Non-centrosymmetric Phase Research Articles

Evolution of crystallographic structure and ferroelectricity of Hf0.5Zr0.5O2 films with different deposition rate

Hf0.5Zr0.5O2 films are one of the most attractive HfO2-based ferroelectric films because of good ferroelectricity, extreme thinness, and excellent compatibility with silicon devices. The origin of the ferroelectricity of Hf0.5Zr0.5O2 films is the noncentrosymmetric orthorhombic phase (space group Pca21). The effects of process temperature, annealing temperature, thickness, and doping to increase the portion of the orthorhombic phase, which contributes to ferroelectricity, have been studied extensively. However, although most studies have used atomic layer deposition, no study has been reported on the effect of the deposition rate on the ferroelectricity of Hf0.5Zr0.5O2 films. In this work, the influences of the deposition rate on the ferroelectricity and crystal structure of Hf0.5Zr0.5O2 films were examined. In order to conduct systematic and quantitative analysis, measurements of switching transient current, ferroelectric P-E curve, dielectric constant, deconvolution of grazing angle incidence X-ray diffraction, and piezoresponse force microscopy were performed. Hf0.5Zr0.5O2 films with a deposition rate of 1.1 Å/cycle have a more ideal hysteresis curve shape, higher remanent polarization (initial state: 16 μC/cm2, wake up state: 22 μC/cm2), and a higher orthorhombic phase portion than other deposition rates.

Physical properties of hexagonal BaPtAs with noncentrosymmetric SrPtSb-type and centrosymmetric YPtAs-type crystal structures: Effects of spin-orbit coupling

Recently, superconductivity in BaPtAs with the noncentrosymmetric SrPtSb and the centrosymmetric YPtAs-structure has been discovered. Its noncentrosymmetric and centrosymmetric structures make BaPtAs a charming compound for searching the effect of spin-orbit coupling (SOC) onto superconductors with broken and preserved spatial inversion symmetry. We have investigated the effect of SOC on the physical and electron-phonon interaction properties of these phases of BaPtAs by using the generalized gradient approximation of the density functional theory and the plane-wave pseudopotential method. The inclusion of SOC has moderate effect on the elastic and electronic properties, and on phonon frequencies for both phases of BaPtAs. However, SOC makes an opposite impact on their Eliashberg spectral function. For the noncentrosymmetric phase, this coupling decreases the strength of dominant peaks of Eliashberg spectral function, reducing the values of average electron-phonon coupling and superconducting transition temperature. The scenario is exactly opposite for the centrosymmetric phase. For both phases, the hybridized Pt-As vibrations play a strongly significant role in determining their electron-phonon interaction properties since their electronic states have the dominant contribution near the Fermi level. The superconducting temperature is estimated to be 2.87 K for the SrPtSb phase and 2.38 K for the YPtAs phase. These values compare well with the reported measured values of 2.8 K and 2.1--3.0 K, respectively.

Effect of hydrogen derived from oxygen source on low-temperature ferroelectric TiN/Hf0.5Zr0.5O2/TiN capacitors

The ferroelectric (FE) properties of 10-nm-thick Hf0.5Zr0.5O2 (HZO) films deposited by an atomic layer deposition technique were improved by adopting O3 as an oxygen source instead of H2O. All HZO films were annealed at 400 °C for 1 min in an N2 atmosphere after TiN top electrode deposition. Regardless of the oxygen source, the HZO films exhibited the formation of a noncentrosymmetric orthorhombic phase, which is responsible for FE behavior with the suppression of the monoclinic phase. However, compared to the O3-based HZO film, it was confirmed that the H2O-based HZO film was more incorporated with hydrogen derived from H2O, thereby degrading FE polarization and leakage behavior. The results indicate that the strategy of using O3 as the oxygen source is useful for the fabrication and integration of FE HZO films for next-generation memory applications.

Crystal Phase Distribution and Ferroelectricity in Ultrathin HfO2–ZrO2 Bilayers

(Hf,Zr)O2 ultrathin films are used as ferroelectric layers in emerging digital logic and nonvolatile memory devices. The ferroelectric properties of (Hf,Zr)O2 can be improved by interface engineering, such as the formation of nanolaminates with distinct HfO2 and ZrO2 layers. Herein, the ferroelectric performance of HfO2–ZrO2 ultrathin bilayer devices is shown to depend on the stacking order of HfO2 and ZrO2, which affects the quantity of the noncentrosymmetric orthorhombic Pca21 crystal phase. By combining X‐ray diffraction with a novel extended X‐ray absorption fine structure (EXAFS) analysis procedure, the orthorhombic, tetragonal, and monoclinic phase fractions are quantified for bilayers composed of 3 nm HfO2 and 3 nm ZrO2. A significantly larger orthorhombic ZrO2 phase fraction is found when ZrO2 has an unconstrained surface during annealing, whereas the presence of a ZrO2 interface with the substrate results in a substantial tetragonal ZrO2 phase fraction and a 2.4× smaller remanent polarization. HfO2 is found to be less susceptible than ZrO2 to crystal phase templating. The methods presented herein enable mechanistic studies of ferroelectric wake‐up, fatigue, and processing effects in (Hf,Zr)O2 films, accelerating the development of electronic devices that rely on ferroelectric oxides.

Theoretical calculation of ferroelectric Hf1−xZrxO2 by first-principle molecular dynamic simulation

The origin of the ferroelectricity in HfO2 is considered to be the formation of a non-centrosymmetric polar orthorhombic phase. The phase stability and the ferroelectricity of orthorhombic Hf1−xZrxO2 ferroelectric material are theoretically investigated with the density functional computations. The percentage of each phase is estimated based on the Maxwell–Boltzmann distribution, and the orthorhombic phase has the largest distribution when Zr/Hf = 1. The double-well landscape of the energy as a function of the polarization for the orthorhombic Hf1−xZrxO2 is obtained. Our calculation shows that the orthorhombic HfO2 has the ferroelectricity with a saturated polarization of 66.25 μC cm−2 and the barrier height of 77.4 meV atom−1. To consider the phase distribution for different Zr content, the calculated remnant polarization of Hf0.5Zr0.5O2 has the largest value of 21.5 μC cm−2. The metastable life time from zero polarization to saturated polarization is 0.19 ps and 0.17 ps for orthorhombic HfO2 and ZrO2, respectively, and depend on the Zr/Hf ratio.

Effect of furnace annealing on the ferroelectricity of Hf0.5 Zr0.5O2 thin films

The effect of furnace annealing on the ferroelectricity and crystal phase of Hf0.5ZrO2 (HZO) ultrathin films is studied as a function of film thickness. HZO films are deposited using atomic layer deposition (ALD) in a Ge-HZO-TiN stack with Pt as the top contact electrode. Furnace annealing is carried out after crystallizing the films with rapid thermal annealing in the presence of a TiN capping electrode. While furnace annealing did not have much impact on the 108 ALD cycles (~11 nm) film, it enhanced the ferroelectricity of the 44 ALD cycles film (~4.5 nm). Positive-up-negative-down tests provide evidence of ferroelectricity in the 40 ALD cycles (~4 nm) furnace annealed film after cycling the film at higher fields. Grazing incidence X-ray diffraction shows that the non-centrosymmetric orthorhombic phase responsible for ferroelectricity increased after furnace annealing in thinner films, but little change occurred in the 108 ALD cycles film that was rich in orthorhombic phase prior to furnace annealing. An analysis of the HZO films with a tapping mode atomic force microscope shows grain growth in the 44, and 40 ALD cycles films after furnace annealing.

Structural Correlation of Ferroelectric Behavior in Mixed Hafnia-Zirconia High-k Dielectrics for FeRAM and NCFET Applications

ABSTRACTThe recent discovery of ferroelectric behavior in doped hafnia-based dielectrics, attributed to a non-centrosymmetric orthorhombic phase, has potential for use in attractive applications such as negative differential capacitance field-effect-transistors (NCFET) and ferroelectric random access memory devices (FeRAM). Alloying with similar oxides like ZrO2, doping with specific elements such as Si, novel processing methods, encapsulation and annealing schemes are also some of the techniques that are being explored to target structural modifications and stabilization of the non-centrosymmetric phase. In this study, we utilized synchrotron-based x-ray diffraction in the grazing incidence in plane geometry (GIIXRD) to determine the crystalline phases in hafnia-zirconia (HZO) compositional alloys deposited by atomic layer deposition (ALD). Here we compare and contrast the structural phases and ferroelectric properties of mechanically confined HZO films in metal-insulator-metal (MIM) and metal-insulator-semiconductor (MIS) structures. Both MIM and MIS structures reveals a host of reflections due to non-monoclinic phases in the d-spacing region between 1.75Å to 4Å. The non-monoclinic phases are believed to consist of tetragonal and orthorhombic phases. Compared to the MIS structures a suppression of the monoclinic phase in MIM structures with 50% zirconia or less was observed. The correlation of the electrical properties with the structural analysis obtained by GIIXRD highlights the importance of understanding the effects of the underlying substrate (metal vs. Si) for different target applications.

Ferroelectricity mediated by ferroelastic domain switching in HfO2-based epitaxial thin films

Herein, ferroelastic domain switching from the nonpolar b-axis to the polar c-axis oriented domain in 7%-YO1.5-substituted HfO2 (YHO-7) epitaxial ferroelectric films is demonstrated. Scanning transmission electron microscopy (STEM) indicates that the polarization of a pristine film deposited on a Sn-doped In2O3/(001)YSZ substrate by the pulsed laser deposition method tends to be along the in-plane direction to avoid a strong depolarization field with respect to the out-of-plane direction. Applying an electric field aids in ferroelastic domain switching in YHO-7 films. Such films exhibit ferroelectric characteristics with a relatively large saturated polarization around 30 μC/cm2 by polarization reorientation from the in-plane to the out-of-plane directions and an increased dielectric constant. The synchrotron X-ray diffraction measurements with a focused beam for the pristine and poled area indicate ferroelastic 90° domain switching as the odd number reflection disappears, which is only allowed in the nonpolar b-axis orientation. STEM observations also show a significant increase in the c-axis oriented domain. This observation of ferroelastic domain switching strongly supports the conclusion that the ferroelectricity of HfO2 originates from the non-centrosymmetric orthorhombic phase.

Investigation of Co6(OH)3(TeO3)4(OH)~0.9(H20): Synthesis, crystal and magnetic structures, magnetic and dielectric properties

We have re-investigated the synthesis and the crystal structure of the non-centrosymmetric phase Co6(OH)3(TeO3)4(OH) published by Perez et al. in 1975 and we have obtained by hydrothermal synthesis the hydrated phase Co6(OH)3(TeO3)4(OH)~0.9(H20). The crystal structure related to the Ellenbergerite mineral was determined using single-crystal X-ray diffraction data. The non-centrosymmetric hexagonal structure (P63mc; a = 13.1640(7) Å; c = 5.0321(6) Å) is based on [CoO6] octahedra and [TeO3] polyhedra which formed a tunnel framework with a formal charge 1+ balanced by one OH- group located in large tunnels. Compared to Co6(OH)3(TeO3)4(OH) case we succeeded in locating the hydrogen atoms of the OH- groups bound to the Co and showed that a small amount of water resides also in the large tunnels with the OH- groups. The presence of water molecules was confirmed by infrared spectroscopy and thermogravimetric analyses. This phase behaves as a canted antiferromagnet below TN = 75.5 K. The average magnetic structure was solved from powder neutron diffraction. Antisymmetric Dzyaloshinsky-Moriya interactions in the (ab) plane have been highlighted and must be responsible for the spin canted antiferromagnetic ground state. Moreover, DFT calculations with an Ising model show the presence of a frustrated spin state for the two Co2+ cations involved in the antisymmetric Dzyaloshinsky-Moriya interaction. Under an applied magnetic field, a metamagnetic-like behaviour is observed with three different canted antiferromagnetic states. At low temperature, dielectric measurements evidence a magneto-structural coupling but no measurable magnetocapacitance.

Spin-Resolved Electronic Response to the Phase Transition in MoTe2

The semimetal MoTe_{2} is studied by spin- and angle-resolved photoemission spectroscopy across the centrosymmetry-breaking structural transition temperature of the bulk. A three-dimensional spin-texture is observed in the bulk Fermi surface in the low temperature, noncentrosymmetric phase that is consistent with first-principles calculations. The spin texture and two types of surface Fermi arc are not completely suppressed above the bulk transition temperature. The lifetimes of quasiparticles forming the Fermi arcs depend on thermal history and lengthen considerably upon cooling toward the bulk structural transition. The results indicate that a new form of polar instability exists near the surface when the bulk is largely in a centrosymmetric phase.

Dispersion in Ferroelectric Switching Performance of Polycrystalline Hf0.5Zr0.5O2 Thin Films.

Interests in nanoscale integrated ferroelectric devices using doped HfO2-based thin films are actively reviving in academia and industry. The main driving force for the formation of the metastable non-centrosymmetric ferroelectric phase is considered to be the interface/grain boundary energy effect of the small grains in polycrystalline configuration. These small grains, however, can invoke unfavorable material properties, such as nonuniform switching performance. This study provides an in-depth understanding of such aspects of this material through careful measurement and modeling of the ferroelectric switching kinetics. Various previous switching models developed for conventional ferroelectric thin-film capacitors cannot fully account for the observed time- and voltage-dependent switching current evolution. The accurate fitting of the experimental results required careful consideration of the inhomogeneous field distribution across the electrode area, which could be acquired by an appropriate mathematical formulation of polarization as a function of electric field and time. Compared with the conventional polycrystalline Pb(Zr,Ti)O3 film, the statistical distribution of the local field was found to be three times wider. The activation field and characteristic time for domain switching were larger by more than 1 order of magnitude. It indicates that doped HfO2 is inhomogeneous and "hard" ferroelectric material compared with conventional perovskite-based ferroelectrics.

Fabrication of ferroelectric Fe doped HfO2 epitaxial thin films by ion-beam sputtering method and their characterization

In this study, the effect of Fe doping on the crystal structure and electrical properties in 20-nm-thick HfO2 epitaxial thin films were systematically investigated. X-ray diffraction measurements revealed that undoped HfO2 films were composed of a paraelectric monoclinic phase. On the other hand, the formation of non-centrosymmetric orthorhombic phase was observed in Fe doped HfO2 films and was most promoted at an optimum doping concentration. In addition, high-temperature X-ray diffraction measurements showed that an orthorhombic phase to a highly symmetric phase transition occurs between 500 and 600 °C. Microstructural analysis using scanning transmission electron microscopy revealed multidomain structure consisting of orthorhombic and monoclinic phases. Ferroelectricity depended on Fe doping concentration, and the maximum remanent polarization value was 8.8 µC/cm2. These results indicate that Fe doped HfO2 thin films can be applied as nanoscale ferroelectrics.

Multiferroism in Iron-Based Oxyfluoride Perovskites.

Multiferroic materials with simultaneous magnetic and ferroelectric ordering that persist above room temperature are rare. Using first-principles density functional theory calculations, we demonstrate fluorination of oxygen-deficient AA'Fe2O5 perovskites, where A and A' are cations with +3 and +2 oxidation states, respectively, and have a layered ordering, as an effective strategy to obtain room-temperature multiferroics. We show that by controlling the size of the A and A' cations, it is possible to stabilize a noncentrosymmetric phase arising due to the hybrid improper ferroelectricity mechanism, with polarization as high as 13 μC/cm2. The fluorination also stabilizes Fe in +3 oxidation state, which results in superexchange interactions that are strong enough to sustain magnetic order well above room temperature. We also show the presence of a magnetoelectric coupling wherein the switching mode that reverses the direction of the spontaneous polarization also affects the strength of the magnetic interactions. The results show that low-temperature fluorination of anion-deficient perovskites with layered cation ordering can be an effective approach to design new multiferroics.

Mechanical control of crystal symmetry and superconductivity in Weyl semimetal MoTe2.

The noncentrosymmetric Weyl semimetal candidate MoTe2 was investigated through neutron-diffraction and transport measurements at pressures up to 1.5 GPa and at temperatures down to 40 mK. Centrosymmetric and noncentrosymmetric structural phases were found to coexist in the superconducting state. Density functional theory (DFT) calculations reveal that the strength of the electron-phonon coupling is similar for both crystal structures. Furthermore, it was found that by controlling nonhydrostatic components of stress, it is possible to mechanically control the ground-state crystal structure. This allows for the tuning of crystal symmetry in the superconducting phase from centrosymmetric to noncentrosymmetric. DFT calculations support this strain control of crystal structure. This mechanical control of crystal symmetry gives a route to tuning the band topology of MoTe2 and possibly the topology of the superconducting state.

(Invited) Teaching a New Dog Old Tricks: Ferroelectric HfZrO Films and Devices

The recent discovery that with certain dopants hafnium oxide can be crystallized in a form that exhibits ferroelectricity has opened up a range of device possibilities(1). We have chosen to work within the Hf/Zr system for our initial studies. The advantages of the Hf/Zr doping system include the similarity in precursors which can enable several running modes for the ALD process including a co-pulsing scenario, as well a cycle ratio scenario for controlling the Zr doping. Because Zr and Hf are so similar structurally as well as chemically, the isologous precursors we employ have essentially identical delivery characteristics, including vapor pressure, relative sticking coefficient and relative decomposition point. Thus we expect the process to be capable of maintaining a highly consistent composition over a broad range of topology. In addition, the relative range of doping for which a strong remnant polarization is observed is much broader for the Hf/Zr system than for other dopants such as Al, Si, etc. which means this system should be more tolerant of small changes in composition than the other doping schemes. Generally, the ferroelectric phase of doped Hf oxide is thought to be a non-centrosymmetric orthorhombic phase that is co-crystallized with some other observable phases. In our studies we have found a strong correlation between the polarizability we observe and signals attributed to a tetragonal phase by grazing incidence X-ray diffraction using synchrotron radiation(2). In terms of electrical performance, we have shown reasonable polarization characteristics for films as thin as 5nm, and demonstrated the feasibility of using these films for multiple potential applications. We have explored the possibility of incorporating these films as gate dielectrics for a ferroelectric memory and have also demonstrated that we can fabricate a transistor exhibiting a steep subthreshold slope (<60mV/dec.), due to a negative capacitance effect observed as the transistor switches and sweeps through the subthreshold region simultaneously(3). Other potential uses for these films include the possibility to create multi-domain ferroelectric FETs that can be used within a neuromorphic device to mimic synapse behavior. This talk will review and update our work to date on these films and their potential uses.

Evolution of the Charge Trap Density during Endurance of Ferroelectric HfO2:La

Before 2011, hafnium oxide was considered as a paraelectric material until the observation of the ferroelectric effect in doped thin HfO2 films after high­temperature annealing [T.S. Böscke et al., Appl. Phys. Lett. 99, 102903 (2011); S. Mueller et al., Adv. Function. Mater. 22, 2412 (2012)]. Dopping by lantanum leads to the largest remanent polarization of HfO2 films [U. Schroeder et al., Jpn. J. Appl. Phys. 53, 08LE02 (2014)]. Ferroelectricity in these materials is associated with the ability to stabilize noncentrosymmetric orthorhombic phase Pbc21 [J. Müller et al., Nano Lett. 12, 4318 (2012)]. It should be noted that hafnia-­based materials have a number of advantages over conventional ferroelectric regarding compatibility with the technological processes used in microelectronics, and they have already demonstrated their ability to provide a very high density of elements. Considering the advantages of ferroelectric random access memory (FRAM) as non­volatile, high­speed performance, high number of switching cycles, the discovery of ferroelectric effect in these materials gave an impetus for the development of the universal memory concept which may lead to a significant breakthrough in the development of memory devices [M.H. Park et al., Adv. Mater. 27, 1811 (2015)]. An unsolved problem in the way of development of FRAM­-based memory are is a reason of memory window of FRAM instability during set/reset cycling, i.e. endurance. One of the possible reasons for these effects is the presence of defects in HfO2:La thin films. The purpose of the present work is to study the evolution of charge trap density in ferroelectric HfO2:La after set/reset cycling. Transport measurements were performed for TiN/HfO2:La/TiN structures. Test structures were fabricated with the atomic layer deposition (ALD) technique. A 10-­nm­-thick TiN layer was deposited on the oxidized Si (100) substrate. Then the 10­-nm­-thickHfO2:La films were deposited at 235°C from TEMAH (heated to 100°С) and La(iPrCp)3 + (heated to 170°С) precursors using O2+Ar plasma. Laser ellipsometry and Rutherford backscattering spectroscopy confirmed the thickness and stoichiometry of HfO2:La films. TiN top layer (10 nm thick) was deposited using the ALD technique. For transport measurements, round (area is 7.854×103 μm2) electrodes were formed by the photolithography process. The presence of ferroelectric properties ofHfO2:La films is confirmed by observing the characteristic hysteresis on the polarization­voltage (P-­V) plate for TiN/HfO2:La/TiN structures. The P-­V and current-­voltage (I-­V) dependences were measured by the standard PUND technique at room temperature. The first “Positive” and the third “Negative” impulses aligned dipoles in the ferroelectric films (set and reset, respectively) and they were used to measure polarization, while, during the second “Up” and the forth “Down” impulses, the leakage currents were measured. The leakage currents were extracted from the current responses by removing displacement currents. The trap density was extracted from the leakage currents within phonon-assisted tunnelling between traps model [K. Nasyrov et al., J. Appl. Phys. 109 097705 (2011)].

Оxygen Vacancy Influence on the Stabilization Properties of Ferroelectric Hf0.5Zr0.5O2: First Principle Study

The aim of the study is the investigation of the oxygen vacancy (VO) role for the stabilization of orthorhombic noncentrosymmetric (Pbc21) phase in Hf0.5Zr0.5O2 films. The simulations carried out in terms of the hybrid DFT using Quantum-ESPRESSO code for the four low temperatures Hf0.5Zr0.5O2 crystalline phases: orthorhombic ferroelectric (of-), monoclinic (P21c), orthorhombic oI (Pbca) and orthorhombic oII (Pnma). It is shown that the VO concentration increasing leads to the fact that the pressure range under which the of-Hf0.5Zr0.5O2 structure can exist is narrowed. It is concluded that high VO concentration has a negative impact on the ferroelectric phase stabilization even for thin Hf0.5Zr0.5O2 films. It is established that of-Hf0.5Zr0.5O2 with O vacancies in any concentration is not stable for bulk crystal at any value of external pressure in which the structure is able to exist. However, it is shown that VO have a positive impact on the stabilization of the centrosymmetric oII phase of Hf0.5Zr0.5O2. Thus, the presence of oxygen vacancies and polyvacancies not only does not contribute to the Hf0.5Zr0.5O2 ferroelectric phase stabilization, but also leads to the destruction of the ferroelectric structure. This is consistent with the hypothesis that the degradation ferroelectric response of FeRAM elements during repeated reprogramming, is caused by the oxygen vacancies generation. The work is supported by the Russian Science Foundation grant #14-19-00192.

Direct Observation at Room Temperature of the Orthorhombic Weyl Semimetal Phase in Thin Epitaxial MoTe2

AbstractThe direct observation at room temperature (RT) of the noncentrosymmetric orthorhombic topological Weyl semimetal phase in epitaxial thin films of MoTe2 grown on InAs(111)/Si(111) substrates by molecular beam epitaxy (MBE) is reported. The orthorhombic phase is typically found at lower temperatures but its observation at RT in this work is attributed to the enlarged lattice parameters, influenced by the substrate, which stabilize an interlayer antibonding state compatible with the orthorhombic stacking. First‐principles calculations predict eight type II Weyl nodes which are located below (but near) the Fermi energy making them accessible to charge transport and creating the prospect for practical applications exploiting the nontrivial topological properties. The orthorhombic phase coexists with an unconventional triclinic layer stacking which is different than the monoclinic or orthorhombic structures but it is centrosymmetric and topologically trivial.

Phase transitions, optical and electronic properties of the layered perovskite hybrid [NH3(CH2)2COOH ]2CdCl4 of Y-aminobutyric acid (GABA)

A new organic-inorganic hybrid with the formula (NH3C3H6CO2H)2CdCl4 has been crystallized and investigated by X-ray diffraction. Structural investigations highlight a first-order reversible structural phase transition occurring within the range (290–370 K) between a chiral (phase II) and non-centrosymmetric (Phase I) crystal packing. This strong structural reorganization is the result of conformational changes in the organic chains accompanied by a decrease in octahedral distortion. The accurate crystallographic analysis illustrates the crucial role of organic moieties. The experimental energy gap value (3.65 eV) is in good agreement with the theoretical value obtained by density functional theory.

Effects of Hf buffer layer at the Y-doped HfO2/Si interface on ferroelectric characteristics of Y-doped HfO2 films formed by reactive sputtering

10 nm-thick ferroelectric (FE) HfO2 films with 1.5 mol% yttrium-doping were fabricated by mid-frequency reactive magnetron co-sputtering deposition on bare Si and underlying metal Hf. Yttrium was incorporated into the HfO2 layers by simultaneously sputtering from Y and Hf metal targets under oxygen atmosphere. The effects of interfacial layer on structural and electrical properties of Y:HfO2 films have been systemically studied using high-resolution transmission electron microscopy (TEM), X-ray diffraction (XRD) and electrical measurements. Based on TEM and XRD measurements, the presence of a non-centrosymmetric orthorhombic phase which is responsible for ferroelectricity in yttrium-doped HfO2 (Y:HfO2) films could be detected. As an initial protective layer, the ultra-thin metal Hf (~1 nm) layer covers the silicon surface and prevents the native oxide growth during the deposition and post-annealing process. Results reveal that the thickness of interfacial layer is significantly reduced by deposit a Hf buffer layer and a remanent polarization Pr of up to 14 μC/cm2 can be detected in P-V measurement. The strategy of using Hf buffer layer to improve electrical properties of HfO2 film is a feasible method for the fabrication of metal-insulator-semiconductor (MIS) capacitor based on FE-HfO2/Si gate stack.