Micromachined on-chip fluxgate magnetometers with low power consumption

A new micromachined on-chip magnetometer with low power consumption has been designed, fabricated, and fully characterized in this research work. Based on permalloy magnetic core, two novel CMOS-compatible micro fluxgate sensors have been developed and characterized in terms of low power consumption. In addition, a low-power interface integrated circuit has been developed and characterized for the developed sensors. Experiment shows that the magnetometer combined with the micro fluxgate sensor and the interface circuit consumes power comparable to that of the other state-of-the-art magnetometer systems.;First, a micromachined ring-core fluxgate sensor utilizing localized core saturation method to reduce its power consumption is presented. The design is accomplished through 3D electromagnetic simulation. A low power design has achieved the power consumption of 14.4 mW and sensitivity of 590 V/T at 60 muT with an excitation current of 80 mA. Based on the design, fabricated devices have shown the power consumption of 14 mW and sensitivity of 650 V/T at 60 muT with an excitation current of 75 mA. The simulation and the experimental results showed a good agreement, which supports the new approach for the design of low-power fluxgates valid. In addition, measurements using a second harmonics-based detection circuit have been adopted, so the noise, stability and perming effect of the fabricated device are explored.;Second, a new micro orthogonal fluxgate sensor with solenoid sensing coils is presented. The sensor consumes the power of 16 mW with an excitation current of 140 mA. The sensor occupies an active area of merely 2 mm by 0.15 mm with sensitivity of 0.1 V/T and linearity of 2.5 %. Its temperature coefficient of offset drift shows only 125 nT/°C even with such small sensitivity. This sensor type shows great potential to be manufactured with small size, low power, and high performance with low cost.;Finally, a pulse-operating interface integrated circuit that can reduce the total power consumption of a fluxgate magnetometer is introduced and developed. The circuit works under power supply of +/-2.5V with 75 mA current driving capability. Total power consumption of 14 mW is achieved in the magnetometer comprised of the circuit and the first low power micro fluxgate sensor. The overall system sensitivity is 250 V/T. The corresponding rms noise is 400 nT/√Hz at 1 Hz.;In this research work, a low power magnetometer system based on micro fluxgate sensors with permalloy magnetic core and pulse-operating integrated IC has been developed and successfully characterized. The newly developed sensors can have numerous applications that are previously untouched by the conventional fluxgate sensors that are bulky, expensive, and high power consumption.