Showing papers in "Journal of Computational Electronics in 2019"

A dual-channel surface plasmon resonance biosensor based on a photonic crystal fiber for multianalyte sensing

Abstract: A dual-channel photonic crystal fiber sensor based on the surface plasmon resonance effect is proposed and numerically investigated. The proposed design consists of two concentric channels, with an external coating of gold (Au) on solid silica. Multiple analytes are analyzed based on two different modes operating in the first and second channel, and wavelength sensitivity of 1000 nm/RIU and 3750 nm/RIU respectively. The proposed sensor design could be used in various sensing applications, e.g., for chemicals, biochemicals, organics, and other lower-index liquids having refractive index in the range of 1.30–1.40.

Comparative analysis of the quantum FinFET and trigate FinFET based on modeling and simulation

Abstract: A comparative analysis of the trigate fin-shaped field-effect transistor (FinFET) and quantum FinFET (QFinFET) is carried out by using density gradient quantization models in the Synopsys three-dimensional (3-D) technology computer-aided design (TCAD) platform. The gate dielectric stack comprising 0.5 nm SiO2 (k = 3.9) and 2 nm HfO2 (k = 22) contributes to an effective oxide thickness of 0.86 nm and is kept constant throughout the study. The results demonstrate that the QFinFET can overcome the limitations of current FinFET devices when scaling down to the atomic level. An analytical model including quantum-mechanical effects for evaluation of the drain current of the FinFET is established and validated using the TCAD software. The degradation in the drive current with downscaling of the fin thickness for the trigate FinFET and the increase in the drive current for the QFinFET are presented. The results are improved by taking into account different channel lengths and body thicknesses to estimate the drain current–gate voltage and gate capacitance–gate voltage characteristics for both the trigate FinFET and QFinFET. The drain-induced barrier lowering and subthreshold swing are also analyzed for the trigate FinFET and QFinFET at different technology nodes, revealing excellent characteristics. It is clearly established that the QFinFET can overcome the limitations faced by current FinFET devices when scaling the silicon down to the atomic level and may represent the next generation of FinFET devices.

Analysis and design of a terahertz microstrip antenna based on a synthesized photonic bandgap substrate using BPSO

Abstract: A microstrip patch antenna based on a synthesized photonic bandgap (PBG) substrate is designed and analyzed by using a technique based on the combination of an evolutionary heuristic optimization algorithm with the CST Microwave Studio simulator, which is based on the finite integral technique. The initial antenna is designed by analyzing air cylinders embedded in a thick silicon substrate, which has high relative permittivity. Then, to synthesize the PBG substrate, a binary particle swarm optimization (BPSO) algorithm is implemented in MATLAB to design a two-dimensional (2D) photonic crystal on a square lattice that improves the initially designed microstrip antenna. The unit cell is divided equally into many square pixels, each of which is filled with one of two dielectric materials, silicon or air, corresponding to a binary word consisting of the binary digits 0 and 1. Finally, the performance of the initial antenna is compared with the BPSO-optimized antenna using different merit functions. The results show remarkable improvements in terms of the return loss and fractional bandwidth. Both microstrip patch antennas based on the synthesized photonic crystal substrate achieve noticeable sidelobe suppression. Furthermore, the first design, which is a dual-band antenna, shows a return loss improvement of 5.39 %, while the fractional bandwidth of the second design is increased by 128 % (bandwidth of 128 GHz), compared with the initial antenna based on the air-hole PBG substrate. Both antennas maintain a gain close to 9.17 dB. Also, the results show that the obtained antennas have resonant frequencies around 0.65 THz, as required for next-generation wireless communication technology and other interesting applications.

A novel structure for realization of an all-optical, one-bit half-adder based on 2D photonic crystals

Abstract: In this paper, a new structure for realizing a one-bit half-adder is proposed based on 2D photonic crystals. The proposed structure consists of 25 × 20 hexagonal lattice silicon rods in an ambient of air. The main advantages of this structure are a proper distinct space between “0” and “1” logical states of outputs, and smooth and stable outputs for a long time. These advantages are found to eliminate the error in identification of logical states (i.e., 0 and 1) at outputs. Working at a 1550-nm wavelength band (the most commonly used wavelength in optical communication known as third window), the simplicity of its structure and also integrable size has made this structure very efficacious for being realized as an all-optical logic gate.

A brief review of frequency, radiation pattern, polarization, and compound reconfigurable antennas for 5G applications

Abstract: All antennas in which frequency and radiation patterns can be modified in a reversible and controlled manner are known as reconfigurable antennas. They are different from other antennas, as their mechanism of reconfiguration is located within the antenna and not controlled by an external beam. For reconfigurable antennas, the potential is not to increase the performance of the antenna in a significantly changed state or to meet the needs of dynamics and efficacy. This study will discuss various aspects related to antennas that are frequency-reconfigurable, their applications and execution frequencies, change in polarization, and changes in far-field patterns or operating frequencies to better deal with changing system parameters. For the reconfigurable antennas in this paper, some past and recent applications will be reviewed, along with examples of their implementation. The arrays and moving mechanical parts are explained, along with recently introduced semiconductor factors, and the tunable material technologies that should be applicable for reconfigurable antennas.

Particle swarm optimization and finite-difference time-domain (PSO/FDTD) algorithms for a surface plasmon resonance-based gas sensor

Abstract: Surface plasmon resonance (SPR) is a spotlight technique for environmental monitoring. In this regard, an optical gas sensor based on SPR is investigated and analyzed here. The sensor is used for detection of toxic gases such as cyanogen, ethanol, propane, nitrogen dioxide, and phosgene. The performance of the sensor is inspected and optimized by considering different parameters such as the thickness of the metal layer, the material used for the prism, and the incident light angle and wavelength. The finite-difference time-domain method is used for simulation, and the optimization algorithm is particle swarm optimization. Simulation results show that the best metal thickness for gold, silver, aluminum, and copper is 44.39 nm, 43.16 nm, 18.195 nm, and 32.5 nm, respectively. Also, utilizing different materials such as SiO2, PMMA, BCB, MgF2, and cyclomer for the prism and the effect of temperature variation on these materials are studied, and it is shown that MgF2 demonstrates better performance. Furthermore, the results of the optimization indicate that the most suitable incident light angles (wavelengths) are 44.43° (900.59 nm), 45.5° (599.7 nm), 44.56° (300.1 nm), and 44.41° (899.4 nm) for gold, silver, aluminum, and copper, respectively. The sensor shows the best full-width at half-maximum and quality factor (Q) of 4.2 nm and 214.28, respectively, for the combination of MgF2 prism and a gold layer. The maximum sensitivity and figure of merit for gold layer are >120 (nm/RIU) and >20, and for copper layer are >270 (nm/RIU) and >30, respectively.

IonMonger: a free and fast planar perovskite solar cell simulator with coupled ion vacancy and charge carrier dynamics

Abstract: Details of an open-source planar perovskite solar cell simulator, which includes ion vacancy migration within the perovskite layer coupled to charge carrier transport throughout the perovskite and adjoining transport layers in one dimension, are presented. The model equations are discretised in space using a finite element scheme, and temporal integration of the resulting system of differential algebraic equations is carried out in MATLAB. The user is free to modify device parameters, as well as the incident illumination and applied voltage. Time-varying voltage and/or illumination protocols can be specified, e.g. to simulate current–voltage sweeps, or to track the open-circuit conditions as the illumination is varied. Typical simulations, e.g. current–voltage sweeps, only require computation times of seconds to minutes on a modern personal computer. An example set of hysteretic current–voltage curves is presented.

Spin–orbit coupling effects on the electronic structure of two-dimensional silicon carbide

Abstract: Two-dimensional silicon carbide (2D-SiC) has attracted incredible research attention recently because of its wide bandgap and high exciton binding energy. Here, we focus on the effect of spin–orbit coupling (SOC) on its electronic structure through a detailed first-principles density functional theory study. The calculated electronic band structure and projected electron density of states indicate that Si 3p and C 2p electrons play a vital role in forming the electronic bandgap. The distribution of the real space charge density in the conduction and valence bands further confirms the electronic structure. It is found that inclusion of SOC causes splitting of both the valence and conduction bands. A wide SOC-induced bandgap of ~ 30 meV is observed in this novel material. Moreover, the effect of strain in modulating the bandgap and the SOC interaction is quantified. We find a linear reduction of both the normal and SOC-induced bandgap with increase of the biaxial tensile strain. Bandgap tuning based on such SOC effects may provide a pathway towards future optoelectronic and novel spintronic devices based on 2D-SiC.

A DFT/TDDFT investigation on the efficiency of novel dyes with ortho -fluorophenyl units (A1) and incorporating benzotriazole/benzothiadiazole/phthalimide units (A2) as organic photosensitizers with D–A2–π–A1 configuration for solar cell applications

Abstract: Novel derivatives of OD1 with D–A2–π–A1 configuration have been designed. The calculated geometrical parameters and optoelectronic properties are compared with those of the parent triphenylamine-based dye molecule (OD1) comprising a triphenylamine terminal electron-rich group (D), 3,4-ethylene dioxythiophene π-spacer, fluorophenyl electron-withdrawing group (A1), and cyanoacrylic acid anchor group. The designed derivatives differ from OD1 with D–π–A1 configuration in the incorporation of an electron-acceptor group (A2) between the donor group and π-spacer unit, namely benzotriazole (BTZ), benzothiadiazole (BTDZ), or phthalimide (PHI), denoted as ND2-BTZ, ND3-BTDZ, and ND4-PHI, respectively. The effects of the incorporation of each electron-deficient unit on the geometry, absorption spectra, and electrochemical properties are investigated by using density functional theory (DFT) and time-dependent (TD)DFT methods. Additionally, the preferred dye adsorption process on model Ti(OH)4 is investigated. The results for the binding energy, selected bond distances, highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels and their distribution, energy gaps, and total density of states (TDOS) plots are discussed and analyzed. The intermolecular interaction between two monomers of each dye and iodine is also investigated, and the complexation energy [corrected for the basis set superposition error (BSSE)] is calculated and analyzed. The results reveal that the introduction of the BTDZ and PHI functional groups is more promising for formation of organic dyes with D–A2–π–A1 configuration.

Boosting the performance of an ultrascaled carbon nanotube junctionless tunnel field-effect transistor using an ungated region: NEGF simulation

Abstract: This paper focuses on the role of the longitudinal spacing between the auxiliary gate and control gate in boosting the performance of an ultrascaled junctionless carbon nanotube tunnel field-effect transistor (JL CNT-TFET). The investigation is based on self-consistent quantum simulations in the nonequilibrium Green’s function formalism in the ballistic limit. It is found that dilation of the ungated longitudinal space between the gates causes a significant improvement in the leakage current, ambipolar behavior, subthreshold swing, on/off-current ratio, power–delay product, and intrinsic delay. In addition, a substantial enhancement in the swing factor and current ratio is also recorded for the JL CNT-TFET with coaxial control gate length below 10 nm. The results indicate that adjusting the spacing between the auxiliary gate and control gate is a simple, efficient, and promising approach to achieve ultrascaled JL CNT-TFETs with very high performance.

A computational study of short-channel effects in double-gate junctionless graphene nanoribbon field-effect transistors

Abstract: As the channel length shrinks below the 10-nm regime, emerging materials, junctionless technology, and multiple-gate geometries provide an excellent combination to continue progress towards lower-cost high-performance ultrascaled devices. In this study, the double-gate junctionless (JL) graphene nanoribbon field-effect transistor (GNRFET) and its conventional counterpart (C-GNRFET) are compared in terms of short-channel effects (SCEs) using a quantum simulation. The computational approach is based on solving the Schrodinger equation using the mode-space nonequilibrium Green’s function formalism coupled self-consistently with a Poisson equation in the ballistic limit. The analysis of gate length downscaling shows that the JL GNRFET exhibits better leakage current, subthreshold swing (SS), drain-induced barrier lowering, and threshold voltage roll-off in comparison with the conventional GNRFET. In addition, we reveal that a decrease in the n-type doping concentration can enhance the above-mentioned characteristics of both devices. The results indicate that the JL GNRFET can mitigate critical issues and enhance the immunity to SCEs of the GNRFET, making it a promising candidate for high-performance ultrascaled (sub-5-nm) technology.

Ultracompact ultrafast-switching-speed all-optical 4 × 2 encoder based on photonic crystal

Abstract: A novel two-dimensional photonic-crystal-based all-optical encoder was designed, tested, and optimized. The structure is built on a linear square-lattice photonic crystal platform. An ultracompact, simple design occupying an area of only 128.52 μm2 is constructed, 50 % smaller than the smallest design known to date. Ultrafast switching speed with the lowest known delay time is achieved. The proposed design consists of one ring resonator with cylindrical silicon rods suspended in air. No auxiliary or bias input is required for its operation. The proposed platform is not sensitive to the applied input phase shift. Finite-difference time-domain and plane-wave expansion methods were used to analyze the structure and optimize the radius of the rods at 1.525 µm, with radius of the inner rods of 0.19a, for successful operation, resulting in ultrafast switching speed of 10 THz and shorter delay time reaching 0.1 ps. This maximum switching speed is two times faster than recent literature reports. The contrast ratio is calculated to reach an acceptable record of 7.1138 dB. The trade-off between the switching speed and contrast ratio was also examined.

Optimization of the area efficiency and robustness of a QCA-based reversible full adder

Abstract: Recently, quantum dot cellular automata (QCAs) have evolved as the most promising candidate to overcome the fundamental nanoscale limitations of present complementary metal–oxide–semiconductor (CMOS) technology. Owing to their quasiadiabatic switching, QCAs have huge potential for the design of THz-frequency logic circuits and ultralow-power digital circuits with extremely high device density. The aim of the work presented herein is to maximize the benefits of a QCA-based circuit design by deploying reversible computing logic. A highly efficient reversible QCA-based full adder is proposed by using a three-input and five-input majority gate architecture. The proposed design demonstrates significant improvements in circuit complexity, area efficiency, and quantum cost while retaining performance in terms of latency and area usage. Coplanar crossovers are properly realized using 180° clock zones. The performance of the proposed design surpasses that of recent literature designs, with a 25% reduction in the circuit complexity, a 28% saving in the total area, a 24.57% decrease in the cell area, and an approximately 1/4 reduction in the quantum cost. To verify the feasibility of the proposed design, its thermal robustness is analyzed and hazard analysis is also performed. The proposed full adder is further employed to realize reversible ripple-carry adders (RCAs) of variable size. The proposed RCAs also show significant improvements in terms of the mentioned performance parameters.

Germanene nanotube electroresistive molecular device for detection of NO 2 and SO 2 gas molecules: a first-principles investigation

Abstract: We explore the electronic properties of germanene nanotubes (GeNTs) using first-principles calculations with the non-equilibrium Green’s function technique. The adsorption of two different gases, namely NO2 and SO2, onto GeNT is investigated using van der Waals density functional technique. Moreover, the change in the band gap-energy is noticed upon interaction of small NO2 and SO2 gas molecules. The shift in the peaks is observed in the conduction band upon adsorption of small NO2 and SO2 molecules on the GeNT. The calculated adsorption energies range from − 0.156 to − 0.609 eV. The transmission spectrum showed that the transition of electrons is prominent for SO2 molecules rather than NO2 molecules onto the GeNT. In addition, the electron density diagram also indicate that a transfer of electrons occurs among the gas molecules and the GeNT electroresistive molecular device. The I–V characteristics of GeNT device clearly reveal the change in the current, which varies in the magnitude from 10−9 to 10−6 A upon adsorption of gas molecules on GeNT device. Thus, we suggest that germanene nanotube molecular device can be employed for the detection of NO2 and SO2 small molecules.

An FPGA-based real quantum computer emulator

Abstract: While we cannot efficiently emulate quantum algorithms on classical architectures, we can move the weight of complexity from time to hardware resources. This paper describes a proposition of a universal and scalable quantum computer emulator, in which the FPGA hardware emulates the behavior of a real quantum system, capable of running quantum algorithms while maintaining their natural time complexity. The article also shows the proposed quantum emulator architecture, exposing a standard programming interface, and working results of an implementation of an exemplary quantum algorithm.

An alternative method for implementation of frequency-encoded logic gates using a terahertz optical asymmetric demultiplexer (TOAD)

Abstract: All-optical frequency-encoded AND, OR, and NOT logic gates are proposed and their performance simulated to confirm their feasibility. Terahertz optical asymmetric demultiplexer (TOAD)-based logic gates with a control pulse energy as low as 50 fJ are used, and real-time simulations of their input and output pulse patterns reveal a rate of 20 Gbps. Such logic gates could be used for future all-optical logic processors for optical computation and communication systems.

An ultra-sensitive gas nanosensor based on asymmetric dual-gate graphene nanoribbon field-effect transistor: proposal and investigation

Abstract: In this paper, a new ultra-sensitive gas nanosensor based on an asymmetric dual-gate graphene nanoribbon field-effect transistor (ADG GNRFET) is proposed. The performance of the proposed gas nanosensor is examined using an atomistic quantum simulation based on the mode space non-equilibrium Green’s function approach, self-consistently coupled to a two-dimensional Poisson’s equation in the ballistic limit. The gas-induced change in work function of sensitive gates is considered as a sensing mechanism, where the threshold voltage shift is taken as a sensing metric. The sensitivity analysis has shown that the gas-induced shift in threshold voltage can be significantly increased by decreasing the ratio of top-oxide capacitance to that of back-oxide, to less than unity. Moreover, the length and width of graphene nanoribbon are found independent of sensor sensitivity. The possibility of reaching ultra-high sensitivities at the nanoscale domain using the proposed ADG GNRFET-based gas sensor makes it an exciting alternative to the conventional FET-based gas sensors.

1 Tb/s all-optical XOR and AND gates using quantum-dot semiconductor optical amplifier-based turbo-switched Mach–Zehnder interferometer

Abstract: The turbo-switch (TS) architecture conceived for speeding up the response of conventional semiconductor optical amplifiers (SOAs) is combined for the first time with the exceptional ultrafast capability of quantum-dot (QD) SOAs. The possibility of exploiting this combination in the Mach–Zehnder interferometer (MZI) for implementing fundamental all-optical (AO) XOR and AND logic gates run at 1 Tb/s is numerically investigated, assessed, and verified. The simulation results demonstrate the superiority of the QDSOA-based TS-MZI scheme over its QDSOA-based MZI counterpart, as quantified by the improved quality factor, which can be achieved under more favorable operating conditions. The outcomes of the conducted theoretical treatment can help execute AO signal processing tasks with enhanced performance while keeping pace with the perpetual increase of single-channel data rates in an efficient and affordable manner.

An analytical model for the surface potential and threshold voltage of a double-gate heterojunction tunnel FinFET

Abstract: A double-gate (DG) heterojunction tunnel FinFET structure with a source overlap region was analyzed to optimize its performance and validate technology computer-aided design (TCAD) simulation results by modeling the surface potential, electric field, and threshold voltage. A compact model of the surface potential was developed by applying the solution of the two-dimensional (2-D) Poisson equation obtained using the superposition technique. The gate threshold voltage was extracted by using the transconductance change method. The effect of high-k dielectric material (HfO2) on the surface potential model was also addressed. The analytical predictions were compared with and validated against the results obtained using Synopsys TCAD software, revealing excellent agreement. The percentage error of the analytical approach for the threshold voltage was also evaluated with respect to the TCAD simulation results.

A computationally efficient hybrid approach based on artificial neural networks and the wavelet transform for quantum simulations of graphene nanoribbon FETs

Abstract: Numerical modeling of graphene nanoribbon field-effect transistors (GNRFETs) using quantum-mechanical approaches is often associated with a heavy computational burden, indicating the urgent need for new methods to resolve this issue. A computationally efficient hybrid approach for quantum simulations of ballistic GNRFETs is developed herein. The proposed simulation method is based on solving the two-dimensional (2D) Poisson equation using both wavelet-based adaptive meshing and wavelet-based matrix compression techniques, self-consistently, with well-trained neural network models that imitate the mode-space (MS) nonequilibrium Green’s function (NEGF) solver in generating the charge density. The results obtained by applying the hybrid approach show good agreement with NEGF simulations. Numerical experiments reveal that the developed simulation method can offer a speed-up of about one order of magnitude over the conventional MS NEGF approach. The encouraging results obtained in this work indicate that the developed numerical model is particularly appropriate for incorporation into nanoelectronic device simulators to investigate future GNRFET-based circuits.

Analytical modeling for static and dynamic response of organic pseudo all-p inverter circuits

Abstract: This paper presents the performance analysis of an all-p-organic pseudo-inverter circuit using dual gate organic thin film transistors. The proposed inverter design has shown significantly high performance in terms of noise margin, gain and propagation delay, leading to the design of more robust digital circuits that, too, exhibit augmented performance. The parameters of the all-p-organic pseudo-inverter are compared with those of zero-Vgs load logic (ZVLL) and dynamic load logic based conventional inverters, and a substantial improvement is found for the novel combination of a dual gate flexible TFT with a pseudo-design. Performance parameters were deeply analyzed, and we observed that the noise margin is improved by 42.8% as compared to ZVLL based conventional inverters. A bootstrap technique was implemented to further improve the performance and reduce the threshold voltage drop. The performance parameters were analyzed mathematically and compared with simulated values. The static as well as dynamic characteristics of organic pseudo-all-p inverter, with and without bootstrap technique, were observed. Static power consumption of the organic pseudo-all-p inverter was estimated. In this way, improvement of noise margin by the bootstrap circuit of the organic pseudo-inverter is characterized. The reduced threshold voltage applied to design of low power circuits enables longer power backup for various applications.

Design of an add filter and a 2-channel optical demultiplexer with high-quality factor based on nano-ring resonator

Abstract: In this paper, we first present the design of a nano-ring resonator-based filter, in which scattering rods are used at the corners of the structure. By choosing a suitable radius for the dielectric rods in the nano-ring resonator, low channel spacing and high-quality factor parameters have been achieved at 1586.8 nm wavelength. Then, using this filter, a 2-channel demultiplexer is developed. In the proposed demultiplexer, two lattice constants are used: a1 for the main structure and a2 for the structure in the nano-ring resonator. The difference in the lattice constants results in an increase in the quality factor. Some of the advantages of this 2-channel demultiplexer include an average quality factor of 5443, average channel spacing of 0.35 nm, and central wavelengths of 1554.5 nm and 1557.1 nm, respectively, for the first and second channels. Moreover, the minimum and maximum inter-channel cross talks are − 17.63 dB and − 12.1 dB, respectively. Due to the 2.6 nm inter-channels spacing, this structure can be exploited in optical integrated circuits, WDM and DWDM systems.

An accurate and generic window function for nonlinear memristor models

Abstract: Memristors have become promising candidates for the advancement of recent technology as the miniaturization of complementary metal–oxide–semiconductor (CMOS) technology approaches its final stage. Nanoscale size, easy fabrication, compatibility with MOS, and diverse applications have accelerated these devices to new levels. In this paper, we discuss the merits and demerits of existing window functions and propose a novel window function that addresses their limitations. The suggested window function exhibits high nonlinearity at the boundaries and resolves other boundary issues. The results obtained using the proposed window function are compared with data reported in the literature to validate our design approach.

Design of a U-shaped circularly polarized wearable antenna with DGS on a fabric substrate for WLAN and C-band applications

Abstract: A circularly polarized wearable textile antenna for use in WLAN (5.15–5.825 GHz), HIPER LAN/2 (5.15–5.350 GHz, 5.470–5.725 GHz) and C-band applications is presented. The wearable antenna was formed on jeans fabric (as substrate) and is simple in design. The proposed design includes a U-shaped radiating patch with a modified ground. The microstrip linefeed technique is used to excite the antenna. The impedance bandwidth of the antenna is observed to be 60.86%, between 4.8 and 9 GHz. The 3-dB axial ratio bandwidth is found to be 20.08% between 5.1–5.8 and 7.2–7.8 GHz. A peak gain of 5.19 dBi is measured. The effect of the antenna parameters is also analyzed through a parametric study. To verify the operation of the presented design, the antenna was fabricated and tested using a vector network analyzer. Comparison of the simulated and measured results revealed good agreement.

Widely tunable electronic properties in graphene/two-dimensional silicon carbide van der Waals heterostructures

Abstract: Heterostructures based on two-dimensional (2D) materials have attracted considerable research interest recently. Detailed structural and electronic characterization of graphene and 2D silicon carbide (graphene/2D-SiC) van der Waals heterostructure based on first-principles density functional theory calculations is presented herein. Different staking patterns as well as different orientations are proposed for such graphene/2D-SiC bilayer structures. The band structures of all the representational configurations exhibit a direct band gap ranging from 20 meV to 28 meV at the Dirac point. Charge carrier transfer and sublattice symmetry breaking are considered to be the key effects opening the band gap for each structure. For further tuning of the band gap, tensile biaxial strain is applied, resulting in a change in the band gap from 15 to 28 meV. The band gap can also be tuned by changing the interlayer distance between the graphene and SiC. The projected density of states and space charge distribution near the conduction and valence bands reflect the key role of graphene in shaping the electronic properties of the heterobilayers, implying the potentiality of 2D-SiC as a compatible substrate as well. These findings highlight a new avenue of research towards the application of graphene-based heterobilayers in future nanoelectronic devices.

An efficient Verilog-A memristor model implementation: simulation and application

Abstract: Complementary metal–oxide–semiconductor (CMOS) technology is reaching its limits due to the continuous shrinking process, which has an impact on various aspects including device size, performance, and power consumption. The memristor is one of the promising devices under investigation for use with deep-nanometer CMOS, having applicability in several fields due to its nonlinear behavior, nonvolatility, low power consumption, high density, and CMOS compatibility. Several models for memristors have been developed to date, but there is a requirement for compact models that are both flexible and sufficiently accurate. A general memristor model generated in Verilog-A is discussed herein to confirm its behavior in the one-transistor one-resistor (1T1R) oxide-based random-access memory (OxRAM) configuration, and validated at circuit level. The results of the model correlate well with experimental characterization data for the HfO2-based OxRAM memristor device, describing the characteristics of both its bipolar and unipolar memristor behaviors. The 1T1R structure is analyzed using the Spectre circuit simulator. Two cases are considered, using the cell as either programmable read-only memory (PROM) or electrically erasable programmable read-only memory (EEPROM). The simulation results confirm the desired nonlinear memristor characteristic, and the applicability of the model to fit and simulate different switching behaviors. The results are verified against both electrical and experimental characterization data, suggesting that the Verilog-A model is suitable for low-power and high-density logic circuit applications at the industrial level.

Modeling and analysis of an Ni:ZnO-based Schottky pattern for NO 2 detection

Abstract: In recent years, new emerging oxide materials have demonstrated significant potential for use in gas sensors. We performed a theoretical investigation and analysis of an Ni-doped ZnO (NZO)-based gas sensor. The conductivity and sensitivity of the gas-sensing layer are illustrated as functions of the temperature and gas concentration. The analysis was carried out for an oxidizing agent, i.e., NO2, in which charge is attracted to the adsorbent layer and increases its resistance. The simulation results revealed the variation in resistance versus the temperature and gas concentration. To confirm the feasibility of the model, all the simulation results were compared with reported experimental work. This work will aid researchers in a reasonable choice of materials for and optimal design of high-performance gas sensors.

A TCAD device simulator for exotic materials and its application to a negative-capacitance FET

Abstract: A new device simulator named Impulse TCAD was developed, being built on top of a nonlinear finite volume method solver, which is further based on the Python script language and its associated scientific libraries. The user can fully customize the device properties and/or equations using scripts, which allows ready handling of exotic materials with nonstandard physical models. As a demonstration, a transient analysis of a negative-capacitance field-effect transistor (NC FET) is presented. The ferroelectric material in the NC FET is handled by using the time-dependent Ginzburg–Landau–Devonshire (GLD) equation, while standard device equations are applied for the rest of the device. The simulations show that, starting from the spontaneous polarization state, the ferroelectric regions evolve into the negative-capacitance regime, showing the expected characteristics of a NC FET. They also indicate that the Ginzburg term in the GLD equation, which is related to the correlation radius $$r_{\mathrm{c}}$$ , plays an important role in the appearance of the negative-capacitance effect. When $$r_{\mathrm{c}}$$ is too short compared with the channel length, the ferroelectric region becomes segregated into multiple polarization domains, resulting in loss of the NC FET characteristic.

Effect of temperature on the performance analysis of MLGNR interconnects

Abstract: Multi-layer graphene nanoribbons (MLGNR) have been proposed as a possible interconnect material. Based on an equivalent single-conductor model of an intercalation-doped MLGNR (ID-MLGNR) interconnect, along with mixed carbon-nanotube bundle (MCB) interconnects, a comparative temperature-dependent study is performed with regard to their distributed circuit parameters and signal transmission performance in terms of delay, power dissipation, and power–delay product (PDP) at the global domain of interconnects. A similar analysis is carried out for copper (Cu) interconnects, and the results are compared with ID-MLGNR and MCB interconnects at the 14-nm technology node. Four different structures of MCB (MCBs 1–4), with and without tunneling effects, are considered here. The SPICE simulation results reveal that for 1-mm-long interconnects, stage-2 AsF5 ID-MLGNR with nearly specular edges have lower delay, power dissipation, and PDP in comparison to MCBs (1–4) with tunneling effects and conventional Cu interconnects over a temperature range of 300 to 500 K. With regard to propagation delay and power dissipation, it has also been shown that MCB interconnects with non-consideration of tunneling effects outperform MCB interconnects with tunneling effects. Additionally, among the MCB (1–4) structures, MCB-1 consistently has lower delay within a temperature range from 300 to 500 K. Moreover, an average improvement in relative delay of 23.78% and 37.66% is observed for ID-MLGNR interconnects in comparison with the best delay structure of MCBs, i.e. MCB-1, and Cu interconnects, respectively, over a temperature range of 300 to 500 K. It is proposed that, in the context of reduced propagation delay, power dissipation, and PDP, ID-MLGNR interconnects hold greater promise than MCB and Cu interconnects.

First-principles analysis of the detection of amine vapors using an antimonene electroresistive molecular device

Abstract: The nonequilibrium Green’s function and density functional theory methods are employed to investigate the electronic and adsorption properties of diethylamine (DEA), monoethylamine (MEA), and trimethylamine (TMA) organic molecules on an antimonene nanosheet (SbNS). The electron transitions between the organic molecules and the SbNS base material are examined based on the projected density-of-states spectrum and energy band structure. Furthermore, the electron transfer when the organic molecules are adsorbed onto the surface of SbNS is studied based on the bandgap energy, average energy gap variation, Bader charge transfer, and adsorption energy. The mixed physisorption–chemisorption of the organic molecules DEA, MEA, and TMA onto SbNS are explored based on the mentioned attributes. Moreover, the current–voltage (I–V) characteristics and the plot of the electron transitions confirm the utility of the SbNS base material to form a chemiresistive sensor for detecting reducing compounds such as DEA, MEA, and TMA in vapor form.