arXiv subjects

Yogesh Singh Chauhan

Publications and source records attributed to Yogesh Singh Chauhan.

At least 19 recordsLinked to original sources

arXiv2026

Self-Heating and Parasitic Effects in Multi-Tier CFET Design

In this article, we study the impact of self-heating effects (SHEs) and middle of line (MOL) and back-end of line (BEOL) induced parasitics on multi-tier CFET design, where multiple nanosheet devices are vertically stacked. We analyze and compare the 4-tier CFET design with the conventional 2-tier CFET, using TCAD models calibrated to experimental measurements. Additionally, TCAD simulations are used to model and analyze SHE-induced heat distribution and temperature profiles and to extract the detailed parasitic RC network from 3D models of CMOS inverters designed with full MOL and BEOL interconnects. At the device level, the maximum temperature rise (TMAX) caused by SHE in nFET and pFET devices of the 2-tier CFET architecture is 62 K and 74 K, respectively. Due to the increased distance from the substrate heat sink, the upper-tier nFET and pFET devices in the 4-tier design show higher TMAX of 83.5 K and 98.5 K and more heat trapping in the stacked layers. Furthermore, in the 4-tier CFET-based CMOS inverters, the BEOL-induced parasitic RCs are, respectively, 10 and 6.5 times higher in the top-tier than in the 2-tier CFET-based inverters. In the bottom tier, the corresponding parasitic RC elements are 6.26 and 2 times higher, respectively, than in the 2-tier inverters. Finally, compared to the 4-tier design without parasitics, the propagation delay of the top and bottom tier inverters increases by 10% and 8.2%, respectively, due to the interconnect parasitic RCs. For the conventional 2-tier inverter, the corresponding degradation of delay with parasitic RCs is 37.25%.

cs.ET↗

arXiv2024

Harnessing Room-Temperature Ferroelectricity in Metal Oxide Monolayers for Advanced Logic Devices

Two-dimensional ferroelectric materials are beneficial for power-efficient memory devices and transistor applications. Here, we predict out-of-plane ferroelectricity in a new family of buckled metal oxide (MO; M: Ge, Sn, Pb) monolayers with significant spontaneous polarization. Additionally, these monolayers have a narrow valence band, which is energetically separated from the rest of the low-lying valence bands. Such a unique band structure limits the long thermal tail of the hot carriers, mitigating subthreshold thermionic leakage and allowing field-effect transistors (FETs) to function beyond the bounds imposed on conventional FETs by thermodynamics. Our quantum transport simulations reveal that the FETs based on these MO monolayers exhibit a large ON/OFF ratio with an average subthreshold swing of less than 60 mV/decade at room temperature, even for short gate lengths. Our work motivates further exploration of the MO monolayers for developing advanced, high-performance memory and logic devices.

physics.app-ph↗

arXiv2024

Energy-Efficient Cryogenic Ternary Content Addressable Memory using Ferroelectric SQUID

Ternary content addressable memories (TCAMs) are useful for certain computing tasks since they allow us to compare a search query with a whole dataset stored in the memory array. They can also unlock unique advantages for cryogenic applications like quantum computing, high-performance computing, and space exploration by improving speed and energy efficiency through parallel searching. This paper explores the design and implementation of a cryogenic ternary content addressable memory based on ferroelectric superconducting quantum interference devices (FeSQUIDs). The use of FeSQUID for designing the TCAM provides several unique advantages. First, we can get binary decisions (zero or non-zero voltage) for matching and mismatching conditions without using any peripheral circuitry. Moreover, the proposed TCAM needs ultra-low energy (1.36 aJ and 26.5 aJ average energy consumption for 1-bit binary and ternary search, respectively), thanks to the use of energy-efficient SQUIDs. Finally, we show the efficiency of FeSQUID through the brain-inspired application of Hyperdimensional Computing (HDC). Here, the FeSQUID-based TCAM implements the associative memory to support the highly parallel search needed in the inference step. We estimate an energy consumption of 89.4 fJ per vector comparison using a vector size of 10,000 bits. We also compare the FeSQUID-based TCAM array with the 5nm FinFET-based cryogenic SRAM-based TCAM array and observe that the proposed FeSQUID-based TCAM array consumes over one order of magnitude lower energy while performing the same task.

cs.ET↗

arXiv2024

Engineering Si-Qubit MOSFETs: A Phase-Field Modeling Approach Integrating Quantum-Electrostatics at Cryogenic Temperatures

This study employs advanced phase-field modeling to investigate Si-based qubit MOSFETs, integrating electrostatics and quantum mechanical effects. We adopt a comprehensive modeling approach, utilizing full-wave treatment of the Schrodinger equation solutions, coupled with the Poisson equation at cryogenic temperatures. Our analysis explores the influence of interface traps on quantum dot (QD) barrier heights, affecting coupling due to tunneling. A wider trap distribution leads to the decoupling of quantum dots. Furthermore, the oscillations in the transmission and reflection coefficients increase as the plunger/barrier gate length increases, reducing the coupling between the QDs. By optimizing plunger and barrier gate dimensions, spacer configurations, and gap oxide lengths, we enhance control over quantum well depths and minimize unwanted wave function leakage. The modeling algorithm is also validated against the experimental data and can accurately capture the oscillations in the Id Vgs caused by the Coulomb blockade at cryogenic temperature

quant-ph↗

arXiv2024

Room Temperature Ferroelectricity and Electrically Tunable Berry Curvature Dipole in III-V Monolayers

Two-dimensional ferroelectric monolayers are promising candidates for compact memory devices and flexible electronics. Here, through first-principles calculations, we predict room temperature ferroelectricity in AB-type monolayers comprising group III (A = Al, In, Ga) and group V (B = As, P, Sb) elements. We show that their spontaneous polarization, oriented out-of-plane, ranges from 9.48 to 13.96 pC/m, outperforming most known 2D ferroelectric. We demonstrate electric field tunable Berry curvature dipole and nonlinear Hall current in these monolayers. Additionally, we highlight their applicability in next-generation memory devices by forming efficient ferroelectric tunnel junctions, especially in InP, which supports high tunneling electroresistance. Our findings motivate further exploration of these monolayers for studying the interplay between Berry curvature and ferroelectricity and for integrating these ferroelectric monolayers in next-generation electronic devices.

cond-mat.mtrl-sci↗

arXiv2023

Room Temperature Ferroelectricity, Ferromagnetism, and Anomalous Hall Effect in Half-metallic Monolayer CrTe

Two-dimensional materials hosting ferroelectricity and ferromagnetism are crucial for low-power and high-speed information processing technologies. However, intrinsic 2D multiferroics in the monolayer limit are rare. Here, we demonstrate that monolayer CrTe, obtained by cleaving the [002] surface, is dynamically stable multiferroic at temperatures beyond room temperature. We show that it orders ferromagnetically with significant in-plane magnetocrystalline anisotropy, and it is a half-metal featuring a large half-metal gap. Remarkably, the broken inversion symmetry and buckled geometry of monolayer CrTe make it a ferroelectric with a large spontaneous out-of-plane polarization and significant magnetoelectric coupling. In addition, we demonstrate polarization or electric field-induced tunability of the anomalous Hall effect, accompanied by substantial bandstructure modulation. Our findings establish monolayer CrTe as a room-temperature multiferroic with great potential for applications in spintronics and ferroelectric devices.

cond-mat.mes-hall↗

arXiv2023

Versatility of type-II van der Waals heterostructures: a case study with SiH-CdCl2

Unlike bilayers or a few layers thick materials, heterostructures are designer materials formed by assembling different monolayers in any desired sequence. As a result, while multilayer materials come with their intrinsic properties, heterostructures can be tailor-made to suit specific applications. Taking SiH-CdCl 2 as a representative system, we show the potential of heterostructures for several applications, like piezoelectricity, photocatalytic water splitting, and tunnel field effect transistor (TFET). Our study confirms that the characteristics of the heterostructure mainly depend on the potential difference between the constituent monolayers. From the vast database of available layered materials, many such combinations with a suitable potential difference are expected to have similar properties. Our work points to a vast pool of assembled materials with multifunctionality, an excellent asset for next-generation device applications.

cond-mat.mtrl-sci↗

arXiv2023

Powering Disturb-Free Reconfigurable Computing and Tunable Analog Electronics with Dual-Port Ferroelectric FET

Single-port ferroelectric FET (FeFET) that performs write and read operations on the same electrical gate prevents its wide application in tunable analog electronics and suffers from read disturb, especially to the high-threshold voltage (VTH) state as the retention energy barrier is reduced by the applied read bias. To address both issues, we propose to adopt a read disturb-free dual-port FeFET where write is performed on the gate featuring a ferroelectric layer and the read is done on a separate gate featuring a non-ferroelectric dielectric. Combining the unique structure and the separate read gate, read disturb is eliminated as the applied field is aligned with polarization in the high-VTH state and thus improving its stability, while it is screened by the channel inversion charge and exerts no negative impact on the low-VTH state stability. Comprehensive theoretical and experimental validation have been performed on fully-depleted silicon-on-insulator (FDSOI) FeFETs integrated on 22 nm platform, which intrinsically has dual ports with its buried oxide layer acting as the non-ferroelectric dielectric. Novel applications that can exploit the proposed dual-port FeFET are proposed and experimentally demonstrated for the first time, including FPGA that harnesses its read disturb-free feature and tunable analog electronics (e.g., frequency tunable ring oscillator in this work) leveraging the separated write and read paths.

cs.ET↗

arXiv2023

Compact and High-Performance TCAM Based on Scaled Double-Gate FeFETs

Ternary content addressable memory (TCAM), widely used in network routers and high-associativity caches, is gaining popularity in machine learning and data-analytic applications. Ferroelectric FETs (FeFETs) are a promising candidate for implementing TCAM owing to their high ON/OFF ratio, non-volatility, and CMOS compatibility. However, conventional single-gate FeFETs (SG-FeFETs) suffer from relatively high write voltage, low endurance, potential read disturbance, and face scaling challenges. Recently, a double-gate FeFET (DG-FeFET) has been proposed and outperforms SG-FeFETs in many aspects. This paper investigates TCAM design challenges specific to DG-FeFETs and introduces a novel 1.5T1Fe TCAM design based on DG-FeFETs. A 2-step search with early termination is employed to reduce the cell area and improve energy efficiency. A shared driver design is proposed to reduce the peripherals area. Detailed analysis and SPICE simulation show that the 1.5T1Fe DG-TCAM leads to superior search speed and energy efficiency. The 1.5T1Fe TCAM design can also be built with SG-FeFETs, which achieve search latency and energy improvement compared with 2FeFET TCAM.

cs.ET↗

arXiv2022

Multi Spectral Switchable Infra-Red Reflectance Resonances in Highly Subwavelength Partially Oxidized Vanadium Thin Films

Phase transition materials are promising for realization of switchable optics. In this work, we show reflectance resonances in the near-infrared and long-wave infrared wavelengths in highly subwavelength partially oxidized Vanadium thin films. These partially oxidized films consist of a multilayer of Vanadium dioxide and Vanadium as shown using Raman spectroscopy and four-probe measurements. As Vanadium dioxide is a phase transition material that shows insulator to metal phase transition at 68 C, the observed infra-red resonances can be switched with temperature into a high-reflectance state. The wavelength of these resonances are passively tunable as a function of the oxidation duration. The obtained reflectance resonance at near-infrared wavelength red shifts from 1.78 um to 2.68 um with increasing oxidation duration while the long-wavelength infrared resonance blue shifts from 12.68 um to 9.96 um. To find the origin of the reflectance resonances, we model the reflectance spectra as a function of the oxidation duration using the transfer matrix method. The presented model captures the dual reflectance resonances reasonably well. These passive wavelength-tunable and switchable resonances with easy to fabricate lithography-free multilayer structure will be useful for multispectral applications such as camouflage, spectral selective microbolometer, and thermal management.

physics.optics↗

arXiv2022

Static negative susceptibility in ferromagnetic material induced by domain wall motion: an aspect of superconductor state

Domain wall motion in magnetic materiel induces the negative susceptibility leading to a perfect diamagnetism state. The local susceptibility is calculated by the derivative of magnetization ($\vec{M}$) vector w.r.t. magnetic field strength ($\vec{H}$) vector. In the transient region from the upward domain to the downward domain (domain wall width), local $\vec{M}$ and $\vec{H}$ vectors exhibit opposite slopes, which leads to a negative susceptibility value. A negative susceptibility value induces the diamagnetism effect leading to a relative permeability value $<$ 1 $\left(μ_r < 1\right)$. This diamagnetism sate originates due to the domain wall motion, which is an entirely different mechanism from the electron motion's induced diamagnetism. Furthermore, the strength of the diamagnetism state can be enhanced by tuning the gradient energy of a domain that may correspond to a perfect diamagnetism state $\left(χ_v \approx -1 \Rightarrow μ_r \rightarrow 0\right)$. Besides, we believe that there may be a possibility of sustaining such a diamagnetic state (domain wall induced) in a ferromagnetic material that is utterly contradictory to the conventional theory.

physics.app-ph↗

arXiv2022

Physics and modeling of multi-domain FeFET with domain wall induced Negative Capacitance

In this paper, we present the dynamics and modeling of multi-domains in the ferroelectric FET (FeFET). Due to the periodic texture of domains, the electrostatics of the FeFET exhibit an oscillatory conduction band profile. To capture such oscillations, we solve coupled 2-D Poisson's equation with the net ferroelectric energy density (gradient energy + free energy + depolarization energy) equation. Multi-domain dynamics are captured by minimizing the net ferroelectric energy leading to a thermodynamically stable state. Furthermore, we show that the motion of domain walls originates local bound charge density in the ferroelectric region, which induces the negative capacitance (NC) effect. The strength of domain wall-induced NC is determined by the gradient energy of the ferroelectric material. FeFET exhibits variability in the drain current with domain period due to the inherent NC effect. Additionally, the impact of domain wall transition (soft$\rightleftharpoons$hard) on the device's electrostatic/transport is also analyzed. The model also accurately captures both nucleations of a new domain and the motion of the domain wall. Furthermore, the model is thoroughly validated against experimental results and phase-field simulations.

physics.app-ph↗

arXiv2022

Dynamics of Multi-Domains in Ferroelectric Tunnel Junction

The Discovery of giant tunnel electroresistance (TER) in Ferroelectric Tunnel Junction (FTJ) paves a futuristic possibility of utilizing the FTJ as a bistable resistive device with an enormously high ON/OFF ratio. In the last 20 years, numerous studies have reported that the formation of multidomain in ferroelectric material is an inevitable process to minimize the total system energy. Recent studies based on phase-field simulations have demonstrated that domain nucleation/motion substantially alters the electrostatics of a ferroelectric material. However, the impact of domain dynamics on quantum transport in FTJ remains elusive. This paper presents a comprehensive study of multidomain dynamics in a ferroelectric tunnel junction. Analysis of this article is twofold; firstly, we study the impact of domain dynamics on electrostatics in an FTJ. Subsequently, the obtained electrostatics is used to study the variations in tunneling current, and TER originated from multidomain dynamics. We show that ON/OFF current density and TER vary locally in the ferroelectric region. Furthermore, the device's electrostatics and quantum transport exhibit an oscillatory nature due to periodic domain texture. ON/OFF current density shows a sine/cosine distribution in ferroelectric, and approximately one-decade local variation in current density is observed. These local fluctuations in current density cause oscillations in the device's ON/OFF ratio. Optimization techniques to achieve a uniform and maximum TER are also discussed. A 2D analytical and explicit model is derived by solving coupled 2D Poisson's equation and Landau-Ginzburg equation. The model incorporates the switching and nucleation of domains by minimizing net ferroelectric energy (depolarization+free+gradient energy density). Furthermore, the impact of the bottom insulator layer on ferroelectric's gradient energy is also studied.

physics.app-ph↗

arXiv2022

Strain-tunable in-plane ferroelectricity and lateral tunnel junction in monolayer group-IV monochalcogenides

2D Ferroelectric materials are promising for designing low-dimensional memory devices. Here, we explore strain tunable ferroelectric properties of group-IV monochalcogenides MX (M=Ge, Sn; X=S, Se) and their potential application in lateral field tunnel junction devices. We find that these monolayers have in-plane ferroelectricity, with their ferroelectric parameters being on par with other known 2D ferroelectric materials. Amongst SnSe, SnS, GeSe, and GeS, we find that GeS has the best ferroelectric parameters for device applications, which can be improved further by applying uniaxial tensile strain. We use the calculated ferroelectric properties of these materials to study the tunneling electroresistance (TER) of a 4 nm device based on lateral ferroelectric tunnel junction. We find a substantial TER ratio $10^3-10^5$ in the devices based on these materials, which can be further improved up to a factor of 40 on the application of tensile strain.

cond-mat.mtrl-sci↗

arXiv2021

Effect of Vanadium Thickness and Deposition Temperature on VO2 Synthesis using Atmospheric Pressure Thermal Oxidation

Vanadium dioxide (VO2) is a phase transition material that undergoes a reversible insulator-metal phase transition at ~ 68 C. Atmospheric pressure thermal oxidation (APTO) of vanadium (V) is a simple VO2 synthesis method in which V thin film is oxidized in open air. For an optimum oxidation duration, VO2 films are obtained with good phase transition properties. We recently reported a modified APTO process using a step temperature profile for oxidation (Thin Solid Films 706, 138003 (2020)). We demonstrated an ultra-low thermal budget synthesis of VO2 thin films with good electrical and optical phase transition properties. For a 130 nm room-temperature RF sputtered V thin film, an optimum oxidation duration of ~ 30 s was obtained. In this work, we study how the starting V film thickness and deposition temperature affects the optimum oxidation duration. V thin films of varying thickness (15-212 nm) and 120 nm thick V films with varying deposition temperature (~27-450 C) are prepared using RF magnetron sputtering. These films are oxidized for different oxidation durations and characterized using Raman and four-probe measurements to find the optimum oxidation duration for each deposition condition. We find that the optimum oxidation duration increases with the increase in V film thickness and V deposition temperature. We model the effect of V film thickness and deposition temperature on the optimal oxidation time using a parabolic law which can be used to obtain the optimal oxidation times for intermediate V thicknesses/deposition temperatures.

cond-mat.mtrl-sci↗

arXiv2021

High Infrared Reflectance Modulation in VO2 Films Synthesized on Glass and ITO coated Glass substrates using Atmospheric Oxidation of Vanadium

Vanadium Dioxide (VO2) is a strongly correlated material, which exhibits insulator to metal transition at ~68 C along with large resistivity and infrared optical reflectance modulation. In this work, we use atmospheric pressure thermal oxidation of Vanadium to synthesize VO2 films on glass and ITO coated glass substrates. With the optimized short oxidation durations of 2 min and 4 min, the synthesized VO2 film shows high optical reflectance switching in long-wavelength infrared on glass substrates and mid-wavelength infrared on ITO coated glass substrates, respectively. Peak reflectance switching values of ~76% and ~79% are obtained on the respective substrates, which are among the highest reported values. Using the reflectance data, we extract VO2 complex refractive index in infrared wavelengths, in both the insulating and metallic phases. The extracted refractive index shows good agreement with VO2 synthesized using other methods. This demonstration of high optical reflectance switching in VO2 thin films, grown on low cost glass and ITO coated glass substrates, using a simple low thermal budget process will aid in enhancing VO2 applications in the optical domain.

physics.app-ph↗

arXiv2021

Vanadium Dioxide Thin Films Synthesized Using Low Thermal Budget Atmospheric Oxidation

Vanadium dioxide is a complex oxide material, which shows large resistivity and optical reflectance change while transitioning from the insulator to metal phase at ~68 °C. In this work, we use a modified atmospheric thermal oxidation method to oxidize RF-sputtered Vanadium films. Structural, surface-morphology and phase-transition properties of the oxidized films as a function of oxidation duration are presented. Phase-pure VO2 films are obtained by oxidizing ~130 nm Vanadium films in short oxidation duration of ~30 seconds. Compared to previous reports on VO2 synthesis using atmospheric oxidation of Vanadium films of similar thickness, we obtain a reduction in oxidation duration by more than one order. Synthesized VO2 thin film shows resistance switching of ~3 orders of magnitude. We demonstrate optical reflectance switching in long-wave infrared wavelengths in VO2 films synthesized using atmospheric oxidation of Vanadium. The extracted refractive index of VO2 in the insulating and in the metallic phase is in good agreement with VO2 synthesized using other methods. The considerable reduction in oxidation time of VO2 synthesis while retaining good resistance and optical switching properties will help in integration of VO2 in limited thermal budget processes, enabling further applications of this phase-transition material.

physics.app-ph↗

arXiv2021

Temperature Dependence of $β-Ga_2O_3$ Heteroepitaxy on c-plane Sapphire using Low Pressure Chemical Vapor Deposition

$β-Ga_2O_3$ has drawn significant attention for power electronics and deep ultraviolet (UV) photodetectors owing to its wide bandgap of ~ 4.4 - 4.9 eV and high electric breakdown strength ~7-8 MV/cm. Growth of $β-Ga_2O_3$ epitaxial thin films with high growth rate has been recently reported using low pressure chemical vapor deposition (LPCVD) technique. In this work, we have investigated the effect of growth temperature on $β-Ga_2O_3$ films grown on c-plane sapphire substrates using LPCVD. We performed growths by varying temperatures from 800$^°$C to 950$^°$C while keeping all other growth parameters (Ar/O$_2$ gas flow rates, growth pressure, and Gallium precursor to substrate distance) constant. Optical, structural, and surface characterizations are performed to determine the bandgap, phase purity, crystal orientation, and crystalline quality of the grown thin films. Amorphous islands of $Ga_2O_3$ are observed at growth temperature of 800$^°$C while continuous and crystalline (-201) oriented $β-Ga_2O_3$ thin films are achieved for growth temperatures of 850$^°$C to 950$^°$C. Crystallinity of the films is found to improve with increase in growth temperature with a minimum rocking full width at half maximum of 1.52$^°$ in sample grown at 925$^°$C. For all the samples grown at and above 875$^°$C, transmittance measurements revealed an optical bandgap of ~4.77-4.80 eV with high growth rate of ~6 $μ$m/hr.

cond-mat.mtrl-sci↗