Structural and electrical properties of low resistance Pt/Pd/Au contact on p-GaN

We have investigated electrical and structural properties of Pt/Pd/Au ohmic contact on p-type GaN:Mg (2.5 × 10¹⁷ cm⁻³) using Auger electron spectroscopy (AES) and glancing angle x-ray diffraction (GXRD) analysis. It was shown that the specific contact resistivity improved with increasing annealing temperature. The annealing of the contact at 600^∘C for 2 min in flowing N₂ atmosphere resulted in a specific contact resistivity of 3.1 × 10⁻⁵ Ω cm². Both GXRD and AES depth profile results show that Ga₃Pt₅, Ga₂Pd₅, and Au₇Ga₂ phases are formed at the interface region between metal and GaN when annealed at temperatures 600^∘C. Possible explanation is suggested to describe the annealing dependence of the specific contact resistivity of the Pt/Pd/Au contacts.     

Structure and properties of Zn-doped CoFe2O4 thin films via a sol–gel method

Zn-doped cobalt ferrite Co_0.9Zn_0.1Fe₂O₄ (CZFO) films with the spinel structure were fabricated on Pt(111)/Ti/SiO₂/Si(100) using a sol-gel method, and the effect of annealing temperature and time on structure and magnetic properties of the CZFO thin films were investigated. The coercivity and saturation magnetization of the films are not sensitive to annealing time, and increase with a rise in the annealing temperature below 800 °C. The CZFO thin films annealed at 800 °C show the best crystallization and the highest coercivity (3.5 kOe), and above 800 °C, the coercivities of the films decrease as a result of formation of multi-domains, while the saturation magnetization comes to stable.     

Effects of nitridation treatments for SBT/Ta2O5 stack gate capacitors

Abstract

In this study, effects of ICP nitride treatments on characteristics of ferroelectric gate stack capacitor were investigated for FET type ferroelectric memory applications. Pt/SBT(200nm)/Ta₂O₅(20nm)/ Nitride/Si (MeFINS) structure capacitors show wide ΔV (memory window) of 1.06V under ±3V operation, while Pt/SBT(200nm)/ Ta2O₅(20nm)/Si (MeFIS) capacitors without nitride treatments exhibit memory window of 0.60V. At the same time, an accumulation capacitance of the MeFINS structure device is higher than that of the MeFIS structure capacitor. This result implies that the ICP nitride treatment successfully suppresses a formation of low dielectric constant interfacial SiO_x layer and alleviates a series capacitance problem.     

Low dielectric dissipation and enhanced tunability of Ba0.6Sr0.4TiO3 thin films by the modified composition and multilayer structure

Ba_0.6Sr_0.4Ti_1+yO₃ (BST, y?=?0.1, 0.15, 0.2, 0.25, 0.3) thin films were fabricated on Pt-coated silicon substrates by modified sol-gel techniques. It was found that the tunability of BST thin films and dissipation factor decreased with the increase of Ti content. The multilayer structure of Ba_0.6Sr_0.4Ti_1+yO₃(200 nm)/Ba_0.6Sr_0.4TiO₃(100 nm)/Ba_0.6Sr_0.4Ti_1+yO₃ (200 nm; y?=?0.1, 0.2, 0.25) was designed to enhance the tunability. Our results indicated that the modified composition and multilayer structure were beneficial to lowering the dielectric dissipation and enhancing the tunability simultaneously. The tunability of 26.7% and dielectric dissipation of 0.013 were achieved for modified BST thin films.     

Effects of Ti/Ir top electrodes of PZT capacitors on the hydrogen related degradation

Abstract

Hydrogen annealing damages on properties of PZT capacitors and a role of Ti/Ir hybrid structure top electrodes on capacitors are investigated in this study. It is demonstrated that the capacitors with Ti/Ir structure top electrodes improve a resistance against hydrogen related degradation. As the thickness ratio of Ti/Ir increases, the capacitors show enhanced endurance against hydrogen damages. Especially, PZT (350nm) capacitors with Ti(80nm)/Ir(20nm) hybrid top electrodes show only 26% decrease in nonvolatile polarizations (P?_r) under ± 7V, while 67% of P?_r of ferroelectric capacitors with Ir top electrodes is reduced after forming gas annealing at 250°C for 10min. Based on the XPS analysis, ferroelectric characteristics of PZT thin film capacitors are degraded by destruction of Pb-O bond into metallic Pb due to hydrogen anneal on the catalytic top electrodes (Ir, Pt).     

Ionic conduction and crystal structure of aluminum doped NASICON-type LiGe<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic crystallized at different times and temperatures

In this communication, NASICON-type glass-ceramic (lithium germanium phosphate, LiGe₂(PO₄)₃) was prepared as lithium super ionic conductor using aluminum as dopant for ionic conduction improvement. The solid solution was Li_1?+?xAl_xGe_2-x(PO₄)₃ (x?=?0.5) that Ge⁴⁺ ions were partially substituted by Al³⁺ ions in crystal structure. Initial glasses were converted to glass-ceramics at different times and temperatures for maximum ionic conduction achievement. The crystals were characterized by X-ray Diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy-Dispersive X-ray spectroscopy (EDX), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS) methods. The maximum lithium ion conductivity for glass-ceramic, 5.32?×?10^?3 S/cm at 26 °C was obtained for specimen crystallized at 850 °C for 8 h with minimum activation energy of 0.286 eV. Increasing the crystallization temperature results in secondary phase formation in grain boundary and increasing in crystallization time results in microcracks formation in specimen. Both phenomena decreased the ionic conductivity.     

Effect of composite electrode thickness on the electrochemical performances of all-solid-state li-ion batteries

Several ceramic half-cells with differing electrode composite thicknesses but identical formulations were assembled using the spark plasma sintering (SPS) technique, in order to conduct comparable investigations of their kinetic limitations. The SPS technique was used to assemble the composite electrode and the electrolyte together within a few minutes. NASICON-type Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) ceramic was used as solid electrolyte, as it offers high ionic conductivity (3 × 10^?4 S.cm^?1 at 25 °C) with a Li⁺ transport number of 1. LiFePO₄ active material was used as a model material; it offers an average flat potential of 3.45 V vs Li⁺/Li and a reasonably high theoretical capacity of 170 mAh.g^?1. Surface capacity values (from 0.8 to 3.5 mAh.cm^?2), which are proportional to electrode thickness, remained quite close to the initial values after more than 20 cycles, even for a 325 μm thick electrode (3.5 mAh.cm^?2). The overpotential in the flat plateau region was proportional to the current density used, which means that it was dependent only on the cell’s ohmic drop. Performances were not limited by the ion transport into the solid electrolyte and composite electrode volume - as in classical Li-ion batteries - since the transport number of LAGP is one. Therefore, very thick electrode-enabling batteries with high-surface capacity can be considered.     

Low operating temperature CO sensor prepared using SnO<Subscript>2</Subscript> nanoparticles

A low operating temperature CO (carbon monoxide) sensor was fabricated from a nanometer-scale SnO₂ (tin oxide) powder. The SnO₂ nanoparticles in a size range 10–20 nm were synthesized as a function of surfactant (tri-n-octylamine, TOA) addition (0–1.5 mol%) via a simple thermal decomposition method. The resulting SnO₂ nanoparticles were first screen-printed onto an electrode patterned substrate to be a thick film. Subsequently, the composite film was heat-treated to be a device for sensing CO gas. The thermal decomposed powders were characterized by field-emission scanning electron microscopy (FESEM), X-ray diffractometry (XRD), and surface area measurements (BET). The CO-sensing performance of all the sensors was investigated. The experimental results showed that the TOA addition significantly decreased the particle size of the resulting SnO₂ nanoparticle. However, the structure of the powder coating was crucial to their sensing performance. After heat-treatment, the smaller particle tended to cause the formation of agglomeration, resulting in the decline of surface area and reducing the reaction site during sensing. However, the paths for the sensed gas entering between the agglomerated structure may influence the sensing performance. As a CO sensing material, the SnO₂ nanoparticle (~12 nm in diameter) prepared with 1.25 mol% TOA addition exhibited most stable electrical performance. The SnO₂ coating with TOA addition >0.75 mol% exhibited sensor response at a relatively low temperature of <50°C.     

Electrospun SnO2 nanofiber mats with thermo-compression step for gas sensing applications

SnO₂ nanofiber mats fabricated through electrospinning followed by thermo-compression and subsequent calcination steps exhibited unique morphologies facilitating efficient gas transport into the layers combined with high surface area (～73.5 m²/g, measured by BET) and small grain size (～5–15 nm), which are well suited for ultrasensitive gas detection. Single SnO₂ nanofibers were found to have a belt-like structure of closely packed nanocrystallites, facilitating excellent adhesion to the substrate and good electrical contact to the electrodes. I–V measurements of single SnO₂ nanofibers displayed ohmic behavior with electrical conductivity of 1.5 S/cm. Gas sensor prototypes comprising a random network of SnO₂ fibers exhibited high sensitivity when exposed to NO₂ at 225°C and CO at 300°C. A detection limit of 150 ppb NO₂ at 185°C was estimated by extrapolating the sensitivity results obtained on exposure to higher gas concentrations, demonstrating potential of achieving ultra-sensitive gas detection at low operating temperatures enabled by the present synthesis method.     

Dielectric properties of zinc titanate thin films prepared by Rf magnetron sputtering

Zinc titanate thin films of ~500 nm in thickness were synthesized by an RF magnetron sputtering using a sintered ceramic target. After annealing in temperature ranges of 300–800 °C, their phase transition and dielectric properties were investigated as a function of annealing temperature. Crystalline ZnTiO₃ phase was first detected at the annealing temperature of 500 °C within XRD detection limit though the sputtered film was mainly amorphous. ZnTiO₃ still remained as a main phase although the slight decomposition of ZnTiO₃ into Zn₂TiO₄ and TiO₂ occurred in association with the increase of annealing temperature. Dielectric properties were apparently improved with increase of annealing temperature and showed maximum value at 650 °C. Further higher temperature annealing caused inferior dielectric property. These results were explained in terms of the presence of TiO₂ (rutile) phase, resulting from the decomposition of ZnTiO₃ phase, and the morphology of the thin film.     

Effects of transition metal doping and surface treatment to improve the electrochemical performance of Li2MnO3

A novel strategy to improve the electrochemical performance of Li₂MnO₃ using transition metal doping by the mechanochemical process is proposed. Li₂MnO₃ precursors are treated with transition metal containing chemicals in the mechanochemical process, followed by heat treatment. Cr containing Li₂MnO₃, with only 1 mol% Cr doping, exhibits unique electrochemical properties with a large initial discharge capacity of 234.9 mAh?g^?1, which is superior to the 205.0 mAh?g^?1 of pristine Li₂MnO₃, and all other transition-metal containing oxides. The structures of Li₂MnO₃ and Li₂MnO₃ with the transition metal element doping (TM-Li₂MnO₃) are studied by x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM), and the electrochemical characteristics are further investigated using electrochemical impedance spectroscopy (EIS) measurements.     

Low-temperature synthesis in vacuum of c-axis oriented ferroelectric YMnO3 thin films using alkoxy-derived precursors

Abstract

Hexagonal YMnO₃ thin films were prepared on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates using alkoxy-derived precursor solutions. The films were prepared by spin coating the YMnO₃ precursor solutions and then, the films were calcined and crystallized via rapid thermal annealing in oxygen or vacuum ambient. The annealing conditions and substrates were critical for crystallization of ferroelectric YMnO₃ films. When annealed in vacuum, the films both on Pt(111)/TiO_x/SiO₂/Si and Pt(111)/Al₂O₃(0001) substrates crystallized to hexagonal YMnO₃ and the orientation depended on the substrates. The film on Pt(111)/Al₂O₃(0001) had c-axis orientation and the film on Pt(111)/TiO_x/SiO₂/Si had no preferred orientation. In addition, it was found that crystallization behavior, orientation and morphology of YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si substrates depended on the annealing condition. The heat-treatment in vacuum at initial stage for crystallization affected the restraint of perovskite phase and formation of hexagonal phase. The following heat-treatment in oxygen promoted the c-axis orientation and grain growth. The optimum annealing procedure for crystallization of the c-axis oriented YMnO₃ films on Pt(111)/TiO_x/SiO₂/Si was addressed.     

Doping level-dependent dry-etch damage in n-type GaN

The electrical effects of dry-etch on n-type GaN by an inductively coupled Cl₂/CH₄/H₂/Ar plasma were investigated as a function of ion energy, by means of ohmic and Schottky metallization methods. The specific contact resistivity (ρ_c) of the ohmic contact was decreased, while the leakage current in the Schottky diode was increased with increasing ion energy due to the preferential sputtering of nitrogen. At a higher rf power, an additional effect of damage was found on the etched sample, which was sensitive to dopant concentration in terms of the ρ_c of the ohmic contact. This can be attributed to effects such as the formation of deep acceptors as well as the electron-enriched surface layer within the depletion layer. Furthermore, the thermal annealing process enhanced the ohmic and Schottky properties of the heavily damaged surface.     

Characteristics of silver powders synthesized from silver 2-ethylhexanoate and Di-n-octylamine

Uniform spherical submicron silver powders were synthesized from a long-chain alkyl carboxylate of silver 2-ethylhexanoate and an alkylamine of di-n-octylamine in this study. The decomposition of silver 2-ethylhexanoate was observed to accelerate significantly in the presence of di-n-octylamine. SEM results revealed that submicron silver powders with sizes ranging from 200 nm to 300 nm and a high tap density of 4.0 g/cm³ were successfully prepared at 150 °C for 3 h in air. TGA reveals that approximately 1.2 wt.% organic residues composed mainly of 2-ethylhexanoate with a slight amount of di-n-octylamine were attached to the silver particles, as confirmed by the FTIR and XPS results. To evaluate the feasibility for practical applications, silver paste prepared from the silver powders synthesized in this study (NAG 80 paste) was examined and characterized, and the results were compared with those of two commercially available powders (SF80 and GH67 pastes). The electrical resistivities of the NAG80 films fired at 300 and 500 °C respectively read 1.8?×?10^?5?Ω-cm and 1.1?×?10^?5?Ω-cm, both superior to those of the SF80 and GH67 films. The fine quality of the uniform submicron spherical silver powders was verified and its potential use in thick film conductors confirmed.     

Structural, luminescent, and NO2 sensing properties of SnO2-core/V2O5-shell nanorods

SnO₂-core/V₂O₅-shell nanorods were synthesized using a two-step process: thermal evaporation of Sn powders and sputter-deposition of V₂O₅. The core-shell nanorods were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and photoluminescence spectroscopy. The diameters of these core-shell nanorods ranged from 80 to 200 nm with a shell layer thickness in the range of 7–13 nm. The cores and shells of the annealed core-shell nanorods consisted of a single crystal tetragonal-structured SnO₂ and a single crystal orthorhombic-structured V₂O_5, respectively. Photoluminescence measurements revealed the SnO₂ nanorods to have a yellow emission band centered at approximately 590 nm, which was enhanced significantly by the V₂O₅ coating and further by thermal annealing. The sensitivity of the networked SnO₂-core/V₂O₅-shell nanorod sensor to NO₂ gas was slightly higher than that of the bare SnO₂ nanorod sensor. The enhanced sensitivity of the SnO₂ nanorods by the V₂O₅ coating was attributed to the modulation of electron transport by the SnO₂-V₂O₅ heterojunction with an adjustable energy barrier height.     

Annealing temperature effect on ferroelectric and magnetic properties in Mn-added polycrystalline BiFeO3 films

We fabricated 5 at.% Mn-added polycrystalline BiFeO₃ films and investigated the annealing temperature effect on structural, ferroelectric and magnetic properties. In the x-ray diffraction patterns, only the diffraction peaks due to the BiFeO₃ structure were observed and no secondary phase could be observed at annealing temperatures between 773 and 923 K. Adding Mn suppressed the leakage current density in the high electric field region when compared to pure BiFeO₃ films. The conduction mechanism of the Mn-added BiFeO₃ films was dominated by Ohmic conduction. Remanent polarization of the Mn-added polycrystalline BiFeO₃ films for an applied electric field of approximately 1.5 mV/cm was 63 μC/cm² for the specimen annealed at 773 K and 46 μC/cm² for the specimen annealed at 923 K, although the remanent polarization still exhibited a tendency to increase with an increase in the electric field. Spontaneous magnetization was obtained at high annealing specimens. This study revealed that the annealing temperature strongly affected the ferroelectric and magnetic properties in Mn-added polycrystalline BiFeO₃ films. In addition, by optimizing the annealing temperature, we realized multiferroics coexistent with spontaneous magnetization and spontaneous polarization at room temperature in the Mn-added polycrystalline BiFeO₃ film.     

Enhanced dielectric properties of low-temperature-sintered Ba0.6Sr0.4TiO3 thick films

Ba_0.6Sr_0.4TiO₃ thick films were fabricated at a lower temperature of 880°C by adding Li₂O as sintering aid. A novel pretreatment of cold isostatic pressing was introduced to enhance the quality of films. After cold isostatic pressing prior to annealing, the thick film had a more compact morphology and better dielectric properties. The permittivity and tunability were increased to 1,318 and 19.04% from 925 and 14.81% while the dielectric loss was still kept low (1 MHz, 16 kV/cm). The enhanced properties and low-temperature sintering made BST thick films a potential candidate for Low Temperature Co-fired Ceramic (LTCC) and microwave tunable devices.     

Deposition of Europium Oxide on Si and its optical properties depending on thermal annealing conditions

We investigate the influence of the ambient gas during thermal annealing on the photoluminescence (PL) properties of europium compound thin films on Si substrates. The films were deposited by radio-frequency magnetron sputtering and subsequently annealed in N₂ or O₂ ambient gas by rapid thermal annealing (RTA). The results of X-ray diffraction indicate that the resulting europium compound annealed in N₂ ambient have several silicate phases such as EuSiO₃ and Eu₂SiO₄ compared to those annealed in O₂ ambient. The spectral results revealed that a broad luminescence associated with Eu²⁺ ions, with a maximum intensity at 600 nm and a FWHM of 110 nm, was observed from the thin film annealed at 1000 °C in N₂ ambient. However, a series of narrow PL spectra from Eu³⁺ ions were observed from the film annealed in O₂ ambient.     

Effects of rapid thermal annealing in different ambients on structural, electrical, and optical properties of ZnO thin films by sol-gel method

We studied the effects of rapid thermal annealing in different ambients on the structural, electrical and optical properties of the sol-gel derived ZnO thin films. All the films after annealing showed highly degree of (002) oriented in the X-ray diffractometry (XRD) patterns. The effects of annealing ambients on electrical properties of the films were studied. Carrier concentration, resistivity and mobility were found to be distinguished after annealed in different ambients. The sample with the lowest resistivity of 0.095 ??·cm and the largest mobility of 105.1 cm²/v·s was achieved after annealing in vacuum. XPS results indicated that more oxygen vacancies existed on the ZnO surface when annealed in vacuum than that in O₂.     

Fabrication and electrical properties of barium strontium titanate thick films by modified sol–gel method

A modified sol–gel method has been developed to prepare for the barium strontium titanate (Ba_0.6Sr_0.4TiO₃, BST) thick films. The films were deposited on either Pd–Ag electroded alumina substrates (Pd–Ag/Al₂O₃) or silver electroded alumina (Ag/Al₂O₃) substrates by spin coating technique or screen printing technique. The thickness of the film was in the range of 2–10 μm. The key point of the process is to disperse fine-grained BST ceramic powders prepared by high energy ball mill into BST sol solution to form a slurry for spin coating and screen printing. In order to enhance the stability of the slurry and to avoid crack formation of the thick film, organic macromolecular poly-vinylpyrrolidone (PVP) was added to the sol solution. The structure and surface morphology of the films were studied by X-ray diffraction and Scanning Electron Microscope (SEM) techniques. It is revealed that the thick films exhibit pure perovskite phase and are crack-free, dense and homogeneous. The dielectric constant and loss tangent of the thick films are about 1200 and 0.01, at 10 °C and 1 KHz, respectively.