Metal Insulator Research Articles

Multifunctional metasurface for multispectral compatible camouflage of laser and infrared with thermal management

Multispectral compatible camouflage has attracted widespread attention due to the rapid development of various detection technologies. This work presents a multifunctional metasurface that is compatible with laser stealth, infrared shielding, and the thermal management function. To achieve laser stealth, the metasurface is designed as a metal–insulator–metal (MIM) structure for high absorption of laser lights at 1.06 and 1.54 µm, with absorption rates of 97.7 and 95.9%, respectively. Also, the metasurface is designed to minimize the specular reflectance of a 10.6 µm laser light based on the phase cancellation principle. To achieve infrared stealth, the proposed metasurface has achieved an ultralow emissivity in the atmosphere window, with an average emissivity of 0.04 in the 3–5 µm range and 0.11 in the 8–14 µm range. Additionally, the thermal management function is achieved by using the high absorption property of the metasurface in the non-atmospheric window (5–8 µm), which further improves the stealth performance in the infrared band. This work provides a novel, to the best of our knowledge, strategy to realize multispectral compatible camouflage with the thermal management function by using a compact integrated metasurface, indicating that it has promising prospects in future high-performance compatible stealth applications.

Triple Independently Tunable Sensing with Multiple Resonances Based on Metal-insulator-metal Waveguide

In this study, a novel plasmonic refractive index sensor is proposed, featuring a metal–insulator–metal (MIM) waveguide coupled with a composite cavity structure consisting of a double-arc rectangle cavity, a bridge cavity and a three-half-ring configuration cavity. Finite element simulations are used to analyze the transmission characteristics and magnetic field distributions. The results show that six resonance peaks can be produced by three independent resonators. Moreover, there is a good linear relationship between these resonance wavelengths and the structural parameters of the resonators. Then, the refractive index sensing performances of the structure are analyzed by changing the refractive index of the medium within the resonator. The highest sensitivities of the peaks in their resonators are 1732, 2800 and 4568 nm/RIU, respectively. In addition, the proposed structure is tested for the simultaneous detection of the peanut oil concentration of three different blended oils: soybean-peanut, peanut-rapeseed and peanut-sunflower. The ability of the sensor to accurately and simultaneously measure these different oil mixtures highlights its potential for biochemical sensing.

Hetero dielectric based dual material gate AlGaN channel MISHEMT for enhanced electrical characteristics

Herein, we report an AlGaN channel metal insulator semiconductor high electron mobility transistor (MISHEMT) in dual material gate (DMG) architecture with two different dielectrics as gate insulator for enhancing the DC performance of the device. The use of a high-k dielectric material as gate insulator below gate metal 1 and a low-k dielectric below gate metal 2 results in significant threshold voltage variation along the channel. This contributes to improved average carrier velocity which in turn results in better current drive. The proposed device exhibits a peak current of 162 mA/mm at zero gate bias, whereas, the DMG and single material gate (SMG) AlGaN channel HEMTs offer currents of 137 mA/mm and 125 mA/mm respectively. The peak transconductances are about 24.66 mS/mm, 23.68 mS/mm and 22.71 mS/mm respectively for the proposed device, DMG and SMG HEMTs. The proposed device reduces the OFF current by an order of 106 compared to that of DMG HEMT.

Enhanced Carrier Mobility and Thermoelectric Performance by Nanostructure Engineering of PEDOT Thin Films Fabricated via the OCVD Method Using SbCl5 Oxidant

AbstractAir‐stable, lightweight, and electrically conductive conjugated polymers have attracted significant attention for thermoelectric applications, especially in low‐temperature environments. However, their low carrier mobility has limited broader adoption. This study addresses this challenge by investigating the nanostructure of poly(3,4‐ethylenedioxythiophene) (PEDOT) thin films fabricated via oxidative chemical vapor deposition (oCVD) at various deposition temperatures. Through systematic control of the semi‐crystalline orientation and π–π stacking distance, a substantial enhancement in carrier mobility (23.58 ± 1.71 cm2 V−1 s−1) and electrical conductivity (6345 ± 210 S cm−1) is achieved. The thermoelectric power factor demonstrates a direct correlation with deposition temperature, achieving a maximum value of 112.57 ± 4.33 µW m−1 K−2. PEDOT thin films fabricated at higher deposition temperatures show minimal reductions in electrical conductivity as absolute temperature decreased, reflecting a lower resistivity ratio and extended metallic state, as indicated by the metal–insulator transition in the Zabrodskii plot. Incorporating the Seebeck coefficient into the parabolic energy band diagram revealed strong agreement between theoretical and experimental carrier mobility, while also indicating that the energy barrier for intercrystalline charge transport decreases as deposition temperature increases. The highly face‐on orientation and reduced π–π stacking distance in PEDOT thin films facilitate quasi‐1D conduction, thereby enhancing carrier mobility.

Designing ZrO2-blended nanocomposite MIM capacitors for future OFET applications and their characterizations

Organic field-effect transistors (OFETs) have been exploited as sensors for a variety of applications due to their excellent advantages over diodes and other electronic devices. Capacitors are one of the key components of the OFET designs that consist of a dielectric layer sandwiched between two parallel metal plates. The dielectric layer should be thin and/or have a high k constant value to achieve a high capacitance value (Ci, areal capacitance), so more charge carriers can be accumulated at the interface between the dielectric and the organic semiconductor, for OFETs to operate under low voltage (< 3 V). In this study, high-k nanocomposites (NCs) of ZrO2 metal oxide ceramic nanoparticles (NPs) in varying concentrations blended in two different polymer matrixes, poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and cyanoethyl cellulose (CEC) have been utilised as the dielectric layer in metal-insulator-metal (MIM) capacitors. The physical and electrical properties of fabricated MIM capacitors were evaluated. The measured areal capacitance, Ci, values demonstrated a gradual rise with increasing ZrO2 metal oxide content in both polymer matrixes. ZrO2-PVDF-HFP-based capacitors exhibited a two-fold increase in Ci, 91.86 ± 6.1 nF/cm2 (a 140 % increase) for 10 wt % NP content. Similarly, areal capacitance values of 76 ± 3.03 nF/cm2 (a 45 % rise) was measured on MIMs using CZ10 dielectric layer. High average dielectric constant (k) values of 28.61 and 35.68 for CZ5 and PZ5, respectively) were obtained. As expected, leakage current density increased for higher NP % in polymer matrixes. Nevertheless, all MIMs yielded average leakage current density < 1.75 × 10−6 (A/cm2) at 2 V. Therefore, the reported nanocomposites are suitable dielectric layers for OFETs and as platforms for gas, chemical and photoactivated sensing devices.

Single-cell Raman spectroscopy for rapid detection of bacteria in ballast water and UV254 treatment evaluation

The increasing global trade has facilitated the transfer of ship ballast water, which has emerged as a primary pathway for alien species invasion into marine ecosystems, posing significant threats to marine biodiversity. Addressing the technical challenges in rapid microorganism detection and treatment efficiency assessment, this study developed a confocal Raman microscopic imaging (CRMI) system integrated with a metal-insulator-metal (MIM) broadband surface-enhanced Raman scattering (SERS) chip, enabling efficient acquisition of single-cell Raman spectroscopy (SCRS). By incorporating machine learning algorithms, the system achieved precise identification of up to 10 bacterial types in ballast water, exhibiting remarkable performance metrics with average accuracy, sensitivity, specificity, and precision above 95.5 %, 95.5 %, 99.5 %, and 95.5 %, respectively. To evaluate the efficacy of ultraviolet (UV) treatment, a Raman spectroscopy-based approach combined with heavy water labeling was introduced to characterize the changes in bacterial single-cell metabolic activity under UV254 irradiation. Experimental results demonstrated that a 10-min UV254 exposure at an effective intensity of 2 mW/cm2 was sufficient to achieve complete bacterial sterilization for the specific ballast water used in our experiment. This study not only established an efficient and accurate method for rapid detection of mixed bacteria but also provided a novel perspective for assessing UV treatment effects. It holds significance and practical value for optimizing ship ballast water management strategies and safeguarding the safety of marine ecosystems.

Controllable Epitaxial Growth of Adlayer-Free Hexagonal Boron Nitride Monolayers on Silicon-Incorporated Ni(111) Substrates for Metal–Insulator–Metal Tunneling Devices

Controllable Epitaxial Growth of Adlayer-Free Hexagonal Boron Nitride Monolayers on Silicon-Incorporated Ni(111) Substrates for Metal–Insulator–Metal Tunneling Devices

Optical properties of an Au-SiO2-Au nanocube and its application on solar thermal conversion

Nanoparticles with different structures have been extensively studied for solar energy harvesting due to their tunability which can help achieve broadband light absorption. While the utilization of nanoparticles that can generate localized surface plasmon resonance (LSPR) in direct absorption solar collectors (DASCs) has been extensively investigated in previous work, the application of nanoparticle-excited magnetic resonance (MR) in DASCs have not attracted much attention. In this study, we propose an Au-SiO2-Au metal-insulator-metal (MIM) nanocube, which distinguishes from previous spherical or cylindrical pure metal structures. It has been demonstrated that the MIM nanoparticles exhibit broader absorption bands and more pronounced peaks as a consequence of LSPR compared to pure metal nanoparticles. Additionally, peaks of a certain size are generated due to MR. In addition, we demonstrate that the peaks induced by MIM nanocube can be readily tuned by varying the particle size and adjusting the particle structure, thereby facilitating a more uniform distribution of peaks. Further investigation shows that the solar-weighted absorption coefficient Am of the DASC using MIM nanocube type nanofluids is increased by 19.68 % and 8.48 % compared to Au nanosphere and Au nanocylinder types, respectively, at a volume fraction of 10−6 and a collector depth of 2 cm. Consequently, the proposed MIM nanocube represents a promising alternative for the selection of nanofluid suspended particles for the DASCs.

Intelligent microwave absorption of VO2@PDA/RGO composites based on dynamic interfacial polarization performance

To design smart microwave-absorbing materials (MAMs), it is essential to adjust the corresponding electrical conductivity and dielectric parameters according to variable conditions. However, it is still challenging to concurrently adjust the effective absorbing intensity and frequency range in MAMs due to their interdependent constraints. Here, we developed intelligent MAMs by incorporating core–shell structure vanadium dioxide @ polydopamine (VO2@PDA) powders as polarization loss units, while the subwavelength-sized reduced graphene oxide microspheres (RGOms) were used as conduction loss units. When the temperature is higher than the metal–insulator phase transition temperature of the insulator state VO2 (M), the corresponding metal state VO2 (R) could be produced, which, therefore, contributes to an enhanced interfacial polarization loss due to the significant electrical performance differences between the VO2 (R) and the PDA shell. As an optimized result, the changes of the effective absorption frequency band (▵EAF) and reflection loss (▵RL) of the RV3 composite could be approximately 1.5 GHz and 24 dB, respectively, attributable to the phase transition of VO2. This study provides a novel approach for the adjustment of electromagnetic responses based on dynamic interfacial polarization performance, which offers broader prospects for developing next-generation smart electromagnetic absorption devices with both reversible microwave absorption frequency range and intensities.

Magnetic field sensor based on multiple Fano resonance in metal-insulator-metal waveguide coupled with cross-shape resonator

Abstract In this paper, an innovative plasmonic magnetic field sensor (MFS) that exploits a Metal-insulator-Metal (MIM) waveguide configuration with an asymmetric cross-shaped resonator is constructed. The design enables the observation of double Fano resonance in the transmission spectrum, resulting from the coupling between continuous spectrum and discrete spectrum. By incorporating magnetic fluid in the asymmetric cross-shape resonator, the Fano line shapes can be tuned by the external magnetic field. Finite-Difference Time-Domain (FDTD) is used to simulate the spectra response to external magnetic fields and geometrical sizes. The proposed structure exhibits remarkable magnetic field sensitivity of 12.1 p m / O e within the detection range of 15 O e to 199 O e . The resolution of MIM magnetic field sensors can reach 0.0826 O e . The optimal figure of merit (FOM) and maximum Q factor of the Fano dip are about 6.9 × 10 − 4 / O e and 66.74, respectively. Meanwhile, The proposed Fano resonance MFS has some advantages, including compact size, high sensitivity, and cost-effectiveness. A strong linear relationship between the magnetic field and resonance wavelength indicates that the proposed structure can find potential applications in diverse fields such as magnetic field sensors, aircraft navigation, and even nuclear energy generation.

Effect of annealing conditions on resistive switching in hafnium oxide-based MIM devices for low-power RRAM

Abstract This work presents resistive switching (RS) behaviour in HfO2-based low-power resistive random-access memory (RRAM) devices. A metal-insulator-metal (MIM) structure (Au/HfO2/Pt) was fabricated by sandwiching a thin insulating layer of HfO2 between Pt and Au electrodes. HfO2 films deposited by RF sputtering at room temperature were rapid thermally annealed in N2 ambient at 400 °C and 500 °C. Grazing angle x-ray diffraction (GIXRD), Field emission gun-scanning electron microscopy (FEG-SEM), atomic force microscopy (AFM), and x-ray photoelectron spectroscopy (XPS) were employed to analyse the phase, crystal structure, morphology, surface roughness and chemical composition of the HfO2 films. The bipolar RS could be observed in both as-deposited and annealed HfO2 film-based devices from I–V characteristics measured using a source meter. We have investigated the effect of annealing temperature and annealing ambient on the phase formation of HfO2 as well as the RS characteristics and compared with as-deposited film-based device. Annealed HfO2 film-based devices exhibited improved electrical characteristics, including stable and repeatable RS at significantly lower switching voltages (&lt;1 V) which indicates low power consumption in these devices. The relatively lower processing temperature of the HfO2 films and that too in the films deposited by physical vapor deposition (PVD) technique-RF magnetron sputtering makes this study significantly useful for resistive switching based non-volatile memories.

Study on the fabrication of high-quality hafnium oxide thin films using spatial rotated atomic layer deposition and supercritical fluids treatment

This study explores the experimental outcomes and discussions surrounding the deposition of high-quality hafnium oxide (HfO2) thin films using spatial rotated atomic layer deposition (SRALD). The primary objective was to enhance the efficiency of ALD processes while maintaining film quality comparable to conventional methods. The SRALD system, developed by Kudos Nano Technology, was employed to deposit HfO2 films over a four-step process. Following deposition, the films underwent high-pressure annealing and supercritical fluids treatment, which are known for reducing thermal budgets. The key findings revealed that high-pressure annealing resulted in a significant reduction in the leakage current by up to 50%, while supercritical fluids treatment improved the dielectric constant of the films, reaching values as high as 23. These treatments also contributed to enhancing the uniformity and density of the films, as confirmed by cross-sectional transmission electron microscopy and x-ray reflectometry analyses. The electrical properties of the resulting metal–insulator–semiconductor capacitors were thoroughly investigated, demonstrating a marked improvement in capacitance-voltage characteristics with minimal hysteresis.

Plasmonic Sensors Based on a Metal-Insulator-Metal Waveguide-What Do We Know So Far?

Metal-insulator-metal (MIM) waveguide-based plasmonic sensors are significantly important in the domain of advanced sensing technologies due to their exceptional ability to guide and confine light at subwavelength scales. These sensors exploit the unique properties of surface plasmon polaritons (SPPs) that propagate along the metal-insulator interface, facilitating strong field confinement and enhanced light-matter interactions. In this review, several critical aspects of MIM waveguide-based plasmonic sensors are thoroughly examined, including sensor designs, material choices, fabrication methods, and diverse applications. Notably, there exists a substantial gap between the numerical data and the experimental verification of these devices, largely due to the insufficient attention given to the hybrid integration of plasmonic components. This disconnect underscores the need for more focused research on seamless integration techniques. Additionally, innovative light-coupling mechanisms are suggested that could pave the way for the practical realization of these highly promising plasmonic sensors.

SnO2/SiO2/Si solar cell performance dependence on the interface states and the silica layer thickness

The solar cell Metal Insulator Semiconuctor (MIS) SnO2/SiO2/Si where tin dioxide (SnO2) acts as the metal were studied. The silica layer (SiO2) is the insulator, and Si is the semiconductor considered here to be of N-type. The effect of the density of the interface states mainly on the open circuit voltage and on the energy conversion efficiency, as well as the optimal thickness of the silica layer corresponding to the best conversion efficiency were investigated. Both the open circuit voltage and the conversion efficiency are altered as the interface states density increases. This is because of the reduction of the number of free carrers which are trapped by the interface states. The silica optimal thickness were determined to be equal to 19.8 Å. This corresponds to a conversion efficiency of 16.15%. The information derived from the present study can be useful for experimentalists to fabricate the studied MIS solar cell. This permits to reduce both the time and the cost of the experiments.

Electrical properties and conduction mechanisms of ε-GaSe films for selector and phase-change memory applications

Owing to the pressing requirement for advanced memory solutions driven by explosive data growth, nonvolatile and fast-operating 1S1R structured XPoint memory has become a prominent focus, with recent interest shifting towards the 1S structured selector-only memory. The use of chalcogenide-based materials in these technologies constrains the application of such memories because of their complex quaternary compositions. This study investigated the previously unreported potential of GaSe, a simple binary Se-based chalcogenide, for applications as a selector and phase-change memory (PCM). In this study, ε-GaSe thin films were deposited using thermal evaporation and subsequently annealed in a Se atmosphere for 1 and 2 h. These ε-GaSe thin film devices incorporated metal–insulator–metal construction to exhibit both selector and PCM characteristics. The ε-GaSe device that was Se-annealed for 1 h demonstrated superior performance with a lower threshold voltage and off current, high selectivity as a selector, and reduced set voltage and reset power as a PCM. These characteristics render the proposed device a highly promising candidate for dual selector/PCM applications. To explain the electrical behavior of the ε-GaSe device, we propose the conduction mechanism model depending on the Se-annealing time, which is related to the change in the physical properties of ε-GaSe.

Colorimetric Fabry-Pérot Sensor with Hetero-Structured Dielectric for Humidity Monitoring.

A full-color colorimetric humidity sensor with high brightness is proposed by using a hetero-structured dielectric film in a metal-insulator-metal (MIM) resonator. A humidity-responsive polymer is designed to graft on top of a metal-organic frameworks (MOFs) thin film (MOFs-Polymer) as insulator layer in the resonator. Programmable tuning of reflected color is achieved by controlling the polymer thicknesses, and finite difference time domain simulation of light-matter interactions at subwavelength scales proves the dependence of the reflected wavelength on dielectric layer thickness of the resonator. Vivid full-color changing is realized during tracking humidity process due to swelling of the stimuli-responsive polymer. Ultrafast response (≈0.75 s) is achieved for tracking trace H2O from H2O/methanol mixture, which is ≈104 faster than that of the pure polymer-based MIM resonator. Meanwhile, the study observes significant spectral redshift because the porous MOFs film facilitates the preconcentration of external stimulus and improves the detection sensitivity of the resonator. Further, double-channel anti-counterfeiting multiplexing imaging is devised on the MIM resonator by photomask technology. Patterned encoding for security label is achieved on the MIM resonator by engineering humidity-tunable pixels of Au/MOFs-Polymer/Au and humidity-invalid pixels of Au/MOFs/Au.

Multi-Cavity Nanorefractive Index Sensor Based on MIM Waveguide.

Within this manuscript, we provide a novel Fano resonance-driven micro-nanosensor. Its primary structural components are a metal-insulator-metal (MIM) waveguide, a shield with three disks, and a T-shaped cavity (STDTC). The finite element approach was used to study the gadget in theory. It is found that the adjustment of the structure and the change of the dimensions are closely related to the sensitivity (S) and the quality factor (FOM). Different model structural parameters affect the Fano resonance, which in turn changes the transmission characteristics of the resonator. Through in-depth experimental analysis and selection of appropriate parameters, the sensor sensitivity finally reaches 3020 nm/RIU and the quality factor reaches 51.89. Furthermore, the installation of this microrefractive index sensor allows for the quick and sensitive measurement of glucose levels. It is a positive contribution to the field of optical devices and micro-nano sensors and meets the demand for efficient detection when applied in medical and environmental scenarios.

Reset transition in HfO2-Based memristors using a constant power signal

Memristors, also known as resistive switching devices, have great potential for applications in memory and neuromorphic systems. Understanding the switching mechanisms is crucial since ReRAM memories need to operate at high frequencies. It is known the reset transition is dominated by the conductive filament Joule heating. We have studied the reset transition in TiN/Ti/HfO2/W metal–insulator–metal memristors by applying constant power signals to different initial filament thicknesses, which were obtained using different initial low resistance states. The results show that power value controls the reset times, decreasing when the power is increased. On the other hand, larger resistances lead to faster reset transitions. These measurements have allowed us to obtain a value of the thermal resistance of the conductive filament. Moreover, we have observed the reset times as a function of the initial resistance and the power lies on a common plane, which allows us to estimate the transition time by fixing an initial resistance and a power value.

Physical Origin of the Ferroelectric-Type Hysteresis in MIM Structures with Amorphous Dielectric Film.

The ferroelectric-type characteristics in metal-insulator-metal (MIM) structures with amorphous dielectrics are observed, which may open a new window for a class of new ferroelectric devices. However, the working principles of these ferroelectric devices are not well explained. It has been proposed that oxygen ion (O2-) and charged vacancy (Vo2+) migrations are associated with this ferroelectric-like behavior. In this work, a systematic experimental design is carried out to investigate the origin of O2- and Vo2+ (from the interface or bulk oxide?), the transport species (O2-, Vo2+, or both of these two species?), and the ion transport mode (long-range transport or local movement?). The experimental results answered all these questions. In addition, the role of the thickness of the dielectrics is also studied. This work sets the fundamentals of these amorphous oxide-based devices, guiding future explorations to engineer them.

Magnetocaloric effect, magnetotransport and magnetic properties of polycrystalline Pr(0.65-x)GdxSr0.35MnO3 (x ≤ 0.3) compounds

Polycrystalline Pr0.65-xGdxSr0.35MnO3 (x = 0.01, 0.05, 0.1, 0.2, 0.3) manganites were prepared by conventional solid-state method. Structural analysis has revealed a change in structure with x = 0.2, from Rhombohedral (R-3c) to Orthorhombic (Pbnm) symmetry. Small oxygen deficiency was found in the samples. The electrical measurements revealed typical colossal magnetoresistance (CMR) behavior, with single metal–insulator peak at Tp for all investigated samples. The small polaron hopping (SPH) and variable-range hopping (VRH) models were used to describe the electrical conduction above Tp. Magnetic measurements show an increase in magnetization below the Curie temperature, TC. Values of Tc diminish with increasing Gd3+ content. Isothermal measurements around critical points suggest a possible interaction between the 4f-ions and Mn-sublattice The magnetic critical behavior analysis established the tri-critical mean-field model to be the governing model for the series. Large magnetic entropy change ΔSM at near room temperature (278 K) was exhibited by the x = 0.01 sample at 2.2 J/kgK in μ0ΔH = 1 T and 5.36 J/kgK in μ0ΔH = 4 T. The largest |ΔSM| value was shown by the x = 0.1 sample. The values of the relative cooling power (RCP) and the temperature-averaged entropy change (TEC) increased with substitution qualifying these compounds as magnetocaloric materials.