Properties Of HfO2 Thin Films Research Articles

Effects of ion irradiation induced phase transformations and oxygen vacancies on the leakage current characteristics of HfO2 thin films deposited on GaAs

Abstract We report on the ion-induced phase transformations, defect dynamics related to oxygen vacancies and the resulting leakage current characteristics of RF sputtered HfO2 thin films grown on GaAs. A systematic growth of HfO2 grains and Ion prompted phase transformations of HfO2 to crystalline phases such as monoclinic and tetragonal/orthorhombic (mixed phase) in otherwise amorphous HfO2 thin films have been observed after irradiation. At lower fluences, Ion induced enhancement in the dielectric properties of HfO2 thin films resulted in a reduction in the leakage current, whereas ion prompted defect formation at higher fluences caused a systematic increase in the leakage current density. Further, the effects of Poole-Frenkel (PF) tunneling and Fowler-Nordheim (FN) tunneling on the leakage current have also been investigated. These mechanisms showed the existence of impurities in the as-grown films. Photoluminescence (PL) study suggests the variation in the defect configuration related to O-vacancies and slight shift in the peak positions due to SHI irradiation are responsible for the observed changes in electrical characteristics. This study offers worthwhile information for considering the effects of electronic excitation prompted defect annealing or defect creation on the performance of HfO2/GaAs based photonic and optoelectronic devices, particularly, when such devices are operated in a radiation harsh environment.

Effects of Dy on structural, morphology, optical, and resistive switching properties of HfO2 thin films

This paper studies the effect of Dy on the structure, morphology, and optical properties of HfO2 thin films deposited on fused silica substrates and the optical transparency and resistive switching (RS) behavior of the thin films as an active insulator layer in Ag/active insulator layer/ITO/glass memories. Thin films were deposited by spin-coating using a precursor solution obtained by the Pechini-type sol-gel method. The structural analysis revealed that the insertion of Dy ions into the HfO2 lattice caused the phase transformation from the monoclinic to the cubic phase. Morphological analysis revealed that the thin films had thicknesses between 98 and 101 nm, and their surfaces were composed of 3D islands formed by aggregates of spherical particles ranging from 8 to 5 nm. The active insulator layers had thicknesses ranging from 235 to 218 nm, with no cavities or cracks between them. The optical transparency of the active insulator layer/ITO/glass memory structures was between 70 and 87 %. Optical transmittance, optical bandgap, and optical constants were modified incorporating Dy ions into HfO2 thin films compared to the undoped HfO2 thin films. Incorporating Dy ions into HfO2 increased oxygen vacancies in the active insulator layers. The memory with 10 w% of Dy had the highest resistance off/on ratio of 9.04 compared with undoped HfO2 memory. Also, the conduction mechanism in the high resistive state (HRS) of the memory with 10 w% of Dy was related to ohmic conduction and space charge limited conduction (SCLC).

Enhanced physical and electrical properties of HfO2 deposited by atomic layer deposition using a novel precursor with improved thermal stability

With the increased application range of Hf-based oxides in memory devices, such as high-k capacitors, gate dielectrics, and ferroelectric devices, improvement in the properties of HfO2 thin films have been received considerable attention. To achieve improved properties HfO2 thin films deposited by atomic layer deposition (ALD), one strategic way is to develop a process incorporating a new precursor with improved thermal stability. In this paper, HfO2 thin films were deposited by ALD process using a novel precursor modified with a cyclopentadienyl-based ligand to improve thermal stability, and the improved properties were investigated. The ALD process window has been extended to higher temperatures. In addition, with increases in deposition temperature, the impurity concentration, surface roughness, density, and crystallinity of HfO2 were improved. Finally, the HfO2 thin film deposited at a high temperature significantly reduced the leakage current (from 5.2 × 10−7 A/cm2 to 3.1 × 10−9 A/cm2 measured at 0.7 V) without a significant change in dielectric constant, and the remanent polarization characters were also observed. Therefore, we suggest that HfO2 deposited using the proposed hafnium precursor can be applied as a key high-k component in next-generation memory devices and ferroelectric-based semiconductor devices.

Interplay of Precursor and Plasma for The Deposition of HfO2 via PEALD: Film Growth and Dielectric Properties

AbstractHfO2 thin films are appealing for microelectronic applications such as high‐κ dielectric layers, memristors, and ferroelectric memory devices. To fulfill the different requirements of each application, the properties of the deposited material need to be tuned accordingly. In this context, plasma‐enhanced atomic layer deposition (PEALD) is a powerful processing route to tailor the properties of HfO2 thin films, especially at low temperatures. Herein, a comprehensive bottom‐up approach is presented, ranging from the synthesis of molecularly engineered Hf precursors to the development of a HfO2 PEALD process and a detailed evaluation where plasma can be exploited to tune the dielectric properties. With the example of the newly synthesized bis‐(dialkylamido)‐bis‐(formamidinato) Hf(IV) precursor, [Hf{η2‐(iPrN)2CH}2(NMe2)2] which is reactive, thermally robust and volatile, successful implementation in a PEALD process for HfO2 at low temperatures is demonstrated. The typical atomic layer deposition (ALD) characteristics of precursor saturation, linearity, and ALD temperature window are demonstrated with constant growth of 0.7 Å per cycle from 125 to 200 °C, yielding high‐purity layers. The effect of plasma pulse duration on the chemical composition alongside structural, topographical, as well as dielectric properties of the films is investigated. For the latter, the films are incorporated in metal‐insulator semiconductor (MIS) structures.

Characterization of Structural, Optical, Corrosion, and Mechanical Properties of HfO2 Thin Films Deposited Using Pulsed DC Magnetron Sputtering.

Various properties of HfO2, such as hardness, corrosion, or electrical resistance, depend on the method and the conditions of deposition. In this work, a thorough comparison of scarcely investigated mechanical properties of HfO2 thin films deposited with different conditions of reactive magnetron sputtering process is presented. Four thin films were sputtered in processes that varied in plasma ignition method (continuous or sequential) and target-substrate distance. The structural characteristics of the HfO2 thin films were examined using Raman spectroscopy and X-ray diffraction measurements. Furthermore, the optoelectronic properties were determined based on transmittance and current-voltage characteristics. The mechanical properties of the HfO2 thin films were determined using nanoindentation and scratch test. In turn, the corrosion properties were determined by analyzing the voltametric curves. The transparent HfO2 thin films deposited in the continuous process are characterized by better corrosion resistance than the same layer formed in the sequential process, regardless of the target-substrate distance (8 cm or 12 cm). Furthermore, these samples are also characterized by the highest value of Young's modulus and scratch resistance. The combination of good corrosion and scratch resistance could contribute to the new application of HfO2 as a corrosion protective material.

Preparation of Remote Plasma Atomic Layer-Deposited HfO2 Thin Films with High Charge Trapping Densities and Their Application in Nonvolatile Memory Devices.

Optimization of equipment structure and process conditions is essential to obtain thin films with the required properties, such as film thickness, trapped charge density, leakage current, and memory characteristics, that ensure reliability of the corresponding device. In this study, we fabricated metal-insulator-semiconductor (MIS) structure capacitors using HfO2 thin films separately deposited by remote plasma (RP) atomic layer deposition (ALD) and direct-plasma (DP) ALD and determined the optimal process temperature by measuring the leakage current and breakdown strength as functions of process temperature. Additionally, we analyzed the effects of the plasma application method on the charge trapping properties of HfO2 thin films and properties of the interface between Si and HfO2. Subsequently, we synthesized charge-trapping memory (CTM) devices utilizing the deposited thin films as charge-trapping layers (CTLs) and evaluated their memory properties. The results indicated excellent memory window characteristics of the RP-HfO2 MIS capacitors compared to those of the DP-HfO2 MIS capacitors. Moreover, the memory characteristics of the RP-HfO2 CTM devices were outstanding as compared to those of the DP-HfO2 CTM devices. In conclusion, the methodology proposed herein can be useful for future implementations of multiple levels of charge-storage nonvolatile memories or synaptic devices that require many states.

Uniformity of HfO2 Thin Films Prepared on Trench Structures via Plasma-Enhanced Atomic Layer Deposition.

In this study, we assessed the physical and chemical properties of HfO2 thin films deposited by plasma-enhanced atomic layer deposition (PEALD). We confirmed the self-limiting nature of the surface reactions involved in the HfO2 thin film's growth by tracing the changes in the growth rate and refractive index with respect to the different dose times of the Hf precursor and O2 plasma. The PEALD conditions were optimized with consideration of the lowest surface roughness of the films, which was measured by atomic force microscopy (AFM). High-resolution X-ray photoelectron spectroscopy (XPS) was utilized to characterize the chemical compositions, and the local chemical environments of the HfO2 thin films were characterized based on their surface roughness and chemical compositions. The surface roughness and chemical bonding states were significantly influenced by the flow rate and plasma power of the O2 plasma. We also examined the uniformity of the films on an 8″ Si wafer and analyzed the step coverage on a trench structure of 1:13 aspect ratio. In addition, the crystallinity and crystalline phases of the thin films prepared under different annealing conditions and underlying layers were analyzed.

Structural and electronic properties of HfO2 films on Si through H2O2 wet oxidation with improved thermal stability

The thermal stability and material properties of HfO2 thin films on Si substrates with and without H2O2 wet chemical oxidation were investigated. The HfO2 samples were deposited through plasma‐enhanced atomic layer deposition and subjected to thermal annealing. They were then examined using X‐ray diffraction, transmission electron microscopy, X‐ray photoelectron spectroscopy, reflection electron energy loss spectroscopy, and conductive atomic force microscopy. For the Si substrate without H2O2 wet chemical oxidation, a native oxide (~1.8 nm) was formed on the substrate before HfO2 deposition. After the annealing process at 600°C, the band gap (Eg) of the HfO2 films increased from 6.0 to 6.2 eV due to the diffusion of Si into HfO2. Furthermore, the conduction and valence band offsets (ΔEc and ΔEv, respectively) between HfO2 and Si changed from 1.02 to 1.42 and 3.86 to 3.66 eV, respectively. After the H2O2 wet oxidation of the Si substrate, a 1.5‐nm chemical oxide was formed instead of a native oxide. The band offset and Eg values of HfO2 were similar before and after 600°C annealing (ΔEv = 3.86 eV, ΔEc = 1.02 eV, and Eg = 6.0 eV), implying the high thermal stability of the HfO2 films. Accordingly, wet oxidation not only prevents diffusion from chemical oxide but also markedly improves the oxide leakage current, which is useful for developing highly efficient and thermally stable HfO2 gate oxides in Si‐based integrated circuit devices.

Plasma-Enhanced Atomic Layer Deposition of HfO2 with Substrate Biasing: Thin Films for High-Reflective Mirrors.

Tuning ion energies in plasma-enhanced atomic layer deposition (PEALD) processes enables fine control over the material properties of functional coatings. The growth, structural, mechanical, and optical properties of HfO2 thin films are presented in detail toward photonic applications. The influence of the film thickness and bias value on the properties of HfO2 thin films deposited at 100 °C using tetrakis(dimethylamino)hafnium (TDMAH) and oxygen plasma using substrate biasing is systematically analyzed. The HfO2 films deposited without a substrate bias show an amorphous microstructure with a low density, low refractive index, high incorporation of residual hydroxyl (OH) content, and high residual tensile stress. The material properties of HfO2 films significantly improved at a low bias voltage due to the interaction with oxygen ions accelerated to the film. Such HfO2 films have a higher density, higher refractive index, and lower residual OH incorporation than films without bias. The mechanical stress becomes compressive depending on the bias values. Further increasing the ion energies by applying a larger substrate bias results in a decrease of the film density, refractive index, and a higher residual OH incorporation as well as crystalline inclusions. The comparable material properties of the HfO2 films have been reported using tris(dimethylamino)cyclopentadienyl hafnium (TDMACpH) in a different apparatus, indicating that this approach can be transferred to various systems and is highly versatile. Finally, the substrate biasing technique has been introduced to deposit stress-compensated, crack- and delamination-free high-reflective (HR) mirrors at 355 and 532 nm wavelengths using HfO2 and SiO2 as high and low refractive index materials, respectively. Such mirrors could not be obtained without the substrate biasing during the deposition because of the high tensile stress of HfO2, leading to cracks in thick multilayer systems. An HR mirror for 532 nm wavelength shows a high reflectance of 99.93%, a residual transmittance of ∼530 ppm, and a low absorption of ∼11 ppm, as well as low scattering losses of ∼4 ppm, high laser-induced damage threshold, low mechanical stress, and high environmental stability.

Ferroelectric Hf0.5Zr0.5O2 thin films deposited epitaxially on (110)-oriented SrTiO3

Hf0.5Zr0.5O2 (HZO) thin films have been deposited on (110)-oriented SrTiO3 (STO) substrates buffered with epitaxial La0.7Sr0.3MnO3 (LSMO) by pulsed laser deposition. The HZO/LSMO/STO heterostructures show smooth surface and clear interface. It is observed that ferroelectric orthorhombic HZO is enhanced, as non-polar tetragonal HZO is suppressed with the increasing LSMO thickness or decreasing HZO thickness. Completely orthorhombic HZO films are achieved with desired LSMO and HZO thickness. These HZO films are (111)-oriented with in-plane [2¯11] and [01¯1] directions along LSMO [11¯0] and [001], respectively, and exhibit ferroelectric properties at room temperature with an optimized remanent polarization around 26 μC/cm2 without the need of a wake-up process, a long retention up to 104 s and a fatigue endurance up to 109 cycles. Epitaxial HfO2-based films with robust ferroelectric properties deposited on (110)-oriented STO substrates provide additional opportunities to understand the profound effects of orientation, strain, and interface microstructures on the metastable polar phases and ferroelectric properties of HfO2 thin films.

Compensation Charge Control and Modeling for Reproducing Negative Capacitance Effect of Hafnia Ferroelectric Thin Films

AbstractTo enable continuing development of the performance of highly integrated semiconductor chips, it is necessary to dramatically lower the power consumption of transistors. The discovery of the negative capacitance (NC) effect and the ferroelectric properties of HfO2 thin films have raised the possibility of surpassing the known physical limitations of the 60 mV subthreshold slope of the current MOSFETs. However, for commercial application, stable reproducibility of the voltage drop effect due to the ferroelectric polarization and a model that can fully interpret this phenomenon must be obtained. Despite intense recent efforts, guidance for the design of devices for mass production based on the NC effect is currently unavailable. This study has directly observed the NC effect and confirmed that the NC effect can be controlled through analysis based on the equivalent circuit theory. It is experimentally verified that the NC effect is caused by an imbalance between the amount of polarization switching and the amount of charge supplied to compensate for such switching in the initial stage of the applied voltage pulse. The results suggest that a gate structure or peripheral circuit that can actively respond to polarization switching is necessary to implement a novel MOSFET with breakthrough power consumption.

Structural, Optical and Electrical Properties of HfO2 Thin Films Deposited at Low-Temperature Using Plasma-Enhanced Atomic Layer Deposition.

HfO2 was deposited at 80–250 °C by plasma-enhanced atomic layer deposition (PEALD), and properties were compared with those obtained by using thermal atomic layer deposition (thermal ALD). The ALD window, i.e., the region where the growth per cycle (GPC) is constant, shifted from high temperatures (150–200 °C) to lower temperatures (80–150 °C) in PEALD. HfO2 deposited at 80 °C by PEALD showed higher density (8.1 g/cm3) than those deposited by thermal ALD (5.3 g/cm3) and a smooth surface (RMS Roughness: 0.2 nm). HfO2 deposited at a low temperature by PEALD showed decreased contaminants compared to thermal ALD deposited HfO2. Values of refractive indices and optical band gap of HfO2 deposited at 80 °C by PEALD (1.9, 5.6 eV) were higher than those obtained by using thermal ALD (1.7, 5.1 eV). Transparency of HfO2 deposited at 80 °C by PEALD on polyethylene terephthalate (PET) was high (> 84%). PET deposited above 80 °C was unable to withstand heat and showed deformation. HfO2 deposited at 80 °C by PEALD showed decreased leakage current from 1.4 × 10−2 to 2.5 × 10−5 A/cm2 and increased capacitance of approximately 21% compared to HfO2 using thermal ALD. Consequently, HfO2 deposited at a low temperature by PEALD showed improved properties compared to HfO2 deposited by thermal ALD.

Influence of high energy ion irradiation on structural, morphological and optical properties of high-k dielectric hafnium oxide (HfO2) thin films grown by atomic layer deposition

Abstract Modifications and resulting changes in various properties of nanocrystalline HfO2 high-k dielectric thin films with nominal thickness of 20 nm grown by atomic layer deposition technique on silicon and glass substrates were investigated as a function of swift heavy ions (SHI) irradiation. In the present work, our attention is to study the electronic excitation induced modifications in HfO2 thin films cause of formation of defects by 120 MeV Au9+(SHI) irradiation. For the same purpose, the annealed (500 °C) HfO2 thin films were irradiated with the varying fluence in the range of 1E11 to 1E13 ions/cm2. The virgin and irradiated representative HfO2 thin films were investigated by various techniques. The substantial root mean square (RMS) surface roughness (0.5–1 nm) and variation in grain size (40–52 nm) as a function of Au9+ ions irradiation were determined using atomic force microscope (AFM). The optical properties of HfO2 thin films were analyzed by measuring absorbance and transmission (54–62%) spectra in 200–700 nm wavelength range followed by calculation of optical band gap (Eg). The photoluminescence (PL) spectra obtained at excitation wavelength 220 nm indicate the formation of defects due to SHI irradiation. A change in excitation wavelength (220–260 nm) causes the shift in emission peaks towards higher wavelength. Structural investigations have been carried by Grazing Incidence X-ray Diffraction (GIXRD) techniques which reveal the variation in crystallite size as a function of different fluence. The results of a systematic XPS study of virgin and SHI irradiated samples shows the shifting of Hf 4f and O 1s peaks towards lower binding energy as compared to virgin sample. O K-edge XANES were performed to understand the ion-beam irradiation induced defect formation and their consequences on the electronic structure of HfO2 thin films. The obtained peaks in Rutherford backscattering spectrometry (RBS) affirm the existence of Hf and O elements and width of the peaks determine the sample thickness (20 nm).

Domain orientation relationship of orthorhombic and coexisting monoclinic phases of YO1.5-doped HfO2 epitaxial thin films

Domain structures with ferroelectric and ferroelastic characteristics of the epitaxial thin films of the polar orthorhombic phase of 7 mol % YO1.5-doped HfO2 (YHO) were investigated by aberration-corrected scanning transmission electron microscopy (STEM). The high-angle annular dark-field (HAADF)-STEM images of the YHO thin film reveal that the individual domain size is approximately 10 nm. Multislice simulation demonstrated that STEM imaging can detect individual domains on the nanoscale avoiding superposition with other domains in the projection direction. The STEM analysis of the domain structure of the polar orthorhombic phase elucidated that the orientation relationship between neighboring domains was affected by two factors: (i) tilt or twist relationship between the longest b-axis in the domains, and (ii) parallel or perpendicular relationship between the rotation axis and the longest b-axis. Corresponding to the longest b-axis orientation, two types of domain walls (DWs) exist: the strained DWs and the less strained ones. The latter should move more easily with less strain, and are of the tilt type with the longest b-axis parallel to the domain rotation axis. STEM imaging also reveals the coexistence of a nonpolar monoclinic phase, which deforms the orthorhombic phase around the monoclinic phase. This factor should also diminish the DW mobility. We propose that the formation of the monoclinic phase should be inhibited and that the longest b-axis should be oriented in the in-plane direction for improving the ferroelectric properties. The two-dimensional tensile stress is expected to be preferred for preparing a-/c-oriented YHO epitaxial thin films. The elastic constraint plays an important role for these purposes for controlling the ferroelectric properties of HfO2 thin films.

The gas sensing properties of hafnium oxide thin films depending on the annealing environment

The main focus of this study is to investigate the NO2 gas-sensing properties of HfO2 thin films, taking into the account the importance of the annealing environment and temperature. HfO2 films were produced with 10 nm and 20 nm thicknesses by atomic layer deposition (ALD). They were annealed under N2 and O2 environment with rapid thermal annealing system at two different temperatures. It was found that the NO2 responses of annealed in N2 environment were higher than annealed in O2 environment. The response of 10 nm thickness HfO2 thin film was calculated 22% for N2 environment whereas, it was calculated 18% for O2 environment. The highest gas response is obtained for 10 nm thickness of HfO2 thin film annealed in N2 environment. The performance of the HfO2 thin films reveals that the gas responses rely on annealing temperature as well as annealing atmosphere. The linear dependences of the sensitivity were also observed as the NO2 gas concentrations varied from 10 ppm to 30 ppm in logarithmic forms, indicating that HfO2 thin films offer promising potential for future practical applications in monitoring the NO2 gas.

Modification of various properties of HfO2 thin films obtained by changing magnetron sputtering conditions

In this work, properties of hafnium dioxide (HfO2) thin films deposited by magnetron sputtering with different powers (i.e. 200W, 400W and 600W) were described. Based on microstructure measurements obtained by X-ray diffraction, Raman scattering and transmission electron microscopy method it was observed that there is a significant influence of the sputtering power on investigated properties of HfO2 thin films. Increase of the sputtering power caused, e.g. an increase of average crystallite size and surface roughness. Microstructure of thin films deposited with lower power was composed from a large number of voids that resulted in significant changes of their optical and mechanical properties. Results of optical studies showed that all deposited thin films were well transparent in a visible light range. Refractive index increased gradually with an increase of deposition power from 1.86 (200W) to 2.09 (600W). Performed investigations of mechanical properties revealed that hardness and Young's elastic modulus of HfO2 thin films increased with an increase of the sputtering power.

Effect of angle of deposition on micro-roughness parameters and optical properties of HfO2 thin films deposited by reactive electron beam evaporation

Oblique angle deposited oxide thin films, in which refractive index profiles can be tailored across depth by tuning their microstructure using varying angle of deposition, have opened up new dimensions in fabrication of optical interference devices. Since surface morphology plays an important role for the qualification of these thin film devices for optical or other applications, it is important to investigate morphological properties of obliquely deposited thin films. In the present work, a set of HfO2 thin films have been deposited at several oblique angles. Morphological parameters of such thin films viz., correlation length, intrinsic roughness, fractal spectral strength, etc., have been determined through suitable modelling of extended power spectral density measured by atomic force microscopy. It has been found that intrinsic roughness and fractal spectral strength show an interesting behaviour with deposition angle and the same has been discussed in the light of atomic shadowing and re-emission and diffusion of ad-atoms. Further refractive index and thickness of such thin films have been estimated from optical transmission spectra through suitable modelling. Refractive index of such thin film varies from 1.93 to 1.37 as the deposition angle varies from normal to glancing angle (80°). Further, refractive index and grain size depict an opposite trend with deposition angle. This variation has been explained in terms of varying film porosity and column slanting with angle of deposition.

Low-Concentration NO2 Gas Sensor Based on HfO2 Thin Films Irradiated by Ultraviolet Light

In this work, we investigate the gas-sensing properties of HfO2 thin films enhanced by ultraviolet (UV) light irradiation. The films were deposited on silicon substrate by atomic layer deposition (ALD) and annealed at 800°C. X-ray diffraction (XRD) and atomic force microscopy (AFM) were used for characterization of the samples, which revealed that the degree of crystallinity and electrical properties of the HfO2 thin films were affected by the annealing temperature. Different film thicknesses (20 nm and 10 nm) were used for gas-sensing measurements. The gas-sensing properties of the films were affected by the UV irradiation time, with improvements in sensor properties observed for samples with more than 30 min of irradiation. The maximum response was found for the 10-nm sensor annealed at 800°C. Moreover, a linear dependence on NO2 concentration was observed for the response, suggesting that the sensing layer is highly suitable for detecting NO2 gas concentrations as low as 1 ppm.

SHI induced effects on the electrical and optical properties of HfO2 thin films deposited by RF sputtering

The continuous downscaling of Metal Oxide Semiconductor (MOS) devices has reached a limit with SiO2 as a gate dielectric material. Introducing high-k dielectric materials as a replacement for the conservative SiO2 is the only alternative to reduce the leakage current. HfO2 is a reliable and an impending material for the wide usage as a gate dielectric in semiconductor industry. HfO2 thin films were synthesized by RF sputtering technique. Here, we present a study of Swift Heavy Ion (SHI) irradiation with100MeV Ag ions for studying the optical properties as well as 80MeV Ni ions for studying the electrical properties of HfO2/Si thin films. Rutherford Backscattering Spectrometry (RBS), Field Emission Scanning Electron Microscope (FESEM), energy-dispersive X-ray spectroscopy (EDS), profilometer and I–V (leakage current) measurements have been employed to study the SHI induced effects on both the structural, electrical and optical properties.

Microstructure, optical, electrical properties, and leakage current transport mechanism of sol–gel-processed high-k HfO2 gate dielectrics

Deposition of high-k HfO2 gate dielectric films on n-type Si and quartz substrates by sol–gel spin-on coating technique has been performed and the structural, optical and electrical characteristics as a function of annealing temperature have been investigated. The structural and optical properties of HfO2 thin films related to annealing temperature are investigated by X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV–vis), and spectroscopic ellipsometry (SE). Results indicate that the monoclinic form of HfO2 appears when temperature rises through and above 500°C. The reduction in band gap is observed with the increase of annealing temperature. Moreover, the increase of refractive index (n) and density and the decrease of the extinction coefficient with the increase of annealing temperature are obtained by SE measurements. Additionally, the electrical properties based on Al/Si/HfO2/Al capacitor are analyzed by means of the high frequency capacitance–voltage (C–V) and the leakage current density–voltage (J–V) characteristics. And the leakage current conduction mechanisms as functions of annealing temperatures are also discussed.