Abstract
A typical spin-valve sensor consists of magnetic and non-magnetic layers, and its resistivity is very sensitive to external magnetic fields. Substrate roughness transmitted through the layers can expose magnetic poles which affect the magnetic properties of the spin-valve. Three substrates of industrial interest were investigated (listed in order of increasing roughness): (100) silicon, thermally oxidised silicon and deposition-oxidised silicon, the latter being preferable for microchip fabrication processes. The surface roughness was characterised by atomic force microscopy (AFM). The native silicon and thermally oxidised silicon substrates are both smooth on an atomic scale over lateral distances of several microns. Meanwhile, the deposition-oxidised surface appears `tiled' with a width of 0.5 micron and edge heights of 2 nm. No changes in spin-valve properties were observed over a range of Ta buffer layer thickness. However, by correctly choosing the spacer thickness, a sample on the roughest substrate can be made with the following properties: MR ratio=6.2%, sensitivity=1.6%/Oe, and a coupling field of only a few Oersteds greater then a sample on a smooth substrate.
Published Version
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