rf bias sputtered alumina thin films were produced under a variety of sputter conditions and analyzed for composition, thickness, density, and dielectric strength (breakdown field) in order to assess the affect of the inclusion of oxygen in the sputter gas on these films. All of the Al:O ratios for these films, as determined by Rutherford backscattering spectrometry, were lower than or equal to the ratio expected from stoichiometric considerations (0.67). In general, higher partial pressures of oxygen in the sputter system produced oxygen rich films. The Al:O ratios were found to vary from a high of 0.66 to a low of 0.54. These were found to correlate with the breakdown field measurements, with the oxygen rich films proving to be better insulators. Sputter bias was found to have the second greatest influence on dielectric strength. A sputter bias of −40 V in our sputtering system produced the best insulating films both in the presence and absence of oxygen in the sputter gas, with breakdown fields dropping off at lower and higher biases.
A model describing the dynamic response of a single-domain fluxgate magnetometer over a wide range of operating conditions in terms of a single measurement of a hysteresis loop or the permeability of the fluxgate's ferromagnetic core is presented. The model is based on the Landau-Lifshitz-Gilbert equation, which describes the dynamics of a coherently rotating ferromagnet. Measurements of the response of a permalloy thin-film fluxgate and a molybdenum-permalloy tube fluxgate demonstrate the accuracy and limitations of the model.
The magnetic properties of rf sputtered Ni81Fe19 films were studied as a function of thickness from <100 to ∼1200 Å. In contrast to some recently reported studies, there was no evidence of an oscillatory dependence of resistivity on Δρ as a function of thickness. The magnetoresistance, resistance, coercivity, and anisotropy field varied smoothly with thickness. In contrast, the magnetostriction λs had a minimum of −1.5×10−6 at ∼300 Å. The saturation magnetic moment did not decrease with thickness over the thickness range studied here. The derived magnetoresistance of an ‘‘infinitely’’ thick film was 3.92% compared to the bulk value of ∼4%. The analysis indicates that surface and grain-boundary scattering are the primary cause of lower than bulk values of magnetoresistance in these thin permalloy films.
Experimental 120-turn thin-film inductive heads have been built. The key features of this head are the 6-μm pitch helical coils and an omega-shaped, planar yoke structure having dual easy axes. Hardbaked photoresist insulator layers are used to encapsulate the yoke and to smooth out the wafer surface topography. Micro-Kerr studies show that the easy axis remains in the transverse direction in the yokes after multiple anneals. The P1/G/P2 is 3.8/0.3/3.8 μm, and the yoke length is close to 1 mm. The helical coils were built with a novel process that combines yoke/stud coplating and a photoresist planarization process. The coil resistance is 68Ω and the inductance is 5.5 μH. The yoke saturates at 5 mA. The heads were tested over disks having Mrt of 2.5 memu/cm2 and Hc of 1500 Oe. The write threshold current is 5.3 mA (peak-to-peak) and the overwrite is 30 dB. The isolated pulse amplitude Vpp is 10.3 μV/(TwV), where track width Tw is in μm and the linear velocity V in m/s.
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