A MEMS resonant magnetometer based on capacitive detection (original) (raw)
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Optical and capacitive characterization of MEMS magnetic resonator
IEICE Electronics Express, 2016
In this paper a Lorentz force driven Micro ELectro Mechanical Sytems (MEMS) resonator fabricated on PolyMUMP process with optical and capacitive sensing is presented. The resonator is designed by combining the two poly layers which result in an increase in the thickness of the resonator. Lorentz force generates lateral displacements at low driving voltages which are proportional to the magnetic field and the input current. A displacement of more than 9.8 µm was achieved with a magnetic field of 0.12 T and a driving current of 27 mA. Magnetic sensitivity of 1.41 V/T in air was experimentally measured using permanent magnets and capacitive sensing circuitry. Optical results demonstrate the sensitivity values between 0.090 µm/mT and 0.074 µm/mT.
Sensors and Actuators A-physical, 2011
A resonant magnetic field microsensor based on Microelectromechanical Systems (MEMS) technology including a piezoresistive detection system has been designed, fabricated, and characterized. The mechanical design for the microsensor includes a symmetrical resonant structure integrated into a seesaw rectangular loop (700 μm × 450 μm) of 5 μm thick silicon beams. An analytical model for estimating the first resonant frequency and deflections of the resonant structure by means of Rayleigh and Macaulay's methods is developed. The microsensor exploits the Lorentz force and presents a linear response in the weak magnetic field range (40–2000 μT). It has a resonant frequency of 22.99 kHz, a sensitivity of 1.94 V T−1, a quality factor of 96.6 at atmospheric pressure, and a resolution close to 43 nT for a frequency difference of 1 Hz. In addition, the microsensor has a compact structure, requires simple signal processing, has low power consumption (16 mW), as well as an uncomplicated fabrication process. This microsensor could be useful in applications such as the automotive sector, the telecommunications industry, in consumer electronic products, and in some medical applications.
Fabrication Method of Mems Based Clamped-Clamped Resonant Magnetometer
In this paper we present fabrication steps for manufacturing MEMS based magnetometer which is actuated by Lorentz force in the middle point of beam which has been fixed from both two edges (Clamped - Clamped). We utilized two different process sequences in order to fabricate microsystems properly. The structures were first fabricated on bulk Si-wafer and the fabrication of these sensors was characterized by built in stress in the beam and etching methods in the processes. The second approach was performed on SOI Si-wafer. Two fabrication routes are compared in terms of working MEMS structures. The microstructures are manufactured successfully by a process sequence based on SOI-Si wafer.
Resonant Magnetic Field Sensors Based On MEMS Technology
Sensors, 2009
Microelectromechanical systems (MEMS) technology allows the integration of magnetic field sensors with electronic components, which presents important advantages such as small size, light weight, minimum power consumption, low cost, better sensitivity and high resolution. We present a discussion and review of resonant magnetic field sensors based on MEMS technology. In practice, these sensors exploit the Lorentz force in order to detect external magnetic fields through the displacement of resonant structures, which are measured with optical, capacitive, and piezoresistive sensing techniques. From these, the optical sensing presents immunity to electromagnetic interference (EMI) and reduces the read-out electronic complexity. Moreover, piezoresistive sensing requires an easy fabrication process as well as a standard packaging. A description of the operation mechanisms, advantages and drawbacks of each sensor is considered. MEMS magnetic field sensors are a potential alternative for numerous applications, including the automotive industry, military, medical, telecommunications, oceanographic, spatial, and environment science. In addition, future markets will need the development of several sensors on a single chip for measuring different parameters such as the magnetic field, pressure, temperature and acceleration. OPEN ACCESS Sensors 2009, 9 7786 Keywords: Lorentz force; magnetic field sensors; Microelectromechanical Systems (MEMS); resonant structures
A Tunable MEMS Magnetic Sensor
Journal of Microelectromechanical Systems, 2017
This paper introduces a tunable MEMS magnetic field sensor. It uses torsional vibrations excited by Lorentz force to measure the strength of external magnetic fields. The sensor sensitivity and dynamic range can be tuned on-the-fly by varying its dc bias. Experimental demonstration shows that the sensor sensitivity can be tuned in the range of 0.139-0.283 V/mT as the bias voltage varies from 0 to 6 V in air and in the range of 0.038-0.955 V/mT as the bias voltage varies from 0 to 5 V in vacuum. While the sensor can operate in either a forced or a resonant mode, it achieves higher sensitivity and bandwidth when operating near its first torsional resonance. [2015-0285] Index Terms-Magnetic sensor, MEMS, torsional mode. I. INTRODUCTION M AGNETIC sensors are indispensable in many commercial and industrial applications. The demand for magnetic sensors has been increasing for use in electronic compasses, inertial measurement units (IMUs), and inertial navigation systems (INS) [1]. Most industrial magnetic sensors are based on Anisotropic Magneto-Resistance (AMR) and Hall effect, while MEMS magnetic sensors are gaining traction in consumer markets due to their small form-factor and low power consumption. AMR sensors have higher sensitivity, smaller dynamic range, better thermal stability, and lower dc offset than Hall effect sensors [2]. On the other hand, Hall effect sensors have a wider bandwidth and are immune to the hysteresis and saturation phenomena that limit the performance of AMR sensors [3]. MEMS magnetic sensors based on Lorentz force transduction have been proposed as an alternative that avoids many of these limitations. They take advantage of dynamic amplification by operating at resonance [3]-[7]. MEMS magnetic sensors exploit Lorentz force to excite torsional [8], [9] and bending [3], [10]-[12] modes of vibration in the presence of external magnetic fields. Piezoresistors [4], [13] and capacitive sensing [1], [3], [14] are then used to measure the resulting strain and displacement, respectively. Langfelder et al.
Experimental analysis of out-of-plane Lorentz force actuated magnetic field sensor
IEICE Electronics Express, 2017
In this article, we present a simple MEMS magnetic sensor based on Lorentz Force principle. In this work, the sensor is designed, fabricated and characterized capacitively using a standard capacitance to voltage MS3110 circuit. The sensor is fabricated based on double thickness Poly-MUMP surface micromachining process. In this process, the two Poly layers are combined to increase the thickness of the sensor beams and central shuttle. In response to an input excitation current an out of plane motion due to Lorentz force occurs which is detected by the change in capacitance between the moving and static plate. The experimentally detected resonant frequency of the sensor is 5.1 kHz. The experimental sensitivity achieved by the sensor at atmospheric condition is 5.59 V/T for the input current of 30 mA with a damping ratio of 0.010.
Contactless Excitation of MEMS Resonant Sensors by Electromagnetic Driving
A contactless electromagnetic principle for the excitation of mechanical vibrations in resonant structures has been investigated. The principle relies on no specific magnetic property of the resonator except electrical conductivity and can be adopted for employing the structures as resonant sensors for measurements either in environments not compliant with the requirements of active electronics or in limited accessibility environments. An external coil is employed as an excitation source which inductively couples to the conductive surface of the resonator or to a secondary coil connected to conductive paths on the resonant structure. Exploiting the interaction of the induced currents with AC or DC magnetic fields, Lorentz forces are generated which can set the resonator into vibration. Preliminary tests on miniaturized resonators have been performed, namely cantilevers and clamped-clamped beams. The principle has been subsequently implemented in the design of MEMS resonators. Experimental verifications have shown the possibility of contactless exciting microresonators over short-range distances.
Optical Characterization of Lorentz Force Based CMOS-MEMS Magnetic Field Sensor
Sensors, 2015
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.
MEMS micro-Wire Magnetic Field Detection Method at CERN
IEEE Sensors Journal, 2016
This paper reports a novel construction of a micromachined MEMS magnetometer characterized by static magnetic fields of CERN's reference dipole with a custom made capacitive read-out. The magnetic flux density is characterized via the vibration modes of the MEMS structure, which are sensed capacitively. The device consists of a single-crystal silicon clamped-free plate (cantilever) carrying a thin conductor. The cantilever and the thin film metal electrodes are separated by a small gap, forming a vibrating plate capacitor. Movements of the cantilever are read out conveniently by electronic circuits. A static magnetic field generates a force density acting on the conductor that alternates according to the frequency of the current. When the electrical current is known, the deflection amplitude of the cantilever is a measure of the component of the magnetic flux density that points perpendicular to the current. The highest vibration amplitudes are expected, in the vicinity of resonance frequencies of the micromachined structure. At ambient pressure, the prototype sensor has a measured resonance frequency of 3.8 kHz for the fundamental mode and 20 kHz for the first antisymmetric mode. In experiments, the magnetic flux of the dipole has been characterized between 0.1 and 1 T, with a relative uncertainty of 3 × 10 −4 .