Design and Fabrication of a 315 μH Bondwire Micro-Transformer for Ultra-Low Voltage Energy Harvesting

This paper presents a design study of a new topology for miniaturized bondwire transformers fabricated and assembled with standard IC bonding wires and toroidal ferrite (Fair-Rite 5975000801) as a magnetic core. The micro-transformer realized on a PCB substrate, enables the build of magnetics on-top-of-chip, thus leading to the design of high power density components. Impedance measurements in a frequency range between 100 kHz to 5 MHz, show that the secondary self-inductance is enhanced from 0.3 mu H with an epoxy core to 315 mu H with the ferrite core. Moreover, the micro-machined ferrite improves the coupling coefficient from 0.1 to 0.9 and increases the effective turns ratio from 0.5 to 35. Finally, a low-voltage IC DC-DC converter solution, with the transformer mounted on-top, is proposed for energy harvesting applications.