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 similar to 100 muOmega (.) cm, a 4piM(s) of 15 kG, a permeability of similar to 870 up to 1.4 GHz, and an H-c of 0.2 Ge (unpatterned film). These properties were monitored during the process and showed no signs of degradation, even after being exposed to process temperatures of 400 degreesC. Octagonal devices with slotted ground planes had the best frequency response with a cutoff frequency of 3.3 GHz for inductors with 0.4-mum-thick ground planes. Maximum inductive enhancement (over air-core inductors) of 50%-60% has been measured for devices with 1 pm of CoTaZr underneath the inductor. Similarly, two layers of 0.4-mum CoTaZr exhibit increased inductance of 30%-40% with one ground plane and up to 150% with two ground planes.