HfO2 Films Research Articles

Contribution of oxygen vacancies to phase transition and ferroelectricity of Al:HfO2 films

We investigate the effects of oxygen vacancies on the ferroelectric behavior of Al:HfO2 films annealed in O2 and N2 atmosphere. X-ray photoelectron spectroscopy results showed that the O/Hf atomic ratio was 1.88 for N2-annealed samples and 1.96 for O2-annealed samples, implying a neutralization of oxygen vacancies during O2 atmosphere annealing. The O2-annealed films exhibited an increasing remanent polarization from 23 μC cm−2 to 28 μC cm−2 after 104 cycles, with a negligible leakage current density of ∼2 μA cm−2, while the remanent polarization decreased from 29 μC cm−2 to 20 μC cm−2 after cycling in the N2-annealed films, with its severe leakage current density decreasing from ∼1200 μA cm−2 to ∼300 μA cm−2. A phase transition from the metastable tetragonal (t) phase to the low-temperature stable orthorhombic (o) phase and monoclinic (m) phase was observed during annealing. As a result of the fierce· competition between the t-to-o transition and the t-to-m transition, clear grain boundaries of several ruleless atomic layers were formed in the N2-annealed samples. On the other hand, the transition from the t-phase to the low-temperature stable phase was found to be hindered by the neutralization of oxygen vacancies, with almost continuous grain boundaries observed. The results elucidate the phase transformation caused by oxygen vacancies in the Al:HfO2 films, which may be helpful for the preparation of HfO2-based films with excellent ferroelectricity.

VO2-based colorful smart windows with self-cleaning function

Smart windows hold promise for mitigating energy demand for indoor heating or cooling. However, VO2-based thermochromic smart windows face challenges such as high phase transition temperature, limited window color options, and a lack of functional diversity. Herein, we investigated the colorful smart windows utilizing the tungsten-doped VO2 thin films with the phase transition temperature of approximately 23.5 °C. The surface color of these smart windows can be dynamically adjusted from brown to purple, cyan, yellow, and red by tuning the thickness of the wave-impedance matching layer of HfO2 film, resulted from the interference effect of the HfO2 layer and the underlying WxV1-xO2 layer. Moreover, the HfO2-coated WxV1-xO2 thin film with the HfO2 thickness of 132 nm demonstrates superior optical performance with a solar modulation ability of 9.35 %, the low-temperature luminous transmission of 36.81 %, and the high-temperature luminous transmission of 38.03 %. In addition, the incorporation of SiO2 nanoparticles into the HfO2-coated WxV1-xO2 thin films results in the superhydrophobic property with a water contact angle of 162.1° due to the formed rough surface, which is favor to the self-cleaning of the windows surface.

Control of intrinsic ferroelectricity and structural phase in pure HfO2 films via crystalline orientation

The ferroelectricity of hafnia-based thin films has garnered considerable attention in both academic researches and industrial applications. However, the fundamental properties, such as high coercivity, the wake-up effect, and the mechanism of ferroelectricity have not been fully elucidated. Here we report the crystallization orientation control of structural phase and ferroelectricity in pure HfO2 thin films. Both (001)- and (111)-oriented HfO2 thin films exhibit a mixture of ferroelectric orthorhombic and non-ferroelectric monoclinic phases. With decreasing film thickness, the orthorhombic phase ratio increases for both orientations, with a consistently higher proportion for (111)-oriented film. Consequently, the ferroelectricity is significantly enhanced in thinner (111)-oriented film. Remarkably, both (001)- and (111)-oriented pure HfO2 thin films demonstrate an intrinsic ferroelectricity. Moreover, the coercive field of the (001)-oriented film appears to be lower than that of the (111)-oriented film. Additionally, oxygen ions migrate more easily in the (001)-oriented film, which exhibits distinct electronic structure and local atomic ordering compared to the (111)-oriented film. These results provide valuable insights into the ferroelectricity of HfO2 and suggest that crystalline orientation is an effective approach to explore the ferroelectric properties in hafnia-based films.

Processing of hafnium oxide thin films by 2 MeV Kr ion beam for opto-electronic applications

The ion irradiation on 100 nm and 200 nm HfO2 films was performed using a 2 MeV Kr8+ beam at three different fluences viz. 1.5 × 1015 ions/cm2, 2 × 1015 ions/cm2 and 2.5 × 1015 ions/cm2 and various characterization techniques were employed to analyze the as-deposited and irradiated films. The AFM analysis showed that contrary to 200 nm films, the surface roughness of 100 nm films increases with increasing the ion fluence as also validated by FE-SEM. For 100 nm films, the phase analysis done by XRD indicated that the pristine films co-exist in dual phases of cubic and monoclinic; which also prevailed with post-irradiation. However, the pristine 200 nm films coexisted in dual monoclinic and orthorhombic phases and changed to sole orthorhombic phase with increasing ion fluences. The pristine 200 nm film showed more conductivity, which decreases with increasing ion fluences. Interestingly, the optical reflectivity of as-deposited 200 nm film was higher than that of 100 nm film and upon ion irradiation, both films showed inverse trend of reflectivity change; in 100 nm thin films, it decreases with increasing ion fluences. Thus, the ion irradiation seems to be a fascinating tool to tailor HfO2 thin films for their device applications.

Control of Ferroelectricity in Solution‐Processed Hafnia Films Through Annealing Atmosphere

AbstractChemical Solution Deposition enables low‐cost fabrication of ferroelectric HfO2 films suitable for piezoelectric applications. Control of processing parameters is of utmost importance to obtain high‐quality functional films. However, the impact of the annealing atmosphere on ferroelectric properties of solution‐processed HfO2 films is not clear. In this work, the influence of annealing atmosphere and growth methods on orientation, density and electrical properties of La:HfO2 films is studied. The 45 nm‐thick films are grown by two routes, conventional (crystallization of the final 45 nm‐thick film) and layer‐by‐layer (intermediate crystallizations of 5 nm‐thick films). Annealing is performed in N2:O2 and Ar atmosphere. Films grown by layer‐by‐layer method in an oxygen‐rich atmosphere tend to have higher density (87% of theoretical density) and remanent polarization (15 µC cm–2) than the conventional films (density and remanent polarization of 80% and 7.5 µC cm‐2). Secondary ion mass spectrometry reveals higher amounts of carbon presence in the conventional films annealed in Ar. For layer‐by‐layer films, the ability to control the preferential out‐of‐plane orientation from (111) to (002) simply by changing the annealing atmosphere, is demonstrated. The results can guide the path toward high‐quality thicker films for piezoelectric applications.

Improved uniformity of atomic-layer-deposited HfO2 film along the length of glass monocapillary with high length-diameter ratio

It has been a difficult to deposit a uniform film on the inner surface of monocapillary due to the high length-diameter ratio. Atomic layer deposition (ALD) shows great potential to coat conformal film on complex substrates. However, it is still a challenge to coat uniform film along the length of the capillary for regular deposition parameters. In this work, HfO2 film was deposited inside monocapillary via ALD. The film uniformity along the monocapillary was investigated by cross-section scanning electron microscope (SEM) images and the bond states of one of the HfO2 films were studied via X-ray photoelectron spectroscopy (XPS). Using the routine deposition parameters, the gas flowing through the monocapillary is controlled to be small, large and medium qualitatively by covering some of the inlets or outlets, changing the connection between monocapillary and outlets simply. SEM results demonstrate that smooth HfO2 film with uniform thickness can be acquired on the inner surface of monocapillary with length-diameter ratio 200 (length 10 cm and inner diameter 0.5 mm). XPS results show that Hf hydroxide is generated when the gas flowing through the monocapillary is large.

Preparation and patterning of HfO2 film via sol–gel method and resistive switching effect of Pt/HfO2/LaNiO3

Sol–gel method is a low-cost material preparation method; however, it is difficult to obtain a stable sol containing easily hydrolyzable metal ions via this method. In this study, a stable hafnium(IV) oxide (HfO2) sol was prepared by adding benzoyl acetone (BzAcH) modifier. Infrared absorption spectroscopy results showed that the BzAcH additive chelated with the Hf4+ ions in the sol, thus improving the hydrolysis resistance of the HfO2 sol, which in turn improved its stability. It was also found that the BzAcH-modified HfO2 gel film exhibited ultraviolet (UV) photosensitivity. After UV exposure, the film did not dissolve easily in organic solvents. Based on these properties, the micro processing of the HfO2 film was preliminarily explored, and HfO2 microstructures were successfully obtained. Additionally, the relative permittivity (εr) of HfO2 exhibited minimum (∼10.9) and maximum (∼20.6) values at heat-treatment (HT) temperatures of 350 and 450 °C, respectively. With the continuous increase in the HT temperature, εr first decreased and then increased slightly. Moreover, the current–voltage curves showed that the Pt/HfO2/LaNiO3 (LNO) structure exhibited a pronounced bipolar resistive switching (RS) effect, which was attributed to the fact that LNO could be used as an electrode and an oxygen vacancy (OV2+) storage layer for RS materials. Notably, the oxygen ions in HfO2 with a low degree of crystallinity are more likely to migrate within its body (which makes it easier to form OV2+s), therefore, the “Set” voltage of low-crystallinity HfO2 films is lower than that of high-crystallinity HfO2 films. The RS mechanism can be explained by the OV2+ conductive filament model. These results are of great practical significance for the low-cost preparation of HfO2 and the application of LNO as an oxide electrode.

Dielectric properties of hafnium oxide film prepared by HiPIMS at different O2/Ar ratios and their influences on TFT performance

High-k hafnium oxide (HfO2) film was prepared by high power impulse magnetron sputtering (HiPIMS). The influences of oxygen supply on the plasma state, film properties and TFT performance were investigated. The films are near-stoichiometric and preferentially (−1 1 1)-orientated. When the oxygen supply increased from 1% to 3%, the excitation/ionization rate of the plasma species increased, leading to higher crystallinity, higher density, and lower oxygen vacancy defect concentration of the film, therefore improving the dielectric properties of the film. When the oxygen supply further increased to 5%, the excitation/ionization rate decreased, thereby leading to lower crystallinity, lower density, and higher oxygen vacancy defect concentration of the film, therefore deteriorating the dielectric properties of the film. The film deposited at 3% oxygen supply exhibited the best dielectric properties with the highest k value of 24 and the highest breakdown-electric field (4.7 MV/cm), which should be attributed to the high crystallinity, high density and low oxygen vacancy defect concentration of the film. Finally, transparent thin film transistors (TFTs) with ITO gate electrode, HfO2 gate dielectric layer and indium-gallium-zinc oxide channel were fabricated on flexible colorless polyimide substrate at full room temperature by all HiPIMS process. The fixed positive charges and k value of HfO2 film have significant effects on the TFT performance. The best TFT exhibited good electrical performance, featuring a remarkably low subthreshold swing of 0.13 V/decade. It also exhibited fair stability against bending and gate bias stress.

Enhanced polarization switching characteristics of HfO2 ultrathin films via acceptor-donor co-doping

In the realm of ferroelectric memories, HfO2-based ferroelectrics stand out because of their exceptional CMOS compatibility and scalability. Nevertheless, their switchable polarization and switching speed are not on par with those of perovskite ferroelectrics. It is widely acknowledged that defects play a crucial role in stabilizing the metastable polar phase of HfO2. Simultaneously, defects also pin the domain walls and impede the switching process, ultimately rendering the sluggish switching of HfO2. Herein, we present an effective strategy involving acceptor-donor co-doping to effectively tackle this dilemma. Remarkably enhanced ferroelectricity and the fastest switching process ever reported among HfO2 polar devices are observed in La3+-Ta5+ co-doped HfO2 ultrathin films. Moreover, robust macro-electrical characteristics of co-doped films persist even at a thickness as low as 3 nm, expanding potential applications of HfO2 in ultrathin devices. Our systematic investigations further demonstrate that synergistic effects of uniform microstructure and smaller switching barrier introduced by co-doping ensure the enhanced ferroelectricity and shortened switching time. The co-doping strategy offers an effective avenue to control the defect state and improve the ferroelectric properties of HfO2 films.

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.

Effect of the number and distribution of Al2O3 atomic layer deposition cycles within HfO2 layer on ferroelectric characteristics

We comprehensively analyze the effects of the number and distribution of Al2O3 atomic layer deposition (ALD) cycles into a 10-nm-thick HfO2 matrix on the ferroelectric switching behavior. An ALD cycle containing one pulse for Hf (or Al) precursor and one pulse of water as reactant is repeated 150 times for the given thickness of 10 nm. Spontaneous remnant polarization (Pr) is enabled through the formation of crystalline Al-doped HfO2 (Al:HfO2) by incorporating at least two Al2O3 ALD cycles evenly into the HfO2 film under annealing at 600 °C for 3 min following W top electrode (TE) deposition. When more than four Al2O3 cycles are used, the Al elements function as leakage sources rather than stressors, resulting in an open hysteresis loop and a weak endurance of 105 cycles. Notably, an improved 2 Pr of ∼9 μC/cm2 is achieved when the Al2O3 layers are concentrated near the lower region of the HfO2. On the other hand, as the Al2O3 layers are intensively located in the upper region of the HfO2, a dielectric response is observed in the polarization–voltage and current–voltage measurements. Our results indicate that the two mechanical stresses induced by the Al dopant with a size smaller than Hf and the difference in the thermal expansion coefficient between TE and Al:HfO2 effectively activate both the lower and upper sites. Therefore, many dipoles are observed to participate in the polarization owing to the stresses that are applied evenly throughout the Al:HfO2 layer to form the orthorhombic phase.

Ferroelectric and electric field cycling properties of un-doped HfO2 films

As the most promising candidate material for nonvolatile memories, premature occurrence of fatigue phenomenon for ferroelectric HfO2 film has no appropriate solution method. In this paper, HfO2/Y/HfO2 films were deposited with reactive magnetron sputtering and realized ferroelectric property after wake-up process even if without doping and post-metallization annealing (PMA). Different with uniform or symmetrical distribution, oxygen vacancies concentrated in the film middle, resulting in a longer migration path and tardy fatigue. Fatigue appeared after the electric field cycling of 109 in HfO2 film inserted with 0.6 nm metal Y, which is obviously higher than films deposited by other methods. The remanent polarization of un-doped HfO2 films inserted with 0.6 and 1.5 nm metal Y interlayer is 11.8 and 14.8 μC/cm2, respectively. The results provide a method for to improve cycling property and confirm the important role of oxygen vacancies in wake-up and fatigue phenomenon for HfO2 films.

Operando study of HfO2 atomic layer deposition on partially hydroxylated Si(111)

The introduction of atomic layer deposition (ALD), to the microelectronics industry has introduced a large number of new possible materials able to be deposited in layers with atomic thickness control. One such material is the high-κ oxide HfO2; thermally stable and ultrathin HfO2 films deposited by ALD are a significant contender to replace SiO2 as the gate oxide in capacitor applications. We present a mechanistic study of the first deposition cycle of HfO2 on the Si(111) surface using tetrakis(dimethylamido) hafnium (TDMAHf) and water as precursors using operando ambient pressure x-ray photoelectron spectroscopy. Here, we show that the hydroxylation of the clean Si(111) surface by residual water vapor, resulting in a 0.3 monolayer coverage of hydroxyls, leads to instantaneous full surface coverage of TDMAHf. The change in the atomic ratio of Hf to C/N found during the first deposition half-cycle, however, does not match the assumed immediate ligand loss through reaction with surface hydroxyls. One would expect an immediate loss of ligands, indicated by a Hf:N ratio of approximately 1:3 as TDMAHf deposits onto the surface; however, a Hf:N ratio of 1:3.6 is observed. The partial hydroxylation on the Si(111) surface leads to binding through the TDMAHf ligand N atoms resulting in both N and CH3 being found remaining on the surface post water half-cycle. Although there is evidence of ligand exchange reactions occurring at Si–OH sites, it also seems that N binding can occur on bare Si, highlighting the complexity of the substrate/precursor reaction even when hydroxyls are present. Moreover, the initial low coverage of Si–OH/Si–H appears to severely limit the amount of Hf deposited, which we hypothesize is due to the specific geometry of the initial arrangement of Si–OH/Si–H on the rest- and adatoms.

Polarization switching pathways of ferroelectric Zr-doped HfO2 based on the first-principles calculation

Based on the first principles calculation, the mechanisms of polarization switching behavior in ferroelectric Zr-doped HfO2 are investigated. Seven switching pathways, divided into two categories by the identified orientation of polarization switching and value, are analyzed based on atomic migration and energy barrier. The effects of Zr dopant on switching energy barrier (Eb) and spontaneous polarization (Ps) are analyzed as well. In one of the categories, two pathways with tetragonal-like transition states show low energy barriers and can be further minimized with higher Zr dopant proportion, which originates from the stabilizing effect of Zr dopant on the tetragonal phase (T, P42/nmc). Especially, in the two tetragonal-like pathways, a distorted tetragonal-like transient state (T′, Pbcn) resulting from distinct atomic displacement is transformed to a highly symmetric T-phase along with the incorporation of Zr, elucidating this pathway as energy favorable as the regular T-pathway. This work provides an atomic insight for ferroelectric switching behavior and predicts the probable ferroelectric switching pathway in Zr-doped HfO2 films.

Hollow Hafnium Oxide (HfO2) Fibers: Using an Effective Combination of Sol-Gel, Electrospinning, and Thermal Degradation Pathway.

In recent years, hafnium oxide (HfO2) has gained increasing interest because of its high dielectric constant, excellent thermal stability, and high band gap. Although HfO2 bulk and film materials have been prepared and well-studied, HfO2 fibers, especially hollow fibers, have been less investigated. In this study, we present a facile preparation method for HfO2 hollow fibers through a unique integration of the sol-gel process and electrospinning technique. Initially, polystyrene (PS) fibers are fabricated by using electrospinning, followed by dipping in a HfO2 precursor solution, resulting in HfO2-coated PS fibers. Subsequent thermal treatment at 800 °C ensures the selective pyrolysis of the PS fibers and complete condensation of the HfO2 precursors, forming HfO2 hollow fibers. Scanning electron microscopy (SEM) characterizations reveal HfO2 hollow fibers with rough surfaces and diminished diameters, a transformation attributed to the removal of the PS fibers and the condensation of the HfO2 precursors. Our study also delves into the influence of precursor solution molar ratios, showcasing the ability to achieve smaller HfO2 fiber diameters with reduced precursor quantities. Validation of the material composition is achieved through thermogravimetric analysis (TGA) and energy-dispersive spectroscopy (EDS) mapping. Additionally, X-ray diffraction (XRD) analysis provides insights into the crystallinity of the HfO2 hollow fibers, highlighting a higher crystallinity in fibers annealed at 800 °C compared with those treated at 400 °C. Notably, the HfO2 hollow fibers demonstrate a water contact angle (WCA) of 38.70 ± 5.24°, underscoring the transformation from hydrophobic to hydrophilic properties after the removal of the PS fibers. Looking forward, this work paves the way for extensive research on the surface properties and potential applications of HfO2 hollow fibers in areas such as filtration, energy storage, and memory devices.

Experimental determination of reference intensity ratio essential for accurate thickness measurement of HfO2 ultrathin films by XPS

When measuring the thickness of ultrathin overlayer films using X‐ray photoelectron spectroscopy (XPS), accurate values of the reference intensity ratio (R0) and the effective attenuation length (L) are essential. By definition, R0 is the peak intensity ratio for an overlayer and the substrate in “bulk” phases. Two issues need to be addressed in experimental determining R0 for ultrathin films: (i) How might a contamination layer on the sample used for measuring peak intensities impact R0? And (ii) do differences in the structure or chemistry of an ultrathin film make it inappropriate to determine R0 using bulk forms of the overlayer? In this study, we demonstrate the experimental determination of the R0 for an ultrathin HfO2 film on a Si(100) substrate with a 2 nm SiO2 layer. The values of R0 were determined using (i) the bulk materials of the HfO2 film and substrate and (ii) the ultrathin HfO2 films after different cleaning treatments. The results show that the R0 determined by the ultrathin films is higher than that determined by the bulk materials. Also, keeping the same level of carbonaceous contamination on the sample surface by cleaning as much as possible is essential for an accurate experimental determination of R0. In addition, the effective attenuation length was obtained using samples with known thicknesses measured by X‐ray reflectometry. The thicknesses and uncertainty budget of the ultrathin HfO2 films were then evaluated.

Effect of La Spatial Uniformity on Ferroelectric Properties of HfO2 Films Deposited by Atomic Layer Deposition Method

In this study, the effect of supercycle scheme for La‐doping in HfO2 films by atomic layer deposition (ALD) on their ferroelectric properties is investigated along with the variation of La distribution in HfO2 films. La is doped into HfO2 films by two ALD supercycle methods: metal‐oxidant‐dopant‐oxide (MODO) and metal‐dopant‐oxidant (MDO). Secondary ion mass spectrometry analys is shows that the MDO supercycle method results in a uniform distribution of La in the depth direction, while the MODO supercycle method results in depth‐dependent segregation of La in the HfO2 film. For similar La concentrations, HfO2 films doped with La by the MDO supercycle show a higher percentage of orthorhombic phase with higher oxygen vacancy concentrations than films by the MODO supercycle. For 3% La, the HfO2 film by MDO shows a remanent polarization (2Pr) of ≈31 μC cm−2 at ± 4 MV cm−1, which is twice as large as the remanent polarization of 15 μC cm−2 for the HfO2 film by MODO. In addition, the La‐doped HfO2 film by MDO with a larger fraction of orthorhombic phase shows a smaller wake‐up effect than the La‐doped HfO2 film by MODO.

Impact of high-power impulse magnetron sputtering pulse width on the nucleation, crystallization, microstructure, and ferroelectric properties of hafnium oxide thin films

The impact of the high-power impulse magnetron sputtering (HiPIMS) pulse width on the crystallization, microstructure, and ferroelectric properties of undoped HfO2 films is investigated. HfO2 films were sputtered from a hafnium metal target in an Ar/O2 atmosphere, varying the instantaneous power density by changing the HiPIMS pulse width with fixed time-averaged power and pulse frequency. The pulse width is shown to affect the ion-to-neutral ratio in the depositing species with the shortest pulse durations leading to the highest ion fraction. In situ x-ray diffraction measurements during crystallization demonstrate that the HiPIMS pulse width impacts nucleation and phase formation, with an intermediate pulse width of 110 μs stabilizing the ferroelectric phase over the widest temperature range. Although the pulse width impacts the grain size with the lowest pulse width resulting in the largest grain size, the grain size does not strongly correlate with the phase content or ferroelectric behavior in these films. These results suggest that precise control over the energetics of the depositing species may be beneficial for forming the ferroelectric phase in this material.

Formation of a Polar Ferroelectric Phase in HFO2 Films Depending on Annealing Conditions and Chemical Properties of Impurities

Formation of a Polar Ferroelectric Phase in HFO2 Films Depending on Annealing Conditions and Chemical Properties of Impurities

Improved Tauc-Lorentz model: Impacts of roughness/additional oscillator(s) on determination of optical properties of HfO2 films

Accurate determination of optical properties is crucial for optimal application of HfO2 film in optoelectronic industry. In this work, the effects of additional oscillator(s) introduced into Tauc-Lorentz model (the improved TL model) on the extracted optical properties of HfO2 film have been investigated with a roughness layer considered or not. The results show that the effect of additional oscillator(s) on optical properties depends on the electronic structure of HfO2 film, i.e., amorphous and/or polycrystalline character. The appearance of a shoulder-like absorption peak at ∽ 6 eV and a weak discrete absorption peak at ∽ 5.2 eV on the curve of dielectric function of the 350 nm polycrystalline HfO2 film confirms that additional oscillators correspond well with changes of the electronic structure probably induced by crystal field and defects. The results indicate that the improved TL model can be well applied to crystalline/polycrystalline films as well as defects near the absorption edge, and further probably to the fine electronic structure of materials, which greatly extends the application of TL model.