High-resistivity nanogranular Co-Al-O films for high-frequency applications

This work presents a series of high-resistivity nanogranular Co-Al-O films with maximum resistivity of ∼110 m cm. The films were deposited using pulsed dc reactive sputtering of a Co72 Al28 target in an oxygen/argon ambient. The samples were characterized by scanning electron microscopy (SEM), M-H loop measurements, and s -parameter measurements on microstrip transmission lines with Co-Al-O magnetic cores. The high-frequency magnetic permeability profile was extracted from the microstrip measurements. Reduction of deposition power resulted in resistivity enhancement, as well as reduction of coercivity and permeability. SEM images reveal an average grain size of ∼80 nm for films with the highest resistivity.