Design and fabrication of a 315 uH 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 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 secondary self-inductance is enhanced from 300 nH with an epoxy core to 315 µH with a ferrite toroidal 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 an IC integrated solution with the transformer mounted on-top of a low-voltage DC-DC converter for energy harvesting applications is proposed