Development of CMOS-MEMS in-plane magnetic coils for application as a three-axis resonant magnetic sensor

This study designs and implements a single unit three-axis magnetic sensor using the standard TSMC 0.35 mu m 2P4M CMOS process. The magnetic sensor consists of springs, a proof-mass with embedded magnetic coils, and sensing electrodes. Two sets of in-plane magnetic coils respectively arranged in two orthogonal axes are realized using the stacking of metal and tungsten layers in the CMOS process. The number of turns for the proposed in-plane magnetic-coil is not restricted by the space and thin film layers of the CMOS process. The magnetic coils could respectively generate Lorentz and electromagnetic forces by out-of-plane and in-plane magnetic fields to excite the spring-mass structure. Capacitance sensing electrodes could detect the dynamic response of the spring-mass structure to determine the magnetic fields. Measurements indicate the typical sensitivities of the sensor are 0.21 mu V mu T-1 (x-axis), 0.20 mu V mu T-1 (y-axis), and 0.90 mu V mu T-1 (z-axis) at 1 atm. Moreover, the resolutions of the sensor are respectively 384 nT rtHz(-1) for the x-axis, 403 nT rtHz(-1) for the y-axis, and 62 nT rtHz(-1) for the z-axis at 1 atm. The presented magnetic sensor could monolithically integrate with other CMOS-MEMS devices for various applications.