Optical Characterization of Lorentz Force Based CMOS-MEMS Magnetic Field Sensor

Abstract

Magnetic field sensors are becoming an essential part of everyday life due to the improvements in their sensitivities and resolutions, while at the same time they have become compact, smaller in size and economical. In the work presented herein a Lorentz force based CMOS-MEMS magnetic field sensor is designed, fabricated and optically characterized. The sensor is fabricated by using CMOS thin layers and dry post micromachining is used to release the device structure and finally the sensor chip is packaged in DIP. The sensor consists of a shuttle which is designed to resonate in the lateral direction (first mode of resonance). In the presence of an external magnetic field, the Lorentz force actuates the shuttle in the lateral direction and the amplitude of resonance is measured using an optical method. The differential change in the amplitude of the resonating shuttle shows the strength of the external magnetic field. The resonance frequency of the shuttle is determined to be 8164 Hz experimentally and from the resonance curve, the quality factor and damping ratio are obtained. In an open environment, the quality factor and damping ratio are found to be 51.34 and 0.00973 respectively. The sensitivity of the sensor is determined in static mode to be 0.034 µm/mT when a current of 10 mA passes through the shuttle, while it is found to be higher at resonance with a value of 1.35 µm/mT at 8 mA current. Finally, the resolution of the sensor is found to be 370.37 µT.

Micro Magnetic Field Sensors Manufactured Using a Standard 0.18-μm CMOS Process

“…The rotation angle of the micromirror was recorded using an optical measurement. Dennis [ 14 ] used a CMOS process to manufacture resonant MMF sensors. The sensor was fabricated using the stacked layers of the CMOS process, and a post-CMOS processing with reactive ion etch (RIE) dry etching was adopted, releasing the device structure.…”

“…The sensor shuttle was excited using the Lorentz force and external MF, and the resonance amplitude was detected by an optical instrument. These resonant MMF sensors [ 12 , 13 , 14 ] required movable suspension structures, so sacrificial layer technology was used to release the suspension structures. For example, after completion of the CMOS process, the resonant MMF sensors, proposed by Dennis [ 14 ], used an RIE dry etching post-processing to obtain the suspension structures of the devices.…”

“…These resonant MMF sensors [ 12 , 13 , 14 ] required movable suspension structures, so sacrificial layer technology was used to release the suspension structures. For example, after completion of the CMOS process, the resonant MMF sensors, proposed by Dennis [ 14 ], used an RIE dry etching post-processing to obtain the suspension structures of the devices. In this work, we design a magnetotransistor/Hall element MMF sensor without a suspension structure using a CMOS process, so the sensor does not need post-CMOS processing.…”

“…In this work, we design a magnetotransistor/Hall element MMF sensor without a suspension structure using a CMOS process, so the sensor does not need post-CMOS processing. Therefore, the sensor fabrication in this work is easier than that of these sensors [ 12 , 13 , 14 ].…”

Optical and capacitive characterization of MEMS magnetic resonator

“…Lorentz force actuators do not require any special magnetic materials or large area for sensing, these advantages results in small structures, having linear motion, low power consumption, and ideal for large displacement applications [1,2]. Multiple readout mechanisms have been employed with the Lorentz force sensors which include piezoresistive [3,4], capacitive [5] and optical ones which are mainly used for out-of-plane detection [6,7]. Resonant frequency shifts using Lorentz force has also been presented in some designs by applying axial stress which result in an increase in the stiffness of the sensor [8,9].…”