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Paulo P. Freitas - One of the best experts on this subject based on the ideXlab platform.
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Optimization of the Gap Size of Flux Concentrators: Pushing Further on Low Noise Levels and High Sensitivities in Spin-Valve Sensors
IEEE Transactions on Magnetics, 2019Co-Authors: Marília Silva, Susana Cardoso, Diana C. Leitao, João J. R. Fraústo Da Silva, Paulo P. FreitasAbstract: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.
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Ultra-Compact 100 × 100 μm2 Footprint Hybrid Device with Spin-Valve Nanosensors
MDPI AG, 2015Co-Authors: Diana C. Leitao, Susana Cardoso, Paulo Coelho, Jerome Borme, Simon Knudde, Paulo P. FreitasAbstract: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
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Article Ultra-Compact 100 × 100 µm2 Footprint Hybrid Device with Spin-Valve Nanosensors
2015Co-Authors: Diana C. Leitao, Susana Cardoso, Paulo P. Freitas, Paulo Coelho, Jerome Borme, Simon Knudde, Vittorio M. N. PassaroAbstract: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 µm2 pixel sensors can be integrated in modular devices for surface mapping without moving parts
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Field Detection in Spin Valve Sensors Using CoFeB/Ru Synthetic-Antiferromagnetic Multilayers as Magnetic Flux Concentrators
IEEE Transactions on Magnetics, 2012Co-Authors: Diana C. Leitao, Susana Cardoso, Luis Gameiro, Ana V. Silva, Paulo P. FreitasAbstract: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 (χ = 196 for SAF vs. χ = 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 ~ 61 nT/Hz0.5 for single spin valve sensors down to ~ 1.8 nT/Hz0.5 when CZN Concentrators with a steep-profile are used.
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Three dimensional magnetic Flux Concentrators with improved efficiency for magnetoresistive sensors
Journal of Applied Physics, 2011Co-Authors: Zita Marinho, R C Chaves, Susana Cardoso, Ricardo Ferreira, L.v. Melo, Paulo P. FreitasAbstract:Three dimensional (3D) magnetic Flux Concentrators (FC) based on 7000-A-thick Co86Zr5Nb9 films were optimized for increased sensitivity in hybrid Flux guide-magnetoresistive sensor structures. The vertical profile of the Flux guide patterned by lift-off was replaced by a 3D structure where the sensor is recessed from the FC with a controlled edged slope defined by ion milling at controlled angles (20°, 45°, 60°, 75°, and 85°). In this work, spin valve linear sensors (3 × 14 μm2) with initial sensitivity of 0.084%/Oe were integrated with the Flux guides patterned with these 3D tapered profiles. Optimized Flux guides with 45° slope could increase the sensitivity up to 7.4%/Oe, corresponding to a concentrator Flux gain of ∼100.
P P Freitas - One of the best experts on this subject based on the ideXlab platform.
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improved efficiency of tapered magnetic Flux Concentrators with double layer architecture
IEEE Transactions on Magnetics, 2017Co-Authors: Joao Valadeiro, D C Leitao, S Cardoso, P P FreitasAbstract:Being able to increase the sensitivity of magnetoresistive sensors, by orders of magnitude, provides a route toward challenging detection levels, and opens the way for new applications. This paper describes a novel architecture of magnetic Flux Concentrators to achieve an improved guiding efficiency, combining materials with different magnetic properties, and a vertical tapering. The novelty consists in the concentration of the magnetic Flux kept by the entire structure in a reduced cross-sectional area within the vicinity of the spinvalve sensor. Depending on the configuration of the double-layer magnetic Flux Concentrators, average sensitivity gains of $\sim 90\times$ and $\sim 400\times$ were obtained. This enhanced guiding efficiency also reduced the impact of a misalignment between the device sensing direction and the applied magnetic field, since the device performance is not compromised until a misalignment angle $\theta = 45$ °. This further stabilization may arise from the vertical tapering of the magnetic Flux concentrator, being consistent with 2-D finite-element simulations.
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field detection in spin valve sensors using cofeb ru synthetic antiferromagnetic multilayers as magnetic Flux Concentrators
IEEE Transactions on Magnetics, 2012Co-Authors: D C Leitao, S Cardoso, Luis Gameiro, Ana Roberta Vilarouca Da Silva, P P FreitasAbstract: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 (χ = 196 for SAF vs. χ = 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 ~ 61 nT/Hz0.5 for single spin valve sensors down to ~ 1.8 nT/Hz0.5 when CZN Concentrators with a steep-profile are used.
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field detection in mgo magnetic tunnel junctions with superparamagnetic free layer and magnetic Flux Concentrators
Journal of Applied Physics, 2009Co-Authors: J M Almeida, P P FreitasAbstract:Magnetic tunnel junctions (MTJs) were deposited with CoFeB free layer thickness ranging from 1.3 to 3 nm. The samples were processed with areas of 10, 100, and 1000 μm2, presented RA products of ∼10 kΩ μm2, and tunneling magnetoresistance ratio values varying from ∼10% (t=1.3 nm) to ∼210% (t=3 nm). All the samples with t<1.5 nm presented linear responses (coercivity of <1 Oe) for all the studied areas; this behavior was associated with the CoFeB free layer transition from ferromagnetic to superparamagnetic. Noise measurements made in samples with superparamagnetic free layer showed negligible magnetic noise in the sensitive region. The sensitivity loss caused by the reduced free layer thickness was partially recovered using magnetic Flux Concentrators (MFCs). The MFC had a maximum gain of ∼3, a limited value to ensure a uniform gain for the MTJs with larger area (up to 1000 μm2). The MFC’s influence on the sensor’s noise behavior appears to increase with the sensor area, for both white noise background an...
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control of hysteretic behavior in Flux Concentrators
Applied Physics Letters, 2009Co-Authors: I G Trindade, D C Leitao, S Cardoso, Y G Pogorelov, J B Sousa, R C Chaves, P P FreitasAbstract:The magnetic states of Flux Concentrators (FCs), consisting of poles and yokes with lateral dimensions in the range of 100 μm and integrating either single layer films of amorphous alloys of Cox(Zr–Nb)1−x with x=90 and x=88 or a synthetic antiferromagnet (SAF) of (NiFe/Ru)xn, are analyzed by Bitter pattern and magnetic force microscopy. Magnetic field sensors, placed in the gap of the FC by microfabrication processes, exhibited magnetoresistive responses strongly correlated with the magnetic states of the FC. The hysteresis of the field produced by the FC is reduced to a minimum when the SAF is used.
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improving magnetic field detection limits of spin valve sensors using magnetic Flux guide Concentrators
IEEE Transactions on Magnetics, 2007Co-Authors: Andre Guedes, S Cardoso, J M Almeida, R Ferreira, P P FreitasAbstract:The magnetic field detection limit of spin valve sensors in the thermal noise regime is improved from 1.3 nT/Hz1/2 to 0.064 nT/Hz1/2 by incorporating a Co93Zr3Nb 4 soft magnetic Flux guide concentrator structure. Linear spin valve sensors were processed down to 20times2 mum2 dimensions, with and without an additional 3500-Aring-thick Flux guide concentrator, with a magnetic Flux gain factor ranging from 5 to 20. Spin valves show a starting sensitivity of 0.2 %/Oe, improved to 3.8 %/Oe with the Flux concentrator. Noise measurements from dc to 500 kHz were performed, indicating similar noise levels with and without Flux Concentrators. In terms of magnetic field detection, sensors with Flux Concentrators show a detection limit of 2 nT/Hz1/2 at 10 Hz, compared to 47 nT/Hz1/2 without Flux Concentrators. No additional 1/f noise is measured in the spin valve sensor response upon the addition of the soft magnetic Flux Concentrators in the frequency range studied
Xixiang Zhang - One of the best experts on this subject based on the ideXlab platform.
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PicoTesla magnetic tunneling junction sensors integrated with double staged magnetic Flux Concentrators
Applied Physics Letters, 2018Co-Authors: Yiou Zhang, Lijuan Qian, Gang Xiao, Qiang Zhang, J. Carlos Santamarina, Tadeusz W Patzek, Xixiang ZhangAbstract:Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic Flux Concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the Flux Concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic Flux Concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the Flux Concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.
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picotesla magnetic tunneling junction sensors integrated with double staged magnetic Flux Concentrators
Applied Physics Letters, 2018Co-Authors: Yiou Zhang, Lijuan Qian, Gang Xiao, Qiang Zhang, Tadeusz W Patzek, Carlos J Santamarina, Xixiang ZhangAbstract:Ultra-sensitive solid-state magnetic sensors are in strong demand in many applications where currently available sensors are inadequate. We have used high performance magnetic tunneling junction (MTJ) sensors and pushed the magnetic sensing limit to a high level. We have incorporated double-staged magnetic Flux Concentrators, one on the MTJ chip level and the other on a more macroscopic level, to amplify the external field of interest. With this approach and undergoing a process of optimization on the Flux Concentrators, we have increased the sensitivity of the MTJ sensor by a large factor of 517 to 775.4%/Oe in terms of magnetoresistance response. The coercivity of the sensor is only 0.12 Oe. We have achieved a detectable field limit of 30 pT/Hz at 10 kHz. We have presented the noise spectrum and the sensitivity spectrum up to a maximum frequency of 100 kHz.
Alan S. Edelstein - One of the best experts on this subject based on the ideXlab platform.
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THE MEMS Flux CONCENTRATOR: POTENTIAL LOW-COST, HIGH- SENSITIVITY MAGNETOMETER
2016Co-Authors: Alan S. Edelstein, William Benard, Edmond Nowak, Greg Fischer, Shu Fan ChengAbstract:Progress on the development of a device, the MEMS Flux concentrator, for mitigating the problem of 1/f noise in magnetic sensors will be presented. The MEMS Flux concentrator essentially eliminates the effect of 1/f noise by increasing the operating frequency of the sensor to a frequency region where 1/f noise is small. This is accomplished by putting Flux Concentrators on MEMS structures whose motion modulates the magnetic field at the position of the magnetic sensor. Depending on the sensor, mitigating the effect of 1/f noise will increase the sensitivity of magnetic sensors by one to three orders of magnitude. Combining the MEMS Flux concentrator with magnetic tunnel junctions with MgO barriers should lead to low cost magnetic sensors that are able to detect 1 pT signals at 1 Hz
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Approved for public release; distribution is unlimited. The MEMS Flux Concentrator: A Device for Minimizing 1/f Noise in Magnetic Sensors
2016Co-Authors: Alan S. Edelstein, Gregory A. FischerAbstract:Magnetic sensors typically have a considerable amount of 1/f noise that limits their performance in detecting slow-moving military vehicles. Here we describe a Micro Electro-Mechanical Systems (MEMS) Flux concentrator, which is a new device that can minimize 1/f noise in magnetic sensors by modulating the magnetic field at the position of the sensor. The modulation is accomplished by a periodic motion of Flux Concentrators on each side of the magnetic sensor. Modulating the sensor field shifts the operating frequency to higher frequencies where the 1/f noise can be one or two orders of magnitude smaller. We will also present magnetic and mechanical modeling results on a design that will operate at 29 kHz. Though 1/f noise occurs in electronic devices, it also occurs in a variety of other places.1 For example, it also occurs in the stock market, emissions from quasars, highway traffic, the global temperature, and the flow of the river Nile. The subject of 1/f noise in solid-state microstructures has been review by Kirten and Uren2. Most magnetic devices, such as magnetic sensors3-5, also have a considerable amount of 1/f noise due
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Tuning magnetic nanostructures and Flux Concentrators for magnetoresistive sensors
Spintronics VIII, 2015Co-Authors: Xiaolu Yin, Yen Fu Liu, Dan Ewing, Carmen K. Ruder, Paul J. De Rego, Alan S. Edelstein, Sy_hwang LiouAbstract:The methods for the optimization of the magnetoresistive (MR) sensors are to reduce sources of noises, to increase the signal, and to understand the involved fundamental limitations. The high-performance MR sensors result from important magnetic tunnel junction (MTJ) properties, such as tunneling magnetoresistance ratio (TMR), coercivity (Hc), exchange coupling field (He), domain structures, and noise properties as well as the external magnetic Flux Concentrators. All these parameters are sensitively controlled by the magnetic nanostructures, which can be tuned by varying junction free layer nanostructures, geometry, and magnetic annealing process etc. In this paper, we discuss some of efforts that an optimized magnetic sensor with a sensitivity as high as 5,146 %/mT. This sensitivity is currently the highest among all MR-type sensors that have been reported. The estimated noise of our magnetoresistive sensor is 47 pT/Hz1/2 at 1 Hz. This magnetoresistance sensor dissipates only 100 μW of power while operating under an applied voltage of 1 V at room temperature.
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Macro-magnetic Modeling of the ARL Microelectromechanical System (MEMS) Flux Concentrator
2011Co-Authors: Gregory A. Fischer, Alan S. EdelsteinAbstract:Abstract : Magnetic Flux Concentrators are soft magnetic materials typically used to focus magnetic field lines in an effort to increase the sensitivity of a magnetic sensor. The use of magnetoresistive sensors, especially given the recent development of magnetic tunnel junctions (MTJ) with magnesium oxide (MgO) barriers exhibiting magnetoresistance values as large as 400%, has created interest in Flux Concentrators as an avenue to not only increase sensitivity but also mitigate the 1/function noise that is prevalent in these devices at low frequencies. Here we describe the magnetic modeling performed at the U.S. Army Research Laboratory (ARL) that has facilitated the development of the microelectromechanical system (MEMS) Flux concentrator, a device that uses magnetic Flux Concentrators deposited on MEMS structures that modulate low frequency signals at the position of the sensor, essentially shifting the signal of interest to a frequency range in which 1/function noise is much lower. We present magnetic modeling results of various designs, including our current design, focusing on key design elements.
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Magnetic Modeling of a Rotating Flux Concentrator System Designed to Mitigate Noise in Large Magnetic Sensors
2010Co-Authors: Gregory A. Fischer, Alan S. EdelsteinAbstract:Abstract : This report discusses the magnetic modeling results of a proof of concept system for 1/f noise mitigation in "large" sensors. The 1/f noise reduction is achieved by rotating Flux Concentrators that shift the operating frequency of the sensor to higher frequencies where 1/f noise is lower. The goal is to design systems with magnetic Flux Concentrators that maximize the enhancement of the field and the percentage modulation of the field but minimize size. These issues in execution and necessary tradeoffs in performance are discussed, and magnetic modeling is presented, showing a clear road map to increased performance from the viewpoint of field enhancement and modulation.
Susana Cardoso - One of the best experts on this subject based on the ideXlab platform.
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Optimization of the Gap Size of Flux Concentrators: Pushing Further on Low Noise Levels and High Sensitivities in Spin-Valve Sensors
IEEE Transactions on Magnetics, 2019Co-Authors: Marília Silva, Susana Cardoso, Diana C. Leitao, João J. R. Fraústo Da Silva, Paulo P. FreitasAbstract: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.
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Ultra-Compact 100 × 100 μm2 Footprint Hybrid Device with Spin-Valve Nanosensors
MDPI AG, 2015Co-Authors: Diana C. Leitao, Susana Cardoso, Paulo Coelho, Jerome Borme, Simon Knudde, Paulo P. FreitasAbstract: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
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Article Ultra-Compact 100 × 100 µm2 Footprint Hybrid Device with Spin-Valve Nanosensors
2015Co-Authors: Diana C. Leitao, Susana Cardoso, Paulo P. Freitas, Paulo Coelho, Jerome Borme, Simon Knudde, Vittorio M. N. PassaroAbstract: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 µm2 pixel sensors can be integrated in modular devices for surface mapping without moving parts
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Field Detection in Spin Valve Sensors Using CoFeB/Ru Synthetic-Antiferromagnetic Multilayers as Magnetic Flux Concentrators
IEEE Transactions on Magnetics, 2012Co-Authors: Diana C. Leitao, Susana Cardoso, Luis Gameiro, Ana V. Silva, Paulo P. FreitasAbstract: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 (χ = 196 for SAF vs. χ = 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 ~ 61 nT/Hz0.5 for single spin valve sensors down to ~ 1.8 nT/Hz0.5 when CZN Concentrators with a steep-profile are used.
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Three dimensional magnetic Flux Concentrators with improved efficiency for magnetoresistive sensors
Journal of Applied Physics, 2011Co-Authors: Zita Marinho, R C Chaves, Susana Cardoso, Ricardo Ferreira, L.v. Melo, Paulo P. FreitasAbstract:Three dimensional (3D) magnetic Flux Concentrators (FC) based on 7000-A-thick Co86Zr5Nb9 films were optimized for increased sensitivity in hybrid Flux guide-magnetoresistive sensor structures. The vertical profile of the Flux guide patterned by lift-off was replaced by a 3D structure where the sensor is recessed from the FC with a controlled edged slope defined by ion milling at controlled angles (20°, 45°, 60°, 75°, and 85°). In this work, spin valve linear sensors (3 × 14 μm2) with initial sensitivity of 0.084%/Oe were integrated with the Flux guides patterned with these 3D tapered profiles. Optimized Flux guides with 45° slope could increase the sensitivity up to 7.4%/Oe, corresponding to a concentrator Flux gain of ∼100.