A comparison of two micromachined inductors (bar-type and meander-type) for fully integrated boost DC/DC power converters

Two micromachined integrated inductors (bar-type and meander-type) are realized on a silicon wafer by using modified, IC-compatible, multilevel metallization techniques. Efforts are made to minimize both the coil resistance and the magnetic reluctance by using thick electroplated conductors, cores, and vias. In the bar-type inductor, a 25 μm thick nickel-iron permalloy magnetic core bar is wrapped with 30 μm thick multilevel copper conductor lines. For an inductor size of 4 mm×1.0 mm×110 μm thickness having 33 turns of multilevel coils, the achieved specific inductance is approximately 30 nH/mm² at 1 Mhz. In the meander-type inductor, the roles of conductor wire and magnetic core are switched, i.e., a magnetic core is wrapped around a conductor wire. This inductor size is 4 mm×1.0 mm×130 μm and consists of 30 turns of a 35 μm thick nickel-iron permalloy magnetic core around a 10 μm thick sputtered aluminum conductor lines. A specific inductance of 35 nH/mm² is achieved at a frequency of 1 Mhz. Using these two inductors, switched DC/DC boost converters are demonstrated in a hybrid fashion. The obtained maximum output voltage is approximately double an input voltage of 3 V at switching frequencies of 300 kHz and a duty cycle of 50% for both inductors, demonstrating the usefulness of these integrated planar inductors