Multilayer Devices Research Articles

Enhanced Giant Magnetoresistance in Heusler Alloy (Co2FeSi/Ag)N Multilayers for Read Sensor applications

Abstract We theoretically investigate the spin transport behavior of multilayer (Co2FeSi/Ag)N structure for the application of next-generation read sensor in hard disk drive. To demonstrate the potential of Heusler alloy-based current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) device, we employ the atomistic model coupled with the spin accumulation model including the effect of diffuse interface. The dynamic of magnetization is observed by the atomistic model and the calculation of magnetoresistance (MR) and MR ratio of the magnetic structure can be achieved by the spin accumulation model enabling us investigate the spin transport behavior within the structure. The MR value can be directly calculated from the gradient of spin accumulation and spin current. The effect of injected current density is first investigated. It is found that increasing current density results in high MR ratio. Subsequently, to achieve high performance reader, the number of coupled layers (N) is varied up to 16 to study its effect on the MR ratio. The calculated results indicate that increasing the number of layers N gives rise to the enhancement of the resistance change and MR ratio. At the critical point N=5, further increasing N does not affect the MR ratio, which remains relatively unchanged. Interestingly, the MR ratio is doubled for N>5 compared to N=1. Our results show the possibility to enhance the performance of multilayer CPP-GMR device.

Magnetic soliton-based LIF neurons for spiking neural networks (SNNs) in multilayer spintronic devices

Neuromorphic computing, inspired by biological nervous systems, is gaining traction due to its advantages in latency, energy efficiency, and algorithmic complexity compared to traditional artificial neural networks. This has spurred research into artificial synapses and neurons that replicate brain functions. Spintronic-based technologies, particularly domain walls (DWs) and skyrmions (SKs), have shown remarkable potential for brain-inspired computing, facilitating energy-efficient data storage and advancing beyond CMOS computing architectures. Researchers have proposed various DWs- and Sks-based neuromorphic architectures for neurons and synapses. Leveraging magnetic multilayer structures, we propose a magnetic soliton that incorporates both DWs- and Sks-based magnetic tunnel junction (MTJ) device structures to emulate leaky integrate-and-fire (LIF) characteristics. These characteristics are controlled by spin–orbit torque (SOT)-driven motion within ferromagnetic thin films. By strategically placing the reading block and utilizing a combination of SOT and varying demagnetization energy, we achieve modified LIF neuron characteristics in both DW and Sks MTJ devices. The co-action of soliton dynamics across the nanotrack during the application of the current pulse, along with edge repulsion and variations in demagnetization energy, exploits LIF spiking behavior. Theoretical and micromagnetic analyses reveal that the transitory tunable positions of Sks and the total magnetization of the free layer for DWs mimic the membrane potential of biological neurons. Initial studies on multilayer DW-based LIF characteristics showed promise; however, maintaining leaky behavior required a constant negative current, which is energy inefficient. By incorporating the non-volatile properties of skyrmions and adding a chiral Dzyaloshinskii–Moriya interaction term, we further explored LIF dynamics, yielding encouraging results. Our proposed neuron model, implemented in fully connected and convolutional layers, achieves over 95% classification accuracy on the MNIST and Fashion MNIST datasets using a modified spike-based backpropagation method. With nanosecond latency, these spiking neuron devices, when integrated with CMOS, pave the way for high-density, energy-efficient neuromorphic computing hardware.

Like-layers resolution deficiency in structure function-based thermal test for multilayer semiconductor device and its potential cure by interface design

Like-layers resolution deficiency in structure function-based thermal test for multilayer semiconductor device and its potential cure by interface design

Spintronic Pathways in a Nonconjugated Radical Polymer Glass

AbstractRadical chemistries have attracted burgeoning attention due to their intriguing technological applications in organic electronics, optoelectronics, and magneto‐responsive systems. However, the potential of these magnetically active glassy polymers to transport spin‐selective currents has not been demonstrated. Here, the spin‐transport characteristics of the radical polymer poly(4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl) (PTEO) allow for sustained spin‐selective currents when incorporated into typical device geometries with magnetically polarized electrodes. Annealing thin films of PTEO above its glass transition temperature results in a giant magnetoresistance effect (i.e., an MR of ≈80%) at 4 K. Additionally, ferromagnetic resonance spin‐pumping results in a relatively large effective spin‐mixing conductance of 1.18 × 1019 m−2 at the NiFe/PTEO interface. Due to the large spin‐density and radical‐radical exchange interactions, there is effective propagation of pure spin currents through PTEO in the NiFe/PTEO/Pd multilayer devices. This results in the transport of spin current over long distances with a spin diffusion length of 90.4 nm. The spin diffusion length and spin mixing conductance values surpass those reported in inorganic and metallic systems and are comparable to conventional doped conjugated polymers. This is the first example of spin transport in a nonconjugated radical polymer, and these findings underscore the promising spin‐transporting potential of radical polymers.

Convolutional neural network for colorimetric glucose detection using a smartphone and novel multilayer polyvinyl film microfluidic device

Detecting glucose levels is crucial for diabetes patients as it enables timely and effective management, preventing complications and promoting overall health. In this endeavor, we have designed a novel, affordable point-of-care diagnostic device utilizing microfluidic principles, a smartphone camera, and established laboratory colorimetric methods for accurate glucose estimation. Our proposed microfluidic device comprises layers of adhesive poly-vinyl films stacked on a poly methyl methacrylate (PMMA) base sheet, with micro-channel contours precision-cut using a cutting printer. Employing the gold standard glucose-oxidase/peroxidase reaction on this microfluidic platform, we achieve enzymatic glucose determination. The resulting colored complex, formed by phenol and 4-aminoantipyrine in the presence of hydrogen peroxide generated during glucose oxidation, is captured at various glucose concentrations using a smartphone camera. Raw images are processed and utilized as input data for a 2-D convolutional neural network (CNN) deep learning classifier, demonstrating an impressive 95% overall accuracy against new images. The glucose predictions done by CNN are compared with ISO 15197:2013/2015 gold standard norms. Furthermore, the classifier exhibits outstanding precision, recall, and F1 score of 94%, 93%, and 93%, respectively, as validated through our study, showcasing its exceptional predictive capability. Next, a user-friendly smartphone application named “GLUCOLENS AI” was developed to capture images, perform image processing, and communicate with cloud server containing the CNN classifier. The developed CNN model can be successfully used as a pre-trained model for future glucose concentration predictions.

Efficient and Stable Quantum‐Dot Light‐Emitting Diodes with Trilayer PIN Architecture

AbstractAlthough the performance of quantum dot light‐emitting diodes (QLEDs) has been greatly improved in recent years, the multilayer device structure has become increasingly complex, limiting the practical application of QLEDs. Here, a novel trilayer PIN QLED with only three functional layers, which are Spiro‐OMeTAD:TFB bulk‐heterojunction (BHJ) hole transport layer (HTL), quantum‐dot emitting layer and ZnMgO electron transport layer is demonstrated. Due to the enhanced hole injection capability and suppressed electron leakage of Spiro‐OMeTAD:TFB BHJ HTL, the trilayer PIN QLED can show an excellent external quantum efficiency (EQE) of 25.1% and an impressive brightness of 299300 cd m−2 at only 8 V, which are significantly higher than those of conventional QLED. Moreover, the device stability is also remarkably improved due to the mitigation of hole accumulation and removal of unstable PEDOT:PSS. By using liquid alloy EGaIn as cathode, a fully solution‐processed vacuum‐free trilayer PIN QLED with a higher EQE of 27.3% can be further realized. The developed trilayer PIN QLEDs, with better performance and fewer functional layers, can promote the commercialization of QLED technology.

Fully Solution‐Processed Polymeric Multilayer Piezoelectric Devices

AbstractThis study demonstrates fully solution‐processed polymeric multilayer piezoelectric devices. The key challenge, the effective control of the redissolution issue that will cause severe electrical shorting and inconsistent piezoelectric output, is overcome by searching for and using a solvent that offers adequate solubility but extremely slow dissolution for the piezoelectric polymer. The solvent screening methodology is established and demonstrated. The process parameters is systematically optimized to maximize the piezoelectric performance of the multilayer devices. The multilayer devices can output a high charge density of 376 µC m−2, even higher than the record charge density of 250 µC m−2 achieved by traditional contact electrification‐based triboelectric nanogenerators operated in ambient air. The crucial factors for increasing device fabrication yield, namely resistance to short circuits and poling‐induced breakdown, are analyzed. The potential of multilayer devices in practical applications is demonstrated using a five‐layer device as a direct power source and energy harvester. More importantly, the process developed here is transferrable for cost‐effective high‐throughput roll‐to‐roll production. This work thus lays the foundation for the mass production of polymeric multilayer piezoelectric devices and paves the way for their future commercialization.

Molecular beam epitaxial growth of HgCdTe mid-wave infrared dual-band detectors

The technique of molecular beam epitaxy (MBE) has been utilized to fabricate high-performance HgCdTe infrared detectors, which exhibit sensitivity to mid-wave infrared radiation in adjacent spectral bands for two-color thermal imaging applications. The growth of a multilayer HgCdTe device structure by MBE enables the use of an n-p-n device architecture, which facilitates pixel-level registration of images in two separate spectral bands. Device structures are grown on CdZnTe (211)B substrates using CdTe, Te, and Hg sources with in situ indium (In) and arsenic (As) doping. The composition of the HgCdTe alloy layers is adjusted to achieve detection of infrared radiation in adjacent spectral bands within the wavelength range of 3.0–5.0 µm. The as-grown device structures are characterized using X-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. The 640 × 512, 20-μm-pixel-pitch dual-band MWIR1/MWIR2 focal-plane arrays (FPAs) are fabricated by mesa etching, sidewall passivation and other processes. Ohmic contacts are made to the two n-type layers for operation of the detectors in a sequential detection mode. The MWIR1/MWIR2 FPAs, which are fabricated using these HgCdTe heterostructures with exceptionally high-quality layers, exhibit a band 1 (MWIR1) operability of 98.65 % and a band 2 (MWIR2) operability of 99.93 %. The NETD values of both MWIR1 and MWIR2 modes are less than 15 mK.

Design and fabrication of tetradymites-based vertically oriented single and multilayer thin-film thermoelectric generators

Tetradymites-based thermoelectric materials and devices have received renewed attention due to their engineering and design flexibility, large scalability, and commercial viability in producing electricity from waste heat for niche applications in small power generation and micro refrigeration. In fact, most commercially available bulk thermoelectric generators (TEGs) are made from tetradymites. In contrast to their bulk counterparts, thin-film vertical TEGs have not been widely adopted. This can be attributable to complexities in design and fabrication methodologies, device measurement challenges, and the hurdle of maintaining a large enough temperature gradient for optimal device performance. In this study, we utilize a facile approach for the design, fabrication, and characterization of tetradymite-based n-type Bi2Te3 and p-type Sb2Te3 single-layer thermoelectric generators, as well as n-type Bi2Te3/Bi2Te2.83Se0.17 and p-type Sb2Te3/Bi0.4Sb1.6Te3 alternating multilayer superlattice TEGs. State-of-the-art characterization techniques were employed to investigate the structural, chemical, and thermoelectric properties of the materials. XRD analysis showed a preferential orientation along the (100) plane with a high intensity peak at 2θ = 25.5°, and XPS spectra exhibited a high-resolution peak at 531.5 eV corresponding to the Bi 4f7/2 core level. The structural data analysis confirmed the dominant metallic phase of the materials as well as their high crystalline nature. Device characterization showed that the multilayer device performed better than the single-layer devices with a recorded voltage, power, and power density of 11 mV, 12 pW, and 15.87 mW/m3 at ΔT = 18 °C, respectively, in comparison to 9.4 mV, 7.8 pW, and 10.31 mW/m3 for the most performing single-layer devices.

Fabrication of heterostructure multilayer devices through the optimization of Bi-metal sulfides for high-performance quantum dot-sensitized solar cells.

In this work, a titanium dioxide and lead sulfide (TiO2/PbS) nano-size heterostructure with tin sulfide was fabricated and coated via a two-step direct deposition process. Its microstructure, morphology, elemental composition, optical absorption, and photochemical activity were investigated. Linear sweep voltammetry and cyclic voltammetry curves substantiated its catalytic activity, indicating quantum dot effects of a well-developed space charge domain on the surface of the hybrid structure. These give rise to electron-hole recombination suppression and a high charge mobility rate. Moreover, direct stabilization was identified in current density, corresponding to the hybrid structures limiting the diffusion current process. Higher J SC values observed were substantiated by the role of quantum dot-size effects and enhanced crystalline structures, leading to a reduction in series resistance and an improved conversion efficiency of 10.05%. Overall, theoretical analyses and empirical findings indicated that the seamless migration of photoexcited electrons across the interfaces of SnS and PbS is linked to quantum dot effect synergy. This is facilitated by the space charge region, which serves as a conduit for efficient electron transfer between the respective materials.

A Polyimide Composite-Based Electromagnetic Cantilever Structure for Smart Grid Current Sensing.

Polyimides (PIs) have been extensively used in thin film and micro-electromechanical system (MEMS) processes based on their excellent thermal and mechanical stability and high glass transition temperature. This research explores the development of a novel multilayer and multifunctional polymer composite electro-piezomagnetic device that can function as an energy harvester or sensor for current-carrying wires or magnetic field sensing. The devices consist of four layers of composite materials with a polyimide matrix. The composites have various nanoparticles to alter the functionality of each layer. Nanoparticles of Ag were used to increase the electrical conductivity of polyimide and act as electrodes; lead zirconate titanate was used to make the piezoelectric composite layer; and either neodymium iron boron (NdFeB) or Terfenol-D was used to make the magnetic and magnetostrictive composite layer, which was used as the proof mass. A novel all-polymer multifunctional polyimide composite cantilever was developed to operate at low frequencies. This paper compares the performance of the different magnetic masses, shapes, and concentrations, as well as the development of an all-magnetostrictive device to detect voltage or current changes when coupled to the magnetic field from a current-carrying wire. The PI/PZT cantilever with the PI/NdFeB proof mass demonstrated higher voltage output compared to the PI/Terfenol-D proof mass device. However, the magnetostrictive composite film could be operated without a piezoelectric film based on the Villari effect, which consisted of a single PI-Terfenol-D film. The paper illustrates the potential to develop an all-polymer composite MEMS device capable of acting as a magnetic field or current sensor.

Bifocal lenses with adjustable intensities enabled by bilayer liquid crystal structures.

In this paper, we propose bifocal lenses based on bilayer structures composed of a liquid crystal (LC) cell and LC polymer, and the relative intensity of two foci can be adjusted arbitrarily through applying an external voltage. Two LC layers have different light modulation functions: when circularly polarized light passes through the first layer, part of the outgoing light is converted with PB phase modulation and another part is not converted; followed by the second layer, PB modulation of these two parts would be simultaneously realized but with opposite signs; thus the transmitted left- and right-handed circularly polarized (LCP and RCP) light can be independently controlled. As proof-of-concept examples, longitudinal and transverse bifocal lenses are designed to split an incident LCP light into two convergent beams with orthogonal helicity, and the position of the two foci can be flexibly arranged. Benefitting from the electrically controlled polarization conversion efficiency (PCE) of the LC cell, the relative intensity of the two foci can be adjusted arbitrarily. Experimental results agree well with theoretical calculations. Besides, a broadband polarization and an edge imaging system based on the proposed bifocal LC lenses have also been demonstrated. This paper presents a simple method to design a functional multilayer LC device and the proposed bifocal lenses may have potentials in the optical interconnection, biological imaging, and optical computing.

Deep blue high-efficiency solution-processed triplet-triplet annihilation organic light-emitting diodes using bis(8-carbazol-N-yl)fluorene- and benzonitrile-modified anthracene/chrysene fluorescent emitters

Triplet-triplet annihilation (TTA) emitters can effectively utilize non-radiative triplet excitons through the interaction of low triplet energy excitons to produce high energy singlet excitons, but they are mostly restricted by their multilayered device structure fabricated using layer-by-layer thermal vacuum evaporation. It is a great challenge to develop, for the first time, efficient solution-processed non-doped TTA organic light-emitting diodes (OLEDs). In this study, two solution-processable blue emissive TTA molecules (FAnCN and FCsCN) bearing (anthracen-9-yl)benzonitrile (AnCN) and (chrysen-6-yl)benzonitrile (CsCN) as TTA emissive cores modified with 9,9′-bis(8-(carbazole-N-yl)octyl)fluorene (F) are designed and synthesized, respectively. The experimental and theoretical studies reveal that both molecules exhibit deep blue emissions, amorphous morphology with good thermal stability, high-quality solution-cast thin films, decent hole mobility, high-lying HOMO levels (∼-5.45 eV), and suitable lowest singlet (S1)/triplet (T1) excited states (2T1 > S1) for TTA process. FAnCN and FCsCN are successfully employed as solution-processed non-doped emissive layers (EML) in simple structured TTA OLEDs. These devices show intense blue emissions, low turn-on voltages (∼3.6 V), excellent electroluminescent (EL) performances (EQEmax = 5.47–6.84 % and LEmax = 5.66–5.83 cd/A), and TTA characteristics. Especially, FCsCN-based TTA OLED emits deep blue EL emission peaked at 435 nm with a high EQEmax of 6.84 %. This work not only presents a new strategic design for the preparation of solution-processable TTA emitter, but also further ratifies that the TTA mechanism can also be applicable in solution-processed OLEDs.

Multilayer Core-Shell Fiber Device for Improved Strain Sensing and Supercapacitor Applications.

1D fiber devices, known for their exceptional flexibility and seamless integration capabilities, often face trade-offs between desired wearable application characteristics and actual performance. In this study, a multilayer device composed of carbon nanotube (CNT), transition metal carbides/nitrides (MXenes), and cotton fibers, fabricated using a dry spinning method is presented, which significantly enhances both strain sensing and supercapacitor functionality. This core-shell fiber design achieves a record-high sensitivity (GF ≈ 4500) and maintains robust durability under various environmental conditions. Furthermore, the design approach markedly influences capacitance, correlating with the percentage of active material used. Through systematic optimization, the fiber device exhibited a capacitance 26-fold greater than that of a standard neat CNT fiber, emphasizing the crucial role of innovative design and high active material loading in improving device performance.

Synthesis, Photoluminescence, and Electroluminescence of Phosphorescent Dipyrido[3,2-a;2'3'-c]phenazine-Platinum(II) Complexes Bearing Hole-Transporting Acetylide Ligands.

In this study, novel phosphorescent dipyrido[3,2-a;2'3'-c]phenazine (dppz)-platinum(II)-phenylacetylide complexes were developed to fabricate non-doped organic light-emitting diodes (OLED) by solution-processing. To facilitate the charge carrier injection into the emitting layer (EML), 3,6-di-tert-butylcarbazole-functinalized phenylacetylides were employed. As for the dppz ligand, 9,9-dihexylfluoren-2-yl and 4-hexylthiophen-2-yl side-arms were introduced to the 2,7-positions, which led to reddish orange and red photoluminescence (PL), respectively, in solution and film states (PL wavelength: ca. 600 and ca. 625 nm, respectively). The carbazole-appended phenylacetylide ligands hardly affected the emission color, although unsubstituted phenylacetylides gave rise to aggregate- or excimer-based near-infrared PL with a low quantum yield. Two types of non-doped OLEDs were fabricated: single-layer and multilayer devices. In both devices, the organic layers were fabricated by spin-coating, and the EML consisted of a neat film of the corresponding platinum(II) complex. Therein, electroluminescence spectra corresponding to those of PL were observed. The single-layer devices exhibited low device efficiencies due to a deteriorated charge carrier balance. The multilayer devices possessed hole- and electron-transporting layers on the anode and cathode sides of the EML, respectively. Owing to an improved charge carrier balance, the multilayer devices exhibited higher device performance, affording considerably improved values of luminance and external quantum efficiency.

Fabrication tolerant multi-layer integrated photonic topology optimization.

Optimal multi-layer device design requires consideration of fabrication uncertainties associated with inter-layer alignment and conformal layering. We present layer-restricted topology optimization (TO), which we believe to be a novel technique which mitigates the effects of unwanted conformal layering for multi-layer structures and enables TO in multi-etch material platforms. We explore several approaches to achieve this result compatible with density-based TO projection techniques and geometric constraints. Then, we present a robust TO formulation to design devices resilient to inter-layer misalignment. The novel constraint and robust formulation are demonstrated in 2D grating couplers and a 3D polarization rotator.

High Curvature of Polymer‐Based Miniaturized Flexible Actuator at Very Low Electric Field

AbstractThe use of high electric fields, as well as pre‐stressing, are the two main obstacles to the widespread use of poly(vinylidene fluoride (PVDF)‐based actuators. In response, a new double‐sided multilayer device has been developed which, coupled with a polarization procedure, enables high bending performance at low voltages. The actuator's symmetry allows zero bending at rest, while the high number of layers enables a strong field to be maintained while reducing the applied voltage. X‐ray and permittivity studies reveal the ultimate links between the microscopic material displacement and the actuator deflection. These results, coupled with the analytical model developed in this work, demonstrate that the optimization of complex multilayer systems requires a detailed understanding of mechanics, design, and microstructure. Experimental, analytical and finite element results confirm that such a double‐sided multilayer actuator is of 50% more efficient than a conventional single‐sided actuator, up to 40 V µm−1. These achievements open up new prospects for PVDF‐based actuators in application of healthcare, such as arterial navigation.

Highly stretchable dynamic hydrogels for soft multilayer electronics.

Recent progress in the development of synthetic polymer networks has enabled the next generation of hydrogel-based machines and devices. The ability to mimic the mechanical and electrical properties of human tissue gives great potential toward the fields of bioelectronics and soft robotics. However, fabricating hydrogel devices that display high ionic conductivity while maintaining high stretchability and softness remains unmet. Here, we synthesize supramolecular poly(ionic) networks, which display high stretchability (>1500%), compressibility (>90%), and rapid self-recovery (<30 s), while achieving ionic conductivities of up to 0.1 S cm -1. Dynamic cross-links give rise to inter-layer adhesion and a stable interface is formed on account of ultrahigh binding affinities (>1013 M-2). Superior adherence between layers enabled the fabrication of an intrinsically stretchable hydrogel power source, paving the way for the next generation of multi-layer tissue mimetic devices.

Recent Advances in CMP Slurries: Composition and Analysis Perspectives

Chemical Mechanical Planarization (CMP) slurries play key role during planarization process in advanced semiconductor manufacturing, serving to planarize wafer surfaces and minimize unevenness in multi-layered device scheme. This paper provides a comprehensive review of the composition of CMP slurries and the analytical methods used to evaluate their components. The primary constituents of CMP slurries―abrasive particles, chemical agents, and various additives―are examined in detail, highlighting their roles and interactions. We report the latest research trends in CMP slurry composition and analytical methods, offering insights into future research directions and providing foundational information for optimizing CMP slurry performance. This, in turn, is expected to contribute to the ongoing advancement of the semiconductor industry and the fabrication of high-performance devices.

Mitigating Delamination in Perovskite/Silicon Tandem Solar Modules

As perovskite/silicon tandem solar cells head toward industrialization, one emerging challenge relates to the mechanical reliability of these organic–inorganic multilayer devices. Herein, the fracture toughness and interfacial strength of monolithic p–i–n perovskite/silicon tandems are assessed in the context of module integration. While the weakest layer in the tandem stack investigated is found to be C60, used here as electron‐transport layer (interfacial tensile strength of 0.64 MPa), more concerningly, the fracture energy of the C60/tin‐oxide interface is found to be only 1.2 J m−2. The low fracture toughness of perovskite/silicon tandems can encourage crack propagation and large‐scale delamination during processes used for their integration into modules such as cell cutting, interconnection, and vacuum lamination. By improving the tin oxide buffer layer properties and reducing sputtering‐induced internal stress (associated with the transparent top electrode deposition onto the tin the oxide buffer layer), the fracture energy is improved to over 160 J m−2. A second strategy to mitigate delamination due to the low fracture toughness of the cells is tailoring encapsulation and cell processing techniques specifically toward the perovskite/silicon tandem technology. In this work, a critical reliability issue, relevant for any perovskite‐based optoelectronic technology requiring device packaging, is addressed.