Giant Magnetoresistive Sensors Research Articles

An Early Cancer Diagnosis Platform based on Micro-magnetic Sensor Array Demonstrates Ultra-high Sensitivity

In this paper a highly sensitive detection methodology for obtaining the concentration of protein tumor markers via the selective incorporation of super paramagnetic iron oxide nanoparticles (MNP) onto an antigen is reported. The tumor marker concentration is measured with a nano-oxide layer inserted giant magneto-resistive (GMR) sensor that determines the attenuation of an external magnetic field that is induced by the MNP. The 15 nm MNPs, used herein, exhibit a super paramagnetic behavior with saturation magnetization of 36 emu/g. The output voltage signal of the Specular GMR sensor is 500 μV/Oe. The patterned GMR multiple-bio-sensor array, has demonstrated real-time measurements of carcinoembryonic antigen (CEA) protein concentrations down to femtomole level (10-15 mole) in a variety of clinically relevant media with a linear dynamic range of over five orders of magnitude. The sensitivity of the GMR bio-array platform is 1000 times higher than conventional enzyme-linked immunosorbent assay (ELISA) technique. The arrays of magnetoresistive sensors offer great promise in applications for early cancer diagnosis.

Rapid Methods for the Detection of Bacteria via Giant Magnetoresistance Sensor and Biomagnetic Marker

Rapid Methods for the Detection of Bacteria via Giant Magnetoresistance Sensor and Biomagnetic Marker

An Automated Sensing System for Steel Bridge Inspection Using GMR Sensor Array and Magnetic Wheels of Climbing Robot

Corrosion is one of the main causes of deterioration of steel bridges. It may cause metal loss and fatigue cracks in the steel components, which would lead to the collapse of steel bridges. This paper presents an automated sensing system to detect corrosion, crack, and other kinds of defects using a GMR (Giant Magnetoresistance) sensor array. Defects will change the relative permeability and electrical conductivity of the material. As a result, magnetic field density generated by ferromagnetic material and the magnetic wheels will be changed. The defects are able to be detected by using GMR sensor array to measure the changes of magnetic flux density. In this study, magnetic wheels are used not only as the adhesion device of the robot, but also as an excitation source to provide the exciting magnetic field for the sensing system. Furthermore, compared to the eddy current method and the MFL (magnetic flux leakage) method, this sensing system suppresses the noise from lift-off value fluctuation by measuring the vertical component of induced magnetic field that is perpendicular to the surface of the specimen in the corrosion inspection. Simulations and experimental results validated the feasibility of the system for the automated defect inspection.

Hysteresis Compensation Based on Controlled Current Pulses for Magnetoresistive Sensors

This paper presents a novel hysteresis compensation method for increasing the measurement accuracy of magnetoresistive (MR) sensors such as anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and tunnel magnetoresistance (TMR) sensors. A coil consisting of one winding is processed on top of the sensor element. This configuration allows short current pulses (positive and negative) to generate a defined magnet field, which should be much stronger than the field to be measured. In this case, the MR sensors can always be kept in the same magnetic loop (major loop) during the measurement cycle. By demodulating or averaging the output signal of the sensor, the influence of the sensors hysteresis can be largely reduced. A mixed signal circuit consisting of a field-programmable gate array, analog-to-digital converters and analog switches is used to generate the pulses. AMR, GMR, and TMR current sensors are chosen as examples in the experiment. Current measurements with and without controlled magnetic field pulse are compared. A hysteresis reduction to nearly 20% of the original value, by using the novel hysteresis compensation method, is reached.

A Novel High-Sensitivity Cardiac Multibiomarker Detection System Based on Microfluidic Chip and GMR Sensors

We have developed a novel cardiac multibiomarker detection system, wherein cardiac biomarkers NT-proBNP and cTnI could be detected simultaneously in 20 min. The lower limits of detection of NT-proBNP and cTnI were 0.33 and 1.43 pg/ml, respectively. Furthermore, based on a microfluidic chip and a giant magnetoresistance sensor, the detecting system was realized in a small platform to decrease the manufacturing cost and the difficulty of operation. In addition, owing to the usage of the superparamagnetic nanoparticles of suitable diameter and bovine serum albumin blocker in nanoparticles solution, the system achieved a high signal-to-noise ratio in the whole dynamic range. This magnetic immunoassay system can be adapted to detect a variety of clinically important biomolecules in human samples and provide accurate information to diagnose human diseases.

Research of weak pulsed magnetic field system derived from the time, displacement, and static magnetic field.

The accurate measurement of dynamic characteristics in weak magnetic sensors is urgently required as a greater number of applications for these devices are found. In this paper, a novel weak pulsed magnetic field system is presented. The underlying principle is to drive a permanent magnet passing another magnet rapidly, producing a pulsed weak magnetic field. The magnitude of the field can be adjusted by changing the velocity and distance between the two magnets. The standard value of the pulsed dynamic magnetic field can be traced back to the accurate measurement of time, displacement, and static magnetic field. In this study a detailed procedure for producing a pulse magnetic field system using the above method is outlined after which a theoretical analysis of the permanent magnet movement is discussed. Using the described apparatus a milli-second level pulse-width with a milli-Tesla magnetic field magnitude is used to study the dynamic characteristics of a giant magnetoresistance sensor. We conclude by suggesting possible improvements to the described apparatus.

High signal output in current-perpendicular-to-the-plane giant magnetoresistance sensors using In–Zn–O-based spacer layers

We report current-perpendicular-to-the-plane giant magnetoresistance (CPP-GMR) sensors with a conductive Ag/In–Zn–O (IZO)/Zn trilayer as the spacer layer. Magnetoresistance ratios as high as 26% at resistance–area product (RA) = 60–120 mΩ µm2 were obtained in thin, polycrystalline spin valves suitable for modern read sensors of hard disk drives (HDDs). The large CPP-GMR values are attributed to the large spin-dependent scattering at the interfaces of the ferromagnet/IZO-based spacer junctions. The maximum voltage output of sensors with Ag/IZO/Zn spacers was ΔVmax = 11.3 mV, significantly larger than that observed for metallic AgSn spacers (2.3 mV). Such improved properties are important for HDD read heads with recording densities larger than 1 Tbit/in.2.

Designs of Novel Magnetic Flux Guides for Three-Axis Magnetic Sensor

In general, giant magnetoresistance (GMR) sensors are only sensitive to the magnetic field in the plane of the substrate due to fabrication restraints. Then, a three-axis magnetic sensor based on GMR sensors has to be assembled to obtain three magnetic field components. Novel magnetic flux guides for three-axis magnetic sensor are described in this paper. These novel flux guides are designed with flux conversion structure and are able to bring magnetic flux out-of-plane to in-plane. With these flux guides, the magnetic field perpendicular to the chip surface can be detected with the GMR sensors in-plane. Then, numerical simulations are performed to validate the designs, and optimizations are made to improve the flux guides’ performance. Based on these works, a three-axis magnetic sensor based on the in-plane GMR sensors is proposed. Without assembling the $z$ -axis sensor, the integrated three-axis magnetic sensor is expected to have better angular position. According to the designs, the flux guides can be deposited with good symmetry. Therefore, Wheatstone bridges are configured to deduce a differential voltage, only relative to a certain component of the magnetic field. In addition, the magnetic field at the active region of the GMR sensor would be intensified. In addition, the sensitivity of the sensor can be improved due to the amplification ability of the flux guides.

Application of GMR Sensors to Liquid Flow Sensing

This paper presents a feasibility study of the application of giant magneto resistive (GMR) sensors in detecting motion of slow moving fluids. A motivating application for the proposed effort is the development of a smart catheter capable of monitoring the amount of body fluid drained from the ventricles of the brain. Microfabricated ferromagnetic flaps are used to detect motion of the surrounding fluid. The deflection of the flaps is detected by an ultrasensitive GMR sensor placed outside of the lumen of the catheter. Numerical and experimental results are provided demonstrating a resolution of 1.4 mL/h. Numerical analysis of the fluid past the sensing element show an optimal hinge length of the flexible flaps, as well as a significant increase in sensitivity with reduction of the by-pass gap to $\sim 50~\mu $ m. The effect of electro-magnetic interference and other sources of low-frequency noise (drift) has also been investigated. The results from the study are used to derive a set of design rules that may lead to the successful development of a smart catheter. [2014-0148]

Nitrogen-Vacancy centers in diamond for current imaging at the redistributive layer level of Integrated Circuits

We present a novel technique based on an ensemble of Nitrogen-Vacancy (NV) centers of diamond to perform Magnetic Current Imaging (MCI) on an Integrated Circuit (IC). NV centers of diamond permit to measure the three components of the magnetic fields generated by mA range current in an IC structure over a field of 50×200μm with sub-micrometric resolution. Vector measurements allow the use of a more robust algorithm than those used for MCI using GMR or SQUID sensors and it is opening new current reconstruction prospects. Calculated MCI from these measurements shows a very good agreement with theoretical current path. Acquisition time is around 10s, which is much faster than scanning measurements using Superconducting Quantum Interference Device (SQUID) or Giant Magneto Resistance (GMR). The experimental set-up relies on a standard optical microscope, and the measurements can be performed at room temperature and atmospheric pressure. These early experiences, not optimized for IC, show that NV centers in diamond could become a real alternative for MCI in IC.

Current-perpendicular-to-the-plane magnetoresistance from large interfacial spin-dependent scattering between Co50Fe50 magnetic layer and In-Zn-O conductive oxide spacer layer

We have investigated electrically conductive indium-zinc-oxide (IZO) deposited by magnetron sputtering as spacer layer for current-perpendicular-to-the-plane giant magnetoresistance sensor devices. Spin-valves with a Co50Fe50/IZO/Co50Fe50 trilayer showed resistance-area product (RA) ranging from 110 to 250 mΩ μm2, significantly larger than all-metal structures with Ag or Cu spacers (∼40 mΩ μm2). Magnetoresistance ratios (ΔR/R) of 2.5% to 5.5% depending on the IZO spacer thickness (1.5–6.0 nm), corresponding to ΔRA values from 3 to 13 mΩ μm2, were obtained. The values of ΔRA with the IZO spacers and Co50Fe50 magnetic layers were significantly larger than those with conventional metal spacers and Co50Fe50 magnetic layers (∼1–2 mΩ μm2). The dependence of ΔRA on the magnetic layer thickness suggests that the larger ΔRA obtained with IZO spacer is due to a large interfacial spin-dependent scattering caused by the large specific resistance at the Co50Fe50/IZO interface. From structural characterization by TEM and the observed dependence of the RA dispersion on device size, the electric current flowing through the IZO spacer is thought to be laterally uniform, similar to normal metal spacers.

Detection of Localized Damage in Water Wall Tubes of Thermal Power Plants Using GMR Sensor Array Based Magnetic Flux Leakage Technique

A flexible giant magneto-resistive (GMR) sensor array based magnetic flux leakage technique has been developed for nondestructive inspection of carbon steel water wall tubes (outer diameter 64.0 mm and wall thickness 6.3 mm) used in a thermal power plant. Two saddle coils are used for magnetisation of the tube and a flexible GMR sensor array is used for detection of leakage fields from localized damage in the tube. 3D-nonlinear finite element modeling has been performed to optimize the magnetizing current, inter-coil spacing of the saddle coils and location of the GMR sensor array within the saddle coils. The performance of the technique has been evaluated by measuring the axial component of leakage flux from outer diameter (OD) erosion and inner diameter (ID) corrosion type flaws artificially machined on the water wall tube. Studies reveal that the proposed technique detects both OD erosion and ID corrosion damage in the water wall tubes.

An Integrated Giant Magnetoresistance Microfluidic Immuno-sensor for Rapid Detection and Quantification of D-dimer

A method for rapid detection and quantification of D-dimer as a biomarker of thrombosis was developed by utilizing giant magnetoresistance (GMR) sensor integrated with microfluidic technique and 100 nm magnetic particles (MPs) as signal probes. The MPs binding on the chip through specific immune reaction were measured by the GMR sensor and the concentration of D-dimer was obtained at the same time. The detection range of this method was from 5 ng mL−1 to 6500 ng mL−1, the detection limit was 5 ng mL−1, the intra relative standard deviation was less than 12% and the inter relative standard deviation was less than 14%. The whole analysis process could be completed within 9 min, and a good linear correlation between the results of GMR biosensor and Sysmex CA1500 was obtained. The method had the advantages such as high sensitivity, fast detection and good accuracy.

Reactivable passive radio-frequency identification temperature indicator

A low cost, passive radio-frequency identification (RFID) temperature indicator with (re-) activation at any point of time is presented. The capability to detect a temperature excursion is realized by magnets and a solution with a melting point at the critical temperature. As the critical temperature is exceeded, a magnetic indicator switches to non-reversible and this can be monitored via a giant magnetoresistance sensor connected to a RFID tag. Depending on the solutions or metal alloys, detection of critical temperatures in a wide range from below 0 °C and up to more than 100 °C is possible. The information if a threshold temperature was exceeded (indicator state) as well as the identification number, current temperature, and user defined data can be obtained via RFID.

Superparamagnetic nanoparticle quantification using a giant magnetoresistive sensor and permanent magnets

Magnetic nanoparticles are used in various biological applications such as magnetic resonance imaging (MRI), biological separation, drug delivery or as biomarker. In the case of biomarker, the magnetic particle and a measurand are combined via biological reactions and then detected by magnetic field sensors for a qualitative or quantitative measurement. In the present work, we introduce a commercially available giant magnetoresistive (GMR) sensor for the quantitative measurement of superparamagnetic nanoparticles, which were injected into a glass capillary tube. A pair of permanent magnets standing diagonally opposite to each other was utilized to provide vertical and horizontal magnetic fields for particle magnetization and sensor bias, respectively. In addition, the permanent magnets solved the uniformity problem of generated magnetic fields in previous biomarker detection systems. Using the proposed measurement setup, an output signal change of 0.407V was achieved for a 1μg change in the magnetic particle mass. The detection limit was 43.5ng.

High-performance giant magnetoresistive sensorics on flexible Si membranes

We fabricate high-performance giant magnetoresistive (GMR) sensorics on Si wafers, which are subsequently thinned down to 100 μm or 50 μm to realize mechanically flexible sensing elements. The performance of the GMR sensors upon bending is determined by the thickness of the Si membrane. Thus, bending radii down to 15.5 mm and 6.8 mm are achieved for the devices on 100 μm and 50 μm Si supports, respectively. The GMR magnitude remains unchanged at the level of (15.3 ± 0.4)% independent of the support thickness and bending radius. However, a progressive broadening of the GMR curve is observed associated with the magnetostriction of the containing Ni81Fe19 alloy, which is induced by the tensile bending strain generated on the surface of the Si membrane. An effective magnetostriction value of λs = 1.7 × 10−6 is estimated for the GMR stack. Cyclic bending experiments showed excellent reproducibility of the GMR curves during 100 bending cycles.

Magnetic-based biomolecule detection using giant magnetoresistance sensors

This paper presents a novel microfluidic chip for in-vitro detection of biomolecules tagged by magnetic microparticles (MAPs) suspended in a static fluid. The system consists of two microfluidic channels: a reference channel in which bare MAPs are suspended and a detection channel in which magnetically tagged biomolecules are suspended (LMAPs). The LMAPs are functionalized MAPs (of the same magnetic volume as the ones in the reference channel) with attached biomolecules. The overall, non-magnetic volume of the LMAPs is greater than that of the bare MAPs. Current carrying microconductors are positioned underneath the channels in order to impose a magnetic field gradient to the MAPs and LMAPs and move them from the inlet to the outlet of the channels without flow. The innovative aspect of the proposed method is that the induced velocity on the MAPs and LMAPs, while imposed to the same magnetic field gradient, is inversely proportional to their overall, non-magnetic volume. This is due to the enhanced Stokes drag force exerted on the LMAPs, resulting from the greater volume and altered hydrodynamic shape. This induced velocity is measured by utilizing Giant Magnetoresistance (GMR) sensor pairs fabricated underneath the first and the last microconductors. Detected differences in velocity between the LMAPs and the reference MAPs indicate the presence of biomolecules in the static liquid sample. We also present a novel method for signal acquisition and demodulation: expensive function generators, data acquisition devices, and lock-in amplifiers were substituted by a generic PC sound card and an algorithm combining the Fast Fourier Transform of the signal with a peak detection routine. Experiments with functionalized MAPs and magnetically tagged Escherichia coli (representing the LMAPs) were carried out as a proof of concept. In order to identify the detection limit of the GMR sensor, single MAP (2.8 μm diameter) detection was performed.

Needle-type GMR sensor to estimate the magnetic properties of diluted ferrofluid for biomedicine application

This paper proposes a needle-type giant magnetoresistance (GMR) sensor for very low magnetic fluid weight density of ferrofluid estimation. The magnetic fluids or ferrofluids due to their biocompatibility are used for various applications in medicine such as cancer treatment, magnetic resonance imagining (MRI), cell separation and also to detect the bacteria. The high sensitivity of GMR sensor gives us to accurately measure the magnetic properties of ferrofluid in a weak magnetic field. The results were obtained by GMR sensor are compared by theoretical results and show that the GMR sensor has a good ability for biofluid magnetic characterization.

Tri-axis magnetometer with in-plane giant magnetoresistance sensors for compass application

A tri-axis magnetometer comprising three giant-magnetoresistance sensors and a cylindrical fluxguide are implemented for compass application. The sensors are mounted on a single printed circuit board (PCB) board with their sensing axes in a plane. A calibration process involving matrix manipulation was employed to make the device function as a tri-axis magnetometer with orthogonal sensing directions. The capability of the device for compass application was demonstrated by measuring its azimuth response to the geomagnetic field about different rotation axes. The proposed calibration technique can be used for the magnetometer system with either orthogonal or non-orthogonal sensor arrangement.

Giant magnetoresistive-based biosensing probe station system for multiplex protein assays.

In this study, a sensitive immune-biosensing system capable of multiplexed, real-time electrical readout was developed based on giant magnetoresistive (GMR) sensor array to detect a panel of protein biomarkers simultaneously. PAPP-A, PCSK9, and ST2 have been regarded as promising candidate biomarkers for cardiovascular diseases. Early detection of multiple biomarkers for a disease could enable accurate prediction of a disease risk. 64 nano-size GMR sensors were assembled onto one 16 mm × 16 mm chip with a reaction well, and they could work independently and be monitored simultaneously. A detect limit of 40 pg/mL for ST2 antigen had been achieved, and the dynamic ranges for the three proteins detection were up to four orders of magnitude. The GMR sensing platform was also selective enough to be directly used in serum samples. In addition, a lab-based probe station has been designed to implement quick lab-on-a-chip experiments instead of wire bonding. It has a potential application in clinical biomarkers identification and screening, and can be extended to fit other biosensing schemes.