Hafnium Oxide Thin Films Research Articles

Low temperature thermal oxidation towards hafnium-coated magnesium alloy for biomedical application

Low temperature thermal oxidation treatment is performed on the PVD (physical vapor deposition) hafnium-coated magnesium alloy. The results indicate that thin hafnium oxide film and new shallow grain boundaries were appeared on the coating surface. Surface oxidation and densification of the coating induced by the post treatment significantly decreased its susceptibility to corrosion. Moreover, the release of the residual stress produces a positive effect on suppressing the delaminating of the coating as magnesium is corroded. Consequently, the treated coating exhibits more positive corrosion potential, lower corrosion current density and higher polarization resistance than that of the untreated coating in Hanks’ solution. Salt spray test further reveals that the post-treated hafnium coating can provide a longer-term and more efficient protection for magnesium alloy.

离子束溅射氧化铪薄膜的能带特性

离子束溅射氧化铪薄膜的能带特性

Highly flexible resistive switching memory based on amorphous-nanocrystalline hafnium oxide films.

Flexible and transparent resistive switching memories are highly desired for the construction of portable and even wearable electronics. Upon optimization of the microstructure wherein an amorphous-nanocrystalline hafnium oxide thin film is fabricated, an all-oxide based transparent RRAM device with stable resistive switching behavior that can withstand a mechanical tensile stress of up to 2.12% is obtained. It is demonstrated that the superior electrical, thermal and mechanical performance of the ITO/HfOx/ITO device can be ascribed to the formation of pseudo-straight metallic hafnium conductive filaments in the switching layer, and is only limited by the choice of electrode materials. When the ITO bottom electrode is replaced with platinum metal, the mechanical failure threshold of the device can be further extended.

Optical characterization of hafnia films deposited by ALD on copper cold-rolled sheets by difference ellipsometry

Hafnium oxide (HfO2) thin films could be potentially used as thermal diffusion barrier coatings for copper absorbers used in solar thermal collectors. Atomic layer deposition (ALD) was used to deposit thin, dense, non-columnar HfO2 films on copper sheets, which are established base materials for solar absorbers. The aim of this work is to find a simple and efficient method for quantitative characterization of thin hafnium oxide films deposited on imperfect rough copper sheets. The difference ellipsometry applied in infrared region was found to be a practical tool for non-destructive characterization of thin films deposited onto metal surfaces even when these surfaces are imperfect. The presented method enables us not only to identify the presence of hafnium oxide but also to perform quantitative characterization, i.e. to determine the thickness of the film. Moreover, a simple method, in which the thickness is determined from the height of the structure in the difference ellipsometric data, is presented. This method is demonstrated on HfO2 film with nominal thickness 60nm deposited by ALD on copper cold-rolled sheet.

Study of electrical properties of hafnium oxide thin film based metal–insulator–metal capacitors: pre and post metallic annealing

Metal–insulator–metal (MIM) capacitors having hafnium oxide (HfO2) high-κ dielectric thin film were fabricated and subsequently studied for their electrical and micro-structural properties. The MIM capacitors were found to possess low leakage current density of about 2.7 × 10−9 A/cm2 at −1 V, high capacitance density of about 18.1 fF/μm2 at 0 V, 1 MHz and improved quadratic voltage coefficient of capacitance (VCC) of about 120 ppm/V2 at 1 MHz. The electrical properties of MIM capacitors are found to be governed by Frenkel–Poole mechanism at low and intermediate fields ( 1500 kV/cm). The dielectric thin films have amorphous structure which has been correlated with the electrical properties of MIM capacitors. The HfO2 thin film possess good micro-structural properties in term of low roughness, which is in agreement with the obtained electrical properties of thin film based MIM capacitors. Further, post metallic annealing of MIM capacitors results in decrease in leakage current density to ~5.1 × 10−10 A/cm2 at −1 V, increase in capacitance density to ~23.1 fF/μm2 at 0 V, 1 MHz and improvement in quadratic VCC to reach a value of ~95 ppm/V2 at 1 MHz. The electrical characteristics of as-fabricated and annealed MIM capacitors are in accordance with the International Technology Roadmap for Semiconductor 2013 guidelines. The obtained electrical properties suggest the possible use of MIM capacitors in analog/mixed-signal applications.

Science and technology of diamond films grown on HfO2 interface layer for transformational technologies

This paper describes the science underlying the synthesis and characterization of microcrystalline diamond (MCD) to ultrananocrystalline diamond (UNCD) films on hafnium oxide (HfO2) thin films, grown on flat Si substrates and micro-pillars on Si substrates, for the first time. HfO2 is used as a novel inter-phase layer for the integration of microcrystalline (1–3μm grain size), nanocrystalline (10–200nm grain size), and ultrananocrystalline diamond (3–5nm grain size) as coatings on substrates used in transformational technologies such as silicon, oxides, and metals that need protective corrosion/mechanical abrasion resistant coatings developed in this work. Atomic layer deposition was used to grow HfO2 films with 5, 10, 30 and 100nm in thickness, while hot filament chemical vapor deposition was used to grow diamond films, respectively. High resolution transmission electron microscopy, X-ray photoelectron and Raman spectroscopies revealed the formation of an atomic scale hafnium carbide (HfC) interphase layer on the surface of the HfO2 film, which provides efficient nucleation for diamond film growth to produce tailored diamond surfaces on flat Si substrates and Si micro-pillars on flat Si substrates, for new transformational micro/nano-electronics and other high-tech technologies.

Charge-Trapping Phenomena in HfO2-Based FeFET-Type Nonvolatile Memories

Ferroelectric field effect transistors (FeFETs) based on ferroelectric hafnium oxide (HfO2) thin films show high potential for future embedded nonvolatile memory applications. However, HfO2 films besides their recently discovered ferroelectric behavior are also prone to undesired charge trapping effects. Therefore, the scope of this paper is to verify the possibility of the charge trapping during standard operation of the HfO2-based FeFET memories. The kinetics of the charge trapping and its interplay with the ferroelectric polarization switching are analyzed in detail using the single-pulse $I_{D}$ – $V_{G}$ technique. Furthermore, the impact of the charge trapping on the important memory characteristics such as retention and endurance is investigated.

Hafnium carbide formation in oxygen deficient hafnium oxide thin films

On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO2−x) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfCx) at the surface during vacuum annealing at temperatures as low as 600 °C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfCx surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO2 thin films prepared and measured under identical conditions, the formation of HfCx was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films provides a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus, the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating.

Study of Hf-Ti-O Thin Film as High-k Gate Dielectric and Application for ETSOI MOSFETs

This work focused on the metal–oxide–semiconductor (MOS) capacitor and extremely thin silicon-on-insulator (ETSOI) p-type MOS field-effect transistor (pMOSFET) with laminated hafnium and titanium oxide (Hf-Ti-O) thin films as gate dielectric. The electrical behavior of the MOS capacitor shows that the capacitor with Hf-Ti-O gate dielectric has high performance with low equivalent oxide thickness (EOT, ~0.77 nm), small hysteresis (ΔVfb, ~4 mV), and gate current density of 0.33 A/cm2 at Vg = Vfb − 1 V. The dominant conduction mechanism of the Hf-Ti-O thin film (25°C to 125°C) was Schottky emission at lower gate voltage (−0.8 V to −0.2 V) and Fowler–Nordheim (F–N) tunneling at higher gate voltage (<−0.8 V). An ETSOI pMOSFET with 25 nm gate length (Lg) also exhibited good electrical properties with switch ratio of 3.2 × 104, appropriate threshold voltage of −0.16 V, maximum transconductance (Gmax) of 2.63 mS, drain-induced barrier lowering of 53 mV/V, and subthreshold swing of 65 mV/dec.

Effects of oxygen partial pressure and annealing temperature on the residual stress of hafnium oxide thin-films on silicon using synchrotron-based grazing incidence X-ray diffraction

Synchrotron radiation-based grazing incidence X-ray diffraction (GI-XRD) technique is employed here to estimate the residual stress of < 10nm thin hafnium oxide film deposited on Si (100) substrate at different argon/oxygen ratios using reactive rf sputtering. A decrease in residual stress, tensile in nature, is observed at higher annealing temperature for the samples deposited with increasing argon ratio in the Ar/O2 plasma. The residual stress of the films deposited at higher pAr (Ar:O2=4:1) is also found to be decreased with increasing annealing temperature. But the stress is more or less constant with annealing temperature for the films deposited at lower Ar/O2 (1:4) ratio. All the above phenomena can be explained on the basis of swelling of the interfacial layer and enhanced structural relaxation in the presence of excess Hf in hafnium oxide film during deposition.

Effect of post-deposition annealing on the structural and electrical properties of RF sputtered hafnium oxide thin films

Hafnium oxide films were deposited on silicon substrates by RF sputtering at room temperature. Post-deposition rapid thermal annealing of the sputtered HfO2 films was carried out in the temperature range of 400°C to 800°C in oxygen ambient. The structural properties ware studied by X-ray diffraction (XRD), where the enhancement in the crystallinity of HfO2 (1¯11) orientation was observed. The Capacitance —Voltage (C-V) and Current density —Voltage (J-V) characteristics of the annealed dielectric film were investigated employing Al/HfO2/Si Metal Oxide Semiconductor (MOS) capacitor structure. The flatband voltage (Vfb) and oxide charge density (Qox) were extracted from the high frequency (1 MHz) C-V curve. Leakage current was found to be minimum for the annealing temperature of 600°C.

Interface and electrical properties of ultra-thin HfO2 film grown by radio frequency sputtering

Interfacial composition and electrical properties of ultra-thin hafnium oxide (HfO2) films on p-type <100> Si substrate are reported. Hafnium oxide (HfO2) thin films are prepared using radio-frequency sputtering method and subsequently annealed at different temperature. The effect of post-deposition annealing on the interfacial and chemical state of HfO2/Si gate stack has been characterised by means of X-ray reflectivity and X-ray photoelectron spectroscopy studies. Peaks of X-ray photoelectron spectroscopy spectra at 530.50 and 532.25eV originate from Hf–O–Si bond illustrated the creation of Hf-silicate based interfacial layer at the high-k/Si interface. X-ray reflectivity fitting result also corroborated the formation of Hf silicate interfacial layer. Capacitance-voltage measurements revealed insignificant hysteresis in case of film annealed at 600°C. Interface trap density has been extracted using Terman method and is found to be 3.18×10−11cm−2eV−1 at −1.0V. Minimum equivalent oxide thickness (EOT) of 1.3nm was obtained for the film annealed at 600°C. The gate leakage current density of the HfO2 film annealed at 600°C is 1.5×10−5A/cm2 at a bias voltage of −2V.

Ferroelectricity in Rare-Earth Modified Hafnia Thin Films Deposited by Sequential Pulsed Laser Deposition

Room temperature ferroelectricity in pulsed laser deposited rare-earth doped hafnium oxide (HfO2) thin films is discussed. Maximum values of remnant polarizations (Pr) ∼13.5 and 12 μC/cm2 along with coercive fields (EC) ∼334 and 384 kV/cm are observed in 6 mol. % of rare-earth (Sm or Gd) doped-HfO2 thin films (Sm:HfO2 and Gd:HfO2), respectively. Piezoresponse force microscopy measurements confirmed ferroelectric nature of films by showing phase hysteresis and butterfly amplitude loops. It is noticed that wake-up cycles improved the remnant polarization and found to be necessary for the forming of well saturated hysteresis loops. Our results showed potential toward realization of future highly scaled non-volatile ferroelectric memories.

Evolution of microstructural and electrical properties of sputtered HfO2 ceramic thin films with RF power and substrate temperature

Hafnium oxide (HfO2) ceramic thin films were deposited on p-type silicon substrate by radio frequency magnetron sputtering at various RF powers and substrate temperatures. The morphological and electrical properties of the sputtered films were investigated and a correlation between the surface and interface properties of the HfO2 films was established with the variation of sputtering parameters. The evolution of monoclinic structure of the hafnium oxide thin films was observed by XRD studies. The surface of the HfO2 ceramic thin films became smooth with the decrease in grain size for higher power and growth temperature. The characteristic FTIR absorption peaks in the range from 550cm−1 to 900cm−1 depicted the formation of Hf–O bond for all the samples. The oxide charge density and leakage current density was found to be increased with the increase in RF power and substrate temperature, which was mainly due to the evolution of smaller grains. HfO2 thin films, grown at room temperature with a RF power of 150W, have shown better electrical properties.

Changes in the Young Modulus of hafnium oxide thin films

Hafnium-oxide (HfO2)-based materials have been extensively researched due to their excellent optical and electrical properties. However, the literature data on the mechanical properties of these materials and its preparation for heavy machinery application is very limited. The aim of this work is to deposit hafnium oxide thin films by DC reactive magnetron sputtering with different Young’s Modulus from the Ar/O2 concentration variation in the deposition chamber. The thin films were deposited by DC reactive magnetron sputtering with different Ar/O2 gas concentrations in plasma. After deposition, HfOx thin films were characterized through XRD, AFM, RBS and XRF. In this regard, it was observed that the as-deposited HfO2 films were mostly amorphous in the lower Ar/O2 gas ratio and transformed to polycrystalline with monoclinic structure as the Ar/O2 gas ratios grows. RBS technique shows good compromise between the experimental data and the simulated ones. It was possible to tailored the Young Modulus of the films by alter the Ar/O2 content on the deposition chamber without thermal treatment.

Investigation of microstructure, micro-mechanical and optical properties of HfTiO4 thin films prepared by magnetron co-sputtering

Titania (TiO2) and hafnium oxide (HfO2) thin films are in the focus of interest to the microelectronics community from a dozen years. Because of their outstanding properties like, among the others, high stability, high refractive index, high electric permittivity, they found applications in many optical and electronics domains. In this work discussion on the hardness, microstructure and optical properties of as-deposited and annealed HfTiO4 thin films has been presented. Deposited films were prepared using magnetron co-sputtering method. Performed investigations revealed that as-deposited coatings were nanocrystalline with HfTiO4 structure. Deposited films were built from crystallites of ca. 4–12nm in size and after additional annealing an increase in crystallites size up to 16nm was observed. Micro-mechanical properties, i.e., hardness and elastic modulus were determined using conventional load-controlled nanoindentation testing. the annealed films had 3-times lower hardness as-compared to as-deposited ones (∼9GPa). Based on optical investigations real and imaginary components of refractive index were calculated, both for as-deposited and annealed thin films. The real refractive index component increased after annealing from 2.03 to 2.16, while extinction coefficient increased by an order from 10−4 to 10−3. Structure modification was analyzed together with optical energy band-gap, Urbach energy and using Wemple–DiDomenico model.

Study of hafnium oxide thin films deposited by RF magnetron sputtering under glancing angle deposition at varying target to substrate distance

Glancing angle deposition of HfO2 thin films by RF magnetron sputtering technique has been explored with respect to two vital deposition parameters visualizing angle of deposition (at 82° and 86° glancing angles) and target to substrate distance, DTS in the range 70–125mm. AFM and spectroscopic ellipsometry measurements show that at optimum DTS of 110mm and glancing angle 82°, the films exhibit nanostructures with an estimated lowest refractive index ∼1.63 at 550nm. For both the deposition angles, with decrease in DTS the round shaped grains of the film surface as obtained from AFM images are found to coalesce and produce films with elliptical shaped grains at shorter target to substrate distance. With increase in DTS the deposition rate first decreases up to DTS=110mm and subsequently increases. The phenomenon has been ascribed to the competition between reduced deposition flux density and increased sticking coefficient due to decrease in adatom kinetic energy with the increase in DTS. GIXRD measurement reveals that all the films exhibit monoclinic crystal structure. At lower DTS, the crystallinity has improved with increase in deposition angle whereas at higher DTS (>90mm) the crystallinity becomes poorer with increase in deposition angle. The fact has been explained in light of variation of shadowing effect and deposition rate.

Ferroelectricity in undoped hafnium oxide

We report the observation of ferroelectric characteristics in undoped hafnium oxide thin films in a thickness range of 4–20 nm. The undoped films were fabricated using atomic layer deposition (ALD) and embedded into titanium nitride based metal-insulator-metal (MIM) capacitors for electrical evaluation. Structural as well as electrical evidence for the appearance of a ferroelectric phase in pure hafnium oxide was collected with respect to film thickness and thermal budget applied during titanium nitride electrode formation. Using grazing incidence X-Ray diffraction (GIXRD) analysis, we observed an enhanced suppression of the monoclinic phase fraction in favor of an orthorhombic, potentially, ferroelectric phase with decreasing thickness/grain size and for a titanium nitride electrode formation below crystallization temperature. The electrical presence of ferroelectricity was confirmed using polarization measurements. A remanent polarization Pr of up to 10 μC cm−2 as well as a read/write endurance of 1.6 × 105 cycles was measured for the pure oxide. The experimental results reported here strongly support the intrinsic nature of the ferroelectric phase in hafnium oxide and expand its applicability beyond the doped systems.

Surface and interface studies of RF sputtered HfO2 thin films with working pressure and gas flow ratio

In this work, hafnium oxide (HfO2) thin films were deposited on p-type silicon substrate by radio frequency magnetron sputtering at various working pressure ranging from 4 × 10−3 to 1 × 10−2 mbar and Ar/O2 flow ratio from 1:4 to 4:1. The morphological and electrical properties of the sputtered films were investigated and a correlation between the surface and electrical properties of the HfO2 films was established with the variation of sputtering parameters. The evolution of monoclinic structure of the hafnium oxide thin films was observed by XRD studies. The surface of the HfO2 films became rough with the increase in grain size at the sputter pressure of 8 × 10−3 mbar and Ar/O2 gas flow ratio of 1:4. The formation of HfO2 bond was seen from FTIR spectra. The oxide charge density has a lower value for the sputter pressure of 8 × 10−3 mbar and Ar/O2 gas flow ratio of 1:4 due to the evolution of larger grains. The interface charge density was found to be minimum at a sputter pressure of 8 × 10−3 mbar.

AFM applications to study the morphology of HfO2 multilayer thin films

Atomic force microscopy (AFM) is a technique that has extensively been used to reveal details on surfaces using different scanning techniques. Multilayer hafnium oxide (HfO2) thin films deposited by electron beam evaporation at room temperature on three different glass substrates (including Corning, commercial and wind screen glasses) are discussed for their surface analysis using atomic force microscopy. AFM characterization involves structural morphology, grain size and grain distribution, etc. AFM micrographs show that the films are uniform and crack-free. The average roughness, maximum peak to valley height, root mean square (RMS) roughness, surface skewness and kurtosis parameters are investigated to analyze the surface morphology of HfO2 multilayer thin films. Results show that the RMS surface roughness decreases for commercial glass substrate to Corning to wind screen glass. On the other hand grain size demonstrates an opposite trend. Thus an increase in grain boundary area with decreasing grain size might be associated with the rise in RMS surface roughness. These films show an almost homogeneous and uniform distribution of grains according to AFM images.