Dielectric Interface Research Articles

Impact of Bottom Electrode in HfO2-Based Rram Devices on Switching Characteristics

Resistive random-access memory (RRAM) devices with hydrogen plasma treated HfO2 have shown low power switching (1) and good conductance quantization with programing pulsed operation (2) that qualify them to be used for in-memory computing. Engineering the distribution of defects or oxygen vacancies near the top and bottom electrodes has a significant impact on reducing the switching power and improving the multi-level cell (MLC) characteristics of the device. A graded distribution with higher concentration of oxygen vacancies closer to the top electrode (TE) due to hydrogen plasma treatment and lower concentration near the bottom electrode (BE) reduces switching energy (power) (1). However, the impact of the bottom electrode is not well understood. In this work we investigated three RRAM stacks as shown in Figure 1 that have the same top electrode metal (50nm PVD TiN/5nm ALD TiN) and dielectric (HfO2 with hydrogen plasma treatment at the mid-point) but with different BE for each stack: TiN (device A (control)), TiN plus Mo with thermal anneal (device B), and TiN plus Mo with plasma nitridation (device C). Choosing a more inert metal as the BE provides a lower oxygen vacancy concentration at the interface between the BE and the dielectric (3) which in turn reduces the switching power as noted with device C (TiN plus Mo with plasma nitridation) which switches at a minimum compliance current (Icc) of 500pA. It is possible that the presence of nitrogen prevents the increase in oxygen vacancy concentration near the BE. On the other hand, a higher concentration of oxygen vacancies at the BE and the dielectric interface leads to a larger magnitude of band bending and increases the height of Schottky barrier. This possibly leads to an increase in the switching power in device A and device B as compared to device C (3-4). Note that device A (TiN) switched at Icc=30µA and device B (TiN plus Mo with thermal anneal) switched at Icc=8µA, which is superior compared to device A in switching power. This suggests that the alloy of TiN with Mo is reducing the oxygen vacancies near the BE. To study the MLC characteristics of the devices, we performed a train of 36 RESET pulses with fixed amplitude Vp= -1V and pulse width starting at 4µs and increasing by 20µs every 3 pulses, while we applied Vr=0.1V and tr=10µs after each pulse to measure the conductance. Figure 2 shows that device B (TiN plus Mo with thermal anneal) has good MLC with no overlap between the states while device A shows unstable MLC behavior due to time constant variation. Figure 3a shows the results of device C for the same RESET pulse train that was applied to devices A and B. Since device C switches at very low current and voltage, the conductance quantization was unstable after 15 pulses due to overstress of the conductive filament. Figure 3b shows the results after selecting the proper pulse set Vp= -0.5V and pulse width starting at tp=100ns and increasing by 100ns every 3 pulses, while we applied Vr=0.05V and tr=100ns after each pulse, resulting in a better conductance quantization compared to the previous setup. Appropriate engineering of the BE and managing of the oxygen vacancy distribution by hydrogen plasma treatment can significantly reduce the switching power.

Suppressing the Intrinsic Photoelectric Response of Organic Semiconductors for Highly-Photostable Organic Transistors.

Suppressing the photoelectric response of organic semiconductors (OSs) is of great significance for improving the operational stability of organic field-effect transistors (OFETs) in light environments, but it is quite challenging because of the great difficulty in precisely modulating exciton dynamics. In this work, photostable OFETs are demonstrated by designing the micro-structure of OSs and introducing an electrical double layer at the OS/polyelectrolyte dielectric interface, in which multiple exciton dynamic processes can be modulated. The generation and dissociation of excitons are depressed due to the small light-absorption area of the microstripe structure and the excellent crystallinity of OSs. At the same time, a highly efficient exciton quenching process is activated by the electrical double layer at the OS/polyelectrolyte dielectric interface. As a result, the OFETs show outstanding tolerance to the light irradiation of up to 306 mW·cm-2 , which far surpasses the solar irradiance value in the atmosphere (≈138 mW·cm-2 ) and achieves the highest photostability ever reported in the literature. The findings promise a general and practicable strategy for the realization of photostable OFETs and organic circuits.

Theoretical study of perovskite nano material based surface plasmon resonance biosensor for cancers cell detection

The present study reports screening of cancer cells at the earliest stages using prism coupling-based surface plasmon resonance biosensors in a theoretical manner. The SPR sensors designed on Kretschmann configuration consisting of several layers like silver (Ag) metal, beryllium oxide (BeO) and hetero-structure BlueP/WSe2 layer deposited over BK7 glass prism. For maximum light absorption, a perovskite nano material, barium titanate (BaTiO3) layer is placed between BeO and hetero-structure BlueP/WSe2 to enhance the angular sensitivity. The light of 633 nm wavelength has been used for excitation of surface plasmon at metal dielectric interface. The refractive index of cancer cells lies between 1.360 and 1. 400. The optimized angular sensitivity of 216°/RIU and 360°/RIU for PCI-2 (normal, adrenal gland cancer), 248°/RIU and 254°/RIU for MDA-MB-231(normal, breast cancer cell) as well as 248°/RIU and 254°/RIU for MCF-7 (normal, breast cancer cell) respectively has been obtained. The maximum optimized angular sensitivity for adrenal gland cancer is 360°/RIU on employing perovskite layer. The sensor offers excellent performance parameters and covers wide range of refractive index sensing.

Electron transfer induced contact-electrification at oil and oleophobic dielectric interface

The oil dielectric has been used for enhancing the performance and durability of triboelectric nanogenerators (TENGs), but little is known about the contact-electrification (CE) (or triboelectrification) characteristics of the oil. Here, the CE behavior of different oil droplets with oleophobic surfaces is systematically investigated by dropping oil on a single-electrode TENG. The electrification trace is clearly imaged using a high-voltage scanning probe approach. Thermally stimulated discharge techniques are adopted for studying the detailed trapping characteristics of contact-generated charges with a homemade instrument, and the results are consistent with the thermionic emission model. The research provides systematic understandings on oil CE with oleophobic surfaces, together with general investigation paradigms and characterization methods for electrification phenomena on surfaces. Meanwhile, because typical oils are regarded as free of ions, their CE is attributed to electron transfer, which may contribute to the understanding of fundamental CE mechanisms.

High Performance Amorphous In0.5Ga0.5O Thin‐Film Transistor Embedded with Nanocrystalline In2O3 Dots for Flexible Display Application

AbstractHigh‐performance, coplanar amorphous In0.5Ga0.5O (a‐IGO) thin film transistor (TFT) on a polyimide (PI) substrate deposited by spray pyrolysis (SP) is reported. The SP a‐IGO film deposited at 370 °C has less than 8% nanocrystalline‐In2O3 dots and a mass density of 6.6 g cm−3. The a‐IGO TFT on PI exhibits linear mobility over 30 cm2 V−1 s−1 and a negligible shift in threshold voltage (ΔVTH = <0.3 V) under positive bias (+20 V) at 60 °C for 1 h. The TFT performance is stable even when bent to a radius of ≈1 mm. The X‐ray photoelectron spectroscopy results of the SP a‐IGO deposited at 370 °C indicate the O‐vacancy (Vo) related defects of 25.79% and hydroxyl (OH) at less than 3%, indicating a good active/gate insulator interface. A seven‐stage ring oscillator made of SP a‐IGO TFTs exhibits a high oscillation frequency (>2.3 MHz) with a low propagation delay time of ≈30 ns per stage at a supply voltage (VDD) of 15 V. The fabricated gate shift register circuit works up to the last stage without any decrement of the input voltage (15 V) with rising and falling times less than 0.8 µs. Therefore, the coplanar a‐IGO TFT by SP deposited at 370 °C is a promising candidate for low‐cost, flexible TFT backplanes of foldable electronics.

Dielectric Interfaces in High-Voltage Technology: Overview and Theoretical Approaches to the Modeling of Functional and Breakdown Behavior

This article provides a broad overview of dielectric interfaces, including the wide range of technologies that feature them, basic theoretical treatment of interfacial phenomena, and a brief discussion of interfacial breakdown.

Dispersive surface-response formalism to address nonlocality in extreme plasmonic field confinement

Abstract The surface-response formalism (SRF), where quantum surface-response corrections are incorporated into the classical electromagnetic theory via the Feibelman parameters, serves to address quantum effects in the optical response of metallic nanostructures. So far, the Feibelman parameters have been typically obtained from many-body calculations performed in the long-wavelength approximation, which neglects the nonlocality of the optical response in the direction parallel to the metal–dielectric interface, thus preventing to address the optical response of systems with extreme field confinement. To improve this approach, we introduce a dispersive SRF based on a general Feibelman parameter d ⊥(ω, k ‖), which is a function of both the excitation frequency, ω, and the wavenumber parallel to the planar metal surface, k ‖. An explicit comparison with time-dependent density functional theory (TDDFT) results shows that the dispersive SRF correctly describes the plasmonic response of planar and nonplanar systems featuring extreme field confinement. This work thus significantly extends the applicability range of the SRF, contributing to the development of computationally efficient semiclassical descriptions of light–matter interaction that capture quantum effects.

A FEM in frequency domain for a transient electric field in non-sinusoidal steady state under the non-sinusoidal periodic voltage

PurposeThis paper aims to focus on the finite element method in the frequency domain (FD-FEM) for the transient electric field in the non-sinusoidal steady state under the non-sinusoidal periodic voltage excitation.Design/methodology/approachFirstly, the boundary value problem of the transient electric field in the frequency domain is described, and the finite element equation of the FD-FEM is derived by Galerkin’s method. Secondly, the constrained electric field equation on the boundary in the frequency domain (FD-CEFEB) is also derived, which can solve the electric field intensity on the boundary and the dielectric interface with high accuracy. Thirdly, the calculation procedures of the FD-FEM with FD-CEFEB are introduced in detail. Finally, a numerical example of the press-packed insulated gate bipolar transistor under the working condition of the repetitive turn-on and turn-off is given.FindingsThe FD-CEFEB improves numerical accuracy of electric field intensity on the boundary and interfacial charge density, which can be achieved by modifying the existing FD-FEMs’ code in appropriate steps. Moreover, the proposed FD-FEM and the FD-CEFEB will only increase calculation costs by a little compared with the traditional FD-FEMs.Originality/valueThe FD-CEFEB can directly solve the electric field intensity on the boundary and the dielectric interface with high accuracy. This paper provides a new FD-FEM for the transient electric field in the non-sinusoidal steady state with high accuracy, which is suitable for combined insulation structure with a long time constant.

The Detecting System and Method of Quasi-Distributed Fiber Bragg Grating for Overhead Transmission Line Conductor Ice and Composite Insulator Icing Load

Transmission lines icing is destructive to the operation of the power grid. There is a lack of methods to monitor overhead transmission line conductors and insulators for icing load simultaneously. In this paper, we implanted six optical fibers with three quasi-distributed FBGs each into the interface of a 110kV composite insulator and built an icing detection system, and proposed three ways for measuring overhead transmission lines icing load. A method for quasi-distributed FBG to differentiate between the measurement of running insulator umbrella and conductor icing load was proposed and validated. The effect of the number of implanted optical fibers on the measurement accuracy was studied. The results show that the relative error of simulated insulator umbrella skirt icing load measurement is -7.3%∼-2.7%. The 200m-span running conductor insulator umbrella skirt icing load measurement relative error is -11.5%∼-3.8%; the relative error of conductor ice measurement is -16.5%∼9.0% and absolute error is -0.83∼1.5mm. The composite insulator with an optical fiber embedded can accurately warn of serious icing on the conductor, with two can achieve the conductor icing measuring absolute error of about ±1mm. As for accurately measuring both the umbrella skirt and the conductor icing, it is necessary to implant six optical fibers.

Room‐Temperature Charge‐to‐Spin Conversion from Quasi‐2D Electron Gas at SrTiO3‐Based Interfaces

Interfacial two-dimensional electron gas (2DEG), especially the SrTiO3-based ones at the unexpected interface of insulators, have emerged to be a promising candidate for efficient charge-spin current interconversion. In this article, to gain insight into the mechanism of the charge-spin current interconversion at the oxide-based 2DEG, we focused on conducting interfaces between insulating SrTiO3 and two types of aluminium-based amorphous insulators, namely SrTiO3/AlN and SrTiO3/Al2O3, and estimated their charge-spin conversion efficiency, {\theta}_cs. The two types of amorphous insulators were selected to explicitly probe the overlooked contribution of oxygen vacancy to the {\theta}_cs. We proposed a mechanism to explain results of spin-torque ferromagnetic resonance (ST-FMR) measurements and developed an analysis protocol to reliably estimate the {\theta}_cs of the oxide based 2DEG. The resultant {\theta}_cs/t, where t is the thickness of the 2DEG, were estimated to be 0.244 nm-1 and 0.101 nm-1 for the SrTiO3/AlN and SrTiO3/Al2O3, respectively, and they are strikingly comparable to their crystalline counterparts. Furthermore, we also observe a large direct current modulation of resonance linewidth in SrTiO3/AlN samples, confirming its high {\theta}_cs and attesting an oxygen-vacancy-enabled charge-spin conversion. Our findings emphasize the defects' contribution to the charge-spin interconversion, especially in the oxide-based low dimensional systems, and provide a way to create and enhance charge-spin interconversion via defect engineering.

Resistive switching behaviors of oxygen-rich TaOx films prepared by reactive magnetron sputtering

ABSTRACT In this work, Ta2O5 films were first deposited on Si substrates by reactive magnetron sputtering of a Ta metal target at various substrate temperatures, RF powers and sputtering pressures. The crystal characteristics of these films can be effectively tailored by controlling the sputtering process. Based on the optimized process parameters, tantalum oxide (TaOx) films with different oxygen component content were sputtered on ITO buffered Si substrates and comparatively investigated. The results show that the film with Ta/TaOx/ITO structure has a resistance switching (RS) behavior and its conduction mechanism is closely related to the O2-/O concentration related to the oxygen partial pressure at the dielectric layer and electrode interface. This study provides an in-depth understanding of the component/structure design and structure-activity relationship for high-performance TaOx-based resistive memory.

Shaped Omnidirectional Reflector Fed by a Dielectric Lens Associated with a Coaxial Feed Horn

The paper explores an omnidirectional antenna configuration composed of a reflector fed by a shaped dielectric lens associated with a coaxial TEM horn. A simple formula describes the lens shape obtained by applying Fermat’s principle to control the rays’ caustic emerging from the dielectric interface. Based on geometrical optics (GO) principles, a synthesis technique defines the reflector shape to control the antenna radiation pattern in the vertical plane. Concatenated conic describes the reflector generatrix. The study employs a full-wave analysis to validate the designs and explores the proposed configuration to attend two distinct far-field specifications.

Generation and detection of sound at the effect of femtosecond pulses on a metal film on a dielectric substrate

The excitation of sound by a femtosecond laser pulse in a metal layer on a dielectric substrate has been studied. The modulations of the reflection coefficient of the metal, which arise due to the propagation of sound in it, are described in detail. It is shown that, in addition to oscillations corresponding to odd harmonics of sound waves, oscillations corresponding to even harmonics can be present on the profile of the Fourier image of the reflection coefficient change. The efficiency of even harmonic generation depends on the substrate material and the metal film thickness. The dependence of the reflection coefficient change on time has been studied. It has been established that if the electron heat flux reaches the metal–dielectric interface before the energy of the electrons is transferred to the lattice, then modulations are present both due to sound that occurs at the metal–vacuum interface and at the metal–dielectric interface. The wavelength of probe radiation also affects the reflection coefficient change. If real and imaginary parts of the permittivity at the wavelength of probing radiation are comparable in magnitude, then the Fourier image of the reflection coefficient change contains a smaller number of maxima, and the change in the reflection coefficient over time is accompanied by splitting of peaks.

A Combined Theoretical and Experimental Approach to Deduce the Role of Dielectric Layer on Interface Trap Density in Single Crystal Organic Field‐Effect Transistors

AbstractA detailed understanding of charge transport at the interface is necessary to explore the potential of organic field‐effect transistors. This can be realized by adequately analyzing the trap states at the interface. In the present work, rubrene‐based organic field‐effect transistors have been fabricated with three different interfaces. The device properties are used along with a technology computer‐aided design to deduce the interface trap density quantitatively. The transfer characteristics are simulated using a double Gaussian density of states and fitted with experimental data by adding traps to the semiconductor dielectric interface. A typical transistor with SiO2 interface has shown an interface trap density of about ≈1016 cm−2, and it is reduced to 1014 cm−2 when poly(methyl)methacrylate or polystyrene is coated on SiO2 interface, attributed to the surface passivation. This approach provides a simple and accurate way to estimate the interfacial traps and offers the possibility to tune the device architecture and performance.

Biological UV Photoreceptors‐Inspired Sn‐Doped Polycrystalline β‐Ga2O3 Optoelectronic Synaptic Phototransistor for Neuromorphic Computing

AbstractIn this study, the authors fabricate Sn‐doped 100‐nm thick polycrystalline β‐Ga2O3 synaptic field‐effect transistors (FETs) emulating optical and electrical spike stimulation. When stimulated by deep ultraviolet (UV) optical spikes or electric voltage spikes at the gate, the devices exhibit several essential synaptic functions of excitatory‐postsynaptic currents (EPSCs), inhibitory‐postsynaptic currents (IPSCs), paired‐pulse facilitation (PPF), spike‐number‐dependent plasticity (SNDP), and spike‐timing‐dependent plasticity (STDP). Following UV optical stimulation, the devices mimic synaptic plasticity with a photogate effect, and the gate voltage stimulation emulates the synaptic weights according to the state of the gate dielectric interface. The β‐Ga2O3 synaptic FET demonstrates synergistic functions in various optoelectronic stimulation modes and successfully mimics the visual memory formation in bees with UV photoreceptors. Moreover, to verify the translation of optoelectrical‐derived synaptic behaviors of β‐Ga2O3 synaptic FETs into artificial neuromorphic computing, handwritten digit image recognition of the Modified National Institute of Standards and Technology dataset is performed using a convolutional neural network, and a learning accuracy of 96.92% is achieved. The realization of these fundamental functions of biological synapses suggests the utility of Ga2O3‐based optoelectronic devices for next‐generation neuromorphic computing.

Characteristics and development of damage in the interface of polyimide multilayer films under a repetitive-frequency-pulsed voltage

To study the initiation and development of interfacial electrical damage in multi-layer dielectrics, an aging test of 3-layer polyimide films was conducted under pulsed voltage with a repetitive frequency of 500 Hz and a maximal amplitude of 30 kV. The variation in the damage morphology with the number of applied pulses was analyzed by a statistical method. The circuit current and partial discharge at different aging stages was measured, and the Fourier transform infrared spectrum analysis results of the aged and unaged sample regions were compared. The results demonstrate that the partial discharge in the dielectric interface gap, which is unavoidable in manufacturing, is the main cause of damage. It initiates from the interface and grows into the interior of the dielectric with the application of pulses. When there are no macroscopic defects on dielectric films, damage presents a punctiform morphology. The damage process can be divided into the following three stages: surface roughening damage, steady growth stage of damage points, and pre-breakdown stage. Differing from dielectrics without macroscopic defects, dielectrics with original void defects present transverse dendritic damage channels that initiate from the edge of the defect.

Longitudinal and Transverse Optical Beam Shifts Show Non‐separability

AbstractUnder the introduction of any tilted interface in its trajectory, an optical beam experiences polarization‐dependent deflections in the longitudinal and transverse directions with respect to the plane of incidence. The physics of such optical beam shifts are connected to profound universal wave phenomena governed by the fine interference effects of wave packets and have opened up avenues toward metrological applications. Here, the inherent non‐separability of the longitudinal and transverse optical beam shifts is revealed by considering a rather simple case of a partially reflecting Gaussian laser beam from a dielectric interface. This non‐separability appears substantially at some particular regions in the corresponding experimental parameter space. This manifests as a position–position non‐separable state of classical light field. The tunability of the related experimental parameters offers control over the degree of non‐separability. These findings are expected to be a step forward in the exploration of optical beam shifts and a number of analogous universal phenomena. The initial observation also indicates its practical impact on metrology and generation of high‐quality tunable position–position non‐separable states of classical light fields.

Simulation of a Self-Referenced Meta-Grating Sensor With High Figure of Merit in NIR Communication Window

A meta-grating-based surface plasmon resonance (SPR) sensor was theoretically investigated to act as a self-referenced sensor in the near-infrared region using a spectral interrogation technique. Introduction of a high refractive index (RI) dielectric material, silicon (Si) oxynitride (SiON) film, in between the dielectric metasurface and metal layer gives rise to a self-referencing operation in the sensor. The Si meta-grating excites the SPR at the metal–analyte interface which is sensitive to the changes in the RI of the analyte and the surface plasmon (SP) mode at the metal–dielectric interface remains fixed. The geometrical parameters of the proposed sensor were optimized to obtain the self-referencing operation with superior sensing performance. The self-referencing behavior considerably reduces the error contributions due to an unsteady ambience. The maximum sensitivity of this sensor has been achieved upto 1150 nm/RIU with the figure of merit (FOM) as high as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$442.31\,\,\text {RIU}^{-{1}}$ </tex-math></inline-formula> .

Focusing enhancement of terahertz surface plasmon polaritons

Subwavelength-sized metallic structures exhibit extraordinary responses to electromagnetic waves due to their geometry, generating surface plasmon polaritons (SPPs) at the metal–dielectric interface. The development and application of terahertz (THz) science, which is an emerging science, can be advanced by studying SPPs in the THz band. Because the field strength of SPPs gradually weakens in the propagation direction, a coherent phase-matched THz SPP enhancement structure was designed. Here, we demonstrated an asymmetrical circular groove structure. And using this structure, THz SPPs can be excited and can be focused and enhanced under the illumination of linearly polarized THz pulses, generating a subwavelength-sized focal spot. These functions are achieved via phase matching. Furthermore, the original structure was modified by controlling the propagation phase of the THz SPPs and a periodic enhancement structure was designed. Compared to the original structure, the periodic enhancement structure has a stronger focusing effect on THz SPPs. Moreover, we imaged the THz SPPs by using a THz real-time near-field spectral imaging system and verified the feasibility of the designed structure by comparing with the simulation results. The study results are of great significance to the application of THz SPPs and the fabrication of related devices.

Intrinsic Optical Properties and Emerging Applications of Gold Nanostructures.

The collective oscillation of free electrons at the nanoscale surface of gold nanostructures is closely modulated by tuning the size, shape/morphology, phase, composition, hybridization, assembly, and nanopatterning, along with the surroundings of the plasmonic surface located at a dielectric interface with air, liquid, and solid. This review first introduces the physical origin of the intrinsic optical properties of gold nanostructures and further summarizes stimuli-responsive changes in optical properties, metal-field-enhanced optical signals, luminescence spectral shaping, chiroptical response, and photogenerated hot carriers. The current success in the landscape of nanoscience and nanotechnology mainly originates from the abundant optical properties of gold nanostructures in the thermodynamically stable face-centered cubic (fcc) phase. It has been further extended by crystal phase engineering to prepare thermodynamically unfavorable phases (e.g., kinetically stable) and heterophases to modulate their intriguing phase-dependent optical properties. A broad range of promising applications, including but not limited to full-color displays, solar energy harvesting, photochemical reactions, optical sensing, and microscopic/biomedical imaging, have fostered parallel research on the multitude of physical effects occurring in gold nanostructures.