Design, modeling, simulation, and testing of resonant micromachined magnetic field sensors.

摘要

This thesis is about the development of a novel micromachined magnetic field sensor. A linear response to a wide range of magnetic fields makes this design suitable for applications where large fields need to be measured with high resolution. The operation of this sensor is based on a shift of the resonant frequency of a resonating microstructure in presence of a magnetic field. The flexural beams of the micromachined resonator are designed so that an axial force is exerted on them when exposed to a magnetic field. The axial force will cause a positive or negative shift in the resonant frequency of the structure, depending on the directions of the magnetic field and a DC current that flows in the crossbars of the sensor. The design of the sensor allows for its fabrication in many standard MEMS processes, and therefore sensor prototypes can be quickly and inexpensively fabricated and transferred to mass production.; A comprehensive model of the sensor is derived which encompasses the interaction of the mechanical operation of the device and its magneto- and electrostatic response. This model is verified using finite element simulations and confirmed with experiments on four different sensor geometries. Three different process flows are employed to fabricate the sensors. The pros and cons of each of the process flows are pointed out. Custom signal processing electronics are designed and used to analyze the sensor data. The noise behavior of each sensor is investigated, the minimum detectable signal determined, and the best configuration selected.; The measured resolution of the sensors is about 80muT if they are used with the designed signal processing electronics. The theoretical minimum detectable signal with current devices is on the order of 200nT. Methods to improve the noise performance of the current sensors are suggested as well as fabrication and signal processing techniques that allow for device designs with better sensitivities.