HfO2 Thin Films Research Articles

Dipole formation to modulate flatband voltage using ALD Al2O3 and La2O3 at the interface between HfO2 and Si or Ge substrates

In this study, we have studied the flatband voltage (VFB) modulation by the formation of Al and La-induced dipoles at the interface between Si or Ge substrates and HfO2 gate dielectric in the metal–oxidesemiconductor (MOS) devices. The Al2O3 and La2O3 layers deposited on the HfO2 thin film serve to form dipoles. These Al2O3 and La2O3 thin film layers were atomically deposited using trimethyl-aluminum (TMA) and La(iPrCp)3 for the metal precursor and H2O and O3 for the oxidant, respectively. The dipole, an enabler that modulates the VFB in MOS devices, is formed at the interface between the high-k thin film and substrates upon subsequent annealing. As the thickness of the Al2O3 increases, VFB shifts in the positive direction on both substrates. The VFB shifted by about 230 mV with a 1.5 nm thick Al2O3 capping layer on Si substrate and 610 mV on the Ge substrate. On the other hand, VFB shifted in a negative direction of about 181 mV in the 1.5 nm thick-La2O3 capping layer. Our results indicate that electronegative atoms using Al2O3 and La2O3 are an efficient way to modulate VFB for Si or Ge-based 3D device structures without sufficient space margin for gate stack film formation.

(Invited) Advances in Atomic Layer Processing of Hafnia-Zirconia Ferroelectrics

The limits of integrating ferroelectric materials on commercial semiconductor chips were demolished the moment ferroelectricity in hafnia and zirconia films was reported in 2011. This breakthrough moment in the history of ferroelectric materials was made possible by the fortuitous interplay between advances in atomic layer processing and the strong surface energy dependence of crystal phases in HfO2 and ZrO2. Aided by commercial investment in using both materials as high-k gate and DRAM dielectric materials, atomic layer deposition (ALD) processes are beginning to take full advantage of the completely solid-soluble hafnia-zirconia (Hf1-xZrxO2) ferroelectric system with new precursors and new insights obtained by systematically evaluating film growth conditions. The capability to precisely adjust the compositional profile and to alter oxidation conditions during atomic layer deposition film growth are giving an unprecedented level of control to engineer Hf1-xZrxO2 and doped HfO2 thin films for ferroelectric applications.The latest advances in atomic layer processing of Hf1-xZrxO2 and doped-HfO2 are presented where the dynamic interaction between composition and film growth conditions provide an engineering roadmap to adjust the physical and structural properties of the dielectric films. Metal precursors play a crucial role in the ensuing film properties. The adjustability of the electrical and structural properties of Hf1-xZrxO2 with ozone exposure during ALD film growth is discussed with respect to the important role oxygen and oxygen vacancies have in the overall phase stability of these novel ferroelectric materials, as well as C incorporation caused by ALD precursors. Just as atomic layer deposition has proven to be instrumental in the discovery and stabilization of the ferroelectric phase in HfO2-based thin films, atomic layer etching (ALE) of HfO2/ZrO2-based layers is now being used to preserve ferroelectricity while pushing the thickness dimension to new limits, yielding high performance films for ferroelectric tunnel junction applications. Further innovations in atomic layer processing will continue to be a harbinger of high performance ferroelectrics in the coming years based on the current status and future outlook for ferroelectric Hf1-xZrxO2 and other emerging ferroelectric materials.

Quantifying the Structure and Chemistry of Semiconductor Devices with the Latest Advancements in Scanning Transmission Electron Microscopy

Electron microscopy has been revolutionized by the advent of the aberration corrector and advances in detector both for imaging and spectroscopy. Aberration correction dramatically improved spatial resolution into the sub-ångstrom regime, while new detectors have unlocked information about materials that was previously only imaginable.While these recent advances have proven essential to the atomic scale characterization of materials, many measurements have remained largely semi-quantitative. In particular, accuracy and precision for scanning transmission electron microscopy (STEM) was significantly hampered by the presence of sample drift and scan distortion. Until recently, this limitation has obscured the capabilities to characterize minute changes to the atomic structure that can ultimately define material properties.In this talk, we will introduce revolving scanning transmission electron microscopy (RevSTEM) for the characterization of semiconductors. The method uses a series of fast-acquisition STEM images, but with the scan coordinates rotated between successive frames. This scan rotation introduces a concomitant change in image distortion that is then used to analyze the sample drift rate and direction. Multiple case studies will be presented to demonstrate the power of this technique to characterize electronic materials. For example, we will show how picometer level precision and accuracy enabled the capability to directly quantify ferroelectric HfO2 thin films. We will also show how RevSTEM images can be used to accurately determine crystallographic parameters in real-space, and to determine the structural origins of polarization.When combined with modern spectroscopy tools, the technique can directly inform growth mechanisms in AlN based materials for fabrication of quantum well structures. Specifically, We will show the interface quality between various AlGaN/AlN quantum wells using a combination of high-angle annular dark-field (HAADF) imaging and energy dispersive X-ray spectroscopy (EDS). We will show that we can directly measure the lattice parameters for each layer and how they vary across each AlN/AlGaN interface. Using EDS, we correlate the lattice parameters and lattice parameter values to the chemical composition in each layer. We show that throughout multiple quantum well structures, there is an asymmetrical interface with a diffusion of Ga on one side of the AlGaN layer. Further, we will discuss fluctuation in the composition present throughout each layer and the role on the local strain distribution.

(Invited, Digital Presentation) Investigation of Polarization Behavior of HfO2 Thin Films Via Piezoelectric Characterization

Nonvolatile memory based on field-effect transistors with ferroelectric gate dielectrics (FeFET) was first proposed in the 1960s[1]. Later, in the 1990s, FeFETs were proposed to operate as neuromorphic devices and were actively studied[2]. However, it has not been realized due to the difficulty of forming ferroelectric thin films on Si and obtaining a good Si/ferroelectric interface. This situation was greatly changed by the discovery of ferroelectricity in hafnium oxides [3]. Now, FeFETs have attracted attention again due to the high CMOS process compatibility of hafnium oxides as well as their good ferroelectricity even in ultra-thin films. FeFETs have many potential applications, including steep switching transistors and reservoir computing as well as nonvolatile memory. In addition, the understanding of the ferroelectric properties of HfO2-based thin films has been deepened. On the other hand, reliability issues such as robustness, switching endurance, fatigue characteristics, wake-up effects, and imprinting still remain to be addressed for practical applications. These are problems common to ferroelectric thin films, but because HfO2 is an ultra-thin film, they are not easy to analyze. Therefore, in this study, we focused on the evaluation of ferroelectricity by the direct piezoelectric effect. In contrast to the inverse piezoelectric response, the direct piezoelectric response is, in principle, independent of the film thickness, so we expect that the direct piezoelectric response could be analyzed even for HfO2-based thin films.TaN/Hf0.5Zr0.5O2 (HZO)/TaN capacitor was prepared on a Si wafer. TaN electrodes were deposited by DC sputtering method. The thickness of the TaN films was 10 nm. The HZO film was then deposited by the RF magnetron sputtering method using HfO2 and ZrO2 targets. The fabricated capacitor was annealed in a rapid thermal annealing system at 700 °C. The details of the deposition are described in Ref. 4. The direct piezoelectric response of the HZO film was measured using the wafer flexure technique [5]. The strain was applied periodically to the sample, and the charge induced via the direct piezoelectric response wasmeasured using a lock-in amplifier. While the conventional ferroelectric characterization, including the P-E measurement, might be influenced by the space charge, leakage current so on, the direct piezoelectric response only depends on the remaanenrt polarization because there are no other physical phenomena similar to the direct piezoelectric response. We investigated the state of polarization during the retention and wake-up process. The film showed a time-dependent imprint at room temperature during polarization retention. The internal electric field that generated the imprint gradually increased from 0.05 to 0.6 MV/cm. In contrast, the magnitude of the direct piezoelectric response did not change during the polarization retention. Similar analyses were also carried out for the wake-up process. Based on the obtained results, we concluded that the non-ferroelectric layer exists at the interface between the HZO film and TaN electrode and gradually transitions to ferroelectric phases through the electric field cycle[6]. The presentation will also cover the domain observation of HZO films by the direct piezoeelectric response.[1] J. L. Moll and Y. tarui, IEEE trans. Elect. Dev., ED-10, 338 (1963)[2] H. Ishiwara, Jpn. J. Appl. Phys., 32, 442 (1993)[3] T. S. Boscke, J. Muller, D. Brauhaus, U. Schroder, and U. Bottger, Appl. Phys. Lett. 99, 102903 (2011).[4] S. Migita, H. Ota, H. Yamada, K. Shibuya, A. Sawa, and A. Toriumi, Jpn. J. Appl. Phys., Part 1 57, 04FB01 (2018).[5] J. F. Shepard, P. J. Moses, and S. Trolier-McKinstry, Sens. Actuators, A 71, 133 (1998).[6] K. Takada, M. Murase, S. Migita, Y. Morita, H. Ota, N. Fujimura, and T. Yoshimura, Appl. Phys. Lett. 119, 032902 (2021)

Influence of Low Molarity Hafnium Synthesis on the Reflection Properties of Polished and Textured Crystalline Silicon Substrates Coated with HfO2 Thin Films

Influence of Low Molarity Hafnium Synthesis on the Reflection Properties of Polished and Textured Crystalline Silicon Substrates Coated with HfO2 Thin Films

High Linearity Synaptic Devices Using Ar Plasma Treatment on HfO2 Thin Film with Non-Identical Pulse Waveforms.

We enhanced the device uniformity for reliable memory performances by increasing the device surface roughness by exposing the HfO2 thin film surface to argon (Ar) plasma. The results showed significant improvements in electrical and synaptic properties, including memory window, linearity, pattern recognition accuracy, and synaptic weight modulations. Furthermore, we proposed a non-identical pulse waveform for further improvement in linearity accuracy. From the simulation results, the Ar plasma processing device using the designed waveform as the input signals significantly improved the off-chip training and inference accuracy, achieving 96.3% training accuracy and 97.1% inference accuracy in only 10 training cycles.

Modulating the microscopic lattice distortions through the Al-rich layers for boosting the ferroelectricity in Al:HfO2 nanofilms

Combining the experimental characterization with the large-scale density functional theory calculations based on finite-element discretization (DFT-FE), we address the stabilization of polar orthorhombic phases (o-HfO2) in Al:HfO2 nanofilms by means of the atomic registry distortions and lattice deformation caused by Al substitutional defects (AlHf) and Schottky defects (2AlHf + VO) in tetragonal phases (t-HfO2) or monoclinic phases (m-HfO2). The phase transformation directly from the t-HfO2 into polar o-HfO2 are also elucidated within a heterogeneous distribution of Al dopants in both t-HfO2 bulk crystal structure and Al:HfO2 nanofilm. It is revealed using large-scale DFT calculations that the Al substitutional defects (AlHf) or the Schottky defect (2AlHf + VO) could induce the highly extended atomic registry distortions or lattice deformation in the t- and m-HfO2 phases, but such effects are greatly diminished in ferroelectric orthorhombic phase. By purposely engineering the multiple AlHf defects to form dopant-rich layers in paraelectric t-HfO2 nanofilm or bulk crystal, the induced extended lattice distortions surrounding the defect sites exhibit the shearing-like atomic displacement vector field. The large-scale DFT calculations further predicted that the shearing-like microscopic lattice distortions could directly induce the phase transformation from the t-HfO2 into polar orthorhombic phase in both Al:HfO2 bulk crystal and nanofilms, leading to the large remanent polarization observed in Al:HfO2 nanofilms with the presence of Al-rich layers. The current study demonstrates that the ferroelectricity of HfO2 bulk crystal or thin film can be optimized and tuned by delicately engineering both the distribution and concentration of Al dopants in atomic layer deposition without applying the top capping electrode, providing the extra flexibility for designing the HfO2 based electronic devices in the future.

Different polymorphs of Y doped HfO2 epitaxial thin films: Insights into structural, electronic and optical properties

We report the investigation of local structure, electronic and optical properties of different polymorphs of (YO1.5)x(HfO2)1-x (x = 0, 0.05, 0.10, 0.15, and 0.20) epitaxial thin films on YSZ(100) substrate prepared by pulsed laser deposition technique. The X-ray diffraction results confirm that the deposited films are epitaxial and crystal structure changes from monoclinic to orthorhombic to cubic/tetragonal as Y concentration increases in HfO2 thin films. Spectroscopic identification of phase transformation in these thin films was investigated using Fourier transform infrared and X-ray absorption spectroscopy (XAS). Effect of crystal structure on Hf-O & Hf-Hf bond distances and disorder were investigated by extended X-ray absorption fine structure. O K-edge XAS spectra show profound changes in eg and t2g peaks for different HfO2 polymorphs. X-ray photoelectron spectroscopic studies confirm that different chemical environments are present in different polymorphs of HfO2 thin film. The photoluminescence measurements validate the wide band spectral emission in wavelength region of 400–550 nm for all polymorphs and photoluminescence areal intensity shows strong dependence on phase and local structure disorder. This work will be helpful in understanding the basic material properties and spectroscopic identification of different HfO2 phases of high application relevance in semiconductor industry.

Effect of Al2O3 interlayers on the microstructure and electrical response of ferroelectric doped HfO2 thin films

Novel devices based on ferroelectric hafnium oxide comply with the increasing demand for highly scalable embedded non-volatile memory devices, especially for in-memory computing applications. However, due to the polycrystalline nature of these hafnium oxide films, highly scaled devices face variability concerns. In order to enable smaller grains to circumvent the current limitations, the introduction of Al2O3 interlayers to interrupt the columnar grain growth is presented herein. Transmission Kikuchi diffraction is utilized to investigate influences of the Al2O3 layer on the microstructure of hafnium oxide. Moreover, electrical analysis indicates how the interlayer affects the wake-up phenomena as well as the electric field distribution within the stack. These results provide evidence on how to control grain size, electric behavior, and crystallization temperature by the insertion of Al2O3 interlayers.

Enhanced ferroelectricity by strain gradient in few-layer HfO2thin films

Due to the great potential in reducing the size of ferroelectric memory cells and the good compatibility with traditional silicon process, the ferroelectricity of few-layer HfO2 thin films has received huge attention, but its microscopic mechanism is still unclear. Based on first-principles calculations, the ferroelectricity of few-layer HfO2 thin films in the presence of both strain and strain gradient has been investigated systematically. It is shown that the orthorhombic ferroelectric phase exists stably with the strain between −7% and 3%, and the ferroelectric polarization decreases monotonically with the strain increasing, which is consistent with previous studies. In particular, the ferroelectric polarization increases monotonically with the strain gradient increasing within the strain less than −2.5%, which is due to the fact that the strain gradient further separates the positive and negative centers. Our findings provide possible theoretical explanations for recent experimental results and technical guidance for the design of ultra-thin ferroelectric devices.

Effects of etching process and annealing temperature on the ferroelectric properties of atomic layer deposited Al-doped HfO2 thin film

An investigation was conducted with regard to the effect of etching process on the ferroelectric (FE) characteristics of different device structures with Al-doped HfO2 thin films; further, the effect of the rapid thermal annealing temperature on the FE properties was elucidated using metal-ferroelectric-metal (MFM) capacitors using TiN electrodes with varying thickness and 4 at.% Al-doped HfO2 FE layer. The capacitors were annealed at different temperatures after lithography and etching process; this was aimed at incorporating the FE-orthorhombic phase. The samples annealed after patterning were able to obtain improved FE characteristics due to the amount of tensile stress. The MFM devices that were initially patterned were also studied as a reference. We found that even though it required higher temperature and shorter time to introduce the FE phase, it exhibited more stable as well as promising FE properties and electrical performances with a relatively large remnant polarization (2P r ∼ 60 μC cm−2), a coercive electric field of approximately 2 MV cm−1 and high switching current density with less leakage. Our results indicate how the FE properties of the HfO2-based thin films can be engineered through suitable process sequence and post-annealing conditions, thereby verifying the applicable flexibility of FE-HfO2 for semiconductor device integration.

Memory Effects in Nanolaminates of Hafnium and Iron Oxide Films Structured by Atomic Layer Deposition

HfO2 and Fe2O3 thin films and laminated stacks were grown by atomic layer deposition at 350 °C from hafnium tetrachloride, ferrocene, and ozone. Nonlinear, saturating, and hysteretic magnetization was recorded in the films. Magnetization was expectedly dominated by increasing the content of Fe2O3. However, coercive force could also be enhanced by the choice of appropriate ratios of HfO2 and Fe2O3 in nanolaminated structures. Saturation magnetization was observed in the measurement temperature range of 5–350 K, decreasing towards higher temperatures and increasing with the films’ thicknesses and crystal growth. Coercive force tended to increase with a decrease in the thickness of crystallized layers. The films containing insulating HfO2 layers grown alternately with magnetic Fe2O3 exhibited abilities to both switch resistively and magnetize at room temperature. Resistive switching was unipolar in all the oxides mounted between Ti and TiN electrodes.

Independent Effects of Dopant, Oxygen Vacancy, and Specific Surface Area on Crystal Phase of HfO2 Thin Films towards General Parameters to Engineer the Ferroelectricity

Many factors have been confirmed to affect ferroelectric phase formation in HfO2-based thin films but there was still a lack of general view on describing them. This paper discusses the intrinsic parameters to stabilize the ferroelectric phase of HfO2 thin films to approach this general view by investigating the separate effects of dopant, oxygen vacancy (VO), and specific surface area on the crystal phase of the films. It is found that in addition to extensively studied dopants, the ferroelectric orthorhombic phase can also be formed in pure HfO2 films by only introducing sufficient VO independently, and it is also formable by only increasing the specific surface area. By analyzing the common physics behind these factors, it is found that orthorhombic phase formation is universally related to strain in all the above cases with a given temperature. To get a general view, a physical model is established to describe how the strain influences ferroelectric phase formation during the fabrication of HfO2-based films based on thermodynamic and kinetics analysis.

Hafnium Oxide Nanostructured Thin Films: Electrophoretic Deposition Process and DUV Photolithography Patterning.

In the frame of the nanoarchitectonic concept, the objective of this study was to develop simple and easy methods to ensure the preparation of polymorphic HfO2 thin film materials (<200 nm) having the best balance of patterning potential, reproducibility and stability to be used in optical, sensing or electronic fields. The nanostructured HfO2 thin films with micropatterns or continuous morphologies were synthesized by two different methods, i.e., the micropatterning of sol-gel solutions by deep ultraviolet (DUV) photolithography or the electrophoretic deposition (EPD) of HfO2 nanoparticles (HfO2-NPs). Amorphous and monoclinic HfO2 micropatterned nanostructured thin films (HfO2-DUV) were prepared by using a sol-gel solution precursor (HfO2-SG) and spin-coating process following by DUV photolithography, whereas continuous and dense monoclinic HfO2 nanostructured thin films (HfO2-EPD) were prepared by the direct EPD of HfO2-NPs. The HfO2-NPs were prepared by a hydrothermal route and studied through the changing aging temperature, pH and reaction time parameters to produce nanocrystalline particles. Subsequently, based on the colloidal stability study, suspensions of the monoclinic HfO2-NPs with morphologies near spherical, spindle- and rice-like shapes were used to prepare HfO2-EPD thin films on conductive indium-tin oxide-coated glass substrates. Morphology, composition and crystallinity of the HfO2-NPs and thin films were investigated by powder and grazing incidence X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-visible spectrophotometry. The EPD and DUV photolithography performances were explored and, in this study, it was clearly demonstrated that these two complementary methods are suitable, simple and effective processes to prepare controllable and tunable HfO2 nanostructures as with homogeneous, dense or micropatterned structures.

Intrinsic ferroelectricity in Y-doped HfO2 thin films.

Ferroelectric HfO2-based materials hold great potential for the widespread integration of ferroelectricity into modern electronics due to their compatibility with existing Si technology. Earlier work indicated that a nanometre grain size was crucial for the stabilization of the ferroelectric phase. This constraint, associated with a high density of structural defects, obscures an insight into the intrinsic ferroelectricity of HfO2-based materials. Here we demonstrate that stable and enhanced polarization can be achieved in epitaxial HfO2 films with a high degree of structural order (crystallinity). An out-of-plane polarization value of 50 μC cm-2 has been observed at room temperature in Y-doped HfO2(111) epitaxial thin films, with an estimated full value of intrinsic polarization of 64 μC cm-2, which is in close agreement with density functional theory calculations. The crystal structure of films reveals the Pca21 orthorhombic phase with small rhombohedral distortion, underlining the role of the structural constraint in stabilizing the ferroelectric phase. Our results suggest that it could be possible to exploit the intrinsic ferroelectricity of HfO2-based materials, optimizing their performance in device applications.

Oxygen‐Scavenging Effects of Added Ti Layer in the TiN Gate of Metal‐Ferroelectric‐Insulator‐Semiconductor Capacitor with Al‐Doped HfO2 Ferroelectric Film

AbstractTi layer inserted in the TiN gate electrode effectively scavenges the oxygen in the low‐k interfacial SiO2 of the metal–ferroelectric–insulator–semiconductor (MFIS) capacitors with the ferroelectric Al‐doped HfO2 (HAO) thin film. The scavenging effect increases remanent polarization (Pr) and reduces coercive voltage (Vc) and capacitance equivalent thickness (CET) of the HAO films, particularly when the MFIS capacitor is annealed at 800 °C. Additionally, frequency dispersion of capacitance characteristics and interface trap density (Dit) calculations reveal that actively‐triggered oxygen‐scavenging effects also reduce defect or trap‐induced degradation. The Ti‐inserted MFIS structure exhibits fatigue‐free endurance and relatively low leakage current characteristics as compared to a structure without the Ti scavenging layer in high annealing temperature conditions required for crystallization of the HAO ferroelectric films.

Effects of post cooling on the remnant polarization and coercive field characteristics of atomic layer deposited Al-doped HfO2 thin films

A study was conducted on how the cooling rate after the phase change heat treatment required to secure the ferroelectric (FE) properties affects the ferroelectricity of Al-doped HfO2 (Al:HfO2) thin films. When cooling the thin film to room temperature after heat treatment, the cooling rate was controlled through slow chamber cooling, which maintains and cools the sample inside the heat treatment equipment, slightly faster air cooling, and rapid cooling using deionized water. We achieved the dramatic increase of remnant polarization (Pr) and coercive electric field (Ec) using rapid quenching after phase change heat treatment. The 2Pr and 2Ec values of rapid quenched FE Al:HfO2 thin film are approximately ∼100 μC/cm2 and ∼9.5 MV/cm, respectively, which are the highest records among HfO2-based FE thin films reported so far. These significant improvements are attributed to inducing homogeneously distributed defects complexes and higher stress/confinement strain within Al:HfO2 thin film, leading to preventing pinched hysteresis loop and stabilize orthorhombic crystal structure. Furthermore, endurance up to 2 × 106 cycles and reasonable projected 10 years retention properties were achieved, stably without wake-up and fatigue in quenched FE Al:HfO2 capacitor. These results propose a beneficial method to improve the ferroelectricity of HfO2-based thin films.

Improved ferroelectric characteristics of ALD lanthanum-doped hafnium oxide thin film by controlling post-cooling time

A study was conducted on how the subsequent cooling time affects the ferroelectric (FE) characteristics of atomic layer deposited (ALD) lanthanum (La) doped HfO2 thin films after the crystallization heat treatment in the form of TiN/La-doped HfO2/TiN metal-ferroelectric-metal (MFM) device structure. The ALD La-doped HfO2 thin film was cooled to room temperature in a chamber (“chamber cooling” - slower cooling) or in an air atmosphere (“air cooling” - faster cooling). Based on the polarization vs electric field (P-E) hysteresis curve, the double remanent polarization (2Pr) values of the chamber cooling and air-cooling are 9.5 μC/cm2 and 40 μC/cm2, respectively. This drastic improvement stems from more orthorhombic phase formation within La-doped HfO2 thin film, which is confirmed by smaller grain size, higher amount of oxygen vacancies, and more tensile stress within HfO2 thin film. Our results suggest that FE properties of La-doped HfO2-based thin film can be significantly modulated by post cooling processes.

Investigation on HfO2 properties grown by ALD using TDMAH as precursor

HfO2 films have increasingly extensive applications in optical and electronic industry. In order to obtain controllable properties of HfO2 film, its growth behavior needs to be studied. HfO2 thin films prepared by Atomic Layer Deposition (ALD) were studied in this work. Growth behavior was elucidated by controlling the cycles of ALD and characterized by both structural and optical measurements. As the increase of thickness of the film, HfO2 converts from amorphous to monoclinic and the preferred orientation of (200) and (020) lattice plane is strengthened in monoclinic phase. Oriented arrangement of atoms is relevant to the gradient structure of HfO2 film and abundant protuberant islands on the surface of HfO2 film. Annealing experiment proved the orientation of atomic arrangement in amorphous HfO2 which promotes the continuous variation of HfO2 films in refractive index (n). And the orientation arrangement eventually contributes to crystallization of the film which will significantly reduce the laser induced damage threshold (LIDT) of the film. Analysis of optical properties in this work can provide useful information for the preparation of optical coating containing HfO2.

Thermal stability of antiferroelectric-like Al:HfO2 thin films with TiN or Pt electrodes

HfO2-based antiferroelectric-like thin films are increasingly being considered for commercial devices. However, even with initial promise, the temperature sensitivity of electrical properties such as loss tangent and leakage current remains unreported. 50 nm thick, 4 at. % Al-doped HfO2 thin films were synthesized via atomic layer deposition with both top and bottom electrodes being TiN or Pt. A study of their capacitance vs temperature showed that the Pt/Al:HfO2/Pt had a relative dielectric permittivity of 23.30 ± 0.06 at room temperature with a temperature coefficient of capacitance (TCC) of 78 ± 86 ppm/°C, while the TiN/Al:HfO2/TiN had a relative dielectric permittivity of 32.28 ± 0.14 at room temperature with a TCC of 322 ± 41 ppm/°C. The capacitance of both devices varied less than 6% over 1 to 1000 kHz from −125 to 125 °C. Both capacitors maintained loss tangents under 0.03 and leakage current densities of 10−9–10−7 A/cm2 between −125 and 125 °C. The TiN/Al:HfO2/TiN capacitor maintained an energy storage density (ESD) of 18.17 ± 0.79 J/cm3 at an efficiency of 51.79% ± 2.75% over the −125 to 125 °C range. The Pt/Al:HfO2/Pt capacitor also maintained a stable ESD of 9.83 ± 0.26 J/cm3 with an efficiency of 62.87% ± 3.00% over the same temperature range. Such low losses in both capacitors along with their thermal stability make antiferroelectric-like, Al-doped HfO2 thin films a promising material for temperature-stable microelectronics.