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The ferroelectric field-effect transistor (FEFET) is an emerging nonvolatile memory technology that can offer ultra-scalability, fast operation, and reduced power consumption. However, a limited understanding of FEFET physics poses challenges for optimum device design. In this article, we provide physical insights into the operation of FinFET-based FEFETs (FEFinFETs) using a phase-field framework built on time-dependent Landau–Ginzburg (TDGL) thermodynamic theory. We exploit the source–drain fringing field to stabilize a monodomain configuration in the OFF state of short channel FEFinFETs. Based on recent experiments, we first analyze the switching dynamics of FEFinFETs with low remnant polarization (${P}_{r}$) and high coercive field (${E}_{c}$) hafnium zirconium oxide (HZO) FE. We find that the switching in these FEFinFETs occurs via domain nucleation and growth from the gate metal edges at the source–drain spacers. We also show that a non-zero drain bias can be used for dynamically modulating the memory window (MW) of FEFinFET to lower its power consumption. Furthermore, we find the spacer permittivity to be a crucial design parameter to control the MW and show that a lower spacer permittivity can significantly increase the MW. Finally, we show that the commonly held idea that a large ${P}_{r}$ leads to a large MW is not always valid. For a large ${P}_{r}$ , the formation of multiple domains in the FE layer can lead to a significant reduction in the MW. In addition, these devices can suffer from low write endurance due to exposure of the interfacial oxide layer to high electric fields. [ABSTRACT FROM AUTHOR]

We propose a rectifier concept, simultaneously utilizing the Hall effect and the spin–orbit-torque, that is well matched to the low impedance of antennas. This rectifier is promising for general radio detection and, particularly, for harvesting ambient weak radio signals, where conventional rectification fails to operate. The Hall effect and spin–orbit-torque are both proportional to current density, which improves inversely with the device cross-sectional area, providing a large signal at the nanoscale. A single device made using existing materials can provide 200 μV DC from 500 nW of radio frequency (RF) power. A series array of such devices can efficiently enhance the DC voltage to 300 mV while matching the receiver antenna impedance. Such magnetic devices can convert weak RF power into DC power with substantial efficiency at low voltage and low impedance where conventional semiconductor rectifiers fail. [ABSTRACT FROM AUTHOR]

We compare the results of self-consistent ballistic quantum transport simulation of Zener tunneling in InAs, a direct bandgap semiconductor, with corresponding semi-classical solutions using the well-known Kane's model and the Wentzel-Kramers-Brillouin (WKB) approximation. We find a qualitative difference between solutions obtained from Kane's formulation and rigorous quantum-mechanical formalism. However, the WKB solution, with evaluation of action integral along the tunneling paths determined from the nearest neighbor sp3s* Hamiltonian, is shown to provide qualitative agreement. We discuss the issues involved in fitting semi-classical solutions with their quantum counterpart and also present a brief comparison of our results with experimental data. [ABSTRACT FROM AUTHOR]

We propose a generic formalism to estimate the anisotropies, exchange energies, and the surface antiferromagnet (AFM) moment of AFM-ferromagnet (FM) heterostructure systems that show spin glass like behavior. This scheme provides quantitative agreement with multiple experiments on epitaxial bismuth ferrite (BFO)-FM system that have been reported recently. We find that a single value of the interface coupling energy can reproduce both the exchange bias and the coercivity enhancement observed in experiments. We also find a surprisingly high surface AFM moment density that agrees well with measured values. This high moment on the BFO surface is indicative of a significant modulation of magnetic properties at the BFO-FM interface. [ABSTRACT FROM AUTHOR]

The article discusses the potential of the spin-transfertorque magnetic random access memory (STT-MRAM) devices using different physical mechanisms. Details about the STT-MRAM are provided which store information in the magnetization of a nanoscale magnet. Also tackled are the difference in which the design specifications for memory.

One important use of layered semiconductors such as molybdenum disulfide (MoS2) could be in making novel heterojunction devices leading to functionalities unachievable using conventional semiconductors. Here we demonstrate a metal-semiconductor-metal heterojunction photodetector, made of MoS2 and amorphous silicon (a-Si), with rise and fall times of about 0.3 ms. The transient response does not show persistent (residual) photoconductivity, unlike conventional a-Si devices where it may last 3-5 ms, thus making this heterojunction roughly 10X faster. A photoresponsivity of 210 mA/W is measured at green light, the wavelength used in commercial imaging systems, which is 2-4X larger than that of a-Si and best reported MoS2 devices. The device could find applications in large area electronics, such as biomedical imaging, where a fast response is critical. [ABSTRACT FROM AUTHOR]

We show that the established physics of spin valves together with the recently discovered giant spin-Hall effect could be used to construct Read and Write units that can be integrated into a single spin switch with input-output isolation, gain and fan-out similar to complementary metal oxide semiconductor inverters, but with the information stored in nanomagnets making it non-volatile. Such spin switches could be interconnected, with no external amplification, just with passive circuit elements, to perform logic operations. Moreover, since the digitization and storage occur naturally in the magnets, the voltages can be used to implement analog 'weighting' for non-Boolean logic. [ABSTRACT FROM AUTHOR]

This paper estimates the temperature distribution within a spin-torque-transfer RAM (STTRAM) cell due to self-heating using a thermal simulation based on the finite volume method. The analysis shows that, due to high switching current and small volume of the magnetic tunnel junction (MTJ), there can be significant rise in temperature in the MTJ as well as the silicon transistor. The impacts of the increased temperature on operational reliability metrics of the STTRAM cell, i.e., read disturb, write failure, and sensing accuracy, are evaluated. It is shown that, due to the self-heating effect, the operational reliability of an STTRAM cell depends on the read–write history of that cell. [ABSTRACT FROM AUTHOR]

• Negative capacitance (NC) may enable gate-all-around FET scaling beyond 0.5 nm node. • 3-D Ginzburg-Landau-Khalatnikov model is adopted in the TCAD simulation. • The parameters of ferroelectric are extracted from an experimental C-V result. • The NC benefits are retained over a varying set of ferroelectric parameters. We present a TCAD simulation of the negative capacitance gate-all-around (NCGAA) field-effect transistor with the 3-D Ginzburg-Landau-Khalatnikov Model. The baseline device is based on the 2020 IRDS Table, and the mobility model is calibrated to account for ballistic transport and to match the "1.5 nm node" IRDS on-current requirement. The NC parameters are extracted from experimental C-V data. The NC-GAA shows reduction in the off current by one order of magnitude and a 40% on-current boost. If the gate work function is shifted to align the NC-GAA's off-current with the IRDS high performance requirement, it is shown that NC-GAA can achieve the on-current and V DD requirement of every node through the "0.7 eq node," which is the last node predicted in the 2020 IRDS Table. Furthermore, NC-GAA can even achieve a "0.5 eq node," which is three additional nodes beyond the baseline "1.5 nm node." We also show that these benefits are retained over a varying set of ferroelectric parameters. [ABSTRACT FROM AUTHOR]

Currently, nanowire-based circuits are being considered as candidates for future high-speed electronics. Signal propagation in metallic carbon nanotubes has been analyzed using the Luttinger liquid theory to develop a transmission-line model showing features that can not be obtained from a conventional transmission-line theory. The Luttinger liquid theory, however, Is governed by strict conditions which restrict its application to metallic carbon nanotubes and it can not be used for any nanowire in general. In this paper, we present a unified theory that can be applied to wires ranging all the way from conventional three-dimensional conductors to one-dimensional carbon nanotubes. We show that when the number of current-carrying modes is less than a critical value, and the small-signal propagation characteristics are significantly influenced by transport effects which go beyond the conventional transmission-line theory. We also use our model to quantitatively examine a few potential applications. [ABSTRACT FROM AUTHOR]

This paper presents an improved thresholding technique for speech enhancement in the discrete cosine transform (DCT) domain. The signal-bias-compensated noise level is used as the threshold parameter. The probability of speech presence in the noisy DCT coefficients at the finest level is exploited for compensating the signal-bias. The performance of the proposed algorithm is evaluated on speech corrupted by background Gaussian white noise and real noise recorded inside a moving car. A relative comparison in the enhancement of the degraded speech is performed using the uncompensated and compensated noise levels for the same denoising filter. Both objective and subjective evaluations are presented to show improved performance for the case when the compensated noise level, estimated by the proposed algorithm, is used rather than the uncompensated noise level obtained using the median absolute deviation method. Simulation results are also given to show the superiority of the proposed method over a recently reported enhancement algorithm. [Copyright &y& Elsevier]

In this brief, we present a compact model of nanoscale ferroelectric (FE) capacitors. We first use the phase-field simulation to study the polarization switching of very small FE capacitor that contains only a few grains. We show that at higher applied voltage, the entire grain undergoes a single-domain-like switching, but at lower applied voltage, the domain wall growth mechanism dominates due to the difference between the domain wall energies of bulk and defect nuclei. To create a compact model that includes this voltage dependence, we use a time-dependent domain switching model for each discrete grain with empirical modifications capturing the two different switching mechanisms. In addition, a voltage-dependent dielectric model is included to represent the nonlinear capacitance of the FE capacitor. We verify this compact model by fitting the results of phase-field modeling results with excellent agreement. [ABSTRACT FROM AUTHOR]

Ultra‐wide bandgap semiconductor AlGaN is a promising candidate for high‐power and high‐frequency electronics. AlGaN‐heterostructures with nitrogen (N)‐polarity can offer added benefits of low‐leakage and large drive current. However, electro‐thermal transport in such heterostructures remains unexplored, although they are essential for electronic device functionality. Here, the thermal and electrical properties of N‐polar AlxGa1‐xN‐channel heterostructures (Al percentage, x = 15–90%) are explored and compared with their GaN counterpart. The thermal measurements uncover that the effective thermal resistance of the thin channel and barrier layers are similar in magnitudes for N‐polar‐ AlGaN and GaN heterostructures, however, the total effective thermal conductivity in N‐polar AlGaN heterostructure is ≈4× smaller. This reduction originates from the larger thermal resistance of the thick Al0.15Ga0.85N buffer layer within the AlGaN stack. N‐polar AlxGa1‐xN stack displays a thermal conductivity almost independent of temperature, measured from room temperature up to 200 °C. Hall measurements of an N‐polar Al0.30Ga0.70N‐channel heterostructure further reveal that electrical properties such as resistivity, carrier density, and mobility remain nearly unchanged with temperature, indicating the dominance of alloy‐phonon scattering in such material systems. These results offer important insights into material‐device co‐design and reliability of N‐polar AlGaN heterostructures. [ABSTRACT FROM AUTHOR]

In this work, we report a massively parallel and time domain implementation of the 3D phase field model that can reach beyond micron scale and consider for arbitrary electrical and mechanical boundary conditions. The first part of the paper describes the theory and the numerical implementation of the model. A mixed-mode approach of finite difference and finite element grid has been used for calculating the nonlocal electrostatic and elastic interactions respectively. All the local and non-local interactions are shown to scale linearly up to thousands of processors. This massive paralleling allows to compare our results directly with experiments at the same length scales where the experiments themselves are performed. The second part of the paper presents results of ferroelectric domain switching in devices based on the multi-ferroic BiFeO3. We have particularly emphasized the importance of charge driven domain growth and the effect of electrical boundary conditions that explain the temporal evolution of ferroelectric domains observed in recent experiments. We also predict a mechanism of controlling domain size in the multi-domain ferroelectric switching that could be useful for practical applications. [ABSTRACT FROM AUTHOR]

Recently it has been experimentally shown that a graphene nanoribbon (GNR) can be obtained by unzipping a carbon nanotube (CNT). This makes it possible to fabricate all-carbon heterostructures that have a unique interface between a CNT and a GNR. Here we demonstrate that such a heterojunction may be utilized to obtain a unique transistor operation. By performing a self-consistent nonequilibrium Green’s function based calculation on an atomistically defined structure, we show that such a transistor may reduce energy dissipation below the classical limit while not compromising speed—thus providing an alternate route toward ultralow-power, high-performance carbon-heterostructure electronics. [ABSTRACT FROM AUTHOR]

By performing an atomistic transport calculation, we examine the temperature dependence of the tunneling current in a graphene nanoribbon band-to-band tunneling transistor. The subthreshold swing is shown to be a nonlinear function of temperature, and in stark contrast to a conventional FET, the swing versus temperature shows a negative slope below a certain drain current. The nonlinear threshold voltage shift with temperature is also examined. A method to capture the distinguishing nonlinearity in the voltage shift with temperature and drain current is proposed. [ABSTRACT FROM AUTHOR]

Surface acoustic waves (SAW) on piezoelectric substrates can excite spin wave resonance (SWR) in magnetostrictive films through magnetoelastic coupling. This acoustically driven SWR enables the excitation of a single spin wave mode with an in-plane wave vector k matched to the magnetoelastic wave vector. A 2D frequency domain finite element model is presented that fully couples elastodynamics, micromagnetics, and piezoelectricity with interface spin pumping effects taken into account. It is used to simulate SAW driven SWR on a ferromagnetic and piezoelectric heterostructure device with an interdigital transducer configuration. These results, for the first time, present the spatial distribution of magnetization components that, together with elastic wave, exponentially decays along the propagation direction due to magnetic damping. The results also show that the system transmission rate S21(dB) can be tuned by both an external bias field and the SAW wavevector. Acoustic spin pumping at magnetic film/normal metal interface leads to damping enhancement in magnetic films that decreases the energy absorption rate from elastic energy. This weakened interaction between the magnetic energy and elastic energy leads to a lower evanescence rate of the SAW that results in a longer distance propagation. With strong magnetoelastic coupling, the SAW driven spin wave is able to propagate up to 1200 μm. The results give a quantitative indication of the acoustic spin pumping contribution to linewidth broadening. [ABSTRACT FROM AUTHOR]

This letter first shows that dynamic switching schemes can be used to reduce energy dissipation below the thermodynamic minimum of NkT ln r (N=number of information carriers and 1/r=error probability), but only at the expense of the error immunity inherent in thermodynamic processes for which the final state is insensitive to the switching dynamics. It is further shown that, for a system which has internal feedback, e.g., nanomagnets, such that all N spins act in concert, it should be possible to switch with an energy dissipation of the order of kT ln r (considerably less than the thermodynamic limit of NkT ln r), while retaining an error immunity comparable to thermodynamic switching. [ABSTRACT FROM AUTHOR]

This letter presents a self-consistent solution of quantum transport, using the nonequilibrium Green’s function method, and magnetization dynamics, using the Landau-Lifshitz-Gilbert formulation. This model is applied to study “spin-torque” induced magnetic switching in a device where the transport is ballistic and the free magnetic layer is sandwiched between two antiparallel (AP) ferromagnetic contacts. A hysteretic current-voltage characteristic is predicted at room temperature, with a sharp transition between the bistable states that can be used as a nonvolatile memory. It is further shown that this AP pentalayer device may allow significant reduction in the switching current, thus facilitating integration of nanomagnets with electronic devices. [ABSTRACT FROM AUTHOR]

In this article, we present a compact model of metal–ferroelectric (FE)–insulator–semiconductor (MFIS) tunnel junction. Unlike the metal–FE–metal (MFM) structure with only one insulator layer, MFIS–FE tunnel junction (FTJ) contains two insulator layers and a semiconductor electrode. The complex structure makes it difficult to self-consistently solve the Poisson and charge equations. We report the first compact model of MFIS-FTJ to our knowledge. Previous modeling studies focused on numerical simulation, which is time-consuming and not applicable to circuit simulation. The presented compact model is suitable for commercial SPICE IC simulation. It includes a FE model that can capture polarization switching under arbitrary applied voltage, an insulator–semiconductor model that calculates the potential profile of the MFIS stack, and an analytical tunneling current model. We demonstrate that this model can be used to simulate and fit both n-type and p-type MFIS-FTJs. [ABSTRACT FROM AUTHOR]

We show that a coupling exists between nitrogen vacancy (NV) centers in diamond in proximity to magnetoelastic spin waves generated by a voltage driven surface acoustic wave. Experimental measurements show the presence of coupling driven by both dipolar fields induced by a spin wave-like excitation and off-resonant coupling of the NV energy levels driven by acoustically driven ferromagnetic resonance dynamics. A model is proposed based on chiral coupling of the NV centers to the stray field that originates from a propagating magnetoelastic wave in a thin magnet, and model predictions are validated by experimental observations. Understanding of the coupling enables a direct measurement of the stray field polarization, which in turn provides a detailed picture of the resonantly coupled magnon–phonon interaction. [ABSTRACT FROM AUTHOR]

We present a compact model of polycrystalline ferroelectric (FE) capacitors. The polycrystalline thin-film material is modeled as a collection of independent grains or grain groups. Each grain or grain group is characterized by its local field-dependent switching rate, which is characterized by a distribution function such as Gaussian or type-2 generalized beta distribution. This computationally efficient model accurately reproduces the published experimental polarization switching waveforms and the switching current waveforms in response to all reported applied voltage waveforms. The model tracks the polarization history so that it can simulate the transition between major and minor and among minor loops as well as accumulative polarization which cannot be captured by the conventional models. This model is intended for simulating circuits containing FE capacitors using commercial SPICE simulators for arbitrary applied voltage waveforms. It also has the capability of simulating the discrete switching and device variability in small-area FE capacitors having a small number of grains, although there is no available experimental data to check the model accuracy in this regard. [ABSTRACT FROM AUTHOR]

The article presents a study that describe a computing scheme, which combine the physics of charge motion in a magnetic field with conventional electronic devices to give an important step towards a spintronic computing technology. Improvement is required before the scheme can be viable for practical applications.

Continuum phase-field simulations show how a multidomain ferroelectric capacitor in series with a resistor can exhibit a transient response in which the ferroelectric behaves as a negative capacitor. We show that accelerating domain growth leads to negative capacitance (NC), and this happens even when there is no initial switching of the domains. The observed behavior is in close agreement with experimental results of NC transients seen recently in a number of ferroelectric material systems. [ABSTRACT FROM AUTHOR]

We have studied quantum transport in graphene nanoribbon tunnel field-effect transistors. Unlike other studies on similar structures, we have included dissipative processes induced by inelastic electron-phonon scattering and edge roughness in the nanoribbon self-consistently within a non-equilibrium transport simulation. Our results show that the dissipative scattering imposes a limit to the minimum OFF current and a minimum subthreshold swing that can be obtained even for long channel lengths where direct source-drain tunneling is inhibited. The edge roughness, in the presence of dissipative scattering, somewhat surprisingly, shows a classical behavior where it mostly reduces the maximum ON current achievable in this structure. [ABSTRACT FROM AUTHOR]

Transient negative capacitance effects in epitaxial ferroelectric Pb(Zr0.2Ti0.8)O3 capacitors are investigated with a focus on the dynamical switching behavior governed by domain nucleation and growth. Voltage pulses are applied to a series connection of the ferroelectric capacitor and a resistor to directly measure the ferroelectric negative capacitance during switching. A time-dependent Ginzburg-Landau approach is used to investigate the underlying domain dynamics. The transient negative capacitance is shown to originate from reverse domain nucleation and unrestricted domain growth. However, with the onset of domain coalescence, the capacitance becomes positive again. The persistence of the negative capacitance state is therefore limited by the speed of domain wall motion. By changing the applied electric field, capacitor area or external resistance, this domain wall velocity can be varied predictably over several orders of magnitude. Additionally, detailed insights into the intrinsic material properties of the ferroelectric are obtainable through these measurements. A new method for reliable extraction of the average negative capacitance of the ferroelectric is presented. Furthermore, a simple analytical model is developed, which accurately describes the negative capacitance transient time as a function of the material properties and the experimental boundary conditions. [ABSTRACT FROM AUTHOR]

The critical size limit of voltage-switchable electric dipoles has extensive implications for energy-efficient electronics, underlying the importance of ferroelectric order stabilized at reduced dimensionality. We report on the thickness-dependent antiferroelectric-to-ferroelectric phase transition in zirconium dioxide (ZrO2) thin films on silicon. The emergent ferroelectricity and hysteretic polarization switching in ultrathin ZrO2, conventionally a paraelectric material, notably persists down to a film thickness of 5 angstroms, the fluorite-structure unit-cell size. This approach to exploit three-dimensional centrosymmetric materials deposited down to the two-dimensional thickness limit, particularly within this model fluorite-structure system that possesses unconventional ferroelectric size effects, offers substantial promise for electronics, demonstrated by proof-of-principle atomic-scale nonvolatile ferroelectric memory on silicon. Additionally, it is also indicative of hidden electronic phenomena that are achievable across a wide class of simple binary materials. [ABSTRACT FROM AUTHOR]

The discovery of ultrafast helicity‐independent all‐optical switching (HI‐AOS), as well as picosecond all‐electrical switching of a ferrimagnet, has inspired the ultrafast spintronics community to explore ultrafast switching of a ferromagnet to achieve practical ultrafast storage and memory devices. Two explored mechanisms of HI‐AOS of a ferromagnet in ferromagnet‐ferrimagnet heterostructure are: a) exploiting the indirect exchange coupling with and b) injection of non‐local spin current originated from a switching ferrimagnet. In this manuscript, exchange mediated HI‐AOS of a Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange coupled "[Co/Pt]‐multilayers/Pt spacer/CoGd" heterostructure is demonstrated. The authors have measured layer‐resolved static magnetic properties, single‐shot HI‐AOS, and magnetization dynamics of the ferromagnetic Co/Pt multilayers (MLs), that are ferromagnetically or antiferromagnetically coupled with ferrimagnetic CoGd layers. Time‐resolved magnetization dynamics reveal a 3.5 ps switching time of the Co/Pt MLs, which is the fastest switching of a ferromagnet reported to date. Employing an extended microscopic three‐temperature model, the temporal dynamics of the exchange coupled ferromagnet–ferrimagnet heterostructure are simulated, qualitatively and quantitatively explaining the experimental switching phenomena. This work experimentally as well as theoretically establishes the mechanism of exchange mediated all‐optical switching of ferromagnet‐ferrimagnet heterostructures, which can be integrated with a magnetic tunnel junction for efficient reading after ultrafast energy‐efficient switching. [ABSTRACT FROM AUTHOR]

The discovery of ultrafast helicity‐independent all‐optical switching (HI‐AOS), as well as picosecond all‐electrical switching of a ferrimagnet, has inspired the ultrafast spintronics community to explore ultrafast switching of a ferromagnet to achieve practical ultrafast storage and memory devices. Two explored mechanisms of HI‐AOS of a ferromagnet in ferromagnet‐ferrimagnet heterostructure are: a) exploiting the indirect exchange coupling with and b) injection of non‐local spin current originated from a switching ferrimagnet. In this manuscript, exchange mediated HI‐AOS of a Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange coupled "[Co/Pt]‐multilayers/Pt spacer/CoGd" heterostructure is demonstrated. The authors have measured layer‐resolved static magnetic properties, single‐shot HI‐AOS, and magnetization dynamics of the ferromagnetic Co/Pt multilayers (MLs), that are ferromagnetically or antiferromagnetically coupled with ferrimagnetic CoGd layers. Time‐resolved magnetization dynamics reveal a 3.5 ps switching time of the Co/Pt MLs, which is the fastest switching of a ferromagnet reported to date. Employing an extended microscopic three‐temperature model, the temporal dynamics of the exchange coupled ferromagnet–ferrimagnet heterostructure are simulated, qualitatively and quantitatively explaining the experimental switching phenomena. This work experimentally as well as theoretically establishes the mechanism of exchange mediated all‐optical switching of ferromagnet‐ferrimagnet heterostructures, which can be integrated with a magnetic tunnel junction for efficient reading after ultrafast energy‐efficient switching. [ABSTRACT FROM AUTHOR]

Spin-based computing schemes could enable new functionalities beyond those of charge-based approaches. Examples include nanomagnetic logic, where information can be processed using dipole coupled nanomagnets, as demonstrated by multi-bit computing gates. One fundamental benefit of using magnets is the possibility of a significant reduction in the energy per bit compared with conventional transistors. However, so far, practical implementations of nanomagnetic logic have been limited by the necessity to apply a magnetic field for clocking. Although the energy associated with magnetic switching itself could be very small, the energy necessary to generate the magnetic field renders the overall logic scheme uncompetitive when compared with complementary metal-oxide-semiconductor (CMOS) counterparts. Here, we demonstrate a nanomagnetic logic scheme at room temperature where the necessity for using a magnetic field clock can be completely removed by using spin-orbit torques. We construct a chain of three perpendicularly polarized CoFeB nanomagnets on top of a tantalum wire and show that an unpolarized current flowing through the wire can 'clock' the perpendicular magnetization to a metastable state. An input magnet can then drive the nanomagnetic chain deterministically to one of two dipole-coupled states, '2 up 1 down' or '2 down 1 up', depending on its own polarization. Thus, information can flow along the chain, dictated by the input magnet and clocked solely by a charge current in tantalum, without any magnetic field. A three to four order of magnitude reduction in energy dissipation is expected for our scheme when compared with state-of-the-art nanomagnetic logic. [ABSTRACT FROM AUTHOR]

We present a phenomenological compact model of the inversion charge centroid considering both the structural and electrical confinements in multigate FETs. The developed new model shows a good match with Technology-CAD (TCAD) data for both physical parameters such as fin thickness in FinFET and wire radius in cylindrical FET, channel doping, and electrical bias variation. With the introduction of fitting parameters, the model is capable of handling hole and electron carriers, various channel materials, and process variations, such as fin shape, etc. [ABSTRACT FROM PUBLISHER]

The possible use of spin rather than charge as a state variable in devices for processing and storing information has been widely discussed, because it could allow low-power operation and might also have applications in quantum computing. However, spin-based experiments and proposals for logic applications typically use spin only as an internal variable, the terminal quantities for each individual logic gate still being charge-based. This requires repeated spin-to-charge conversion, using extra hardware that offsets any possible advantage. Here we propose a spintronic device that uses spin at every stage of its operation. Input and output information are represented by the magnetization of nanomagnets that communicate through spin-coherent channels. Based on simulations with an experimentally benchmarked model, we argue that the device is both feasible and shows the five essential characteristics for logic applications: concatenability, nonlinearity, feedback elimination, gain and a complete set of Boolean operations. [ABSTRACT FROM AUTHOR]

We study the effects of the variation of ferroelectric material properties (thickness, polarization, and coercivity) on the performance of negative capacitance FETs (NCFETs). Based on this, we propose the concept of conservative design of NCFETs, where any unintentional yet reasonable and simultaneous variation ( $\sim \pm 3$ %) in ferroelectric parameters does not result in the emergence of hysteresis and causes only a reasonable variation in the ON-current (≤5%) and, within these constraints, the enhancement of ON-current due to the addition of the ferroelectric gate oxide, which is is maximized. [ABSTRACT FROM AUTHOR]

The resonant interaction between surface acoustic waves and ferromagnetic thin films, a phenomenon known as acoustically driven ferromagnetic resonance (ADFMR), provides a way to control magnetic resonance with purely voltage excitation. However, devices have historically been operated at harmonic frequencies, leading to large insertion losses. In this work, we demonstrate a harmonic-free drive of ADFMR devices where the strain reaches very high values, comparable to the saturation magnetostriction of the magnetic element. The acoustic energy transfer is highly efficient and reaches almost 99.9%. Furthermore, we report the presence of multiple absorption maxima across the range of applied magnetic fields, a property not previously observed in the literature. [ABSTRACT FROM AUTHOR]

We present compact models that capture published cryogenic temperature effects on silicon carrier mobility and velocity saturation, as well as fully depleted silicon on insulator (FDSOI) and fin field effect transistor (FinFET) devices characteristics within the industry-standard Berkeley short-channel IGFET model (BSIM) framework for cryogenic IC applications such as quantum computing. For the core model charge density/surface potential calculation, we introduce an effective temperature formulation to capture the effects of the band tail states. We also present a compact model that corrects the low-temperature threshold voltage for the band-tail states, Fermi–Dirac statistics, and interface traps. New temperature-dependent mobility and velocity saturation models are accurate down to cryogenic temperature. In addition, we propose that experimentally observed ${I}_{D}$ dependence of subthreshold swing (SS) at cryogenic temperatures is a consequence of the expectedly higher rate of Coulomb scattering of free carriers. [ABSTRACT FROM AUTHOR]

In this article, we analyze how a ferroelectric (FE) acts as a rechargeable energy storage medium which stores, releases, and retrieves energy, and helps the gate achieve a desired charge density with reduced energy (voltage) from the external gate drive. During transistor turn-on, the FE releases energy, while the whole system is absorbing energy, and during turn-off, the FE retrieves energy, while the whole system is releasing energy. Capacitor energy is analyzed using two different approaches: static material free energy integrals and transient circuit power integrals. The two results agree within 1%. Energy analysis is also performed for a metal–oxide–semiconductor field-effect transistor structure for two gate lengths, 20 nm and 2 μm, in an inverter circuit. At 2-μm gate length, the values of energy match under these two different approaches with less than a 6% difference. The difference is larger in the 20-nm gate length case due to larger parasitic capacitances, such as gate-to-drain and gate-to-source capacitance, affecting the transient circuit analysis. Even so, most of the energy storage and retrieval benefit is retained even in small size negative capacitance transistors. [ABSTRACT FROM AUTHOR]

Measurements on ultrathin body negative-capacitance (NC) field-effect transistors are shown to display subthreshold behaviors that cannot be explained as a classical MOSFET. Subthreshold swing (SS) at low drain bias decreases with increased gate bias for devices measured over multiple gate lengths down to 30 nm. In addition, improvement in the SS relative to control devices shows a nonmonotonic dependence on the gate length. Using a Landau–Khalatnikov ferroelectric (FE) model calibrated with measured Capacitance-Voltage and combining it with TCAD simulations, we show that these anomalous behaviors can be quantitatively explained and interpreted as field-induced permittivity enhancement. The model predicts substantial scaling improvement at the end of the roadmap. [ABSTRACT FROM AUTHOR]

Nanosheet gate-all-around transistors are analyzed for RF applications using calibrated TCAD simulations. The effects of stack spacing and number of stacks on device performance are studied and a substack design for improved RF performance is proposed. The novel substack design can improve cut-off frequency (Ft) by ~10% and minimum number of substacks and minimum substack spacing should be used. [ABSTRACT FROM AUTHOR]

In this article, we will analyze and provide new insights into the polarization gradient effect of a ferroelectric using TCAD simulation and demonstrate how to model the polarization gradient effect using the negative capacitance FET (NCFET) compact model based on the BSIM framework. A larger value of g (the coefficient of polarization gradient effect) results in improved subthreshold slope, smaller OFF-current, smaller drain-induced barrier lowering (DIBL), and smaller output conductance. Inclusion of the polarization gradient effect in the NCFET compact model improves usability because it accurately captures the effects of negative DIBL and negative output conductance. [ABSTRACT FROM AUTHOR]

The article offers information on Electric-field control of spin dynamics during magnetic phase transitions. It mentions an approach to manipulate the damping by using the large damping enhancement induced by the two-magnon scattering and a nonlocal spin relaxation process in which spin currents are resonantly transported from antiferromagnetic domains to ferromagnetic matrix in a mixed-phased metallic alloy FeRh.

We report self-consistent NEGF transport simulation results in graphene nanoribbon transistors with phonon scattering in real space. Unlike mode space approach, this technique can account for interband scattering in addition to intraband scattering. We show a seamless transition from ballistic to dissipative transport by varying channel length over a wide range. We find acoustic phonon (AP) scattering to be the dominant scattering mechanism within the relevant range of voltage bias. Optical phonon scattering is significant only when a large gate voltage is applied. In a longer channel device, the contribution of AP scattering to the dc becomes more significant. [ABSTRACT FROM AUTHOR]

We perform atomistic simulations and energy-delay analysis on tunnel FETs (TFETs) based on partially unzipped carbon nanotubes (CNTs) and compare their performance against conventional homojunction CNT-TFETs. The device simulations show that the carbon heterojunctions could provide much larger on current compared to homojunction CNT-TFETs due to the effective small bandgap for the injected carriers, without paying a large penalty for off current and subthreshold swing. Subsequent energy-delay analysis shows that these heterojunctions could enable high performance operation and could prove favorable compared to a conventional Ge-source heterojunction TFET. Homojunction TFETs are found to be useful for low-frequency and low-power applications. [ABSTRACT FROM AUTHOR]

Using self-consistent quantum transport simulation on realistic devices, we show that InAs band-to-band Tunneling Field Effect Transistors (TFET) with a heavily doped pocket in the gate-source overlap region can offer larger ON current and steeper subthreshold swing as compared to conventional tunneling transistors. This is due to an additional tunneling contribution to current stemming from band overlap along the body thickness. However, a critical thickness is necessary to obtain this advantage derived from “vertical” tunneling. In addition, in ultra small InAs TFET devices, the subthreshold swing could be severely affected by direct source-to-drain tunneling through the body. [ABSTRACT FROM AUTHOR]

Complex oxide-based ferroelectric tunnel junctions (FTJs) show excellent nonvolatile memory characteristics promising for emerging technology. However, integration of these epitaxially grown FTJs electrically with a silicon substrate remains challenging due to their incompatible lattice structures and poor electronic interfaces resulting from the direct synthesis techniques. Here, we present an epitaxial SrRuO3/PbZr0.2Ti0.8O3/SrRuO3 FTJ integrated electrically with a doped silicon substrate after a layer transfer process. The tunnel currents of the FTJ on silicon show a large tunneling electroresistance (∼1 × 105%) effect, which is explained by a numerical FTJ model incorporating pinned dipoles at the interfaces. This proof of concept of the integration of functional oxide heterostructures with silicon opens a pathway to beyond-CMOS computing devices using unconventional materials. [ABSTRACT FROM AUTHOR]

Target Skyrmions (TSks) are extended topological spin textures with a constant chirality where the rotation of the z component of the magnetization is larger than π. TSks have topological charge 1 or 0, if the z component of the magnetization Mz goes through a rotation of nπ where n is an odd or even integer, respectively. TSks with a rotation of the z component of up to 4π have been imaged via high spatial resolution element-specific x-ray imaging. The TSks were generated by weakly coupling 30 nm thin Permalloy (Ni80Fe20, PY) disks with a 1 μm diameter to asymmetric (Ir 1 nm/Co 1.5 nm/Pt 1 nm) × 7 multilayers that exhibit Dzyaloshinskii-Moriya interaction. The PY disks stabilize the TSks in the multilayers due to reduced stray field energy and enforced circular symmetry from pinning of domain walls at the edges of the disks. Upon applying external magnetic fields, it is the skyrmion core at the center that ensures stability of the TSk, whereas the collapse of the extended structures in the TSk does not depend on the topological charge. [ABSTRACT FROM AUTHOR]

Ultrafast magnetization switching at picosecond and sub-picosecond time scales has tremendous technological potential but still poses numerous questions regarding the underlying quantum mechanical phenomena, including the roles of and interactions between the electrons, spins, and phonons (lattice). At the nanometer-scale dimensions relevant for modern applications, these phenomena become increasingly more pronounced. Until now, helicity-independent all-optical switching (HI-AOS) has been largely limited to amorphous Gd-Fe-Co alloys, for which scaling was challenging due to their relatively low anisotropies. In this work, we demonstrate HI-AOS in amorphous GdCo and scale it to nanometer dimensions while still maintaining uniform out-of-plane magnetization. Single shot HI-AOS is demonstrated in these patterned samples down to a minimum optically detectable magnetic dot size of 200 nm. The ultrafast switching behavior was also confirmed using time-resolved magneto-optic Kerr effect measurements and found to settle to its opposite magnetization state at faster rates for smaller dot diameters, passing a threshold of 75% magnetization reversal within approximately 2 ps for a 200 nm dot compared to approximately 40 ps for a 15 μm pattern. The size dependence of the ultrafast switching is explained in terms of the electron-phonon and spin-lattice interactions. [ABSTRACT FROM AUTHOR]

We investigate the impact of inner fringing fields on the negative capacitance FinFET (NC-FinFET) and how this scales with the technology node. The 8-/7-nm technology node of the p-type body NC-FinFET is modeled using the Sentaurus technology-aided design (TCAD), which couples Poisson with Landau equations. It is found that the NC effect is beneficial for device scaling. The OFF current is well suppressed in short-channel devices (64.4% reduction at LG = 16 nm) because the inner fringing field induces negative gate charges and decreases the channel potential. For longer channel devices, the influence of inner fringing field disappears, and the depletion charges dominate the subthreshold characteristics. As reducing remnant polarization, the ON current is boosted (11.4% improvement at LG = 16 nm) for all lengths due to better matching between MOSFET and ferroelectric capacitances. In comparison with FinFET, the drain-induced barrier lowering of NC-FinFET is also well controlled (50% reduction at LG = 16 nm) due to the inner fringing field-induced gate charges, showing the scaling capability of NC-FinFET. Furthermore, a compact model to capture the spatial distribution of the inner fringing field is also proposed based on the Gaussian quadrature method, and it is validated with the TCAD simulated data with multiple gate lengths and remnant polarizations. [ABSTRACT FROM AUTHOR]

In the quest for novel, scalable and energy-efficient computing technologies, spin-based logic devices are being extensively explored due to their potential for nonvolatility, small cell area, and low operational power. Spin torque majority gate (STMG) is one of the most promising options for beyond CMOS nonvolatile logic circuits for normally-off computing. However, significant problems arose with cascade-ability, signal nonreciprocity, and complicated circuit configurations based on STMG. In this paper, a novel magnetic majority gate (MMG) logic has been proposed, utilizing both spin transfer torque and spin–orbit torque effects. A logic family including and/nand and or/nor functions can be achieved with an easy configuration and under a stable operation. Communication between logic units is realized by spin current injection through a nonferromagnetic metal wire to ensure its cascade-ability and nonreciprocity to design multiple logic-depth circuits. With all of these advantages, the proposed cascadable MMGs can be utilized to design logic functions such as the BUFFER/ NOT, XOR/ XNOR, and complicated logic gates, which pave the pathway for designing robust and comprehensive logic circuits using full spintronic devices. [ABSTRACT FROM AUTHOR]

We propose a new scheme to consider the dielectric (DE) phases inside polycrystalline ferroelectric (FE) materials. The scheme is used to extract material parameters from experimental polarization-electric field (P-E) measurements from the literature. A Sentaurus TCAD structure is constructed with the extracted parameters, and the simulated P-E curve is in a good agreement with the experimental data. Furthermore, variation of the device performance in a negative capacitance field-effect transistor (NCFET) due to the spatial distribution of DE and FE phases is studied using Sentaurus TCAD. It is found that the resultant variations of on and off currents can be up to 14.44% and 30.23%, respectively, thus showing the impact of inhomogeneous crystalline phases of the FE material on device performance. [ABSTRACT FROM AUTHOR]

The article focuses on different physical phenomena to enable a highly efficient excitation nitrogen-vacancy (NV) centers such as magnetoelastic drive of ferromagnetic resonance and NV-magnon coupling. It mentions combination of acoustics and magnonics that enables highly energy-efficient and local excitation of NV centers without need for any external radio frequency (RF) excitation. It also mentions superconducting quantum interference devices and spin-exchange relaxation-free magnetometers.