Fabrication of MEMS xylophone magnetometer by anodic bonding technique using SOI wafer

This paper reports the design, fabrication and characterization of Lorentz force based MEMS magnetometer. The paper focuses on fabrication process of the device by anodic bonding technique using SOI and glass wafers. The fabrication is a three-mask process. The structure is a xylophone resonator fabricated using highly doped Si as the structural layer. The highly doped structural layer avoids the need of an extra metallized top electrode, which in turn reduces the fabrication step. The proposed fabrication technique for the xylophone bar magnetometer is reported for the first time. The ease in fabrication, low temperature (<= 400 A degrees C) process, repeatable, reliable, reduced lithography steps and the ability to precisely control the gap between the electrodes makes it better from the conventional fabrication methods. The device exploits the Lorentz force transduction mechanism and operates at its primary resonant mode at about 108.75 kHz. The current is applied at the resonant frequency and magnetic field of 118 Gauss is applied orthogonal to the current direction. The frequency and transient response characterization of the out-of-plane vibration is carried out at atmospheric pressure with a quality factor of 4.2. Also, vacuum packaging at die level is done and a quality factor of 180 is achieved. The power consumption and theoretical Brownian noise limited resolution of the sensor is 0.45 mW and 215 nT/root HZ.