Hafnium Dioxide Thin Films Research Articles

Microstructural and Current-voltage Characteristics in Mo/HfO2/n‑Si Based Metal-Insulator-Semiconductor (MIS) Diode using Different Methods for Optoelectronic Device Applications

This paper investigates the effect of hafnium dioxide (HfO2) thin film as interlayer between the Mo and n-Si semiconductor on the electrical characteristics of the Mo/n-Si Schottky diode (SD). The X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) results confirmed that HfO2 films were formed on the n-Si semiconductors. The image from SEM and AFM displays that the deposited HfO2 thin film had a uniform appearance good smoothness of the surface. The smooth surfaces of the insulating layer strongly influence the electrical properties of the diode. The electrical properties of the Mo/HfO2/n-Si metal/insulator/semiconductor (MIS) diode were obtained via current-voltage (I-V) measurements in the voltage range from −3 V to +3 V at room temperature. A better rectifying ability and a reduced reverse leakage current were demonstrated by the MIS diode. The MIS dide's barrier height (Bh) and ideality factor value were calculated to be 0.85 eV and 1.21, respectively. The MIS diode was able to achieve a higher b, which allowed the HfO2 interlayer to change BH. The calculated BH values from the I-V, Hernandez, Cheung, and Norde approaches were comparable to one another, demonstrating their validity and consistency. The MIS diode's forward bias log (I) - log (V) curve demonstrated that it was ohmic in low-voltage regimes and that conduction was space-charge-limited in high-voltage regimes. However, for the MIS diode, the Poole-Frenkel and Schottky emissions are the dominant current conduction mechanisms in the lower and higher bias regions. These outcomes indicate that the HfO2 film can be chosen as dielectric materials in the construction of MIS devices.

High Performance and High Yield Solution Processed IGZO Thin Film Transistors Fabricated with Low‐Temperature Annealed Hafnium Dioxide Gate Dielectric

AbstractSolution‐processed microelectronics offer advantages, including cost‐effectiveness, higher energy efficiency, and compatibility with rapid prototyping compared to their counterparts fabricated through traditional semiconductor manufacturing processes. Unfortunately, solution‐processed transistors exhibit wide performance variability and low yield. In this work, a solution‐processed transparent indium gallium zinc oxide (IGZO) thin film transistor with a low temperature‐annealed hafnium oxide dielectric layer is described. Post‐annealing temperatures for the sol–gel hafnium dioxide thin film are reduced to below 200 °C, significantly expanding the range of substrates on which the metal oxide dielectric can be deposited. The fabricated devices exhibit excellent characteristics with high field‐effect mobilities of over 85 cm2 V−1 s−1, along with low subthreshold swing below 140 mV dec−1, high on/off ratios, and near‐zero threshold voltages when operating stably at low‐operating voltages of 2 V. The solution processed transparent hafnium dioxide gate dielectric IGZO transistors are shown to exhibit comparatively significantly lower device variation and high yield, allowing for the reproducible fabrication of large‐area and transparent solution processed microelectronics systems.

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

The effects of reactive and sputtering oxygen partial pressure on the structure, stoichiometry and optical properties of hafnium oxide (HfO2) thin films have been systematically investigated. The electron cyclotron resonance ion beam deposition (ECR-IBD) technique was used to fabricate the films on to JGS-3 fused silica substrates. The amorphous structure of HfO2 films were determined by X-ray Diffraction. Energy-dispersive X-ray Spectroscopy and Rutherford Backscattering Spectrometry were carried out for the composition and stoichiometry analysis, where this suggests the formation of over-stoichiometric films. The data suggests that the O:Hf ratio ranges from 2.4 – 4.45 to 1 for the ECR-IBD fabricated HfO2 films in this study. The transmission and reflectance spectra of the HfO2 films were measured over a wide range of wavelengths (λ = 185 – 3000 nm) by utilizing a spectrophotometer. The measured spectra were analyzed by an optical fitting software, which utilizes the model modified by O'Leary, Johnson and Lim, to extract the optical properties, refractive index (n) and the bandgap energy (E0). By varying the reactive and sputtering oxygen partial pressure, the optical properties were found to be n = 1.70 – 1.91, and E0 = 5.6 – 6.0 eV. This study provides a flexible method for tuning the optical properties of HfO2 coatings by controlling the mixture of reactive and sputtering gas.

Laser-driven detonation wave in a dielectric film prior to ablation

Illumination of hafnium dioxide (HfO2) thin films with a nanosecond pulsed laser reaching peak intensities of 180 GW / cm2 has been shown to trigger a laterally expanding plasma wave prior to ablation that reaches speeds of up to 100 km / s. The phenomenon has recently been described as a defect-initiated laser-driven detonation (LDD) wave propagating in the electron–hole subspace, but the electron/hole effective masses that would be required for quantitative agreement were found to be at least 100 times heavier than band structure calculations predicted for HfO2. The results are re-examined in the context of a more general description of LDD that accounts for a change in the electron effective mass between the pre- and post-detonation states. Reasonable agreement between theory and experiment is found under the assumption that the electron’s effective mass decreases by a factor of 20 and approaches the free electron mass in the final state.

Non-doped HfO2 crystallization controlled by dwell time in laser annealing

Laser annealing is performed to crystallize a 10 nm thick non-doped hafnium dioxide (HfO2) thin film. The influence of the laser annealing dwell time on the crystallization process is investigated considering the Gibbs free energy diagram of various HfO2 phases (i.e. monoclinic, cubic, tetragonal, and orthorhombic). Progressive phase transformations as a function of the dwell time are evidenced and discussed. Furthermore, for the sample showing ferroelectricity, the endurance property is much improved compared to the previously reported ferroelectric non-doped HfO2.

Growth of hafnium dioxide thin films via metal-organic chemical vapor deposition

Metal-organic chemical vapour deposition (MOCVD) is a key technique for depositing thin solid film materials for use in important technological applications. To obtain thin films of the desired standard, it is essential to design volatile, reactive and thermally stable precursors. A metal-organic precursor consisting of Hf with excellent vaporization characteristics and low decomposition temperature has been reported. Hafnium dioxide thin films on a Mo substrate were obtained via thermal MOCVD using Hafnium(IV) acetylacetonate(Hf(acac)4) in a horizontal cold-wall reactor. The Hf(acac)4 precursor was synthesized from HfCl4 and Hthd in methanol. Hf(acac)4 was characterized using elemental analysis and infrared spectroscopy. The thermal decomposition properties were studied using thermogravimetric analysis under a nitrogen atmosphere. The results showed that Hf(acac)4 was completely volatised at 245 °C. The thin films products were investigated using x-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The results from these measurements revealed that the main crystalline phase was the monoclinic phase, the surface consists of hafnium and oxygen and the morphology was densely packed and composed of visible grains.

Effect of film growth thickness on the refractive index and crystallization of HfO2 film

A series of Hafnium dioxide (HfO2) thin films with nominal thickness of 5–350 nm were reactively deposited on silicon（100）substrates at 200 °C using electron-beam evaporation. Based on the measurement and characterization techniques of spectroscopic ellipsometry, X ray diffraction, scanning electron microscopy and atomic force microscopy, the effect of growth thickness on the refractive index and crystallization of HfO2 film grown under the same conditions was studied. The results indicate that the change of refractive index of HfO2 film is closely related to the change of microstructure i.e., grain size and crystallization which change obviously with the increasing growth thickness. The average refractive index at 633 nm decreases about from 1.97 to 1.84 with the increase of the average size about from 0.5 nm to 7~8 nm and the crystallinity from zero to 74% when the thickness of HfO2 film increases from 5 nm to 350 nm. Meanwhile, a critical growth thickness of HfO2 film, somewhere on order of 130 nm, is confirmed at which the film transforms from an amorphous to a polycrystalline monoclinic structure. The sharp change of microstructure near the critical thickness value of HfO2 film leads to the abrupt change of optical properties of HfO2 film, such as the turning behaviors of the refractive index curve. The correlation between phase transformation, size and orientation of crystallite, packing density and hence the refractive index is established. The possible interpretations are proposed to well understand the underlying mechanism of the evolution of optical properties in HfO2 film-forming process.

Tribological study of hafnium dioxide and aluminium oxide films grown by atomic layer deposition on glass substrate

In the present work we studied the mechanical properties of hafnium dioxide (HfO2) and aluminium oxide (Al2O3) thin films deposited on glass at low temperature by means of atomic layer deposition method. The scratch resistance and tribological properties of HfO2 and Al2O3 were investigated. During scratch tests the first small cracks in the films were detected with a relatively low load of 3.4–4.9 N. However, up to a load of 30 N, crushing, cracking, and delamination of the Al2O3/glass system not occurs. The tribological experiments revealed a significant difference in the wear between the HfO2 and Al2O3 films. The microcrystalline structure observed for HfO2 resulted in better tribological properties than the Al2O3 film. The addition of a thin zinc oxide interlayer significantly improved the mechanical properties of the system with HfO2 film.

Correlation between ferroelectricity and nitrogen incorporation of undoped hafnium dioxide thin films

The ferroelectric characteristics of undoped hafnium oxide (HfO2) in titanium nitride (TiN)/HfO2/TiN stacks exhibited improved remanent polarization by controlling the nitrogen gas flow during TiN deposition in this work. Electrical measurements revealed that samples with a higher N2/(Ar + N2) ratio obtained a higher remanent polarization of approximately 10 μC/cm2 at 2.5 V but exhibited a larger leakage current and less reliability. Among all the samples, the sample with a N2/(Ar + N2) ratio of 33% exhibited a relatively high remanent polarization of 12 μC/cm2 and excellent endurance over 108 cycles. Through X-ray photoelectron spectroscopy (XPS) analysis, it was observed that increasing the N2 gas flow during TiN electrode deposition contributed to excessive N-diffusion, leading to the creation of more oxygen vacancies and subsequently to device failure. Therefore, controlling the appropriate N2 gas flow during TiN deposition is crucial to enhance the ferroelectric characteristics of undoped HfO2. The results of this study may be applicable to future work on nonvolatile memory applications.

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

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

Mesostructured HfO2/Al2O3 Composite Thin Films with Reduced Leakage Current for Ion-Conducting Devices.

Mesoporous hafnium dioxide (HfO2) thin films (around 20 nm thick) were fabricated by a sol–gel-based spin-coating process, followed by an annealing process at 600 °C to realize the ion-conducting media for the ionics (e.g., Na+ and K+ for rechargeable ion batteries). Another film of aluminum metal (10 nm thick) was deposited by direct current sputtering to soak into the mesopores. A monitored thermal treatment process at 500 °C in the air yields mesostructured HfO2/Al2O3 composite thin films. However, aluminum dioxide (Al2O3) is formed during annealing as an insulating film to reduce the leakage current while retaining the ionic conductivity. The obtained mesostructured HfO2/Al2O3 films show a leakage current at 3.2 × 10–9 A cm–2, which is significantly smaller than that of the mesoporous HfO2 film (1.37 × 10–5 A cm–2) or HfO2/Al film (0.037 A cm–2) at a bias voltage of 1.0 V, which is enough for ion conduction. In the meantime, among all the thin films, the mesostructured HfO2/Al2O3 composite thin films display the smallest Nyquist arc diameter in 1.0 M KOH electrolyte, implying a lower impedance at the electrode/electrolyte interface and reflecting a better ion diffusion and movement.

Study of aging effects on optical properties and residual stress of HfO2 thin film

Hafnium dioxide (HfO2) thin films are generally used as high refractive index layers in optical coating devices. Aging effects on optical and mechanical properties of the films are very crucial for long-standing performance and stability of the devices, therefore knowledge of the aging effects is very important. In the present work, HfO2 thin film has been prepared using electron beam evaporation. The optical properties and residual stress of the film have been investigated in six months interval over a period of one-year in ambient condition to probe its aging behaviour. The measured refractive index increases with aging and its change is Δn = 0.011 at wavelength of 550 nm. The dispersion parameters such as εL, N/m*, εs, and Ed increase with aging, while E0 decreases. The measured film residual stress is tensile in nature. The residual stress decreases with aging and the change in stress in the film is around 78% in a year. A simple model has been utilized to establish and explain a correlation between the measured stress and the film porosity which varies with aging time. The results suggest that the change in the residual stress is significant in contrast to a very small change in the refractive index with aging.

Characterization of HfO2 Optical Coatings Deposited by MF Magnetron Sputtering

The aim of this work is to determine the influence of medium frequency magnetron sputtering powers on the various properties of hafnium dioxide (HfO2) thin films. Microstructure observations show that an increase in the sputtering power has a significant influence on HfO2 films’ microstructure. As-deposited hafnia thin films exhibit nanocrystalline structure with a monoclinic phase, however the rise of the sputtering power results in an increase of crystallite sizes. Atomic force microscopy investigations show that the surface of the deposited films is smooth, crack-free, and composed of visible grains. The surface roughness and the value of the water contact angle increase with the increase of the sputtering power. Measurements of the optical properties show that HfO2 coatings are transparent in the visible wavelength range. A higher sputtering power causes a decrease of an average transmittance level and a simultaneous increase of the real part of the refractive index. Nanoindentation measurements reveal that the thin film hardness and Young’s elastic modulus increase with an increase in the sputtering power. Moreover, the results of plasticity index H/E and plastic resistance parameter H3/E2 are discussed. Based on the obtained results, a correlation between the sputtering power and the structural, surface, and optical properties, as well as the hardness and Young’s elastic modulus, were determined.

Rapid thermal processing of hafnium dioxide thin films by remote plasma atomic layer deposition as high-k dielectrics

Hafnium oxide (HfO2) thin films have received significant attention due to its excellent properties, such as large band gap, good thermodynamic stability, high density and high dielectric constant. The post-annealing temperature is also essential to their properties and application possibilities. In this work, HfO2 thin films were prepared on p-type silicon (100) substrates by remote plasma atomic layer deposition using tetrakis (ethylmethylamino) hafnium and remote oxygen plasma at 250 °C. The effect of rapid thermal annealing on the properties of the thin films was investigated using grazing incidence X-ray diffraction (GIXRD), X-ray photoelectron spectroscopy and field-emission transmission electron microscope (FE-TEM). FE-TEM and GIXRD results show that the as-deposited films are mostly amorphous and the crystallization initiates at about 500 °C. They also unveil a positive correlation between interface properties of the HfO2 thin films and a dependence of the crystallinity on annealing temperature.

Hafnia-based resistive switching devices for non-volatile memory applications and effects of gamma irradiation on device performance

ABSTRACTNon-volatile memory (NVM) devices were fabricated as a Metal– Insulator–Metal (MIM) structures by sandwiching Hafnium dioxide (HfO2) thin film in between two metal electrodes. The top and bottom metal electrodes were deposited by using the thermal evaporation, and the oxide layer was deposited by using the RF magnetron sputtering technique. The Resistive Random Access Memory (RRAM) device structures such as Ag/HfO2/Au/Si were fabricated and I-V characteristics for the pristine and gamma-irradiated devices with a dose 24 kGy were measured. Further we have studied the thermal annealing effects, in the range of 100°–400°C in a tubular furnace for the HfO2/Au/Si samples. The X-ray diffraction (XRD), Rutherford Backscattering Spectrometry (RBS), field emission-scanning electron microscopy (FESEM) analysis measurements were performed to determine the thickness, crystallinity and stoichiometry of these films. The electrical characteristics such as resistive switching, endurance, retention time and switching speed were measured by a semiconductor device analyser. The effects of gamma irradiation on the switching properties of these RRAM devices have been studied.

Investigation of various properties of HfO2-TiO2 thin film composites deposited by multi-magnetron sputtering system

In this work the properties of hafnium dioxide (HfO2), titanium dioxide (TiO2) and mixed HfO2-TiO2 thin films with various amount of titanium addition, deposited by magnetron sputtering were described. Structural, surface, optical and mechanical properties of deposited coatings were analyzed. Based on X-ray diffraction and Raman scattering measuremets it was observed that there was a significant influence of titanium concentration in mixed TiO2-HfO2 thin films on their microstructure. Increase of Ti content in prepared mixed oxides coatings caused, e.g. a decrease of average crystallite size and amorphisation of the coatings. As-deposited hafnia and titania thin films exhibited nanocrystalline structure of monoclinic phase and mixed anatase-rutile phase for HfO2 and TiO2 thin films, respectively. Atomic force microscopy investigations showed that the surface of deposited thin films was densely packed, crack-free and composed of visible grains. Surface roughness and the value of water contact angle decreased with the increase of Ti content in mixed oxides. Results of optical studies showed that all deposited thin films were well transparent in a visible light range. The effect of the change of material composition on the cut-off wavelength, refractive index and packing density was also investigated. Performed measurements of mechanical properties revealed that hardness and Young’s elastic modulus of thin films were dependent on material composition. Hardness of thin films increased with an increase of Ti content in thin films, from 4.90GPa to 13.7GPa for HfO2 and TiO2, respectively. The results of the scratch resistance showed that thin films with proper material composition can be used as protective coatings in optical devices.

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.

Structural and Optical Properties of Co-doped HfO2 Multi-layer Deposited by Spray Pyrolysis Technique

ABSTRACTThe optical and structural properties of co-doped HfO2 thin films with rare earth trivalent ions prepared by ultrasonic spray pyrolysis technique, are reported. An arrangement of multi-layer (Si-SiO2-HfO2:Eu3+-HfO2:Tb3+-HfO2:Tm3+-SiO2) were deposited on silicon substrates at temperatures from 400 to 550°C, using acetyl acetonates as precursory reagents. A refractive index value of 2.1 was determined by spectral ellipsometry. The surface morphology was obtained by AFM measurements. For 50 to 550 nm thickness films, an average roughness value of ∼56.8 Å was obtained for different substrate temperatures and grown deposition times. EDS measurements showed the presence of hafnium, and rare earths dopants as elemental composition. XPS measurements demonstrated that hafnium and rare earths oxidation species are formed at hafnium dioxide thin films. Photoluminescence emission spectra of multi-layer structures present characteristic emission peaks associated with Tb+3, Eu3+, and Tm3+ dopants. The results presented above motivate us to consider that these multilayer structures could be appropriate to be used as a rare earth host to improve optical emission.

Initial Growth Mechanism of Atomic Layer Deposited Hafnium Dioxide Using Cyclopentadienyl-Type Precursor: A Density Functional Theory Study

The initial growth mechanisms of atomic layer deposition of Hafnium dioxide thin films using Cp2Hf (CH3)2 precursor have been investigated. The calculations show that CH4 elimination reaction is energetically more favorable than CpH elimination reaction. As a result, the two ―CH3 ligands of Cp2Hf (CH3)2 may be dissociated prior to the two ―Cp rings. According to the activation barrier analysis, one CpH elimination may occurs sequentially following the first CH4 elimination reaction. During the pulse of Cp2Hf (CH3)2 precursor, the byproduct CH4 and a small amount of CpH are released.

Electrical properties of HfO2 high-k thin-film MOS capacitors for advanced CMOS technology

We deposited the hafnium dioxide (HfO2) thin films on p-Si (100) substrates. The thin films were deposited with deposition time variations, viz 2, 4, 7 and 20 min using RF-sputtering technique. The thickness and refractive index of the films were measured using spectroscopic ellipsometer. The thicknesses of the films were measured to be 13.7, 21.9, 35.38 and 92.2 nm and refractive indices of 1.90, 1.93, 1.99 and 1.99, respectively, of the films deposited for 2, 4, 7 and 20 min deposition time. The crystal structures of the deposited HfO2 thin films were determined using XRD spectra and showed the monoclinic structure, confirmed with the ICDD card no 34-0104. Aluminum metallization was carried to form the Al/HfO2/p-Si MOS structures by using thermal evaporation system with electrode area of 12.56 × 10−4 cm2. Capacitance voltage and current voltage measurements were taken to know electrical behavior of these fabricated MOS structures. The electrical parameters such as dielectric constant, flat-band shift and interface trap density determined through CV measurement were 7.99, 0.11 V and 6.94 × 1011 eV−1 cm−2, respectively. The low leakage current density was obtained from IV measurement of fabricated MOS structure at 1.5 V is 4.85 × 10−10 Acm−2. Aforesaid properties explored the suitability of the fabricated HfO2 high-k-based MOS capacitors for advanced CMOS technology.