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We investigate the stability of hafnium borides at zero pressure via the evolutionary crystal structure prediction and first-principles calculations. Our results indicate that the well-known P6/mmm-HfB2 is the only thermodynamically stable phase at zero temperature and pressure, and two more phases (Pnma-HfB and F m 3 ¯ m - Hf B 12) become thermodynamically stable at higher temperatures. We compute the mechanical properties including bulk, shear and Young's moduli, Vickers hardness, and fracture toughness for all stable and metastable hafnium borides (∼30 phases) and then study in detail the effect of boron concentration and topology of B-sublattice on their mechanical properties. We show that not only the concentration of boron, but also the topology of the boron sublattice is important for the mechanical properties of hafnium borides. Among the predicted stable and low-energy metastable hafnium borides, the highest possible hardness is exhibited by P6/mmm-HfB2 with graphenelike boron sheets and by phases with 3D boron networks and high B/Hf ratios (e.g., Pnnm-HfB5 and F m 3 ¯ m - Hf B 12). [ABSTRACT FROM AUTHOR]

Control of bipolar conduction is essential to improve the high-temperature thermoelectric performance of materials for power generation applications. Recently, Hf(Te1−xSex)2 alloys have gained much attention due to their potential use in thermoelectric power generation. Increasing the Se alloying content significantly increases the band gap while decreasing its carrier concentration. These two factors affect bipolar conduction substantially. In addition, the weighted mobility ratio is estimated from the experimental electronic transport properties of Hf(Te1−xSex)2 alloys (x = 0.0, 0.025, 0.25, 0.5, 1.0) by using the Two-Band model. From the bipolar thermal conductivity also calculated using the Two-Band model, we find that it peaks near x = 0.5. The initial bipolar conductivity increase of x < 0.5 is mostly due to the decrease in the weighted mobility ratio and carrier concentration with increasing x. For x > 0.5, the drop in the bipolar conductivity can be understood with significant band gap enlargement. [ABSTRACT FROM AUTHOR]

Manifold research has been done to understand the detailed mechanisms behind the performance instabilities of ferroelectric capacitors based on hafnia. The wake-up together with the imprint might be the most controversially discussed phenomena so far. Among crystallographic phase change contributions and oxygen vacancy diffusion, electron trapping as the origin has been discussed recently. In this publication, we provide evidence that the imprint is indeed caused by electron trapping into deep states at oxygen vacancies. This impedes the ferroelectric switching and causes a shift of the hysteresis. Moreover, we show that the wake-up mechanism can be caused by a local imprint of the domains in the pristine state by the very same root cause. The various domain orientations together with an electron trapping can cause a constriction of the hysteresis and an internal bias field in the pristine state. Additionally, we show that this local imprint can even cause almost anti-ferroelectric like behavior in ferroelectric films. [ABSTRACT FROM AUTHOR]

Manifold research has been done to understand the detailed mechanisms behind the performance instabilities of ferroelectric capacitors based on hafnia. The wake-up together with the imprint might be the most controversially discussed phenomena so far. Among crystallographic phase change contributions and oxygen vacancy diffusion, electron trapping as the origin has been discussed recently. In this publication, we provide evidence that the imprint is indeed caused by electron trapping into deep states at oxygen vacancies. This impedes the ferroelectric switching and causes a shift of the hysteresis. Moreover, we show that the wake-up mechanism can be caused by a local imprint of the domains in the pristine state by the very same root cause. The various domain orientations together with an electron trapping can cause a constriction of the hysteresis and an internal bias field in the pristine state. Additionally, we show that this local imprint can even cause almost anti-ferroelectric like behavior in ferroelectric films. [ABSTRACT FROM AUTHOR]

We performed density functional theory (DFT) calculations on binary and ternary oxo/fluoro crystals of the geochemical twin pair zirconium and hafnium to evaluate and compare their stabilities. This is the first DFT study on bulk ZrF4 or HfF4, as well as on a hypothetical ZrOF2 or HfOF2 bulk crystal. For α-MO2, β-MF4 and MOF2, we have found significantly higher cohesive energies for the respective hafnium species. This suggests a considerable gap in affinity toward fluorine and oxygen between the twin pair in the solid state. In agreement with experimental findings, this gap is slightly more pronounced for fluorine. This study is also the first to evaluate the theoretical, endothermic mono-hydroxylation of the respective fluorides or oxyfluorides to model the difference in affinity toward fluoride versus hydroxide. For these, we could also find a slight energetic preference for the hafnium compound. [ABSTRACT FROM AUTHOR]

This article presents the comparison of the dielectric properties of three different refrigerant fluids, HFE-7100, HFC-245fa, and HFO-1336mzz(E) (R-1336E Opteon ME), the latter having a global warming potential of two orders of magnitude lower than the other two. Refrigerant fluids are used, among others, in generator circuit breaker applications where good thermal and chemical properties must be coupled with excellent dielectric strength and low electric conductivity. This article describes in detail the applied measurement techniques and the results obtained, as well as comparisons to previous measurements and literature. The comparison includes dielectric breakdown in liquid and vapor phase, dc conductivity, real permittivity, and dissipation factor. [ABSTRACT FROM AUTHOR]

Abstract The interface trap charges (ITC) associated reliability analysis of a charge‐plasma based asymmetric double‐gate (ADG) dopingless tunnel field effect transistor (DLTFET) with Si/Ge heterojunction and high‐κ gate dielectric (HJADGDLTFET) has been studied. The HJADGDLTFET uses silicon at the drain and the channel region, and germanium at the source region, which enhances the band‐to‐band tunnelling at the source‐channel junction, and hence drive current is increased by one order concerning ADGDLTFET. Also, ADG and high‐κ dielectric (HfO2) have been used to maintain low off‐state current values. The primary intention of this work is to investigate the impact of ITC for HJADGDLTFET and compare it for ADGDLTFET considering DC, analog/RF, and linearity parameters such as transfer characteristics, electric‐field, electric potential, first‐, second‐, and third‐order transconductances (gm1, gm2, and gm3), gate‐to‐drain capacitance (Cgd), cut‐off frequency (fT), gain–bandwidth product, device efficiency, second‐ and third‐order voltage intercept points (VIP2, VIP3), third‐order input intercept points (IIP3), and third‐order intermodulation distortion. The ATLAS simulation results show that the HJADGDLTFET is more immune to ITC variation than conventional ADGDLTFET concerning different polarities of ITC available at the semiconductor‐oxide interface.

Using the method of high-temperature chemical synthesis, material samples with a high-temperature protection system were fabricated. The study of the thermochemical effect of high-enthalpy air flows on a carbon-containing composite material with a high-temperature antioxidant coating based on hafnium compounds at surface temperatures of 1400–1600°C was carried out in a free subsonic jet of high-enthalpy air of a VGU-4 100-kilowatt high-frequency induction plasma torch. The experiments were carried out at a pressure of 100 hPa in a stepwise heating mode and in a constant surface temperature mode of 1400, 1500, and 1600°C. The duration of each test cycle in the constant temperature mode was 1500 s. [ABSTRACT FROM AUTHOR]

For the synthesis of B C b SB B 1 b sb , to a solution of Hf(O I i i Pr)4( I i i PrOH)] (0.42 g, 1.0 mmol) in hexane solution of SP CMe2Ph sp BTP-H (0.90 mg, 2.0 mmol) in hexane (20 ml) was added. For the synthesis of B C b SB B 6 b sb , 30 ml toluene solution containing 0.7486 g (0.85 mmol) of (N-((6E)-6-(butylimino- N)-1-cyclohexen-1-yl)-2,6-bis(1-methylethyl)-benzenaminato- N)triiodohafnium was added to 0.88 ml (2.65 mmol) of 3 M MeMgBr solution in (C SB 2 sb H SB 5 sb ) SB 2 sb O at ambient temperature. For the synthesis of B C b SB B 2 b sb , to a toluene suspension of the imidazolium chloride salt (358.0 mg, 0.695 mmol) precooled to -35 °C, a precooled toluene solution of Hf(Bn) SB 4 sb (210.8 mg, 0.388 mmol) was added through a pipet. Keywords: Hafnium complexes; organometallic; synthesis EN Hafnium complexes organometallic synthesis 89 120 32 03/11/22 20220301 NES 220301 Introduction Organometallic compounds are those which have at least one carbon atom bonded with a metal ion that exists between the organic compound, molecule or ion, and metal or maybe metalloid ([42]). For the synthesis of B C b SB B 2 b sb , to a solution of Hf(O I i i Pr) SB 4 sb ( I i i PrOH)] (0.42 g, 1.0 mmol) in hexane solution (30 C) of SP I t i Bu sp BTP-H (0.65 mg, 2.0 mmol) in hexane (20 ml) was added. [Extracted from the article]

Compared with Pb(Zr,Ti)O3 (PZT) ceramics, piezoelectric ceramic composites (PCCs), and piezoelectric polyvinylidene fluoride (PVDF) polymer, piezoelectric single crystal composites (PSCCs) are thought to be the promising candidates for hydrophone applications because of their superior hydrostatic performance. However, due to the brittleness and small dimensions of single crystals, the preparation of large-area or conformal PSCCs is to be challenged. Herein, we prepared a large-area PSCC with dimensions of 50 mm $\times \,\, 50$ mm $\times \,\, {5}$ mm using 3-D-printing-assisted dice-and-insert technology. The hydrostatic piezoelectric performances for PSCC were investigated using a quasi-static method. The hydrostatic figure-of-merit (HFOM) of PSCC is approximately $1469\times 10^{-{15}}\,\,\text{m}^{{2}}$ /N, which is higher by 69.4% than that of PCC. Furthermore, PSCC shows advantages in the dielectric loss, frequency constant, electromechanical coupling coefficient, and hydrostatic pressure stability. The results suggest that PSCCs have great potential in substantially improving the sensitivity of hydrophones. In addition, 3-D-printing-assisted dice-and-insert technology breaks through the restriction of as-grown piezoelectric crystal size so as to make it possible for the applications where large-scale piezoelectric composites are required. [ABSTRACT FROM AUTHOR]

In this article, the preparation of HfLaOx gate dielectric thin films by the spin coating method is proposed. The in-depth physical properties of the as-prepared HfLaOx films were investigated as functions of annealing temperatures. Decided by the key performance indicators of current density, smooth surface, and areal capacitance of HfLaOx films with different annealing temperatures, optimized performance parameters with annealing temperature 550 °C have been obtained. To verify the feasibility of HfLaOx films as dielectric material, In2O3/HfLaOx thin-film transistors (TFTs) have been fabricated and device characterizations have been carried out. As a result, it has been detected that the In2O3/HfLaOx TFTs with optimized annealing temperature of 300 °C demonstrate superior electrical performance, including a high ${I}_{ \mathrm{\scriptscriptstyle ON}} / {I}_{ \mathrm{\scriptscriptstyle OFF}}$ of ~106, a high $\mu _{\text {FE}}$ of 17.09 cm2V−1s−1, a low ${V}_{\text {TH}}$ of 0.09 V, a small interfacial trap states (${D}_{\text {it}}$) of $1.94\times 10^{{12}}$ cm−2, and a small threshold voltage shift of 0.23 V under PBS test and 0.11 V under NBS test after 3600 s bias stress, respectively. To confirm TFTs’ potential applications in logic circuits, a resistor-loaded inverter was integrated and the maximum voltage gain of 7.60 was demonstrated at an ultra-low operating voltage of 2.5 V. Current observations have indicated the great application prospects of solution-derived HfLaOx-gated TFTs in low-cost and excellent performance electronic devices. [ABSTRACT FROM AUTHOR]

This article proposes an autonomous docking control for nonholonomic constrained mobile robots and applies it to an intelligent mobility device or wheelchair for assisting the user in approaching resting furniture such as a chair or a bed. We defined a virtual landmark inferred from the target docking destination. Then, we solve the problem of keeping the targeted volume inside the field of view (FOV) of a tracking camera and docking to the virtual landmark through a novel definition that enables to control for the desired end pose. In this article, we proposed a nonlinear feedback controller to perform the docking with the depth camera's FOV as a constraint.Then, a numerical method is proposed to find the feasible space of initial states where convergence could be guaranteed. Finally, the entire system was embedded for real-time operation on a standing wheelchair with the virtual landmark estimation by three-dimensional object tracking with an RGB-D camera and we validated the effectiveness in simulation and experimental evaluations. The results show the guaranteed convergence for the feasible space depending on the virtual landmark location. In the implementation, the robot converges to the virtual landmark while respecting the FOV constraints. [ABSTRACT FROM AUTHOR]

HfB2, Si, and activated carbon powders were selected to fabricate 0–30 vol% SiC reinforced HfB2-based composite. Pressureless sintering process was performed at 2050 °C for 4 h under a vacuum atmosphere. Microstructural studies revealed that in situ SiC reinforcement was formed and distributed in the composite according to the following reaction: Si + C = SiC. A maximum relative density of 98% was measured for the 20 vol% SiC containing HfB2 composite. Mechanical investigations showed that the hardness and the fracture toughness of these composites were increased and reached up to 21.2 GPa for HfB2-30 vol% SiC and 4.9 MPa.m1/2 for HfB2-20 vol% SiC, respectively. Results showed that alpha-SiC reinforcements were created jagged, irregular, and elongated in shape which were in situ formed between HfB2 grains and filled the porosities. Formation of alpha-SiC contributed to improving the relative density and mechanical properties of the composite samples. By increasing SiC content, an enhanced trend of thermal conductivity was observed as well as a reduced trend for electrical conductivity. [ABSTRACT FROM AUTHOR]

In this work, we used the first-principles calculations based on density functional theory and quasi-harmonic Debye to predict the electronic structures, phonon dispersions and thermodynamic properties of HfTM (TM = Fe, Ru, Os) compounds. The obtained phonon dispersions of HfTM indicate that they are thermodynamically stable. Moreover, HfFe, HfRu and HfOs show metallic properties from the electronic structures. The bulk moduli and thermal expansion coefficients of HfTM compounds under temperature of 0 ~ 1500 K and pressure of 0 ~ 20 GPa were considered, and the results indicate that the bulk modulus reduces as the temperature increases, and thermal expansion coefficient changes quickly to temperature at low temperatures. The order of thermal expansion coefficient is HfFe > HfRu > HfOs and that of thermal stability is HfOs > HfRu > HfFe. Besides, Debye temperature is opposite to the trend of Grüneisen parameter under the same temperature and pressure. [ABSTRACT FROM AUTHOR]

We propose a novel method to measure and analyze depth resolution in near range. Depth resolution is the smallest depth difference that can be detected by a depth camera, which is an important parameter but is hard to be measured accurately. Intuitively, a stair-shaped target is preferred to measure depth resolution but has many limitations. To overcome the difficulties, we use a flat target and move a depth camera at specified steps to form a stair-shaped depth map. Then, the depth map is compressed to one-dimensional profile by an average cross-section method. The 68-95-99.7 rule is applied for identifying the depth resolution. In order to obtain accurate data, a computer-controlled positioning platform is used to move or rotate a depth camera and a target in high precision. Three types of targets are made and tested, including a stair-shaped metal plate, a flat acrylic board, and a tensioned electric screen. A procedure is provided for aligning the optical plane of depth camera to the target before measuring. The Intel RealSense D400 series depth cameras are adopted for verification. Their theoretical depth resolution is derived and compared to the measured depth resolution. The effect of image resolution (x, y) on the depth resolution (z) is also analyzed. The experimental results offer useful information for researchers to design a depth camera and verify its depth resolution. [ABSTRACT FROM AUTHOR]

Direct visualization of the dynamics of structural glasses and amorphous solids on the sub-nanometer scale provides rich information unavailable from bulk or conventional single molecule techniques. We study the surface of hafnium diboride, a conductive ultrahigh temperature ceramic material that can be grown in amorphous films. Our scanning tunneling movies have a second-to-hour dynamic range and single-point current measurements extend that to the millisecond-to-minute time scale. On the a-HfB2 glass surface, two-state hopping of 1-2 nm diameter cooperatively rearranging regions or "clusters" occurs from sub-milliseconds to hours. We characterize individual clusters in detail through high-resolution (<0.5 nm) imaging, scanning tunneling spectroscopy and voltage modulation, ruling out individual atoms, diffusing adsorbates, or pinned charges as the origin of the observed two-state hopping. Smaller clusters are more likely to hop, larger ones are more likely to be immobile. HfB2 has a very high bulk glass transition temperature Tg, and we observe no three-state hopping or sequential two-state hopping previously seen on lower Tg glass surfaces. The electronic density of states of clusters does not change when they hop up or down, allowing us to calibrate an accurate relative z-axis scale. By directly measuring and histogramming single cluster vertical displacements, we can reconstruct the local free energy landscape of individual clusters, complete with activation barrier height, a reaction coordinate in nanometers, and the shape of the free energy landscape basins between which hopping occurs. The experimental images are consistent with the compact shape of ɑ-relaxors predicted by random first order transition theory, whereas the rapid hopping rate, even taking less confined motion at the surface into account, is consistent with β-relaxations. We make a proposal of how "mixed" features can show up in surface dynamics of glasses. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on positive-bias temperature stress (PBTS) induced degradation of nitrided hafnium silicate (HfSiON)/SiO2 gate stack in n+-poly crystalline silicon (polySi) gate p-type metal-oxide-semiconductor (pMOS) devices. The measurement results indicate that gate dielectric degradation is a composite effect of electron trapping in as-fabricated as well as newly generated neutral traps, resulting a significant amount of stress-induced leakage current and generation of surface states at the Si/SiO2 interface. Although, a significant amount of interface states are created during PBTS, the threshold voltage (VT) instability of the HfSiON based pMOS devices is primarily caused by electron trapping and detrapping. It is also shown that PBTS creates both acceptor- and donor-like interface traps via different depassivation mechanisms of the Si3 ≡ SiH bonds at the Si/SiO2 interface in pMOS devices. However, the number of donor-like interface traps ΔNitD is significantly greater than that of acceptor-like interface traps ΔNitA, resulting the PBTS induced net interface traps as donor-like. [ABSTRACT FROM AUTHOR]

HfW2O8 undergoes a dramatic softening where the average bulk modulus (P = 52-414 MPa) drops from 69GPa at 298K to 48GPa at 430K as the temperature of the WO4 orientation order-disorder transition is approached. This is accompanied by increasingly negative thermal expansivity11 (-10 ppm * K-1 to - 15 ppm* K-1 ) and reversible WO4 orientational disordering upon compression in α-HfW2O8. Additionally, α-HfW2O8 becomes elastically softer upon compression at constant temperature. The α → β phase transition temperature decreases by ~30K between 52 and 414 MPa. Above this phase transition, no further temperature-dependent softening or pressure-dependent changes in the coefficient of thermal expansion occurred. [ABSTRACT FROM AUTHOR]

Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at .%. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution. [ABSTRACT FROM AUTHOR]

Si-doped HfO2 was prepared by solid state synthesis of the starting oxides. Using Rietveld refinement of high resolution X-ray diffraction patterns, a substitutional limit of Si in HfO2 was determined as less than 9 at .%. A second phase was identified as Cristobalite (SiO2) rather than HfSiO4, the latter of which would be expected from existing SiO2-HfO2 phase diagrams. Crystallographic refinement with increased Si-dopant concentration in monoclinic HfO2 shows that c/b increases, while β decreases. The spontaneous strain, which characterizes the ferroelastic distortion of the unit cell, was calculated and shown to decrease with increasing Si substitution. [ABSTRACT FROM AUTHOR]

The observation of ferroelectric, ferromagnetic, and ferroelastic phases in thin films of binary oxides attracts the broad interest of scientists and engineers. However, the theoretical consideration of the physical nature of the observed behavior was performed mainly for HfO2 thin films from the first principles, and in the framework of Landau–Ginzburg–Devonshire (LGD) phenomenological approach with special attention to the role of oxygen vacancies in both cases. Allowing for the generality of the LGD theory, we applied it to the group of binary oxides in this work. The calculations have been performed based on the assumption that oxygen vacancies, as elastic dipoles, can be partially transformed into electric dipoles due to the defect site-induced and/or surface-induced inversion symmetry breaking (via, e.g., piezoelectric effect), and can “migrate” throughout the depth of an ultrathin film. Since many films of binary oxide are ferroelectric and ferromagnetic due to the oxygen vacancies, they can be multiferroics. Performed calculations have shown that thin films of binary oxides can be considered as new multiferroics with physical properties useful for broad spectra of applications in nanoelectronics and nanotechnology. The properties can be controlled by the choice of oxygen vacancy concentration, film thickness, and special technological treatment, such as annealing. [ABSTRACT FROM AUTHOR]

InAlAs has the potential to be used as a barrier layer in buried channel quantum well field effect transistor devices due to favorable lattice-matching and carrier confinement properties with InGaAs. Field effect device structures of this nature may also require a high-k oxide deposited on the InAlAs surface to reduce leakage current. This study investigates the impact of surface preparations and atomic layer deposition of HfO2 on these surfaces using x-ray photoelectron spectroscopy to analyse the chemical interactions taking place, as well as the electrical performance of associated capacitor devices. A large concentration of As related surface features is observed at the InAlAs surface, and is attributed to a large Dit response in electrical measurements. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate highly scaled, non-volatile memory transistors with ferroelectric Zr-doped HfO2(HZO) as gate insulator. ${\Omega }$ -gate transistors with gate length ~30 nm and width ~85 nm were fabricated on ~20 nm thick SOI. We demonstrate robust memory operation with ≤100 ns program and erase speed at ±5 V, projected memory retention time up to 10 years at 85 °C, and ~0.5 V memory window after 108 endurance cycles. The impact of ${V} _{\text {D}}$ on erase speed provides insights into the importance of holes on memory operation. [ABSTRACT FROM AUTHOR]

This study proposed a novel nonvolatile static random access memory (nvSRAM) cell with two ferroelectric capacitors (FeCAPs) embedded inside a 4T SRAM cell, i.e., 4T2C, for minimal area penalty and full logic compatibility. The FeCAP with 10-nm-thick Hf0.5Zr0.5O2 film shows excellent ferroelectricity (Pr $= 15\,\,\mu \text{C}$ /cm2) and good memory characteristics (cycles $> 10^{11}$). The 4T2C nvSRAM is capable of storing and restoring previous memory states for nonvolatile data storage. To compensate the leakage current in the dynamic nodes of 4T load less SRAM, we propose a dynamic current compensation operation scheme by exploiting the polarization-dependent leakage current of FeCAP. Outstanding characteristics were achieved in this nvSRAM cell: 1) elimination of the dc path; 2) ultralow store and restore power consumption; and 3) high area efficiency. [ABSTRACT FROM AUTHOR]

The dc characteristics of AlGaN/gallium nitride (GaN) metal–oxide–semiconductor-high electron mobility transistor (MOS-HEMT) with an AlInN back-barrier layer has been studied here. An analytical model is proposed for evaluating the charge density (σtot), carrier concentration (nS), drain current (ID), and transconductance (gm) of the device by incorporating Hafnium oxide (HfO2) as a high-k dielectric layer. The charges created between the oxide and the AlGaN barrier layer influence the enhancement of carrier concentration of up to 6.2 × 1013 cm−2, at the two-dimensional electron gas (2DEG). The AlInN back-barrier increases the conduction band (CB) level of the GaN buffer and eliminates the confinement problems near the channel. By deriving the mathematical dependence of these parameters, this device demonstrated a positive threshold shift and a high current drive of 880 mA/mm. Cubic spline interpolation (CSI) technique is employed here to model the parameters in a more precise manner. The outcomes are evidence that the device could be a potential solution for high power switching as well as microwave applications. [ABSTRACT FROM AUTHOR]

The effects of NH3-plasma treating HfO2 gate dielectric on electrical characteristics of top-gate (TG) MoS2 FETs are investigated. The experimental results show that the increase of off-state current after growing HfO2 top-gate dielectric can be considerably decreased by NH3-plasma treating HfO2, because the N incorporation from the NH3-plasma treatment can effectively eliminate the oxygen vacancies and reduce the positive oxide charges in HfO2. The fabricated TG MoS2 FETs with the NH3-plasma treated HfO2 as gate dielectric achieve excellent electrical performances: high on–off ratio of $2.1 \times 107$ , high carrier mobility of 78~87 cm2/Vs and near-ideal subthreshold swing of 72mV/dec. Therefore, the NH3-plasma treated HfO2 as gate dielectric is highly beneficial for fabricating highperformance TG MoS2 FETs. [ABSTRACT FROM AUTHOR]

An optimization principle for ferroelectric FET (FeFET), centered around charge matching between the ferroelectric and its underlying semiconductor, is theoretically investigated. This letter shows that, by properly reducing the ferroelectric polarization charge and its background dielectric constant, charge matching can be improved to enable simultaneously: i) reduction of the interlayer and semiconductor electric fields during programming, reading, and retention, leading to prolonged endurance and retention; ii) improvement of the memory window; and iii) suppression of device-to-device variations by affording full polarization switching. These attributes provide an incentive for the presentation of the proposed guidelines for FeFET optimization as detailed in this letter. [ABSTRACT FROM AUTHOR]

In this work, we discuss the mitigation of threshold voltage (${V}_{{TH}}$) variability in nanoscale FinFET by exploiting the interaction of oxygen vacancies (OV) against metal gate granularity (MGG). Deposition of a metal gate on high- $\kappa $ dielectric HfO2 is known to generate OV in the dielectric which induces variability in surface potential. A higher workfunction of metal grain increases the probability of OV formation. Interestingly, while a higher workfunction metal grain decreases the surface potential of the channel underneath, the positive charge of OV increases the potential. Therefore, the concentration of OV can be controlled to negate the surface potential variability induced by MGG. We discuss the law of mass action-based concentration models of OV under MGG to analyze this. We also present TCAD simulations supporting the above hypothesis. In our simulations, for 10-nm channel FinFET, MGG-induced $\sigma $ (${V}_{{TH}}$) can be reduced to ~20 mV from ~35 mV for four-sided planar grains with 8 nm average edge length under the optimal OV concentration. [ABSTRACT FROM AUTHOR]

This study determines the relationship between retention and endurance reliability for a HfOx-based resistive random access memory (ReRAM). A TiN (15 nm) / HfOx (6 nm) / Ti (10 nm) / TiN (40 nm) stacked structure is fabricated and tested to verify its basic characteristics and reliability. The high resistance states (HRS) retention behavior is characterized and is found to degrade over 100x on the endured bits because there is a sequential high temperature procedure. The degradation is reduced slightly to a ~30x drop for the endured devices with one single refresh cycle. During the endurance and retention test procedures, the HRS resistance decreases because neutral oxygen vacancy filaments grow and this cannot be reversed. The I-V characteristics for endured devices are also determined. The results show that isothermal treatment causes a gradual SET and RESET process with multiple feasible states. The thermally induced filament degradation model (isolated filament vs. continuous filament) is verified by the relationship between retention and endurance reliability. Design guidance is recommended for an improvement in ReRAM reliability. [ABSTRACT FROM AUTHOR]

The hot carrier (HC) induced degradation has become a major concern in advanced CMOS technologies because of non-scalable $\text{V}_{\mathrm{ DD}}$. In this work, we have shown that the HC induced degradation in gate-first HKMG nMOS transistors can be modulated by optimizing the device width, lanthanum capping layer thickness, and pre-gate carbon (C) implant. The physics responsible for these observations are investigated and attributed to the reduction in the number of defects (traps) in hafnium oxide (HfO2) and reduction in carrier injection into these defects. It is also shown that the HC performance of these transistors could be further improved by increasing the active-to-active spacing. [ABSTRACT FROM AUTHOR]

Bionic electronic synapses with weight-modulation properties are promising alternative candidates when compared with traditional CMOS based neuromorphic hardware when building at-scale neural networks for efficient neuromorphic computing. In this Letter, due to the partial polarisation switching of multi-domain properties in polycrystalline Zr-doped HfO2 (HZO) ferroelectric materials, a capacitor-based bionic synapse was proposed, which showed multi-level capacitance modulation characteristics. By switching the voltage-controlled polarisation, the capacitance was gradually modulated via the variation of net polarisation vectors in the HZO layer. The potentiation and depression properties can be achieved with better linearity, symmetry and multiple states. This Letter laid the groundwork for realising the high-density integration neuromorphic computing system by using ferroelectric capacitors as the bionic synapse. [ABSTRACT FROM AUTHOR]

We demonstrate a novel ferroelectric-gate field effect transistor with recessed channel (R-FeFET) to improve memory window (MW), program/erase speed, long-time retention, and endurance simultaneously. Based on technology computer-aided design (TCAD) simulations including calibrated ferroelectric material (FE) parameters, it is revealed that the polarization is enhanced by the larger electric field (e-field) across the FE compared to a conventional planar FeFET, resulting in the wider MW and the faster program/erase speed. Moreover, the endurance/retention of the R-FeFET is expected to be improved as the e-field across the SiO2 interlayer is significantly reduced. [ABSTRACT FROM AUTHOR]

A novel design of a tunable optical switch based on epsilon-near-zero (ENZ) metasurface is proposed, which can work as an electro-optical or an all-optical switch, and be tuned by gate-voltages, incident angles, and intensity of pump light. The result shows that the coupling of the ENZ mode and plasmon resonance lead to an obvious Rabi splitting which can be observed in the transmission spectrum. Numerical analysis also demonstrates that the coupling belongs to the ultra-strong coupling regime. The proposed design can achieve electro-optical switching with a large modulation depth of up to ∼ 17 dB, all-optical switching with an extinction ratio exceeding 5 dB and an ultrafast response time of 650 fs. [ABSTRACT FROM AUTHOR]

We report the experimental realization of ferroelectricity in Al-doped HfO2 (HAO) with the lowest reported thermal budget of 500 °C. A HAO film annealed at 500 °C for 30 s exhibits ferroelectricity with a remnant polarization (${P}_{{\text {r}}}$) of $2.95~\mu \text{C}$ /cm2. The ${P}_{{\text {r}}}$ increases to $10.40~\mu \text{C}$ /cm2 when annealing duration is increased to 5 min, and approaches the values annealed at much higher temperatures of 700 to 1000 °C in other previous works. The presence of ferroelectricity has been confirmed by a series of typical phenomena, including the polarization-switched Positive-Up-Negative-Down measurement, the hysteretic polarization-voltage loop, and the butterfly-shaped C-V curves. In addition, comparable endurance characteristics are also obtained with other HfO2-based ferroelectric films. [ABSTRACT FROM AUTHOR]

In this letter, we report a stretchable HfO2-based resistive switching memory device utilizing the wavy structured strategy. The fabricated Cu/HfO2/Au device shows reliable and reversible resistive switching behaviors up to a stretching strain of 20%. After being released, the reproducible memory characteristics of the device can still be maintained. The statistical resistive switching parameters under various stretching strains in the range from 0% to 20% are counted, which exhibit a large OFF/ON resistance ratio (103), low operation voltage (2 V), good endurance and retention (104s), demonstrating the good and reliable stretchable memory characteristics. Moreover, the device-to-device distributions are carried out in these stretched states, further validating the device robustness on stretching strains. Our results show a promising approach to achieve the stretchable memory by rendering inorganic-based resistive switching devices with the wavy structure, which extends rigid and brittle memory towards future highly flexible, even stretchable data storage and computing. [ABSTRACT FROM AUTHOR]

In this letter, we experimentally demonstrated a novel resistive device with a hybrid switching mode that can be alternated between volatile threshold switching and non-volatile resistive switching. The device consists of dual-functional layers VO2 /HfO2 sandwiched by symmetrical TiN electrodes. A >20 unified ratio for selectivity and memory window is obtained. Owing to the stable resistive behavior of HfO2 and insulator-metal transition of VO2, the device shows excellent uniform switching parameters in both switching modes with a high on-state current density (1E4 A/cm2) and fast switching/recovery speed (< 30 ns). This self-selective resistive memory is of great potential in the high-density crossbar array, particularly for the future 3D-Vertical resistive random access memory (RRAM) integration. [ABSTRACT FROM AUTHOR]

We report high performance amorphous Indium-Gallium-Zinc-Oxide (a-IGZO) thin-film transis- tors (TFTs) with 10 nm atomic-layer-deposited HfO2 as the gate dielectric, achieving subthreshold swing (SS) of 70.2 mV/decade, high effective mobility (μeff) of 55.3cm2/V⋅s at an inversion carrier density (Ninv) of 5 × 1012 cm−2, and large ION/IOFF of > 109. Furthermore, very good device-to-device uniformity has been confirmed by the statistical distribution of SS and maximum transconductance (Gm, max) measured from 20 pristine TFT devices. This a-IGZO TFT has immense potential for the ultrafast and low power electronic devices for next-generation cost-effective emissive display, image sensing, and hardware for artificial intelligence (AI). [ABSTRACT FROM AUTHOR]

Feature extraction plays a vital role in visual action recognition. Many existing gradient-based feature extractors, including histogram of oriented gradients, histogram of optical flow, motion boundary histograms, and histogram of motion gradients, build histograms for representing different actions over the spatio-temporal domain in a video. However, these methods require to set the number of bins for information aggregation in advance. Varying numbers of bins usually lead to inherent uncertainty within the process of pixel voting with regard to the bins in the histogram. This article proposes a novel method to handle such uncertainty by fuzzifying these feature extractors. The proposed approach has two advantages: it better represents the ambiguous boundaries between the bins and, thus, the fuzziness of the spatio-temporal visual information entailed in videos; and the contribution of each pixel is flexibly controlled by a fuzziness parameter for various scenarios. The proposed family of fuzzy descriptors and a combination of them are evaluated on two publicly available datasets, demonstrating that the proposed approach outperforms the original counterparts and other state-of-the-art methods. [ABSTRACT FROM AUTHOR]

Gate controllable electronic trap detection method has been demonstrated by regulating the gate potential of MIS devices. This method is based on shift of capacitance–voltage (CV) curve as well as flatband voltage (VFB) measure in < 10 μs due to injection or ejection of electrons through the metal gate. Using this method, an electronic trap energy distribution was measured in the HfO2 dielectric film and it confirms a maximum number of traps (Δ NT) of 1.7 × 1012 cm-2 corresponding to an energy level (Δ EIL) of 0.45 eV above silicon conduction band (Si-ECB). In comparison, ZrO2-based MIS devices showed a broader distribution of electronic traps throughout the band gap. However, HfO2 contained more than 60% traps in deep level compared to 50% in ZrO2, which establishes the effects of material variation. [ABSTRACT FROM AUTHOR]

In this paper, we propose a novel mechanism for the Vth shift of amorphous-indium gallium zinc oxide (a-IGZO) thin film transistors under negative bias illumination stress (NBIS). Three kinds of IGZO TFTs with different gate dielectrics and valence band offsets (VBO) were used in this experiment. Gate dielectric materials used were Al2O3, HfO2 and SiO2. Initial parameters, VBO, and state density (DOS) for each TFT were extracted. After NBIS, the Vth shift was greatest at −3.82 V using a TFT with an HfO2 gate dielectric. VBO was the lowest at 0.38 eV using a TFT with an HfO2 gate dielectric. The smaller the VBO, the larger the generated Vth shift. DOS measurements confirmed the interfacial properties between the gate dielectric and IGZO, and the highest DOS resulted from the interface between Al2O3 and IGZO. Through the experimental results, the correlation between VBO and Δ Vth after NBIS was investigated. We found that the main cause of Vth shift in NBIS is injection of photoinduced hole carriers that cross the VBO by tunneling from IGZO channel to gate oxide. [ABSTRACT FROM AUTHOR]

In this letter, we demonstrate the key role of the Hf/Si interfacial layer (IL) in Al/Cu/IL/MoS2/TiN conductive bridge RAM. Owing to controlling Cu migration through Hf rather than Si, the Hf interface device offers consecutive >4000 DC cycles and long program/erase (P/E) endurance of > 2 × 109 cycles under the low current operation of 100 μA at the fast switching speed of 100 ns. The Hf interface device shows gradual RESET, long-term potentiation/depression (LTP/LTD) pulses of 40/100 with small pulse width of 100 ns and a low power consumption of < 13 pJ is needed for artificial synapse applications. [ABSTRACT FROM AUTHOR]

In this article, structure optimization of high-k interfacial layer (IL), deposited between the gate and the gate sidewall spacer, was performed in a 5-nm node nanosheet field-effect transistor (NSFET). High-k IL can be formed during the high-k gate dielectric and metal gate (HKMG) with gate-last process. By optimizing the structure of thickness of high-k IL (Thk) with gate length (LG), spacer length (Lext), and source/drain (S/D) length (LS/D), improved electrical performances were obtained. By optimizing Thk with properly adjusted LG, Lext, and LS/D, highly saturated ON-/OFF-current ratio (ION/IOFF) was obtained with appropriate drain-induced barrier lowering (DIBL). Besides, reduced intrinsic gate delay (Cgg) properties and OFF-state leakage current were identified. In addition, the reason of increased OFF-state leakage, which can be shown when Lext shrinks with extending Thk, was also investigated. Finally, the optimized electrical characteristics were obtained when Thk is adjusted with LG and LS/D. The power was reduced about 27% with the same performance and 18% enhanced performance was obtained when Thk is optimized through LG. On the contrary, reduced OFF-state leakage current and DIBL were confirmed in the case of optimization point with LS/D, which result in lower static power. Based on this comparison, optimization method and guideline for high-k IL was proposed. [ABSTRACT FROM AUTHOR]

HFO1234zeE is an environmental-friendly gas with the potential to replace sulfur hexafluoride (SF6). Therefore, research on the breakdown and decomposition characteristics of the HFO1234zeE gas mixture was conducted. The breakdown experiments of the 20% HFO1234zeE/80% N2 gas mixture under different electric fields were performed, and the feasibility of replacing SF6 with HFO1234zeE was verified in terms of insulation strength. Based on the density functional theory, the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) wave function distributions of the HFO1234zeE molecule were obtained. According to the frontier orbital theory, the possible position of reaction in the molecule may occur at the carbon–carbon double bond and carbon–hydrogen bond. Moreover, reaction force field-molecular dynamics (ReaxFF-MD) was used to simulate the decomposition of the 20% HFO1234zeE/80% N2 gas mixture, the effect of the temperature and pressure on the decomposition reaction was studied, and the main decomposition paths were analyzed. The research results show that the main decomposition products are C2F2, CN, CNF, H, N, F, and HN2. With the increase in temperature and pressure, the number of molecules decomposed increases. The conclusions provide the theoretical basis for the application of HFO1234zeE. [ABSTRACT FROM AUTHOR]

Bottom-gate indium aluminum zinc oxide thin-film transistors (TFTs) are fabricated with a HfO2 dielectric layer using plasma enhanced atomic layer deposition (PEALD). The electrical properties and photoresponse are both affected by the method of post annealing. A device that is annealed at a temperature of less than 200°C has a better Ion/Ioff of $1.71\times 10^{{8}}$ and a lower subthreshold swing (S.S.) of only 0.21 V/dec. This demonstrates that proper annealing treatment increases the performance of the device. The photoresponse is also calculated. A TFT that is not annealed has a poor photoresponse and a lower rejection ratio. Annealing at a temperature of less than 200 °C gives a good photoresponse of 0.2 A/W and a high rejection ratio of $2.86\times 10^{{5}}$. An IAZO TFT with a HfO2 dielectric layer that is deposited using PEALD is applicable in UV sensing technology. [ABSTRACT FROM AUTHOR]

RF and millimeter-wave designers continue to use wire bonds and flip chip in their designs when bonding chips or multichip systems. Due to electrical and mechanical constraints of wire bonding and flip chip, designers are forced to compensate for mismatched impedances, high loss, or mechanically unreliable interconnects. In this article, we propose microcoaxial cables (MCCs) as an alternative interconnect, specifically, 30–75- $\Omega $ MCCs for signals, and low-inductance MCCs for bias and supply. In addition, each shielded interconnect provides sufficient isolation to prevent electromagnetic interference (EMI) and crosstalk. The in situ fabrication method presented here utilizes only conventional wire bonding and microfabrication techniques, providing a high-feasibility path toward a new interconnect paradigm based on MCCs. Each cable measured consists of a 25.4- $\mu \text{m}$ gold bond wire coated first with a dielectric and then with a 5.0- $\mu \text{m}$ -thick gold shield. MCCs appropriate for signals have a 38- $\mu \text{m}$ -thick Parylene C dielectric and a characteristic impedance of 39– $68~\Omega $. For the first time, to the best of our knowledge, we introduce low-inductance MCCs, where the dielectrics evaluated are 1.0- $\mu \text{m}$ -thick Parylene C dielectric and 100-nm-thick HfO2. Their inductances are measured to be no more than 140 pH/mm. For 3.5-mm-long wire with a 0.51-mm pitch, the crosstalk is −62 dB at 1 GHz for signal MCCs. Crosstalk increases to −30 dB at 26.5 GHz. [ABSTRACT FROM AUTHOR]

Hafnium dioxide is a wide band-gap, high-κ material, and Hafnium based compounds have already been integrated into micro-electronic devices. The pure cubic HfO2 phase is promising as it presents a higher permittivity (κ > 25), but needs to be stabilized by addition of divalent or trivalent dopants, which in turn modify the electronic properties of HfO2. Here, we employ a one-pot synthesis approach to produce undoped cubic and monoclinic HfO2 nanoparticles by choice of solvent alone. The average size of these nanoparticles from transmission electron microscopy studies was estimated to be around 2.6 nm. We present a study of the morphology and microstructure and also demonstrate the presence of a strong visible photoluminescence linked to the nanosize of the particles. Furthermore, the synthesis in equivalent conditions of these two phases of HfO2 provides means for direct comparison of the chemical composition and electronic structures of the two polymorphs. This has therefore allowed us to experimentally elucidate similarities and differences in the valence band, band gap states, and conduction band of these pure phases seconded by first principles calculations within the density functional theory. [ABSTRACT FROM AUTHOR]

The solution behavior of dopants, Si, La, and N, in HfO2 polymorphs, monoclinic, tetragonal, and cubic was investigated by using a first principles calculation based on density functional theory within the local density approximation. It was found that the Si and La solutions are more preferable under oxidization atmosphere than reduction atmosphere, and the most efficient nitridation condition for the HfO2 is NO/NO2 atmosphere. By comparing the energy difference between the monoclinic and the tetragonal phases, it was found that the energy difference is decreased by the Si or La doping, whereas influence of the N doping is small, indicating that the phase transition from the monoclinic to tetragonal phase would be enhanced by the Si or La doping. [ABSTRACT FROM AUTHOR]

Vanadium oxide (VO2) is a narrow band gap material (Eg = 0.7 eV) with a thermally induced insulator-metal phase transition at ∼343 K and evidence of an electric field induced transition at T < 343 K. To explore the electronic properties of VO2, a sandwich structure was prepared with a 2 nm VO2 layer embedded between an oxidized Si(100) surface and a 2 nm hafnium oxide (HfO2) layer. The layer structure was confirmed with high resolution transmission electron microscopy. The electronic properties were characterized with x-ray and ultraviolet photoemission spectroscopy, and the band alignment was deduced on both n-type and p-type Si substrates. The valence band offset between VO2 and SiO2 is measured to be 4.0 eV. The valence band offset between HfO2 and VO2 is measured to be ∼3.4 eV. The band relation developed from these results demonstrates the potential for charge storage and switching for the embedded VO2 layer. [ABSTRACT FROM AUTHOR]