Showing papers on "Hafnium published in 2020"

Phase-Exchange-Driven Wake-Up and Fatigue in Ferroelectric Hafnium Zirconium Oxide Films.

Abstract: Ferroelectric hafnium zirconium oxide holds great promise for a broad spectrum of complementary metal-oxide-semiconductor (CMOS) compatible and scaled microelectronic applications, including memory, low-voltage transistors, and infrared sensors, among others. An outstanding challenge hindering the implementation of this material is polarization instability during field cycling. In this study, the nanoscale phenomena contributing to both polarization fatigue and wake-up are reported. Using synchrotron X-ray diffraction, the conversion of non-polar tetragonal and polar orthorhombic phases to a non-polar monoclinic phase while field cycling devices comprising noble metal contacts is observed. This phase exchange accompanies a diminishing ferroelectric remanent polarization and provides device-scale crystallographic evidence of phase exchange leading to ferroelectric fatigue in these structures. A reduction in the full width at half-maximum of the superimposed tetragonal (101) and orthorhombic (111) diffraction reflections is observed to accompany wake-up in structures comprising tantalum nitride and tungsten electrodes. Combined with polarization and relative permittivity measurements, the observed peak narrowing and a shift in position to lower angles is attributed, in part, to a phase exchange of the non-polar tetragonal to the polar orthorhombic phase during wake-up. These results provide insight into the role of electrodes in the performance of hafnium oxide-based ferroelectrics and mechanisms driving wake-up and fatigue, and demonstrate a non-destructive means to characterize the phase changes accompanying polarization instabilities.

An indirect way to achieve comprehensive performance improvement of resistive memory: when hafnium meets ITO in an electrode

Abstract: Emerging resistive random access memory has attracted extensive research enthusiasm. In this study, an indirect way to improve resistive random access memory (RRAM) comprehensive performance through electrode material re-design without intensive switching layer engineering is presented by adopting a hafnium-indium-tin-oxide composite. Working parameters of the device can be effectively improved: not only are low operation power consumption and high working stability achieved, but the memory window is significantly enlarged, accompanied by an automatic self-current-compliance function. The correlation between hafnium incorporation and performance improvements and the corresponding current conduction mechanisms have been thoroughly investigated to clarify the resistive switching behavior and to explain the oxygen absorption buffer effect. The hafnium atom, with large atomic radius, is surrounded by soft electron clouds and has high chemical activity to attract oxygen ions. It facilitates the accumulation of more oxygen ions around the interface of the top electrode and the resistive switching layer, leading to lower current and Schottky conduction. This study presents an important strategy for designing and developing electrode materials to improve the characteristics of RRAM and offers an indirect method to modify device working behaviors, also unveiling a promising prospect for its potential future application in low-power information storage and calculation technology.

Multispecies Diffusion of Yttrium, Rare Earth Elements and Hafnium in Garnet

Abstract: We report experimental data for Y, La, Lu and Hf diffusion in garnet, in which diffusant concentrations and silica activity have been systematically varied. Experiments were conducted at 950 and 1050 °C, at 1 atm pressure and oxygen fugacity corresponding to the quartz–fayalite–magnetite buffer. At Y and REE concentrations below several hundred ppm we observe both slow and fast diffusion mechanisms, which operate simultaneously and correspond to relatively high and low concentrations, respectively. Diffusivity of Y and REE is independent of silica activity over the studied range. General formulae for REE diffusion in garnet, incorporating data from this and previous studies, are logDREE(f)(m2 s−1)=−10·24(±0·21)−221057(±4284)2·303RT(K) for the ‘fast’ REE diffusion mechanism at 1 atm pressure, and logDREE(s)(m2 s−1)=−9·28(±0·65)−265200(±38540)+10800(±2600)×P(GPa)2·303RT(K) for the ‘slow’ REE diffusion mechanism. These slow and fast diffusion mechanisms are in agreement with previous, apparently conflicting, datasets for REE diffusion in garnet. Comparison with high-pressure experiments suggests that at high pressures (>∼1 GPa minimum) the fast diffusion mechanism no longer operates to a significant degree. When Y and/or REE surface concentrations are greater than several hundred ppm, complex concentration profiles develop. These profiles are consistent with a multi-site diffusion–reaction model, whereby Y and REE cations diffuse through, and exchange between, different crystallographic sites. Diffusion profiles of Hf do not exhibit any of the complexities observed for Y and REE profiles, and can be modeled using a standard (i.e. single mechanism) solution to the diffusion equation. Hafnium diffusion in garnet shows a negative dependence on silica activity, and is described by logDHf(m2 s−1)=−8·85(±0·38)−299344(±15136)+12500(±900)×P(GPa)2·303RT(K)−0·52(±0·09)×log⁡10aSiO2. In many natural garnets, diffusion of both Lu and Hf would be sufficiently slow that the Lu–Hf system can be reliably used to date garnet growth. In cases in which significant Lu diffusion does occur, preferential retention of 176Hf/177Hf relative to 176Lu/177Hf will skew isochron relationships such that their apparent ages may not correspond to anything meaningful (e.g. garnet growth, peak temperature or the closure temperature of Lu or Hf). Late-stage reheating events are capable of causing larger degrees of preferential retention of 176Hf/177Hf relative to 176Lu/177Hf and partial to full resetting of the Sm–Nd system within garnet, thus increasing the separation between garnet Lu–Hf and Sm–Nd isochron dates, owing to the fact that these systems are more significantly disturbed through diffusion as more radiogenic 176Hf and 143Nd have accumulated.

Compositional dependence of linear and nonlinear optical response in crystalline hafnium zirconium oxide thin films

Abstract: Composition dependence of second harmonic generation, refractive index, extinction coefficient, and optical bandgap in 20 nm thick crystalline Hf1−xZrxO2 (0 ≤ x ≤ 1) thin films is reported. The refractive index exhibits a general increase with increasing ZrO2 content with all values within the range of 1.98–2.14 from 880 nm to 400 nm wavelengths. A composition dependence of the indirect optical bandgap is observed, decreasing from 5.81 eV for HfO2 to 5.17 eV for Hf0.4Zr0.6O2. The bandgap increases for compositions with x > 0.6, reaching 5.31 eV for Hf0.1Zr0.9O2. Second harmonic signals are measured for 880 nm incident light. The magnitude of the second harmonic signal scales with the magnitude of the remanant polarization in the composition series. Film compositions that display near zero remanent polarizations exhibit minimal second harmonic generation while those with maximum remanent polarization also display the largest second harmonic signal. The results are discussed in the context of ferroelectric phase assemblage in the hafnium zirconium oxide films and demonstrate a path toward a silicon-compatible integrated nonlinear optical material.

A 30-nm thick integrated hafnium zirconium oxide nano-electro-mechanical membrane resonator

Abstract: This paper reports a 30 nm-thick integrated nano-electro-mechanical resonator based on atomically engineered ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2) film. A 10 nm-thick Hf0.5Zr0.5O2 layer is atomically engineered through capping with 10 nm-thick titanium nitride (TiN) layer and rapid thermal annealing to promote the orthorhombic crystal phase with strong ferroelectric properties. The resulting metal-ferroelectric-metal (MFM) membrane is then patterned to create an integrated nano-electro-mechanical resonator with an overall thickness of 30 nm and a planar-to-vertical aspect ratio exceeding 104:1. Benefiting from large electrostrictive effects in ferroelectric Hf0.5Zr0.5O2, the 30 nm-thick nanomechanical resonator is excited into flexural resonance at 195 kHz with a very large vibration amplitude of ∼100 nm. The transmission response of the nano-electro-mechanical resonator is extracted, using a two-port apodization of the TiN electrodes, showing quality factors (Q) of 15 and 3300 at atmospheric and 10−7 Torr ambient pressures, respectively. Finally, the structural robustness of the MFM nano-membrane is explored through the application of a ∼24 μm deflection, using a point-force by a micro-probe, highlighting the extended elasticity despite the small thickness and ultra-high aspect ratio. The atomic-level thickness, fully integrated operation, high Q, and structural robustness of the Hf0.5Zr0.5O2-based nano-membrane resonator promise its potential for the realization of highly integrated transducers for chip-scale classical and quantum information processing and sensing applications.

Comparison of Hafnium Dioxide and Zirconium Dioxide Grown by Plasma-Enhanced Atomic Layer Deposition for the Application of Electronic Materials

Abstract: We report the growth of nanoscale hafnium dioxide (HfO2) and zirconium dioxide (ZrO2) thin films using remote plasma-enhanced atomic layer deposition (PE-ALD), and the fabrication of complementary metal-oxide semiconductor (CMOS) integrated circuits using the HfO2 and ZrO2 thin films as the gate oxide. Tetrakis (dimethylamino) hafnium (Hf[N(CH3)2]4) and tetrakis (dimethylamino) zirconium (IV) (Zr[N(CH3)2]4) were used as the precursors, while O2 gas was used as the reactive gas. The PE-ALD-grown HfO2 and ZrO2 thin films were analyzed using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The XPS measurements show that the ZrO2 film has the atomic concentrations of 34% Zr, 2% C, and 64% O while the HfO2 film has the atomic concentrations of 29% Hf, 11% C, and 60% O. The HRTEM and XRD measurements show both HfO2 and ZrO2 films have polycrystalline structures. n-channel and p-channel metal-oxide semiconductor field-effect transistors (nFETs and pFETs), CMOS inverters, and CMOS ring oscillators were fabricated to test the quality of the HfO2 and ZrO2 thin films as the gate oxide. Current-voltage (IV) curves, transfer characteristics, and oscillation waveforms were measured from the fabricated transistors, inverters, and oscillators, respectively. The experimental results measured from the HfO2 and ZrO2 thin films were compared.

Effect of in situ hydrogen plasma on the ferroelectricity of hafnium zirconium oxide films

Abstract: The emerging field of ferroelectric hafnium zirconium oxide has garnered increased attention recently for its wide array of applications from nonvolatile memory and transistor devices to nanoelectromechanical transducers. Atomic layer deposition is one of the preferred techniques for the fabrication of hafnium zirconium oxide thin films, with a standard choice of oxidizer being either O3 or H2O. In this study, we explore various oxidizing conditions and report on the in situ treatment of hydrogen plasma after every atomic layer during the deposition of hafnium zirconium oxide to increase the virgin state polarization. Three different oxidization methods were utilized during the fabrication of the Hf0.5Zr0.5O2 films: H2O, O2 plasma, and O2 plasma followed by H2 plasma. The 10 and 8 nm thick films oxidized with only O2 plasma result in initially anti-ferroelectric films. Comparatively, the addition of H2 plasma after every O2 plasma step results in films with strong ferroelectric behavior. Peak shifting of the GIXRD pattern suggests that the sequential O2-H2 plasma films tend more to the orthorhombic phase as compared to the O2 plasma and H2O oxidized films.

FCC phase formation in immiscible Mg–Hf (magnesium–hafnium) system by high-pressure torsion

Abstract: Magnesium and hafnium, two hydride-forming and biocompatible metals with hexagonal close-packed crystal structures, are thermodynamically immiscible even in the liquid form. In this study, these two elements were mechanically mixed by high-pressure torsion straining, and a new FCC (face-centered cubic) phase was formed although these two elements do not form the FCC phase even under high pressure or at high temperature. Microstructural examination by scanning-transmission electron microscopy combined with an ASTAR automatic crystal orientation and phase mapping technique confirmed that the FCC phase was stabilized mainly in the Hf-rich nanograins with localized supersaturation. Attempts to control the phase transformations under a hydrogen atmosphere to produce ternary magnesium–hafnium hydrides for hydrogen storage applications were unsuccessful; however, the material exhibited enhanced hardness to an acceptable level for some biomedical applications.

Anticorrosion performance of hafnium oxide ultrathin films on AZ31 magnesium alloy

Abstract: Amorphous hafnium oxide films from 15 to 60 nm in thickness were deposited by atomic layer deposition (ALD) on AZ31 magnesium alloy. The films exhibited high anticorrosion performance in the Hank's balanced salt solution, whose pH and ion concentrations were close to those of the human blood plasma. Voltammetry identified reduction of the corrosion rates to be above three orders of magnitude. The electrochemical impedance spectroscopy (EIS) implied a localized corrosion with diffusion limitations within the corrosion products. Scanning electron microscopy equipped with energy dispersive X-ray spectrometer (SEM-EDS) identified a phosphating process with development of a distinctive surface network structure composed of oxygen, phosphorous and calcium. Protection of Mg alloys by the ultrathin hafnium oxide films provides an opportunity to tailor the corrosion rate and, at the same time, to release only trace amounts of hafnium in vivo. The anticorrosion performance was also evaluated by testing the samples under continuous condensation conditions according to standards ISO 6270-1:2018 and ISO 12944-6:2018. The specimens have met the protection requirements for the corrosivity, which is typical of industrial and coastal areas as well as indoor areas, such as those in chemical plants, swimming pools, coastal ship and boat yards.

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Abstract: Hafnium is an elemental superconductor which crystallizes in a hexagonal close packed structure, has a transition temperature $T_{C} \simeq 400 mK$, and has a high normal state resistivity around $90 \mu \Omega. cm$. In Microwave Kinetic Inductance Detectors (MKIDs), these properties are advantageous since they allow for creating detectors sensitive to optical and near infra-red radiation. In this work, we study how sputter conditions and especially the power applied to the target during the deposition, affect the hafnium $T_{C}$, resistivity, stress, texture and preferred crystal orientation. We find that the position of the target with respect to the substrate strongly affects the orientation of the crystallites in the films and the internal quality factor, $Q_{i}$, of MKIDs fabricated from the films. In particular, we demonstrate that a DC magnetron sputter deposition at a normal angle of incidence, low pressure, and low plasma power promotes the growth of compressive (002)-oriented films and that such films can be used to make high quality factor MKIDs with $Q_{i}$ up to 600,000.

Effect of hafnium contaminant present in zirconium targets on sputter deposited ZrN thin films

Abstract: Zirconium nitride thin films deposited by reactive magnetron sputtering recurrently present small amounts of hafnium (~1 at.%) in their composition derived from an inherent impurity existing in Zr targets. Hf presence in ZrN coatings is neglected by most of the researchers despite its known potential to modify properties of thin films. In this work, pure ZrN (0.9 at.% Hf contaminant) and ZrHfN thin films with intentional hafnium addition of 1.8, 3.7 and 5.5 at.% were deposited by reactive magnetron sputtering and characterized by RBS, GAXRD, SEM, nanohardness and high temperature oxidation tests. Based on the results, it is suggested that inherent hafnium presence in zirconium targets contributes for the good hardness values and oxidation resistance at 773 K registered for ZrN thin films.

Thermophysical properties for hafnium carbide (HfC) versus temperature from 2000 to 5000 K (experiment)

Abstract: Hafnium carbide HfC (at%: 42%C; 49%Hf; 7%O) was investigated under rapid heating by a current pulse, in a time of 5–8 μs. The temperature was measured by radiance of a flat surface of a carbide plate (thickness 130 microns) at a given emissivity. This carbide plate was clamped between two K-8 plates, to prevent evaporation of the carbide and to prevent surface discharge at high voltage along the sample. Input specific energy (enthalpy), melting heat, solidus and liquidus temperatures (4000–4200 K), electrical resistance and heat capacity for solid and liquid states were measured up to 5000 K.

Chemical Vapor Deposition of an Iridium Phase on Hafnium Carbide and Tantalum Carbide

Abstract: Nanocrystalline iridium coatings on hafnium carbide and tantalum carbide substrates are prepared by chemical vapor deposition (MOCVD) at 600°С. Subsequent high-temperature treatment at 1100°С gives rise to chemical reactions between iridium and hafnium carbide or tantalum carbide to yield nanosized substitutional intermetallic solid solutions MIr3 – x and evolve free carbon. The occurrence of intermetallic interaction is proved by X-ray photoelectron (XPS) spectroscopy.

Characterization of sputtered hafnium thin films for high quality factor microwave kinetic inductance detectors

Abstract: Hafnium is an elemental superconductor which crystallizes in a hexagonal close packed structure, has a transition temperature TC 400 mK, and has a high normal state resistivity around 90 μΩ.cm. In Microwave Kinetic Inductance Detectors (MKIDs), these properties are advantageous since they allow for creating detectors sensitive to optical and near infra-red radiation. In this work, we study how sputter conditions and especially the power applied to the target during the deposition, affect the hafnium TC, resistivity, stress, texture and preferred crystal orientation. We find that the position of the target with respect to the substrate strongly affects the orientation of the crystallites in the films and the internal quality factor, Qi, of MKIDs fabricated from the films. In particular, we demonstrate that a DC magnetron sputter deposition at a normal angle of incidence, low pressure, and low plasma power promotes the growth of compressive (002)-oriented films and that such films can be used to make high quality factor MKIDs with Qi up to 600,000.

Solution-based hafnium oxide thin films as potential antireflection coating for silicon solar cells

Abstract: Hafnium oxide (HfO2) thin films were formed by spin coating deposition and annealed in ambient air. Following the molarity optimization of hafnium content in the solution, effect of spin coating and thermal processes on the antireflection properties were analyzed. Characterizations were carried out by spectrophotometer, X-ray diffraction, spectroscopic ellipsometer and scanning electron microscopy measurements. Post deposition annealing temperatures range from 500 to 1000 °C. Annealing led the crystallinity of the films above 500 °C and possess monoclinic phase. Average reflectivity of 11.32% was achieved with 71.36 nm HfO2 film after annealing at 700 °C. Ellipsometer measurements reveals refractive index of such a film as 1.934 at 600 nm. Average reflectance increases when annealing temperature is over 700 °C mainly due to the increase of refractive index which is recorded as 2.05 after annealing at 800 °C. Fresnel equations, transfer matrix method and PC1D simulations were carried out for reflectance spectra approximations. The experimental results and the theoretical data were relatively comparable. Spin coating HfO2 thin films are found promising as an antireflection layer for solar cells.

Excitation of high-frequency in-plane bulk acoustic resonance modes in geometrically engineered hafnium zirconium oxide nano-electro-mechanical membrane

Abstract: A nano-electro-mechanical membrane created from atomic-layered ferroelectric hafnium zirconium oxide (Hf0.5Zr0.5O2), titanium nitride (TiN), and silicon dioxide is engineered to localize high quality factor (Q) in-plane bulk acoustic resonance modes over 80–840 MHz. The in-plane geometry of the membrane, with an overall thickness of 50 nm and an aspect ratio exceeding 104:1, is optimized to simultaneously preserve the stress profile needed for sustaining ferroelectric polarization and enable propagation and constructive interaction of extensional and shear waves to create bulk acoustic modes. A ferroelectric polarization of 11.2 μC/cm2 is measured at the transduction ports, which is consistent after nano-membrane release. The first, third, and seventh order width extensional modes (WE1,3,7) and the third order of the width shear mode (WS3) are electrically measured at 109, 389, 766, and 267 MHz, respectively, showing Qs over 50–100 that are dominated by the large electrical resistance of TiN electrodes. High mechanical Qs of 538, 407, 781, and 594 are extracted for the WE1,3,7 and WS3 modes, respectively, after de-embedding the TiN electrode impedance, resulting in large resonance frequency (f0) × Q products as high as 6 × 1011. The measured characteristics, along with numerical simulations, are used to extract a Young's modulus of ∼340 GPa for the 10 nm-thick Hf0.5Zr0.5O2 film, which is in close agreement with the reported ab initio estimations.

Mechanical, thermal and thermoelectric properties of MX2 (M = Zr, Hf; X = S, Se)

Abstract: In this paper, we used density functional theory to study the mechanical and thermal properties of MX2 (M = Zr, Hf; X = S, Se) in P21/m structure. Results from elastic constants and phonon band structure indicated that the structures were found to be stable against mechanical distortions. These MX2 are brittle and their dominant bonding type is ionic in nature based on our computed mechanical properties. Thermal properties show that the specific heat capacity at constant volume of the selenides is greater than that of the sulphides of hafnium and zirconium. Additionally, we computed the lattice thermal conductivity as well as the transport coefficients with respect to temperature over a range of charge carrier concentrations, ranging from the Seebeck coefficient, electrical conductivity, electronic contribution to total thermal conductivity and consequently fuse them so as to calculate their respective power factors as well as the dimensionless figure of merit of the hafnium and zirconium dichalcogenides considered hereby.