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Almeida M.J.,Fraunhofer Institute for Electronic Nano Systems | Almeida M.J.,TU Chemnitz | Gotze T.,Fraunhofer Institute for Electronic Nano Systems | Gotze T.,TU Chemnitz | And 7 more authors.
Materials Today: Proceedings | Year: 2015

The determination of the local field direction enables, for instance, migratory birds to find their annual routes from one continent to another, or magnetotactic bacteria to move towards soil rich in nutrients. In analogy, for microelectromechanical systems (MEMS), the ability of detecting the local direction of a magnetic field as a 2D or 3D vector can allow, in principle, a reliable autonomous navigation through environments with a complex or unknown topology. These applications demand, however, a very low power consumption, miniaturizability and fast response times in the milliseconds range. In the following, we present novel 2D sensors based on exchange-biased IrMn/CoFe/Cu/CoFe - NiFe spin valves fulfilling all these requirements. In addition, we test different sensor arrangements. The spatial sensitivity of the constituent single GMR meanders is defined by means of microscopic laser heating and subsequent in-field cooling. By this, a relative pairwise geometric alignment of 90° or 180°, respectively, is achieved for the individual antiferromagnetic pinning layers, providing a maximum signal response for each sensor layout. On the basis of fabricated prototypes with a size of < 0.5 mm2, we demonstrate that these sensors can readily be employed to detect small magnetic fields as a 2D vector with a high temporal resolution of 100μs. © 2015 Elsevier Ltd. Source


Ueberschar O.,Fraunhofer Institute for Electronic Nano Systems | Almeida M.J.,Fraunhofer Institute for Electronic Nano Systems | Almeida M.J.,TU Chemnitz | Matthes P.,TU Chemnitz | And 6 more authors.
IEEE Transactions on Magnetics | Year: 2015

We have designed and fabricated 2-D giant magnetoresistance spin-valve sensors on the basis of exchange-biased NiFe-CoFe/Cu/CoFe/IrMn nanolayers in monolithic integration for high-sensitivity compass applications. For a maximum signal-to-noise ratio, we have realized a focused double full-bridge layout with an antiparallel alignment of the pinned layer magnetization for neighboring meanders. This precise alignment is achieved with microscopic resolution by laser heating and subsequent in-field cooling. Striving for high-signal sensitivity and low hysteresis, we study in detail how the geometry of the constituent single meanders influences their magnetic structure and the resulting electronic transport properties. The investigated geometrical parameters include stripe width, stripe length, U-turn material, and total meander length. Moreover, the influence of the relative alignment between reference magnetization and shape anisotropy is studied. We compare our experimental results to the predictions of tailored micromagnetic simulations. Applying the best-suited meander geometry, we demonstrate how the developed 2-D sensor may be readily employed to determine the direction of small magnetic fields, such as that of the Earth, as a 2-D vector with high spatial (∼ 1 mm) and temporal (∼ 1 ms) resolution. © 2015 IEEE. Source


Almeida M.J.,Fraunhofer Institute for Electronic Nano Systems | Almeida M.J.,TU Chemnitz | Matthes P.,TU Chemnitz | Ueberschar O.,Fraunhofer Institute for Electronic Nano Systems | And 6 more authors.
Physics Procedia | Year: 2015

The specific local alignment of the magnetization of a reference layer in spin valves has a rapidly growing significance in the implementation of monolithically integrated sensor devices. The spatial sensitivity of such sensors is defined by the exchange bias effect arising in strongly coupled ferromagnetic (FM) and antiferromagnetic (AFM) heterostructures. The (re-)setting of the orientation of the exchange bias direction can be achieved through local annealing by means of a focused laser beam and subsequent cooling in the presence of a magnetic field. The parameters of such a laser exposure will have a significant influence to the FM/AFM system as well as the remaining layers, playing therefore an important role on the sensing characteristics. In order to analyse this effect, bottom-pinned IrMn / CoFe / Cu / CoFe/ NiFe spin valves are patterned into a meander shape and further annealed using a focused pulsed laser beam. Different processing peak intensities are tested. The analysis of the magnetotransport properties after this exposure shows how strongly the electrical conductivity is affected for higher intensities, as well as the effect of the laser peak intensity on the magnetic coupling between the ferromagnetic electrodes. These changes are discussed as a result of the structural modifications induced by the laser exposure on the spin valve structures. © 2015 The Authors. Published by Elsevier B.V. Source


Almeida M.J.,TU Chemnitz | Ueberschar O.,Fraunhofer Institute for Electronic Nano Systems | Ecke R.,Fraunhofer Institute for Electronic Nano Systems | Schulz S.E.,Fraunhofer Institute for Electronic Nano Systems | And 3 more authors.
5th IMEKO TC19 Symposium on Environmental Instrumentation and Measurements 2014 | Year: 2014

The natural geomagnetic field has been used for millions of years by various organisms for navigation. The determination of the local field direction (in terms of magnetic north and inclination) enables, for instance, migratory birds to find their annual routes from one continent to another and back home, or magnetotactic bacteria to move towards soil areas rich in nutrients. In analogy, for microelectromechanical systems (MEMS), the capability of detecting the local direction of the geomagnetic field as a 2D or 3D vector enables a reliable autonomous navigation through environments with a complex or unknown topology while being independent of GPS or any other radio-based navigation system (and thus being operable also in obstructed or shielded environments). Such mobile MEMS applications demand, however, a very low power consumption and a high miniaturizability of the sensor, as well as a very fast sensor response time. In the following, we present an innovative 2D GMR spin valve sensor on the basis of exchange-biased NiFe- CoFe / Cu / CoFe / IrMn nanolayers in monolithic integration that fulfils all these requirements. For a maximum signal-to-noise ratio, we have realized a focused double full-bridge layout with an antiparallel alignment of the pinned layers of neighbouring meanders by means of microscopic laser heating and subsequent in-field cooling. A systematic optimization of geometry and magnetic structure further contributed to a maximum signal level and a minimum sensor hysteresis. On the basis of fabricated prototypes with a size of 1.5 mm times we demonstrate that these sensors are readily employed to detect the geomagnetic field as a 2D vector with temporal ( 1 ms) resolution. Source


Olbrich M.,Laserinstitut Hochschule Mittweida | Punzel E.,Laserinstitut Hochschule Mittweida | Roesch R.,Friedrich - Schiller University of Jena | Oettking R.,Friedrich - Schiller University of Jena | And 3 more authors.
Applied Physics A: Materials Science and Processing | Year: 2016

Laser ablation using ultra-short pulsed laser radiation allows the removing of thin films with very high spatial resolution, and working with high repetition rate as well with high through-put. The ultrafast ablation of thin films of aluminum on float glass is investigated using focused femtosecond laser radiation (λ = 1028 nm, tH = 200 fs, sech2, pf = 1 MHz) as function of the number of pulses Np per point (1–10) and the film thickness d (30–300 nm). It is observed that two thresholds are derived simultaneously for thin films with a thickness thicker than 100 nm by irradiating the metal with single pulsed laser radiation exhibiting a Gaussian intensity distribution: one threshold for gentle ablation Hthr,gentle and the other for strong ablation Hthr,strong. Multi-pulse irradiation varying the number of pulses per point identifies the incubation effect described by Jee et al. (J Opt Soc Am B 5(3):648, 1968). This model was applied on the thresholds for gentle and strong ablation. Also, varying the layer thickness reducing the thresholds for thin films due heat accumulation. To quantify the experimental data, numerical simulations solving the coupled heat transfer equation of the two-temperature model were performed. A new approach including the temperature dependence of the reflectivity is presented based on the model proposed by Brückner et al. (J Appl Phys 66:1326, 1989). The results of the simulation fit qualitative well to the experimental data of gentle ablation. Theoretical investigation for double pulses with a variable pulse separation time of 1–300 ps were performed in comparison with a single pulse. © 2016, Springer-Verlag Berlin Heidelberg. Source

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