The Multiple‐Target Method for Sputtering Amorphous Films for Bubble‐Domain Devices

Abstract

Previously, sputtered amorphous metal alloys for bubble applications have ordinarily been prepared by standard sputtering techniques using a single target electrode. We report for the first time the deposition of these alloys using a multiple target rf technique in which we use a separate target for each element contained in the alloy. One of the main advantages of this multiple‐target approach is that the film composition can be easily changed by simply varying the voltages applied to the elemental targets. In our apparatus, the centers of the targets are positioned on a 15 cm‐radius circle. The platform holding the film substrate is on a 15 cm‐long arm which can rotate about the center, thus bringing the sample successively under each target. The platform rotation rate is adjustable from 0 to 190 rpm. That this latter speed is sufficient to homogenize the alloys produced is demonstrated by measurements we have made of the uniaxial anisotropy constant in ${\mathrm{Gd}}_{\text{0.12}}{\mathrm{Co}}_{\text{0.59}}{\mathrm{Cu}}_{\text{0.29}}$ films. The anisotropy is ${\text{6.0\hspace{0.17em}×\hspace{0.17em}10}}^5\hspace{0.17em}{\mathrm{ergs/cm}}^3$ and independent of rotation rate above ∼25 rpm, but it drops rapidly for slower rotation rates, reaching ${\text{1.8\hspace{0.17em}×\hspace{0.17em}10}}^5\hspace{0.17em}{\mathrm{ergs/cm}}^3$ for 7 rpm. The film quality is equal to that of films made by conventional methods. We have observed coercivities of a few oersteds in samples with stripe widths of 1 – 2 μm and magnetizations of 800 – 2800 G.