Magnetoresistive Stacks with Improved Thermal Resilience

Magnetic sensors are widely used in state-of-the-art electronics and play a crucial role in industrial applications. These sensors act as transducers between magnetic fields and electrical currents and are required to have exceptional performance even in harsh environments. The design of each thin film component is essential to ensure that these technologies remain competitive for next-generation applications. The unidirectional reference of the sensors is typically established through exchange coupling in antiferromagnetic/ferromagnetic bilayers.

This work explores the use of two different antiferromagnets (MnIr and MnNi) to enhance the thermal stability of tunnel magnetoresistive devices. The growth conditions and the seed layers (Ta, Ru, CuN), were modified to produce thermally stable structures compatible with operation in harsh environments. Additionally, the stability of tunnel magnetoresistive sensorsto magnetic fields was analyzed for applications as angular sensors. Different synthetic antiferromagnets were studied, along with their impact on the angular performance of the devices.

Magnetic anisotropies and interlayer couplings were investigated using a macrospin model, which allowed the definition of material limits to minimize device output errors. Subsequently, the electrical characterization of microfabricated sensors contributed to the understanding of the operational limits and verification the applicability of the developed model. Finally, this work explored a new way to tune the linear range of magnetic sensors (anisotropic and tunnel magnetoresistive sensors) using magnetic antidot structures.

When applied to the ferromagnetic layers of the sensors, this methodology enabled the control to the linear region of such devices and modifications to their sensitivity at device/wafer level. This work demonstrates several strategies that can be used to improve spintronic sensing technologies and extend their operational limits. The results are shown to leverage the design of robust sensors targeting harsh environment applications.