Road infrastructure plays a critical role in the support and development of the Cooperative Intelligent Transport Systems (C-ITS) paradigm. Roadside Units (RSUs), equipped with vehicular communication capabilities, traffic radars, cameras, and other sensors, can provide a multitude of vehicular services and enhance the cooperative perception of vehicles on the road, leading to increased road safety and traffic efficiency. Moreover, the central C-ITS system responsible for overseeing the road traffic and infrastructure, such as the RSUs, needs an efficient way of collecting and disseminating important information to road users. Warnings of accidents or other dangers, and other types of vehicular services such as Electronic Toll Collection (ETC), are examples of the types of information that the central C-ITS system is responsible for disseminating. To remedy these issues, we present the design of an implemented roadside and cloud architecture for the support of C-ITS services. With the main objectives of managing Vehicle-to-Everything (V2X) communication units and network messages of a public authority or motorway operator acting as a central C-ITS system, the proposed architecture was developed for different mobility testbeds in Portugal, under the scope of the STEROID research project and the pan-European Connected Roads (C-Roads) initiative. RSUs, equipped with ETSI ITS-G5 communications, are deployed with a cellular link or fiber optics connection for remote control and configuration. These are connected to a cloud Message Queuing Telemetry Transport (MQTT) broker where communication is based on a geographical tiling scheme, which allows the selection of the appropriate coverage areas for the dissemination of C-ITS messages. The architecture is deployed in the field, on several Portuguese motorways, where road traffic and infrastructure are monitored through a C-ITS platform with visualization and event reporting capabilities. The provided architecture is independent of the underlying communication technology and can be easily adapted in the future to support Cellular-V2X (PC5 interface) or 5G RSUs. Performance results of the deployed architecture are provided.

Perpendicular magnetic tunnel junctions (p-MTJs) attract great interest because of their excellent performance in spin-transfer-torque magnetic random access memories (STT-MRAMs). The annealing process is critical to achieve the required structural and magnetic properties, therefore obtaining high perpendicular tunneling magnetoresistance (p-TMR) and lower switching current. In this work, the CoFeB/MgO/CoFeB-based p-TMR stack was prepared and a high p-TMR value of 155.9% was obtained from CIPT. The p-MTJs were patterned with pillar sizes ranging from 50 nm to 1000 nm and were annealed upon different annealing temperatures (T-A) of 300 and 340 degrees C. The resistance at parallel (R-P) and antiparallel (R-AP) state in p-MTJs was obtained upon the application of a +/- 30 mT perpendicular magnetic field, where the angle of magnetization between storage and reference layer at memory state, theta(P) and theta(AP), were derived from the P and AP resistance ratios with and without magnetic field. The condition theta(P)= theta(AP) of about 63.5 degrees was found in as-deposited samples, indicating a ferromagnetic interlayer coupling between storage and reference layers, where theta(P)= 0 degrees and theta(AP)= 180 degrees at T-A= 300 degrees C and 340 degrees C demonstrate a stable memory state. The stability of the resistance state was modeled by considering the evolution of effective perpendicular magnetic anisotropy (K-eff) and interlayer coupling constant (J), showing a method to evaluate the ratio of K-eff/J via the memory state resistance characterization, where the K-eff/J of about -1.26 was obtained in our as-deposited samples. Our study assesses the effect of T-A on the theta(P) and theta(AP) and supplies the method to enhance the stability through the optimization of perpendicular magnetic anisotropy and interlayer coupling, so to better control the performance of p-MTJ-based STT-MRAMs.

Perpendicular magnetic tunnel junctions (p-MTJs) have been explored for spin transfer torque magnetic random access memory devices (STT-MRAMs). The current-induced switching (CIS) of the p-MTJs requires a relatively high current density (J); thereby, very thin insulating barriers are required, consequently increasing the risk of non-tunneling conduction mechanisms through the MgO film. In this work, we fabricated CoFeB/MgO/CoFeB p-MTJs and studied the CIS characteristics, with the obtained switching current densities of about 2 × 1010 A/m2. The filament conduction through the MgO film was induced by applying a high set current (Iset) until a significant decrease in the resistance (R) is observed. A decrease in R with increasing current (I) for parallel (P) and antiparallel (AP) states was observed. In contrast, an increase in R with the increasing I value was observed for filament p-MTJs. We used a two-channel model to extract the filament resistance (Rf) and filament current (If). The Rf dependence on the electrical power (Pf) was linearly fitted, and a heating coefficient β of about 6%/mW was obtained, which was much higher than 0.15%/mW obtained from the bulk metallic multilayers of the top electrode. The CIS for filament p-MTJs was modeled by considering the bias dependence of the tunneling and the thermal dependence of Rf, showing a significant change in the CIS curves and switching currents. Our study addresses the effect of filament conduction on the tunneling current of CoFeB/MgO/CoFeB p-MTJs, critical for the design and control of the p-MTJ based devices, such as STT-MRAMs.

Optically detectable labels and probes are commonly used in bioapplications. Together with the miniaturization of analytical platforms based on microfluidic technology, with tuneable properties, they yield unparalleled opportunities towards faster, cheaper and more efficient biomolecule analysis. This work describes the preparation and testing of uniformly shaded polydimethylsiloxane (PDMS) membranes and microfluidic devices used to enhance or inhibit optical detection of fluorescent labels. The uniformly pigmented black-PDMS nanocomposite mixtures have been prepared by adding a known quantity of black pigment to PDMS, and its optical, spectroscopic and morphological properties have been characterized. The effect of pigment-to-DMS mixing ratio has been investigated by Ultra-Violet/Visible, near infrared and middle infrared spectroscopies; scanning electron microscopy and atomic force microscopy; and contact angle measurements. The results demonstrate that optical and spectroscopic properties of black-PDMS are strongly altered with the progressive inclusion of black pigment while wetting behaviour and morphology are maintained. Surface contact angle decreases more prominently with the decreasing ratio of DMS-to-curing agent than for the inclusion of pigment nanocomposite in the mixture. The ability to tune optical properties of PDMS has been experimentally demonstrated in a Black-PDMS nanocomposite microfluidic chip cast and bonded to glass. The results show double the signal-to-noise in fluorescence images as compared to pure PDMS devices, demonstrating a very promising integrated optical detection strategy for portable microfluidic systems.

Spintronic nanodevices are consolidating a highly reputed position in advanced manufacturing industry, not only due to progresses in magnetic hard disk sensors, but also the memory market. The ability to integrate magnetic thin films on large area wafers and subsequent nanofabrication into functional devices is key for such success. This work describes methodologies used for definition of sub-100 nm pillars, using reliable via opening to contact nanopillars buried in a dielectric film. A two consecutive step electron beam lithography process is used to fabricate current-perpendicular-to plane nanodevices. The first step is required to pattern nanopillars down to 30 nm. The second provides access to nanopillar top through nanovias definition and reactive ion etching. Optimum alignment of multilevel exposures ensures the most accurate positioning in the shortest time. Most importantly, the results are obtained on 150 mm diameter wafers, where additional challenges of uniformity of resists, oxides and metals are critical for end-point control and improved yield of fabricated devices. The design of customized test structures allowed control of etching end-point. (C) 2018 The Society of Manufacturing Engineers. Published by Elsevier Ltd. All rights reserved.

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 similar to 1.4 Omega mu m(2) and both free layer and barrier are patterned down to a 90 x 180 nm(2) 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.

Ultrasensitive magnetic field sensors envisaged for applications on biomedical imaging require the detection of low-intensity and low-frequency signals. Therefore linear magnetic sensors with enhanced sensitivity low noise levels and improved field detection at low operating frequencies are necessary. Suitable devices can be designed using magnetoresistive sensors, with room temperature operation, adjustable detected field range, CMOS compatibility and cost-effective production. The advent of spintronics set the path to the technological revolution boosted by the storage industry, in particular by the development of read heads using magnetoresistive devices. New multilayered structures were engineered to yield devices with linear output. We present a detailed study of the key factors influencing MR sensor performance (materials, geometries and layout strategies) with focus on different linearization strategies available. Furthermore strategies to improve sensor detection levels are also addressed with best reported values of similar to 40 pT/root Hz at 30 Hz, representing a step forward the low field detection at room temperature.

In vivo experiments to detect the neuronal magnetic field require high-sensitivity magnetoresistive sensors incorporated in micromachined silicon probes that do not damage the organic tissues and enhance the sensors proximity to the signal sources. When in touch with the tissues, the probe experiences a mechanical stress induced by an unavoidable bending moment. To evaluate its impact on sensor performance, the transfer curves and the noise level were measured for different applied stresses. A saturation field reduction (increase) was observed upon a compressive (tensile) stress as a consequence of the magnetostrictive effect, while the magnetoresistance value remained constant. Besides the clear influence of magnetostricition in the sensor transfer curves, no significant changes in the noise level were obtained, which will not affect the experiment feasibility.

The ability to detect the magnetic fields that surround us has promoted vast technological advances in sensing techniques. Among those, magnetoresistive sensors display an unpaired spatial resolution. Here, we successfully control the linear range of nanometric sensors using an interfacial exchange bias sensing layer coupling. An effective matching of material properties and sensor geometry improves the nanosensor performance, with top sensitivities of 3.7% mT(-1). The experimental results are well supported by 3D micromagnetic and magneto-transport simulations.

Magnetic tunnel junctions with exchange biased sensing-layer provide a promising solution for nanoscale sensors with improved spatial resolution [1]. In order to design optimized sensors a complete micromagnetic model for a double exchange MTJ stack with coupled magneto-transport was established.

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 × 130 nm- 120 nm × 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 ~1%/mT up to ~2%/mT is observed with the use of a CoFe/CoFeB/Ta/NiFe/MnIr free-layer. The sensitivity values are almost independent on the size for circular devices, consistent with a linear operation range dominated by the exchange field strength. For elliptical devices, a high sensitivity is also observed, although displaying a dependence on the size, due to a competition with the demagnetizing field. The low-frequency noise features were also addressed revealing a detectivity in the tens of μT/√Hz with Hooge parameters within 1-3 × 10 -9 μm 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.

Highly sensitive nanosensors with high spatial resolution provide the necessary features for high accuracy imaging of isolated magnetic nanoparticles. In this work, we report the fabrication and characterization of MgO-barrier magnetic tunnel junction nanosensors, with two exchange-pinned electrodes. The perpendicular magnetization configuration for field sensing is set using a two-step annealing process, where the second annealing temperature was optimized to yield patterned sensors responses with improved linearity. The optimized circular nanosensors show sensitivities up to 0.1%/Oe, larger than previously reported for nanometric sensors and comparable to micrometric spin-valves. Our strategy avoids the use of external permanent biasing or demagnetizing fields (large for smaller structures) to achieve a linear response, enabling the control of the linear operation range using only the stack and thus providing a small footprint device.

This work provides a systematic simulation study of magnetic tunnel junction (MTJ) nanodevices behavior, consisting of a multilayered stack incorporating an in-plane CoFeB free layer and a synthetic antiferromagnetic CoFe-based pinned layer, and including exchange and interlayer couplings. A finite element tool is used to simulate both the magnetic and magneto-transport behaviors of these MTJ nanopillars with distinct geometries, namely circles with diameter ranging from 20nm up to 250nm and ellipses with aspect ratios of 1/2, 1/3 and 1/5, corresponding to sizes from 20×40nm2 up to 50×250nm2. This study envisages two clear applications for nanopillars: memory and sensor devices. We address the impact of the nanopillar size on the coercivity and saturation field, as figures of merit for device performance. In particular a competitive sensitivity of 0.15%/Oe is envisaged for sensors with a size of 50×100nm2. Our results provide a validation of this simulation method as a expedite tool to assist the nanofabrication process.

The switching field dependence on the size of nanometric magnetic tunnel junctions was studied. CoFe/Ru/CoFeB/MgO/CoFeB nanopillars were fabricated down to 150 × 300 nm2 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.

A thorough study of exposure parameters for electron beam lithography using AR7520 negative tone electron beam resist is here presented. We optimized the beam voltage, apertures diameter and resist thickness in order to achieve the smaller dimensions possible for each resist thicknesses. Monte Carlo simulations of the electrons scattering process correlated the experimental results indicating a less efficient energy deposition into the resist layer for larger beam energies and resist thicknesses, thus resulting in larger doses required to expose a selected dot size. Furthermore, for the particular exposure conditions used we determined a forward scattered electrons range between 50 nm and 170 nm, depending on the dot nominal size. On the other hand, a reduced backscattering electrons range was observed showing a constant value of ~ 560 nm, being therefore more significant when larger dimensions are exposed in a point-by-point exposure, and thus supporting the smaller doses observed for larger sizes. Finally, a baking step is used to further improve the etch resistance of the resist, which allied to the optimized exposure parameters, opens a pathway to achieve sub-100nm critical dimensions for the reproducible fabrication of nanometric devices using a simple lift-off method.

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.