Integrated solenoid inductors with patterned, sputter-deposited Cr/Fe₁₀Co₉₀/Cr ferromagnetic cores

Ferromagnetic (FM) films suitable for implementation in between interconnect layers of a standard CMOS fabrication process are demonstrated to yield considerable size reduction of monolithic radio frequency (RF) inductors, leading to lower cost. The deposition of a FM Cr(5 nm)/Fe10 Co90 (500 nm)/Cr(15 nm) stack is performed by magnetron sputtering at room temperature under a dc magnetic field of ∼ 10 mT along the magnetic easy-axis. A lift-off technique, using a four-layer shadow mask, is used for pattern transfer to the magnetic stack to circumvent apparent difficulties in the patterning of FM films. A series of solenoid-type inductors with FM cores are demonstrated and compared to control devices with air cores. A more than eight-fold enhancement of the inductance and a seven-fold improvement of the quality factor are achieved.