Schlüsselwort: GMR-Sensors

In this thesis a measuring system for the analysis of the dominant noise sources and noise processes of magnetoresistive (MR-) magnetic field sensors is developed, presented and characterized. The most important magnetoresistive sensors are the AMR-, GMR-, and TMR-sensors. The intrinsic noise processes of these sensors are determined by the physical processes at the microscopic and macroscopic level and restrict the detection limits. A characterization and analysis of these noise processes is necessary to specify the detection limit, to understand the sensor physics and to improve the sensor characteristics. The investigation of noise is a complex measurement task. The intrinsic signals depend on the sensor and environmental conditions (magnetic working point, temperature, etc.) and are superimposed and disturbed by the noise sources of the measurement electronics. For this reason, the characterisation of the output noise is processed in a very low-noise, shielded and stable measurement environment. For the analysis of interaction and interdependencies of the noise sources, the measurement system features the analysis as a function of the temperature, the sensor supply, the bias magnetic field and the magnetic working point. In this context, the temperature system with a temperature range of ±175 °C and the current source for the generation of ultra-low noise and dynamic magnetic fields in a 3-axis Helmholtz-coil system are highlighted. Additionally and independently of the MR-sensors, a GMI-electronics was integrated in the measurement setup, which features the analysis and the characterization of in-house manufactured GMI-elements in an open and closed loop. After the characterisation of the measurement system, measurements on commercially available AMR-, GMR-, and TMR-sensors are performed. Therefore, an overview of the magnetic noise of different AMR-sensors is presented and a noise source analysis of a sensor is carried out. The measurement results of different GMR- and TMR-sensors show a pronounced 1/f- noise and reveal the problems of these technologies directly.