Optimization of ferroelectricity and endurance of hafnium zirconium oxide thin films by controlling element inhomogeneity

Ferroelectric thin films based on HfO2 have garnered increasing attention worldwide,primarily due to their remarkable compatibility with silicon and scalability,in contrast to traditional perovskite-structured ferroelectric materials.Nonetheless,significant challenges remain in their widespread commercial utilization,particularly concerning their notable wake-up effect and limited endurance.To address these challenges,we propose a novel strategy involving the inhomogeneous distribution of Hf/Zr elements within thin films and explore its effects on the ferroelectricity and endurance of Hf_(0.5)Zr_(0.5)O_(2) thin films.Through techniques such as grazing incidence X-ray diffraction,transmission electron microscopy,and piezoresponse force microscopy,we investigated the structural characteristics and domain switching behaviors of these materials.The experimental results indicate that the inhomogeneous distribution of Hf/Zr contributes to improving the frequency stability and endurance while maintaining a large remnant polarization in Hf_(0.5)Zr_(0.5)O_(2) ferroelectric thin films.By adjusting the distribution of Zr/Hf within the Hf_(0.5)Zr_(0.5)O_(2) thin films,significant enhancements in the remnant polarization(2Pr>35μC/cm2)and endurance(>109)along with a reduced coercive voltage can be achieved.Additionally,the fabricated ferroelectric thin films also exhibit high dielectric tunability(≥26%)under a low operating voltage of 2.5 V,whether in the wake-up state or not.This study offers a promising approach to optimize both the ferroelectricity and endurance of HfO_(2)-based thin films.

Production of HfO_2 thin films using different methods: chemical bath deposition, SILAR and sol–gel process

Hafnium oxide thin films （HOTFs） were successfully deposited onto amorphous glasses using chemical bath deposition, successive ionic layer absorption and reaction （SILAR）, and sol-gel methods. The same reactive precursors were used for all of the methods, and all of the films were annealed at 300℃ in an oven （ambient conditions）. After this step, the optical and structural properties of the films produced by using the three different methods were compared. The structures of the films were analyzed by X-ray diffTaction （XRD）. The optical properties are investigated using the ultraviolet-visible （UV-VIS） spectroscopic technique. The film thickness was measured via atomic force microscopy （AFM） in the tapping mode. The surface properties and elemental ratios of the films were investigated and measured by scanning electron microscopy and energy-dispersive X-ray spectroscopy （EDX）. The lowest transmittance and the highest reflectance values were observed for the films produced using the SILAR method. In addition, the most intense characteristic XRD peak was observed in the diffraction pattern of the film produced using the SILAR method, and the greatest thickness and average grain size were calculated for the film produced using the SILAR method. The films produced using SILAR method contained fewer cracks than those produced using the other methods. In conclusion, the SILAR method was observed to be the best method for the production of HOTFs.

Benzylation of arenes and heteroarenes catalyzed by HfCl_4/HfO_2

A highly efficient benzylation of arenes and heteroarenes catalyzed by HfCl4/HfO2 has been developed. Broad scope of benzylation reagents have been used in this process with high yields under mild condition. Additionally, the HfO2 can be re-used after the reaction. ？2009 Xin Qin Gao. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Room temperature ferromagnetism in un-doped amorphous HfO_2 nano-helix arrays

Amorphous HfO2 nano-helix arrays with different screw pitches were fabricated by the glancing angle deposition technique. Room temperature ferromagnetism was achieved in this undoped amorphous HfO2 nanostructure, which is attributed to singly charged oxygen vacancies. The different magnetic behavior and photoluminescence in flat film and nano-helix arrays originate from the distinction of defect components. This study could facilitate the understanding of ferromagnetism origin in undoped HfO2, it also suggests a possible way to alter the intrinsic defects in amorphous HfO2.

HfO_2-based ferroelectric modulator of terahertz waves with graphene metamaterial

Tunable modulations of terahertz waves in a graphene/ferroelectric-layer/silicon hybrid structure are demonstrated at low bias voltages. The modulation is due to the creation/elimination of an extra barrier in Si layer in response to the polarization in the ferroelectric Si:HfOlayer. Considering the good compatibility of HfOwith the Si-based semiconductor process, the highly tunable characteristics of the graphene metamaterial device under ferroelectric effect open up new avenues for graphene-based high performance integrated active photonic devices compatible with the silicon technology.

Electrical Properties of Compositional Al2O3 Supplemented HfO2 Thin Films by Atomic Layer Deposition

With advanced research for dielectrics including capacitors in DRAMs, decoupling filters in microcircuits and insulating gates in transistors, a lot of demand for the new challenging of high-k materials in semiconductor industries has been emerged. This study explores and addresses the experimental approach for composite materials with one of the major concerns of high capacitance, and low leakage, as well as ease of integration technology. The characteristics of Al2O3 supported HfO2 (AHO) thin films for a series of different Hf ratios with Al2O3 dielectrics by atomic layer deposition demonstrated as a candidate material. A composite AHO films with the homogeneous compositions of Al and Hf atoms into the Al-Hf-O mixed oxide system could stabilize the polycrystalline structure with increasing of dielectric constant (k) and decreasing of leakage current density, as well as a higher breakdown voltage than HfO2 film on its own. 70 nm thick AHO thin films with different composition of Al and Hf contents were prepared by atomic layer deposition technique on titanium nitride (TiN) and silicon dioxide (SiO2) coated Si substrates. Photolithography and metal lift-off technique were used for the device fabrication of the metal-insulator-metal (MIM) capacitor structures. AHO films on TiN/SiO2/Si were measured by semiconductor analyzer and source/ measure system with probe station in the voltage range from -5 to 5 V with a frequency range from 10 kHz to 1 MHz were used to conduct capacitance-voltage (C-V) measurements with low/medium frequency range and current-voltage (I-V) measurements. It was found that Au/AHO/TiN/SiO2/Si MIM capacitors demonstrate a capacitance density of 1.5 - 4.5 fF/μm2 at 10 kHz, a loss tangent of 0.02 - 0.04 at 10 kHz, dielectric constant of 11.7 - 35.5 depending on the composition and a low leakage current of 1.7 × 10-9 A/cm2 at 0.5 MV/cm at room temperature. The acquired experimental results could show the possibility of compositional alloy thin films that could potentially replace or open new market for high-k challenges in semiconductor technology.

Performance analysis of silicon nanowire transistors considering effective oxide thickness of high-k gate dielectric

We have analyzed the effective oxide thickness （EOT） of the dielectric material for which we have optimum performance and the output characteristics of the silicon nanowire transistors by replacing the traditional Si02 gate insulator with a material that has a much higher dielectric constant （high-k） gate, materials like Si3N4, Al2O3, Y2O3 and HfO2. We have also analyzed the channel conductance, the effect of a change in thickness, the average velocity of the charge carrier and the conductance efficiency in order to study the performance of silicon nanowire transistors in the nanometer region. The analysis was performed using the Fettoy, a numerical simulator for ballistic nanowire transistors using a simple top of the barrier （Natori） approach, which is composed of several matlab scripts. Our results show that hafnium oxide （HfO2） gate insulator material provides good thermal stability, a high recrystallization temperature and better interface qualities when compared with other gate insulator materials; also the effective oxide thickness of lifO2 is found to be 0.4 nm.

Recent Progress and Applications of HfO_(2)-Based Ferroelectric Memory

The discovery of ferroelectricity in hafnium oxide (HfO_(2)) based thin films in 2011 renewed the interest inferroelectrics. These new ferroelectrics possess completely different crystal morphology with conventional perovskiteferroelectrics, and present more robust ferroelectric properties upon aggressive scaling and compatibility withstandard integrated circuit fabrication processes. In this article, we give a brief introduction to the conventionalferroelectric memories, then review the basic properties, recent progress, and memory applications of theseHfO_(2)-based ferroelectrics.

Effects of interaction between defects on the uniformity of doping HfO_2-based RRAM:a first principle study

The physical mechanism of doping effects on switching uniformity and operation voltage in Al-doped HfO_2 resistive random access memory(RRAM) devices is proposed from another perspective:defects interactions, based on first principle calculations.In doped HfO_2,dopant is proved to have a localized effect on the formation of defects and the interactions between them.In addition,both effects cause oxygen vacancies(V_O) to have a tendency to form clusters and these clusters are easy to form around the dopant.It is proved that this process can improve the performance of material through projected density of states(PDOS) analysis.For V_O filament-type RRAM devices, these clusters are concluded to be helpful for the controllability of the switching process in which oxygen vacancy filaments form and break.Therefore,improved uniformity and operation voltage of Al-doped HfjO_2 RRAM devices is achieved.

Thermomechanical analysis of nodule damage in HfO_2/SiO_2 multilayer coatings

Samples with nodular defects grown from gold nanoparticles are prepared, and laser-induced damage tests are conducted on them. Nodular defects, which are in critical state of damage, are cross-sectioned by focusing on the ion beam and by imaging using a field emission scanning electron microscope. The crosssectional profile shows that cracks are generated and propagated along the nodular boundaries and the HfO2/SiO2 interface, or are even melted. The thermomechanical process induced by the heated seed region is analyzed based on the calculations of temperature increase and thermal stress. The numerical results give the critical temperature of the seed region and the thermal stress for crack generation, irradiated with threshold fluence. The numerical results are in good agreement with the experimental ones.

Ferroelectricity in dopant-free HfO_(2) thin films prepared by pulsed laser deposition

As a high-k material,hafnium oxide(HfO_(2))has been used in gate dielectrics for decades.Since the discovery of polar phase in Si-doped HfO_(2) films,chemical doping has been widely demonstrated as an effective approach to stabilize the ferroelectric phase in HfO_(2) based thin films.However,the extra capping layer deposition,post-growth annealing and wake-up effect are usually required to arouse the ferroelectricity in HfO_(2) based thin films,resulting in the increase of complexity for sample synthesis and the impediment of device application.In this study,the ferroelectricity is observed in non-capped dopant-free HfO_(2) thin films prepared by pulsed laser deposition(PLD)without post-growth annealing.By adjusting the deposited temperature,oxygen pressure and thickness,the maximum polarization up to 14.7 m C/cm^(2) was obtained in 7.4 nm-thick film.The fraction of orthorhombic phase,concentrations of defects and size effects are considered as possible mechanisms for the influences of ferroelectric prop-erties.This study indicates that PLD is an effective technique to fabricate high-quality ferroelectric HfO_(2) thin films in the absence of chemical doping,capping layer deposition and post-growth annealing,which may boost the process of nonvolatile memory device application.

Accumulation effect of SiO_2 protective layer on multi-shot laser-induced damage in high-reflectivity HfO_2/SiO_2 coatings

The accumulation effects in high-reflectivity （HR） HfO2/SiO2 coatings under laser irradiation are investigated. The HR HfO2/SiO2 coatings are prepared by electron beam evaporation at 1 064 nm. The laser-induced damage threshold （LIDT） are measured at 1 064 nm and at a pulse duration of 12 ns, in 1-on-1 and S-on-1 modes. Multi-shot LIDT is lower than single-shot LIDT. The laser-induced and native defects play an important role in the multi-shot mode. A correlative theory model based on critical conduction band electron density is constructed to elucidate the experimental phenomena.

Study on high-reflective coatings of dif ferent designs at 532 nm

Conventional HfO2/SiO2 and Al2O3/HfO2/SiO2 double stack high reflective （HR） coatings at 532 nm are deposited by electron beam evaporation onto BK7 substrates. The laser-induced damage threshold （LIDT） of two kinds of HR coatings is tested, showing that the laser damage resistance of the double stack HR coatings （16 J/cm2） is better than that of the conventional HR coatings （12.8 J/cm2）. Besides, the optical properties, surface conditions, and damage morphologies of each group samples are characterized. The results show that laser damage resistance of conventional HR coatings is determined by absorptive defect, while nodular defect is responsible for the LIDT of double stack HR coatings.

Preparation of Al-Hf master alloy by aluminothermic reduction of HfO_(2)

The Al-Hf alloy was prepared by open aluminothermic reduction of HfO_(2) using CaF_(2) and Na F as the flux. The influence of the slag composition, the amount of aluminum, and the heat energizer was studied detailly to establish optimum conditions for the sufficient recovery of the alloy and the complete slag-alloy separation. The Al-Hf alloy with 40 wt% Hf was obtained by this method, and the maximum recovery was 70.7%. The microstructure of the alloy was observed by scanning electron microscope(SEM). Moreover, X-ray diffraction(XRD) analysis and energy-disperse spectrometry(EDS) were applied to characterize the formation of the phases. The results show that the alloy consists of Al and Al_(3)Hf phases and the oxygen content is about 0.2 wt%.