Magnetic sensors with superior performance: materials and design optimization for angular sensing

This thesis presents the optimization of magnetoresistive sensors based on magnetic tunnel junctions (MTJs) for high-precision angular sensing. The work combines numerical modeling, material design, and experimental validation to develop sensors capable of achieving sub-degree angular accuracy with improved linearity and thermal stability. A macrospin Stoner–Wohlfarth simulation framework was implemented to evaluate how magnetic anisotropies, interlayer coupling, and geometry influence sensor behavior. These simulations guided the design of optimized MTJ multilayers and led to the adoption of a Wheatstone bridge configuration with orthogonal reference layers to suppress non-linearities in the output signal.

Prototypes were fabricated using standard microfabrication techniques and characterized under rotational magnetic fields and controlled temperature conditions. The results show that the bridge-based configuration produces a near-sinusoidal output over 360° with angular deviation limited to ±2.5°, representing a tenfold improvement over single-element sensors. The calculated angular error profile closely matches the experimental measurements, confirming the validity of the model and indicating that residual error arises from physical asymmetries in the device.

Thermal stability was investigated through annealing experiments and modeled using a grain-level thermal activation approach. The exchange-bias field was observed to degrade substantially at temperatures above 140°C, in agreement with calculation results. These findings underscore the importance of material selection and stack engineering—such as buffer layer optimization and the use of high blocking-temperature antiferromagnets—for stable high-temperature operation.

Overall, the combination of simulation and experimental methods has enabled the development of a angular sensor with improved performance. The findings provide insight into the physical mechanisms that govern angle accuracy and establish a foundation for future sensors that combine high resolution with thermal robustness for demanding industrial and scientific applications.