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The effects of gamma rays on two kinds of GaN high-electron-mobility transistors (HEMTs) have been investigated in this paper. We have identified a gate degradation using a combination of optical and electrical measurements. We have demonstrated that the channel current under the degradation position is outside of the gate’s control. This degradation prevents the gate from fully pinching off the channel, creating a current concentration region when applying a reverse gate voltage. An integrated analysis, including ${I}$ – ${V}$ characterization, the emission microscope (EMMI) technique, and temperature-dependent measurements, was applied to study its mechanism. It is attributed to an irradiation-induced degradation in the Schottky contact. [ABSTRACT FROM AUTHOR]

Confocal gyrotron traveling-wave tube (gyro-TWT) is capable of operating in higher order modes, so it is attractive in high-frequency (> 100 GHz) band. However, the reported experimental and simulation results of confocal gyro-TWT usually operated at fundamental harmonic, so high external magnetic field was essential. In this paper, a second harmonic 220-GHz confocal gyro-TWT was designed through linear and nonlinear theory and particle-in-cell (PIC) simulation. The key problem of suppressing the backward-wave oscillations (BWOs) of both fundamental and second harmonics was solved by limiting the cavity length of the first section less than the critical BWOs length. In PIC simulations, the gyro-TWT operates at HE07 mode with an output power of 4.55 kW, the efficiency of 2.2% gain of 21.8 and the −3 dB bandwidth of 6 GHz. The calculated results from the nonlinear theory are in good agreement with the results from PIC simulation. [ABSTRACT FROM AUTHOR]

As a promising new generation of nonvolatile memory, HfO2-based resistive random-access memory (RRAM) has attracted extensive research. However, the problem of data retention has prevented its industrial production as embedded memory. In this paper, from the microscopic understanding, a Monte Carlo simulator is developed to investigate the effects of an oxygen reservoir layer (ORL) on the resistance instability of HfO2-based RRAM. The evolution of conductive filaments (CF) during the retention degradation is visualized by our simulation considering the physical mechanisms of oxygen ions absorbed and released by the ORL. The simulation results are further validated with experiments to provide the prediction of retention performance of RRAMs with different ORLs and operation schemes. [ABSTRACT FROM AUTHOR]

This paper reports wafer-level backside process technology, established with the intent to ensure stable operation of InP ICs in the submillimeter wavelength band, which generally suffer from ground bounce and substrate resonance. Our process consists of thinning a 3-in InP wafer, forming dense vias with interval cooling steps, backside metallization with single-level wiring and crack-free dicing. We investigate the effects of the backside process on InP-based heterojunction bipolar transistors and high electron mobility transistors. The results show that the backside process contributes to stable operation up to the 300-GHz range without any degradation of transistor characteristics. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) has shown substantial promise in the fabrication of high-power devices, and SiC Schottky diodes and field-effect transistors (FETs) have been considered as potential candidates for outerspace and sensors applications. Due to the multipolar structure, SiC gate turn-off thyristor (GTO) device is relatively sensitive to the irradiation-induced point defects. However, how SiC GTO devices perform under neutron irradiation still needs to be clarified. In this paper, the effects of neutron irradiation on the static and dynamic switch characteristics of high-voltage 4H-SiC GTOs are investigated for the first time. For the static electrical properties, it is found that the forward current significantly decreases with the increasing neutron irradiation fluence. While the cathode leakage current in the blocking characteristics shows an insignificant change up to a neutron fluence of ${1.0} \times {10}^{{13}}$ n/cm2. For the switching characteristics, both the pulse peak current and di/dt show substantial reduction as the neutron fluence increases while the delay time increases after irradiation. The degraded performance of the static and dynamic characteristics of SiC GTO devices was then analyzed and attributed to the weakened conductivity modulation and reduced carrier injection efficiency into the drift layer. These two aspects originate from the significantly reduced carrier lifetime and deteriorated forward characteristics of anode-gate diodes, respectively. [ABSTRACT FROM AUTHOR]

In this paper, we demonstrate a tunable Schottky diode based on amorphous indium–gallium–zinc–oxide (a-IGZO) film with high performance for rectifying circuit and bipolar one diode-one resistor (1D1R) crossbar applications. By modulating the oxygen content in the a-IGZO film, the device shows adjustable behavior. Under the high oxygen content condition, the device displays outstanding diode features with a large rectification ratio up to 108 at ±1 V and a high forward current density of 100 A/cm2 at ±1 V when used Cu as the top electrode. The thermionic emission model is proposed to explain the Schottky diode behavior. And by utilizing the superior rectifying performance, we successfully demonstrate the dynamic rectifying application. In addition, we combine the optimized Schottky diode device with the bipolar-type resistive random access memory (RRAM) device to investigate the Schottky diode device in 1D1R crossbar application. As a result of its tunable nature and low processing temperature, the a-IGZO Schottky diode is a promising element for rectifying circuit and bipolar 1D1R crossbar applications. [ABSTRACT FROM AUTHOR]

In this paper, we present the operation principle of an organic metal–insulator–semiconductor (MIS) capacitor where the organic semiconductor is undoped. In spite of a low charge concentration within the semiconductor, this device exhibits a capacitance variation with respect to the applied gate voltage yielding the capacitance–voltage characteristics similar to that of a traditional MIS capacitor based on the doped semiconductor. A physics-based model is developed to derive the charge concentration, surface potential, and the capacitance of the organic MIS capacitor. The model is validated with TCAD simulation results as well as with experimental data obtained from the fabricated organic MIS capacitor consisting of poly(4-vinylphenol) and poly(3-hexylthiophene-2, 5-diyl) as an insulator and a semiconductor, respectively. [ABSTRACT FROM AUTHOR]

Spin-transfer torque magnetic random-access memory (STT-MRAM) based on a single-barrier magnetic tunnel junction (SBMTJ) and a double-barrier magnetic tunnel junction (DBMTJ) has evolved along with a low switching current and low energy consumption to obtain a high areal density and a fast switching speed. The increment of initial temperature, ${T}_{{\text {in}}}$ , in STT-MRAM can achieve low switching energy, ${E}_{{\text {SW}}}$. However, this leads to an unavoidable decrease in $\Delta $ and switching efficiency. In this paper, SBMTJ and DBMTJ were analyzed in terms of the switching efficiency factor with ${E}_{{\text {SW}}}$ reduction by increasing the ${T}_{{\text {in}}}$. The switching temperature, ${T}_{{\text {SW}}}$ , was investigated using a finite-element method simulation. The results show that the DBMTJ(A) and SBMTJ with the same MgO layer thickness of 0.9 nm provide a higher switching current, ${I}_{{\text {C}}}$ , than the DBMTJ(B) with a MgO layer thickness of 1.3 nm. The ${T}_{{\text {SW}}}$ in a DBMTJ(A) is higher than that in an SBMTJ, while ${T}_{{\text {SW}}}$ for a DBMTJ(B) is the smallest because of its low ${I}_{{\text {C}}}$. The DBMTJ(A) and DBMTJ(B) can be applied in a higher temperature range than the SBMTJ at a $\Delta $ of 40. In addition, the STT efficiency factor, $\Delta /{I}_{{\text {C0}}}$ , for a DBMTJ is better than the factor for an SBMTJ. Although the temperature increment would cause an undesirable reduction in $\Delta $ , it can reach a low ${E}_{{\text {SW}}}$ for the requirement of a fast write access time. Therefore, the control device for increasing the ${T}_{{\text {in}}}$ in the MTJs is attractive and should be promoted in the advancement of memory technology. [ABSTRACT FROM AUTHOR]

The gate–source overlap length (${L}_{{\text {OV}}}$) in the line tunneling FET (L-TFET) can be used as a design parameter to improve the analog circuit performance. In this paper, we investigate the drain current (${I}_{D}$) dependence on ${L}_{{\text {OV}}}$ , considering the electrostatics of the gate–source overlap region. It is observed that ${I}_{D}$ increases with ${L}_{{\text {OV}}}$ exhibiting a nonlinear behavior. This happens as the impact of the lateral electric field at the far end of the tunnel junction reduces, thereby reducing the tunneling rate. Based on our semiempirical physical ${I}_{D}$ – ${L}_{{\text {OV}}}$ model, a novel ${L}_{{\text {OV}}}$ variation-aware small signal model for L-TFET is also proposed. The output resistance and the gate–drain capacitance remain almost independent of ${L}_{{\text {OV}}}$ in the saturation regime. The gate–source capacitance and the transconductance linearly increase with ${L}_{{\text {OV}}}$. A common source amplifier is demonstrated with ~2.4 times increase in the voltage gain when ${L}_{{\text {OV}}}$ is increased from 20 to 50 nm, with a penalty of ~10% in the bandwidth. We observe that it is not possible to achieve the gain similar to one obtained using 2.5 times increase in ${L}_{{\text {OV}}}$ even after increasing the device width five times. However, the bandwidth reduces 30% at such width owing to an increase in the gate capacitances. [ABSTRACT FROM AUTHOR]

In this paper, we study the self-heating mechanism and its impact on electrical performance of short gate length GaN high electron mobility transistors (HEMTs) based on electrothermal TCAD simulations. We propose an equivalent channel temperature to quantify the current degradation due to self-heating and also resolve the discrepancies between temperature measurements through electrical methods and thermal methods in the literature. We then explain the equivalent channel temperature’s behavior using the temperature- and field-dependent electron transport theory for short gate length HEMTs. The implications and guidelines to the various aspects of device design are also discussed. [ABSTRACT FROM AUTHOR]

In this paper, ZnO nanorod humidity sensors with dye-sensitized solar cells (DSCs) were prepared on indium tin oxide conductive glass. The average diameter and length of the ZnO nanorods were ~100 nm and $\sim 1.5~\mu \text{m}$ , respectively. After ZnO nanorods were grown, TiO2 film was coated by TiO2 with a nanoparticle size of approximately 26 nm through the doctor blade method. The sensitizer N3 was used for charge transfer on the DSCs. The solar photovoltaic conversion efficiency of the DSCs was approximately 4.7%. Humidity sensors were used for measurement under ultraviolet (UV) light at 365 nm. During UV illumination, the current increased under low humidity and gradually decreased under high humidity. The integrated device exhibited similar stable and sensitive performance as the traditional ZnO humidity sensor. Experimental results revealed that DSCs could be integrated with ZnO nanorod humidity sensors to create a self-powered integrated device that has potential Internet of Things applications. [ABSTRACT FROM AUTHOR]

In this paper, we show that quantum Hall resistance measurements using two terminals may be as precise as four-terminal measurements when applying superconducting split contacts. The described sample designs eliminate resistance contributions of terminals and contacts such that the size and complexity of next-generation quantized Hall resistance devices can be significantly improved. [ABSTRACT FROM AUTHOR]

In this paper, the field analysis of a triangular corrugated coaxial cavity with misaligned insert is carried out for a megawatt-class sub-terahertz wave gyrotron. In misalignment analysis, both parallel displacement of the insert axis and tilting of the insert axis with the outer resonator axis are considered. Graff’s addition theorem is used for deriving the eigenvalue equation of the coaxial cavity with such a misaligned insert. Mathematical formulations are carried out to include the effect of insert misalignment on the beam coupling coefficient and ohmic wall loading of the outer cavity and insert of the coaxial cavity gyrotron. The effect of structural misalignment of the insert on the operation of 2-MW, 220-GHz coaxial cavity gyrotron is analyzed. It is shown that insert misalignment reduces RF output power as well as increases ohmic wall loading of the insert beyond the prescribed cooling limit. Compared to tilting of the insert, parallel displacement of the insert causes more deterioration in the gyrotron operation. Comparative studies are also performed for a coaxial cavity with rectangular slots on the insert. [ABSTRACT FROM AUTHOR]

Pd, reduced graphene oxide (RGO), and MnO2 nanoflowers-based ternary hybrid junction was fabricated, characterized, and its gas sensing potentiality was established and reported in this paper. Four different types of devices, viz., pristine MnO2 nanoflowers (Device I), Pd/MnO2 nanoflowers (Device II), RGO/MnO2 nanoflowers (Device III), and Pd/RGO/MnO2 nanoflowers (Device IV) were fabricated to study the influence of each of the elements and to account for its contribution towards improving the gas sensor device performance towards alcohol vapors as the test species. After detailed structural characterizations, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy, alcohol vapor sensing performance was studied using methanol, ethanol, and 2-propanol in the temperature range of room temperature (~27 °C) to 150 °C targeting the concentration range of 5–100 ppm. Ternary structure (Device IV) was found to offer remarkably superior performance in terms of response magnitude (RM) (~92.52% at 100 ppm), response time (~11 s), and recovery time (~16 s) compared to its binary (For Pd/MnO2: (~86.86%, ~36 s, ~43 s and for RGO/MnO2: ~80.85%, ~21 s, ~27 s) or pristine counterparts (~27.22%, ~59 s, ~67 s). The plausible cause of such remarkable improvement was attributed to the synergistic contribution of both RGO and Pd. While Pd as a catalyst helped in easy dissociation of target species ensuring the improved performance at low temperature, RGO enhanced the vapor adsorption rate due to of its additional adsorption sites and fast response/recovery kinetics due to high carrier mobility. [ABSTRACT FROM AUTHOR]

A partially dielectric-loaded (PDL) nonuniform grating with lower ohmic losses for a sheet beam backward wave oscillator (BWO) and a clinotron is proposed in this paper. The expressions of the electromagnetic fields for the PDL nonuniform-grating-based slow-wave structure (SWS) are derived by using Maxwell’s equations and Floquet’s theorem. The dispersion equation is derived using the field-matching method and is verified by simulation. The expression of the Pierce small signal gain of a BWO with a PDL nonuniform grating is obtained by using the electromagnetic field expressions and the small signal gain theory. The effects of different parameters on the gain of a BWO with a nondielectric-loaded (NDL) nonuniform grating and those of a BWO with a PDL nonuniform grating are discussed, and the mode competition of this kind of BWO is analyzed in terms of gain. The oscillation frequencies obtained from the mode competition analysis are verified by a particle-in-cell (PIC) simulation, confirming the validity of the analysis. [ABSTRACT FROM AUTHOR]

The impact of scaling of the base layer on the noise performance, spectral responsivity, and frequency response of Ge/Ge1–xSnx/Ge p-n-p heterojunction phototransistor (HPT) is presented and evaluated by simulation. The proposed structure consists of Ge1–xSnx alloy in the base layer, allowing extension of the photodetection to the mid-infrared (MIR) region, enabling photodetection over a wide range. This paper also includes the effect of Sn concentration and base bias voltage on the frequency performance of the HPT. In addition, various noise components and signal-to-noise ratio (SNR) are estimated as a function of base layer thickness and base resistance. The simulated results show that cutoff frequency (${f}_{T}$) and maximum frequency (${f}_{\text {max}}$) are not only strongly dependent on the base layer thickness but also on the Sn composition in the base layer and applied base-bias voltage. The results show that the proposed HPT provides higher ${f}_{T} >45$ GHz and SNR of >70 dB for the base layer thickness of 50 nm (with Sn = 9%) can be achieved. Therefore, the GeSn p-n-p HPT is promising for future fiber-optic telecommunication and MIR applications. [ABSTRACT FROM AUTHOR]

This paper deals with the design of an ac switch structure for specific ac mains applications 230 V–50 Hz. The targeted power level is about a hundred watts, and the currently used converter circuits make use of bidirectional switches that are realized using anti-series connected MOS transistors. Despite the improvements in performance provided by some of these structures, their fabrication cost is still high and limits their widespread diffusion in a market shared with the triac. To replace the triac, an original current and voltage bidirectional bipolar device called a Bipolar ac (Bipac) is proposed, designed, realized, and characterized. It can be controlled both to turn-on and turn-off with respect to a single reference electrode. It exhibits a very low ON-state voltage drop that makes it interesting for specific mains applications with low load current (0.5 $\text{A}_{{\text {rms}}}$). The study of the Bipac structure is carried out using 2-D Sentaurus physical simulations. The Bipac structure is realized on n-type and on p-type substrates for two different wafer thicknesses. The operating modes of the monolithic bidirectional Bipac switch were validated through electrical characterizations. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel compact statistical model for the low-frequency noise (LFN) of MOS devices with halo implants. The compact model is suited for the incorporation in modern models, such as BSIM, PSP, and EKV, and can be used to predict the dependence of the LFN of halo-implanted MOSFETs with bias, temperature, geometry, and technological parameters. This compact model is based on the physics-based random telegraph noise (RTN) model, previously published by our group. The previous model was simplified in analytical expressions dependent on parameters and on physical quantities already calculated in modern compact models. Following the physics-based model, the LFN compact model predicts the large bias dependence of the LFN statistics induced by the halo implants in long-channel devices. Moreover, we show for the first time that the halo implants also induce a large temperature dependence of the LFN statistics for devices operated near the weak inversion or saturation, and the proposed compact model predicts this dependence. [ABSTRACT FROM AUTHOR]

The aim of this paper is to investigate the degradation mechanisms of UV-B AlGaN-based light-emitting diodes (LEDs) submitted to constant current stress beyond the typical application conditions. We demonstrate the existence of two main degradation mechanisms that significantly impact the relative amplitude of the main quantum well (QW) peak at 310 nm and of a parasitic peak at ~340 nm related to the electron overflow toward the last quantum barrier before the p-side. These mechanisms are thoroughly investigated by means of electrical and optical measurements, and by photocurrent (PC) spectroscopy. We demonstrate that in the first 50 h of stress, degradation is caused by an increased defect density in the last quantum barrier and/or carrier escape from the QWs, which results in a decrease in the QW emission and in an increase in the parasitic peak at 340 nm. For longer stress times, degradation is dominated by a diffusion process, causing an increase in defect density and nonradiative recombination in the LED. This has a direct impact on both the QW peak and the parasitic peak, which show a significant decrease for long stress times. PC spectroscopy demonstrates that the defects responsible for degradation are most likely located next to mid-gap, thus acting as efficient nonradiative recombination centers. [ABSTRACT FROM AUTHOR]

This paper proposes a strained Si-based single drift nano-mixed tunnel avalanche transit time (MITATT) oscillator capable of generating high RF power in the terahertz regime, inaccessible by conventional Si devices. The authors have developed a quantum modified classical drift-diffusion model to study the nanoscale properties of strained Si oscillator. The study reveals that 14.72-GW/m2 RF power could be generated from 0.715-THz strain-engineered Si oscillator. Such performance enhancement of the Si device is due to selective incorporation of trace amounts of Ge in the Si active region. This generates in-plane biaxial strain which in turn degrades the in-plane electron mobility, hence unsuitable for conventional MOSFETs. However, such strain remarkably enhances the out-of-plane mobility, and uniqueness of the current research is the utilization of in-plane strain to boost up the out-of-plane mobility depending on geometry and dimensions of the oscillator’s active region. The model incorporates parasitic series resistance and elevates junction temperature effects on terahertz properties of the device. Incorporation of the strained layer in the active region reduces the parasitic series resistance effect on high frequency properties of the oscillator. Validity of the developed model is established by comparing simulated data with the corresponding experimental observations. The authors have further studied photo irradiation effects on terahertz characteristics of the new class of devices. The structure-induced quantum confinement effect has made the Si-based active region to behave as a partially direct bandgap material, and therefore, a significant improvement is observed in optical sensitivity. To the best of the authors’ knowledge, this is the first report on strain-engineered asymmetrically doped Si/SiGe based avalanche photosensor in the high-frequency terahertz domain. [ABSTRACT FROM AUTHOR]

In this paper, we present two accurate physics-based models of ballistic metal–oxide–semiconductor field-effect transistors (MOSFETs), both using less than ten parameters. These models—the capacitor model and the virtual source model—are based on the Landauer–Büttiker formalism. We show that the nonthermalization of charge carriers in the channels of ballistic MOSFETs leads to two critical effects that need to be considered in the modeling: the ballistic drain-induced barrier lowering (DIBL) effect and the floating source effect. The ballistic DIBL effect is responsible for a drain voltage dependence of the DIBL parameter; the floating source effect intensifies the injection of high-energy carriers from the source as the gate voltage increases. Specifically, the analysis is carried out on devices composed of monolayer black phosphorus, a 2-D semiconductor with unique electronic and mechanical properties, which make it a promising candidate for 2-D digital logic applications. [ABSTRACT FROM AUTHOR]

In this paper, we report the characterization and modeling of multi-finger gate all around (GAA) nanowire (NW) FETs (NWFETs) from dc to 14 GHz. The self-heating effect (SHE) in NWFETs is investigated experimentally using the small-signal output conductance (${g}_{{\text {ds}}}$) technique. The frequency-dependent complex thermal impedance, ${Z}_{{\text {th}}}({f})$ , is extracted by fitting an ${n}$ th-order thermal network with the experimental data. We show that the temperature rise $\Delta {T}$ (=85 °C) due to SHE is significant in short-channel silicon on insulator (SOI) NWFETs. Finally, we have evaluated the RF figure of merit (FOM) for these NWFETs as ${f}_{T}$ (=70 GHz) and ${f}_{\text {max}}$ (=80 GHz). We also report the RF performance metric sensitivity on temperature, $\partial {f}_{\text {max}}/\partial {T}_{{\text {amb}}}$ ($\approx -0.104$ GHz/K). The reported BSIM-CMG compact model shows a good correlation with the measurement data. [ABSTRACT FROM AUTHOR]

In this paper, we carried out a systematic investigation on gate degradation and the physical mechanism of the Schottky-type ${p}$ -GaN gate HEMTs under positive gate voltage stress. The frequency- and temperature-dependent measurements have been conducted. It is found that the time-dependent gate degradation exhibits weak relevance with frequencies ranging from 10 to 100 kHz under dynamic gate stress and is similar to that in static gate stress. Both the gate breakdown voltage (BV) and mean-time-to-failure (MTTF) show positive temperature dependence. Moreover, the current–voltage (I–V) characteristics and threshold voltage (${V}_{\text {TH}}$) instability of ${p}$ -GaN devices before/after gate degradation are compared and analyzed. The degraded Schottky junction exhibits an ohmic-like gate behavior. It is revealed that under a large gate bias stress, high-energy electrons accelerated in the depletion region of the ${p}$ -GaN layer would promote the formation of defect levels near the metal/ ${p}$ -GaN interface, leading to the initial ${p}$ -GaN layer degradation. The subsequent high gate leakage density could cause the final degradation of the AlGaN barrier. [ABSTRACT FROM AUTHOR]

In this paper, we have reported a renovated silicon-based tunnel field-effect transistor (TFET) structure with a channel length of 21 nm. The proposed structure has been optimized and analytically modeled. The broken gate TFET (BG-TFET) shows very low ambipolar current, good subthreshold swing (SS) and ON-currents comparable to the contemporary structures of similar dimensions. The surface potential and the electric field inside the device are modeled by solving the 2-D Poisson’s equation. The drain current is also modeled based on Kane’s generation rate. The results obtained from the analysis are validated against Synopsys Sentaurus TCAD nonlocal tunneling model-based simulations. [ABSTRACT FROM AUTHOR]

The growth of industries and other human activities have led to ever increasing amounts of pollutants in both outdoor and indoor spaces. These pollutants have hazardous effects on humans and the wider ecology. Hence, air quality monitoring (AQM) is essential and involves the robust monitoring of various toxic gases and volatile organic compounds (VOCs)—in case, the concentration of any pollutant exceeds the safe limit in a given location. This paper describes the different sources of indoor and outdoor pollutants, reviews the current status of gas sensors, and discusses the role of new two dimensional (2-D) materials in detecting these hazardous gases at low power, i.e., close to the ambient temperature. Here, we review different synthesis techniques of 2-D materials and discuss the sensing performances of pristine and functionalized nanomaterials for some of the important pollutants such as NOx, NH3, SOx, CO, formaldehyde, toluene, and so on. The review concludes with some proposed methods to help in reducing air pollution today. [ABSTRACT FROM AUTHOR]

This paper reports the very first systematic study on the physics of avalanche instability and safe operating area (SOA) reliability in AlGaN/GaN high-electron-mobility transistor (HEMT) using submicroseconds pulse characterization, poststress degradation analysis, well-calibrated TCAD simulations, and failure analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Impacts of electrical and thermal effects on SOA boundary and avalanche instability are investigated. Trap-induced cumulative nature of degradation is studied in detail. The root cause for avalanche instability in AlGaN/GaN HEMTs is investigated. Postfailure SEM, energy dispersive X-ray (EDX), and TEM analysis reveal distinct failure modes in the presence and absence of carrier trapping. [ABSTRACT FROM AUTHOR]

In this paper, we report an impregnated type of tungstate dispenser cathode prepared by Ba5Sr(WO6)2. The direct-current (dc) and pulsed-current (pc) emission properties and their evaporation rates have been investigated compared with the traditional Ba-W dispenser cathodes. Experimental results show that the current densities of the impregnated tungstate cathodes are twice larger than that of a typical 6-1-2 aluminate cathode, e.g., the dc and pc emission densities of the tungstate cathode can reach up to 10.6 and 56.6 A/cm2 at $1050~^{\circ }\text{C}_{{\text {br}}}$ , respectively. The evaporation rate of the impregnated tungstate cathode is $2.02\times 10^{-{9}}\text{g}\cdot $ cm $^{-2}\cdot \text{s}^{-1}$ at $1050~^{\circ }\text{C}_{{\text {br}}}$ , which is only 54% as much as that of the aluminate cathode, as measured by a quartz crystal oscillating method. The work function model of the tungstate cathode was studied by ab initio density functional theory (DFT) calculation. It is found that free Ba is preferentially adsorbed on the hollow site of ZrO2-W (001), and on BaZrO3 (001) in a more stable way during operation, resulting from its fine emitting and evaporation characteristics. [ABSTRACT FROM AUTHOR]

Emittance effects are becoming increasingly important in high-frequency electron devices, especially in recent and proposed high-frequency traveling wave tubes and klystrons. The ratio of beam radius to the beam pipe, typically referred to as “fill factor,” is a critical parameter for high-frequency tubes. Fill factors, typical of lower frequency tubes, such as 0.5–0.8, can lead to significant beam current loss in high-frequency tubes when transported over long distances in the beam pipe because the beam in such tubes is more subject to emittance effects. The increased beam loss, in turn, leads to large dissipation of beam power at the RF circuit, damaging the circuit itself and limiting tube’s duty cycle. Traditionally, the beam emittance has been largely studied and measured in linear accelerators (linacs) where emittance effects are larger than space-charge effects at high beam energy. In this paper, we apply the beam physics developed for linacs to high-frequency tubes for the first time. We provide necessary theoretical tools to determine the fundamental limit of the beam pipe sizes for a desired limit of beam interception. Specifically, the effect of both space charge and emittance is incorporated into iterative solution of equilibrium distributions of charge densities in the presence of a uniform focusing axial magnetic field. The numerical solutions and tools provided here can be used to determine the beam pipe size for any beam emittance. The theoretical formulation and results are expected to be particularly useful for devices operating from mm-wave to subterahertz frequency regimes. [ABSTRACT FROM AUTHOR]

Ferroelectric (FE) materials are being studied for a variety of applications in memory, logic, and neuromorphic computing, for which predictive models of FE polarization are essential. In this paper, we present a Monte Carlo simulation framework capable of predicting the dynamic, history-dependent response of an FE under arbitrary input waveforms. The simulation is developed by generalizing the physics-based nucleation-limited switching model for polarization reversal in a polycrystalline FE. Measured polarization reversal data from fabricated FE Hf0.5Zr0.5O2 capacitors are used to extract the statistical distribution of FE grains. After parameter extraction, the model is able to predict the dynamics of the FE capacitor without further calibration. Finally, the model is applied to characterize the dynamic response of FE–dielectric bilayer structures and quantify the reduction in memory window due to device variability. [ABSTRACT FROM AUTHOR]

This paper reports the fabrication of a broadband near-infrared response (vis-NIR) photodetector (PD) using Cu2SnS3 (CTS) quantum dots (QDs) as photoactive semiconductor material and graphene as a carrier transport medium. The QDs of earth abundant, nontoxic, and inexpensive CTS have been synthesized by solvothermal method, and the chemical vapor deposition (CVD) technique is used to synthesize few layers and monolayers of graphene. The fabricated CTS QDs/graphene/SiO2/Si PD demonstrated high values of responsivity (~110.089 A/W), detectivity ($\sim 1.25 \times 10^{{12}}\,\,\text {cm} \cdot \text {Hz}^{\text {1/2}} \cdot \text {W}^{-{1}}$), and quantum efficiency (~160.9) for broadband (vis-NIR) region due to high absorption coefficient of CTS QDs and very high mobility (~200 000 cm2/V–s) of graphene. The time-response analysis of PD was also performed under vis-NIR and ON and OFF time were found to be 10.2 and 11.34 s. [ABSTRACT FROM AUTHOR]

Acetone, a colorless volatile organic compound (VOC), is exhaled in large concentrations in the breath of diabetic patients. In this paper, a simple liquid exfoliation technique-based few-layered NiO (111) plane exposed nanosheets (diameter 125 nm) were synthesized [in dimethylformamide (DMF) as solvent] and used as highly selective trace level (15–450 ppm) acetone sensors. The sensors were found to be fast (response and recovery time of 82 and 80 s, respectively) and repetitive with a maximum response of 196% (for 450 ppm acetone). The limit of detection of the device is 830 ppb. The operating temperature of the sensor was optimized at 200 °C in comparison to other reported NiO-based VOC sensors mainly due to high surface energy aiding oxygen adsorption at a lower temperature. An “assistive binding model” is proposed to explain sensor performance in the presence of humid air. The model showed positive sensitivity and binding coefficients (${s}_{a} = {0.242}$ ppm−1 and ${k}_{{{aw}}} = {2.04} \times 10^{-{3}}$), proposing a synergistic effect of water on the sensor response for acetone vapors. [ABSTRACT FROM AUTHOR]

In this paper, we argue that communication at the speed of light (CaSoL) through on-chip copper interconnects is possible in the near future based on giga-scale integration (GSI) technologies. A three-step algorithm is introduced to design the optimum buffers in such systems. HSPICE simulations show that a $1.3\times $ time of flight (${T}_{\text {F}}$) is reachable in 7-nm FinFET technology. It is also shown that such a design is by nature, robust, and immune to process variations and crosstalk noise. [ABSTRACT FROM AUTHOR]

In this paper, we present analytical models which are valid in all regions of operation and can accurately predict the potential profile and the output, as well as the transfer characteristics of the gate-all-around heterojunction tunnel field-effect transistors. Our potential model takes into account the charge carriers in the channel, as well as the space charges in the depletion regions of the two reservoirs. Later, this potential model is utilized to calculate the band-to-band tunneling generation rates at any spatial coordinate in the tunneling volume. Next, these rates are integrated over tunneling volume to find the total tunneling current. This leads to an analytical model for the drain current. We validate our models against the data obtained via numerical simulations for several common heterojunction tunnel devices at various geometries and bias conditions. [ABSTRACT FROM AUTHOR]

In this paper, the transition rate (TR) from the high-resistance state to the low-resistance state of a HfO2-based resistive random access memory (RRAM) is investigated. The TR is statistically characterized by applying constant voltage stresses in the range from 0.45 to 0.65 V. It is found that TR follows a voltage dependence which closely resembles the one exhibited by metal-insulator-semiconductor / metal-insulator-metal structures when subjected to constant voltage stress, but with remarkably different fitting parameters. This result suggests a common underlying mechanism in both evolutionary behaviors. Furthermore, the investigation provides additional evidence supporting the micro-structural changes in the oxide after the forming step as well as the role played by the atomic species during the SET event. [ABSTRACT FROM AUTHOR]

The investigation of the heterojunction properties in InGaN-based light-emitting diodes (LEDs) is important to the development of LEDs, because charge carrier transport in the LED is governed by the junctions. In this paper, it is proven that the impedance properties of the significant junctions in InGaN/GaN multiple quantum well (MQW) LEDs can be characterized by electric modulus ($M$) spectroscopy. An equivalent circuit is given to represent the significant junctions of the LEDs. The bias and temperature dependence of impedance parameters of the main active junction and the p-type AlGaN/GaN junctions were studied by ${M}$ spectroscopy. The existence of the AlGaN/GaN junction degrades the efficiency in ac signal transmission and causes a transition in the effective capacitance of the device. [ABSTRACT FROM AUTHOR]

3D printing offers a novel, time-efficient, and multi-material fabrication platform for numerous applications owing to its potential to rapidly manufacture low-cost and 3D printed (3DP) structures. In this paper, polylactic acid (PLA) and conductive composite graphene/PLA filaments were used to fabricate 3DP microchannels and electrodes intended for enzymatic biofuel cells (EBFCs) using a commercial bench-top 3D printer. This 3D printing technology delivers a simplistic, cost-effective, and quick fabrication process, which eliminates the requirement of any further amendment and post-processing. With this technology, we demonstrate structurally simple, miniature 3DP microfluidic membraneless EBFCs (3DP-MM-EBFCs), served with glucose and oxygen with the utilization of redox mediators generating continuous power. The cell performance was evaluated at different flow rates, obtaining open circuit potential (OCP) 0.425 V and maximum peak power density (PD) $4.15~\mu \text{W}$ /cm2 at a current density (CD) of $13.36~\mu \text{A}$ /cm2. The advancement in 3DP electrode surface characteristic and the dimethylformamide (DMF) treatment is carried onto the electrode surface followed by the immobilization of the enzymes individually. The 3DP fabrication technology demonstrated the feasibility of simple and advanced microfabrication techniques to build a well-organized plug-and-play and rapidly analyzed device to power several portable low-power devices. [ABSTRACT FROM AUTHOR]

Multipactor is an electron discharge driven by secondary electron emission (SEE) that plagues microwave components, accelerator structures, space-borne systems, and other related electronics. Recently, a novel theoretical approach for multipactor based on principles from nonlinear dynamics and chaos theory has been expanded to a parallel-plate geometry. In this paper, this new theory is used to construct multipactor susceptibility diagrams that portray breakdown boundaries as a function of device parameters. These results are compared to industrial design standards and particle-in-cell simulations. [ABSTRACT FROM AUTHOR]

Electrolyte-gated, printed field-effect transistors exhibit high charge carrier densities in the channel and thus high on-currents at low operating voltages, allowing for the low-power operation of such devices. This behavior is due to the high area-specific capacitance of the device, in which the electrolyte takes the role of the dielectric layer of classical architectures. In this paper, we investigate intrinsic double-layer capacitances of ink-jet printed electrolyte-gated inorganic field-effect transistors in both in-plane and top-gate architectures by means of voltage-dependent impedance spectroscopy. By comparison with deembedding structures, we separate the intrinsic properties of the double-layer capacitance at the transistor channel from parasitic effects and deduce accurate estimates for the double-layer capacitance based on an equivalent circuit fitting. Based on these results, we have performed simulations of the electrolyte cutoff frequency as a function of electrolyte and gate resistances, showing that the top-gate architecture has the potential to reach the kilohertz regime with proper optimization of materials and printing process. Our findings additionally enable accurate modeling of the frequency-dependent capacitance of electrolyte/ion gel-gated devices as required in the small-signal analysis in the circuit simulation. [ABSTRACT FROM AUTHOR]

A physics-based threshold voltage model of junction-less (JL) double gate (DG) FETs with vertical structural and doping asymmetry is being proposed in this paper. The numerical implementation of vertical asymmetric doping in the FET devices modeling has been studied extensively. A linear approximation, as suggested in the post-annealed implantation technique, is introduced to account for asymmetric-doped profile falling within the channel thickness. Furthermore, Bhaskar’s approximation of sinusoidal has been implemented in the solution to impart due accuracy in the modeling overextended range of device parameters. Overall, appropriate implementation of these mathematical techniques has reduced the complexity of the full evanescent mode analysis immensely and has together retained the accuracy in the solution. The simplicity of the model has provided flexibility to study structural and doping asymmetry together for JL DG FET. Synopsys Sentaurus Device simulation tool has been used for verification of the model results. [ABSTRACT FROM AUTHOR]

In this paper, metallic thermoelectric generators were studied and fabricated using copper (Cu) and cobalt (Co) as their respective positive and negative thermoelements. Thus, the chosen Cu-clad polyimide substrate alleviated the deposition of Cu and eased the microfabrication. A lateral device structure might assist in generating larger output power through its longer thermoleg length. Hence, the fabricated thick-film devices had planar and lateral structures with lateral heat flow and lateral thermopile layout. The strong correlations of electrical and thermal conductivities in metal thermoelements have resulted in lower Seebeck coefficient along with reduced thermoelectric power-generating performances. Alternatively, a thermoleg cross-sectional area (${A}$) optimization approach may optimize these disrupting correlations and improve their power-generating effectiveness, whereas a sandwiched planar structure can allow more thermopiles to be integrated without influencing the generator’s size. Both A optimization and sandwiched planar structure have rarely been applied and studied in the past works and have never been implemented using metal thermoelements. Hereafter, a Cu–Co device was enhanced through ${A}$ optimization by increasing the thickness of Co over 3.86 times the Cu thickness, and the implementations of a sandwiched planar structure. Herein, a flexible sandwiched planar thermoelectric generator was fabricated for the first time, using simpler microfabrication. This enhanced Cu–Co generator achieved a thermoelectric efficiency factor of ${6.6} \times {10}^{-{3}}\,\,\mu $ Wcm−2K−2($12.89~\mu $ Wcm−2) at a temperature difference of 44.2 K. It remarked 3.1 times of improvement (by stacking three sets of thermopile) than its similar single Cu–Co thermopile of ten thermocouples. [ABSTRACT FROM AUTHOR]

In this paper, AlGaN/GaN high-electron mobility transistors (HEMTs) with different fin configurations are fabricated and analyzed. Through S-parameter measurements and modeling of the designed devices, a detailed RF investigation on small-signal model parameters is performed under different biasing conditions. Good agreements between measured and simulated scattering parameters up to 40 GHz illustrate the validity and accuracy of the model. The influence of different fin structures on model parameters and linearity improvement is examined, and this can help to improve the frequency characteristics of fin structure by optimizing the fin length, fin width, and trench width. The significant linearity of Fin-HEMTs is confirmed by the analysis of the model parameters, which is the first time to study the small-signal characteristic of AlGaN/GaN Fin-HEMTs in detail. [ABSTRACT FROM AUTHOR]

Stochastic computing (SC) is a promising technology that can be used for low-cost hardware designs. However, SC suffers from its long latency. Although parallel processing can efficiently shorten the latency, duplicated stochastic number generators (SNGs) are necessary, which cause substantial hardware overhead. This paper proposes a scalable SNG based on the spin-Hall-effect (SHE), which is capable of generating multiple independent stochastic streams simultaneously. The design takes advantages of the efficient charge-to-spin conversion from the Spin-Hall material and the intrinsic stochasticity of nanomagnets. Compared to previous spintronic SNGs, the SHE-SNG can reduce the area by $1.6\times -7.8\times $ and the power by $4.9\times -13\times $ while increasing the degree of parallelism from 1 to 16. Compared to CMOS-based SNGs, the proposed SNG obtained $24\times -120\times $ and $53\times $ reduction in terms of area and power, respectively. Finally, three benchmarks were implemented, and the results indicate that SC implementations with the proposed SHE-SNG can achieve $1.2\times -29\times $ reduction of hardware resources compared to implementations with previous CMOS- and spintronic-based designs while scaling the degree of parallelism from 1 to 64. [ABSTRACT FROM AUTHOR]

Self-heating in fully depleted silicon-on-insulator (FDSOI) metal–oxide–semiconductor field-effect transistors (MOSFETs) is experimentally studied using the gate resistance thermometry technique, in a wide temperature range from 300 down to 4.2 K. We demonstrate that below 160 K, the channel temperature increase ($\Delta {T}$) due to self-heating starts to deviate significantly from the linear variation with the dissipated power, leading to an apparent power dependent thermal resistance. This power dependence is interpreted in terms of temperature dependent thermal conductivity. The thermal resistance dependence on the active device temperature (${T}_{\text {Device}}$) indicates that the former one is mainly driven by the thermal conductivity of the oxide layer. Moreover, based on this dependence we reconstructed the channel temperature increase for each dissipated power and ambient temperature, and we found that the calculated values were in a good agreement with the experimental ones. Results indicate that even at low temperatures, thermal resistance does not depend significantly on the silicon channel thickness (ranging from 7 up to 24 nm), whereas the buried-oxide thinning (145 and 25 nm) strongly reduces the magnitude of the thermal resistance. Finally, this paper intends to fill the gap of experimental data concerning self-heating in advanced FDSOI transistors at low temperatures, revealing limitations and perspectives that should be taken into account for future work. [ABSTRACT FROM AUTHOR]

In this paper, converters of TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{21}}$ mode and TE $^{\Box }_{{10}}$ –TE $^{\circ }_{{01}}$ mode with similar exciting topologic structures are designed and verified for a cold test of gyro-TWT. Both the proposed converters are composed of three sections, including TE $^{\Box }_{{10}}$ to TE $^{\Box }_{{20}}$ mode converter with ridged twist waveguide, TE $^{\Box }_{{20}}$ to TE+22 mode converter with variable cross-shaped waveguide, and the last section TE+22 to TE $^{\circ }_{{21}}$ or TE $^{\circ }_{{01}}$ mode converter ($^{\Box }$ represents the rectangular waveguide, + represents the cross-shaped waveguide, and ° represents the circular waveguide). The mode converters can be designed step-by-step and exhibit excellent wideband performance and high conversion efficiency. Simulation results reveal that the proposed TE $^{\circ }_{{21}}$ mode and TE $^{\circ }_{{01}}$ mode converters have less than 0.04 and 0.03 dB loss over 13.5- and 12-GHz bandwidths, respectively, while the return loss is below −25 dB. Prototype TE $^{\circ }_{{21}}$ and TE $^{\circ }_{{01}}$ mode converters were fabricated and back-to-back millimeter-wave measurements were performed to verify the design. [ABSTRACT FROM AUTHOR]

In this paper, we report the experimental extraction of ballistic transport parameters of high-performance Germanium Nanowire nMOSFETs (Ge NWTs) with lengths ${L}_{\text {NW}} = {40}$ –100 nm, width ${W}_{\text {NW}} = {40}$ nm, and height ${H}_{\text {NW}} = {10}$ nm using temperature-dependent measurements. The extracted contact resistivity ($\rho {c}$) and sheet resistance (Rsh) imply that parasitic series resistance (${R}_{\text {SD}}$) of fabricated Ge NWTs is affected by $\rho _{c}$ of the metal-nGe (${3.42} \times {10}^{-{5}}\,\,\Omega \cdot \text {cm}^{{2}}$ at 292 K), which decreases with the increase in temperature. Ballistic efficiency (BE) is found to be 22%–47% at 292 K depending on the dimension of the device. It decreases with increased temperature and increases with ${L}_{\text {NW}}$ scaling down to 40 nm. The transition region with fluctuating BE is observed near ${L}_{\text {NW}} = {50}$ –60 nm, where the electron transport enters deeper into bthe allistic regime. BE is found to be sensitive to temperature and drops from 58% (170 K) to 37% (390 K) for ${L}_{\text {NW}} = {40}$ -nm Ge NWT. Therefore, in order to maintain the high ballisticity of the devices, it is important to optimize the device structure and eliminate the self-heating effect. [ABSTRACT FROM AUTHOR]

To continue with the scaling of high-performance transistors, alternate materials and device architectures are being explored as replacements for contemporary strained-silicon (s-Si) FinFETs. While III–V materials, such as In0.53Ga0.47As, offer higher electron mobilities and injection velocities than s-Si, emerging 2-D materials and nanowire (NW) device architectures promise better immunity to short-channel effects. In this paper, we present a detailed device-level performance comparison of s-Si, In0.53Ga0.47As, monolayer black phosphorus (BP), and WS2-based planar and multigate (Fin and NW) n-MOSFETs across three successive future technology nodes. The analysis incorporates both intrinsic device characteristics obtained from an advanced quantum mechanical simulation tool and the effect of nonidealities using a physics-based analytical model. The results indicate that 2-D materials, such as monolayer BP, offers higher ON currents than s-Si and In0.53Ga0.47As for planar device architectures. However, compared to modern s-Si and In0.53Ga0.47As Fin and NW FETs, monolayer BP and WS2 double-gate MOSFETs are reported to offer lower ON currents due to the smaller footprint at scaled technology nodes. [ABSTRACT FROM AUTHOR]

Part I of this paper discussed the design of a four-terminal skewed straintronic magnetotunneling junction (ss-MTJ) switch, and its adaptation to a non-Boolean “one transistor, one trench capacitor, and one ss-MTJ” ternary content-addressable memory (TCAM) cell. This part of the paper discusses a TCAM array based on ss-MTJ-TCAM cells and the associated peripherals for search operation. We show that non-Boolean associative processing of the ss-MTJ-TCAM cells enhances energy-efficiency and performance of an ss-MTJ-based TCAM array. The energy-delay-product (EDP) of ss-MTJ-based TCAM is compared against CMOS-based TCAM for a $144\times256$ array. The minimum EDP in ss-MTJ-based TCAM is $\sim 10.8\times $ lower than the minimum EDP in CMOS-based TCAM. Additionally, the operational frequency at which the ss-MTJ-based design shows the minimum EDP is $\sim 9.4\times $ higher than the respective frequency in the CMOS-based design. We also compare ss-MTJ-based TCAM against other state-of-the-art MTJ-based TCAMs. The comparison shows that the ss-MTJ-based TCAM also outperforms MTJ-based TCAMs in cell density, search delay, and search energy. Finally, we discuss implications of process variability in ss-MTJ to TCAM implementation and identify critical design parameters in ss-MTJ-based TCAM to enhance its robustness and area/ energy-efficiency. [ABSTRACT FROM PUBLISHER]

This paper presents a ternary content-addressable memory (TCAM) cell based on a skewed straintronic magnetotunneling junction (MTJ) switch. A straintronic magnetotunneling junction (s-MTJ) is a three-terminal switch, where the resistance between two of the terminals switches when a potential is applied to the third (gate) terminal that induces strain in the magnetostrictive free-layer. An s-MTJ is a highly energy-efficient switch that would dissipate only ~aJ of energy during switching. This paper discusses a novel variant of s-MTJ, namely skewed s-MTJ (ss-MTJ), where the MTJ switching can be controlled by two gate terminals. The current through an ss-MTJ is minimum when the potentials at the first and second gate terminals ( V2 and V3 , respectively) obey the relation V3 = V2+VF . Here, VF is a fixed voltage (“offset voltage”). Current in an ss-MTJ increases steeply when V2 and V3 deviate from the above “match” condition. This unconventional I – V characteristic of an ss-MTJ is exploited to design a non-Boolean TCAM cell based on just one transistor, one trench capacitor, and one ss-MTJ. We also discuss search and write operations in the ss-MTJ-TCAM cell, and show that the cell requires very small voltages to operate because of the unique I – V characteristics of the ss-MTJ. [ABSTRACT FROM PUBLISHER]

This paper presents the 2-D numerical simulation results of the single-event burnout (SEB) in the floating field ring (FFR) termination of a power MOSFET for the first time. We investigate the SEB triggering mechanism and SEB performance based on a 140-V typical FFR termination, and find that the structure is sensitive to SEB because of a sharp temperature rise appearing at the p+ base/n-drift junction. A 140-V hardened FFR termination (an n-type buffer layer is added between the epitaxial layer and substrate layer) is also studied in this paper that can demonstrate much better SEB performance without sacrificing the basic characteristics compared to the standard one. In addition, the hardening mechanism is explained, and the performances of the hardened structures with different buffer layer thickness are discussed. As a result, the safe operating area can reach the value of the breakdown voltage when the thickness achieves or exceeds 3~\mu \textm . [ABSTRACT FROM AUTHOR]

This paper presents the first fully integrated sigma–delta modulator implemented in an in-house silicon carbide (SiC) bipolar technology for high-temperature applications. A second-order 1-b continuous-time architecture is adopted. Dual-loop compensation technique is employed to accommodate one clock period comparator delay. The circuits are designed to have enough margins without degrading the modulator’s performance, considering the variation of device parameters over a large temperature range. The measurement results show that from room temperature to 500 °C, the modulator’s peak SNDR is constant around 30 dB at a clock speed of 512 kHz. The chip area of the modulator is 6.9~\text mm \times 2.8 mm with one metal layer. It consumes around 1 W from a 15 V power supply. This paper demonstrates the feasibility to further develop highly integrated SiC bipolar junction transistor integrated circuits for extremely high-temperature sensing applications. [ABSTRACT FROM AUTHOR]