Optimisation of spin-valves on rough substrates

A typical spin-valve sensor consists of magnetic and non-magnetic layers, a nd its resistivity is very sensitive to external magnetic fields. Substrate roughness transmitted through the layers can expose magnetic poles which a ffect the magnetic properties of the spin-valve. Three substrates of indust rial 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 surfac e roughness was characterised by atomic force microscopy (AFM). The native silicon and thermally oxidised silicon substrates are both smooth on an ato mic scale over lateral distances of several microns. Meanwhile, the deposit ion-oxidised surface appears 'tiled' with a width of 0.5 micron and edge he ights of 2 nm. No changes in spin-valve properties were observed over a ran ge of Ta buffer layer thickness. However, by correctly choosing the spacer thickness, a sample on the roughest substrate can be made with the followin g 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. (C) 200 0 Elsevier Science S.A. All rights reserved.