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

Two micromachined integrated inductors (bar- 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-mu m thick nickel-iron permalloy magnetic core bar is wrapped with 30-mu m thick multilevel copper conductor lines, For an inductor size of 4 mm x 1.0 mm x 110 mu m thickness having 33 turns of multilevel coils, the achieved specific inductance is approximately 30 nH/mm(2) 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 x 1.0 mm x 130 mu m and consists of 30 turns of a 35-mu m thick nickel-iron permalloy magnetic core around a 10-mu m thick sputtered aluminum conductor lines, A specific inductance of 35 nH/mm(2) 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.