Papers by Keyword: HfO₂

Abstract: In this paper, we have investigated the threshold voltage (V_TH) control of metal-oxide-nitride-oxide-Si (MONOS) nonvolatile memory (NVM) with high-k HfN/HfO₂ stacked layers for analog memory application. The Si surface atomically flattening was found to significantly improve the V_TH controllability of the MONOS NVM with high-k HfN/HfO₂ stacked layers. The multi-level-cell (MLC) operation by controlling the program voltage at the source and drain was demonstrated utilizing MONOS NVM with high-k HfN/HfO₂ stacked layers.

Abstract: 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.

Abstract: It is important to specify the Cu diffusion path in the oxide layer of a Cu/oxide/Pt-structured conducting-bridge random access memory (CB-RAM), in terms of both the elucidation of resistive switching mechanism and optimization of memory performance. A first-principle calculation is effective in specifying the Cu diffusion path with atomic resolution. However, reported results of first-principle calculations are based on too simplified model to depict the actual system of CB-RAM. In this paper, a periodic slab model for the first-principle calculation of Cu diffusion process in HfO₂-CB-RAM was proposed based on experimental results. Both the most probable Cu diffusion surface and Cu diffusion path were suggested by the first-principles calculations based on the model. It was also suggested that the Cu diffusion path was modified by introducing oxygen vacancy into the Cu diffusion surface.

Abstract: HfO₂ gate stack has been one of the most popular subjects of research in recent years due to its outstanding material properties, such as high-k (20~25), wide band gap (~5.68eV), and the compatibility with Si-based semiconductor process technology. However, the interfacial layer (IL) with a reduced k-value between HfO₂ dielectric and Si channel is still a critical issue for future ultra large scale integration (ULSI) technology application of the HfO₂ gate stack. Various ways have been studied to improve the IL properties of HfO₂ gate stack and to achieve ~1nm-thick equivalent oxide thickness (EOT) of the gate stack. Recently, fluorine incorporations into the HfO₂ gate stack have been suggested for improvement of the electrical properties of the gate stack by defect passivation.^1,2 However, it was reported that the SiO_x IL grows during the fluorine treatment of HfO₂ film, which finally led to degradation of electrical characteristics.² In this paper, we present interesting findings on the IL removal effect of fluorine incorporation into the HfO₂ gate stack where a post-gate dry cleaning technique is used with the NF₃/NH₃ plasma.

Abstract: A Compact and precise gonio-stage for Grazing incidence X-ray absorption fine structure (GIXAFS) measurement is presented in this paper. The gonio-stage can provide a range of 0-35mrad and a resolution of 0.012mrad. An expert alignment can be realized automatically by computer program to obtain precise initial condition. An accuracy verification test of angle control carried out on BL7C station in KEK gives a satisfied result. At last, high quality GIXAFS spectra for 200nm thick HfO₂/Si thin film were obtained.

Abstract: Aluminium and hafnium oxide films doped with CeCl₃/TbCl₃/MnCl₂ were deposited at 300 °C by ultrasonic spray pyrolysis. The films analysed by X-Ray diffraction exhibit a very broad band typical of amorphous materials. Non-radiative energy transfer from Ce³⁺ to Tb³⁺ and Mn²⁺ is observed upon UV excitation at 280 nm (peak emission wavelength of AlGaN-based LEDs). Such energy transfer gives place to a simultaneous emission of the donor and acceptor ions in the blue, green, yellow and red regions, resulting in cold white light emission, with chromaticity coordinates and colour temperatures: (0.30,0.32) and 7300 K (AOCTM film), and (0.32,0.37) and 6400 K (HOCTM film). Thus, this type of thin films might contribute to the development of efficient AlGaN-based LEDs pumped phosphors for cold white light generation.

Abstract: HfO₂ high-k dielectric films of 4nm and 5nm were both grown on Si substrate with the method of PEALD at 160°C. Both were treated with rapid thermal annealing (RTA) process at 500°C. High resolution transmission electron microscopy (HRTEM) indicated both films were not crystallized. X-ray photoelectron spectra (XPS) indicated that Hf-silicate was formed in the interfacial layer, and the valence-band offset (VBO) between the dielectric film and the substrate interface was calculated to be 3.5 eV. The electrical measurements indicated that the leakage current densities of the four and five nanometers’ sample were 1.0mA/cm² and 0.8mA/cm² at gate bias of 1V, and the equivalent oxide thicknesses of them were 0.9nm and 1.2nm respectively. Densities of interfacial states of them were calculated.

Abstract: HfO₂ Has High Effective Atomic Number and No Radioactive-Isotope as the Background Source, and it Can Be the Candidate for the High-Stopping Scintillator Instead of Lu₂SiO₅:Ce Scintillator Used in Medical Imaging, Astronomy and etc. However, HfO₂ Has an Extremely High Melting Point of 2774 °C, and it Is Difficult to Grow the Crystal from the Melt Using Crucible, as there Is No Suitable Metals, which Can Survive around that Temperature. Thus, Czochralski, Bridgman, and Micro-Pulling down Method Cannot Be Applied. Therefore we Investigated Optical Properties of a 17-mol% b-Doped (Stabilized) HfO2 Crystal Grown by the Skull Melting Method, and this Crystal Had a High Refractive Index of 2.5 at 550 nm, and the Maximum Emission Peak at ~550 nm from ⁵D₄ Excited States of Tb³⁺. In Addition, we Found the Radiation Reaction of the Crystal Irradiated with Alpha and Gamma Rays Measuring with a Photomultiplier.

Abstract: The reactively sputtered HfO₂ and HfSi_xO_y dielectrics have been investigated comparatively for metal-insulator-metal (MIM) capacitor applications. X-ray photoelectron spectroscopy analyses reveal the presence of Hf-O, Hf-O-Si and Si-O chemical bonds in the HfSi_xO_y films as well as lots of oxygen vacancies. The relative concentrations of Hf-O-Si and Si-O bonds increase with an increment of the power applied to the Si target. Further, it is found that the quadratic voltage coefficient of MIM capacitor decreases with increasing the Si content in the HfSi_xO_y dielectric in despite of a decrease in the resulting capacitance density. The HfSi_xO_y dielectric MIM capacitors with a capacitance density of ~8.4fF/μm² exhibit a quadratic voltage coefficient of 1840 ppm/V² at 100kHz, which is much smaller than 2750 ppm/V² for the HfO₂ dielectric MIM capacitors with a density of ~11.8fF/μm².

Abstract: HfO₂/Gd₂O₃/Si stack and Gd-doped HfO₂ (GDH) High-k films have been grown on p-type Si (001) substrates by RF sputtering. The amorphous structures of GDH high k film which be grown and annealed at 700°C have been determined by HRTEM. There is a interface layer between Gd₂O₃ film and Si in HfO₂/Gd₂O₃/Si stack. XPS measurement reveals that the peak shift to small binding energy for Hf4f due to the formation of Hf-O-Gd, and there are formations of gadolinium and hafnium silicate. A leakage current density of 1×10^-6 A/cm² at -1 V, a hysteresis voltage of 13 mV, a dielectric constant of 23 and a CET of 1 nm are obtained from a capacitor with Pt/HfO₂/Gd₂O₃/Si/Ag stack through C-V and I-V measurements. In addition, the HfO₂/Gd₂O₃/Si stack film has a higher breakdown voltage (~ 30 V) than that of GDH films.