Design and technology for 3D MEMS device for vibration energy harvesting

In this work we present a new concept of a threedimensional vibration power generator made by micro-electromechanical systems (MEMS) technology, which can convert electric energy through transverse mode piezoelectric effect. The presented power generator is based on a long, thick-film, piezoelectric beam configured as a conical helical spring structure. The controlled release metal layer (CRML) MEMS technology has been used to realize the structure from photolithography-defined pattern on a silicon wafer. The advantage of CRML technology is the high repeatability and resolution and its compatibility with back-end of line (BEOL) processes of the integrated circuit (IC) industry. The purpose of the helical structure is also to combine the piezoelectric generator with a conical-helical antenna for RF applications in low-power, autonomous sensors network. The novel construction process of the piezoelectric generator and its structure are presented with finite element method (FEM) simulations to determine its resonant frequencies. This energy-harvesting structure is made enclosing a piezoelectric material between two metal layers. The presented structures operate, as antenna, in the 55-85 GHz frequency band and resonate with mechanical vibrations in the kHz region. These two characteristics are the ideal components for the deployment of miniaturized battery-free low-cost sensors in the emerging 60 GHz band and energy harvesting for power supply.