High-performance, 3D-microtransformers on multilayered magnetic cores

We present the fabrication of 3D-microtransformers combining a new type of multilayered magnetic core and coil winding with an automatic wirebonder. For the magnetic cores we stapled up to 30 layers of 20 μm thick amorphous metal layers with an industrial laminator. Intermediate layers of 10 μm thick double-sided sticky tape provided adhesion and electrical insulation. Electrical discharge machining was used to precisely cut these magnetic stacks to sub-millimeter cubes. To flip the cubes by 90° and assemble them onto a wafer for coil winding, we produced a receptor wafer providing magnetic landing sites. Subsequently, to wind a primary and secondary coil, one on top of the other, an automatic wirebonder was employed with 25 μm thick insulated Gold wire. A fabricated transformer with a core size of 0.9*0.8*1 mm³ yielded an inductance of 1412 nH and a coupling factor of 97%. The maximum transformer efficiency of 73% was measured at a load of 50 Ω.