Formation and composition of titanium oxinitride nanocrystals synthesized via nitridizing titanium oxide for nonvolatile memory applications

Formation and composition analyses of titanium oxinitride nanocrystals (NCs) fabricated via treating a magnetron co-sputtered thin film of titanium and silicon dioxide with a rapid thermal annealing in nitrogen ambient were demonstrated for nonvolatile memory applications. Phase separation characteristics with different annealing conditions were examined by transmission electron microscopy and chemical bonding characteristics were confirmed by X-ray photon emission spectra. It was observed that a blanket layer composed mainly of titanium oxide was still present as annealing temperature was increased to 700 °C, associated with the thermodynamically stable phase of titanium oxide. Furthermore, a higher thermal treatment of 900 °C induced formation of a well-separated NC structure and caused simultaneously partial nitridation of the titanium oxide, thereby forming titanium oxinitride NCs. A significant capacitance-voltage hysteresis in threshold voltage shift at 1 V was easily achieved under a small sweeping voltage range of + 2 V/−2 V, and a memory window retention of 2.2 V was obtained after 10⁷ s by extrapolation under a 1 s initial-program/erase condition of + 5 V/−5 V, respectively.     

Low temperature synthesis and electrical characterization of germanium doped Ti-based nanocrystals for nonvolatile memory

Chemical and electrical characteristics of Ti-based nanocrystals containing germanium, fabricated by annealing the co-sputtered thin film with titanium silicide and germanium targets, were demonstrated for low temperature applications of nonvolatile memory. Formation and composition characteristics of nanocrystals (NCs) at various annealing temperatures were examined by transmission electron microscopy and X-ray photon-emission spectroscopy, respectively. It was observed that the addition of germanium (Ge) significantly reduces the proposed thermal budget necessary for Ti-based NC formation due to the rise of morphological instability and agglomeration properties during annealing. NC structures formed after annealing at 500 °C, and separated well at 600 °C annealing. However, it was also observed that significant thermal desorption of Ge atoms occurs at 600 °C due to the sublimation of formatted GeO phase and results in a serious decrease of memory window. Therefore, an approach to effectively restrain Ge thermal desorption is proposed by encapsulating the Ti-based trapping layer with a thick silicon oxide layer before 600 °C annealing. The electrical characteristics of data retention in the sample with the 600 °C annealing exhibited better performance than the 500 °C-annealed sample, a result associated with the better separation and better crystallization of the NC structures.     

Formation and nonvolatile memory characteristics of W nanocrystals by in-situ steam generation oxidation

The authors provide the formation and memory effects of W nanocrystals nonvolatile memory in this study. The charge trapping layer of stacked a-Si and WSi₂ was deposited by low pressure chemical vapor deposition (LPCVD) and was oxidized by in-situ steam generation system to form uniform W nanocrystals embedded in SiO₂. Transmission electron microscopy analyses revealed the microstructure in the thin film and X-ray photon-emission spectra indicated the variation of chemical composition under different oxidizing conditions. Electrical measurement analyses showed the different charge storage effects because the different oxidizing conditions influence composition of trapping layer and surrounding oxide quality. Moreover, the data retention and endurance characteristics of the formed W nanocrystal memory devices were compared and studied. The results show that the reliability of the structure with 2% hydrogen and 98% oxygen at 950 °C oxidizing condition has the best performance among the samples.     

Formation of the distributed NiSiGe nanocrystals nonvolatile memory formed by rapidly annealing in N2 and O2 ambient

In this work, electrical characteristics of the Ge-incorporated Nickel silicide (NiSiGe) nanocrystals memory device formed by the rapidly thermal annealing in N₂ and O₂ ambient have been studied. The trapping layer was deposited by co-sputtering the NiSi₂ and Ge, simultaneously. Transmission electron microscope results indicate that the NiSiGe nanocrystals were formed obviously in both the samples. The memory devices show obvious charge-storage ability under capacitance-voltage measurement. However, it is found that the NiSiGe nanocrystals device formed by annealing in N₂ ambient has smaller memory window and better retention characteristics than in O₂ ambient. Then, related material analyses were used to confirm that the oxidized Ge elements affect the charge-storage sites and the electrical performance of the NCs memory.     

Formation of NiSi2/SiNX compound nanocrystal for nonvolatile memory application

In this paper, the NiSi₂/SiN_X compound NCs (CNCs) structure is studied to further improve the retention. To introduce the nitride based traps, NiSi₂ was also sputtered in the mixture gas of Ar (50 sccm) and NH₃ (10 sccm) at room temperature, and the NiSi₂/SiN_X CNCs can be easily formed after rapid thermal annealing. In addition, standard memory devices with single and double NiSi₂ nanocrystal were also prepared for comparison. By XPS analyses, the nanocrystals fabricated in the ambiance of NH₃ can be confirmed to be composited of NiSi₂ and SiN_X compound. According to memory characteristics results, better retention characteristic of device with single-layer NiSi₂/SiN_X compound nanocrystal NVMs can be observed after 10⁴ s, raises from 50% to 72% in comparison with the control sample, even better than the double-layer NiSi₂ nanocrystal, 58%. Indeed, the formation of NiSi₂/SiN_X CNCs can improve the retention characteristics remarkably due to the additional tunnel barrier and deep traps in the nitride.     

Resistive switching characteristics of ytterbium oxide thin film for nonvolatile memory application

This paper studies the effects of both the positive and negative forming processes on the resistive switching characteristics of a Pt/Yb₂O₃/TiN RRAM device. The polarity of the forming process can determine the transition mechanism, either bipolar or unipolar. Bipolar behavior exists after the positive forming process, while unipolar behavior exists after the negative forming process. Furthermore, the bipolar switching characteristics of the Pt/Yb₂O₃/TiN device can be affected by using a reverse polarity forming treatment, which not only reduces the set and reset voltage, but also improves the on/off ratio.     

二氧化硅基质包埋硅纳米晶的微观结构和发光性能

利用离子注入和后续高温退火的方法制备了包埋在二氧化硅(Si02)基质中的硅纳米晶,研究了不同离子注入浓度试样的微观结构和发光性能,以及硅纳米晶的生长机理和发光机制.结果表明:较小的硅纳米晶(<5 nm)其生长机理符合Ostwald熟化机理,较大的纳米晶(>10 nm)则是由多个小纳米晶粒通过孪晶组合或融合而成的;离子注入浓度为8×1016cm-2的样品其发光强度是离子注入浓度为3×1017cm-2样品发光强度的5倍;硅纳米晶内部的微观结构缺陷(如孪晶和层错)对其荧光强度有很大的影响.     

Charge storage characteristics of iridium silicide nanocrystals embedded in SiO2 matrix for nonvolatile memory application

In this work, the nanostructure-assisted “Al/SiO₂/Ir-silicide-NCs/SiO₂/P-Si-sub/Al” stack with iridium silicide nanocrystals (Ir-silicide-NCs) embedded between two SiO₂ layers has been demonstrated in the application of nonvolatile memory for the first time. A significant memory window voltage of 14.2 V at sweeps of +/− 10 V by capacitance-voltage measurement can be reached, when well-distributed Ir-silicide-NCs are observed in cross-sectional TEM examination. In this case, the trap density is estimated to be about 1.06 × 10¹³ cm^− 2, indicating a high trapping efficiency stack for nonvolatile memory application.     

Optimization of silicon nanocrystals growth process by low pressure chemical vapor deposition for non-volatile memory application

The processes of silicon nanocrystals (Si-NCs) growth on both SiO₂ and Si₃N₄ substrates by low pressure chemical vapor deposition have been systematically investigated. A two-step process was adopted for Si-NCs growth: nucleation at a high temperature (580-600 °C) and growth at a low temperature (550 °C). By adjusting the pre-deposition waiting time and deposition time, the density, size and uniformity can be effectively controlled. Compared to the growth of Si-NCs on SiO₂, the coalescence speed of Si-NCs on Si₃N₄ is faster. Uniform Si-NCs with a high density of 1.02 × 10¹² cm^− 2 and 1.14 × 10¹² cm^− 2 have been obtained on SiO₂ and Si₃N₄, respectively. Finally, a Si-NCs-based memory structure with a 2.1 V memory window was demonstrated.     

Fabrication of titania films by sol-gel method using transparent colloidal aqueous solutions of anatase nanocrystals

The fabrication of dense or porous titania films by the sol-gel method using anatase colloidal solutions was examined. When anatase colloidal solutions without surfactants were deposited on a substrate, the anatase films thus obtained had a relatively high refractive index (~ 2.0). Porous films were fabricated using the anatase colloidal solutions with surfactants. Some films had phase separation structures on the submicron scale, such as spinodal decomposition, which consisted of anatase nanocrystal agglomerate regions and surfactant regions. When the dispersion of the anatase colloids was improved, mesoporous films could also be fabricated, although mesopores were irregular in size, shape, and arrangement.     

Electromagnetic wave absorption properties of multi-walled carbon nanotubes decorated with La-doped BaTiO3 nanocrystals synthesized by a solvothermal method

Ba_1−xLa_xTiO₃/multi-walled carbon nanotube (MWCNT) nanocomposites with different concentrations of La³⁺ doping, were synthesized by a solvothermal process. The prepared nanocomposites had a hybrid microstructure in which Ba_1−xLa_xTiO₃ nanocrystals with diameter of 10–30 nm were firmly immobilized on the MWCNTs sidewalls. Electromagnetic (EM) wave absorption properties of La-doped BaTiO₃/MWCNT nanocomposites were investigated in the 7.5–18 GHz frequency range for an absorber thickness of 1 mm. The reflection loss (RL) calculated from the EM parameters of the samples, moved to low frequencies with increasing La³⁺ doping. The widest absorption bandwidth, with the lowest frequency range, was observed in a nanocomposite doped with 1.5 at% La³⁺. An RL exceeding −5 dB for this sample was obtained in the frequencies ranging from 9.6 to 16.3 GHz, with the optimal RL of −17.4 dB at 10.9 GHz, due to enhanced interfacial polarization resulting in developed ε^″r${{\epsilon }^{″}}_{\text{r}}$. In addition, the RL for the sample shifted to the low frequency region and the peaks became sharper in the 2–18 GHz frequency range with increasing absorber thickness. For BaTiO₃/MWCNT nanocomposites, La³⁺ doping can greatly improve the EM wave absorbing ability in a thin absorber thickness and the donor-doped nanocomposites show promise for application in EM wave shielding materials with broad absorption bandwidths.     

Characterization of indium tin oxide film and practical ITO film by electron microscopy

In order to clarify the structure of indium oxide film containing tin and tin oxides, various In₂O₃ based films prepared by vacuum evaporation were studied using high-resolution electron microscope (HREM). Indium tin oxide (ITO) film was composed of In₂O₃ and SnO. SnO crystal also contained (110) or (101) crystallographic shear (CS) structures that indicate excess amounts of tin. The CS structure was also found in a commercial ITO film having the resistivity of 2×10⁻⁴ Ω cm.     

Strain distribution in freestanding Si/SixNy membranes studied by transmission electron microscopy

Strain was induced in a bridge-shaped freestanding Si membrane (FSSM) by depositing an amorphous Si_xN_y layer to surround the Si membrane. Convergent beam electron diffraction revealed that compressive strain is distributed uniformly along the horizontal direction in Si_xN_y-deposited FSSM. On the other hand, strain decreases to almost zero at the ends of the FSSM, where the Si_xN_y layer beneath the Si layer is replaced by a SiO₂ buried oxide layer.     

Characterization of copper sulfide nanostructured spheres and nanotubes synthesized by microwave-assisted solvothermal method

Copper sulfide nanostructured spheres and nanotubes were successfully synthesized, using a microwave-assisted solvothermal method, by the decomposition of [Cu(CH₃CSNH₂)₂]Cl₂ complexes, formed by the reaction of CuCl₂·2H₂O and CH₃CSNH₂ in ethylene glycol at different pH values, and identified by CHNS/O and FTIR analyses. The decrease in bonding energy of N-H revealed the coordination of copper ions and thioacetamide molecules. It was specified that nitrogen atoms of thioacetamide molecules were used to form Cu-thioacetamide complexes. XRD, SEM, TEM and SAED analyses show that the products were hexagonal CuS spheres in an extremely low pH solution, and hexagonal CuS nanotubes at a pH 13. Their Raman spectra show sharp peaks at 473 cm^− 1, identified as the S-S stretching mode of S₂ ions at the 4e sites.     

Three-dimensional analytical techniques for evaluation of osseointegrated titanium implants

Abstract

Osseointegration, the direct bonding of titanium implant materials with bone, is critical for implant success where nanostructured surface features contribute to nano-osseointegration. However, we also know that features and processes on the microscale influence the biocompatibility of implant materials. We highlight the advantages of using mutlilength scale analyses, focusing on three-dimensional techniques, ranging from X-ray microcomputed tomography, to focused ion beam, to high resolution electron tomography to identify markers of osseointegration. A titanium implant with modified biomimetic coating studied in vitro and in vivo at various time points is used to exemplify the complementary information gained from three-dimensional analyses from the micro- to nanoscale.     

Silicon nano-crystalline structures fabricated by a sequential plasma hydrogenation and annealing technique

Silicon nano-crystalline structures have been prepared from amorphous silicon films on silicon substrates using direct-current plasma hydrogenation and annealing at temperatures about 450 °C. Plasma power densities about 5.5 W/cm² were found to be suitable for the creation of nano-porous layers. The nano-porous structures produced visible luminescence at room temperature as confirmed by photoluminescence spectroscopy. The effects of plasma power and annealing temperature on the grain size and luminescence properties of these layers have been investigated by scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and photoluminescence. Lowering the temperature during the hydrogenation step led to an increase in the diameter of the grains. In addition, lowering the plasma power density caused the distribution of the porous surface structures to become less widely distributed and the formation of more packed structures resulted.     

Influence of fluorine substitution on the morphology and structure of hydroxyapatite nanocrystals prepared by hydrothermal method

Hydroxyapatite (HAp) nanocrystals with different levels of fluorine substitution (P/F = 0, 6, 4 and 2) on the OH sites were produced via hydrothermal method. The fluorine substitution was found to alter the morphology of crystals appreciably. The aspect ratio and the crystallinity of HAp crystals increased with increasing fluorine substitution. The presence of broad ring and hallow ring patterns in electron diffraction suggests the low-crystalline nature of HAp crystals. With increasing fluorine substitution, the diffraction patterns exhibited discrete rings and numerous diffraction spots, implying the increased crystallinity. Raman spectra from the HAp nanoparticles also support the less-crystalline nature of the pristine HAp and the enhanced crystallization by fluorine substitution. In HAp crystals processed with no fluorine substitution, surface energy and planar Ca²⁺ density are less sensitive to the crystallographic orientation because of its low-crystalline nature, favoring equi-axed or slightly elongated particles. The addition of fluorine apparently increased the crystallinity, enhancing the orientation dependent growth and accordingly the aspect ratio. Osteoblast proliferation was observed to be enhanced by fluorine substitution in HAp. In vitro biological data support that the excellent osteoblastic cell viability and functional activity of the fluoridated apatite.     

Investigation of the microstructure, mechanical properties and tribological behaviors of Ti-containing diamond-like carbon films fabricated by a hybrid ion beam method

Diamond-like carbon (DLC) films with various titanium contents were investigated using a hybrid ion beam system comprising an anode-layer linear ion beam source and a DC magnetron sputtering unit. The film composition and microstructure were characterized carefully by X-ray photoelectron spectroscopy, transmission electron microscopy and Raman spectroscopy, revealing that the doped Ti atoms had high solubility in the DLC films. The maximum solubility was found to lie between about 7 and 13 at.%. When the Ti content was lower than this solubility, the doped Ti atoms dissolved in the DLC matrix and the films exhibited the typical features of the amorphous DLC structure and displayed low compressive stresses, friction coefficients and wear rates. However, as the doped content exceeded the solubility, Ti atoms bonded with C atoms, resulting in the formation of carbide nano-particles embedded in the DLC matrix. Although the emergence of the carbide nano-particles promoted graphitizing due to a catalysis effect, the film hardness was enhanced to a great extent. On the other hand, the hard carbides particles caused abrasive wear behavior, inducing a high friction coefficient and wear rate.     

Direct evidence for dislocation-free zone in Fe–5% Si fractured by Charpy impact test

Defect structure in the subsurface region below a fracture surface of an Fe–5% Si specimen that had been fractured by a Charpy impact test at 77 K was examined by transmission electron microscopy. The specimen was fabricated by a focused ion beam technique to enable analysis of areas that had been carefully selected on the basis of observation. Near the nucleation site of the crack, many dislocations were observed just beneath the fracture surface. Far away from the nucleation site, no dislocations at all were observed in the subsurface region of the fracture surface. Between these two extreme positions, a dislocation-free zone was observed.     

Interfacial microstructure and defect analysis in Cu(In,Ga)Se([sub]2)-based multilayered film by analytical transmission electron microscopy and focused ion beam

Interfacial microstructures of Cu(In,Ga)Se₂(CIGS)-based multilayered film are closely characterized by TEM (transmission electron microscopy), SEM (scanning electron microscopy) and FIB (focused ion beam). A cross-sectional TEM, energy dispersive X-ray spectroscopy and energy-filtered TEM reveal that a pronounced Cu diffusion occurs across the interface of the CdS/CIGS, which leads to a large amount of Cu rich in the CdS layer and a Cu-deficient sub-surface in the CIGS layer as well as a rough interfacial structure. TEM studies further reveal that the interface microstructures in the multilayered film are dissimilar, both ZnO/CdS and CdS/CIGS interfaces are strongly bonded whereas the CIGS/Mo interface is weakly bonded and interface separation occasionally occurs. Mo back contact layer shows a well adhesion to glass substrate.Detailed observation on defects in the CIGS-based multilayered film is carried out by 3D (3-dimensional) FIB and SEM techniques. Sequential 2D (2-demensional) cross-sectioning shows that dominant growth-defects in the CIGS and top SiO₂ layers are micro-scale crack, appearing as diversified morphologies. The micro-scale crack in the CIGS layer is possibly released by propagating into the adjacent layer while the crack in the SiO₂ layer is relieved usually by forming a small particle behind. It is noted that in the multilayered film the interface frequently acts as crack initiation sites due to distinct thermal expansion coefficients.