Magnetic micro-transformers realized with a flip-chip process

Micromachined transformers are complex devices. Conductors, insulators and magnetic materials are manufactured on the same substrate, thus leading to transformer structures often with many manufacturing levels. We describe here a new low cost solution to make quasi-planar transformer structures. The primary and secondary coils are manufactured separately and assembled by flip-chip technology. This novel structure allows a single conductor level process. The influence of different parameters of the design on expected performances is discussed. A set of transformers was made with 1 μm thick Al conductors to assess the process validity. First measurements were carried out. A current mode operation was tested and showed an output voltage proportional to the operation frequency up to 10 MHz. Tests were carried out under no-load conditions and with resistive load (1 k and 470 values). A resonance mode appeared for frequency above 15 MHz but was not measured.