same modelled structures. Keywords: MEMS on silicon, piezoelectric micro generator, porous silicon, self-powered microsystem