Jo De Boeck

On-chip magnetic particle transport by alternating magnetic field gradients

We have demonstrated an on-chip magnetic bead transport device based on a set of two tapered current conductors. We have fabricated and tested two types of devices. Both devices are capable of trapping single magnetic microbeads and guiding them along a defined magnetic track. We examined scaling of the basic repetitive element and found good agreement among experiment, theory, and simulations. This novel magnetic transport mechanism opens possibilities for controlled manipulation of magnetically labeled biomolecules.

Highly efficient room temperature spin injection in a metal-insulator-semiconductor light-emitting diode

We demonstrate highly efficient spin injection at low and room temperature in an AlGaAs/GaAs semiconductor heterostructure from a CoFe/AlOX tunnel spin injector. We use a double-step oxide deposition for the fabrication of a pinhole-free AlOX tunnel barrier. The measurements of the circular polarization of the electroluminescence in the Oblique Hanle Effect geometry reveal injected spin polarizations of at least 24% at 80 K and 12% at room temperature.

Single magnetic particle detection: Experimental verification of simulated behavior

In the past, magnetoresistive sensor based biosensors, using superparamagnetic particles, have shown to be promising candidates for highly sensitive biosensors. These sensors can detect a single micron-sized magnetic particle. For single particle detection, research groups have developed models to predict the signal per particle. In these models, the separation distance plays an important role for the quantitative determination of the signal. However, mostly only the passivation layer thickness is included as the separation distance. In this paper, we describe a detection system based on a magnetic spin-valve sensor that is capable of giving position-time information of the magnetic behavior of one single bead. The results obtained with this system for the detection of a single particle signature are then compared with simulations. For this comparison, we developed a model where an additional particle-substrate separation distance is included. This distance is determined by a force balance of the perpendi...

Hybrid magnetic-semiconductor nanostructures

Publisher Summary This chapter considers systems consisting of a semiconductor with a patterned ferromagnetic material on top of it. The electrons move in local nonhomogeneous magnetic fields that alter the orbital motion of the electrons through the Lorentz force. Such a magnetic field will also induce a shift in the energy of the electrons. Because in typical III-V semiconductors the effective g factor is small, the spin will be of secondary importance in this case. Structures are considered in which the electron (or hole) current passes through the ferromagnetic/semiconductor (FM/SC) interface. Here, one relies on spin-dependent scattering and the Zeeman spin splitting as the fundamental mechanisms on which the action of the device is based. Spin-up and spin-down electrons now become different types of carriers. Several device concepts have been proposed, including an all-metal spin transistor based on the accumulation of a spin-up or spin-down population, an analog of the electrooptic modulator based on a precession of the electron spin, and systems where one uses the FM/SC analog of the giant magnetoresistance. When the magnetic/semiconductor structures are reaching the nanoscale dimensions, effects such as Coulomb blockade may start to appear. First attempts are being made today in tunneling into magnetic clusters to observe a magnetotransport phenomenon in structures working in the Coulomb blockade regime.

Impact of seed layer on post-annealing behavior of transport and magnetic properties of Co/Pt multilayer-based bottom-pinned perpendicular magnetic tunnel junctions

The magnetic and transport properties of Co/Pt multilayer-based bottom-pinned perpendicular magnetic tunnel junctions (pMTJs) on Ru, Hf, and Ru/Hf seed layers (SLs) were investigated after annealing at different temperatures. The perpendicular synthetic antiferromagnetic (pSAF) layer on the Ru SL was found to be thermally robust (after annealing at 400 °C for 30 min). A high tunnel magnetoresistance (TMR) ratio of 100% was achieved at a low resistance-area product (5.5 Ωµm2) and was stable up to 350 °C. For the stack on Ru SL, TMR degradation after annealing was caused by the degradation of the pMTJ (CoFeB/MgO/CoFeB), while in the Hf and Ru/Hf SL, both the pMTJ and pSAF were affected.

Game-changing opportunities for wireless personal healthcare and lifestyle

In recent years, Personalized, Predictive, Preventive, and Participatory healthcare have become more than just buzzwords. Silicon is playing an important enabling role in this gradual, but certain revolution of our healthcare system: Silicon will become more essential, in view of the many challenges in realizing ubiquitous monitoring, real-time diagnostics, and patient-centric therapies. By reviewing world-wide technology breakthroughs, as well as healthcare-related trials with wireless sensors in Body-Area-Network (BAN) configurations, we will demonstrate that application validation for personal diagnostics and theranostic products is driving game-changing circuit and system innovation. Visionary applications such as brain-computer interfaces sound like magic! However, with every new generation of technology and application algorithms, wearable wireless systems become less obtrusive, higher performing, and more autonomous. The envisaged large-scale deployment of wearable healthcare and lifestyle add-ons that can monitor systemic factors such as stress and emotions, will revolutionize how we live, play, and work. But, none of these developments is heralding a “Brave New World” instead, they will foster and strengthen the role and impact of each individual along the path to a longer, healthier and happier life.

Epitaxial-tau(Mn,Ni)Al/(Al,Ga)As heterostructures: Magnetic and magneto-optic properties

Ferromagnetic Perpendicularly magnetized epitaxial thin films of tau (Mn,Ni)AI have been successfully grown on AlAs/GaAs heterostructures by molecular beam epitaxy. We have investigated the polar Kerr rotation and magnetization of tau MnAl and (Mn,Ni) Al as a function of Mn and Ni concentration. The largest polar Kerr rotation and remnant magnetization were obtained for Mn0.5Al0.5 thin films with values of 0.16-degrees and 224 emu/cm3, respectively. We observed that the Kerr rotation and magnetization remained constant with Ni additions up to about 12 at. % and subsequently decreased with further Ni additions. We discuss these results and one possible method of enhancing the Kerr rotation.

IoT: The impact of things

Starting from the application perspective, this paper addresses on the needs for sensor node architecture, wireless communication, security and infrastructure for IoT.

Seed Layer Effect on the Magnetic Properties of Ultrathin Co/Pt Multilayers With Perpendicular Magnetic Anisotropy

The effect of four different seed layers-Ru, Hf/Ru, Ru/Hf, and Hf on the magnetic properties of [Co 5/Pt 3 Å] multilayer (ML) stack with perpendicular magnetic anisotropy was investigated. The structural quality of the ML stacks was studied and correlated with the magnetic properties. Among the abovementioned seed layers, Ru promotes stronger fcc (111) texture in the ML due to less lattice mismatch (8% between Ru and Co) in Co/Pt MLs. As a result, higher anisotropy field (HK ~ 17 kOe) and larger effective perpendicular anisotropy (Keff ~ 1.2 × 107 erg/cm3) were achieved for the MLs on Ru seed layer compared with other seed layers after annealing at 300 °C for 30 min. The perpendicular magnetic anisotropy of the MLs is improved at higher annealing temperature up to 400 °C for Ru and Hf/Ru seed layer. For the Co/Pt MLs on Ru, 1.3 × 107 erg/cm3 perpendicular magnetic anisotropy was obtained even after annealing at 400 °C. Detail investigations of postannealing stability of the ML films on different seed layers were also discussed. The magnetic properties and structural properties of the films on four different seed layers were characterized after rapid thermal annealing process at 300 °C, 350 °C, and 400 °C for 30 min annealing duration. The high temperature endurance limit up to 400 °C for 30 min of the Co/Pt MLs on Ru and Hf/Ru seed layers makes them compatible with the back-end-of-line process temperature.

Enhanced magnetic particle transport by integration of a magnetic flux guide : Experimental verification of simulated behavior

In the past, magnetic biosensors have shown to be promising alternatives for classical fluorescence-based microarrays, replacing the fluorescent label by a superparamagnetic particle. While on-chip detection of magnetic particles is firmly established, research groups continue to explore the unique ability of manipulating these particles by applying controlled magnetic forces. One of the challenging tasks in designing magnetic force generating structures remains the generation of large forces for a minimal current consumption. Previously, a simple transporting device for single magnetic particles has been demonstrated using a magnetic field that is generated by two tapered current carrying conductors [R. Wirix-Speetjens, W. Fyen, K. Xu, J. De Boeck, and G. Borghs, IEEE Trans. Magn. 41(10), 4128 (2005)]. We also developed a model to accurately predict the motion of a magnetic particle moving in the vicinity of a solid wall. Using this model, we now present a technique that enhances the magnetic force up to...