Metal Insulator Research Articles

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.

Flexibility, Dispersion Property, and Giant Sunlight Absorption of Monolayer MX2 (M = Zr, Hf; X = S, Se) and Related Janus MXY (M = Zr, Hf; X = S, Y = Se)

IVB–VIA transition metal dichalcogenides (TMDs) MX2 (M = Zr, Hf; X = S, Se) and related Janus MXY (M = Zr, Hf; X = S, Y = Se) have garnered significant attention due to their unique optoelectronic properties. To further explore their potential in flexible photonics, their mechanical, band dispersion, and optical dielectric properties using orbital hybrid theory are investigated. The results reveal that the out‐of‐plane linear compression resistance of these materials is considerably lower than their in‐plane resistance, primarily because van der Waals interactions are much weaker compared to ionic bond interactions. This characteristic makes them less susceptible to external pressure and torsional forces, positioning them as promising candidates for flexible optoelectronic devices. Furthermore, the presence of multiple energy bands at the same momentum state suggests a tendency toward metal–insulator transitions. Notably, the materials exhibit a high photon flux, indicating robust photoelectric conversion capabilities, making them suitable for applications in photoelectric transducers. This study not only deepens the understanding of the optoelectronic and mechanical properties of IVB–VIA TMD materials, but also offers theoretical guidance for the development and application of flexible optoelectronic devices based on IVB‐VIA TMDs and related Janus materials.

Modeling of the metal–insulator transition temperature in alio-valently doped VO2 through symbolic regression

The correlated semiconductor vanadium dioxide (VO2) exhibits an insulator–metal transition (IMT) near room temperature, which is of interest in various device applications. Precise IMT temperature control is crucial to determine the use cases across technologies such as thermochromic windows, actuators for robots or neuronal oscillators. Doping the cation or anion sites can modulate the IMT by several tens of degrees and control hysteresis. However, modeling the effects of control parameters (e.g., doping concentration, type of dopants) is challenging due to complex experimental procedures and limited data, hindering the use of traditional data-driven machine learning approaches. Symbolic regression (SR) can bridge this gap by identifying nonlinear expressions connecting key input parameters to target properties, even with small data sets. In this work, we develop SR models to capture the IMT trends in VO2 influenced by different dopant parameters. Using experimental data from the literature, our study reveals a dual nature of the IMT temperature with varying tungsten (W) doping concentrations. The symbolic model captures data trends and accounts for experimental variability, providing a complementary approach to first-principles calculations. Our feature-driven analysis across a broader class of dopants informs selectivity and provides qualitative insights into tuning phase transition properties valuable for neuromorphic computing and thermochromic windows.

Signature of the Kondo effect in superparamagnetic GO incorporated Cobalt substituted Ni/NiO nanoparticles

The study reports on the magnetization, magnetoresistance, and transport properties of superparamagnetic 10% Co-doped Ni/NiO (C10-NN), Graphene Oxide (GO) incorporated 10% Co-doped Ni/NiO (C10-NNG), and 15% Co-doped Ni/NiO (C15-NN) nanoparticles synthesized via a microwave-assisted sol-gel auto-combustion method. All samples show hysteresis in negative Magnetoresistance (M-R) at different temperatures. Resistivity ρ(T) versus temperature plots of samples C10-NN and C15-NN show metallic behavior with applied fields of 0, 1, 5, 8 T, and at 0 T, 1 T respectively. However, the plot of R-T of the C15-NN sample shows a significant difference at 0 T and 1 T. At 0 T for this sample, the metallic behavior is observed for temperature T > TM, with the resistivity falling abruptly at and above TM = 246 K. The resistivity decreases with increasing temperature, exhibiting metallic behavior again above TMM < 276 K. This jump at 276 K, indicating a metal-to metal transition. The Kondo effect is observed for the first time in C10-NNG sample. The upturn of resistivity ρ(T) towards low temperature in the C10-NNG sample is well described by the power series equation and Kondo term. This sample exhibits the upturn resistivity along with a metal–insulator transition above and below the Kondo temperature TK≈ 93.51(2) K at the 0 T, 1 T, 5 T, and 8 T fields.

Fabrication and electrical properties of flexible polymer-based MIM capacitors of high-k nanolaminate dielectrics of HfO2–SnO2–TiO2 with ultrathin Al2O3 insertion layer by plasma-enhanced atomic layer deposition

Abstract Flexible metal–insulator–metal (MIM) capacitors of high-k nanolaminate HfO2–SnO2–TiO2 thin films were fabricated on several polymer substrates of polyethylene terephthalate, polyimide and epoxy resin at 80 °C by plasma-enhanced atomic layer deposition. The electrical properties were optimized by adjusting the sub-cycle ratio of Hf: Sn: Ti to 6: 5: 4. In order to reduce the leakage current density of flexible capacitors, the ultrathin Al2O3 layer varying from 0.5 to 1.5 nm was inserted to form Al2O3/HfO2–SnO2–TiO2/Al2O3 stacking capacitors. The effect of the Al2O3 insertion layer thickness and the super-cycle number of HfO2–SnO2–TiO2 on the capacitance density, leakage, and quadratic voltage linearity was investigated. Under optimal processing, flexible MIM capacitors could stand 40 000 bending cycles at curvature radius of 8.2 mm, indicative of better electrical stability. Moreover, compared with the polymer-based HfO2–SnO2–TiO2 capacitors, the introduction of 1 nm Al2O3 ultrathin layer greatly decreases the leakage current density by 4 orders of magnitude (10−8 A cm−2) with relative lower voltage linearity (350–540 ppm V−2), but the capacitance density also declines (∼3 fF μm−2) simultaneously. Despite this, the method of inserting Al2O3 ultra-thin layer is still an effective method to improve the electrical performances of polymer-based HfO2–SnO2–TiO2 nanolaminate capacitors for flexible electronics.

Enhanced Oxidation Resistance and Interface Stability of Atomic-Layer-Deposited MoNx Electrodes via TiN Passivation for DRAM Cell Capacitor Applications.

The continuous miniaturization of dynamic random-access memory (DRAM) capacitors has amplified the demand for electrode materials featuring specific characteristics, such as low resistivity, high work function, chemical stability, excellent interface quality with high-k dielectrics, and superior mechanical properties. In this study, molybdenum nitride (MoNx) films were deposited using a plasma-enhanced atomic layer deposition (PEALD) employing bis(isopropylcyclopentadienyl)molybdenum(IV) dihydride and NH3 plasma for DRAM capacitor electrode applications. Depending on the deposition temperatures of the PEALD MoNx films ranging from 200 to 400 °C, the Mo/N ratio and crystal structure varied, transitioning from the cubic NaCl-B1-type MoN phase with Mo/N ratio of 1.4 to the cubic γ-Mo2N phase with Mo/N ratio of 1.9. Notably, MoNx films grown at 400 °C exhibited low resistivity (435 μΩ·cm), a high work function (5.28 eV), and superior mechanical hardness (11.3 GPa) compared to ALD TiN films. Despite these excellent properties, the PEALD MoNx electrode demonstrated insufficient chemical stability, particularly in terms of oxidation resistance and interface quality with ALD HfxZr1-xO2 (HZO) films. This resulted in poor morphology and the formation of significant oxygen-deficient HZO layers (such as HfO2-x), leading to considerable degradation in the electrical performance of metal-insulator-metal (MIM) capacitors. To mitigate this issue, a thin (2.5-14 nm) ALD TiN layer was introduced as a passivation layer between the MoNx bottom electrode and HZO dielectric. The TiN-passivated MoNx (TiN/MoNx) electrode showed substantially enhanced oxidation resistance and reduced interfacial reactions with the HZO dielectric. Consequently, MIM capacitors with TiN/MoNx bottom electrodes demonstrated outstanding electrical performance, including excellent dielectric properties, low leakage current density, and high mechanical strength. Hence, this study proposes a promising candidates for storage nodes in the next-generation DRAM capacitors.

Consequences of Annealing on Metal–Insulator–Semiconductor Water Splitting Photoelectrocatalysts

Consequences of Annealing on Metal–Insulator–Semiconductor Water Splitting Photoelectrocatalysts

Numerical characterizations of the thermomechanical response of power modules with ceramic substrates and lead-free bonds

PurposeThe present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations.Design/methodology/approachParticularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations.FindingsThe simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures.Originality/valuePower electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings.

The incorporation of armchair and zigzag boron nitride nanoribbons in graphene monolayers: An examination of the structural, electronic, and magnetic properties

The opening of an energy gap and generating magnetism in graphene are certainly the most significant and urgent topics in your current research. The majority of proposed applications for it require the ability to modify its electronic structure and induce magnetism in it. Here, using first-principles calculations utilizing the PBE and HSE06 functionals, we examine the structural, energetic, electronic, magnetic, and phonon transport characteristics of armchair graphene and boron nitride nanoribbons (aGNRs and aBNNRs), and zigzag graphene and boron nitride nanoribbons (zGNRs and zBNNRs) with varying widths. We shall emphasize the impact of incorporating aBNNRs and zBNNRs of varying widths into graphene monolayers (GMLs). The findings suggest that zBNNRs are easier to insert into GMLs than aBNNRs. A study of the average formation energies of graphene and boron nitride nanoribbons reveals that BNNRs have a formation energy that is at least twenty times greater than GNRs. We have observed energy gaps that can be classified into three distinct families in aGNRs, aBNNRs, and aBNNRs inserted into GML. In the zGNRs and zBNNRs inserted in GML, depending on the width, different magnetic orderings (antiferromagnetic, ferrimagnetic, and ferromagnetic), and electronic behaviors are observed (metallic, semimetallic, semiconductor, and topological insulator).

CMOS-compatible plasmonic magnetic field sensor: An alternative approach using ultra-compact MIM configuration

This paper introduces a novel magnetic field sensor (MFS) that utilizes a metal-insulator-metal (MIM) waveguide integrated with a resonator structure and incorporates water-based Fe3O4 magnetic fluid. The sensor uses titanium nitride (TiN) as the plasmonic material which offers numerous advantages over conventional noble plasmonic materials. The sensor takes advantage of the tunable optical properties of the magnetic fluid and TiN to detect changes in the external magnetic field and quantify the magnetic field strength which has been demonstrated using the Finite Element Method (FEM). Our proposed MFS exhibits a high sensitivity of 11.97 pm/Oe, a narrow-band full-width half maximum of 93.66 nm, and a resolution of 8.36 × 10−4 Oe. The sensor is also compatible with complementary metal oxide semiconductor (CMOS) fabrication techniques, which enables chip-scale integration and low-cost production. The sensor can be used for various applications in navigation, military, space, healthcare, and beyond.

Vectorial spatial differentiation of optical beams with metal–dielectric multilayers enabled by spin Hall effect of light and resonant reflection zero

We theoretically describe and numerically investigate the operation of “vectorial” optical differentiation of a three-dimensional light beam, which consists in simultaneous computation of two partial derivatives of the incident beam profile with respect to two spatial coordinates in different transverse electric field components. It is implemented upon reflection of the beam from a layered structure by simultaneously utilizing the effect of optical resonance and the spin Hall effect of light. As an example of a layered structure performing this operation, we propose a three-layer metal–dielectric–metal (MDM) structure. We show that by choosing the parameters of the MDM structure, it is possible to achieve the so-called isotropic vectorial differentiation, for which the intensity of the reflected optical beam (squared electric field magnitude) is proportional to the squared absolute value of the gradient of the incident linearly polarized beam. The presented numerical simulation results demonstrate high-quality vectorial differentiation and confirm the developed theoretical description.

Resistivity characteristics near the metal–insulator transition in the half-filled Anderson–Hubbard model

Resistivity characteristics near the metal–insulator transition in the half-filled Anderson–Hubbard model

Review of Innovative Cavity Designs in Metal–Insulator-Metal Waveguide-Based Plasmonic Sensors

AbstractPlasmonic sensors utilizing metal–insulator-metal (MIM) waveguides represent a significant advancement in sensing technology due to their high sensitivity and versatility. These sensors leverage surface plasmon polaritons to detect minute changes in the surrounding environment, making them highly effective for a range of applications. For instance, they can precisely measure variations in the Refractive Index, which is crucial for monitoring chemical concentrations and biological interactions. Additionally, MIM waveguides can be adapted to sense temperature fluctuations, pressure changes, and the presence of specific gases, providing valuable insights in fields such as environmental surveillance, medical diagnostics, and industrial processes. In recent years, a variety of sensor cavity shapes have been proposed to enhance sensor performance. This review examines how these innovative geometries optimize sensor cavities to achieve unprecedented levels of resolution and sensitivity, underscoring their transformative potential across a broad spectrum of scientific and practical applications.

Comparing post-deposition and post-metallization annealing treatments on Al2O3/GaN capacitors for different metal gates

Vertical Metal–Insulator–Semiconductor (MIS) capacitors with an Al2O3 thin film as a gate insulator have been fabricated on homoepitaxial GaN-on-GaN samples. The effect of the annealing treatments on the MIS characteristics has been investigated exploring two different approaches: Post-insulator-Deposition-Annealing (PDA) and Post-gate-Metallization-Annealing (PMA), i.e., annealing on the bare Al2O3 layer and annealing after the gate metallization deposition on Al2O3. The direct comparison between PDA and PMA is crucial to understand the impact of the metal/dielectric interface quality on the behavior of the Al2O3/GaN MIS capacitors. The efficacy of annealing has been monitored as a function of metal gates having different work functions: nickel (Ni), molybdenum (Mo), and tantalum (Ta). It has been found that both PDA and PMA approaches are equally able to improve the Al2O3/GaN interface electrical quality. However, the PMA demonstrates an additional beneficial effect on the metal/Al2O3 interface. In particular, the possible chemical reactions activated by the annealing process at the metal/dielectric interface can perturb the known metal/dielectric dipole responsible for Fermi-level pinning phenomena, causing a positive shift of the flat voltage (VFB), which depends on the metal, and approaching the theoretical value in the case of Mo and Ta.

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.

Role of ex-situ HfO2 passivation to improve device performance and suppress X-ray-induced degradation characteristics of in-situ Si3N4/AlN/GaN MIS-HEMTs

The role of ex-situ HfO2 passivation in in-situ Si3N4/AlN/GaN-based metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) to improve the device performance and protect the device from severe degradation under high-energy X-ray irradiation has been investigated. Here, the root cause and mechanism for the degradation have been studied utilizing different material/device characterizations. X-ray photoelectron spectroscopy results suggest that several Si-N bonds in stoichiometric Si3N4 and Hf-O bonds in HfO2 passivation film can be broken under X-ray irradiation, where numerous charges might be trapped easily and deteriorate the interface quality. Furthermore, due to the generation of chemical vacancies under X-ray, a band tail near the edge of valence band maximum in Si3N4 and HfO2 films can be created. The obtained results suggest that MIS-HEMT fabricated with an atomic layer deposited (ALD)-HfO2 (MIS-HEMT B) has relatively greater performance compared to MIS-HEMT fabricated without ex-situ HfO2 (MIS-HEMT A) according to the higher maximum drain current (Idmax), peak transconductance (gmmax) and lower current collapse, denoting the effectiveness of ALD-HfO2 to passivate the surface traps. It is noticed that X-ray irradiation induces numerous negative charges in the dielectric layers and degrades the device performance. Interestingly, after X-ray irradiation, the degradation rates in Idmax, gmmax, and current collapse are significantly lower in MIS-HEMT B compared to MIS-HEMT A, suggesting the potential irradiation hardening mechanism of ALD-HfO2 to protect the MIS-HEMTs from unexpected degradations during X-ray irradiation. Finally, these results emphasize the importance of high-quality dielectric films in MIS-HEMTs to enhance the device performance and safeguard the device under high-energy irradiation, especially in the space environment.

Pseudo-proper two-dimensional electron gas formation

Abstract In spite of the interest in the two-dimensional electron gases (2DEGs) experimentally found at surfaces and interfaces, important uncertainties remain about the observed insulator–metal transitions (IMTs). Here we show how an explicit pseudo-proper coupling of carrier sources with a relevant soft mode significantly affects the transition. The analysis presented here for 2DEGs at polar interfaces is based on group theory, Landau–Ginzburg theory, and illustrated with first-principles calculations for the prototypical case of the LaAlO 3 / SrTiO 3 interface, for which such a structural transition has recently been observed. This direct coupling implies that the appearance of the soft mode is always accompanied by carriers. For sufficiently strong coupling an avalanche-like first-order IMT is predicted.

Charge trapping gate stack enabled non-recessed normally off AlGaN/GaN HEMT with high threshold voltage stability

This paper reports a non-recessed normally off AlGaN/GaN high-electron-mobility transistor (HEMT) with a charge trapping gate dielectric stack. The charge trapping gate dielectric stack featuring a low density of fixed positive charges consists of an O3-based Al2O3 tunneling layer and an O3-based HfO2 blocking layer, both deposited via atomic layer deposition. For HEMT with a 15 nm AlGaN barrier layer, a threshold voltage of 2.57 V and an on-resistance of 8.50 Ω × mm are achieved. For positive bias temperature instability (PBTI) testing, the electric field provided by the 15 nm AlGaN layer serves as a barrier to channel carriers, significantly enhancing the PBTI test stability. The optimized gate dielectric stack enables the fabrication of the non-recessed normally off metal–insulator–semiconductor-HEMT with enhanced threshold voltage (Vth) stability.