Lateral and Vertical Hall Microsystems

Future integrated systems will benefit significantly from the progress in batch manufactured silicon sensors and signal processing techniques. Silicon technologies make possible to produce sensing microdevices combining extreme sensitivity, accuracy and compact devices. Smart sensors on the base of vertical vector Hall effect devices offer a number of benefits including reducing mass, volume and power consumption; greater redundancy of system functions and simpler architecture. In view of these remarkable characteristics, it can be expected that such smart sensors will be used extensively wide if an adequate solution is found to reduce the design cost and simplify the electrical interface. Consequently, cost effective microsystems including vector magnetic sensors, circuits and eventually actuators can be fabricated, opening new perspective markets. This paper presents a new approach in the field of signal processing for magnetic field sensors based on vertical Hall micro structures. A design example is illustrated specific problems and solutions associated with data converters and signal-processing functions for smart sensors.

The first commercially available teslameter with a fully integrated 3-axis Hall probe is described. The Hall probe chip contains horizontal and vertical Hall elements, analogue electronics, and a synchronisation circuit. A horizontal Hall element measures the perpendicular component, and two vertical Hall devices measure the two in-plane components of a magnetic field. Current spinning in the Hall devices cancels offset, 1/f noise, and the planar Hall voltage. The analogue electronic module of the teslameter cancels the residual offset and compensates temperature dependence and non-linearity of the Hall voltages. The digital module provides A/D conversion and communication to a computer.

A 3-D vertical hall magnetic-field sensor in CMOS technology

Influence of silicon anisotropy on the sensitivity of Hall devices and on the accuracy of magnetic angular sensors

In the present paper, the stability of a compressible rotating Walters’ B' viscoelastic fluid through a porous medium is considered in the presence of uniform vertical magnetic field, Hall current and suspended particles. It is found that the region of stability increases with the increase in magnetic field, rotation and compressibility and it decreases with the increase in suspended particles and Hall currents. Also, it has been established that the medium permeability has destabilizing effect in the absence of rotation while in the presence of rotation it may have stabilizing effect on the system. Graphs are plotted to find the region of stability in the presence of various physical parameters like Hall current parameter, suspended particles, rotation, magnetic field and medium permeability. The principle of exchange of stabilities holds good under certain conditions and the modes may be non-oscillatory or oscillatory.

Equatorial ionospheric responses during two magnetic storms of moderate intensity are investigated, for the first time, by conjugate point observations in Brazil. The study focuses on storm‐induced changes in the evening prereversal vertical drift, thermospheric trans‐equatorial winds, spread F/plasma bubble irregularity development, electron density/plasma frequency heights, the EIA strength, and zonal plasma drifts. It is based on data obtained from five Digisondes operated in Brazil, three of them being part of a conjugate point equatorial experiment (COPEX) involving a dip equatorial and two magnetic conjugate sites at ±12°. The other two were operated at the equatorial ionization anomaly (EIA) trough and crest locations at nearby magnetic meridians. The results bring out, and clarify, many outstanding aspects of the strong influence of storm time electric fields on the equatorial ionosphere at different phases of the two long lasting storm sequences. During both storms prompt penetration electric fields dominated the ionospheric response features as compared to the disturbance wind dynamo effects that were not very conspicuous. An under‐shielding (over‐shielding) electric field occurring in the evening hours causes enhancement (suppression) of the prereversal vertical drift and post sunset spread F/plasma bubble generation. The same electric fields cause post sunset EIA enhancement and suppression, respectively. Post sunset (post midnight) spread F can develop from under‐shielding (over‐shielding) electric fields, while it can be disrupted by over‐shielding (under‐shielding) electric field. Trans‐equatorial winds are found to be ineffective to stabilize the post sunset F region against the destabilizing effect of strong prereversal vertical drift. Storm time westward plasma drifts are found to be driven by prompt penetration eastward electric fields (through their effect of inducing vertical Hall electric fields), rather than by a disturbance westward thermospheric wind during these storms.

<p>The Hall-effect based Teslameters (also called Gaussmeters) are the mostly applied instruments for measuring DC and AC magnetic flux densities in modern science and industry. This paper gives an overview of commercially available Teslameters at the high-end performance level. The Teslameters have been evaluated by following characteristics that are published by suppliers: probe dimensions, magnetic field sensitive volume, accuracy, magnetic resolution, measurement range, frequency bandwidth, temperature coefficient sensitivity, and price/performance ratio.</p><p>The Teslameter that best matches the measurement needs in various application fields incorporates a 3-axis integrated Hall probe, analog electronics based on the spinning-current technique, an analog-to-digital converter, an embedded computer, and a touch-screen display. The 3-axis Hall probe is a single silicon chip integrating both horizontal and vertical Hall magnetic sensors and a temperature sensor. The spinning-current eliminates most of the Hall probe offset, low-frequency noise, and the planar Hall voltage. The errors due to the Hall sensor non-linearity and the variations in the probe and electronics temperatures are eliminated by a calibration procedure. The errors due to the angular imperfections of the Hall probe are eliminated by a calibration of the sensitivity tensor of the probe. This Teslameter can measure magnetic field vectors from about 100 nT to 30 T, with the spatial resolution of 100 µm, magnetic resolution ±2 ppm of the range, the accuracy 0.002 % of the range, a temperature coefficient less than 5 ppm/°C, and angular errors less than 0.1°.</p>

This paper presents a fully integrated device for ECG acquisition on an MRI environment with on chip 3D HALL sensor for signal correction submitted in standard 0.35 µm CMOS technology. Based on a CMOS current conveyor (60 µA @ ± 1.65 V power supply, 100 MHz bandwidth and 10 GHz equivalent GBW circuit) the instrumentation amplifier used in this IC he circuit. The 3D Hall sensor features two vertical Hall devices (VHD) to measure component of the magnetic field oriented in the plane of the chip as well as one horizontal Hall device (HHD) to measure the component of the field orthogonally oriented to the plane of the chip. The 3D Hall sensor allows measuring the static field up to 1.5 T as well as the magnetic pulses of ± 20 mT generated during the MRI acquisition. The size of the complete design makes biological signal measurement in very hostile environment such MRI possible.

Four different geometries of a vertical Hall sensor are presented and studied in this paper. The current spinning technique compensates for the offset and the sensors, driven in current-mode, provide a differential signal current for a possible capacitive integration over a defined time-slot. The sensors have been fabricated using a 6-metal 0.18μm CMOS technology and fully experimentally tested. The optimal solution will be further investigated for bendable electronics. Measurement results of the four structures over the 10 available samples show for the best geometry an offset of 41.66 ± 8 μT and a current-mode sensitivity of 9 ± 0.1 %/T. Since the figures widely change with geometry, a proper choice secures optimal performance.

We report on the design and simulation of a novel vertical Hall sensor, which exhibits highly nonlinear characteristics between Hall voltage and bias voltage, featuring a region of large negative differential sensitivity. Based on these features, novel techniques for exciting the Hall plate and for signal extraction are suggested, allowing for further enhancement of the residual offset-limited dc resolution of in-plane magnetic field-sensitive Hall sensors, in particular, and integrated three-dimensional Hall sensors, in general.

A Hall probe has been developed in the form of a miniaturized analog system, consisting of two silicon vertical Hall devices, current stabilizers, amplifiers, and error-correcting circuits. The output signal has a calibrated sensitivity of 1 V/T, with a residual error less than 10/sup -4/ in the ranges /spl plusmn/2 T, (15-35)/spl deg/C, and dc to 10 kHz. The probe features high long-term stability, low-offset drift, and low noise.

Typically, a magnetic sensor microsystem is a combination of a Hall device, some electronics, and ferromagnetic components. Usually, the Hall device has the form of a plate buried into the chip surface. Non conventional forms include: a vertical Hall device, sensitive to a magnetic field parallel with the chip surface; and a cylindrical Hall device, optimized to sense the circular magnetic field around a current carrying wire. Using a merged combination of two vertical Hall devices, a simple angular position sensor was made. A combination of vertical and horizontal devices gives a high accuracy 3D Hall probe.

This paper introduces a current-mode low-offset and high-sensitivity full symmetric vertical Hall device (FSVHD). The effect of device geometry structure and contact size on sensitivity and offset was studied by TCAD simulation. Based on current-mode, the structure of FSVHD was optimized to achieve both high sensitivity and low offset in 0.18-μm standard CMOS technology. TCAD simulation reveals that the sensitivity in the current-mode is twice larger than that in the voltage-mode. Further, the current-mode sensitivity is increased from 1.8% T−1 to 2.4% T−1 and the offset is reduced by an order of magnitude by optimizing the structural parameters.

High-speed CMOS magnetic angle sensor based on miniaturized circular vertical Hall devices

The free-electron laser (FEL) project at the Advanced Photon Source (APS) will use a 400-MeV particle beam from the APS linac with RMS beam transverse size of 100 micrometers and requires very high performance of the insertion devices in order to achieve high intensity radiation. Averaged over period, the trajectory must deviate from the ideal on-axis trajectory by not more than 10% of the RMS beam size. Meaning that the second field integral should be straight within {+-}1,300 G-cm{sup 2} over the length of the device for both horizontal and vertical directions for the 400-MeV particle beam. Under such conditions, special attention should be given to the measurement technique and tuning. Two types of probes were tested to examine the possibility to measure small horizontal field in presence of strong (up to 1 T) vertical magnetic field without the distortion associated with planar Hall probe effect. They are a two-axis Sentron analog Hall transducer and a two-axis Bell probe. The Sentron probe is a new type of Hall probe, a so-called vertical Hall device, which is sensitive to the magnetic field parallel to the chip plan. The Bell probe is a conventional-type probe sensitive to the magnetic field perpendicular to the chip plane. A flipping coil and an 81-mm-long moving coil were used to make the reference measurements. Insertion device Undulator A {number_sign}3 was used for these measurements with a gap of 11 mm and a peak field of about 0.85 T.