Hall Plate Research Articles

Sheet Resistance Determination Using Symmetric Structures With Contacts of Finite Size

This paper proposes an extension of van der Pauw's celebrated method for the extraction of the sheet resistance R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sq</sub> of planar homogeneously conducting samples with four point-like contacts to symmetric samples with contacts of finite length. Using the method, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sq</sub> can be extracted, e.g., from symmetric integrated Hall plates and stress sensors, without having to resort to dedicated van der Pauw structures. First, the analog of van der Pauw's formula for arbitrarily shaped samples with four extended contacts separated by point-like insulations is derived. Based on this and van der Pauw's original result, an interpolation formula applicable to symmetric samples with contacts of arbitrary length is constructed. The new formalism was successfully put to the test using ten widely differing CMOS sensor structures, with contacts covering between 10.1% and 91.3% of the device periphery. The extracted R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sq</sub> values lie within the range specified by the CMOS foundry used for the fabrication of the samples and show a relative standard deviation of 1.04%.

Electromagnetically compatible CMOS auto-balanced current sensor for highly integrated power control System-On-Chip

This paper describes the design and prototyping of an auto-balanced contactless current sensor in standard Complementary Metal–Oxide–Semiconductor (CMOS) technology, without any additional post-processing cost. The architecture includes two high-sensitivity Hall plates with differential amplification electronics. A high common mode rejection is insured by the integrated auto-balancing system based on the use of integrated coils. When a common current is applied in the embedded coils, the integrated system provides a feedback signal to a digital control unit which in turn adjusts the biasing current of one of the Hall plates in order to balance the amplification of the two Hall plates. Designed in a standard CMOS technology, this sensor can be integrated in power control System-On-Chip requiring extremely electro-magnetically compatible current sensor.

Hall effect sensors integrated in standard technology and optimized with on-chip circuitry

While silicon is not the best semi-conductor material to design Hall effect sensors, it is widely used because Hall devices are fully compatible with standard processes such as CMOS or Bi-CMOS. Hall effect sensors can thus take advantage of on-chip circuitry to counterbalance the poor intrinsic metrological characteristics of silicon Hall devices, and low cost integrated smart magnetometers can be designed using standard technologies. Conventional Hall plate as well as the spinning-current method, which is the present state of the art technique to improve performances of integrated Hall devices, are reviewed in this paper. Then a new multi-strips Hall device and its specific biasing circuit are introduced. This new device allows to multiply by n the absolute sensitivity of the Hall sensor where n is the number of strips, but it suffers from offset. To overcome this drawback, a Hall sensors network which also allows to increase the sensitivity while reducing the offset is proposed. Finally a comparison between the Hall sensors network and the spinning-current is done, showing that both techniques are complementary and should be combined to design high resolution Hall sensor systems.

CMOS magnetic sensors with integrated ferromagnetic parts

The paper deals with Hall and flux-gate magnetic field sensors consisting of integrated combination of CMOS ASICs and planar ferromagnetic components. Ferromagnetic parts are made of a soft amorphous alloy, integrated at the CMOS wafer in a post-processing production phase. When the sensors are exposed to an in-plane magnetic field, under the peripheries of ferromagnetic parts appears a strong magnetic induction perpendicular to the wafer surface. This perpendicular field is sensed either by Hall plates or planar coils. In the case of Hall magnetic sensors, such ferromagnetic parts give a magnetic gain of 2–10. Compared to conventional integrated Hall magnetic sensors, the new sensors have up to 10 times higher magnetic resolution and they respond to a magnetic field parallel with the surface of the chip. They are used as current sensors or angular position sensors. In the case of flux-gate sensors, both the saturation-forcing coil and the pick-up coils are realized as planar coils, using metallization layers that exist in the CMOS process. The integrated flux-gate technology is illustrated by a low-power two-axis magnetic field sensor suitable for a portable electronic compass.

Thermomagnetic residual offset in integrated hall plates

Integrated Hall plates show self-induced offset due to the current flow in their current leads. The magnetic field surrounding these current leads generates a magnetic offset signal, while their resistive heating causes thermoelectric offset voltages. This paper reports experimental results on these two effects. They are obtained using a novel test structure enabling to separate the two contributions. In addition, the experimental results concerning the thermal behavior of the test structure are compared with finite element (FE) simulations.

Field decay and snapback measurements using a fast Hall plate detector

In superconducting particle accelerators significant changes occur in tune and chromaticity during the injection of particles and their subsequent acceleration. This behavior is caused by the decay of magnetic field components in the superconducting accelerator magnets during injection and their so-called to the original hysteresis curve during the first few seconds after the start of the energy ramp. The two effects are closely related to a spatially periodic modulation of all field components along the magnet axis. In order to avoid a loss of particles the sextupole component in the dipoles has to be compensated with a very high accuracy. Standard magnetic measurements using rotating coils do not have the time resolution required to completely resolve the snapback. For this reason we have developed a fast system for sextupole measurements consisting of three Hall plates mounted on a ring. A new calibration procedure for the first time allows quantitative results. The detector is used to measure decay and snapback as a function of several parameters in the operation cycle. The results obtained help to better understand the interaction between current distribution and magnetization in the coil.

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

An orientation dependence has been measured for vertical Hall (VH)-sensors and for horizontal CMOS Hall plates fabricated on n-doped (1 0 0) silicon wafers. A sensitivity difference up to 15% at 6.5 T is measured for VH-sensors in the (0 1 0) plane in comparison with the one in the (0 1 1 ̄ ) plane. When non-conventional orientations are used in an angular sensor, an angular shift up to 4° is measured at 2 T. Planar Hall effect in CMOS devices can be minimized by a proper choice of the sensor orientation. A model is derived that relates these effects to the silicon material anisotropy. Design rules have been derived for the realization of highly linear and accurate silicon Hall magnetometers.

Numerical Offset Optimization of Magnetic Field Sensor Microsystems (Numerische Offsetverminderung in Magnetfeld-Mikrosensoren)

This paper rewievs the modeling of magnetic field sensor microsystems with respect to the origins of offsets. We cover the modeling of silicon-based semiconductor Hall sensors in an inhomogeneous magnetic field, including 3D transport effects. In particular we discuss the automatic geometric optimization of sensor devices. The optimization strategy achieves offset reduction with simultaneous maximazation of device sensitivity. The topology optimization method changes the conductivity of a Hall plate locally, converging to an optimum conduction geometry. After showing representative results, we discuss currently available commercial and experimental software tools and their capabilities.

Temperature cross-sensitivity of Hall plate in submicron CMOS technology

The temperature coefficient of the current-related sensitivity of a Hall plate in submicron CMOS technology was measured. A zero-temperature-coefficient region was observed. A model of the temperature coefficient based on the freeze-out effect and the temperature dependence of the Hall scattering factor was developed. Using a Hall sensor in the observed zero-temperature-coefficient region may significantly improve its measurement accuracy. The additional, very high influence of mechanical stress, due to the piezo-Hall effect, on the temperature coefficient has been analyzed for two packaging techniques.

Highly sensitive Hall sensor in CMOS technology

We present a highly sensitive Hall device fabricated in a standard CMOS technology and combined with integrated flux concentrators acting as magnetic amplifiers. The active area of the Hall plate is in a buried n-well with a shape optimized by removing the parts less sensitive to the magnetic field. The effect of the shape of the concentrators is studied. This results in the design of elliptical shape integrated concentrators for the optimization of the sensitivity, and of the measurement range, as well as for the decrease of the overall chip size. The CMOS sensor combined with the optimized concentrators has a sensitivity of 2.1 V/T with a 4 V bias, the lowest detectable field is 0.2 μT in a frequency range of 10 −3–10 Hz and the linearity is better than 1% in a ±16 mT measurement range.

Offset reduction in silicon Hall sensors

In this paper, we analyse the Anti-Hall (AH) method for offset reduction and the spinning-current method. The first method uses Hall plates with an inner and an outer boundary with multiple current injections at the same time. Simultaneously one obtains a magnetic field sensitive voltage at one contact pair and a magnetic-field independent voltage sensitive to an in-plane shear stress at another contact pair. The second method uses consecutive current injections in different orientations of a symmetric Hall plate and the average of the measurement results is the output signal. Both methods exploit the different symmetries of the Hall effect and various effects that contribute to the offset. Nevertheless, both methods have significant differences that can be understood with the reciprocity principle for macroscopic samples concerning the exchange of current and voltage leads on the Hall measurements. Numerical simulations of the potential distribution of the Anti-Hall structures were carried out with a lumped-discrete approach. Experimental data measured with both offset-reduction methods are shown.

A fast sextupole probe for snapback measurement in the LHC dipoles

In superconducting particle accelerators a fast change of the magnetic field occurs during the first few seconds after the start of an energy ramp. Standard magnetic measurements using a coil rotating at 1 Hz do not have the time resolution required to completely resolve this phase, usually called snapback. For this reason we have developed a new and fast system dedicated to sextupole measurements. The basic component consists of three Hall plates mounted on a ring. In an ideal case this arrangement compensates the main dipole field and produces a signal proportional to the sextupole only. Mechanical tolerances and differences in the sensitivity of the Hall plates are compensated by instrumentation amplifiers and an in situ fine adjustment of the probe orientation. Using this hybrid compensation technique we have measured sextupole variations in an LHC dipole prototype during snapback at a rate of 5 Hz. In this paper we present details on the device and the results of our measurements.

Trench-Hall devices

A trench-Hall device sensitive to magnetic inductions parallel to the chip surface is reported in this paper. The vertically oriented active region is defined by two parallel trenches with a distance of only 2.4 /spl mu/m. Deep contacts connect the active region of the device at its bottom at a depth of 20 /spl mu/m. These deep contacts allow a symmetrical operating condition of the active region analogous to a lateral symmetrical Hall plate, which is favorable for dynamic offset reduction. With the presented technology, trench-Hall devices with a sensitivity of 320 V/A with a nonlinearity below 0.1% are realized. Additionally, the presented fabrication technique enables the electrically insulated cointegration of sensor and circuitry on a single CMOS chip.

CMOS versus bipolar Hall plates regarding offset correction

Integrated silicon Hall devices are used to measure magnetic fields. Unfortunately, they cannot be used in low field applications because they suffer from a large, unpredictable and drifting offset. Using the spinning-current method the offset can be reduced to a few microtesla, which enables low field applications. This paper reports on the influence of the fabrication process, CMOS or bipolar, on the offset of spinning-current Hall plates. The depletion layer width of the junction that defines the boundaries of the Hall plate, which is different for the two fabrication processes, influences the sensitivity, resistance, and offset of integrated Hall plates. Theoretical studies can predict the sensitivity and resistance, but not the offset. The depletion layer width depends on the bias current and the substrate voltage. To study the influence of the depletion layer width on the Hall plates' characteristics these two parameters are varied. Experiments show that the spinning-current principle drastically reduces the offset, independent of the bias current and substrate voltage, and therefore independent of the depletion layer width and fabrication method.

A non-plate like Hall Sensor

Conventional Hall devices are plate-like, i.e., made in a thin semiconductor layer. We present here a Hall device made in a semi-infinite piece of semiconductor. Its active zone is limited by only one non-conductive surface. Although the base of the device is open, the part of the limited active zone filled by the current remains thin. The novel device exhibits a sensitivity of 0.33 V/mAT. We have shown that the characteristics of the non-plate like Hall device when its size is small asymptotically approach the characteristics of the conventional Hall plate. It opens the door to the realisation of 3D Hall device in the technology of the vertical Hall devices. In order to use the novel sensor as a stand-alone device, we improved it by an additional doping at the surface.

Hall factors of Si NMOS inversion layers for MAGFET modeling

Hall factors of Si NMOS inversion layers for the modeling of CMOS MAGFET's are given for a wide range of effective fields, temperatures and doping concentrations. The Hall factors are simulated with a microscopic transport model of the quasi-two-dimensional electron gas (2DEG). The model is verified by measured data of different MOS Hall plates.

Offset reduction of Hall plates in three different crystal planes

Silicon Hall plates show an offset of a few millitesla. A large portion of this offset is caused by mechanical stress in the device. The offset can be reduced by a factor 1000 to 10 000 when the spinning-current principle is applied. This paper presents a model for the influence of mechanical stress in (spinning-current) Hall plates, realized in different crystal planes. Devices realized in a (110) plane show a larger stress than devices fabricated in a (100) or (111) plane, as predicted by the model presented. However, independent of the original offset, the offset after spinning is reduced to only a few microtesla. This is in agreement with the model, which predicts only a periodic offset voltage as a result of the mechanical stress. Periodic offset voltages are removed by the spinning-current method.

Offset reduction in Hall devices by continuous spinning current method

A novel method for dynamic offset compensation in a Hall plate is presented. The continuous spinning current method is based on minimalsize four-contact Hall devices and, therefore, the lowest possible offset resulting from material inhomogeneities is achieved. A continuous spinning current vector is generated in the device by spatially superimposing two periodic biasing currents. The resulting voltages allow the constant Hall voltage to be separated from the periodic offset voltage. Remaining offsets are below 10 μT, which corresponds to fractions of the earth's magnetic field.

Monolithic magnetic Hall sensor using dynamic quadrature offset cancellation

The offset voltage and its temperature drift and production spread, which generally degrades the zero-level stability and reproducibility of magnetic Hall sensors, can be reduced using a single Hall plate and switching means for periodic permutation of the supply and output contact pairs. The present work describes a chopper-based 5-V monolithic linear Hall sensor with a /spl plusmn/0.1 T full scale where this dynamic plate offset cancellation technique has been employed together with a cost-effective signal conditioner. The device was integrated using a 2-/spl mu/m conventional BiCMOS process and the final chip, measuring 15/spl times/1.5 mm/sup 2/, shows, after packaging in a 3-pin plastic package, a residual offset with a production spread and a temperature-induced drift five to ten times smaller than in currently used multiplate dc quadrature cancellation approaches. The device does not require external components and provides an output free of HF residues.

A stretched wire system for accurate integrated magnetic field measurements in insertion devices

Abstract A simple and precise system for the measurement of both first and second magnetic field integral distributions and integrated multipole errors in insertion devices has been developed. The method, the characteristics and the performance of the system are presented. A comparison is also made with the more traditional Hall plate and flipping coil techniques.