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Information encoding in barcodes using magnetic-based technology is a unique strategy to read data buried underneath non-transparent surfaces since a direct line-of-sight between the code and the reader is not required. This technology is of particular interest in secure labeling and recyclable packaging applications. However, current magnetic reading heads, such as those employed for magnetic ink character recognition (MICR), need to be placed in contact with the magnetic structures, limiting the depths at which the information can be read. This article describes a strategy to overcome that limitation by replacing the traditional inductive heads with tunnel magnetoresistive (TMR) sensors. Soft-magnetic codes can be printed using conventional LaserJet toners and, by having their magnetization set with a permanent magnet (PM) included in the device, the resulting magnetic field can be read using a TMR sensor. We demonstrate that such a device can read barcodes at depths of at least 1 mm. It can also resolve individual structures as thin as $200 ~\mu \text{m}$ when used in contact. [ABSTRACT FROM AUTHOR]

Hydrogenated amorphous silicon thin film photodetectors combined with optical filters are routinely used for biological detection applications based on fluorescence. Monolithic integration of these filters to the photodetectors further enhances the portability and simplicity of the system. However, due to the multitude of fluorophores used in such applications, it is often necessary to combine multiple filters in a single chip for increased ease of application and portability of the system. In this work, we report a novel facile technique to integrate multiple filters in a chip with four photodiodes, in an innovative methodology that leverages the beneficial characteristics of different types of deposition techniques to fabricate precise multilayer interference filters. Ion beam deposited MgO layers with different thicknesses are successively patterned by lift-off and sandwiched between two standard dielectric mirrors deposited via plasma-enhanced chemical vapor deposition to produce the filter array. The successful integration of the devices is demonstrated through fluorescence measurements of grape fluorescence at two different wavelengths which are utilized in grape maturation monitoring in the viticulture sector. [ABSTRACT FROM AUTHOR]

The tracking of eye gesture movements using wearable technologies can undoubtedly improve quality of life for people with mobility and physical impairments by using spintronic sensors based on the tunnel magnetoresistance (TMR) effect in a human–machine interface. Our design involves integrating three TMR sensors on an eyeglass frame for detecting relative movement between the sensor and tiny magnets embedded in an in-house fabricated contact lens. Using TMR sensors with the sensitivity of 11 mV/V/Oe and ten <1 mm3 embedded magnets within a lens, an eye gesture system was implemented with a sampling frequency of up to 28 Hz. Three discrete eye movements were successfully classified when a participant looked up, right or left using a threshold-based classifier. Moreover, our proof-of-concept real-time interaction system was tested on 13 participants, who played a simplified Tetris game using their eye movements. Our results show that all participants were successful in completing the game with an average accuracy of 90.8%. [ABSTRACT FROM AUTHOR]

The sensor technology and the packaging method influence drastically the device performance by conditioning its sensitivity, the operating conditions and the distance between the magnetic source and the sensor. Magnetic encoders based on magnetoresistive (MR) sensors standout as a technology immune to dust, oil and fluids, and a cheaper system than optical solutions. Furthermore, they provide a higher spatial resolution, sensitivity and bandwidth than Hall effect sensors. However, to achieve a competitive prototype for applications with high constraints, it is necessary to combine state-of-the-art MR sensors with a packaging solution that entails a minimum impact on the sensor performance. Therefore, a new packaging method developed at wafer level is proposed for motion and positioning systems in planar architectures. The final prototype consists on a hybrid rigid-flexible MR probe combining a sensing chip with a flexible polyimide (PI) connector. This packaging technique pushes the contacts and establish electrical contact with the outer electronics on the back side or at a lower level parallel to the sensor plane, achieving a minimum distance of $7.5~\mu \text{m}$ between the sensor and the magnetic source. Finally, the device was successfully implemented as a magnetic encoder on a linear magnetic scale with $80~\mu \text{m}$ bit length revealing a sin/cos like signal with an amplitude of 42 mV $_{\mathrm {RMS}}$ at a reading distance of $80~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

This paper discloses two high-sensitivity probes for Eddy Current Nondestructive Test (NDT) of buried and surface defects. These probes incorporate eight and 32 magnetoresistive sensors, respectively, which are optimized for high sensitivity and spatial resolution. The signal processing and interfacing are carried out by a full-custom application-specific integrated circuit (ASIC). The ASIC signal chain performs with a thermal input-referred noise of 30 nV/ $\sqrt{\text{Hz}}$ at 1 kHz, with 66 mW of power consumption, in a die with 3.7×3.4 mm $^2$. NDT results are presented, showing that there is an increase in spatial resolution of surface defects when contrasted to prior art, enabling the probes to resolve defects with diameters of 0.44 mm, pitches of 0.6 mm, and minimum edge distance as low as 0.16 mm. The results also show that the probe for buried defects is a good all-round tool for detection of defects under cladding and multiple-plate flat junctions. [ABSTRACT FROM AUTHOR]

Industrial requirements are continuously pushing the sensor limits toward higher signal-to-noise ratio under harsh environments, without compromising production costs by additional electronics. Non-full resistive Wheatstone bridge architectures arise as a compact and cheaper alternative to full-bridge measurement schemes, despite a lower output, linearity, and immunity to thermal drifts promoted by the replacement of the out-of-phase sensing elements by passive elements. However, the combination of state-of-the-art magnetoresistive (MR) sensors with thermally compatible materials used as tunable thin-film resistor at wafer level can lead to competitive prototypes for applications with high constraints. Therefore, the resistivity and the temperature coefficient of resistance (TCR) of Cr, Ti, and TiW thin films were evaluated as potential candidates for a thermal and electrical stable non-full MR bridge. Within a TCR around 1059 ± 12 ppm/°C for a spin-valve sensor lying between the values observed for a Ti thickness range of 300 Å up to 500 Å (571.9 ± 8.3 and 1347 ± 69 ppm/°C, respectively), a sin/cos magnetic encoder was prototyped in a non-full-bridge architecture with a thermal offset drift of 51.48 ± 0.25 nV/Vcc/°C and an offset voltage of 16 mV/Vcc. [ABSTRACT FROM AUTHOR]

Precision healthcare brings many technological challenges for the development of new tools. Among these, the detection of biomagnetic fields in the pico-Tesla range, at room temperature, requires the state-of-the-art sensors with high signal-to-noise ratio. Also, given that biomedical signals are characterized by their low frequency, minimizing the sensor noise has to be addressed simultaneously with the efforts to increase sensor sensitivity. In this paper, we maximize the spin-valve sensors sensitivity by optimizing the distance between the poles of double-layer magnetic flux concentrators (MFCs). An enhancement of the sensitivity from 1.5%/mT (3.8 mV/mT) to 654%/mT (1765 mV/mT) could be observed for a double-layer architecture when a distance from the recessed steep CoZrNb MFC to the NiFe pole is $100~\mu \text{m}$. The impact on the detectivity was evaluated through noise enabling the detection of magnetic fields of 322 pT/Hz1/2 at 10 Hz. [ABSTRACT FROM AUTHOR]

Magnetoresistive (MR) sensors have been identified as promising candidates for the development of high-performance magnetometers due to their high sensitivity, low cost, low power consumption, and small size. The rapid advance of MR sensor technology has opened up a variety of MR sensor applications. These applications are in different areas that require MR sensors with different properties. Future MR sensor development in each of these areas requires an overview and a strategic guide. An MR sensor roadmap (non-recording applications) was therefore developed and made public by the Technical Committee of the IEEE Magnetics Society with the aim to provide an research and development (R&D) guide for MR sensors intended to be used by industry, government, and academia. The roadmap was developed over a three-year period and coordinated by an international effort of 22 taskforce members from ten countries and 17 organizations, including universities, research institutes, and sensor companies. In this paper, the current status of MR sensors for non-recording applications was identified by analyzing the patent and publication statistics. As a result, timescales for MR sensor development were established and critical milestones for sensor parameters were extracted in order to gain insight into potential MR sensor applications (non-recording). Five application areas were identified, and five MR sensor roadmaps were established. These include biomedical applications, flexible electronics, position sensing and human–computer interactions, non-destructive evaluation and monitoring, and navigation and transportation. Each roadmap was analyzed using a logistic growth model, and new opportunities were predicted based on the extrapolated curve, forecast milestones, and professional judgment of the taskforce members. This paper provides a framework for MR sensor technology (non-recording applications) to be used for public and private R&D planning, in order to provide guidance into likely MR sensor applications, products, and services expected in the next 15 years and beyond. [ABSTRACT FROM AUTHOR]

Biomedical applications and point-of-use devices often rely on nanoparticle concentration strategies. In this paper, on-chip magnetic trapping and manipulation of 300–500 nm superparamagnetic nanoparticles are achieved using thin-film planar circular copper coils. The trap configuration combining a central coil surrounded by four other coils, all connected in series, successfully enables simultaneous attraction and repulsion, enhancing concentration of magnetic nanoparticle (MNP). The simultaneous attraction and repulsion has advantages over static permanent magnets, where unidirectional actuation allows either attraction or repulsion. Because the distance between traps and the MNP is large (hundred micrometer), large electric currents up to 500 mA are needed to achieve fields of the order of hundreds of microtesla, which requires thermal management. Joule heating is effectively tackled by resorting to a novel cooling scheme comprising triangular microchannels milled onto copper substrates. Experimental results combining thermal surface mapping, magnetic field mapping, and optical (fluorescence microscope) observations could validate the trapping efficacy of Estapor microspheres functionalized with BODIPY 515 fluorophores. [ABSTRACT FROM AUTHOR]

The ability to fabricate MgO magnetic tunnel junction nanopillars with low RA and high TMR opens the door to new devices such as magnetic memories or nanooscillators. Here, we address the dynamic behavior of a CoFeB/MgO/CoFeB MTJ with a synthetic-antiferromagnetic pinned layer as a potential candidate for spin-transfer torque (STT) driven applications. The unpatterned stack presents an RA of \sim 1.4~\Omega \mu \textm^2 and both free layer and barrier are patterned down to a $90 \times 180$ nm2 elliptical shape. The observed high-frequency spectra displayed deviations from the uniform precession modes due to additional coupling fields. A dependence of the STT magnitude on the analyzed mode was obtained, differing from previous reports, most likely due to the very low RA employed. [ABSTRACT FROM AUTHOR]

The development of giant magnetoresistive (GMR) sensors has demonstrated significant advantages in nanomedicine, particularly for ultrasensitive point-of-care diagnostics. To this end, the detection system is required to be compact, portable, and low power consuming at the same time that a maximum signal to noise ratio is maintained. This paper reports a CMOS front-end with integrated magnetoresistive sensors for biomolecular recognition detection applications. Based on the characterization of the GMR sensor's signal and noise, CMOS building blocks (i.e., current source, multiplexers, and preamplifier) were designed targeting a negligible noise when compared with the GMR sensor's noise and a low power consumption. The CMOS front-end was fabricated using AMS $\mathrm{{\text{0.35}}\;\mu{\text{m}}} technology and the magnetoresistive sensors were post-fabricated on top of the CMOS chip with high yield ( \text97.9\%). Due to its low circuit noise (16 \mathrm\textnV/\sqrt\textHz) and overall equivalent magnetic noise ( $\mathrm{{\text{11.5}}\;{\text{nT}}/\sqrt{{\text{Hz}}}}$), the full system was able to detect 250 nm magnetic nanoparticles with a circuit imposed signal-to-noise ratio degradation of only $-$1.4 dB. Furthermore, the low power consumption (6.5 mW) and small dimensions ($\mathrm{{\text{7.59: mm}}^{2}}$ ) of the presented solution guarantees the portability of the detection system allowing its usage at the point-of-care. [ABSTRACT FROM PUBLISHER]

Eddy current testing (ECT) is a high impact technology to detect surface flaws. However, its reliability is reduced for low conductive titanium alloys, which are broadly integrated into the industry. ECT tools based on magnetoresistive (MR) sensors offer advantages over inductive sensors due to an enhanced spatial resolution, high sensitivity, and bandwidth. In this paper, we demonstrate successful non-destructive testing inspection of titanium surfaces, not achieved by other ECT tools. Here, single surface defect (length = 0.6 mm; width =100~\mu \textm ; depth =50~\mu \textm ) in a non-polished TA6V \alpha titanium mock-up was measured using an MR-ECT probe. The detection was made by an array of magnetic tunnel junctions with 50 \times 50~\mu \text{m}^{\mathrm { {2}}} with optimized field detectivity. A differential measurement employing a heterodyne technique isolated the magnetic field component ( f_{H}- f_{\mathrm { {bias}}} = 1 kHz) from the electric biasing component ( f\mathrm { {bias}} = 4999 kHz) and electromagnetic coupling ( fH = 5 MHz), revealing a bipolar defect signature of 6.01~\mu \textV\text {0-p} amplitude. [ABSTRACT FROM PUBLISHER]

The reduction of the noise level of magnetoresistive (MR) micrometric sensors is often achieved by increasing the sensor area and/or connecting MR elements in large arrays. This paper introduces an innovative strategy to increase the sensing area without increasing the area occupied by the MR sensors on a wafer, therefore minimizing the sensor footprint. Here, the idea is to deposit vertically spin-valve (SV) films, separated by an insulator. This packed structure is then incorporated into arrays, connected in parallel and series, as a general noise reduction strategy. Using calculations, the number of SVs vertically packed ( Z ), combined in series ( X elements) and parallel ( Y elements) was investigated, so that the optimum geometry, which minimizes the field detectivity, can be obtained. The magnetic field detection of SV sensors in the thermal noise limit can be improved from 39 pT/Hz for Z = 1 with a total number of 500 SVs (distributed in plane) to 12 pT/Hz ^1/2 for Z =10 with a total number of 5000 SVs. Besides, the device footprint is also demonstrated to decrease from 0.7 mm2 ( $Z = 1$ ) to 0.07 mm2 ( $Z = 10$ ). These limits of detection are competitive with single SV sensors using magnetic flux concentrators, with the advantage of a high spatial resolution with fewer fabrication steps (at least three). [ABSTRACT FROM PUBLISHER]

The bacterial infection degree of a real biological sample can be determined by using magnetoresistive (MR) cytometry. In this case, it is required to count detection events and to precisely determine the bacterial cells concentration detected by the sensor in each detection event. Here, we are proposing a method to evaluate the bacterial concentration from experimental obtained data. By simulating and analyzing the signals created by clusters with a different number of cells, shapes, and orientations relative to the sensor sensitive direction, clusters that can fit the experimental signals are found. The simulation results are compared with the experimental obtained signals in order to quantify the number of cells that are detected by the MR sensor in different detection events. [ABSTRACT FROM PUBLISHER]

This paper reports on the integration of magnetic tunnel junction (MTJ) sensing devices with magnetoresistance responses above 150% on flexible substrates. The sensors are integrated in a fabrication process based on polyimide materials, and demonstrate sensitivities up to 250~\mu \textV /Oe for bias currents in the 100- \mu \textA range. Assessment of the sensors performance is done under controlled mechanical load conditions, and the magnetoresistance is only slightly affected (1% variation) while sensitivity changes by 7.5% when the bending radii reduce down to 5 mm. The results demonstrate the high potential of the MTJ sensors to be used in applications requiring bending and conforming to non-planar geometries, bringing magnetoelectronic technologies to hard-to-reach regions of space. [ABSTRACT FROM PUBLISHER]

This paper describes how magnetoresistive materials can be optimized and integrated in magnetic field sensor devices. Giant magnetoresistive (GMR) and tunnel magnetoresistive (TMR) can provide advantageous solutions for a wide range of applications, of which some are described here. Considerations on field sensitivities, intrinsic noise mechanisms, biasing, and integration schemes are presented. [ABSTRACT FROM PUBLISHER]

This paper reports on the development and the fabrication of a novel atomic force microscopy cantilever with integrated magnetoresistive sensors at its tip for scanning magnetoresistance applications. A 2-D scan over an area of 100\times 100~\mu \textm^2 simultaneously generates topographic and magnetic maps with a spatial resolution better than 1 \mu \textm . The magnetic field is detected using two spin valve sensors with a field sensitivity of 61.33 \mu \textV /Oe. The device operation is demonstrated with a ferromagnetic test feature of 1\times 20~\mu \textm^2 . The results demonstrate that this scanning technique is capable of accurately quantifying the absolute magnitude of magnetic stray fields. [ABSTRACT FROM AUTHOR]

In the pursuit of point-of-care systems that present high sensitivity and fast turnaround time, lateral flow is considered a remarkable promising class of in vitro diagnostics, and popularized by the pregnancy tests. A variety of lateral flow tests have emerged able to provide cardiac panels in emergency conditions, infectious disease screening, drug abuse, among others. However, most commercial tests only provide qualitative results, limiting their applicability for quantification thresholds of most biomarkers. In this paper, we propose a novel detection architecture for quantification of biomolecules labeled with magnetic nanoparticles employing two spin valve sensors. The main goal of this paper is to demonstrate that this architecture can detect and monitor MNPs flowing in a LFT strip for detection and quantification of different solutions varying in MNP concentration. In addition, we present preliminary analytical results that support our strategy for achieving biomolecular quantification using the proposed solution. [ABSTRACT FROM AUTHOR]

Highly sensitive nanosensors with high spatial resolution provide the necessary features for high-accuracy imaging of isolated magnetic nanoparticles or mapping of magnetic fields. Here, we fabricated nanosensor devices based on MgO-magnetic tunnel junctions with soft pinned sensing layer. The exchange interaction at the free-layer is tuned to yield distinct linear operation ranges for the nanosensors. Circular (diameter D = 120–500 nm) and elliptical pillars with low aspect ratio (120 nm \times 130 nm–120 nm \times 200 nm) displaying a linear non-hysteretic transfer curves with tunnel magnetoresistance values up to 143% were obtained. A noticeable improvement in the sensitivity for circular structures from an average value of \sim 1 %/mT up to \sim 2 Hz with Hooge parameters within 1– 3 \times 10^{-9} \mu m ^{2}$ in the linear range. Nevertheless, such high sensitivity values are a major improvement in comparison with those reported previously for nanometric sensors, and extremely competitive with values reported for micrometric spin-valve sensors, with the advantage of providing a reduced device footprint suitable for highly resolved measurements. [ABSTRACT FROM AUTHOR]

Spin valves (SVs) with synthetic-antiferromagnet (SAF) pinned layers and synthetic-ferrimagnet (SF) free-layers deposited by ion beam deposition are optimized for incorporation in nanometric sensors. The results on combined SAF-SF structures indicate a reduced saturation and offset fields when compared with the simple top-pinned or SAF structure. Therefore, SAF-SF SV display sensitivities of $\sim 0.025$ %/Oe (200 nm sensor), \sim 0.1$ %/Oe (500 nm sensor), and \sim 0.2$ %/Oe (1 sensor), which correspond to an improvement of $2\times $ , $4.5\times $ , and $7\times $ , respectively, when compared with all other SV stacks tested. The results are relevant for geometries where nanometric SVs are incorporated within very narrow gaps of magnetic flux concentrators leading to superior and competitive gains in sensitivity. These geometries have the unique feature of submicrometric spatial resolution, and have high impact on surface scanning applications. [ABSTRACT FROM AUTHOR]

This paper presents a neuronal signal detector for biologically generated magnetic fields. The system includes a hardware section implemented with discrete electronics, which has an ultralow-noise dc or dc+ac current source for magnetoresistive sensor biasing, and signal amplification and filtering, and a software interface that allows signal demodulation, visualization, and digital postprocessing. Compared with the previous measurement setup, the results show that, for the same bandwidth, the proposed instrumentation system has approximately 50 times better noise performance, making the sensor noise the dominant noise source. The system is able to record the magnetic field generated by ionic currents from action potentials of in vitro experiments with mice brain slices. In addition, to obtain an increased spatial resolution, by scaling the number of sensors that can be read, and to enhance the system immunity to external interferences, two integrated circuits with an ultralow-noise current source for MR biasing and a low-noise variable gain amplifier were developed and are also presented. [ABSTRACT FROM PUBLISHER]

In this work an alternative neuroscience tool for electromagnetic measurements of neurons at the level of individual cells is developed. To perform such measurements we propose the integration of an array of magnetoresistive sensors on micro-machined Si probes capable of being inserted within the brain without further damage. Si-etch based micromachining process for neural probes is demonstrated in the manufacture of a probe with 15 magnetoresistive sensors in the tip of each shaft. Magnetic tunnel junction sensors with dimensions of 30\ \mum\times 2\ \mum, sensitivities of 3.32 V/T and detectivity of \approx13 nT/Sqrt (Hz) are placed in the end of the sharply defined probe tips. In order to measure the small signals coming from the neurons, a homemade signal amplifying system was used with a noise level of 240 nVRMS for the system bandwidth. The full system noise is 2772 nVRMS. [ABSTRACT FROM AUTHOR]

The switching field dependence on the size of nanometric magnetic tunnel junctions was studied. CoFe/Ru/CoFeB/MgO/CoFeB nano-pillars were fabricated down to 150\,\times\,300 nm^2 and characterized, revealing a squared transfer curve with a sharp transition between magnetic states. A micromagnetic finite element tool was then used to simulate the magnetic behavior of the studied nanopillar. The simulations indicated a single-domain like state at remanence, also displaying a sharp transition between parallel/antiparallel free-layer configurations. Overall, the experimentally measured switching fields (Hsw) were smaller than those obtained from simulations. Such trend was consistent with the presence of a particular free layer profile, signature of the two angle etching step used for pillar definition. Further decrease of experimental Hsw was attributed to local defects and thermal activated processes. This study was able to validate this particular simulation tool for the control of the nanofabrication process. [ABSTRACT FROM AUTHOR]

Full Wheatstone bridge electrical current sensor incorporating 114 MgO-based magnetic tunnel junction elements (3\times 30\ \mum^2) connected in series was produced for improved electrical robustness. To that end, magnetic tunnel junctions with R\timesA\sim 7\ k\Omega\ \mum^2, tunneling magnetoresistance of 200%, were produced. The sensor was designed with an integrated Ru thin film resistive thermal detector (RTD) for temperature drift monitoring and compensation. In order to achieve a full bridge signal, a U-shaped copper trace was placed under a printed circuit board (PCB) specifically designed for this type of device. The resulting device exhibit sensitivities of 63.9 V/Oe/A in a 75 Oe linear range biased with 1 mA current, providing a significantly advantageous alternative to AMR and GMR based bridges. [ABSTRACT FROM AUTHOR]

In this work, arrays of MgO-based magnetic tunnel junction elements (5\times 20\ \mum^2) connected in series are studied for sensor applications. Linearization is obtained by combining shape anisotropy with a longitudinal hard bias field set by CoCrPt permanent magnets integrated on the sides of the array. We show that this architecture has the drawback of a large footprint in the chip, but is largely compensated by the weak bias voltage dependence and huge electric robustness, when comparing with individual magnetic tunnel junctions. [ABSTRACT FROM PUBLISHER]

This work compares the performance of spin valve sensors comprising magnetic flux concentrators (MFCs) composed of Co93Zr3Nb4 (CZN) or (Co70Fe30)80B20-based synthetic-antiferromagnet (SAF) multilayer stacks. In addition, the influence of a tapered MFC tip is also studied. When compared to CZN films, SAFs have the disadvantage of lower magnetic susceptibility (\chi =196 for SAF vs. \chi =753 for CZN), which affects negatively the field gain in gap (10 for SAF vs. 43 for CZN). However, from the overall noise spectrum, one can conclude that the magnetic field detections for sensors incorporating CoFeB/Ru multilayers as MFCs are close to the ones obtained with CZN, being mainly determined by the sensor intrinsic properties instead. For low frequencies, field detection levels at 10 Hz improved from \sim61 nT/Hz^0.5 for single spin valve sensors down to \sim1.8 nT/Hz^0.5 when CZN concentrators with a steep-profile are used. [ABSTRACT FROM PUBLISHER]

Full Wheatstone Bridge incorporating a serially connected ensemble of Magnetic tunnel junctions was produced, targeting an application as a magnetic field compass. To that end, MTJs with RxA\sim 10\ k\Omega\ \mum^2, TMR\sim 150–200%, Hf=5\ Oe and Hf=5\ Oe were produced. In order to achieve a full bridge signal, two stacks with an asymmetric SAF reference structure where used to produce MTJs with opposite dR/dH upon annealing in the same substrate. The resulting Bridges exhibit sensitivities between 13.5–32 mV/V/Oe depending on the field range and provide a significantly advantageous alternative to AMR and GMR based bridges. [ABSTRACT FROM PUBLISHER]

This paper proposes techniques for the extraction of biological information in a recently developed handheld biochip-based microsystem. The microsystem is based on a mag- netoresistive array biochip composed of a number of sensing sites with magnetic tunneling junctions (MTJ) and diodes. Different techniques are addressed to drive the MTJs with different types of signals. Different filtering strategies that allow the recovery of biological signals from the noise without overly increasing either the time required for accessing the sensors or the power consumption of the board are proposed. Finally, new techniques and algorithms are proposed to deal with the variability of the fabrication parameters of the MTJ and the diodes. Experiments with the system in a setup to detect actual biological signals are presented with encouraging results. [ABSTRACT FROM AUTHOR]

In this paper, we describe the development of multilayer (ML) thin films suitable for flux concentrators (FC). We prepared ML films having magnetic thicknesses n · tF in the range of 400 Å to 3000 Å by ion beam deposition (IBD). The films exhibit Ruderman-Kittel-Kasuya-Yosida (RKKY) long range antiferromagnetic (AF) coupling through very thin Ru interlayers. We prepared two types of samples: (CoFeB tF/Ru tRu)xn and (NiFe tF/Ru tRu)xn, where CoFeB is (Co70Fe30)80at%B20at% and NiFe is Ni81Fe19. The former has good thermal stability and high magnetic moment while the latter, previously reported, has poor thermal stability and low spontaneous magnetic moment. We discuss the magnetic properties of the films in terms of the remanent magnetic moment Mr and saturation field Hs. Despite having higher spontaneous magnetic moment of 1200 emu/cm3, (CoFeB/Ru)xn films with adequate magnetic proper. ties for sensor-in-gap devices with FC could not be prepared. By contrast, samples consisting of NiFe350 Å/(Ru7 Å/NiFe350 Å)x7 exhibited suitable magnetic properties. We lithographically patterned the films into FC and test structures to investigate their magnetization processes by anisotropic magnetoresistance (MR) measurements. The MR curves indicate magnetization processes by uniform rotation and show absence of hysteresis. [ABSTRACT FROM AUTHOR]

An analog isolator device, based on linear magnetic tunnel junctions is presented. Elemental single structures and full Wheatstone bridge devices are designed, fabricated and tested. In addition, the ranges of functionality of the devices are analyzed, mainly in terms of linearity, signal reconstruction and frequency response. [ABSTRACT FROM AUTHOR]

A dc to ac magnetic field transformer was developed using a magnetic tunnel junction (MTJ)/microelectromechanical system (MEMS) mixed device. A MEMS torsionator was fabricated with an incorporated magnetic flux guide, that when actuated by a gate electrode, modulates an external dc field into the same frequency.of the micro-torsionator oscillation. Attached to it a MgO based MTJ was fabricated, performing the detection of the generated ac magnetic field. This dc to ac field transformation enables the detection of dc magnetic fields in the high frequency thermal noise regime, where the 1/f noise is typically two orders of magnitude lower. Measurements show the detection of a modulated field at 460 kHz, coming from the MEMS torsionator designed to exhibit high modulation efficiency. This efficiency was of 11%, i.e., 11% of the external dc field is modulated. As a result, from a MTJ exhibiting a noise of S[supMTJ][subV] = 4.4 nT/Hz[sup⅛] at 460 kHz, this hybrid device enables a dc magnetic field detection of 40nT/Hz[sup⅛]. This work acts as a major improvement to a previous one [7], mainly through the optimization of the MEMS magnetic field modulation efficiency. [ABSTRACT FROM AUTHOR]

Presents a study where the changes in the tunnel magnetoresistance (TMR) values with annealing temperatures were observed to be associated with changes in barrier parameters. Overview of tunnel junction random access memories; Estimated head parameters for 100 gigabit.

Presents information on a study which reported the elaboration by ion beam deposition (IBD) of manganese-iridium-biased spin valves. Advantages of the IBD technique over other physical deposition methods; Experimental considerations; Characterization of the spin valve layer materials in terms of composition and resistivity; Discussion on the thermal stability of the spin valves; Conclusion.

Presents information on a study which tested the fabricated dual-stripe giant magnetoresistive (GMR) devices with an insulating spacer on tape media. Dual stripe GMR sensor fabrication; Head design and process description; Tape head fabrication; GMR elements transfer curves in static field; Head tests on tape; Tape head results; Conclusion.

Presents information on a study which described shielded spin-valve tape heads with permanent magnet stabilization. Head design and fabrication; Head performance on tape; Conclusions.

Describes the structure of Manganese-Rh (MnRh) exchange layer which has a good corrosion resistance and good exchange coupling. Structure of the spin valve; Study of the corrosion resistance of the exchange material; Results and analysis of the study.

Studies the effect of high temperature processing on the transfer curves by fabricating and annealing unshielded spin-valve sensors. Simulation program used to analyze the changes on the curves; Causes for the loss of magnetoresistance (MR) signal; Results and analysis of the study.

Magnetic tunnel junctions (MTJs) incorporating GeSbTe thermal barriers and weakly pinned free layers (Hex ∼ 60 Oe) have been produced with areas between 1 × 1 μm² and 3 × 8μm². Current pulses lasting from 100 μs down to 20 ns were used to heat the MTJs and reverse the free layer pinning field. It is demonstrated that pulses with 7 mW/μm² can be used to switch the free layer of MTJs incorporating GeSbTe (20 mW/μm² without GeSbTe). The dependence of the power required to switch the MTJs is studied with respect to sample area, pulse duration, and GeSbTe thickness. [ABSTRACT FROM AUTHOR]

A spin-valve sensor biochip was used to detect cystic fibrosis related DNA targets for the purpose of developing an affordable diagnostic chip. The strategy used was based on the ac field focusing of magnetically labeled target DNA at sensor sites using U-shaped current lines. U-shaped spin-valve sensors, fabricated within the line structures, detected in real-time the hybridization of DNA targets to complementary DNA probes, previously immobilized onto the chip surface. Hybridization occurred in relatively short times (15-30 min) in comparison with conventional hybridization approaches (3 to 12 h). Statistical data on detection signals for single probe and multiprobe experiments was obtained, showing a significant difference between complementary binding signals and noncomplementary and background ones. [ABSTRACT FROM AUTHOR]

On-chip spin valve sensors were used to measure the flow velocity within fabricated poly(dimethylsiloxane) (PDMS) microchannels. Superparamagnetic particles with dimensions of 250 nm in diameter were introduced into a 100 μm wide microchannel, bonded to the chip surface. The flow velocity was determined by measuring the changes in resistance of a pair of spin-valve sensors, 1.65 mm apart from each other, caused by the passage of ensembles of superparamagnetic particles, flow velocities ranging from 50 to 300 μm/s were estimated, depending on the pressure used to drive the flow. The application of this system provides a means to measure and control flow velocities on microfluidic devices. [ABSTRACT FROM AUTHOR]

In this paper, junctions with reduced Hf coupling were fabricated by ion beam deposition and oxidation, using CoFeB electrodes. The CoFeB layer has a strong (111) texture that can be the origin of lower Hf and coercivity when compared, with CoFe. Junctions processed down to 2 × 4 μm² with 40-Å-thick CoFeB bottom electrodes have 42% of tunneling magnetoresistance (TMR), (R × A ∼ 400 Ω·μm²), Hc of ∼10 Oe and Hf of ∼2 Oe. CoFe-based junctions (R × A ∼ 500 Ω·μm²) have lower TMR (∼35%) and larger Hf (∼5-6 Oe) and Hc (∼12-14 Oe). Local chemical. composition analysis of the cross section indicated Fe-O segregation with very little Co grown on top of the barrier for CoFe-based junctions and not for CoFeB ones. [ABSTRACT FROM AUTHOR]

Presents a study which utilized a remote oxide ion source for the formation of nano-oxide layers. Experimental procedure; Oxide layer characterization; Conclusion.