Nanocrystalline Thin Films for Tunable High Q UHF/VHF Devices

Recent studies indicate that reactively sputtered FeCrTaN nanocrystalline thin films have many of the properties [large magnetization (4πMs), anisotropy (Han), and resistivity (ρ)] required for application in high Q (>1000), magnetically tunable devices operating in the VHF/UHF (∼50 MHz to 500 MHz) frequency range. These films had thickness (d) of ∼0.1 -µm, but film thickness of ∼1-µm may be required for many devices. Although most previous research has shown that the magnetic properties of sputtered films are significantly deteriorated when d∼1-µm, there are recent reports that those of reactively sputtered nanocrystalline films of similar alloys (FeTaN, CoAl/SiO) are independent of thickness to d≈1-2-µm. Accordingly, this work investigated the possibility of reactively sputtering FeCrTa alloys in O/N gas mixtures to obtain films with device quality properties, that are independent of thickness to 1-2µm. The correlations between their magnetic and electrical properties, and their nano-heterogeneous microstructure, were studied to determine optimum reactive gas mixtures and sputtering parameters. Cross-section TEM studies were conducted to investigate the origins of the thickness independent properties, and the unexpected increases in anisotropy.