arXiv subjects

Christoph Adelmann

Publications and source records attributed to Christoph Adelmann.

At least 19 recordsLinked to original sources

arXiv2026

Frequency-Division Multiplexing in Magnonic Waveguides

Frequency-division multiplexing is a key functionality for wave-based information processing, enabling multiple information channels to coexist within the same physical medium. Here, we experimentally investigate spin-wave multiplexing in a CoFeB waveguide using all-electrical excitation and detection. Two independently generated microwave signals are simultaneously coupled into the same spin-wave waveguide through inductive antennas and characterized using broadband vector network analyzer measurements. The transmission spectra obtained under single-channel and multiplexed operation exhibit excellent agreement, demonstrating that spin waves with different frequencies and wavelengths propagate simultaneously without measurable interaction in the linear regime. The observation is confirmed using both dual-sweep and sweep-plus-single-tone excitation schemes. A theoretical analysis based on linear superposition and phase-sensitive detection explains the absence of observable inter-channel interference for independent microwave sources. Micromagnetic simulations further confirm that the amplitudes and wavevectors of the individual spin-wave modes remain unchanged during co-propagation, demonstrating the absence of interaction over the entire propagation distance. The results provide direct experimental evidence that independent spin-wave channels can coexist in a single waveguide and support the implementation of frequency-division multiplexing in future magnonic computing and microwave signal-processing architectures.

cond-mat.mes-hall↗

arXiv2026

Composite based magnetoelectric scaled devices with large output voltages

In this work, we investigate the differential voltage generation arising from the direct magnetoelectric (ME) effect in nanoscale composite devices upon magnetization rotation from the magnetic ground state to an out-of-plane (OOP) configuration. These composite devices comprise a magnetostrictive ferromagnetic layer and a piezoelectric layer, mechanically coupled through strain. Using a finite element method (FEM) model, developed in COMSOL Multiphysics, we provide a comprehensive analysis of strain transfer mechanisms and resulting voltage generations. Here, the influence of dimensional and material parameters on the device performance is systematically examined. Our results indicate the presence of two distinct strain transfer mechanisms at scaled dimensions, where the device aspect ratio and the magnetic state both determine the dominant mechanism influencing the strain transfer to the piezoelectric layer. Moreover, we observed that the influence of surface clamping diminished as the pillar area was reduced. We also saw that the strain transfer to the piezoelectric layer can be enhanced by using stiffer electrodes or clamping layers. Lastly, we concluded that magnetostrictive materials with large magnetoelastic coupling constants or large Poisson ratios may strongly increase the output voltage at small dimensions. This study provides insight in the dimension and material selection when designing scaled ME pillars, with the aim of generating large output voltages. We showed that output voltages exceeding 200 mV can be achieved in scaled devices, underscoring the potential of these structures for integration into microelectronic applications.

cond-mat.mes-hall↗

arXiv2026

Gilbert Damping Parameters of Epitaxially-Stabilized Iron Gallium Thin Films from Ferromagnetic Resonance

Iron gallium (FeGa) alloys are excellent rare-earth-free magnetostrictors. Through epitaxial stabilization, the disordered A2 alloy can be extended from 19% to 30% gallium resulting in a magnetostrictive coefficient almost twice than that which is seen in rare earth magnetostrictors like SmFe2. In a composite magnetoelectric structure, this makes epitaxially-stabilized iron gallium a key material for energy-efficient beyond CMOS technologies. The energy dissipation and speed of magnetoelectric switching, however, is affected by the magnetic resonance frequency and damping. Here we report the evolution of the ferromagnetic resonance and key materials parameters (magnetic anisotropy, magnetic damping, and magnetostriction coefficient) for 70 nm thick epitaxially-stabilized single crystal A2 FeGa films beyond 19% Ga. Using flip chip ferromagnetic resonance (1-14 GHz), we find that the Gilbert damping parameter spans the range of 0.09-0.16 and decreases as the Ga concentration increases. This correlates an increasing magnetoelastic coupling with a reduction in the Gilbert damping. We find that the effective damping is a mix of contributions from the intrinsic magnon-phonon scattering and other scattering/dissipation mechanisms, with the latter being dominant especially at high Ga composition. Our results provide insight into the mechanism of magnetic relaxation in metastable high magnetostriction materials and potential switching behavior of composite magnetoelectrics.

cond-mat.mtrl-sci↗

arXiv2025

Nonlinear Strain-Mediated Magnetoelectric Coupling in Sub-Microscale Ni/BPZT Thin-Film Devices

Strain-mediated magnetoelectric (ME) heterostructures enable electric-field control of magnetism and are promising for ultra-low-power spintronic logic. Yet achieving spatially selective, low-voltage control in thin films and quantifying ME coupling across the full ferroelastic loop remains challenging. Here, we investigate sub-micrometer Ni/BPZT thin-film devices with laterally patterned gates that localize in-plane strain beneath the Ni stripe and modulate its magnetization. We use anisotropic magnetoresistance to measure magnetization changes across the ferroelastic loop under different magnetic bias fields. Combined with Multiphysics strain simulations and micromagnetic modeling, this provides a quantitative framework that captures the convolution of ferroelastic and magnetoelastic nonlinearities and provides critical insight for device design, while enabling multi-state, bias-field-free magnetization control for non-conventional computing. The extracted coupling coefficient in linear range is 1.3 mT/V across a 700 nm gap, with a clear pathway to improving voltage efficiency through device scaling, establishing a scalable CMOS-compatible platform for energy-efficient spintronic devices.

physics.app-ph↗

arXiv2025

Modelling spin-wave interference with electromagnetic leakage in micron-scaled spin-wave transducers

Utilization of spin-wave transducers for radio-frequency signal processing provides significant potential due to intrinsic tunability, scalability and nonlinearity. However, such components can exhibit passband ripples diminishing their operation and functionality. Here, we experimentally identify the electromagnetic crosstalk (EM) as a major source of passband ripples and provide a simple analytic model to predict the impact on device operation. The results are in good agreement with the experimental observation. In addition, we test multiple transducer geometries to identify operational regimes and minimize the EM impact. Finally, the effect of nonlinear device operation on the passband ripples is addressed, which is of relevance for the exploitation of the spin-waves intrinsic nonlinear traits.

physics.app-ph↗

arXiv2025

Charge accumulation by Direct Magnetoelectric Effect in ScAlN/Ni Nanoscale Devices

This work investigates the direct magnetoelectric effect in thin-film lab scale composite heterostructures comprising a 100 nm thick piezoelectric Sc0.4Al0.6N (ScAlN) and a magnetostrictive Ni with 100-200 nm thickness, fabricated on Si/SiO2 substrates. The films are patterned into square pillar arrays with lateral dimensions down to 500 nm x 500 nm. Vibrating sample magnetometry (VSM) measurements reveal in-plane magnetic anisotropy in the Ni films, attributed to strain induced by the underlying ScAlN layer. Nitrogen-vacancy (NV) magnetometry imaging confirms the formation of magnetic domains at remanence in polycrystalline Ni when patterned in sub-microscale structures. Capacitance measurements reveal a ScAlN dielectric constant at the device level consistent with unpatterned thin films, confirming the preservation of electrical integrity at the sub-microscale. The direct magnetoelectric effect is demonstrated through quasi-static charge measurements under applied out-of-plane DC magnetic fields, yielding equivalent open-circuit voltages up to 1.17 mV.

physics.app-ph↗

arXiv2025

Power Transfer in Magnetoelectric Resonators: a Combined Analytical and Finite Element Study

We present an analytical model for power transfer in a magnetoelectric film bulk acoustic resonator (FBAR) comprising a piezoelectric-magnetostrictive bilayer. The model describes the power flow between the elastic and magnetic systems, quantifying the transduction efficiency when the FBAR operates as a magnetic transducer. By applying the model to example systems using piezoelectric ScAlN and magnetostrictive CoFeB, Ni, or Terfenol-D layers, we demonstrate the potential for achieving high efficiencies in magnetoelectric transducers, rendering them ideal for efficient ferromagnetic resonance excitation. The validity of the model's assumptions is confirmed through comparison with a numerical finite element resonator model in COMSOL\texttrademark. The finite element model further enables a comprehensive study of the resonator's dynamic behavior, including transient and steady-state regimes, and the identification of resonant frequencies within the system.

cond-mat.mes-hall↗

arXiv2025

Exploring binary intermetallics for advanced interconnect applications using ab initio simulations

The challenge of increasing copper (Cu) resistivity with diminishing Cu interconnect dimensions in complementary metal-oxide-semiconductor (CMOS) transistors, along with the imperative for efficient electron transport paths to fulfill scaling requirements in interconnects is significant. First-principles electronic structures calculations based on density functional theory have been performed to evaluate the potential scalability of some Cu, Al, Ru and Mo based binary alloys to replace Cu. We evaluate the expected sensitivity of the resistivity of these binary alloys to reduced line dimensions with a figure of merit that is based on generalized finite-temperature transport tensors. These transport tensors allow for a straightforward comparison between highly anisotropic intermetallics with given transport directions and Cu, and are evaluated together with their resistance to electromigration. Based on the figure-of-merit analysis, we identify several aluminides that show potential to outperform Cu at reduced interconnect dimensions in terms of their electronic transport and reliability properties.

cond-mat.mtrl-sci↗

arXiv2025

Self Biased Integrated Magnonic Device

In the race towards "beyond 6G" telecommunication platforms, magnonics emerges as a promising solution due to its wide tunability within the FR3 band (7-24 GHz). So far, however, the need for an external magnetic bias field to allow the coherent excitation of spin waves has been a major bottleneck. Conventional bulky electromagnets are power-intensive and challenging to integrate on-chip, restricting magnonic applications largely to academic research. Here, we present the first demonstration of a standalone, tunable magnonic device featuring all-electric input and output, fully integrated on a silicon substrate with a compact footprint of 100 x 150 $\mu$m. The device consists of a CoFeB waveguide equipped with two radio frequency antennas, flanked by a symmetric configuration of T-shaped magnetic flux concentrators and rectangular SmCo permanent micromagnets. By varying the distance D between the flux concentrators and the permanent magnets from 0 to 12 $\mu$m, the transverse bias field can be tuned from 20.5 mT to 11 mT, respectively. This variation directly modulates the dispersion relation of Damon-Eshbach spin wave modes in the CoFeB waveguide. In these proof-of-concept devices, the spin wave frequency band ranges from 3 to 8 GHz, with precise phase shift tuning of up to 120 degrees at 6 GHz achieved by varying D within the 0-8 $\mu$m range. The operational frequency band could even be pushed to higher frequencies through optimized micromagnet engineering.

physics.app-ph↗

arXiv2025

Correlation between structural and magnetic properties of epitaxial YIG films by pulsed laser deposition

In this study, we investigate the relationships between film growth conditions, crystalline microstructure, and magnetic properties of epitaxial Yttrium Iron Garnet (Y$_3$Fe$_5$O$_{12}$, YIG) thin films, deposited on Gallium Gadolinium Garnet (Ga$_3$Gd$_5$O$_{12}$, GGG). A direct correlation was observed between the residual epitaxial strain, bulk magnetic properties like saturation magnetization and magnetic damping), and the performance of spin-wave transmission devices based on these films. This correlation offers a pathway for a simplified, rapid assessment of YIG film quality, avoiding the need for complex time-consuming characterization techniques. In addition, we report a comprehensive investigation into the influence of pulsed-laser deposition parameters, including deposition temperature, pressure, laser fluence, frequency, and annealing conditions. Through systematic deposition optimization, state-of-the-art YIG films exhibiting ultralow magnetic damping could be obtained, which is critical for high-performance spintronic applications.

cond-mat.mtrl-sci↗

arXiv2024

Selecting Alternative Metals for Advanced Interconnects

Interconnect resistance and reliability have emerged as critical factors limiting the performance of advanced CMOS circuits. With the slowdown of transistor scaling, interconnect scaling has become the primary driver of continued circuit miniaturization. The associated scaling challenges for interconnects are expected to further intensify in future CMOS technology nodes. As interconnect dimensions approach the 10 nm scale, the limitations of conventional Cu dual-damascene metallization are becoming increasingly difficult to overcome, spurring over a decade of focused research into alternative metallization schemes. The selection of alternative metals is a highly complex process, requiring consideration of multiple criteria, including resistivity at reduced dimensions, reliability, thermal performance, process technology readiness, and sustainability. This tutorial introduces the fundamental criteria for benchmarking and selecting alternative metals and reviews the current state of the art in this field. It covers materials nearing adoption in high-volume manufacturing, materials currently under active research, and potential future directions for fundamental study. While early alternatives to Cu metallization have recently been introduced in commercial CMOS devices, the search for the optimal interconnect metal remains ongoing.

physics.app-ph↗

arXiv2024

Cu$_x$Al$_{1-x}$ films as Alternatives to Copper for Advanced Interconnect Metallization

Cu$_x$Al$_{1-x}$ thin films with $0.2 \le x \le 0.7$ have been studied as potential alternatives for the metallization of advanced interconnects. First-principles simulations were used to obtain the Cu$_x$Al$_{1-x}$ electronic structure and cohesive energy to benchmark different intermetallics and their prospects for interconnect metallization. Next, thin Cu$_x$Al$_{1-x}$ films were deposited by PVD with thicknesses in the range between 3 and 28 nm. The lowest resistivities of 9.5 $μΩ$cm were obtained for 28 nm thick stochiometric CuAl and CuAl$_2$ after 400$^\circ$C post-deposition annealing. Based on the experimental results, we discuss the main challenges for the studied aluminides from an interconnect point of view, namely the control of the film stoichiometry, the phase separation observed for off-stoichiometric CuAl and CuAl$_2$, as well as the presence of a nonstoichiometric surface oxide.

cond-mat.mtrl-sci↗

arXiv2024

Al$_3$Sc thin films for advanced interconnect applications

Al$_x$Sc$_{1-x}$ thin films have been studied with compositions around Al$_3$Sc ($x$ = 0.75) for potential interconnect metallization applications. As-deposited 25 nm thick films were x-ray amorphous but crystallized at 190°C, followed by recrystallization at 440°C. After annealing at 500°C, 24 nm thick stoichiometric Al$_3$Sc showed a resistivity of 12.6 $μΩ$cm, limited by a combination of grain boundary and point defect (disorder) scattering. Together with ab initio calculations that found a mean free path of the charge carriers of 7 nm for stoichiometric Al$_3$Sc, these results indicate that Al$_3$Sc bears promise for future interconnect metallization schemes. Challenges remain in minimizing the formation of secondary phases as well as in the control of the non-stoichiometric surface oxidation and interfacial reactions with underlying dielectrics.

cond-mat.mtrl-sci↗

arXiv2024

Spintronic logic: from transducers to logic gates and circuits

While magnetic solid-state memory has found commercial applications to date, magnetic logic has rather remained on a conceptual level so far. Here, we discuss open challenges of different spintronic logic approaches, which use magnetic excitations for computation. While different logic gate designs have been proposed and proof of concept experiments have been reported, no nontrivial operational spintronic circuit has been demonstrated due to many open challenges in spintronic circuit and system design. Furthermore, the integration of spintronic circuits in CMOS systems will require the usage of transducers between the electric (CMOS) and magnetic domains. We show that these transducers can limit the performance as well as the energy consumption of hybrid CMOS-spintronic systems. Hence, the optimization of transducer efficiency will be a major step towards competitive spintronic logic system.

cs.ET↗

arXiv2024

Selection of Alternative Local Interconnect Metals: Beyond Traditional Criteria Towards Sustainable and Secure Supply Chains

In response to aggressive scaling demands in semiconductor manufacturing and the growing need to apply sustainable practices, this paper presents a holistic sustainability assessment framework for evaluating alternative metals for advanced applications. The framework, consisting of seven sustainability aspects, aims to guide researchers and industry stakeholders towards decisions fostering a more sustainable and secure future for microelectronics. This study applies the framework to assess the sustainability of alternative local interconnect metals. The framework identifies five metals (Ti, Al, Ni, Co, and Mo) with relatively favourable performance in at least six out of nine specific indicators, while others (Pt, Ru, Ir, Rh, and Pd) exhibit poorer sustainability metrics. The study recommends further analyses, suggesting the incorporation of case-specific functional units and the use of normalization and weighting factors for a comprehensive evaluation. Coupled with traditional technological assessments, this framework equips decision-makers with essential tools to broaden criteria for selecting alternative metals, aligning semiconductor manufacturing with broader sustainability objectives.

cond-mat.mtrl-sci↗

arXiv2023

Magnetoelectric Coupling in Pb(Zr,Ti)O3/CoFeB Nanoscale Waveguides Studied by Propagating Spin-Wave Spectroscopy

This study introduces a method for the characterization of the magnetoelectric coupling in nanoscale Pb(Zr,Ti)O3/CoFeB thin film composites based on propagating spin-wave spectroscopy. Finite element simulations of the strain distribution in the devices indicated that the magnetoelastic effective field in the CoFeB waveguides was maximized in the Damon - Eshbach configuration. All-electrical broadband propagating spin-wave transmission measurements were conducted on Pb(Zr,Ti)O3/CoFeB magnetoelectric waveguides with lateral dimensions down to 700 nm. The results demonstrated that the spin-wave resonance frequency can be modulated by applying a bias voltage to Pb(Zr,Ti)O3. The modulation is hysteretic due to the ferroelastic behavior of Pb(Zr,Ti)O3. An analytical model was then used to correlate the change in resonance frequency to the induced magnetoelastic field in the magnetostrictive CoFeB waveguide. We observe a hysteresis magnetoelastic field strength with values as large as 5.61 mT, and a non-linear magnetoelectric coupling coefficient with a maximum value of 1.69 mT/V.

physics.app-ph↗

arXiv2023

Microwave Properties of Ba-Substituted Pb(Zr$_{0.52}$Ti$_{0.48}$)O$_3$ after Chemical-Mechanical Polishing

We have studied the effect of chemical-mechanical polishing (CMP) on the ferroelectric, piezoelectric, and microwave dielectric properties of Ba-substituted PZT (BPZT), deposited by pulsed laser deposition. CMP allowed for the reduction of the root mean square surface roughness of 600 nm thick BPZT films from 12.1nm to 0.79 nm. Ammonium peroxide (SC-1) cleaning was effective to remove Si CMP residuals. Measurements of the ferroelectric hysteresis after CMP indicated that the ferroelectric properties of BPZT were only weakly affected by CMP, while the piezoelectric d33 coefficient and the microwave permittivity were reduced slightly by 10%. This can be attributed to the formation of a thin dead layer at the BPZT surface. Moreover, the intrinsic dielectric permittivity at microwave frequencies between 1 and 25 GHz was not influenced by CMP, whereas the dead layer series capacitance decreased by 10%. The results indicate that the CMP process can be used to smoothen the BPZT surface without affecting the film properties strongly.

physics.app-ph↗

arXiv2022

First-principles-based screening method for resistivity scaling of anisotropic metals

The resistivity scaling of metals is a crucial limiting factor for further downscaling of interconnects in nanoelectronic devices that affects signal delay, heat production, and energy consumption. Here, we generalize a commonly considered figure of merit for selecting promising candidate metals with highly anisotropic Fermi surfaces in terms of their electronic transport properties at the nanoscale. For this, we introduce a finite-temperature transport tensor, based on band structures obtained from first principles. This transport tensor allows for a straightforward comparison between highly anisotropic metals in nanostructures with different lattice orientations and arbitrary transport directions. By evaluating the temperature dependence of the tensor components, we also assess the validity of a Fermi surface-based evaluation of the transport properties at zero temperature, rather than considering standard operating temperature conditions.

cond-mat.mtrl-sci↗