High-frequency microinductors with amorphous magnetic ground planes

For the first time, inductors were fabricated on silicon using standard silicon processing tools. The 2.75 turn device exhibits a cutoff frequency of 3.3 GHz. The study incorporated ground planes of amorphous CoTaZr below and above the inductor. CoTaZr has a resistivity of /spl sim/ 100 /spl mu//spl Omega/ /spl middot/ cm, a 4/spl pi/ M/sub s/ of 15 kG, a permeability of /spl sim/ 870 up to 1.4 GHz, and an H/sub c/ of 0.2 Oe (unpatterned film). These properties were monitored during the process and showed no signs of degradation, even after being exposed to process temperatures of 400/spl deg/C. Octagonal devices with slotted ground planes had the best frequency response with a cutoff frequency of 3.3 GHz for inductors with 0.4-/spl mu/m-thick ground planes. Maximum inductive enhancement (over air-core inductors) of 50%-60% has been measured for devices with 1 /spl mu/m of CoTaZr underneath the inductor. Similarly, two layers of 0.4-/spl mu/m CoTaZr exhibit increased inductance of 30%-40% with one ground plane and up to 150% with two ground planes.