Energy harvesting and conversion - applications of piezoelectric transformer and transducer MEMS

A systematic investigation of the feasibility to integrate complete piezo-based power supply on silicon was done. Up to now, fully integrated off-line power supplies on chip are available as products for below 1 Watts. Higher power levels up to 10 Watts and more are strongly desired for many miniaturized applications as Off-Line LED light sources, integrated power supplies for communication devices as iPhone, portable devices for medical applications, portable beamers an others. The integration of high-efficient power supplies based on magnetic transformers (PT) including galvanic isolation is limited due to the physics of electromagnetism. Piezoelectric transformers can be integrated as MEMS when PZT material is applied on silicon to a height of several Micrometers to form an oscillating device which will be processed after micro-bonding in an etching process. Although power density of discrete PT is already high, it can be increased by a factor of 100 to 1000 in integrated devices on silicon taking advantage of uniform crystal structure of sputtering process and improved heat removal through silicon. Serial piezo-transformer-strings allow for high isolating voltage up to 4 kV and provide efficiency up to 95% or more, but unfortunately on the cost of significant large chip area. However, piezoelectric transformers will gain higher acceptance in power converters if a magnetic-field-free environment is requested as for magnetic resonance tomography. Promising piezoelectric applications can be found for transformer-transducer units to harvest ultrasonic energy, preferably in medical therapy-diagnosis applications, but further, in industrial autonomous sensor supplies with avoidance of electromagnetic disturbance. Piezoelectric energy harvesting becomes attractive using ultrasonic energy harvester MEMS with wide range frequency excitation using permanent magnet cantilever construction. Ultrasonic MEMS loudspeakers are miniaturized alternatives to traditional magnetic devices. The advantage of piezoelectric MEMS applications will result in an extreme miniaturization compared to conventional power conversion by magnetic or electrostatic solutions. High reliability including intelligent integrated functions in some cases may improve the practicability of piezoelectric MEMS.