micro-Hall Sensors Research Articles

Thermal stability study of gallium nitride based magnetic field sensor

We investigated the thermal stability and performance of AlGaN/AlN/GaN Hall-effect sensors under industry-relevant atmospheric conditions. The thermal stability and performance of Hall sensors are evaluated by monitoring Hall sensitivity, two-dimensional electron gas density, and Ohmic contact resistance during aging at 200 °C for up to 2800 h under atmospheric conditions. This was accomplished by characterizing AlGaN/AlN/GaN micro-Hall sensors, with and without contacts, and before and after being placed under different thermal aging times. Observed electrical performance was correlated with the micro-structural evolution of AlGaN/AlN/GaN Hall sensor heterostructures. Results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h aging at 200 °C without any significant degradation of (i) Hall sensitivity, (ii) two-dimensional electron gas, and (iii) Ohmic contacts. However, there was a small change in sheet density and mobility, which is due to a decrease in polarization, resulting from local inhomogeneous strain relief at the barrier layer. During the early stage of thermal aging, a decrease in contact resistance was also observed and attributed to (i) out-diffusion of “Ga” at the vicinity of the contact interface, and (ii) a reduction in oxygen concentration and formation of Al–Ti intermediate alloy at the GaN/Ti interface, resulting in a reduced barrier and enhanced electron transport at the contacts. However, despite these small changes, results indicate that the AlGaN/AlN/GaN Hall sensor provides stable performance for as long as 2800 h thermal aging at 200 °C.

Micro-Hall Sensors Based on Two-Dimensional Molybdenum Diselenide.

Sensors and electronic devices based on semiconductors in their two-dimensional forms have many advantages. In this paper, we studied micro-Hall sensors based on two-dimensional molybdenum diselenide for the first time. The micro-Hall sensor based on a Ti/MoSe₂/Ti structure clearly showed a linear dependence of the Hall voltage as a function of the magnetic field, with a magnetic sensitivity of ∼16 V/AT. The magnetic sensitivity was higher in the Au/MoSe₂/Au structure, with a maximum value of ∼120 V/AT at a bias current of 100 mA; the minimum detectable magnetic field was found to be 1.45 μT/Hz1/2 at the same current value, making our new micro-Hall sensor a very good candidate for magnetic sensing applications.

Effects of Temperature, Thickness and Bias Current on Magnetoelectric Characteristics of Silicon Micro-Hall Sensors

A quest for a quantitative and noninvasive method for the measurement of local magnetic fields with high spatial and field resolution at variable temperatures calls for a selection of suitable magnetic sensor and appropriate scanning system. Scanning Hall probe microscopy (SHPM) is one of the choices as it addresses the stated issues and complements the other magnetic imaging methods. Compatibility of Si-Hall sensor fabrication with standard CMOS fabrication process and controllability of silicon characteristics parameters make them more suitable, for Hall probe applications, over other compound semiconductors (AlGaAs/GaAs, InSb, and AlGaN/GaN). However, the effect of Si-Hall sensor’s device thickness, applied bias current, and impediments in its use at variable temperatures SHPM application need to be investigated. In this article, a systematic study on the optimization of performance parameters of silicon-on-insulator micro-Hall sensors for their dedicated application in SHPM system is presented. Si $$\sim \,0.7\,\upmu \hbox {m} \times 0.7\,\upmu \hbox {m}$$ Hall sensors have been fabricated using monolithic device fabrication steps. These Hall sensors have been investigated based on the electrical, magnetic and noise characteristics to study the effect of thickness of the active layer (300–550 nm) and temperature (25– $$150\,^{\circ }\hbox {C}$$ ). Formation of trapping centers and defects have been observed due to device layer thinning, which not only limit the working temperature, bias current but also the minimum thickness of the device layer to be 300 nm. This compromise in Si-Hall sensor characteristics due to surface morphology of thinned films can be removed by growing the device layer on $$\hbox {SiO}_{2}$$ instead of thinning the device layer.

Detection of the superconducting transition and magnetic flux trapping in a niobium micro-ring by using micro-Hall sensors

An InAs heterostructure-based micro-Hall sensor was used to study the magnetic properties of a superconducting Nb micro-ring, enabling observation of magnetic phenomena such as diamagnetism onset and magnetic flux trapping in the 20-μm-diameter sample. The superconducting diamagnetism of the micro-ring was observed to develop slowly from T = 7.5 K down to 5 K and showed a notably sharp and substantial drop at 7.0 K, the zero-resistivity temperature obtained from transport measurements on a strip-patterned sample. The observed superconducting transition is discussed in terms of a percolation scenario. In magnetic-field-cooling measurements, the Hall signal from the magnetic flux trapped in the Nb ring at 4.5 K was detected at a sufficiently high level for quantitative comparison with the estimate.

First order reversal curves (FORC) analysis of individual magnetic nanostructures using micro-Hall magnetometry

Alongside the development of artificially created magnetic nanostructures, micro-Hall magnetometry has proven to be a versatile tool to obtain high-resolution hysteresis loop data and access dynamical properties. Here we explore the application of First Order Reversal Curves (FORC)-a technique well-established in the field of paleomagnetism for studying grain-size and interaction effects in magnetic rocks-to individual and dipolar-coupled arrays of magnetic nanostructures using micro-Hall sensors. A proof-of-principle experiment performed on a macroscopic piece of a floppy disk as a reference sample well known in the literature demonstrates that the FORC diagrams obtained by magnetic stray field measurements using home-built magnetometers are in good agreement with magnetization data obtained by a commercial vibrating sample magnetometer. We discuss in detail the FORC diagrams and their interpretation of three different representative magnetic systems, prepared by the direct-write Focused Electron Beam Induced Deposition (FEBID) technique: (1) an isolated Co-nanoisland showing a simple square-shaped hysteresis loop, (2) a more complex CoFe-alloy nanoisland exhibiting a wasp-waist-type hysteresis, and (3) a cluster of interacting Co-nanoislands. Our findings reveal that the combination of FORC and micro-Hall magnetometry is a promising tool to investigate complex magnetization reversal processes within individual or small ensembles of nanomagnets grown by FEBID or other fabrication methods. The method provides sub-μm spatial resolution and bridges the gap of FORC analysis, commonly used for studying macroscopic samples and rather large arrays, to studies of small ensembles of interacting nanoparticles with the high moment sensitivity inherent to micro-Hall magnetometry.

Experimental and theoretical investigation of the magnetization dynamics of an artificial square spin ice cluster

We study the magnetization dynamics of a spin ice cluster which is a building block of an artificial square spin ice fabricated by focused electron-beam-induced deposition both experimentally and theoretically. The spin ice cluster is composed of twelve interacting Co nanoislands grown directly on top of a high-resolution micro-Hall sensor. By employing micromagnetic simulations and a macrospin model, we calculate the magnetization and the experimentally investigated stray field emanating from a single nanoisland. The parameters determined from a comparison with the experimental hysteresis loop are used to derive an effective single-dipole macrospin model that allows us to investigate the dynamics of the spin ice cluster. Our model reproduces the experimentally observed non-deterministic sequences in the magnetization curves as well as the distinct temperature dependence of the hysteresis loop.

An Atomic Force Microscope with Dual Actuation Capability for Biomolecular Experiments.

We report a modular atomic force microscope (AFM) design for biomolecular experiments. The AFM head uses readily available components and incorporates deflection-based optics and a piezotube-based cantilever actuator. Jetted-polymers have been used in the mechanical assembly, which allows rapid manufacturing. In addition, a FeCo-tipped electromagnet provides high-force cantilever actuation with vertical magnetic fields up to 0.55 T. Magnetic field calibration has been performed with a micro-hall sensor, which corresponds well with results from finite element magnetostatics simulations. An integrated force resolution of 1.82 and 2.98 pN, in air and in DI water, respectively was achieved in 1 kHz bandwidth with commercially available cantilevers made of Silicon Nitride. The controller and user interface are implemented on modular hardware to ensure scalability. The AFM can be operated in different modes, such as molecular pulling or force-clamp, by actuating the cantilever with the available actuators. The electromagnetic and piezoelectric actuation capabilities have been demonstrated in unbinding experiments of the biotin-streptavidin complex.

High Proton Radiation Tolerance of InAsSb Quantum-Well-Based micro-Hall Sensors

Tolerance of AlInSb/InAsSb/AlInSb heterostructures quantum-well-based micro-Hall sensors against proton irradiation of 380 keV and proton fluence in the range \(10^{11}\) and \(10^{16}\) (proton/cm2) is reported. Defects and deep levels induced by proton irradiation into the heterostructures caused decreases in the mobility of the micro-Hall sensors. Degradation of the magnetic sensitivity started at a proton fluence of \(10^{13}\) (proton/cm2) and continued with increasing proton fluence. The variation of the micro-Hall sensors sensitivity was minimal in low-doped AlInSb/InAsSb/AlInSb heterostructure quantum wells. These micro-Hall sensors were operable even at proton fluence of \(10^{16}\) (proton/cm2), which makes these devices suitable for space applications with lifetime of thousands of years in the outer space.

Proton Irradiation Enhancement of Low-Field Negative Magnetoresistance Sensitivity of AlGaN/GaN-Based Magnetic Sensor at Cryogenic Temperature

The longitudinal and transverse magnetoresistances of AlGaN/GaN heterostructure-based micro-Hall sensors were compared with samples irradiated with protons with an energy of 380 keV and fluence of \(10^{14}\) (protons/cm \(^{2})\) . Increases in the elastic and inelastic scattering were deduced from weak localization behavior in both samples. The AlGaN/GaN micro-Hall sensors showed stable magnetic sensitivity in non and irradiated samples and increased resistivity after proton irradiation yielded an enhanced magnetoresistance sensitivity in nonirradiated sensors from 160 to 417 VA \(^{-1}\textrm {T}^{-1}\) . The minimum detectable magnetic field of irradiated micro-Hall sensors determined from magneto-voltage measurements at \(\sim 4\) K was similar to the minimum detectable magnetic field in the nonirradiated sensors.

Modelling of micro-Hall sensors for magnetization imaging

This paper presents a numerical model for the study of micro-Hall magnetometry applications, aiming at evaluating the sensitivity of semiconductor miniaturized devices to the stray field of permalloy nanostructures with ring and disk geometry. The procedure couples a micromagnetic code, for the calculation of the stray field generated by the nanomagnet, to a 2D classical transport model for the determination of the electric potential distribution inside the Hall plate. The model is applied to study the sensitivity of a micro-Hall device in the detection of magnetization switching processes characterized by vortex state, focusing on the influence of magnetic nanostructure position.

Partial recovery of the magnetoelectrical properties of AlGaN/GaN-based micro-Hall sensors irradiated with protons

The effect of annealing on the magnetoelectrical properties of proton-irradiated micro-Hall sensors at an energy of 380 keV and very high proton fluences was studied. Recovery of the electron mobility and a decrease in the sheet resistance of the annealed micro-Hall sensors, as well as an enhancement in their magnetic sensitivity were reported. Trap removal and an improvement in the crystal quality by removing defects were confirmed through current–voltage measurements and Raman spectroscopy, respectively.

Detection of edge magnetic state by a ballistic bend resistance measurement

We have investigated a magnetization process of a permalloy nanowire by using a ballistic micro-Hall sensor consisting of GaAs/AlGaAs two-dimensional electron gas. Although a conventional bi-stable hysteresis loop with a rectangular shape was observed in the Hall resistance measurement, unexpected extra resistance changes were observed in a bend resistance measurement. These unconventional features are quantitatively explained by the magnetic transitions among the meta-stable edge-domain structures in the ferromagnetic wire. The geometrical dependence of these resistance changes and their application possibility for the multiple-valued memory were also discussed.

Effect of proton irradiation on AlGaN/GaN micro-Hall sensors

The magnetoelectric properties of AlGaN/GaN micro-Hall effect sensors were studied after 380 keV proton irradiation. After irradiation the current-voltage measurements, stability of the magnetic sensitivity of the sensors, and the sheet electron density were degraded with a dramatic decrease of the electron mobility at high temperatures. Raman spectroscopy showed a degradation in the crystalline quality of GaN crystal, but there was no change in the strain.

Effects of Proton Irradiation on the Magnetoelectric Properties of 2DEG AlGaN/GaN Micro-Hall Sensors

The effects of irradiating AlGaN/GaN micro-Hall sensors with 380 keV protons on were investigated by magnetoresistance measurements. The sheet resistance increased after irradiation with a proton dose of 1×1013 cm−2 due to the decrease of carrier mobility rather than the decrease of sheet carrier density. Our experiments showed that AlGaN/GaN two-dimensional electron gas (2DEG) structures are good strong candidates for Hall sensors operable in harsh radiation environments.

Dynamic micro-Hall detection of superparamagnetic beads in a microfluidic channel

We report integration of an InAs quantum well micro-Hall magnetic sensor with microfluidics and real-time detection of moving superparamagnetic beads. Beads moving within and around the Hall cross area result in positive and negative Hall voltage signals, respectively. Relative magnitudes and polarities of the signals measured for a random distribution of immobilized beads over the sensor are in good agreement with calculated values and explain consistently the shape of the dynamic signal.

Micro-Hall position sensing of magnetic nanowires

The Hall voltage output of a micro-Hall magnetic sensor depends on the relative position of a magnetic nanowire with respect to its sensing area. Following this idea, we performed analytical calculations which show that, under certain conditions, these devices can track the position of a magnetic nanowire with subnanometer resolution. Our results suggest that micro-Hall sensors can be utilized to provide a direct electronic readout of the position of magnetic nanowires in their applications as biomolecular manipulators or dynamic components in micro- and nanoscale devices.

The detection of specific biomolecular interactions with micro-Hall magnetic sensors

The detection of reagent-free specific biomolecular interactions through sensing ofnanoscopic magnetic labels provides one of the most promising routes to biosensing withsolid-state devices. In particular, Hall sensors based on semiconductor heterostructureshave shown exceptional magnetic moment sensitivity over a large dynamic field rangesuitable for magnetic biosensing using superparamagnetic labels. Here we demonstrate thecapability of such micro-Hall sensors to detect specific molecular binding usingbiotin–streptavidin as a model system. We apply dip-pen nanolithography to selectivelybiotinylate the active areas of InAs micro-Hall devices with nanoscale precision. Specificbinding of complementarily functionalized streptavidin-coated superparamagnetic beads tothe Hall crosses occurs via molecular recognition, and magnetic detection of theassembled beads is achieved at room temperature using phase sensitive micro-Hallmagnetometry. The experiment constitutes the first unambiguous demonstrationof magnetic detection of specific biomolecular interactions with semiconductormicro-Hall sensors, and the selective molecular functionalization and resultinglocalized bead assembly demonstrate the possibility of multiplexed sensing ofmultiple target molecules using a single device with an array of micro-Hall sensors.

Magnetic bead counter using a micro-Hall sensor for biological applications

Micro-Hall sensors have been fabricated, and various numbers of micron-size magnetic beads have been placed within the sensor area. The Hall resistances measured at room temperature are found to be proportional to the number of the beads, and are in good agreement with the numerically simulated results presented in this study. Our sensors are designed to measure the number of beads between zero and full-scale signals for a given number range of interest. The effects of miniaturizing the beads and sensors to nanoscale are also discussed.

Strained Quantum Well InAs Micro-Hall Sensors: Dependence of Device Performance on Channel Thickness

Magnetic sensitivity and low-frequency noise in micro-Hall sensors based on pseudomorphic InAs quantum well channels are investigated as functions of InAs thickness. The strained InAs quantum wells with thickness between 0 and 20 Aring are added into lattice-matched doped channel In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.53</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> As/In <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.47</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.48</sub> As/InP heterostructures and enhance the absolute magnetic sensitivity by increasing the electron mobility. We show that the increase of the InAs channel thickness also leads to a significant reduction of the low-frequency noise. The result is an improved magnetic field detection over a broad frequency range. A minimum magnetic field detection limit of nT is resolved by a 40-m wide doped channel micro-Hall device at frequencies around kHz.

Low thermal drift in highly sensitive doped channel Al0.3Ga0.7As/GaAs/In0.2Ga0.8As micro-Hall element

Micro-Hall sensors with high sensitivity, low noise, and high thermal stability, 5 μm square, are fabricated using pseudomorphic Al0.3Ga0.7As/GaAs/InyGa1-yAs (0.2 ≤ y ≤ 0.3) heterostructures with Si-doped channels. The structures were optimized for thermal stability using a calculation of the self-consistent solution of Schrodinger-Poisson equations and Fermi-Dirac statistics in Hartree approximation. The optimized structure based on a Si-δ-doped 144 A In0.2Ga0.8As quantum well embedded into uniformly doped GaAs channel showed thermal drifts of only 90 ppm·K−1 in current drive mode and 192 ppm K−1 in voltage drive mode. The measurements of the absolute magnetic sensitivity and the low frequency noise were done. The micro-Hall sensor, optimized for thermal drift, is able to resolve the magnetic field of 438 nT.