Raman and scanning spreading resistance mapping of the evolution of structural phases near the insulator–metal transition in VO2 films

This paper describes the radio-frequency (RF) characteristics of stacked metal–insulator–metal (MIM) capacitors used in RF CMOS technology. To ensure accurate analysis, various de-embedding methods for stacked MIM capacitors were verified, and an improved RF model was constructed accordingly. To develop an equivalent circuit for the improved RF model by analyzing the RF characteristics of stacked MIM capacitors, we compared de-embedding methods for measured stacked MIM capacitors: one-step (open-pattern or short-pattern) de-embedding and two-step (combined open-pattern and short-pattern) de-embedding. For the analysis of stacked MIM capacitors, at least two-step de-embedding was used, while for precise de-embedding, three-step de-embedding using a thru pattern was employed. Based on the measured values obtained using these two-step de-embedding methods, a modified equivalent circuit was constructed. This circuit was analyzed based on various parameters, including MIM capacitance, quality factor, S-parameter, and Y-parameter, and the results were comparatively examined. The findings highlight outstanding accuracy of the modified model, which is maintained even in high frequency bands.

Fano resonance sensors based on metal–insulator–metal (MIM) waveguides often face the challenge of balancing high sensitivity (S) and a high figure of merit (FOM). In this work, a high-performance refractive index sensor is proposed, consisting of a straight MIM waveguide side-coupled to a novel ring–bridge–rounded square (RBS) resonator. The transmission characteristics and the formation mechanism of Fano resonance are systematically analyzed using the finite element method (FEM). The results demonstrate that the synergistic introduction of rounded square units and an internal bridge structure significantly enhances electromagnetic field localization and optimizes the coupling strength. The optimized device achieves a remarkable refractive index sensitivity of 3268 nm/RIU (refractive index unit, RIU) and a high FOM of 55.4. Furthermore, by employing ethanol as the filling medium, the proposed configuration functions as a temperature sensor, exhibiting a high linear sensitivity of 1.644 nm/°C over the range of −70 °C to 70 °C. The proposed RBS resonator holds promise for compact and high-precision nanophotonic sensing applications.

It has been experimentally observed that Bi2O2Se—a semiconductor with nominally metallic conductivity—can undergo a metal–insulator transition (MIT), yet its microscopic origin remains unclear. Our hybrid density functional theory study uncovers the mechanism behind this transition. Under O- and Se-poor growth conditions, donor defects VO+ and VSe+ form at the highest concentrations, pushing the Fermi level above the conduction band minimum (CBM) and inducing metallic behavior in Bi2O2Se. As the chemical potentials of O and Se increase to moderate levels, the concentrations of VO+ and VSe+ drop, shifting the Fermi level down to the CBM and triggering the MIT. Further enrichment in O and Se yields only a weakly insulating phase, because the densities of VO2+ and VSe2+ rise unexpectedly under these rich conditions, preventing the emergence of a highly insulating phase. This counterintuitive trend is explained by defect-correlation mechanism.

Quantum materials exhibit a rich dynamic of physical parameters, which, when combined, can lead to entirely different behaviors. These parameters constantly compete with each other, with the most influential parameters determining the state of the system. For example, in the case of metal–insulator transitions, electron–electron interactions compete with the kinetic energy of the electrons and disorder. Understanding these complex dynamics is crucial for both fundamental physics and the development of novel technological applications, particularly given the role of disorder in tuning critical temperatures, a property with significant potential benefit in the fabrication of new devices where temperature requirements are still the bottleneck. In this article, properties of the Mott metal–insulator transition within disordered electron systems are explored using the disordered Hubbard model, the simplest Hamiltonian for capturing the metal–insulator transition. The model solutions are obtained using the self-consistent statistical dynamical mean-field theory (statDMFT). statDMFT incorporates local electronic correlation effects while allowing for Anderson localization due to disorder.

Metal-Insulator-Metal (MIM) waveguides are known for confining surface plasmon polaritons at subwavelength scale which are preferable for compact and efficient photonic devices. This work proposes a novel MIM based plasmonic filter with a triangular resonator enclosed by a rectangular cavity to get enhanced performance. A localized surface plasmon is generated by this structure whose performance is analysed using the Finite-Difference Time-Domain (FDTD) simulations. Resonance wavelength, bandwidth and Q-factor are studied based on variations in geometric parameters. The triangular resonator results high Q-factors and selective filtering characteristics. Further its integration with a rectangular cavity improves performance, yielding a significantly improved Q-factor of 235.43. TM field distribution confirms precise mode localization with robust optical filtering. The tuning of apex angle of the triangular resonator improves the optical confinement. It is anticipated that this structure will be a promising candidate for embedding in photonic circuits used for optical communication and biosensing applications.

Lately, random telegraph noise (RTN) has been deemed, via specific mathematical metrics, to be possibly deterministic-chaotic rather than stochastic, with severe implications for applications that leverage the RTN stochastic nature. Yet, this was claimed by analyzing a limited number of RTN traces. Here, we analyze several RTN traces measured in different devices and conditions, mathematically generated traces and traces resulting from advanced simulations of RTN in metal-insulator-metal (MIM) structures. It is shown that the mathematical metrics employed to reveal the deterministic-chaotic nature of RTN are not robust enough to support that claim. Complex RTN is likely to result from inherently stochastic processes embedded in a deterministic multi-body system which could show stochastic chaos, but hardly any determinism.

Achieving high‐performance, polarization‐insensitive broadband absorption with wide angular tolerance remains challenging for perfect absorbers. This work proposes a novel Ge 2 Sb 2 Te 5 (GST) metasurface absorber based on a metal–insulator–metal structure, featuring dual‐sized cylindrical amorphous GST meta‐atoms, a MgF 2 spacer, and a gold reflector. The design exhibits fourfold rotational symmetry, enabling polarization‐independent operation. By spectrally overlapping the magnetic and electric dipole resonances supported by the dual meta‐atoms, an average absorptivity of 94% from ultraviolet to near‐infrared is achieved. Moreover, the absorber maintains 83% average absorption even at 70° incidence, showing remarkable angular tolerance. Optical switching is also feasible via GST phase modulation. These attributes make the proposed absorber highly promising for integrated optoelectronic applications.

Robust control over the coupling and propagation of surface plasmon polaritons (SPPs) is essential for advancing various plasmonic applications. Traditional planar structures, commonly used to design SPP directional couplers, face limitations such as low extinction ratios and design complexities. These issues frequently hinder the dense integration and miniaturisation of photonic systems. Recently, exceptional points (EPs)—unique degeneracies within the parameter space of non-Hermitian systems—have garnered significant attention for enabling a range of counterintuitive phenomena in non-conservative photonic systems, including the non-trivial control of light propagation. In this work, we develop a rigorous temporal coupled-mode theory (TCMT) description of a non-Hermitian metagrating composed of alternating silicon–germanium nanostrips and use it to explore the unidirectional excitation of SPPs at EPs in the visible spectrum. Within this framework, EPs, typically associated with the coalescence of eigenvalues and eigenstates, are leveraged to manipulate light propagation in nonconservative photonic systems, facilitating the refined control of SPPs. By spatially modulating the permittivity profile at a dielectric–metal interface, we induce a passive parity–time ()-symmetry, which allows for refined tuning of the SPPs’ directional propagation by optimising the structure to operate at EPs. At these EPs, a unidirectional excitation of SPPs with a directional intensity extinction ratio as high as 40 dB between the left and right excited SPP modes can be reached, with potential applications in integrated optical circuits, visible communication technologies, and optical routing, where robust and flexible control of light at the nanoscale is crucial.

This study presents a novel, to the best of our knowledge, ultra-wideband nanobiosensor based on a double-negative (DNG) metamaterial perfect absorber for early cancer detection through exosomal biomarker analysis. Our biosensor operates across a broad frequency range from 70THz to 3PHz, exhibiting near-unity absorption, i.e.,exceeding 99%, and angular and polarization insensitivity, i.e.,providing polarization-independent absorption across the full spectrum of polarization angles (0° to 90°), ensuring stable performance under both transverse electric (TE) and transverse magnetic (TM) polarized waves. Of particular interest is its performance in the near-infrared (NIR) region (70-400THz), where the sensor's DNG characteristics manifest through simultaneously negative permittivity and permeability, enhancing field confinement and sensitivity. This spectral window is especially conducive to label-free, non-invasive detection of circulating exosomes, critical indicators of early stage oncogenesis. The sensor is constructed using a tri-layer metal-insulator-metal (MIM) architecture comprising nickel (Ni) layers and a silicon dioxide (SiO2) dielectric spacer. The design leverages the plasmonic and thermal stability properties of Ni and the low optical attenuation of SiO2 to achieve optimal absorption and structural robustness. Electromagnetic simulations demonstrate strong electric and magnetic resonances, producing significant near-field enhancements. These improve the detection of subtle dielectric changes associated with exosomal binding events. The sensor maintains high absorption efficiency across oblique incidence angles and various polarization states, making it suitable for real-world biomedical diagnostic applications. By focusing on the NIR regime where tissue transparency and molecular vibrational modes intersect, the proposed biosensor enables the discrimination between cancer-derived exosomes and their normal counterparts, as confirmed through spectral and field distribution analyses. Thedemonstrated performance highlights the sensor's promise for next-generation photonic platforms targeting early cancer diagnostics, with potential extension to environmental monitoring and energy harvesting technologies.

This paper presents a fifth-order inverse Chebyshev bandpass filter (BPF) operating at 600-840 MHz, realized using a stacked glass-based Integrated Passive Device (IPD) technology featuring Through-Glass-Vias (TGVs). The architecture employs a vertically stacked topology that enables the independent optimization of 3D TGV inductors and Metal-Insulator-Metal (MIM) capacitors, which are integrated via a high-precision chip-to-wafer bonding process. The fabricated BPF achieves an exceptionally compact footprint of 0.012λ0×0.008λ0, a sharp shape factor (SF) of 2.62, and a low insertion loss of 1.26 dB. These results represent a superior combination of miniaturization and selectivity compared to other filters realized on competing substrates. This work demonstrates a scalable methodology for co-integrating high-performance passive components on glass interposers, advancing the development of 2.5D/3D ultra-high-density heterogeneous systems by significantly enhancing integration density and RF performance.

Static metasurfaces offer precise control over light but lack reconfigurability, limiting their use in dynamic applications. Introducing tunability via external stimuli, such as magnetic fields, enables active control of their optical response, broadening their functionality. In this computational study, we present the design of a metal–dielectric–metal magnetoplasmonic metasurface with improved magnetic field tunability, surpassing the magneto-optical response of unstructured ferromagnetic materials. This improvement arises from the synergistic effect of localized plasmon excitation, surface lattice resonance, and Fabry–Pérot cavity modes. The design approach presented here consists in matching the characteristic resonance frequencies of the three phenomena by iteratively adjusting the structural parameters of the metasurface: nanostructure size, lattice period, and cavity layer thickness. This optimization led to a substantial enhancement in the reflectance modulation induced by an external magnetic field, with the overall contrast exceeding that of an unstructured cavity by more than an order of magnitude across various regions of the visible to near-infrared spectrum, under relatively low magnetic fields. This unique capability makes the system a promising tool for magnetic field-sensitive optical modulation of reflected light intensity, with potential applications as a laser amplitude modulator.

Nanolaminates─atomically layered stacks of dissimilar oxides─are widely used to engineer dielectric behavior at the nanometer scale. Among these, atomic layer deposition (ALD)-grown Al2O3/TiO2 stacks have been reported to exhibit "giant" dielectric constant (κ ∼ 103) at subnanometer periods. Here we show that the apparent high-κ is not an intrinsic dielectric enhancement but a measurement artifact arising from electrically percolative Al2O3/TiO2 stacks treated as ideal dielectrics. Using Al2O3/TiO2 nanolaminate metal-insulator-metal (MIM) capacitors and a combination of electrical (C-f, I-V, EIS), spectroscopic (XPS, HAXPES), and structural (TEM) measurements, we found that TMA/H2O growth yields Al-deficient Al2O3 on TiO2 that appears morphologically continuous yet lacks full atomic closure, forming electronically percolative pathways that recover insulating behavior only after a fully coalesced overlayer develops. In contrast, TMA/O3 deposition produces fully continuous Al2O3 that remains insulating even at subnanometer thickness. These results establish practical design rules, showing that oxidant chemistry and film thickness together govern film continuity and insulating behavior, thereby clarifying when ultrathin ALD Al2O3 functions as a true insulator versus a quasi-conductive layer. The insights extend directly to applications in microelectronics (gate stacks, MIM/DRAM capacitors), quantum devices (2DEGs, tunnel barriers), and electrochemical/photovoltaic systems (battery electrodes, electrocatalysts, and perovskite interface engineering), where reliable subnanometer coatings are essential.

In this research, a plasmonic metal–insulator–metal (MIM) biosensor is proposed and numerically analyzed for label-free and highly sensitive refractive index detection. The design incorporates a hybrid configuration consisting of a hexagonal resonant cavity coupled with a narrow rectangular slit along its lower boundary. This particular arrangement, which has not been previously reported, enables the excitation of two distinct resonance modes that contribute to improved spectral resolution and sensing precision relative to conventional MIM structures. Finite-difference time-domain (FDTD) simulations were employed to investigate the optical response and optimize the geometrical parameters of the device. The optimized sensor demonstrates strong electromagnetic field confinement, achieving a sensitivity of 770.27 nm/RIU and a figure of merit (FoM) of 160.47, both of which surpass values reported in related studies. Owing to its compact geometry and compatibility with nanoimprint lithography, the proposed design can be fabricated with high practicality. These findings suggest that the device offers an efficient and scalable platform for real-time, label-free detection of carcinoembryonic antigen (CEA) and other biomarkers relevant to early-stage disease diagnostics.

Abstract The growing field of conformable and bio-integrated electronics is enabling the development of innovative applications such as wearable sensors, electronic skin, and implantable devices. This evolution requires advanced materials and fabrication strategies capable of delivering electrical functionality without compromising mechanical compliance. In particular, understanding the electrical behavior of the metal-insulator-semiconductor (MIS) structure is fundamental, as it forms the gate stack in conformable transistors. Therefore, a detailed MIS electrical assessment is essential for the design and integration of reliable, flexible field-effect platforms and wearable electronic
systems. Here, we present conformable MIS capacitors based on few-layer MoS2, inkjet-printed PEDOT:PSS electrodes, and ultrathin bilayer poly(vinyl formal) (PVF) dielectrics on polyimide substrates, and we report their electrical behavior through capacitance-voltage (C-V) profiling and equivalent circuit modeling. To our knowledge, this is the first characterization of such a hybrid MIS structure by C-V measurements, providing direct insight into the dielectric and semiconductor contributions and validating the suitability of this technology for conformable electronics. Our results show a stable and reproducible capacitance modulation of about one order of magnitude under bias voltage changes at low frequencies (∼ 100 Hz), with reliable operation for frequencies up 10 kHz, and robust performance within the investigated bending-induced strain range. This validates the device mechanical resilience and its suitability for integration into
conformable field-effect platforms and wearable electronic systems.

The topochemical reduction process has been demonstrated to generate a range of metastable and structurally distinct phases in transition metal oxides, thereby providing an expansive parameter space for engineering correlated electron systems. Among these systems, La2/3Sr1/3MnO3 (LSMO), a prototypical semi-metallic ferromagnet, has attracted significant attention as a promising candidate for memory and spintronic applications. Here, we demonstrate that utilizing topotactic reduction under compressive stress modulation enables a reversible structural transition from the pristine perovskite phase to a hydrogenated brownmillerite (HBM) phase. Density functional theory calculations reveal that the incorporated H atoms are most likely to occupy oxygen vacancies, preferentially occupying two oxygen vacancies and forming MnO4H2-like octahedral structures. This unique hydrogenation process significantly alters the electronic structure, inducing a transformation from a ferromagnetic metallic state to a weakly ferromagnetic insulating state, accompanied by a decrease in the saturation magnetic moment from 2.87 to 0.59 μB at 10 K. The temperature-dependent resistivity curve of the HBM phase can be effectively fitted using the thermal activation model. After re-oxidation, both the magnetic properties and resistivity are restored to their original states. Unlike conventional control methods, this reversible phase transition provides a unique platform for investigating emergent properties arising from hydrogen-mediated chains and networks, opening new avenues for functional material design.

Abstract Vortex beams (VBs) hold substantial importance within the realms of optics and photonics. Currently, while numerous studies have focused on generating VBs using metasurfaces, most schemes are restricted to static modulation. Vanadium dioxide (VO 2 ) exhibits significant insulator–metal transition properties, and its physical properties change under specific temperature or external stimuli. VO 2 is an ideal candidate for designing dynamic metasurfaces and is expected to break through the static limitations of existing VB generation techniques. In this study, we propose an innovative scheme to generate polymorphic VBs using VO 2 metasurface. In this scheme, meta-atoms are especially designed to exhibit different optical responses at different temperatures. When VO 2 is metallic, multiple VBs with different topological charges (TCs) in the far field are generated in three polarization channels. When VO 2 undergoes insulation, focused VBs with specific TCs in the near field are generated in three different channels. Therefore, multichannel VBs can be switched by temperature response and polarization multiplexing. Our scheme provides a novel way to dynamically generate and manage VBs.

Abstract Iron-based superconductors show great potential for high-field magnet applications. The electromagnetic properties of iron-based superconducting (IBS) uninsulated coils are crucial for their future practical applications, yet characteristics such as charging delay and turn-to-turn contact resistivity (R ct ) remain poorly understood. To address this, we fabricated metal-insulation (MI) and no-insulation (NI) iron-based superconducting double pancake coils (DPCs) and systematically tested their charging and sudden-discharging behaviors. Experimental results revealed that the R ct of the IBS-MI coil is 6.3 times higher than that of the IBS-NI coil, along with a significantly shorter charging delay. Moreover, an interesting phenomenon was discovered: the R ct of uninsulated IBS coils is much lower than that of the REBCO coils reported in previous studies. For rigorous verification of this finding, MI and NI REBCO coils were prepared and subjected to charging and sudden-discharging tests. Through comparison, it is found that the R ct of the REBCO-MI coil is 73.6 times greater than that of the IBS-MI coil, while the R ct of the REBCO-NI coil is 3.6 times greater than that of the IBS-NI coil. The main reasons for this difference will also be analyzed in this paper. From an application perspective, the low R ct of uninsulated coils also means high thermal stability and self-protection. This work lays the foundation for investigating the proportional and integral (PI) feedback control method to eliminate magnetic field delays and for validating the thermal stability of IBS uninsulated coils in future studies.

Accurate modeling of on-chip passive components is vital for reliable integrated circuit (IC) design. However, this is non-trivial due to the inherent heterogeneity of the structures and the wide range of material parameters involved. In this work, we present a single-source boundary integral equation (BIE) for modeling on-chip interconnects and passive elements. To reduce the number of discretization elements—and thus the number of unknowns—we construct a 3-D differential surface admittance (DSA) operator for piecewise homogeneous cuboidal and rectilinear polyhedral objects. Specifically, a novel method is proposed to handle material interfaces efficiently. By combining this new formulation of the DSA operator with the augmented electric field integral equation (EFIE), we obtain a framework that enables accurate modeling and fast broadband impedance extraction of on-chip structures. The proposed approach is validated through several numerical experiments, including important applications such as metal-insulator-metal (MIM) capacitors, and demonstrates excellent agreement with reference solutions while significantly reducing computational cost compared to state-of-the-art solvers.

In this work, a novel low-profile tunable ultra-wideband (UWB) K/Ka-band (14–40 GHz) dual circularly polarized magneto-electric antenna element has been designed, analyzed, and validated through circuit modeling, simulations, fabrication, and experimental testing for application in 5G/6G phased-array antennas. The antenna has compact dimensions of 0.5λ₀× 0.5λ₀ × 0.06λ₀/0.09λ₀, which can be further reduced to 0.25λ₀× 0.25λ₀ × 0.05λ₀ when metal–insulator–metal (MIM) and/or gap capacitors are employed. The proposed antenna exhibits a high gain of 9 dB, a wide scanning angle of ±75°, and an efficiency exceeding 85% across the entire operating frequency band. In addition, it demonstrates high isolation between ports and between co-polarized and cross-polarized radiation patterns, reaching 25 dB. The resonant frequency of the antenna is tunable, with a variation of up to 97% over the K/Ka-band frequency range. This tuning capability is achieved using MIM capacitors connected to the vias of the circular patch and/or gap capacitors, which collectively function as split-ring resonators (SRRs). Fabrication and experimental testing of the antenna confirm good agreement with the simulated results. The antenna is easily fabricated using glass substrates and standard epoxy/glass processes with only two layers, making it highly suitable for antenna-in-package applications based on glass technology. Since the antenna element is specifically designed for phased-array applications, array configurations were also investigated. Analysis of 512-element arrays shows that the Sunflower layout provides enhanced gain and overall performance while utilizing more than 50% fewer antenna elements compared to a conventional rectangular array.