Magnetic Microsensors Research Articles

Optimization of magnetic properties and GMI effect of Thin Co-rich Microwires for GMI Microsensors.

Magnetic microwires can present excellent soft magnetic properties and a giant magnetoimpedance effect. In this paper, we present our last results on the effect of postprocessing allowing optimization of the magnetoimpedance effect in Co-rich microwires suitable for magnetic microsensor applications. Giant magnetoimpedance effect improvement was achieved either by annealing or stress-annealing. Annealed Co-rich presents rectangular hysteresis loops. However, an improvement in magnetoimpedance ratio is observed at fairly high annealing temperatures over a wide frequency range. Application of stress during annealing at moderate values of annealing temperatures and stress allows for a remarkable decrease in coercivity and increase in squareness ratio and further giant magnetoimpedance effect improvement. Stress-annealing, carried out at sufficiently high temperatures and/or stress allowed induction of transverse magnetic anisotropy, as well as magnetoimpedance effect improvement. Enhanced magnetoimpedance ratio values for annealed and stress-annealed samples and frequency dependence of the magnetoimpedance are discussed in terms of the radial distribution of the magnetic anisotropy. Accordingly, we demonstrated that the giant magnetoimpedance effect of Co-rich microwires can be tailored by controlling the magnetic anisotropy of Co-rich microwires, using appropriate thermal treatment.

Application Topics of Amorphous Wire CMOS IC Magneto-Impedance Micromagnetic Sensors for I-o-T Smart Society

We proposed ten requisite conditions for successful development of wearable I-o-T smart magnetic sensors considering recent development of some successful micromagnetic sensors. We reported application topics using the amorphous wire CMOS IC magnetoimpedance micromagnetic sensor (MI sensor) on the geomagnetic field sensor for the electronic compass installed in the smartphones, the pitching ball self-spin analyzer installed in the professional baseball, self-driving magnetic guidance system, and the biomagnetic field sensing. Performances of the MI sensor overcoming the ten requisite conditions are discussed as a smart micromagnetic sensor on the basis of the magnetoimpedance effect in the amorphous wire.

Renewable magnetic ion-selective colorimetric microsensors based on surface modified polystyrene beads

Magnetic ion-selective colorimetric microspheres based on surface modification of polystyrene beads (0.8 μm diameter) are reported for the first time. The common components of ion-selective optode sensing (chromoionophore, ion-exchanger and ionophore) and magnetic nanoparticles are adsorbed onto the surface of the polystyrene particles using a simple mixed solvent method. The average diameter of the magnetic microspheres is evaluated by dynamic light scattering as 0.79 ± 0.06 μm. The reversible microsensors are circulated by flow and accumulated at a single spot by an applied magnet to become observable by digital camera. Hue signals are extracted from the recorded images to quantify the ratio of protonated and deprotonated form of the chromoionophore, which is the basis for optode response. The resulting magnetic microsensors respond to K+ with excellent selectivity over the range of 10−6 M to 10−2 M and a response time of t99 < 2.6±0.5 min above 10−5 M. The use of solvatochromic dyes as pH independent transducers was not successful in this application.

Design and Demonstration of Novel Magnetoencephalogram Detectors

Brain activities have attracted considerable attention in medical and healthcare areas and engineering applications. Magnetoencephalogram (MEG) is a non-invasive technique for mapping and evaluating the functional activity of the brain. It is commonly measured by superconducting quantum interference devices (SQUIDs) which is the most reliable sensitive magnetometer for MEG measurement. However, the SQUIDs are still threatened by the need of cryogenic cooling liquids and a shielding room. For recording non-invasive cranial nerve activity, the technology with no liquid helium and high spatial resolution has been required for about 30 years. Sensitive micro-magnetic sensors referred to as magnetoimpedance (MI) sensors based on MI effect in thin amorphous magnetic wires are utilized as an electronics compass in a cellar phone. We have developed a gradiometer based on MI sensor for the purpose of biomagnetic field measurement. The gradiometer is composed of a pair of MI elements with 1 cm length each: a sensing element and a reference element with a baseline of 3 cm. The developed MI gradiometer has good linearity and a high sensitivity of $1.2 \times 105$ V/T with no amplification by semiconductor device. The noise level of the gradiometer is approximately 2 pT/Hz1/2. The MI sensor has system noise higher than SQUIDs, but it has considerable advantages that can measure closely to the scalp. Because of proximity measurement, the magnetic field from brain measured by MI sensor is larger than the case of SQUIDs. The precise MI gradiometer was tested as MEG detectors. The spontaneous brain activity (alpha rhythm) measurements were carried out on a female subject. As expected, the alpha rhythm signals simultaneously measured by electroencephalogram and MI gradiometer were significantly attenuated when the subject opens eyes and intensified with eyes closed. The subject’s $\alpha $ wave MEG signal has a main frequency component of 10–11 Hz and the maximum amplitude is about 25 pT (effective value). Significant susceptibility of MI sensor to spontaneous brain activity was confirmed by signal-to-noise ratio of 8/1. In addition, the measurement of evoked magnetic field N100 was carried out in the unshielded environment. The measurement results about N100 in this paper are almost consistent with the previous study by SQUIDs.

Small Eddy Current Testing Sensor Probe Using a Tunneling Magnetoresistance Sensor to Detect Cracks in Steel Structures

Small Eddy Current Testing Sensor Probe Using a Tunneling Magnetoresistance Sensor to Detect Cracks in Steel Structures

Experimental Study on Residual Bending Strength of Corroded Reinforced Concrete Beam Based on Micromagnetic Sensor.

This paper presents a nondestructive test method to evaluate the residual bending strength of corroded reinforced concrete beam by analyzing the self-magnetic flux leakage (SMFL) signals. The automatic scanning device was equipped with a micromagnetic sensor and sensor-based experimental details were introduced. Next, the theoretical formula of the normal component HS(z) of the SMFL signal that originated from the corroded region was derived based on the magnetic dipole model and the experimental results were discussed. The results indicate that the experimental data of HS(z) are consistent with the theoretical calculations, both location and extent of the steel bars corrosion can be qualitatively determined by using HS(z). The gradient K of HS(z) is approximately linearly related to the loss rate, S, of the bending strength, which can be used to evaluate the residual bending strength of the corroded reinforced concrete beam. This work lays the foundation for evaluating the residual bending strength of corroded reinforced concrete beams using the SMFL signal; the micromagnetic sensor is further applied to the civil engineering.

A novel integrated microfluidic platform based on micro-magnetic sensor for magnetic bead manipulation and detection

We present a novel integrated microfluidic platform based on micro-magnetic sensor for manipulating and detecting magnetic beads (MB). A micro-spiral planar coil in MB manipulating system microfabricated by micro-electro-mechanical system technology is implemented to manipulate MB, and a giant magnetoimpedance (GMI) based micro-magnetic sensor is employed to detect the trapped MB. In our work, MB can be efficiently trapped by trapping force generated from micro-coil in microchannel. Next, trapped MB are detected by the changing ratio of impedance, as well as the variation of resistance and reactance in GMI sensor for trapped MB induce weak stray magnetic field under the magnetization by external magnetic field. The maximum difference of GMI ratio between with beads condition and without beads condition is 4.0% at the optimum driving frequency of 20 MHz under the external magnetic field of 15 Oe, and resistance ratio varies more significantly than reactance ratio. In comparison with traditional MB detecting methods by GMI sensor, the integrated microfluidic platform based on GMI sensor can not only manipulate and detect MB signal sensitively, but also enhance detection efficiency and decrease the experiment errors. Furthermore, this platform avoids contamination from the solutions in chemically reactive layers and reduces assay time in future biomarker detection. In our work, the microfluidic platform based on GMI sensor has potential applications in biomarker detection via MB manipulation and detection.

Topologically protected vortex structures for low-noise magnetic sensors with high linear range

Micromagnetic sensors play a key role in a variety of industries, including the automotive industry, where they are used, for example, for speed and position detection. The adoption of emerging magnetoresistive sensor technology such as anisotropic magnetoresistance, giant magnetoresistance and tunnel magnetoresistance sensors is driven principally by their enhanced sensitivity and improved integration capabilities compared with conventional Hall effect sensors. At the heart of such sensors is a microstructured ferromagnetic thin-film element that transduces the magnetic signal, but these elements often exhibit a nonlinear hysteresis curve and the performance of the sensors is limited by magnetic noise. Here, we examine the origin of magnetic noise in magnetoresistive sensors and show that a topologically protected magnetic vortex state in the transducer element can be used to overcome these limitations. Using analytic and micromagnetic models, we find that the noise is due mainly to irreproducible magnetic switching of the transducer element at external fields that are close to the Stoner–Wohlfarth switching field. Then, using a flux-closed vortex configuration, we develop a giant magnetoresistance sensor layout that, compared to existing state-of-the-art sensors, has lower magnetic noise, a linear regime that is around an order of magnitude higher and negligible hysteresis.

Broadband ferromagnetic resonance measurements in thin-film structures for magnetoimpedance sensors

Thin magnetic films and multilayer structures are commonly used for the development of micromagnetic sensors, some of them operating at high frequencies, as it is the case of magnetoimpedance sensors. At the same time, high frequency characterization techniques as ferromagnetic resonance are extremely useful to investigate material properties. In this work, we analyze the microwave resonant absorption of magnetron sputtered Permalloy-based magnetic films suitable for magnetoimpedance sensor applications. The dispersion of values of the resonant frequencies obtained in broadband ferromagnetic resonance measurements is used to assess the quality and the repeatability of the samples. The thin-film structures under test are inserted in the measuring circuit, constituting itself a part of the microwave transmission line, i.e. they are characterized in a realistic magnetoimpedance configuration, in which the alternating current flows through the sample. The ferromagnetic resonance frequency as a function of the applied field is determined from the measurement of the transmission coefficient in a network analyzer. We also present the data reduction procedure, adapted to our particular measurement test-fixture, that allows determining the ferromagnetic resonance spectra accurately. The analysis of the resonance is performed among samples identically prepared, either in the same production batch or in different batches. The dispersion observed in the results is used to estimate the fluctuations that can be expected in this kind of measurements and the amount of repeatability of sample preparation. The investigation indicates that variations of the order of 10% can be expected in measurements that are usually considered to provide the same result.

A Three-Axis Magnetic Field Microsensor Fabricated Utilizing a CMOS Process

This study develops a three-axis magnetic field (MF) microsensor manufactured by a complementary metal oxide semiconductor (CMOS) process. The MF microsensor contains a ring emitter, four bases, and eight collectors. Sentaurus TCAD was used to simulate the microsensor characterization. The STI (shallow trench isolation) oxide in the process was used to limit the current direction and reduce leakage current. The microsensor produces a voltage difference once it senses a magnetic field. An amplifier circuitry magnifies voltage difference into a voltage output. Experiments reveals that the MF microsensor has a sensitivity of 1.45 V/T along the x-axis and a sensitivity of 1.37 V/T along the y-axis.

High frequency passive micro-magnetic sensor based on surface acoustic wave transponder and giant magnetoimpedance sensitive element

This paper presents a high frequency micro-magnetic field sensor composed of a surface acoustic wave (SAW) transponder and a giant magnetoimpedance (GMI) sensitive element. The coupling-of-mode(COM) method is used to design and optimize the structure of the SAW transponder. An amorphous wire as the GMI element is used to conjunct with the SAW transponder. The experiment result shows the magnetic sensitivity of the sensor of 1.13dB/Oe changes when the magnetic sensitivity does not exceed 2.0Oe. For the two-dimension intensity measurement of the magnetic field, a two-dimension SAW-GMI sensor is developed and tested.

The Non-Destructive Test of Steel Corrosion in Reinforced Concrete Bridges Using a Micro-Magnetic Sensor.

This paper presents a non-destructive test method for steel corrosion in reinforced concrete bridges by using a 3-dimensional digital micro-magnetic sensor to detect and analyze the self-magnetic field leakage from corroded reinforced concrete. The setup of the magnetic scanning device and the measurement mode of the micro-magnetic sensor are introduced. The numerical analysis model is also built based on the linear magnetic charge theory. Compared to the self-magnetic field leakage data obtained from magnetic sensor-based measurement and numerical calculation, it is shown that the curves of tangential magnetic field at different lift-off height all intersect near the edge of the steel corrosion zone. The result indicates that the intersection of magnetic field curves can be used to detect and evaluate the range of the inner steel corrosion in engineering structures. The findings of this work propose a new and effective non-destructive test method for steel corrosion, and therefore enlarge the application of the micro-magnetic sensor.

Enhanced high-frequency magneto-impedance response of melt-extracted Co69.25Fe4.25Si13B13.5 microwires subject to Joule annealing

We report an enhancement of low-field, high-frequency magneto-impedance (MI) response and circumferential domain structures of melt-extracted amorphous Co69.25Fe4.25Si13B13.5 microwires by dc Joule annealing. The current amplitudes of 5 mA, 10 mA, and 20 mA were applied to amorphous microwires for different time treatments. The magnetic field dependence of impedance and circumferential domain structure of the microwires were explored using an impedance analyzer over a high frequency range (20 MHz–1000 MHz) and magnetic force microscopy (MFM), respectively. Consequently, the optimum value of 5 mA current for 20 min markedly improved the MI ratio up to 610% (1.7 times of 380% from the as-cast state) at a working frequency of 20 MHz. Moreover, the magnetic field sensitivity has been achieved up to 500%/Oe (more than two times of 225%/Oe from the as-cast one) at a frequency of 40 MHz. MFM images clearly show the development of a well-defined circumferential domain structure of the annealed microwire comparing with the as-cast one. The improvement of the high-frequency MI response in Co-rich amorphous microwires is promising for sensitive magnetic microsensors for low field detection.

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.

Enhancement of metal coil quality on selective p-silicon based planar electromagnetic coil by thermal annealing process

In this paper we report an optimization of metal quality of planar MEMS electromagnetic coil through thermal annealing process. The study aims to see the effects of annealing process on the quality of metal layer deposited on localized p-type silicon regions. Two annealing process parameters namely isothermal (annealing under time variations in constant temperature) and isochronal (annealing under temperature variations at constant time) were performed on metal contact on highly doped Si substrate and characterized using transfer length method method by measuring the specific contact resistance źC of the metal traces. The measurement results showed that the annealing process have significant influence on physical and electrical characteristics of the metal layer. Analysis showed that the quality of metal layer was significantly improved through the annealing process after treatment at temperature variations between 425---550 °C. An optimum annealing at 525 °C for 15 min was observed and the contact resistance can be reduced significantly up to 400 %. The results also showed that the surface roughness improves while metal contact resistance decreases 40 times when the metal is annealed for more than 10 min. The planar coil structure was designed to reduce the device density of a compact magnetic micro-sensor system.

Thin-film magneto-impedance structures with very large sensitivity

Thin film-based Magneto-Impedance (MI) structures are well suited for developing highly sensitive magnetic microsensors, which can be directly integrated into microelectronic circuits. Permalloy (Py) based structures benefit from well-established preparation procedures and enhanced structural stability over amorphous based sensors. In this work we use Finite Element Method calculations to complement our previous studies on high permeability Py multilayers, in order to determine the combination of magnetic and non-magnetic layers that maximizes the MI performance in sandwiched structures. The results indicate that optimum behavior is expected when the thickness of the non-magnetic layer equals the magnetic ones. The study is performed with an open flux configuration (Py not enclosing the central non-magnetic conductor), which permits the fabrication of the complete stack of layers in a single deposition process. On the outcome of that analysis, samples with a sandwiched multilayer structure defined as [Py(100nm)/Ti(6nm)]4/Cu(400nm)/[Ti(6nm)/Py(100nm)]4 have been prepared by magnetron sputtering and photolithography, having different dimensions. They were magnetically characterized by magneto-optical Kerr effect, displaying a well-defined transversal anisotropy, and the MI was measured in a network analyzer using a microstrip test-fixture. The measured MI ratio, defined as (Z-Zmin)/Zmin×100, reaches extraordinary values of 350%, while the sensitivity, calculated as the field derivative of the MI ratio, goes up to 300%/Oe (27kΩ/T in absolute units). The MI ratio is lower than the best reported previously for amorphous CoSiB/Ag/CoSiB thin-film samples with closed-flux structure, but the sensitivity, which is the key parameter for the performance of sensors, is six times larger. These figures can be compared favorably with the ones obtained in wire-based samples, and definitely opens the way to incorporate thin-film structures in low-field MI magnetic sensors.

Magnetic Properties of Electroformed Ni and Ni-Fe for Micromagnetic MEMS Applications

This paper reports a new technique which is based on electroforming process for high permeability Ni and Ni-Fe alloy. The magnetic properties of Ni and Ni-Fe alloy are investigated as a function of plating current density via scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and vibrating sample magnetometer (VSM). Concentration-dependent kinetics is used to formulate the deposition rate and also the same is verified by using finite element analysis tool COMSOL Multiphysics. Several experiments are performed to derive the relation between electroplating parameters and magnetic properties. The process conditions are optimized to develop high permeability (∼16000) Ni-Fe alloy (85.71–14.29 %). The higher current density shows a monotonically increasing behavior of relative permeability (μ r ). In addition, the B-H curves indicate that the saturation magnetization (B s a t ) increases and coercivity decreases with increasing plating current density. Our experimental data confirms that the higher current density increase the softness of Ni. The observed properties of Ni and Ni-Fe based on experimental results can be used to study the magnetic behavior of micromagnetic sensors and large force actuators.

Impact of Metallurgical Size Effects on Plasticity of Thin Metallic Materials

Three examples involving size effects are presented with implications concerning the formability: small Ni-20wt.%Cr resistive bridges, magnetic micro-sensors performed with (Ni, Co, Fe) based alloys and copper clad aluminum thin wires. The mechanical properties are directly linked to the ratio thickness over grain size (t/d ratio) of the parts. These metallurgical considerations must be taken into account when we are concerned by the numerical simulation of the process of such components. It is shown that the simulations can correctly reproduce the softening effect linked to a decrease in thickness and in number of grains across the thickness: the quality of the final shape strongly depends on the number of grains across the thickness. Finally the effect of a moderate increase in temperature on these results will be briefly reported.

(Invited) Micromolding of NiFe and Ni Thick Films for 3D Integration of MEMS

Electrodeposition process was studied in order to obtain uniformly thick magnetic films which could be incorporated in magnetic microsensors and actuators. Ni and NiFe patterns of different dimensions were deposited by micromolding on a Cu/Ti seed layer. In the case of NiFe deposit, a linear deposition rate was calculated by measuring the deposit thickness using mechanical profilometry. The optimum pattern composition for the fabrication of magnetic microdevices was 80 at. % of Ni, that was found by comparing the magnetic properties of the deposits obtained from different conditions. The deposits structure was also characterized. All the parameters were studied as a function of the current density so that by controlling the electrodeposition conditions the characteristics of the deposits could be controlled. NiFe films were integrated in multilayered magneto-impedance sensors. They present good adherence even after performing annealing at both 300°C and 500°C and sensor sensitivity reaches 10%/Oe.

Modeling and manufacturing of a micromachined magnetic sensor using the CMOS process without any post-process.

The modeling and fabrication of a magnetic microsensor based on a magneto-transistor were presented. The magnetic sensor is fabricated by the commercial 0.18 μm complementary metal oxide semiconductor (CMOS) process without any post-process. The finite element method (FEM) software Sentaurus TCAD is utilized to analyze the electrical properties and carriers motion path of the magneto-transistor. A readout circuit is used to amplify the voltage difference of the bases into the output voltage. Experiments show that the sensitivity of the magnetic sensor is 354 mV/T at the supply current of 4 mA.