Showing papers in "IEEE Transactions on Nanotechnology in 2021"

Sensitivity Analysis on Dielectric Modulated Ge-Source DMDG TFET Based Label-Free Biosensor

Abstract: This work compares the performance of dielectric modulated (DM) based Ge-source dual material double gate (DMDG) Tunnel Field Effect Transistor (TFET) and conventional (C)-DMDG-TFET as label free biosensor through Technology Computer Aided Design (TCAD) simulator. Here, cavity is introduced both at source and drain sides of the fixed HfO2 dielectric to increase the capture area of biosensors. Sensitivity (Sn) is extracted for both neutral and charged (positive/negative) biomolecules considering cavity is fully filled with different dielectric materials (k). We have reported the sensitivity with the variation in height of nanogap cavity (hbio) for neutral biomolecules in the cavity. The sensitivity of Ge-source DMDG-TFET is found higher than C-DMDG-TFET due to more conduction at the tunnel junction. Also, the subthreshold swing (SS), transfer characteristics, and ION/IOFF ratio of these biosensors are reported for different k and hbio considering neutral/charged biomolecules. The sensitivity of partially filled nanogaps with biomolecules like decreasing, increasing, concave, and convex step profiles are reported for both the biosensors. The dynamic range (DR) of both the biosensors are extracted in presence of positive and negative charged biomolecules. The response time of Ge-source DMDG-TFET is reported at different k. A comparative study of proposed biosensor with other reported work is discussed. Finally, the sensitivity is extracted for DMDG-TFET considering other source material like GaAs, InAs, Si-Ge hetero stacked (HS), GaAs-InAs HS.

Heterojunction Negative-Capacitance Tunnel-FET as a Promising Candidate for Sub-0.4V V DD Digital Logic Circuits

Abstract: The objective of this paper is to exemplify the significant improvements achieved in speed and power-consumption by utilizing negative-capacitance Tunnel FETs in sub-0.4 VDD digital logic applications. A heterojunction negative-capacitance TFET (NCTFET) has been designed using SILVACO TCAD and its accuracy demonstrated by properly fitting the simulated polarization data with calculated L-K equation solution. The prospects of the proposed structure have been manifested in the steep average subthreshold-slope of 27mV/decade over 9 decades of current and high ION/IOFF of 1016, possible due to the internal voltage amplification and voltage pinning effects. The device has been suitably implemented in inverter, ring-oscillator, 2:1 multiplexer and Full-Adder circuits and benchmarked in delay and power-consumption with a reference TFET (R-TFET) and previously proposed structures. The effect of varying thickness of ferroelectric material on the circuit-level performance has also been discussed. Furthermore, the NCTFET has been implemented in a 6-T SRAM which successfully demonstrates the effect of tFE on noise margin and read-write delay, operated at 0.4 VDD. The proposed NCTFET has been presented and justified as a promising candidate for high-speed and low power digital circuits.

Low-Power and High-Performance Ternary SRAM Designs With Application to CNTFET Technology

Abstract: This paper presents two efficient ternary SRAM designs appropriate for several transistor-based technologies. The first design is based on the cycle operator in ternary logic while the second is a buffer-based design that employs the positive and negative ternary inverters. Both the designs consume low power in comparison to existing standard ternary inverter-based SRAM designs. Further, the read and write delay for the proposed designs are much lower than the corresponding ones for existing designs. Detailed analyses of the proposed circuits are presented. Extensive HSpice simulations (and comparisons) using a Carbon Nanotube Field Effect Transistor library are reported. The proposed designs also have noise margins comparable to existing designs.

Exploiting STT-MRAMs for Cryogenic Non-Volatile Cache Applications

Abstract: This paper evaluates the potential of spin-transfer torque magnetic random-access memories (STT-MRAMs) operating at cryogenic temperatures. Our study was carried out at both circuit and architecture levels by exploiting experimental magnetic tunnel junction (MTJ) data and a CMOS technology that was fully characterized down to 77 K. As a main result of our analysis, we show that for medium to large sized cache architectures, STT-MRAMs outperform their six-transistor static random access memory (6T-SRAM) counterparts at 77 K in terms of both dynamic and static (leakage) power as well as read access latency, only underperforming in terms of write latency. For an 8 MB STT-MRAM cache, the read latency is improved by 2× along with a reduction of 45% and 30% in read and write energy, respectively, as compared to an SRAM implementation.

Understanding the Role of Defects in Silicon Nitride-Based Resistive Switching Memories Through Oxygen Doping

Abstract: Resistive memories are promising candidates for replacing current nonvolatile memories and realize storage class memories. Moreover, they have memristive properties, with many discrete resistance levels and implement artificial synapses. The last years researchers have demonstrated RRAM chips used as accelerators in computing, following the new in-memory and neuromorphic computational approaches. Many different metal oxides have been used as resistance switching materials in MIM structures. Understanding of the switching mechanism is very critical for the modeling and the use of memristors in different applications. Here, we demonstrate the bipolar resistance switching of silicon nitride thin films using heavily doped Si and Cu as bottom and top-electrodes respectively. Next, we dope nitride with oxygen in order to introduce and modify the intrinsic nitride defects. Analysis of the current-voltage characteristics reveal that under space-charge limited conditions and by setting the appropriate current compliance, the operation condition of the RRAM cells can be tuned. Furthermore, resistance change can be obtained using appropriate SET/RESET pulsing sequences allowing the use of the devices in computing acceleration application. Impedance spectroscopy measurements clarify the presence of different mechanisms during SET and RESET. We prove through a customized measurement set-up and the appropriate control software that the initial charge-storage in the intrinsic nitride traps governs the resistance change.

Ferroelectric Tunnel Junction Based Crossbar Array Design for Neuro-Inspired Computing

Abstract: Ferroelectric tunnel junction (FTJ) based crossbar array is a promising candidate for the implementation of low-power and area-efficient neuro-inspired computing In this paper, we fabricated and measured a 10 nm thick Hf05Zr05O2 FTJ with > 100 on/off ratio and multi-state storage We found out that the current density of this FTJ is too low for sensing circuitry to distinguish reliably and efficiently To overcome the low current of FTJs, we suggested using an ultra-thin 1 nm FTJ and employing the concept of stacked capacitors from modern DRAM processes Following this idea, we further projected a 1 nm thick stacked FTJ and ran the crossbar arrays in the 20 nm node, which shows a desirable summed current level on the order of 10 μA To model a realistic data pattern of on-state and off-state devices in a 1024 × 1024 array, we mapped quantized weights from a fully connected layer of a deep neural network to the memory cells The current accuracy and delay are evaluated using array-level SPICE simulations with the consideration of interconnect parasitics The overall results suggest that FTJ crossbar array is of the potential for realizing neuro-inspired computing

An Efficient Ultra-Low-Power and Superior Performance Design of Ternary Half Adder Using CNFET and Gate-Overlap TFET Devices

Abstract: This paper presents a novel ultra-low power yet high-performance device and circuit design paradigm for implementing ternary logic based circuits using Gate-Overlap Tunnel FETs (GOTFETs) and Carbon Nanotube FETs (CNFETs). One of the distinguishing novelty reported in this work is the introduction of an innovative GOTFET device, which exhibits more than double the on-currents $I_{on}$ and less than 1/10th the off-currents $I_{off}$ of equivalent, equally-sized mosfet s at the same technology node. Most of the ternary logic designs reported earlier in the literature encode ternary bits into binary for combinational functionality and then use an Encoder to get back ternary output. Unlike the earlier designs, this paper presents a novel and significantly more efficient approach of directly designing ternary logical functions with Low $V_{t}$ Transistors (LVT) and High $V_{t}$ Transistors (HVT) using CNFET and GOTFET technologies. The new approach simplifies the design and reduces the required transistor count & interconnects, thereby reducing the delays and power consumption. The proposed Ternary Half Adder (THA) circuit, designed using CMOS, enables a 52% reduction in transistor count compared to the conventional CMOS designs available in the literature. The THA implemented with CNFET exhibits 27 ps (87% lower delay than similar CMOS design and consumes 2.4 $\mu$ W power (11% lower than CMOS). On the other hand, CGOT THA exhibits 101 ps (51% lower delay than similar CMOS design) and consumes merely 1.26 $\mu$ W power (53% lower than CMOS, in ultra-low power regime). The overall decrease in the Power Delay Products (PDPs) are 88% and 77%, respectively, in the proposed CNFET and CGOT THA circuits compared to the CMOS THA.

Graphene Integrated in a Ring Type Fabry-Perot Cavity: Polarization Insensitive, Low Voltage and Tunable Modulation of Light at Near-IR Telecommunications Band

Abstract: In this article, a novel graphene based resonant free space modulator for modulating optical signals in the wavelength range of 1-2 μm is designed and numerically investigated. The presented modulator is highly versatile. It can function in both transmission and reflection regimes and is polarization insensitive and can be easily tuned to any particular wavelength. In this device, an ingenious Fabry-Perot (FP) cavity composed of concentric Au disks and rings and a single layer graphene is proposed. Incoming light is totally transmitted provided that the wavelength coincides the resonant wavelengths of the cavity, otherwise it is reflected. Hence, unlike common graphene modulators based on electro-absorption, here, the main role of graphene is to shift the resonant wavelengths of the FP cavity and its absorption is indeed negligible. Several highly efficient modulators are designed which can be summarized as follows: A transmission (reflection) type modulator with central wavelength of 1.55 μm, modulation depth of 95% (92%) at this wavelength, modulation depth of 48% (46%) in the wavelength range of 1.42- 1.63 μm (1.46-1.6 μm) covering entire C+S bands, insertion loss of 1.5 dB (1.3 dB) and gate voltage of 4.5 V (4.2 V). Other narrow band low voltage modulators requiring voltages of less than 1.5 V are designed either.

Waste Office Papers as a Cellulosic Material Reservoir to Derive Highly Porous Activated Carbon for Solid-State Electrochemical Capacitor

Abstract: The conversion of biowaste to activated carbon (AC) for supercapacitor applications is recently gaining attention due to its extraordinary high specific surface area (SSA), hierarchical pore size distribution, and very good conductivity. Therefore, in this work, we have utilized waste office papers as a precursor to synthesize highly porous carbon to be used as an electrode material for supercapacitors. The sub-nanometre pores in as-synthesized office paper waste-derived activated carbon (OPDAC) material, facilitate easy flow of ions and surprisingly increase the specific capacitance up to 237 F/g at a current density of 1 A/g. Moreover, an all-solid-state symmetric supercapacitor using OPDAC electrodes delivers an ultrahigh energy density of 31 Wh/kg at a power density of 380 W/kg along with a long cycle life of 95% after 3000 charge-discharge cycles. Hence, these remarkable results pave the path for the usage of different biowastes for varying energy storage applications.

Structure Fortification of Mixed CNT Bundle Interconnects for Nano Integrated Circuits Using Constraint-Based Particle Swarm Optimization

Abstract: The emerging VLSI technology and simultaneously highly dense packaging of devices and interconnects in nano-scale chips have prosperously enabled realization of system-on-chip designs and advanced high-performance computing applications. Concurrently, these have aggravated inevitable challenges in miniaturized integrated circuits (ICs). One of the main limiters in the performance of high-speed VLSI designs is the on-chip interconnects. The emerging graphene based mixed carbon nanotube bundle (MCNTB) interconnects have been investigated as one of the most suited and physically realizable on-chip structure. The present work focuses on utilization of MCNTB as nano-interconnects in the optimized way. Determining optimized placement of CNTs in MCNTB configuration is tedious, skilful task and meagerly explored till date. This has been innovatively taken-up in the current work. In the present paper, novel and efficient particle swarm optimization (PSO) technique is explored and innovatively incorporated to obtain optimal distribution of CNTs in a given rectangular area. The objective function considered for the design is to maximize the tube density. Several signal integrity analyses have been executed. The proposed optimized mixed CNT bundle structure is compared with other different configurations of CNT bundle structures. It is analyzed that the proposed optimized MCNTB configuration produces highly favorable results and is apt suitable for futuristic nano IC designs. The different modelling and performance analyses are performed using MATLAB, SPICE and ADS EDA tools.

System Identification of Micro Piezoelectric Actuators via Rate-Dependent Prandtl-Ishlinskii Hysteresis Model Based on a Modified PSO Algorithm

Abstract: As one of the high-precision actuating mechanisms, the piezoelectric actuators show the advantage of micro/nano stage maneuverability in facilitating the actuating performance of the mechanical systems. To improve the actuating accuracy, it is important to predict the output behavior accurately under the wide operating range, particularly, the change of the driving frequency. The modeling method using the rate-dependent Prandtl-Ishlinskii (RDPI) model is subsequently adopted, which can show the strong nonlinearities relating to the coupling effects between the internal hysteresis and the actuating frequency. Considering the electromechanical characteristics of piezoelectric actuators, a modified particle swarm optimization (MPSO) algorithm is introduced for identifying the RDPI model using the experimental measurement data. The developed MPSO algorithm can overcome the local optimizing limitation of the classical particle swarm optimization (CPSO) algorithm and guarantee the accuracy of predicting the output. The utility and superiority of the MPSO are verified by fitting the identified model to the actual output of the piezoelectric actuators in the micro range at different actuating frequencies. The comparisons with available models using MPSO, CPSO and LS algorithms have examined the validity of the proposed identification method.

Electronic Properties of Graphene Nanoribbons With Defects

Abstract: Graphene nanoribbons (GNRs) are the most important emerging Graphene structures for nanoelectronic and sensor applications. GNRs with perfect lattices have been extensively studied, but fabricated GNRs contain lattice defects the effect of which on their electronic properties has not been studied extensively enough. In this paper, we apply the Non-Equilibrium Green's function (NEGF) method combined with tight-binding Hamiltonians to investigate the effect of lattice defects on the conductance of GNRs. We specifically study, butterfly shaped GNRs, which operate effectively as switches, and have been used in CMOS-like architectures. The cases of the most usual defects, namely the single and double vacancy have been analytically examined. The effect of these vacancies was computed by placing them in different regions and with various numbers on GNR nano-devices, namely edges, main body, contacts and narrow regions. The computation results are presented in the form of energy dispersion diagrams as well as diagrams of maximum conductance as a function of the number of lattice defects. We also present results on the defect tolerance of the butterfly shaped GNR devices.

High Response Formic Acid Gas Sensor Based on MoS 2 Nanosheets

Abstract: In this study, we prepare dispersed MoS2 nanosheets by water bath ultrasonic stripping method uniformly. The MoS2 nanosheets are characterized by SEM, TEM and XRD, and then the gas formic acid is detected in detail. The experimental results show that the sensor patterned with MoS2 nanosheets has high response to formic acid gas with the response time of 11s, and the recovery time of 17s. The sensor exhibits excellent selectivity, repeatability and stability under a linear relationship between the resistance of the sensor and the gas concentration.

First-Principle Analysis of Transition Metal Edge-Passivated Armchair Graphene Nanoribbons for Nanoscale Interconnects

Abstract: In this article, the importance of edge-passivation with transition metals (TM) in armchair graphene nanoribbons (AGNRs) is described for interconnect applications. The electronic and transport properties of TM edge-passivated AGNRs structure is found to be exceptional in comparison to hydrogen edge-passivated AGNRs. Detailed analysis of binding energy, E- k diagram, density of states (DOS), transmission spectrum, current-voltage characteristics and number of conduction channels of TM edge-passivated AGNRs configuration has been performed using density functional theory and non-equilibrium Green function technique. The significant interconnect performance metrics such as delay, energy-delay-product (EDP) have also been evaluated to justify the importance of projected work. The TMs considered in this work are Palladium (Pd), Platinum (Pt), Rhodium (Rh) and Ruthenium (Ru). It is observed that both-side edge-passivation provides better results as compared to single-side. Ru is the potential TM that provides higher currents among all when used in both-edge passivated AGNRs. Ru-AGNR-Ru shows a 10.6x lesser delay and 9.2x lesser EDP as compared to H-AGNR-H interconnects. Therefore, taking all the results into account, both edge Ru-passivated AGNRs i.e., Ru-AGNR-Ru, with the most stable structure in both side TM edge passivation, proves to be the best contender for future interconnect applications.

Gate-Normal Negative Capacitance Tunnel Field-Effect Transistor (TFET) With Channel Doping Engineering

Abstract: In this work, a negative capacitance tunnel FET (NCTFET) with the tunneling current in the normal direction to the gate is proposed with channel doping engineering and its electrical characteristics are investigated using TCAD simulations with calibrated model parameters The new NCTFET has a p+-doping (for n-type operations) in the channel overlap region, which plays a role to suppress the corner (source edge) band-to-band tunneling (BTBT) that degrades the on/off transition By optimizing the doping concentration of the channel overlap region ( N CH,OV), the on-current gets ∼35 times enhanced and the averaged subthreshold swing ( SS AVE) becomes reduced from 825 mV/dec to 439 mV/dec Furthermore, the effects of epi-channel thickness ( T CH) and source overlap length ( L S,OV) variations are analyzed by simulating 2D contour BTBT generation rates and electron densities With the optimized device parameters (4 nm T CH and 35 nm L S,OV), the on-current is additionally ∼16 times improved without the SS and the ambipolar current degradations

Impact of Charge Trapping On Epitaxial p-Ge -on- p-Si and HfO 2 Based Al/HfO 2 /p-Ge -on- p-Si/Al Structures Using Kelvin Probe Force Microscopy and Constant Voltage Stress

Abstract: The quest for the high speed, low power digital logic circuits urge an imperative demand of compatible high-κ dielectric integration on novel Germanium (Ge) based channel material. Here, first ever a methodical nanoscopic and microscopic probes were attempted to Atomic Layer Deposited, Hafnium Dioxide (HfO2) dielectrics on Molecular Beam Epitaxy (MBE) of p-Ge-on-p-Si stack. Kelvin Probe Force Microscopy based contact potential difference (CPD) analysis reveals that the disintegration of trapped charges lasting for ∼18 hours. The impact of constant voltage stress (CVS) on trapped charges results in variation of threshold voltage (Vth) and hysteresis window (W) were studied. The cyclic Capacitance-Voltage (C-V) characteristics at 0.5 MHz exhibit the shift in the flat band (ΔVfb), ΔVth, and ΔW at 10V stress were ∼0.84V, ∼0.62V, and ∼0.47V, respectively. While the computed interface trap density (Dit) and total effective charge density (Qeff) were ∼8.49 × 1012 eV−1cm−2 and ∼1.81 × 1012 cm−2, respectively. The gate leakage current density, (J) at 5V is 26.53 × 10−6 A/cm2 and reduced by a factor of ∼6.8 after 10V, CVS. Whereas the current density (J) increases from ∼26.53 × 10−6 A/cm2 at 25 °C by a factor of ∼2 at 125 °C. To study the retention and effect of charge trapping, the stress-time analysis was performed for 8000s at 3V (CVS). The r.m.s. surface roughness of HfO2 thin films was found to be ∼0.23 nm. X-ray photoelectron spectroscopy (XPS) depth profiling categorized the elemental composition of thin films. These investigations would help to HfO2/p-Ge-on-p-Si system interfacial engineering well before the Ge based nano device realization.

Analytical Modeling of Surface Potential and Figure of Merit Computation for Planar Junctionless pH Sensing BioFET

Abstract: Herein this paper we propose a surface potential based analytical model for planar junctionless field effect transistor (JL-FET) for pH sensing. The electrolyte considered is phosphate buffer saline (PBS) solution which has been modeled as three layered stacked structure consisting of stern layer, ion-permeable membrane and bulk electrolyte. The proposed model has been deduced considering Poisson's equation in the channel region. Relative shift in threshold voltage ( $\rm V_{Th}$ ) and maximum drain current ( $\rm I_{DS,max}$ ) have been used as sensitivity metrics. The low concentrations of electrolyte (0.01), yielded higher $\rm V_{Th}$ sensitivity of $\text{63}\;mV/pH$ and $\text{59}\;mV/pH$ for bottom and liquid gate respectively as compared to higher molar concentrations of electrolyte. For 0.01 PBS the aggregate drain current shift has been found to be $52.8\ \mu A/pH$ and is larger for liquid gate operation while as for bottom gate, shift of $18.9\ \mu A/pH$ is observed. Further considering pH range of 1-14, we computed various figure of merits (FOMs) that include sensitivity, linearity and signal to noise ratio for the device. The FOMs were computed and analyzed for independent operation of liquid and bottom gate for three different molarities of PBS (1, 0.1, 0.01) each with pH range from 1 to 14. Signal to noise ratio of drain current is found maximum for low molar concentrations of electrolyte and also is highest at point of maximum transconductance. The results obtained from analytical model are in good coherence with the TCAD simulation model.

Numerical Analysis of Reconfigurable and Multifunctional Barium Titanate Platform Based on Photonic Crystal Ring Resonator

Abstract: A novel reconfigurable, reversible and multifunctional nanostructure platform is designed with ultracompact size, high extinction ratio, large bandwidth and low optical loss. The proposed structure consists of a ring resonator and photonic crystal waveguides. The single nanoscale structure is used to realize the five different high-performance photonic devices such as, electro-optic tunable filter, reconfigurable switch, 1 × 5 power splitter, 4 × 2 reversible encoder and SR flip-flop. These miniature optical device performance parameters are numerically analyzed and optimized by finite-difference-time-domain (FDTD) method. A multifunctional ring resonator coupled waveguide structure is designed with a very small footprint of 179 μm2, large bandwidth of 45.2 nm, the fast response time of 215 fs and high data rate of 4.651 Tbps. Hence, the proposed nanostructure can be highly suitable for photonic interconnects, lightwave communication networks and quantum computing.

Characterization of Carbon-Based Epoxy Nanocomposite Shield for Broadband EMI Shielding Application in X and Ku Bands

Abstract: Electromagnetic interference (EMI) shielding in the X and Ku bands of electromagnetic spectrum are vital for communication and military applications. This work aims at developing and characterizing nanocomposite shield with two nano fillers- carbon nanotubes (CNT) and carbon nanofibers (CNF) dispersed at various weight combinations for shielding both X and Ku bands at minimum cost. DC conductivity of the prepared CNT-CNF based epoxy nanocomposites obey classical law of percolation theory. AC conductivity follows universal dynamic response (UDR) when CNT concentration is above 0.5wt.%. The rise in permittivity with filler concentration at a particular frequency is more prominent with the increase in CNF concentration. The measurement of shielding effectiveness of the prepared samples demonstrates that maximum shielding obtained is 24 dB and 30 dB in the X and Ku bands respectively and the optimum filler combination is 1wt.%CNT-5wt.%CNF agreeing with the results obtained from characterization. The nanocomposites with higher CNF content exhibit better shielding as compared with higher CNT content owing to the higher aspect ratio of CNF used. The shielding efficiency increases as the frequency band shifts from X to Ku. Absorption loss is the prominent mechanism of shielding in both bands, avoiding the chance for electromagnetic pollution.

Microstructure and Electrical Properties of Novel piezo-optrodes Based on Thin-Film Piezoelectric Aluminium Nitride for Sensing

Abstract: Thin-film piezoelectric materials are currently employed in micro- and nanodevices for energy harvesting and mechanical sensing. The deposition of these functional layers, however, is quite challenging onto non-rigid/non-flat substrates, such as optical fibers (OFs). Besides the recent novel applications of OFs as probes for biosensing and bioactuation, the possibility to combine them with piezoelectric thin films and metallic electrodes can pave the way for the employment of novel opto-electro-mechanical sensors (e.g., waveguides, optical phase modulators, tunable filters, energy harvesters or biosensors). In this work the deposition of a thin-film piezoelectric wurtzite-phase Aluminium Nitride (AlN), sandwiched between molybdenum (Mo) electrodes, on the curved lateral surface of an optical fiber with polymeric cladding, is reported for the first time, without the need of an orientation-promoting interlayer. The material surface properties and morphology are characterized by microscopy techniques. High orientation is demonstrated by SEM, PFM and X-ray diffraction analysis on a flat polymeric control, with a resulting piezoelectric coefficient (d33) of ∼5.4 pm/V, while the surface roughness Rms measured by AFM is 9 ÷ 16 nm. The output mechanical sensing capability of the resulting AlN-based piezo-optrode is investigated through mechanical buckling tests: the peak-to-peak voltage for weakly impulsive loads increases with increasing relative displacements (up to 30%), in the range of 20 ÷ 35 mV. Impedance spectroscopy frequency sweeps (10 kHz-1 MHz, 1 V) demonstrate a sensor capacitance of ∼8 pF, with an electrical Q factor as high as 150. The electrical response in the long-term period (two months) revealed good reliability and durability.

Zinc Oxide Thin-Film Transistor with Catalytic Electrodes for Hydrogen Sensing at Room Temperature

Abstract: Palladium-Titanium (Pd-Ti)/n-ZnO Schottky contact based thin-film transistor (TFT) was fabricated on a thermally oxidized n-Si substrate with a compatible fabrication process and the hydrogen-sensing response was evaluated under room temperature (RT) without the presence of any heating element which reduces design complexity as well as power consumption significantly. Structural, mechanical, chemical and optical properties of the RF (Radio Frequency) sputtered ZnO thin film with 150 nm thickness as a gas sensing element have been investigated. Electrical characteristics and concentration dependent (500 ppm to 4500 ppm) RT sensor response (in the context of increasing drain current as the Schottky barrier height decreases) of the fabricated device with the maximum sensitivity of 70.8% (at 4500 ppm H2) including a minimum response time of 20 s (at 4500 ppm H2) and recovery time of 40 s (at 500 ppm H2) have been demonstrated. Sufficiently impressive performance of the sensor has been observed with respect to repeatability, selectivity, time-depending stability and humidity analysis at RT.

Highly Efficient Dual Band Graphene Plasmonic Photodetector at Optical Communication Wavelengths

Abstract: Graphene has remarkable properties in the optoelectronic field, especially in high speed photodetection. However, the responsivity of the graphene-based photodetectors is limited to tens of mA/W because of the weak absorption of the graphene layer. In this paper, a graphene plasmonic photodetector with high responsivity operating in two optical communication bands (O-band and U-band) is proposed. The combination of the graphene monolayer and the plasmonic structure is used to enhance the light-graphene interaction and consequently to improve the responsivity of the photodetector. The numerical simulation results show that the proposed photodetector has the responsivity of 348 mA/W and 460 mA/W at the wavelengths of 1310 nm and 1675 nm, respectively. Also, this structure exhibits the bandwidth of 60 GHz.

The Role of Oxygen on Anisotropy in Chromium Oxide Hard Mask Etching for Sub-Micron Fabrication

Abstract: Chromium and its oxides have been playing a vital role in the fabrication of micro- and nano-scale structures in numerous applications for several decades. Controllable, robust and anisotropically dry-etched hard masks and their optimal etch recipes are required in state-of-the-art device fabrication techniques. In terms of manufacturability and repeatability, a mechanistic understanding of the plasma-etching process of chromium oxide (Cr2O3) is necessary for its adoption as a hard mask. We present a systematic investigation of plasma etching of chromium oxide films via an inductively coupled plasma-reactive ion etching (ICP-RIE) system in nanoscale. The effects of plasma composition, ICP source power and HF platen power on the etch rate, sidewall profile, surface morphology, and dc-bias have been methodically investigated. We paid particular attention to studying how oxygen content can be used to control the etch profile of nano trenches using chlorine/oxygen gas mixtures, including extremes of very low and very high oxygen content. It was found that chromium oxide etch mechanisms are dependent strongly on the oxygen level. We achieved desirable vertical sidewalls with reasonable etch rates when the oxygen content is in the range 10–40% in the plasma. Oxygen content below 10% resulted in positively tapered etch profiles with low etch rates. On the other hand, bowl-like etch profiles with undercut formation was observed at high oxygen content above 40%, caused by re-emission of the reactive species at this regime. As a hard mask material, patterning Cr2O3 films compared to Cr metal is advantageous in terms of etch uniformity and reproducibility. Contrary to Cr, Cr2O3 is not as sensitive to chamber wall conditions.

Low-Energy Eigenspectrum Decomposition (LEED) of Quantum-Dot Cellular Automata Networks

Abstract: The design and understanding of quantum-dot cellular automata (QCA) networks has been largely influenced by limitations in the approximation methods used in common design tools. In some cases, such limitations have led to unrealistic selections of clock zones which are not feasible for nanoscale QCA implementations given current fabrication constraints on clocking electrodes. A better understanding of the behaviour of larger QCA networks of perhaps tens to hundreds of QCA devices is needed. One approach is by investigating the low energy spectrum; however, diagonalization of the system Hamiltonian even in the 2-state approximation is impractical beyond 20 or so devices. In this work, we present a methodology for understanding the spectrum of the full network in terms of contributions from components of the network. We show that important features of the low energy spectrum can be attributed to specific critical components, and present one scheme for decomposing the network into these components. In addition, we address the question of computing the low energy spectrum of large QCA networks. A method based on basis reduction which naturally emerges from the component decomposition is successfully applied to a 49 cell XOR gate with results compared against a density matrix renormalization group implementation.

Responsivity Spectrum Tailoring of Pentacene:ZnO Multi-Nano Film-Based Bulk Heterojunction Photodetector

Abstract: In the present article, Al/Al2O3/Pentacene:ZnO/ PEDOT:PSS/ITO photodetector structure is proposed and analyzed. The pentacene:ZnO blend film used as an active layer of the device is studied briefly for its structural and optical properties. The proposed photodetector is shown to be tailored for operation in UV and visible region by changing pentacene:ZnO (P:Z) blend film ratio as 1:1, 1:2 and 2:1. For the proposed photodetector optimum performance in the UV region is obtained for P:Z ratio of 1:2. The obtained responsivity is 9.26 A/W, detectivity is 1.74 × 1013 Jones and external quantum efficiency (EQE) is 3.9 × 103%, at wavelength 302 nm. Further, for the visible region, responsivity is 0.71 A/W, detectivity is 0.15 × 1013 Jones and external quantum efficiency (EQE) is 140%, at wavelength 628 nm for P:Z ratio of 2:1. Thus, responsivity tailoring by changing the blend ratio of the active layer facilitates the route for the fabrication of suitable optoelectronic devices for a wide variety of applications.

Modeling and Comparing Gas Sensing Properties of CNT and CNT Decorated With Zinc Oxide

Abstract: The use of hybrid nanostructures is of great interest to take advantage of their constructing components. However, the reason for the improved features of these structures has not yet been fully explained and there are some ambiguities. So we studied and compared sensing properties of carbon nanotube (CNT) and CNT decorated with zinc oxide (ZnO) nanoparticle (CNT/ZnO). Studied target gas molecules were CH4, CO, H2S and NO2. Different performance of CNT and CNT/ZnO structures were defined by calculating their density of sates before and after gas adsorption. The adsorption energy of molecules on both structures and charge transfer between molecules and their surfaces were also estimated using density functional theory (DFT) method. Compared to the pristine CNT, electrical properties of CNT/ZnO is influenced more notably according to the gas adsorption as the molecules have higher adsorption energy and larger charge transfer with the structure. Thus, the band gap of CNT/ZnO is also more affected by gas adsorption. The relation between band gap variations and the gas response of the structures was modeled and showed that the greater the band gap changes due to a gas adsorption, the better the structure gas sensing responses to it. Therefore, it can be concluded that the ZnO decorated CNT shows better gas sensing properties.

Development of Cost-Effective Carbon Nanofiber Epoxy Nanocomposites for Lightweight Wideband EMI Shielding Application

Abstract: Electromagnetic interference (EMI) shielding is essential at minimizing cost in the X and Ku frequency bands utilized for radar and defense applications. Development and characterization of lightweight, cost-effective carbon nanofiber (CNF) based epoxy nanocomposites for wideband EMI shielding application is the primary focus of this work. CNF epoxy nanocomposites are prepared with a minimum thickness of 0.5 mm at various CNF concentrations from 0.1 to 8 wt.%. SEM analysis ensures uniform dispersion of fillers and spectroscopic measurements like Raman and X-ray photoelectron spectroscopy ensures the chemical composition, molecular structure, and electron states of the developed nanocomposite material. DC conductivity follows the classical law of percolation theory with a percolation threshold of 1.5 wt.%. The AC conductivity of prepared CNF-based nanocomposites follows the universal dynamic response when the filler content is beyond the percolation threshold. The variation of permittivity with varying filler concentration exhibits the various polarization mechanisms and dielectric loss in the nanocomposite material. The measured shielding effectiveness for 4 wt.% and 8 wt.% CNF content in the X and Ku bands confirms with 99% and 99.9% diminution of electromagnetic radiation, respectively, absorption is the dominant mechanism, thus lowering the chances for further electromagnetic interference. The high shielding effectiveness of the prepared nanocomposites is due to the inherent stacked cup structure of CNF, and the high aspect ratio of CNF used. The shielding efficiency of the prepared material increases with the frequency change from X-band to Ku-band.

Millimeter-Wave Vertical III-V Nanowire MOSFET Device-to-Circuit Co-Design

Abstract: Vertical III-V nanowire MOSFETs show potential towards the ultimate transistor scaling. A high transconductance and current density are achieved based on the gate-all-around architecture. This work presents a high-frequency design of such devices, achieving more than 600 GHz cut-off frequencies ( f T, f max), at 20 nm gate length. Furthermore, capacitance design and scaling trends, supported by COMSOL Multiphysics simulations derive state-of-the-art parasitics magnitudes for vertical devices in general, reaching gate-drain capacitance values of 17 aF/wire, corresponding to 0.2 fF/μm. A unique co-designed feedback resonant circuit makes the device unilateral, exhibiting up to 15 dB gain in D-band at 0.5 V supply, and with a current density of 0.5 mA/μm. Finally, a 2-stage low noise amplifier is designed using an optimum matching concept to utilize the full available bandwidth. The resulting circuit performance is independent of transistor gate length, since any decrease in device intrinsic capacitance is assisted by an increase in device overlap capacitances in a setting unique to a current implementation of vertical nanowire MOSFETs. With this approach, amplifiers are designed with more than 20 dB gain and minimum noise figure of 2.5 dB in a simulation environment at 140 GHz. The proposed technology and design platform show a great potential in future low-power communication systems.

Scalable Fabrication and Metrology of Silicon Nanowire Arrays Made by Metal Assisted Chemical Etch

Abstract: A scalable fabrication technique for silicon nanowires based on integrating nanoimprint lithography, metal assisted chemical etching (MACE), and spectroscopic scatterometry is presented in this article. The resulting wafer-scale process has demonstrated reliable and repeatable fabrication of high aspect ratio silicon nanostructures, and can provide cost-effective fabrication to enable applications in electronics, energy, point-of-use healthcare and sensing. Traditional pattern transfer using plasma etching suffers from etch taper and loss of feature fidelity at high aspect ratios, unlike MACE. However, MACE has largely been demonstrated in the literature over small areas, with scarce information on full wafer etching, critical dimension control, and etch depth uniformity. In this paper, we demonstrate a 100mm wafer high yield process to fabricate silicon nanowires. A large-area characterization of the process has been developed using imaging spectroscopic scatterometry. This scatterometry technique provides full wafer data on critical dimension control, etch depth uniformity, and presence of nanowire collapse defects. This work shows the promise of MACE as a next generation etch technology.

Skin Effect-Related AC Resistance Study in Macroscopic Scale Carbon Nanotube Yarn Applicable to High-Power Converter

Abstract: This paper presents a study on the skin effect-related AC resistance of macroscopic scale carbon nanotube (CNT) yarn. The range of interest frequency in this study is up to 10 MHz which is considered conventional high-frequency power converters operating range. AC resistance of both CNT yarn and copper (Cu) wires are measured by impedance analyzer for the small-signal frequency-response. The 1-turn core-less layout of inductors made of both CNT yarn and Cu wire are implemented to eliminate the proximity effect and magnetic core. The measurement results are compared with the theoretical model results based on Bessel-Kelvin function. The results show that the increasing rate of AC resistance in CNT yarn is lower than in Cu wire as frequency increases so that it causes lower CNT yarn resistance at higher frequencies. It was found that the Cu wire measurement result follows the theoretical model whereas CNT yarn does not. Therefore, a new skin effect related AC resistance correction factor for CNT yarn is introduced. To verify the same trends in large signal level of current, conduction losses for both CNT yarn and Cu wire are tested as an inductor component in a power converter circuit working like a large signal generator. The losses were collected and presented for the same frequency range (between 1 and 10 MHz). The results show less losses with CNT yarn inductor. Finally, another CNT yarn-based inductor was constructed and tested in around 200 W power converter circuit. The results show 91.72% of high efficiency at 3.125 MHz switching frequency. The study shows that, for power converter circuits working in the range higher than 1 MHz, the CNT yarns are reasonable to replace Cu wires due to the lower skin effect- related losses.