Energy Harvesting

Converting the kinetic energy of human movement into electrical energy has become an attractive approach to powering wireless electronic devices in recent years. The combination of energy harvesting and portable body-worn electronics forms a self-sufficient system that finds application, for example, in fitness gadgets for tracking temperature, speed and position data. Based on novel electroactive polymers, an innovative energy harvesting system has been developed that is small enough to be integrated into a shoe sole. The element, which converts mechanical energy into electrical energy, is based on thin polymer films with high relative permittivity. Compared to traditional piezoelectric concepts, this element operates non-resonantly and can be optimized for energy harvesting from mechanical energy sources even at low frequencies.

A first demonstrator of a polymer energy harvester integrated into a shoe is available. It is capable of generating a few µWs of energy when subjected to mechanical deformation by pressure and frequency range typical of human gait. In this case, the transducer circuit is tuned to supply an RF transmitter module. The harvester system (element and circuit) can be adapted for other applications such as powering a variety of application-specific electronics.

Fraunhofer IPMS develops customized energy harvesters and energy storage devices. Our research focuses on both system-on-chip and system-in-package devices, on the development of CMOS-compatible materials, and on multimodal solutions for power maximization.

For short-term energy storage and buffering, silicon capacitors are being developed that are characterized by particularly high capacitance densities combined with the lowest thermal and field-dependent variability. Profiles with a thickness of less than 100 µm make it possible to integrate the components into standard packages. For long-term storage, we are developing lithium-ion accumulators with solid electrolyte that can be manufactured entirely using established semiconductor technology processes. With this thin-film technology, only the smallest storage capacities can be achieved. However, by manufacturing on structured silicon substrates, our concept combines a high energy storage density per wafer area with a high power density due to very short ion diffusion paths during charge cycles. 

For the utilization of ambient energy, such as heat or motion for autonomous operation of microelectronic systems, we are researching energy harvesters that convert this thermal or mechanical energy into electrical energy. For this purpose, we are developing various silicon-based thermoelectric materials as well as pyroelectric hafnium dioxide thin films. The piezoelectric properties of this promising material are also being evaluated for use in vibration-based energy harvesters.