Development and comparative analysis of fluxgate magnetic sensor structures in PCB technology

In this paper, we present a family of fluxgate magnetic sensors on printed circuit boards (PCBs), suitable for an electronic compass. This fabrication process is simple and inexpensive and uses commercially available thin ferromagnetic materials. We developed and analyzed the prototype sensors with software tools based on the finite-element method. We developed both singleand double-axis planar fluxgate magnetic sensors as well as front-end circuitry based on second-harmonic detection. Two amorphous magnetic materials, Vitrovac 6025X (25 /spl mu/m thick) and Vitrovac 6025Z (20 /spl mu/m thick), were used as the ferromagnetic core. We found that the same structures can be made with Metglas ferromagnetic core. The double-axis fluxgate magnetic sensor has a sensitivity of about 1.25 mV//spl mu/T with a linearity error of 1.5% full scale, which is suitable for detecting Earth's magnetic field (/spl plusmn/60 /spl mu/T full-scale) in an electronic compass.     

A Fluxgate Magnetic Sensor: From PCB to Micro-Integrated Technology

In this paper, a double-axis micro Fluxgate magnetic sensor is presented. The device represents an evolution of a PCB dual axis sensor previously realized. In the PCB version the experimental results exhibit excellent agreement with the simulations performed using a tool based on the finite element method. Using the same design approach a version of double-axis Fluxgate structure is here proposed to be realized in IC technology. The accurate study of the magnetic field distribution allows a 75% area saving for the IC version with respect to a direct scaling of the PCB version. Imposing an external magnetic field of about 60 muT, the simulated differential output voltage of the micro-integrated Fluxgate sensor achieves a peak value of 1 mV with 5 mA sinusoidal excitation current peak at 100 kHz. The integrated microstructure shows a linearity error of about 1.15% of the full scale, in the range of plusmn50 muT, with a sensitivity of about 0.45 mV/muT     

Excitation and temperature stability of PCB fluxgate sensor

Printed circuit board (PCB) integrated inductors have been adapted for operation as fluxgate sensors. A ring core is made from an electrodeposited permalloy thin film and is sandwiched between the layers of the PCB. The sensor excitation winding is also integrated into the PCB design. The pick-up coil is wound around the frame of the PCB core. Different types of current excitation waveforms with tuned and nontuned pick-up coils were used. The achieved sensitivities for 60 turns of tuned/nontuned pick-up coil, a sinusoidal waveform excitation current of Irms=300 mA, and an excitation frequency of 150 kHz were 13100/1800 V/T. The achieved sensitivity for pulse excitation (Ipeak-peak=900 mA, Irms=184 mA, duty 20%) was 2100 V/T. Noise power density for pulse excitation was 1.2 nTrms//spl radic/Hz@1 Hz, noise rms value from 10 mHz to 10 Hz was 3.3 nT. A perming error of 1 /spl mu/T was measured for a wide range of excitation currents.     

A micromachined wide-bandwidth magnetic field sensor based on all-PMMA electron tunneling transducer

All-PMMA-based tunneling magnetic sensors were fabricated by hot embossing replication with silicon templates. The silicon templates had smooth surfaces, positive profiles, and pyramid-like pits with a high aspect ratio. With this fast (20 min), simple (one-step), and repeatable method, the all-PMMA tunneling sensor platform yielded sharp tunneling tips with 75 /spl mu/m in baseline and 50 /spl mu/m in depth. The sensors were assembled and fixed with measurement circuits, after their electrodes were patterned with modified photolithography and Co film was deposited with e-beam evaporation. A natural frequency response of 1.3 kHz was observed, and a tunneling barrier height of 0.713 eV was tested. Due to the quadratic relation between magnetic force and the field, the sensor field response (7.0/spl times/10/sup 6/ V/T/sup 2/) was also quadratic. The noise voltage at 1 kHz is 0.2 mV, corresponding to a magnet field of 0.46/spl times/10/sup -6/ T. The bandwidth of this sensor is 18 kHz. This new type of sensor platform is promising for the next generation of microsensing applications.     

The microfluxgate magnetic sensor having closed magnetic path

This paper presents a microfluxgate magnetic sensor in printed circuit board (PCB). In order to observe the effect of the closed magnetic path, the magnetic cores of rectangular ring and two bars were each fabricated. Each fluxgate sensor consists of five PCB stack layers including one layer magnetic core and four layers of excitation and pickup coils. The center layer as a magnetic core is made of a Co-based amorphous magnetic ribbon with extremely high dc permeability of /spl sim/100,000. Four outer layers as excitation and pickup coils have a planar solenoid structure and are made of copper foil. In the case of the fluxgate sensor having the rectangular ring-shaped core, excellent linear response over the range of -100 to +100 /spl mu/T is obtained with 780-V/T sensitivity at an excitation sine wave of 3 V/sub P-P/ and 360 kHz. The chip size of the fabricated sensing element is 7.3/spl times/5.7 mm/sup 2/. The very low power consumption of /spl sim/8 mW was measured.     

CMOS magnetic field to frequency converter

In this paper, a CMOS magnetic field to frequency converter with high resolution is presented. It is composed of two voltage-controlled ring oscillators whose output frequency differences linearly vary with the magnetic field perpendicular to the chip surface. The prototype circuit has been fabricated in a 0.5-/spl mu/m CMOS process and operated at a 5-V supply voltage. The measured sensitivity is 24 kHz/mT and the power consumption is 5.1 mW. The small equivalent resolution of at least 20 /spl mu/T can be achieved. The frequency offset is 42 kHz when no magnetic field applied. Its nonlinearity within /spl plusmn/120 mT is smaller than 0.56%.     

Reverse-order source/drain formation with double offset spacer (RODOS) for low-power and high-speed application

We proposed "reverse-order source/drain formation with double offset spacer" (RODOS) structure for low-power and high-speed applications. Both simulation and experimental data were used to evaluate the potential of the structure. It showed improved performance in terms of poly-depletion effect, dc characteristics, gate delay (CV/I), switching energy (CV/sup 2/) and linearity (V/sub IP3/). It satisfied all the requirements of LOP and LSTP for 90 nm technology node in ITRS 2002. Simulation predicted 794 /spl mu/A//spl mu/m in on-current, 0.1 nA//spl mu/m in off-current, 65 mV/V in DIBL, 80 mV/dec in SS, 1.29 ps in gate delay, 198 GHz in f/sub T/ and 0.151 fJ in switching energy in addition to enhanced linearity. Finally, we confirmed the high feasibility and potential of the RODOS MOSFET's for low-power and high-speed applications such as an LNA in portable communication appliances.     

A weak magnetic field measurement system using micro-fluxgate sensors and delta-sigma interface

This paper presents a weak magnetic field measurement system using micro-fluxgate (FG) sensors and a sensor signal processing technique using the delta-sigma modulation in the negative feedback loop. The feedback of the lowpass filtered bitstream output of a delta-sigma modulator to the magnetic field improves system linearity, hysteresis, and stability. In spite of the fact that the second-order delta-sigma modulator is used, the third-order noise shaping can be obtained in the digital output bit-stream by the use of an integrator in the loop. This improves the SNR of the digital output. The measured noise of the implemented system meets the measured noise of the FG sensing element itself. The weak magnetic field in the range of the Earth's magnetic field is successfully measured. The nonlinearity error is less than 0.4% in the range of /spl plusmn/100 /spl mu/T.     

Fiber Bragg grating sensor interrogation using chirped fiber grating-based Sagnac loop

We have investigated numerically and experimentally a fiber Bragg grating (FBG) sensor interrogation scheme utilizing a linear chirped grating-based Sagnac loop as a wavelength-dependent receiver. The scheme is suitable for both static and dynamic sensor interrogation with advantages of stable and linear readout response and easily-adjustable sensing resolution and dynamic range. Static and dynamic strain resolutions as high as /spl plusmn/ 4.2 /spl mu//spl epsiv/ and 0.406 /spl mu//spl epsiv///spl radic/ Hz have been demonstrated using this scheme.     

A field deployable, multiplexed Bragg grating sensor system used in an extensive highway bridge monitoring evaluation tests

A multiplexed optical fiber Bragg grating sensor system with a measurement bandwidth of up to 200 Hz enabling dynamic loading events, e.g., road traffic, to be observed has been designed, installed, and tested over an 18-month period on a 346-m road bridge in Norway, for design verification and structural integrity monitoring purposes. A network of 32 fiber Bragg sensors was surface bonded along with a corresponding set of resistive strain gauges for comparative tests to be made. The wavelength data were calibrated against two thermally stabilized (/spl sim/0.15 pm) reference gratings, which rejected common mode noise and provided absolute wavelength scaling. These data provides independent strain and temperature information. Long-term test results showed good linearity and repeatability of <10 /spl mu//spl epsiv/ over the test period with a precision of /spl plusmn/5 /spl mu//spl epsiv/ and a resolution of /spl plusmn/1 /spl mu//spl epsiv/. The readings from the FBG sensors were comparable to those from the foil gauge sensors to within /spl plusmn/4 /spl mu//spl epsiv/.     

50-nm fully depleted SOI CMOS technology with HfO/sub 2/ gate dielectric and TiN gate

In this paper, we demonstrate for the first time CMOS thin-film metal gate FDSOI devices using HfO/sub 2/ gate dielectric at the 50-nm physical gate length. Symmetric V/sub T/ is achieved for long-channel nMOS and pMOS devices using midgap TiN single metal gate with undoped channel and high-k dielectric. The devices show excellent performance with a I/sub on/=500 /spl mu/A//spl mu/m and I/sub off/=10 nA//spl mu/m at V/sub DD/=1.2 V for nMOSFET and I/sub on/=212 /spl mu/A//spl mu/m and I/sub off/=44 pA//spl mu/m at V/sub DD/=-1.2 V for pMOSFET, with a CET=30 /spl Aring/ and a gate length of 50 nm. DIBL and SS values as low as 70 mV/V nand 77 mV/dec, respectively, are obtained with a silicon film thickness of 14 nm. Ring oscillators with 15 ps stage delay at V/sub DD/=1.2 V are also realized.     

Improvement of the /spl mu/-Hall magnetic sensor sensitivity at low frequency

We have developed a configuration for precision magnetic measurements associating a /spl mu/-Hall sensor, a modulated ferromagnetic antenna, and an analog electronic circuitry. This association is not only able to remove the 1/f noise of the Hall sensor, but also to achieve an ultimate noise level even lower than thermal white noise of the Hall sensor. The system main characteristics are the following: bandwidth 645 Hz, noise level white and lower than 10 nT//spl radic/Hz above 0.1 Hz, slew rate 10/sup -1/ T/s and system dynamic 84 dB in a 1-Hz bandwidth. The performances of the modulated sensor are compared to those of a dc operated sensor.     

Optical deflection measurement for characterization of microelectromechanical systems (MEMS)

Nonintrusive measurement of small out-of-plane motions of microscale structures is critical to the development of microelectromechanical systems (MEMS). This paper presents a low-cost deflection measurement system for MEMS structures based on a fiber optic displacement sensor. The system is demonstrated in the characterization of a microwave switch. The deflection system had a demonstrated sensitivity of 290/spl plusmn/32 /spl mu/V/nm over a deflection range of 100 /spl mu/m. The calibration and linearity of the system are described, and the static and dynamic performance is compared to more elaborate systems.     

Horizontal Hall effect sensor with high maximum absolute sensitivity

The sensitivity of conventional Hall effect sensors is strongly limited by the well-known short-circuit effects. Many researches were devoted to reduce offset and noise, but few works were carried out to improve the sensitivity. Here, a new shape of integrated horizontal Hall effect device is presented. This particular shape has been developed in order to minimize the short-circuit effects in the sensor, allowing to reduce its length to width ratio and consequently to reduce its average resistance. Thus, the biasing current of this sensor can be significantly increased in order to obtain a higher absolute sensitivity than for conventional devices. Such a Hall effect device needs a specific biasing circuit which is also presented, first in a simple version and second in an improved one. A resolution of 32 /spl mu/T has been reached on a bandwidth of 5 Hz to 1 kHz with a 39/spl times/9.2 /spl mu/m/sup 2/ sensor biased with a current of 2.07 mA, the corresponding absolute sensitivity being 195 mV/T. The maximal absolute sensitivity of a so shaped device can be increased as much as needed by increasing its width-to-length ratio, without loss on the current related sensitivity.     

High-sensitivity giant magneto-inductive magnetometer characterization implemented with a low-frequency magnetic noise-reduction technique

The Giant Magneto-Inductive (GMI) effect in amorphous magnetic and conducting wires is analyzed using the concepts and words of electronics engineering to show the way high-sensitivity GMI magnetometers may be designed. Starting from a simple modeling of the magneto-impedance, direct and field-locked loop magnetometers are discussed, together with the implementation of a low-frequency noise-reduction technique that makes good use of a basic modulating method. It allows the removal of a part of the 1/f noise in the magnetometer. The unmodulated magnetometer characteristics are the following: bandwidth higher than 100 kHz and white noise level lower than 7 pT//spl radic/Hz above 40 KHz. Similarly, the main auxiliary modulated magnetometer characteristics are as follows: bandwidth of 4.8 kHz and white noise level lower than 60 pT//spl radic/Hz above 3 Hz. The slew rate in both cases is limited by the electronics to 5 mT/s. The dynamic of these magnetometers is about /spl plusmn/25 /spl mu/T, which corresponds to more than 120 dB in 1 Hz bandwidth above 1 Hz.     

Characterization of Core Materials for Microscale Magnetic Components Operating in the Megahertz Frequency Range

Suitable materials forming the core of microscale magnetic components have been characterized for the application of magnetic passive components in the 0.5-10 MHz frequency range. The performance of electrodeposited nickel-iron, cobalt-iron-copper alloys and the commercial alloy Vitrovac 6025 have been assessed through their inclusion within a custom-made solenoid microinductor. Inductance values ranging from 0.3 to 120 H with component power efficiency above 90% have been measured. Although the present inductor, at 500 kHz, achieves 77% power efficiency for 24.7W/cm³ power density, an optimized process predicts a power efficiency of 97% for 30.83 W/cm³ power density.     

An arrayed waveguide grating based multiplexer and interrogator for Fabry-Perot sensors

In this paper, we propose an interrogation system capable of multiplexing four identical Fabry-Perot (FP) interferometric sensors using two wavelength-division multiplexing devices. One is a 40-channel DWDM channel monitor, the other a four-channel CWDM device. The sensors are connected to the output channels of the CWDM device in order to assign a portion of the spectrum to each sensor. The reflected spectra are then analyzed using the DWDM channel monitor. By monitoring the power incident on each of the DWDM channels, the four sensor reflection spectra can be reconstructed in software and information relating to the measurand obtained. Based on software simulations and previous laboratory experiments with single sensors, it is predicted that this system would be capable of interrogating four EFPI strain sensors simultaneously at frequencies greater than 5 kHz with a resolution of approximately 2 /spl mu//spl epsiv/ and a range of 3000 /spl mu//spl epsiv/.     

Interaction between magnetoresistor and magnetotransistor in the longitudinal and folded vertical Hall devices

This study investigates the one-dimensional longitudinal and folded vertical Hall devices, fabricated in a standard 0.35-/spl mu/m CMOS process. The smallest nonlinearity error 0.18%, the minimum offset 0.29 mV, and the maximum supply-current-related sensitivity S/sub RI/=3.837 V/A/spl middot/T, are obtained with a 10-mA bias current excited by the supply voltage of 0.6 V. The main magnetic mechanism is that the filament current of the vertical magnetoresistor is directly injected into the base region of the bulk magnetotransistor (BMT) to increase the density of minority carriers and then enhance the magnetosensitivity. Furthermore, the induced Hall voltage of the longitudinal vertical Hall device is proportional to the bias current, but the folded vertical Hall device is inversely impacted. This advantage makes it possible to get a low-power folded vertical Hall device. The folded style not only reduces the nonlinearity error but also minimizes the offset. Unfortunately, the tradeoff is a fall in sensitivity. The BMT is applied to increase magnetic sensitivity and to compensate for this negative impact.     

Evaluation of a material parameter extraction algorithm using MRI-based displacement measurements

The performance of an inversion algorithm is investigated when applied to measured displacement data for a determination of the material parameters /sup /spl lambda/+2/spl mu////sub /spl rho// (longitudinal wave velocity squared) and /sup /spl mu////sub /spl rho// (shear wave velocity squared) throughout an inhomogeneous test phantom. The vector displacement components throughout a test phantom subject to monochromatic shear excitation measured in time using magnetic resonance imaging (MRI) were temporally Fourier transformed to extract the component of monochromatic excitation, and the data was delivered to the inversion algorithm. A series of inversions is presented demonstrating the effects of subsequent wavenumber filtering, polarization selection, and variation in the size of the incremental volume elements. The resulting performance is assessed, and recommendations for future efforts are discussed.     

A low-noise latching comparator probe for waveform sampling applications

A new latching comparator probe is described. The probe is being developed as part of an effort to augment voltage measurement capability in the 10 Hz to 1 MHz frequency range. The probe offers an input voltage range of /spl plusmn/10 V, input impedance of 1 M/spl Omega/ and root mean square noise referred to the input as low as 55 /spl mu/V. The probe's 3-dB bandwidth is approximately 20 MHz. Total harmonic distortion is as low as -93 dB at 50 kHz. Gain flatness is within /spl plusmn/10 /spl mu/V/V from 100 Hz to 100 kHz. Improved step settling performance is achieved using a technique that minimizes circuit thermal errors. The probe's input range can be extended with a frequency-compensated 1-M/spl Omega/ input impedance attenuator allowing measurement of pulses in the microsecond regime up to 100 V. The attenuator can be compensated further with a digital filtering algorithm to achieve gain accuracy better than 100 /spl mu/V/V.