HfO2 Matrix Research Articles

Improved performance of non-volatile memory with Au-Al2O3 core-shell nanocrystals embedded in HfO2 matrix

In this paper, we demonstrate a charge trapping memory with Au-Al2O3 core-shell nanocrystals (NCs) embedded in HfO2 high-k dielectric. Transmission electron microscopy images clearly show the Au NCs surrounded by Al2O3 shells in the HfO2 matrix. Electrical measurements show a considerable memory window (3.6 V at ±8 V), low program/erase operation voltages, and good endurance. Particularly, data retention is improved both at room temperature and high temperature compared to the NC structure without shell. An energy band model is given for the improved retention characteristic. This Au-Al2O3 core-shell NCs memory device has a strong potential for future high-performance nonvolatile memory application.

Oxygen vacancy mediated large magnetization in chemically synthesized Ni-doped HfO2 nanoparticle powder samples

A cost-effective solution based chemical method of synthesizing nanostructured Hf1−xNixO2 with 0 ≤ x ≤ 0.05 in powder form, from easily available laboratory reagents is presented. Production of uniformly shaped and sized (13–16 nm) nanoparticles with excellent crystallinity is demonstrated by transmission electron microscopy, x-ray diffraction (XRD) studies and Raman spectra. The origin of ferromagnetism in the Ni-doped HfO2 nanoparticle powder samples is investigated. Magnetization studies along with x-ray photoelectron spectroscopy (XPS) studies suggest that some of the Ni-ions are substitutionally incorporated in HfO2 host matrix. The XPS studies also show the presence of a small fraction of Ni metal (most likely Ni nanoclusters), undetected in standard XRD for lightly doped samples, suggesting that the observed room temperature ferromagnetism is at least partly due to Ni nanoclusters. The observed large value (∼6 emu/g) of magnetization, may not be entirely due to the presence of Ni metal cluster, can be understood in terms of oxygen vacancies created to retain charge neutrality of HfO2 matrix as some Ni ions replace Hf4+, resulting in ferromagnetic interactions at lower concentrations.

Microstructural characteristics and phonon structures in luminescence from surface oxidized Ge nanocrystals embedded in HfO2 matrix

Ge nanocrystals embedded in HfO2 matrices were prepared by rf magnetron sputtering technique. Transmission electron micrographs reveal the formation of spherical shape Ge nanocrystals of 4–6 nm diameters for 800 °C and 6–9 nm for 900 °C annealed samples. X-ray photoelectron spectroscopy confirms the formation of surface oxidized Ge nanocrystals. Embedded Ge nanocrystals show strong photoluminescence peaks in visible and ultraviolet region even at room temperature. Spectral analysis suggests that emission in 1.58 and 3.18 eV bands originate from TΣ(TΠ)→S0, and TΠ′→S0 optical transitions in GeO color centers, respectively, and those in the range 2.0–3.0 eV are related to Ge/O defects at the interface of the oxidized nanocrystals. Temperature dependent photoluminescence study has revealed additional fine structures with lowering of temperature, the origin of which is attributed to the strong coupling of electronic excitations with local vibration of germanium oxides at the surface.

Microstructural, chemical bonding, stress development and charge storage characteristics of Ge nanocrystals embedded in hafnium oxide

We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO2 matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively stressed Ge NCs in HfO2 matrix. Frequency dependent electrical properties of HfO2/Ge-NCs in HfO2/HfO2 sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly examined and has been shown to be negligible on the overall device performance.

Room temperature ferromagnetism in Ni-doped HfO2 thin films

In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism. The observed magnetic moment is too large to be attributed to any secondary phase/magnetic clusters.

Stable HfO2 based Layers Fabricated by RF Magnetron Sputtering

Structural and composition properties of HfO2-based layers fabricated by RF magnetron sputtering were studied by means of X-ray diffraction and transmission electron microscopy, Energy dispersive spectroscopy and ATR-FTIR techniques versus the deposition parameters and post-deposition annealing treatment. It was observed that the temperature at which amorphous-crystalline transformation of pure HfO2 layers occurs depends on deposition conditions. It was found that silicon incorporation in HfO2 matrix plays main role in the stability of the layers and allows to increase the temperature of layer crystallization up to 900-1100{degree sign}C.

The Synthesization of Si Nanocrystals Embedded in HfO2 Matrix by Electron Beam co-Evaporation Technique

Silicon nanocrystals synthesized by electron beam co-evaporation (EBCE) of Si and HfO2 mixture are studied. HfO2 and Si powder are uniformly mixed together in certain proportion. The mixed Si & HfO2 powder is evaporated by electron beam evaporation technique. Then the SRO thin films are annealed at different temperatures at 2 hours in N2 ambient to synthesize Silicon nanocrystals. For the sample annealed at 1050 ° at 2 hours, silicon nanocrystals with different size between 3 nm to 5 nm, the mean diameter of 4.0 nm, and the density of 3×1012 cm-2 are evidently observed by high resolution transmission electron microscopy (HRTEM). Then the Raman scattering and photoluminescence spectra arising from Silicon nanocrystals are further confirmed the above result. In addition, the samples annealed at 900 ° for 2 hours to 8 hours are carefully studied by Raman spectra. This way of preparing SRO thin films and Si NCs has unique advantage and is controllable and flexible

Synthesis and electrical characterization of a MOS memory containing Si nanoparticles embedded in high-k HfO2 thin film

The size-controlled, non-agglomerated, 5nm Si nanoparticles were fabricated in the middle of HfO2 layers using a pulsed laser ablation (PLA) system at a relatively low pressure and formed trilayer structure (HfO2/Si-nps/HfO2) on n-type Si. These high density nanoparticles (>1x1011 cm-2) were imaged with SEM. The crystallinity of HfO2 and Si nanoparticles were characterized by HRTEM. The memory effect of a Si nanoparticles floating gate memory structure consisting of HfO2 tunneling and control oxides have been investigated by means of high-frequency (1 MHz) capacitance-voltage (C-V) measurements. HRTEM study revealed that the Si nanoparticles are single crystals with average size of about 5 nm in diameter and are well distributed within the amorphous HfO2 matrix. The memory effect was observed by the hysteresis loop in the C-V curves and a high storage charge density of about 5×1011cm-2 and a large flat-band voltage shift of 4.8V have been achieved due to charging and discharging to the nanoparticles.

HfO2-based Thin Films Deposited by RF Magnetron Sputtering

AbstractHfO2-based layers prepared by RF magnetron sputtering were studied by X-ray diffraction, infrared absorption spectroscopy and transmission electron microscopy techniques. The effect of the deposition parameters and post-deposition annealing treatment on the properties of the layers was investigated. The amorphous-crystalline transformation of pure HfO2 layers is observed to be stimulated by annealing treatment at 800 ° C. It was found that the incorporation of silicon in HfO2 matrix allows to prevent crystallization of the layers and to shift the crystallization temperature to values up to 900 °C.

Broad excitation of Er luminescence in Er-doped HfO2 films

We investigated the broad and sensitized luminescence properties of Er-doped HfO2 films synthesized by pulsed laser deposition (PLD) and ion implantation techniques. In the investigation we focused on the mechanism of energy transfer in the host matrix. Based on the comparison of photoluminescence (PL), photoluminescence excitation (PLE), and cathode-luminescence (CL), as well as on microstructure measurements, an excitation transfer process resulting in the broad excitation for Er, luminescence at 1540 nm, is identified. In this process, the oxygen vacancies and Hf in the host HfO2 serve mainly as effective sensitizers for neighboring Er ions in the nonresonant excitation process. Furthermore, the direct Er3+ intra-4f transitions and full spectral emission of Er ions in the HfO2 matrix are clearly observed under the wide-spectrum excitation in the CL measurement. This reveals more detailed features for the energy transfer and transition processes.

Partial Crystallization of $\hbox{HfO}_{2}$ for Two-Bit/Four-Level SONOS-Type Flash Memory

The nonvolatile memory properties of the partially crystallized HfO2 charge storage layer are investigated using short-channel devices of gate length Lg down to 80 nm. Highly efficient two-bit and four-level device operation is demonstrated by channel hot electron injection programming and hot hole injection erasing for devices of Lg > 170 nm, although the reduction of the memory window is observed for devices of Lg < 170 nm. A memory window of 5.5 V, ten-year retention of Vth clearance larger than 1.5 V between adjacent levels, endurance for 105 programming/erasing cycles, and immunity to programming disturbances are demonstrated. Flash memory with partially crystallized HfO2 shows a larger memory window than HfO2 nanodot memory, assisted by the enhanced electron capture efficiency of an amorphous HfO2 matrix, which is lacking in other types of reported nanodot memory. The scalability, programming speed, Vth control for two-bit and four-level operation, endurance, and retention are also improved, compared with NROM devices that use a Si3N4 trapping layer.

Enhanced electrical characteristics of Au nanoparticles embedded in high-k HfO2 matrix

We present experimental results for laser-induced Au nanoparticle (NP) embedded in a HfO2 high-k dielectric matrix. Cross-sectional transmission electron microscopy images showed that the Au NPs of 8nm in diameter were clearly embedded in HfO2 matrix. Capacitance-voltage measurements of Pt∕HfO2∕AuNPs∕HfO2 on p-type Si substrate reliably exhibited metal-oxide-semiconductor behavior with a large flatband shift of 4.7V. In addition, the charge retention time at room temperature was found to exceed 105h. This longer time was attributed to the higher electron barrier height via high work function of the Au NP.

Effect of Al-content and Post Deposition Annealing on the Electrical Properties of Ultra-thin HfAlxOy Layers

ABSTRACTScaled HfAlxOy/SiO2 stacks down to 1.5 nm EOT have been achieved. Although the addition of Al to the HfO2 matrix can be beneficial, it is observed that the benefit of using a Hf-aluminate is compromised if the film has a high Al-content. This is observed in terms of a dielectric constant close to that of pure Al2O3 (∼ 9) and a large amount of negative fixed charge in the film (∼ 1012 cm-2). Using oxygen post deposition anneals we have been able to reduce flatband voltage shifts associated with fixed charge as well as CV hysteresis. In terms of scaling, the benefit of using a high-k material is compromised if a SiO2 layer is also present in the gate stack. Therefore, it is necessary to perform an O2 PDA at moderate temperatures or in low O2 partial pressures in order to control the thickness of the interfacial oxide layer.