Nanocrystalline Thin Films for Tunable High Q UHF/VHF Devices
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Mat. Res. Soc. Symp. Proc. Vol. 603 © 2000 Materials Research Society
or nitride grain boundaries. The latter are responsible for increasing both their M, and p [3]. Previous reports [4] indicated that the complex permeability of several micron (-2jtm) thick FeTaN films prepared by rf-diode sputtering was nearly that of an ideal single domain state. With the addition of Cr, alloy films with larger M, (1.95 T) and Ha, (50-60 Oe) were obtained by Jin et al [5]. However, the thickness of the films in this study were < 0.1 gim. The present study, investigated the possibility of increasing the thickness of this type of alloy film to >2 pm. FeCrTa:N/O films with thickness 1 jim to 2 gim were deposited by rf-diode reactive sputtering. The objective was to obtain films in which selective reactions with O/N gases could produce Fe and FeN grains with an increased M,, and an increased p produced by surrounding the nanocrystal grains by amorphous Cr and Ta oxynitride boundaries. By adjusting the deposition parameters, an attempt was made to increase the Han by generating a morphology with a large internal shape anisotropy. The investigation focused on a study of the changes in the sputtered film morphology, and in the resultant magnetic properties, as a function of variations in the deposition/process parameters. EXPERIMENT Films were RF-diode sputtered in Ar+N or Ar+(O+N) reactive gas mixtures. The amount of reactive gas incorporated was determined by the relative flow ratios of N and (N+O) to Ar, and as independently controlled by individual digital mass flow controllers. The chamber base pressure was always in the 10-7 Torr range and the total working gas pressure during deposition was a few mTorr. Films were deposited on 22 mm cover glass in the stationary mode. The typical deposition time for a I ýim thick film was about 45 minutes, but inversely proportional to the RF power. Thin film thickness was determined using a stylus profilometer. The DC resistivity was obtained by a conventional four-point probe method and the DC magnetic properties were obtained by either a vibrating sample magnetometer, or hysteresis loop tracer. Complex RF permeability spectra for 20 - 200 MHz were obtained with a permeameter. Higher frequency studies will be reported elsewhere. The morphology / microstructure investigations were made by XRD and TEM. During all depositions, the film thickness was z1-2 jim, the magnetic field bias Z 50 Oe, and the substrate temperature was near ambient. Film were made under the following conditions: (i) fixed RF power and total flow rate, and variable N flow ratio, (ii) fixed RF power and N/(N+Ar) flow ratio, and variable total flow rate, and (iii) fixed total and N 2 flow rate, and variable RF power, and (iv) fixed RF power, total flow, and N+O flow ratio, and variable O/(N+O) flow ratios. RESULTS FeCrTaN Films: Microstructure Figures (la), (lb) and (lc) show the XRD data obtained for the FeCrTa:N films as functions of variations in the ratio of the N2 to total flow rate, pressure and RF power respectively.
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