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Origin of Ferroelectricity in Epitaxial Si-doped HfO2 Films
摘要： HfO2-based unconventional ferroelectric (FE) materials were recently discovered and have attracted a great deal of attention in both academia and industry. The growth of epitaxial Si-doped HfO2 films has opened up a route to understand the mechanism of ferroelectricity. Here, we used pulsed laser deposition (PLD) to grow epitaxial Si-doped HfO2 films in different orientations of N-type SrTiO3 substrates. Using piezoforce microscopy, polar nanodomains can be written and read, and these domains are reversibly switched with a phase change of 180o. Films with different thicknesses displayed a coercive field Ec and a remnant polarization Pr of approximately 4～5 MV/cm and 8～32 μC/cm2, respectively. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) results identified that the as-grown Si-doped HfO2 films have strained fluorite structures. The ABAB stacking mode of the Hf atomic grid observed by HRTEM clearly demonstrates that the ferroelectricity originates from the noncentrosymmetric Pca21 polar structure. Combined with soft X-ray absorption spectra (XAS), it was found that the Pca21 ferroelectric crystal structure manifested as O sublattice distortion by the effect of interface strain and Si dopant interactions, resulting in further crystal-field splitting as a nanoscaled ferroelectric ordered state.
关键词： HRTEM,PLD,XRD,Ferroelectricity,PFM,XAS,Epitaxial Si-doped HfO2 thin films,N-type SrTiO3 substrates
更新于2025-11-14 17:04:02
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Metamaterial emitter for thermophotovoltaics stable up to 1400?°C
摘要： High temperature stable selective emitters can significantly increase efficiency and radiative power in thermophotovoltaic (TPV) systems. However, optical properties of structured emitters reported so far degrade at temperatures approaching 1200 °C due to various degradation mechanisms. We have realized a 1D structured emitter based on a sputtered W-HfO2 layered metamaterial and demonstrated desired band edge spectral properties at 1400 °C. To the best of our knowledge the temperature of 1400 °C is the highest reported for a structured emitter, so far. The spatial confinement and absence of edges stabilizes the W-HfO2 multilayer system to temperatures unprecedented for other nanoscaled W-structures. Only when this confinement is broken W starts to show the well-known self-diffusion behavior transforming to spherical shaped W-islands. We further show that the oxidation of W by atmospheric oxygen could be prevented by reducing the vacuum pressure below 10?5 mbar. When oxidation is mitigated we observe that the 20 nm spatially confined W films survive temperatures up to 1400 °C. The demonstrated thermal stability is limited by grain growth in HfO2, which leads to a rupture of the W-layers, thus, to a degradation of the multilayer system at 1450 °C.
关键词： W-HfO2 layered structure,selective emitters,metamaterial emitter,high temperature stability,thermophotovoltaics
更新于2025-10-22 19:40:53
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High performance, low temperature processed Hf-In-Zn-O/HfO2 thin film transistors, using PMMA as etch-stop and passivation layer
摘要： High performance, low operating voltage and low temperature processed Hf-In-Zn-O/HfO2 thin film transistors (HIZO/HfO2 TFTs), using spin-coated polymethyl-methacrylate (PMMA) as passivation and etch-stop layer (ESL), were fabricated and characterized. Devices showed an average field-effect mobility of 15 cm2/Vs and threshold voltage (VT) of 0.2 V, working in the operating voltage range below 2 V. The Ion/off ratio was 104. Device parameters remained without significant change after months of fabrication. Stability of PMMA passivated devices, after gate and gate-drain bias stress is compared with data reported for other materials used as ESL or passivation layer, showing similar or better performance in preventing threshold voltage shifts, hump, reduction of mobility or of the on/off current ratio.
关键词： Low temperature HfO2/HIZO TFTs,Low operation voltage TFTs,PMMA passivated HIZO TFTs,Stability HfO2/HIZO TFTs
更新于2025-09-23 15:23:52
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Ferroelectric Polarization-Switching Dynamics and Wake-Up Effect in Si-Doped HfO <sub/>2</sub>
摘要： Ferroelectricity in ultra-thin HfO2 offers a viable alternative for ferroelectric memory. Reliable switching behavior is required for commercial applications; however, the many intriguing features of this material have not been resolved. Herein, we report an increase in the remnant polarization after electric field cycling, known as the 'wake-up' effect, in terms of the change in the polarization switching dynamics of a Si-doped HfO2 thin film. Compared with a pristine specimen, the Si-doped HfO2 thin film exhibited a partial increase in polarization after a finite number of ferroelectric switching behaviors. Polarization switching behavior was analyzed using the nucleation-limited switching model characterized by a Lorentzian distribution of logarithmic domain-switching times. The polarization switching was simulated using the Monte Carlo method with respect to the effect of defects. Comparing the experimental results with the simulations revealed that the wake-up effect in HfO2 thin film is accompanied by the suppression of disorder.
关键词： Domain switching,Ferroelectricity,Defects,FeRAM,HfO2,Thin films
更新于2025-09-23 15:23:52
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Enhanced Second Harmonic Generation from Ferroelectric HfO <sub/>2</sub> -Based Hybrid Metasurfaces
摘要： Integrated nonlinear metasurfaces leading to high-efficiency optical second harmonic generation (SHG) are highly desirable for optical sensing, imaging, and quantum photonic systems. Compared to traditional metal-only metasurfaces, their hybrid counterparts, where a non-centrosymmetric nonlinear photonic material is incorporated in the near field of a metasurface, they can significantly boost SHG efficiency. However, it is difficult to integrate such devices on-chip due to material incompatibilities, thickness scaling challenges and the narrow band gaps of nonlinear optical materials. Here, we demonstrate significantly enhanced SHG in on-chip integrated metasurfaces by using nanometer thin films of ferroelectric Y:HfO2. This material has the merit of CMOS compatibility, ultra-violet transparency up to 250 nm and significant scalability down to sub 10 nm when deposited on silicon. We observe a twenty times magnitude enhancement of the SHG intensity from the hybrid metasurface compared to a bare ferroelectric HfO2 thin film. Moreover, a 3-fold SHG enhancement is observed from the hybrid metasurface compared to a control structure using non-ferroelectric HfO2, demonstrating a major contribution to the SHG signal from ferroelectric Y:HfO2. The effective second-order nonlinear optical coefficient χ(2) of Y:HfO2 is determined to be 6.0 ± 0.5 pm/V, which is comparable to other complex nonlinear photonic oxide materials. Our work provides a general pathway to build an efficient on-chip nanophotonic nonlinear light source for SHG using ferroelectric HfO2 thin films.
关键词： second harmonic generation (SHG),nonlinear photonics,metasurface,plasmonics,ferroelectric Y:HfO2
更新于2025-09-23 15:23:52
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[IEEE 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Austin, TX, USA (2018.9.24-2018.9.26)] 2018 International Conference on Simulation of Semiconductor Processes and Devices (SISPAD) - Biaxial Strain based Performance Modulation of Negative-Capacitance FETs
摘要： In this work, we report device simulations conducted to study the performance of biaxially strained ferroelectric-based negative capacitance FETs (NCFETs). We adopted PbZr0.5Ti0.5O3 (PZT) and HfO2 as ferroelectric materials and applied biaxial strain using the first-principles method. It was found that PZT and HfO2 show different trends in the negative capacitance (NC) region under biaxial strain. Biaxial strain strongly affects the NC of PZT, whereas HfO2 is not as susceptible to biaxial strain as PZT. When no strain is applied, HfO2-based NCFETs exhibit a better performance than PZT-based NCFETs. However, the subthreshold slope and ON-state current are improved in the case of PZT-based NCFETs when the compressive biaxial strain is increased, whereas the performance of HfO2-based NCFETs is slightly degraded. In particular, the negative drain-induced barrier lowering and negative differential resistance vary considerably when compressive strain is applied to PZT-based NCFETs.
关键词： strain,negative capacitance FETs,ferroelectrics,density functional theory,HfO2,PZT
更新于2025-09-23 15:22:29
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Structural Stability of Hafnia-Based Materials at Ultra-High Temperature
摘要： This study assesses the structural stability at ultra-high temperature of the following selected compositions: 6.5 and 14 mol. % of RE2O3 (RE = Dy, Y, Er, Yb, and Lu) doped HfO2. Under thermal cycling and thermal shock, the structural stability was evaluated at 2400°C with water vapor flux using a specific test bench with a 3 kW CO2 laser. The cubic phase stability, which is theoretically important in the broad temperature range from 25 to 2800°C, was determined by a quantitative analysis of the X-ray diffractograms. Fully and partially stabilized HfO2, obtained respectively with 14 mol. % and 6.5 mol. % of dopants, showed different behaviors to thermal damage. Thermal expansion was measured up to 1650°C to anticipate dimensional changes of these stabilized samples and to be able to design an optimized material solution fitting with future combustion chamber requirements. All of these results were then considered in order to exhibit a trend on the thermal stability at 2400°C of the ionic radius of the dopants and their optimal doping rates.
关键词： Phase stability,UHTC,Thermal expansion,Spacecraft propulsion,HfO2
更新于2025-09-23 15:22:29
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The Growth Window of Ferroelectric Epitaxial Hf <sub/>0.5</sub> Zr <sub/>0.5</sub> O <sub/>2</sub> Thin Films
摘要： The metastable orthorhombic phase of hafnia is generally obtained in polycrystalline films, whereas in epitaxial films its formation has been much less investigated. We have grown Hf0.5Zr0.5O2 films by pulsed laser deposition and the growth window (temperature and oxygen pressure during deposition, and film thickness) for epitaxial stabilization of the ferroelectric phase is mapped. The remnant ferroelectric polarization, up to around 24 μC/cm2, depends on the amount of orthorhombic phase and strain, and increases with temperature and pressure for fixed film thickness. Leakage current decreases by increasing thickness and temperature, and particularly by reducing oxygen pressure. The coercive electric field (EC) depends on thickness (t) according the EC - t-2/3 scaling, which is observed by the first time in ferroelectric hafnia, and the scaling extends to thickness below 5 nm. The proven ability to tailor functional properties of high quality epitaxial ferroelectric Hf0.5Zr0.5O2 films paves the way towards progress in understanding their ferroelectric properties and prototyping devices.
关键词： Growth parameters,Pulsed laser deposition,Ferroelectric HfO2,Ferroelectric oxides,Epitaxial stabilization,Oxide thin films
更新于2025-09-23 15:22:29
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<i>Operando</i> diagnostic detection of interfacial oxygen ‘breathing’ of resistive random access memory by bulk-sensitive hard X-ray photoelectron spectroscopy
摘要： The HfO2-based resistive random access memory (RRAM) is one of the most promising candidates for non-volatile memory applications. The detection and examination of the dynamic behavior of oxygen ions/vacancies are crucial to deeply understand the microscopic physical nature of the resistive switching (RS) behavior. By using synchrotron radiation based, non-destructive and bulk-sensitive hard X-ray photoelectron spectroscopy (HAXPES), we demonstrate an operando diagnostic detection of the oxygen ‘breathing’ behavior at the oxide/metal interface, namely, oxygen migration between HfO2 and TiN during different RS periods. The results highlight the significance of oxide/metal interfaces in RRAM, even in filament-type devices.
关键词： resistive switching,HfO2,HAXPES,RRAM,interface
更新于2025-09-23 15:22:29
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Reflection coefficient of HfO <sub/>2</sub> -based RRAM in different resistance states
摘要： Impedance spectra of multiple resistive states in a stable-switching Resistive Random-Access Memory device based on a stack of Ru/HfO2/Zr/W was studied in this work. Using these observations, re?ection-coef?cients were extracted for different resistive states. Clear changes in the re?ection coef?cient for different resistive states were observed. The device in a low resistive state showed a signi?cantly higher re?ection coef?cient compared to its high resistive state. An increasing trend in the re?ection coef?cient was observed as the device state was gradually recon?gured towards lower resistances. Maximum frequency for re?ection increased with the decrease in the device area. The physics behind this observation is attributed to the interplay of oxygen ion transport among the interfacial layer, conductive ?lament, and HfO2-?lm.
关键词： resistive states,impedance spectra,HfO2,RRAM,reflection coefficient
更新于2025-09-23 15:21:21