ISBN 9783843944779

978-3-8439-4477-9, Reihe Physik

Svenja Willing
Oblique-incidence deposition of ferromagnetic thin films and their application in magnetoresistive sensors

243 Seiten, Dissertation Universität Hamburg (2020), Softcover, A5

Zusammenfassung / Abstract

Magnetic field sensors can be used for compass applications, to measure electrical currents or to determine position and speed. Layered thin-film sensors based on the giant or tunneling magnetoresistance (GMR or TMR) have a small size, high effect strength and low power consumption. Through the use of oblique-incidence deposition (OID) it is possible to tailor the magnetic and magnetoresistive properties of the sensors in an easy-accessible and flexible way to the needs of an application. The goal of this thesis is to investigate the feasibility of OID in GMR and TMR sensors.

Fundamental questions regarding magnetic coupling and sensor stability are answered with GMR sensors. It is shown that microstructuring and the OID-characteristic wavy surface morphology do not interfere with sensor performance and an effect strength of 10% is achieved.

TMR sensors are based on CoFeB and insulating MgO as tunnel barrier and require a crystallization process. Obliquely deposited CoFeB exhibits a sensitive balance of different anisotropy terms that is surprisingly found to induce a rotation of the preferred magnetization axis. After synchrotron-based investigations to correlate structural and magnetic properties, a model is developed that explains the additional OID-induced anisotropy contributions.

Despite the complex behavior of CoFeB and the combination of wavy interfaces with a sensitive ultra-thin tunnel barrier, the OID-approach is for the first time successfully transferred to TMR systems. A high TMR effect strength of up to 60% is achieved in microstructured sensors and novel functionalities are implemented. Overall, it is shown that oblique-incidence deposition can be used to prepare TMR systems based on MgO and CoFeB that exhibit unique and adjustable functionalities while maintaining a high effect strength, temperature stability and compatibility to common fabrication processes. This paves the way for customizable and simplified magnetoresistive sensors.