Publication
This thesis presents a study on the development of microfabricated fluxgate type magnetic sensors operating within a wide linear operation range. Fluxgate type magnetic sensors are powerful devices due to their high sensitivity, low offset, and high temperature stability. Unfortunately, their linear operation range is limited, since an attempt to increase the linear range also increases the power dissipation of the sensor for the traditionally used parallel fluxgate configuration. In this study, microfabricated fluxgate sensors with wide linear operation range and low power dissipation are developed with the use of the orthogonal fluxgate configuration and a closed magnetization path for the excitation. In the scope of this work, three different fluxgate microsensor structures suitable for operation within a wide linear range are developed, fabricated, and characterized. The sensor structures are named as: rod type orthogonal macro fluxgate sensor, rod type orthogonal micro fluxgate sensor, and ring type micro fluxgate sensor. All of the structures have a CMOS compatible fabrication process flow. Furthermore, the rod type micro sensor and the ring type micro sensor are fabricated by using only standard thin film deposition and photolithography techniques, enabling batch fabrication of these sensor structures. All of the structures use planar sensing coils and an electroplated FeNi core. Apart from the design and development of the sensor, the FeNi electroplating process is intensively investigated since this process directly affects the performance of the sensors. The rod type orthogonal macro fluxgate sensor uses a 20 µm diameter gold bonding wire as the excitation rod, and a 10 µm thick FeNi core electroplated over the bonding wire. The AC current passing through the excitation rod creates a periodical excitation field in the radial direction, which is always perpendicular to the external magnetic field to be detected along the core. With this sensor, the idea of increasing the linear operation range without increasing the power dissipation by using a closed magnetization path and the orthogonal structure is verified. By using a 200 mA-peak sinusoidal excitation current at 100 kHz, passing through the low resistance excitation rod, a linear operation range of ±2.5 mT is reached with a 0.5 mm long core, whereas the linear range is ±250 µT with a 4 mm long core. The rod type orthogonal micro fluxgate sensor presents a modified version of the macro sensor, which can be fabricated in wafer level with standard deposition and photolithography techniques. For this sensor, the excitation rod is formed with an electroplated layer of copper which is sandwiched between two FeNi layers forming the ferromagnetic core. The cross-sectional dimensions of the excitation rod and the core are 8 µm × 2 µm, and 16 µm × 10 µm, respectively. The sensor operates with 100 mA-peak sinusoidal excitation current at 100 kHz, and the linear operation range for different sen