Showing papers by "Stefan E. Schulz published in 2015"

High-performance giant magnetoresistive sensorics on flexible Si membranes

Abstract: We fabricate high-performance giant magnetoresistive (GMR) sensorics on Si wafers, which are subsequently thinned down to 100 μm or 50 μm to realize mechanically flexible sensing elements. The performance of the GMR sensors upon bending is determined by the thickness of the Si membrane. Thus, bending radii down to 15.5 mm and 6.8 mm are achieved for the devices on 100 μm and 50 μm Si supports, respectively. The GMR magnitude remains unchanged at the level of (15.3 ± 0.4)% independent of the support thickness and bending radius. However, a progressive broadening of the GMR curve is observed associated with the magnetostriction of the containing Ni81Fe19 alloy, which is induced by the tensile bending strain generated on the surface of the Si membrane. An effective magnetostriction value of λs = 1.7 × 10−6 is estimated for the GMR stack. Cyclic bending experiments showed excellent reproducibility of the GMR curves during 100 bending cycles.

Surface chemistry of copper metal and copper oxide atomic layer deposition from copper(ii) acetylacetonate: a combined first-principles and reactive molecular dynamics study.

Abstract: Atomistic mechanisms for the atomic layer deposition using the Cu(acac)2 (acac = acetylacetonate) precursor are studied using first-principles calculations and reactive molecular dynamics simulations. The results show that Cu(acac)2 chemisorbs on the hollow site of the Cu(110) surface and decomposes easily into a Cu atom and the acac-ligands. A sequential dissociation and reduction of the Cu precursor [Cu(acac)2 → Cu(acac) → Cu] are observed. Further decomposition of the acac-ligand is unfavorable on the Cu surface. Thus additional adsorption of the precursors may be blocked by adsorbed ligands. Molecular hydrogen is found to be nonreactive towards Cu(acac)2 on Cu(110), whereas individual H atoms easily lead to bond breaking in the Cu precursor upon impact, and thus release the surface ligands into the gas-phase. On the other hand, water reacts with Cu(acac)2 on a Cu2O substrate through a ligand-exchange reaction, which produces gaseous H(acac) and surface OH species. Combustion reactions with the main by-products CO2 and H2O are observed during the reaction between Cu(acac)2 and ozone on the CuO surface. The reactivity of different co-reactants toward Cu(acac)2 follows the order H > O3 > H2O.

Optimized Monolithic 2-D Spin-Valve Sensor for High-Sensitivity Compass Applications

Abstract: 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 ( $\sim 1$ mm) and temporal ( $\sim 1$ ms) resolution.

[Ag{S2CNR(C2H4OH)}] as Single-Source Precursor for Ag2S – Synthesis, Decomposition Mechanism, and Deposition Studies

Abstract: Silver(I) dithiocarbamates [Ag{S2CNR(C2H4OH)}] (3a, R = Me; 3b, R = Bu) were accessible by the reaction of AgNO3 with K{S2CNR(C2H4OH)} (2a, R = Me; 2b, R = Bu). Alternatively, 3b could be prepared by the condensation of CS2 and Ag2O with NHBu(C2H4OH) (1b). The thermal behavior of 3 was studied by thermogravimetric (TG) analysis. A two-step decomposition process leads to the formation of α-Ag2S, as evidenced by X-ray powder diffraction studies. A decomposition mechanism of 3a to form Ag2S through the release of 3-methyloxazolidine-2-thione is discussed based on TG–MS, GC–MS, and NMR experiments. Because of the better solubility of 3b, this complex was tested for Ag2S spin-coating deposition studies on different substrates (SiO2/Si, TiN/SiO2/Si, glass) with subsequent annealing at 450 °C under a N2 atmosphere. Film thickness, composition, and morphology of the as-deposited films were determined by XRD, SEM, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, which showed the formation of 200 nm thick, conformal, adherent, monoclinic α-Ag2S layers.

Quantum cascade laser based monitoring of CF2 radical concentration as a diagnostic tool of dielectric etching plasma processes

Abstract: Dielectric etching plasma processes for modern interlevel dielectrics become more and more complex by the introduction of new ultra low-k dielectrics. One challenge is the minimization of sidewall damage, while etching ultra low-k porous SiCOH by fluorocarbon plasmas. The optimization of this process requires a deeper understanding of the concentration of the CF2 radical, which acts as precursor in the polymerization of the etch sample surfaces. In an industrial dielectric etching plasma reactor, the CF2 radical was measured in situ using a continuous wave quantum cascade laser (cw-QCL) around 1106.2 cm−1. We measured Doppler-resolved ro-vibrational absorption lines and determined absolute densities using transitions in the ν3 fundamental band of CF2 with the aid of an improved simulation of the line strengths. We found that the CF2 radical concentration during the etching plasma process directly correlates to the layer structure of the etched wafer. Hence, this correlation can serve as a diagnostic tool ...

On treatment of ultra-low-k SiCOH in CF 4 plasmas: correlation between the concentration of etching products and etching rate

Abstract: Low-pressure rf plasmas have been applied for etching of ultra-low-k SiCOH wafers using an Oxford Plasmalab System 100. In pure CF4 plasmas, SiCOH layers have been etched for different power values. Using quantum cascade laser absorption spectroscopy in the mid-infrared spectral range, the correlation of online and in situ measured concentrations of two etching products, CO and SiF4, with the ex situ determined etching rates has been studied. The concentration of SiF4 was found to range between 0.6 and 1.4 × 1013 molecules cm−3. In contrast the concentrations of CO were measured to be only about 50 % of the SiF4 density with 7 × 1012 molecules cm−3 in maximum. The production rate of SiF4, determined from the time behavior of its concentration after plasma ignition, was found to be between 1 and 5 × 1012 cm−3 s−1. The etching rates varied between 2 and 7 nm s−1. Both parameters increase nearly linearly with the applied rf power. It was found that for power values of up to 1.1 kW, the etching rate depends nearly linearly on the in situ monitored concentrations of both etching products. Therefore, the concentration of the etching products can be directly used as a measure of the etching rate.

3D integration approaches for MEMS and CMOS sensors based on a Cu through-silicon-via technology and wafer level bonding

Abstract: Technologies for the 3D integration are described within this paper with respect to devices that have to retain a specific minimum wafer thickness for handling purposes (CMOS) and integrity of mechanical elements (MEMS). This implies Through-Silicon Vias (TSVs) with large dimensions and high aspect ratios (HAR). Moreover, as a main objective, the aspired TSV technology had to be universal and scalable with the designated utilization in a MEMS/CMOS foundry. Two TSV approaches are investigated and discussed, in which the TSVs were fabricated either before or after wafer thinning. One distinctive feature is an incomplete TSV Cu-filling, which avoids long processing and complex process control, while minimizing the thermomechanical stress between Cu and Si and related adverse effects in the device. However, the incomplete filling also includes various challenges regarding process integration. A method based on pattern plating is described, in which TSVs are metalized at the same time as the redistribution layer and which eliminates the need for additional planarization and patterning steps. For MEMS, the realization of a protective hermetically sealed capping is crucial, which is addressed in this paper by glass frit wafer level bonding and is discussed for hermetic sealing of MEMS inertial sensors. The TSV based 3D integration technologies are demonstrated on CMOS like test vehicle and on a MEMS device fabricated in Air Gap Insulated Microstructure (AIM) technology.

Towards nanoreliability of CNT-based sensor applications: Investigations of CNT-metal interfaces combining molecular dynamics simulations, advanced in situ experiments and analytics

Abstract: In this paper we present results of our recent efforts to understand the mechanical interface behaviour of single-walled carbon nanotubes (CNTs) embedded in metal matrices. We conducted experimental pull-out tests of CNTs embedded in Pd or Au and found maximum forces in the range 10–102 nN. These values are in good agreement with forces obtained from molecular dynamics simulations taking into account surface functional groups (SFGs) covalently linked to the CNT material. The dominant failure mode in experiment is a CNT rupture, which can be explained with the presence of SFGs. To qualify the existence of SFGs on our used CNT material, we pursue investigations by means of fluorescence labeling of surface species in combination with Raman imaging. We also report of a tensile test system to perform pull-out tests inside a transmission electron microscope to obtain in situ images of CNT-metal interfaces under mechanical loads at the atomic scale.

Investigation of barrier formation and stability of self-forming barriers with CuMn, CuTi and CuZr alloys

Abstract: In this work, we present the recent work on self-forming barriers. Focus on investigation laid on the barrier formation and its stability against copper diffusion. The investigated alloys were Cu(Mn), Cu(Ti) and Cu(Zr) respectively. It can be shown that these alloys are capable to form an enrichment layer on the SiO 2 interface. Here the substrate influences mainly the thickness of the generated barrier. Electrical measurements show the barrier stability against copper diffusion. Mn and Ti are promising elements as barrier materials.

3d magnetfeldsensor und verfahren zu dessen herstellung

Abstract: Ein 3D Magnetfeldsensor zur Erfassung von drei raumlichen Magnetfeldkomponenten in einem Referenzbereich, der beispielsweise bei einer Magnetfeldkamera einsetzbar ist, weist eine erste magnetoresistive Sensorelementeanordnung, eine zweite magnetoresistive Sensorelementeanordnung und eine dritte magnetoresistive Sensorelementeanordnung auf. Die erste magnetoresistive Sensorelementeanordnung ist ausgebildet, eine erste Magnetfeldkomponente bezuglich einer ersten Raumachse und bezuglich des Referenzbereichs zu erfassen. Die zweite magnetoresistive Sensorelementeanordnung ist ausgebildet, um eine zweite Magnetfeldkomponente bezuglich einer zweiten Raumachse und bezuglich des Referenzbereichs zu erfassen. Die dritte magnetoresistive Sensorelementeanordnung ist ausgebildet, um eine dritte Magnetfeldkomponente bezuglich einer dritten Raumachse und bezuglich des Referenzbereichs zu erfassen. Jede der magnetoresistiven Sensorelementeanordnungen ist als Bruckenschaltung mit einer Mehrzahl von magnetoresistiven Sensorelementen angeordnet. Die Raumachsen verlaufen entlang linear unabhangiger Ortsvektoren im Raum.

3d magnetic field sensor and method for producing same

Abstract: The invention relates to a 3D magnetic field sensor for detecting three spatial magnetic field components in a reference region, said sensor being usuable in a magnetic field camera for example. The sensor has a first magnetoresistive sensor element arrangement, a second magnetoresistive sensor element arrangement, and a third magnetoresistive sensor element arrangement. The first magnetoresistive sensor element arrangement is designed to detect a first magnetic field component with respect to a first spatial axis and with respect to the reference region. The second magnetoresistive sensor element arrangement is designed to detect a second magnetic field component with respect to a second spatial axis and with respect to the reference region. The third magnetoresistive sensor element arrangement is designed to detect a third magnetic field component with respect to a third spatial axis and with respect to the reference region. Each of the magnetoresistive sensor element arrangements is arranged as a bridge circuit with a plurality of magnetoresistive sensor elements. The spatial axes run along linearly independent position vectors in space.

Experimental investigations on a plasma assisted in situ restoration process for sidewall damaged ultra low-k dielectrics

Abstract: With the insertion of evaporated repair liquids into remote plasmas, a novel method to restore plasma damaged ultra low-k (ULK) materials will be introduced. The main advantage of this approach is the enhanced repair efficiency due to the formation of small plasma activated multiple repairing fragments. In this study Octamethylcyclotetrasiloxane (OMCTS) and Bis(dimethylamino)dimethylsilane (DMADMS) were chosen for blanket samples with a k-value of 2.4. Furthermore OMCTS with the addition of oxygen, methane or nitrogen was investigated on patterned ULK trench structures with 62 nm feature size.