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Magnetoresistive Sensors under Extreme Conditions

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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Physical Sensors".

Deadline for manuscript submissions: closed (15 March 2016) | Viewed by 49086

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Special Issue Editors

Prof. Dr. Susana Cardoso De Freitas

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Guest Editor

INESC-Microsistemas e Nanotecnologias (INESC-MN), 1000-029 Lisboa, Portugal
Interests: educational games; e-learning and digital education
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Paulo P. Freitas

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Guest Editor

Deputy Director-general at INL- International Iberian Nanotechnology Laboratory, Av. Mestre José Veiga, 4715-330 Braga – Portugal
Interests: magnetic tunneling junctions; non-volatile memories; magnetoresistive sensors (TMR, GMR); spintronics; biochips and biomedical applications

Special Issue Information

Dear Colleagues,

Magnetoresistive (MR) sensors can be designed with variable magnetic field linear range and detectivity (ranging from 10´s pT to 100´s mT), tailor-made geometries (from nanometer size to millimeter size), tunable resistances (in particular for TMR based sensors), can be integrated with CMOS on back-end of the line processes, and are compatible with a wide range of substrate materials (including flexible substrates). MR sensor technology is permeating several application areas, from electronic magnetic compasses, speed/position sensors, magnetic NP and current scanners, to hard disk drives, biochips, and other biomedical applications.

MR sensor technology is being pushed to new areas and limits, such as applications requiring high sensitivity and good spatial resolution (for example in buried defect detection for non-destructive testing), applications requiring high performance in stretchable substrates, and applications in biomedical imaging and neurosciences requiring pT detectivities at RT and low frequencies.

The aim of this Special Issue is to bring together new developments in various areas related to the technology and applications of magnetoresistive sensors pushed to limiting conditions. Challenges concerning fabrication, integration and performance optimization of MR sensors when targeting specific application under highly demanding operational conditions are discussed in this special issue, including but not limited to:

-          Conformal surface mapping, magnetic scanners, non-destructive testing of non-conventional surfaces
-          Flexible electronics, wearable devices
-          Magnetic recording, read heads for high density information, nanosensors
-          Industrial electronics including automotive (current, position, angle)
-          Low power, wireless, wearable applications
-          Smart packaging, 3D integration, ultra-compact devices, material deposition over large area wafers
-          hybrid sensors (e.g., combining magnetoresistance with optical, microfluidics, MEMS, energy harvesting blocks)

Submissions should clearly indicate which challenges in magnetoresistive sensors the work is addressing. Authors are invited to contact the Guest Editors prior to submission if they are uncertain whether their work falls within the general scope of this Special Issue.

Prof. Dr. Susana Cardoso de Freitas
Prof. Dr. Paulo P. Freitas
Guest Editors

Manuscript Submission Information

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Keywords

magnetoresistive sensors
ultra-low field detection
high frequency
low power devices
high thermal stability
cmos integration
wireless devices
biomedical applications

Published Papers (7 papers)

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Research

749 KiB

Open AccessArticle

Tunnel Magnetoresistance Sensors with Magnetostrictive Electrodes: Strain Sensors

by Ali Tavassolizadeh, Karsten Rott, Tobias Meier, Eckhard Quandt, Hendrik Hölscher, Günter Reiss and Dirk Meyners

Sensors 2016, 16(11), 1902; https://doi.org/10.3390/s16111902 - 11 Nov 2016

Cited by 31 | Viewed by 8248

Abstract

Magnetostrictive tunnel magnetoresistance (TMR) sensors pose a bright perspective in micro- and nano-scale strain sensing technology. The behavior of TMR sensors under mechanical stress as well as their sensitivity to the applied stress depends on the magnetization configuration of magnetic tunnel junctions (MTJ)s with respect to the stress axis. Here, we propose a configuration resulting in an inverse effect on the tunnel resistance by tensile and compressive stresses. Numerical simulations, based on a modified Stoner–Wohlfarth (SW) model, are performed in order to understand the magnetization reversal of the sense layer and to find out the optimum bias magnetic field required for high strain sensitivity. At a bias field of −3.2 kA/m under a

0.2 \times 10^{- 3}

strain, gauge factors of 2294 and −311 are calculated under tensile and compressive stresses, respectively. Modeling results are investigated experimentally on a round junction with a diameter of

30 \pm 0.2

μ

m using a four-point bending apparatus. The measured field and strain loops exhibit nearly the same trends as the calculated ones. Also, the gauge factors are in the same range. The junction exhibits gauge factors of

2150 \pm 30

and −260 for tensile and compressive stresses, respectively, under a −3.2 kA/m bias magnetic field. The agreement of the experimental and modeling results approves the proposed configuration for high sensitivity and ability to detect both tensile and compressive stresses by a single TMR sensor. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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1999 KiB

Open AccessArticle

Sensitivity and 3 dB Bandwidth in Single and Series-Connected Tunneling Magnetoresistive Sensors

by Michał Dąbek, Piotr Wiśniowski, Tomasz Stobiecki, Jerzy Wrona, Susana Cardoso and Paulo P. Freitas

Sensors 2016, 16(11), 1821; https://doi.org/10.3390/s16111821 - 31 Oct 2016

Cited by 6 | Viewed by 5108

Abstract

As single tunneling magnetoresistive (TMR) sensor performance in modern high-speed applications is limited by breakdown voltage and saturation of the sensitivity, for higher voltage applications (i.e., compatible to 1.8 V, 3.3 V or 5 V standards) practically only a series connection can be applied. Thus, in this study we focused on sensitivity, 3 dB bandwidth and sensitivity-bandwidth product (SBP) dependence on the DC bias voltage in single and series-connected TMR sensors. We show that, below breakdown voltage, the strong bias influence on sensitivity and the 3 dB frequency of a single sensor results in higher SBP than in a series connection. However, the sensitivity saturation limits the single sensor SBP which, under 1 V, reaches the same level of 2000 MHz∙V/T as in a series connection. Above the single sensor breakdown voltage, linear sensitivity dependence on the bias and the constant 3 dB bandwidth of the series connection enable increasing its SBP up to nearly 10,000 MHz∙V/T under 5 V. Thus, although by tuning bias voltage it is possible to control the sensitivity-bandwidth product, the choice between the single TMR sensor and the series connection is crucial for the optimal performance in the high frequency range. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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2319 KiB

Open AccessArticle

Exchange Bias Tuning for Magnetoresistive Sensors by Inclusion of Non-Magnetic Impurities

by Parikshit Pratim Sharma, Edoardo Albisetti, Marco Monticelli, Riccardo Bertacco and Daniela Petti

Sensors 2016, 16(7), 1030; https://doi.org/10.3390/s16071030 - 04 Jul 2016

Cited by 27 | Viewed by 6117

Abstract

The fine control of the exchange coupling strength and blocking temperature ofexchange bias systems is an important requirement for the development of magnetoresistive sensors with two pinned electrodes. In this paper, we successfully tune these parameters in top- and bottom-pinned systems, comprising 5 nm thick Co₄₀Fe₄₀B₂₀ and 6.5 nm thick Ir₂₂Mn₇₈ films. By inserting Ru impurities at different concentrations in the Ir₂₂Mn₇₈ layer, blocking temperatures ranging from 220 °C to 100 °C and exchange bias fields from 200 Oe to 60 Oe are obtained. This method is then applied to the fabrication of sensors based on magnetic tunneling junctions consisting of a pinned synthetic antiferromagnet reference layer and a top-pinned sensing layer. This work paves the way towards the development of new sensors with finely tuned magnetic anisotropies. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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6171 KiB

Open AccessArticle

Optimal Magnetic Sensor Vests for Cardiac Source Imaging

by Stephan Lau, Bojana Petković and Jens Haueisen

Sensors 2016, 16(6), 754; https://doi.org/10.3390/s16060754 - 24 May 2016

Cited by 9 | Viewed by 6633

Abstract

Magnetocardiography (MCG) non-invasively provides functional information about the heart. New room-temperature magnetic field sensors, specifically magnetoresistive and optically pumped magnetometers, have reached sensitivities in the ultra-low range of cardiac fields while allowing for free placement around the human torso. Our aim is to optimize positions and orientations of such magnetic sensors in a vest-like arrangement for robust reconstruction of the electric current distributions in the heart. We optimized a set of 32 sensors on the surface of a torso model with respect to a 13-dipole cardiac source model under noise-free conditions. The reconstruction robustness was estimated by the condition of the lead field matrix. Optimization improved the condition of the lead field matrix by approximately two orders of magnitude compared to a regular array at the front of the torso. Optimized setups exhibited distributions of sensors over the whole torso with denser sampling above the heart at the front and back of the torso. Sensors close to the heart were arranged predominantly tangential to the body surface. The optimized sensor setup could facilitate the definition of a standard for sensor placement in MCG and the development of a wearable MCG vest for clinical diagnostics. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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2207 KiB

Open AccessArticle

A Novel Attitude Estimation Algorithm Based on the Non-Orthogonal Magnetic Sensors

by Jianliang Zhu, Panlong Wu and Yuming Bo

Sensors 2016, 16(5), 730; https://doi.org/10.3390/s16050730 - 19 May 2016

Cited by 10 | Viewed by 4369

Abstract

Because the existing extremum ratio method for projectile attitude measurement is vulnerable to random disturbance, a novel integral ratio method is proposed to calculate the projectile attitude. First, the non-orthogonal measurement theory of the magnetic sensors is analyzed. It is found that the projectile rotating velocity is constant in one spinning circle and the attitude error is actually the pitch error. Next, by investigating the model of the extremum ratio method, an integral ratio mathematical model is established to improve the anti-disturbance performance. Finally, by combining the preprocessed magnetic sensor data based on the least-square method and the rotating extremum features in one cycle, the analytical expression of the proposed integral ratio algorithm is derived with respect to the pitch angle. The simulation results show that the proposed integral ratio method gives more accurate attitude calculations than does the extremum ratio method, and that the attitude error variance can decrease by more than 90%. Compared to the extremum ratio method (which collects only a single data point in one rotation cycle), the proposed integral ratio method can utilize all of the data collected in the high spin environment, which is a clearly superior calculation approach, and can be applied to the actual projectile environment disturbance. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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3671 KiB

Open AccessArticle

A Magnetoresistive Tactile Sensor for Harsh Environment Applications

by Ahmed Alfadhel, Mohammed Asadullah Khan, Susana Cardoso, Diana Leitao and Jürgen Kosel

Sensors 2016, 16(5), 650; https://doi.org/10.3390/s16050650 - 07 May 2016

Cited by 37 | Viewed by 11021

Abstract

A magnetoresistive tactile sensor is reported, which is capable of working in high temperatures up to 140 °C. Hair-like bioinspired structures, known as cilia, made out of permanent magnetic nanocomposite material on top of spin-valve giant magnetoresistive (GMR) sensors are used for tactile sensing at high temperatures. The magnetic nanocomposite, consisting of iron nanowires incorporated into the polymer polydimethylsiloxane (PDMS), is very flexible, biocompatible, has high remanence, and is also resilient to antagonistic sensing ambient. When the cilia come in contact with a surface, they deflect in compliance with the surface topology. This yields a change of the GMR sensor signal, enabling the detection of extremely fine features. The spin-valve is covered with a passivation layer, which enables adequate performance in spite of harsh environmental conditions, as demonstrated in this paper for high temperature. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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6919 KiB

Open AccessArticle

Ultra-Compact 100 × 100 μm² Footprint Hybrid Device with Spin-Valve Nanosensors

by Diana C. Leitao, Paulo Coelho, Jerome Borme, Simon Knudde, Susana Cardoso and Paulo P. Freitas

Sensors 2015, 15(12), 30311-30318; https://doi.org/10.3390/s151229809 - 04 Dec 2015

Cited by 13 | Viewed by 6944

Abstract

Magnetic field mapping with micrometric spatial resolution and high sensitivity is a challenging application, and the technological solutions are usually based on large area devices integrating discrete magnetic flux guide elements. In this work we demonstrate a high performance hybrid device with improved field sensitivity levels and small footprint, consisting of a ultra-compact 2D design where nanometric spin valve sensors are inserted within the gap of thin-film magnetic flux concentrators. Pole-sensor distances down to 400 nm are demonstrated using nanofabrication techniques combined with an optimized liftoff process. These 100 × 100 μm 2 pixel sensors can be integrated in modular devices for surface mapping without moving parts. Full article

(This article belongs to the Special Issue Magnetoresistive Sensors under Extreme Conditions)

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