Spin Valve Systems for Angle Sensor Applications

A contact-less sensor with the ability to measure over a 360° range has been long sought after in the automotive industry. Such a sensor could be realized by utilizing the angle dependence of the Giant Magneto Resistance (GMR) Effect in a special type of magnetic multilayer called a spin valve arranged in a wheatstone bridge circuit [Spo96]. A spin valve consists of two ferromagnetic layers separated by nonmagnetic spacer layer where the magnetization of one of the ferromagnetic layers is pinned in one direction, the bias direction, by the neighboring antiferromagnetic layer. The resistance changes are therefore dependent on the (external) magnetic field direction. This dissertation focused on the analysis of the spin valve system with the endgoal of fabricating a demonstrator GMR 360° angle sensor. The research began with the determination of the physical effects that cause a cosine deviation and their relation to the angular error of a GMR angle sensor. The magnitude and temperature dependence of the magnetic properties (GMR effect, exchange bias, etc.) of the following spin valve systems (NiO, FeMn, IrMn, PtMn, PtMn with a Synthetic AntiFerromagnet (SAF)) was determined. Three different methods (lift-off, ion irradiation, laser-writing) were tested in terms of their effectiveness in reorienting the bias direction of a spin valve on a µm scale without inducing any degradation in the magnetic properties of a spin valve. The laser-writing method was used in the fabrication of a demonstrator GMR 360° angle sensor