Protein-Assembled Nanocrystal-Based Vertical Flash Memory Devices with Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Integration

This work presents vertical flash memory devices with protein-assembled PbSe nanocrystals as a floating gate and Al₂O₃ as a control oxide. The advantage of a vertical structure is that it improves cell density. Protein assembly improves uniformity of nanocrystals, which reduces threshold voltage variation among devices. The introduction of Al₂O₃ as a control oxide provided lower voltage/faster operation and hence less power consumption compared with the devices fabricated with SiO₂. The integration of Al₂O₃ appeared to be compatible with the protein assembly approach. In conclusion, Al₂O₃ has the potential to become the high-k control oxide due to its relatively high electron/hole barrier heights, and high permittivity.     

Superior suppression of gate current leakage in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors

AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al₂O₃/Si₃N₄ bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si₃N₄-based MIS-HFET devices. Al₂O₃/Si₃N₄ bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si₃N₄-based MIS devices under reverse gate bias, and leakage as low as 1×10⁻¹¹ A/mm at −15 V has been achieved in Al₂O₃/Si₃N₄-based MIS devices. By using ultrathin Al₂O₃/Si₃N₄ bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si₃N₄-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al₂O₃ and nitrides. This work demonstrates that Al₂O₃/Si₃N₄ bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.     

Growth of Polarity-Controlled ZnO Films on (0001) Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

The polarity control of ZnO films grown on (0001) Al₂O₃ substrates by plasma-assisted molecular-beam epitaxy (P-MBE) was achieved by using a novel CrN buffer layer. Zn-polar ZnO films were obtained by using a Zn-terminated CrN buffer layer, while O-polar ZnO films were achieved by using a Cr₂O₃ layer formed by O-plasma exposure of a CrN layer. The mechanism of polarity control was proposed. Optical and structural quality of ZnO films was characterized by high-resolution X-ray diffraction and photoluminescence (PL) spectroscopy. Low-temperature PL spectra of Zn-polar and O-polar samples show dominant bound exciton (I₈) and strong free exciton emissions. Finally, one-dimensional periodic structures consisting of Zn-polar and O-polar ZnO films were simultaneously grown on the same substrate. The periodic inversion of polarity was confirmed in terms of growth rate, surface morphology, and piezo response microscopy (PRM) measurement.     

Electrical properties of InAs-SiO<Subscript>2</Subscript>-In<Subscript>2</Subscript>O<Subscript>3</Subscript> MIS structures with a modified interface

The effect of composition of the electrolyte used in producing a thin anodic oxide layer at the surface of a semiconductor substrate on the electrical properties of the InAs-SiO₂-In₂O₃ metal-insulator-semiconductor structures is studied. It is shown that introduction of ammonium fluoride into the electrolyte results in the formation of an interface with the density of surface states below 5 × 10¹⁰ cm^?2 eV^?1, the built-in charge (4–5 × 10¹¹ cm^?2, and the maximum relaxation time of the surface potential.     

Correlation of in-situ reflectance spectra and resistivity of GaN/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> interfacial layer in metalorganic chemical vapor deposition

The correlation between the resistivity of an undoped GaN/Al₂O₃ interfacial layer and in-situ reflectance spectrum in metalorganic chemical vapor deposition and the mechanism of this correlation were investigated. The first minimum reflectance during the initial high-temperature GaN growth was found to be a good indicator of the resistivity of the GaN buffer. The background electron concentration and mobility were both higher in the samples with higher indicative reflectance at that point. The resistivity of the GaN buffer layer was predominantly determined by an ∼0.25-μm-thick layer near the GaN/Al₂O₃ interface. Atomic force microscope (AFM) and high-resolution x-ray diffraction (HRXRD) results showed that the samples with higher indicative reflectance had smaller sized but higher density nuclei before the high-temperature GaN growth and lower screw threading dislocation (TD) density in the initially grown GaN. The difference in the background electron concentration and mobility of the interfacial layer was related to the relatively higher concentration of the O and Al diffused from Al₂O₃, which is also dependent on the size and density of the nuclei. These differences were found not to affect the structural and electrical properties or the surface morphology of AlGaN/GaN high electron-mobility transistors (HEMTs, except for the buffer conduction) when the GaN buffer is thick enough (e.g., ∼2.5 μm).     

Optical and dielectric characteristics of the rare-earth metal oxide Lu<Subscript>2</Subscript>O<Subscript>3</Subscript>

The characteristics of the Lu₂O₃ oxide and their variations controlled by compositional defects are studied. The defects are anion vacancies produced on partial reduction of the oxide. Such defects exhibit features typical of quantum objects and have a profound effect on the optical transmittance spectrum, the character of conduction (insulator or semiconductor properties) and the order of magnitude of the permittivity ɛ (capable of varying from 11.2 to 125). The structural features of vacancies in the oxides are considered, and the effect of vacancies on the polarization, conductivity, and lattice vibrations is studied. The studies are carried out in the temperature range 200–900 K, the wavelength range 0.03–50 μm, and the current frequency range 10²–10⁵ Hz. The rare-earth metal oxides attract interest for applications in microelectronics due to their high permittivity (several times higher than the permittivity of SiO₂) and, hence, the prospects for use of these oxides instead of SiO₂.     

How r-Plane Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Surface Modifications Impact the Growth of Epitaxial (001) CeO<Subscript>2</Subscript> Thin Films

We present evidence that it is the presence or absence of atomic terraces with a specific crystallographic orientation on the (102) Al₂O₃ surface that promotes growth of single-crystal (001) CeO₂ films over polycrystalline (111) CeO₂ films. The CeO₂ film nucleates so that the [010] and [100] directions of the film align parallel and perpendicular to the terrace edges. In the absence of terraces, multidomain (111) CeO₂ films result in which the in-plane orientation of the two domains are rotated by 85.71°, so that a [110] CeO₂ direction aligns parallel to either the or Al₂O₃ direction.     

Impression Creep of a Lead-Free Sn-1.7Sb-1.5Ag Solder Reinforced by Submicron-Size Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Particles

In the present study, the Sn-1.7Sb-1.5Ag solder alloy and the same material reinforced with 5 vol.% of 0.3-μm Al₂O₃ particles were synthesized using the powder metallurgy route of blending, compaction, sintering, and extrusion. The impression creep behavior of both monolithic and composite solders was studied under a constant punching stress in the range of 20 MPa to 110 MPa, at temperatures in the range of 320 K to 430 K. The creep resistance of the composite solder was higher than that of the monolithic alloy at all applied stresses and temperatures, as indicated by their corresponding minimum creep rates. This was attributed to the dispersive distribution of the submicron-sized Al₂O₃ particles in the composite solder. Assuming a power-law relationship between the impression stress and velocity, average stress exponents of 5.3 to 5.6 and 5.8 to 5.9 were obtained for the monolithic and composite materials, respectively. Analysis of the data showed that, for all loads and temperatures, the activation energy for both materials was almost stress independent, with average values of 44.0 kJ mol⁻¹ and 41.6 kJ mol⁻¹ for the monolithic and composite solders, respectively. These activation energies are close to the value of 46 kJ mol⁻¹ for dislocation climb, assisted by vacancy diffusion through dislocation cores in the Sn. This, together with the stress exponents of about 5 to 5.9, suggests that the operative creep mechanism is dislocation viscous glide controlled by dislocation pipe diffusion.     

Light-emitting nanocomposites on the basis of ZnS:Cu deposited into porous anodic Al<Subscript>2</Subscript>O<Subscript>3</Subscript> matrices

A new nanocomposite material, specifically, copper-doped zinc sulfide deposited by vacuum thermal sputtering into anodic aluminum-oxide matrices is proposed for the production of promising electroluminescent light sources. The structure of the chemical bonds is studied, which makes it possible to determine the mechanisms responsible for ultraviolet photoluminescence and electroluminescence of the materials in an electric field at a voltage amplitude of 220 V and frequency of 50 Hz. This will allow the use of the nanocomposite in electroluminescent light sources connected to the standard electrical network.     

Surface texture of single-crystal silicon oxidized under a thin V<Subscript>2</Subscript>O<Subscript>5</Subscript> layer

The process of surface texturing of single-crystal silicon oxidized under a V₂O₅ layer is studied. Intense silicon oxidation at the Si–V₂O₅ interface begins at a temperature of 903 K which is 200 K below than upon silicon thermal oxidation in an oxygen atmosphere. A silicon dioxide layer 30–50 nm thick with SiO₂ inclusions in silicon depth up to 400 nm is formed at the V₂O₅–Si interface. The diffusion coefficient of atomic oxygen through the silicon-dioxide layer at 903 K is determined (D ≥ 2 × 10^–15 cm² s^–1). A model of low-temperature silicon oxidation, based on atomic oxygen diffusion from V₂O₅ through the SiO₂ layer to silicon, and SiO _x precipitate formation in silicon is proposed. After removing the V₂O₅ and silicon-dioxide layers, texture is formed on the silicon surface, which intensely scatters light in the wavelength range of 300–550 nm and is important in the texturing of the front and rear surfaces of solar cells.     

Er<Subscript>2</Subscript>O<Subscript>3</Subscript> for high-gain waveguide amplifiers

Following the demonstration of room-temperature luminescence, Er₂O₃ has been explored as a high-gain medium for ultra-compact waveguide amplifiers. With sputtered and annealed films, we measure three radiative lifetimes (7 ms, 0.8 ms, and 0.5 ms) and upconversion coefficients at 4.2 K. We have correlated these measurements with three crystalline phases: the thermodynamically stable bcc phase and the metastable fcc and hcp phases. The 7-ms lifetime is correlated with the fcc phase, implying the metastable crystal state has a profound influence on inhibiting upconversion interaction between neighbor Er atoms. Measurements indicate optical gain >3 dB/cm is possible.     

Solid-State Reaction Mechanism and Deliquescence Phenomenon of K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.7</Subscript>Al<Subscript>0.3</Subscript>O<Subscript>3</Subscript> Ceramic

Development of (K,Na)NbO₃-based ceramics has attracted much attention in recent decades. In this work, K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K₂CO₃, Na₂CO₃, and Nb₂O₅ as well as K₂CO₃, Na₂CO₃, and Al₂O₃, which can influence the sintering behavior of the mixture. (K,Na)NbO₃ and (K,Na)AlO₂ were present in the sintered K_0.5Na_0.5Nb_0.7Al_0.3O₃ ceramic, with the latter leading to deliquescence. During the sintering process, Al₂O₃ reacts with alkali oxides (Na₂O and K₂O), which are the decomposition products of carbonates, to form (K,Na)AlO₂. In addition, Al₂O₃ is more likely to react with K₂O compared with Na₂O.     

Conduction Mechanisms in Multiferroic Multilayer BaTiO<Subscript>3</Subscript>/NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/BaTiO<Subscript>3</Subscript> Memristors

Memristive devices and materials are extensively studied as they offer diverse properties and applications in digital, analog and bio-inspired circuits. In this paper, we present an important class of memristors, multiferroic memristors, which are composed of multiferroic multilayer BaTiO₃/NiFe₂O₄/BaTiO₃ thin films, fabricated by a spin-coating deposition technique on platinized Si wafers. This cost-effective device shows symmetric and reproducible current–voltage characteristics for the actuating voltage amplitude of ±10 V. The origin of the conduction mechanism was investigated by measuring the electrical response in different voltage and temperature conditions. The results indicate the existence of two mechanisms: thermionic emission and Fowler–Nordheim tunnelling, which alternate with actuating voltage amplitude and operating temperature.     

Microwave Dielectric Properties of ZnO-2TiO<Subscript>2</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> Ceramics with BaCu (B<Subscript>2</Subscript>O<Subscript>5</Subscript>) Addition

The influence of BaCu(B₂O₅) (BCB) addition on the sintering temperature and microwave dielectric properties of ZnO-2TiO₂-Nb₂O₅ (ZTN) ceramic has been investigated using dilatometry, x-ray diffraction, scanning electron microscopy, and microwave dielectric measurements. A small amount of BCB addition to ZTN can lower the sintering temperature from 1100°C to 900°C. The reduced sintering temperature was attributed to the formation of the BCB liquid phase. The ZTN ceramics containing 3.0 wt.% BCB sintered at 900°C for 2 h have good microwave dielectric properties of Q × f = 19,002 GHz (at 6.48 GHz), ε _r = 45.8 and τ _f  = 23.2 ppm/°C, which suggests that the ceramics can be applied in multilayer microwave devices, provided that Ag compatibility exists.     

Effect of Proton Irradiation on Interface State Density in Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/GaN and Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgO/GaN Diodes

Proton irradiation of Sc₂O₃/GaN and Sc₂O₃/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 10⁹ cm⁻², corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 10¹¹ cm⁻² to 1.03 × 10¹² cm⁻² in Sc₂O₃/GaN diodes and from 2.33 × 10¹¹ to 5.3 × 10¹¹ cm⁻² in Sc₂O₃/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.     

Structural studies of ZnS:Cu (5 at %) nanocomposites in porous Al<Subscript>2</Subscript>O<Subscript>3</Subscript> of different thicknesses

We present EXAFS, XANES, and X-ray diffraction data on nanoscale ZnS:Cu (5 at %) structures fabricated by the thermal deposition of a ZnS and Cu powder mixture in porous anodic alumina matrices with a pore diameter of 80 nm and thicknesses of 1, 3, and 5 μm. The results obtained are compared with data on ZnS:Cu films deposited onto a polycor surface. According to X-ray diffraction data, the samples contain copper and zinc compounds with sulfur (Cu₂S and ZnS, respectively); the ZnS compound is in the cubic (sphalerite) and hexagonal (wurtzite) modifications. EXAFS and XANES studies at the K absorption edges of zinc and copper showed that, in samples deposited onto polycor and alumina with thicknesses of 3 and 5 μm, most copper atoms form the Cu₂S compound, while, in the sample deposited onto a 1-μm-thick alumina layer, copper atoms form metallic particles on the sample surface. Copper crystals affect the Zn–S interatomic distance in the sample with a 1-μm-thick porous Al₂O₃ layer; this distance is smaller than in the other samples.     

Thin-film reactions during diffusion soldering of Cu/Ti/Si and Au/Cu/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> with Sn interlayers

The multilayer thin-film systems of Cu/Ti/Si and Au/Cu/Al₂O₃ were diffusion-soldered at temperatures between 250°C and 400°C by inserting a Sn thin-film interlayer. Experimental results showed that a double layer of intermetallic compounds (IMCs) η-(Cu_0.99Au_0.01)₆Sn₅/δ-(Au_0.87Cu_0.13)Sn was formed at the interface. Kinetics analyses revealed that the growth of intermetallics was diffusion-controlled. The activation energies as calculated from Arrhenius plots of the growth rate constants for (Cu_0.99Au_0.01)₆Sn₅ and (Au_0.87Cu_0.13)Sn are 16.9 kJ/mol and 53.7 kJ/mol, respectively. Finally, a satisfactory tensile strength of 132 kg/cm² could be attained under the bonding condition of 300°C for 20 min.     

Optical Properties of K<Subscript>2</Subscript>O-Li<Subscript>2</Subscript>O-WO<Subscript>3</Subscript>-B<Subscript>2</Subscript>O<Subscript>3</Subscript> Glasses: Evidence of Mixed Alkali Effect

Glass with compositions xK₂O-(30 ? x)Li₂O-10WO₃-60B₂O₃ for 0 ≤ x ≤ 30 mol.% have been prepared using the normal melt quenching technique. The optical reflection and absorption spectra were recorded at room temperature in the wavelength range 300–800 nm. From the absorption edge studies, the values of the optical band gap (E _opt) and Urbach energy (ΔE) have been evaluated. The values of E _opt and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple Di-Domenico model.     

Phenomenological description of dispersion of 8-60-nm-thick silicon thin films into drops on Al<Subscript>2</Subscript>O<Subscript>3</Subscript> inert surface

The dispersion of 8-60-nm-thick amorphous silicon thin films on a surface of aluminum oxide was studied using scanning electron microscopy and measuring the current through a thin film during vacuum heating. The temperature of the observed process of silicon thin film dispersion does not correspond to its expected melting temperature, which suggests a dispersion, rather than melting, process, since the thin amorphous silicon film already has a yield property. It was found that the dispersion temperature increases as the silicon thickness is reduced. It is assumed that this phenomenon is caused by the structure and energy effect of the Al₂O₃ substrate, which propagates into silicon to a certain depth.     

Fabrication and Characterization of Pb(Zr<Subscript>0.53</Subscript>,Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>-Pb(Nb<Subscript>1/3</Subscript>,Zn<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> Thin Films on Cantilever Stacks

0.9Pb(Zr_0.53,Ti_0.47)O₃-0.1Pb(Zn_1/3,Nb_2/3)O₃ (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO₂/Si or SiO₂/Si₃N₄/SiO₂/poly-Si/Si membranes capped with a sol–gel-derived ZrO₂ buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO₃ (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO₂ surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.