Degradation and breakdown characteristics of Al/HfYOx/GaAs capacitors

Effects of surface passivation and the interfacial layer on the reliability characteristics of Al/HfYO_x/GaAs metal-oxide-semiconductor capacitor structures are reported. Stress-induced leakage current mechanism, critical for understanding the degradation and breakdown in Al/HfYO_x/GaAs capacitors, has been studied in detail. While the devices fabricated with (NH₄)₂S-passivated GaAs substrates show both the soft and hard breakdown failure modes, capacitors with ultrathin interfacial layer (Ge or Si) show only hard breakdown. It is shown that the degradation dynamics follows more closely the logistic power-law relationship rather than the conventional power-law model, frequently used to describe leakage current conduction in high-k gate dielectrics.     

Preparation and photoluminescence properties of Eu-doped Ga2O3 nanorods

GaOOH:Eu³⁺ nanorods with different aspect ratios were prepared by hydrothermal method at 140 °C. - and β-Ga₂O₃:Eu³⁺ were converted from as-prepared GaOOH:Eu³⁺ particles by calcination at 500 and 850 °C, respectively. The products were characterized with X-ray diffraction (XRD), transmission electron microscope (TEM) and photoluminescence (PL). Results show that solution pH values play a key role in the formation of the GaOOH:Eu³⁺ powders with different morphologies and - and β-Ga₂:Eu³⁺ inherit the morphology of GaOOH:Eu³⁺ exactly. The photoluminescence characteristics of β-Ga₂O₃:Eu³⁺ were also investigated. Experimental results reveal that the color purity of β-Ga₂O₃:Eu³⁺ nanorods with high aspect ratio is enhanced in comparison with β-Ga₂O₃:Eu³⁺ nanorods with low aspect ratio.     

Electrical properties of Ge metal-oxide-semiconductor capacitors with La2O3 gate dielectric annealed in different ambient

Ge metal-oxide-semiconductor capacitors with La₂O₃ as gate dielectric are fabricated by e-beam evaporation of La₂O₃ followed by post-deposition annealing in different gases (NH₃, N₂, NO, N₂O and O₂). Experimental results indicate that the NH₃, NO, N₂O and O₂ anneals give higher interface-state and oxide-charge densities, and thus larger gate leakage current, with the highest for the O₂ anneal due to the growth of an unstable GeO_x interlayer. On the other hand, the NH₃ annealing improves the k value of the dielectric, while the annealings in O₂-containing ambients (NO, N₂O and O₂) lead to the formation of a low-k GeO_x interlayer, thus decreasing the equivalent k value. Compared with the above four samples, the sample annealed in N₂ exhibits not only larger k value (18.3) and smaller capacitance equivalent thickness (2.14 nm), but also lower leakage current density (~ 10⁻³ Acm^− 2 at V_g = 1 V) and smaller interface-state density (4.5 × 10¹¹ eV^− 1 cm^− 2).     

Preparation and studies of Eu and Tb co-doped Gd2O3 and Y2O3 sol-gel scintillating films

Eu³⁺ (2.5 at.%) and Tb³⁺ (0.005-0.01 at.%) co-doped gadolinium and yttrium oxide (Gd₂O₃ and Y₂O₃) powders and films have been prepared using the sol-gel process. High density and optical quality thin films were prepared with the dip-coating technique. Gadolinium (III) 2,4-pentadionate and yttrium (III) 2,4-pentadionate were used as precursors, and europium and terbium in their nitrate forms were used as doping agents. Chemical and structural analyses (infrared spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy) were conducted on both sol-gel precursor powders and dip-coated films. The morphology of thin films heat-treated at 700 °C was studied by means of atomic force microscopy. It was shown that the highly dense and very smooth films had a root mean roughness (RMS) of 2 nm ± 0.2 (A = 0.0075 Tb³⁺) and 24 nm ± 3.0 (B = 0.01 Tb³⁺). After treatment at 700 °C, the crystallized films were in the cubic phase and presented a polycrystalline structure made up of randomly oriented crystallites with grain sizes varying from 20 to 60 nm. The X-ray induced emission spectra of Eu³⁺- and Tb³⁺-doped Gd₂O₃ and Y₂O₃ powders showed that Tb³⁺ contents of 0.005, 0.0075 and 0.01 at.% affected their optical properties. Lower Tb³⁺ concentrations (down to 0.005 at.%) in both systems enhanced the light yield.     

The erosion behaviors of Y2O3 and YF3 coatings under fluorocarbon plasma

We deposited Y₂O₃ and YF₃ coatings using the electron beam evaporation method and investigated their erosion behavior under fluorocarbon plasma at various bias voltages. TEM analysis revealed that the Y₂O₃ coating was strongly fluorinated under the plasma, and the thickness of the fluorinated layer was increased up to a few hundred nm with bias voltage. XPS analysis also confirmed a significant Y-F bonding on the surface and showed fluorine content at a maximum on the surface, decreasing with the depth from the surface. The etch rate increased with bias voltage and it was slightly higher in YF₃ coating, implying that the etch rate depends on the surface fluorination and its removal by incident ions. Without applying bias voltage, the chemical reaction with the fluorocarbon plasma dominated, resulting in the formation of fine fluoride particles on the Y₂O₃ surface, but the YF₃ coating was intact and clean for the same condition. These results indicate that the YF₃ coating may be a new plasma-facing material that produces fewer contamination particles.     

Investigation of Ti-doped Gd2O3 charge trapping layer with HfO2 blocking oxide for memory application

In this study, Ti-doped gadolinium oxide (Gd₂TiO₅) is investigated by X-ray diffraction, atomic force microscopy, and capacitance voltage curves (C-V) as the charge trapping layer in metal-oxide-high-k material-oxide-silicon structure memories. It was found that the Gd₂TiO₅ charge-trapping layer with an HfO₂ blocking layer annealed at 900 °C had a larger window of 4.8 V in the C-V hysteresis loop, a faster program/erase speed and good retention without significant drift up to 10⁴ cycles. This excellent performance was attributed to the well-crystallized Gd₂TiO₅ structure and the higher probability of charges being trapped in the deep trap energy level of the Gd₂TiO_5. This Gd₂TiO₅ memory device with post-annealing shows considerable promise for use in future flash memory applications.     

Effects of Y2O3 addition on microwave dielectric characteristics of Al2O3 ceramics

Microwave dielectric characteristics of alumina ceramics with yttria addition were investigated. The sintering temperature was lowered, and the dielectric constant (ε_r) did not remarkably change by adding yttria. The microwave dielectric loss (tan δ) increased from 8.4 × 10^− 5 to 2.2 × 10^− 4, due to the presence of Al₅Y₃O₁₂ secondary phase. The grain size had significant effects on the dielectric loss, and there was an optimum grain size where the dielectric loss reached the minimum.     

Structural and optical properties of heteroepitaxial beta Ga2O3 films grown on MgO (100) substrates

Gallium oxide (Ga₂O₃) films were deposited on MgO (100) substrates by metalorganic vapor phase epitaxy. Structure analyses showed that the films deposited at 550-700 °C were epitaxial β-Ga₂O₃ films with an out of plane relationship of β-Ga₂O₃(100)||MgO(100). The film deposited at 650 °C showed the best crystallinity and the microstructure of the film was investigated by high resolution transmission electron microscopy. A theoretical model of the growth mechanism was proposed and the in-plane epitaxial relationship was given to be β-Ga₂O₃[001]||MgO<011>. A four-domain structure inside the epitaxial film was clarified. The β-Ga₂O₃ film deposited at 650 °C showed an absolute average transmittance of 95.9% in the ultraviolet and visible range, which had an optical band gap of 4.87 eV.     

Charge trapping characteristics of Al2O3/Al-rich Al2O3/SiO2 stacked films fabricated by radio-frequency magnetron co-sputtering

A thin-film structure comprising Al₂O₃/Al-rich Al₂O₃/SiO₂ was fabricated on Si substrate. We used radio-frequency magnetron co-sputtering with Al metal plates set on an Al₂O₃ target to fabricate the Al-rich Al₂O₃ thin film, which is used as a charge storage layer for nonvolatile Al₂O₃ memory. We investigated the charge trapping characteristics of the film. When the applied voltage between the gate and the substrate is increased, the hysteresis window of capacitance-voltage (C-V) characteristics becomes larger, which is caused by the charge trapping in the film. For a fabricated Al-O capacitor structure, we clarified experimentally that the maximum capacitance in the C-V hysteresis agrees well with the series capacitance of insulators and that the minimum capacitance agrees well with the series capacitance of the semiconductor depletion layer and stacked insulator. When the Al content in the Al-rich Al₂O₃ is increased, a large charge trap density is obtained. When the Al content in the Al-O is changed from 40 to 58%, the charge trap density increases from 0 to 18 × 10¹⁸ cm^− 3, which is 2.6 times larger than that of the trap memory using SiN as the charge storage layer. The device structure would be promising for low-cost nonvolatile memory.     

Modulation of luminescence emission spectra of N-doped ß-Ga2O3 nanowires by thermal evaporation

In this study, we have synthesized N-doped ß-Ga₂O₃ nanowires on a p-type Si (100) substrate at the temperature of 850 °C through evaporation to modulate the spectra of the luminescence emission. Both TEM and XRD analyses confirmed that N-doped ß-Ga₂O₃ is monoclinic with a uniform mean diameter of 30 nm and a length up to several tens of micrometers. As determined by selected area diffraction (SAD), the growth direction of N-doped ß-Ga₂O₃ nanowires is [002]. The optical properties of the N-doped ß-Ga₂O₃ nanowires were studied by cathodoluminescence (CL) at the 10 and 300 K, exhibiting a UV and red light emission as a function of the nitrogen dopant. The results serve to reinforce the potential of N-doped ß-Ga₂O₃ nanowires for optoelectronic device applications.     

Enhanced leakage current behavior of Sr2Ta2O7−x/SrTiO3 bilayer dielectrics for metal-insulator-metal capacitors

Metal-Insulator-Metal (MIM) capacitors are one of the most essential components of radio frequency devices and analog/mixed-signal integrated circuits. In order to obtain high capacitance densities in MIM devices, high-k materials have been considered to be promising candidates to replace the traditional insulators. The challenging point is that the dielectric material must demonstrate high capacitance density values with low leakage current densities.In this work, SrTiO₃ based MIM capacitors have been investigated and the electrical performance of the devices have been optimized by using bilayered systems of Sr₂Ta₂O_7−x/SrTiO₃ with different thicknesses of Sr₂Ta₂O_7−x. Sputtering X-Ray photoelectron spectroscopy (XPS) measurements have been applied to investigate the interfaces between the thin film constituents of the MIM stacks. The optimized bilayered system provides a leakage current density of 8∗10^− 8 A/cm² at 2 V (bottom electrode injection) and a high capacitance density of 13 fF/μm².     

Preparation of Y2O3:Ce phosphors by homogeneous precipitation inside bicontinuous cubic phase

Yttrium oxide doped with cerium (Y₂O₃:Ce³⁺) blue emitting phosphors was prepared by a new method called the bicontinuous cubic phase (BCP) method. The experimental results showed that the prepared precursors were amorphous yttrium hydroxide with a spherical shape and primary size 30-50 nm. After heat treatment, high crystallinity and luminescence efficiency phosphors were obtained. The obtained Y₂O₃:Ce³⁺ phosphors had a strong blue emitting at 400 nm. The optimum Ce³⁺ concentration was 1 mol% to obtain the highest PL intensity. This study indicated that the calcining temperature of 700 °C needed for high luminescence efficiency in this work is much lower than 1000 °C or above needed for the conventional solid-state method.     

Growth of La2Mo2O9 films on porous Al2O3 substrates by radio frequency magnetron sputtering

Synthesis conditions of La₂Mo₂O₉ thin film by radio frequency (RF) sputtering technique on Al₂O₃ ceramic substrates are studied. It is found that the deposition temperature and oxygen partial pressure are the most important factors for obtaining pure La₂Mo₂O₉ films. Varying both parameters, Mo-rich, stoichiometric, and Mo-deficient films are obtained. With increasing the La:Mo ratio, films become denser. A crust layer is observed on top of the Mo-rich and the Mo-deficient films. The formation of the La₂Mo₂O₉ phase is discussed with respect to the sputtering mechanism.     

Interface phenomena in the Y2O3/(Al–Cu) system

Wetting behavior and the interface reaction in the Y₂O₃/(Cu–Al) system were investigated at 1423 K. A contact angle of about 130° was measured in the Y₂O₃/Cu system. Aluminum addition to copper improves wetting and the transition from non-wetting to wetting (θ ≤ 90°) was observed for the alloy with 50 at.% Al. The microstructure examination of the interface indicates that Al reacts with yttria, yttrium dissolves in the melt and a crater of AlYO₃ is formed at the substrate. The interface interaction in the Y₂O₃/(Cu–Al) system is in a good agreement with the results of a thermodynamic analysis in the Y–Al–Cu–O system. The crater depth and the macroscopic final contact angles are correlated with the Y and Al activities in the melt.     

Growth and stability of Ga2O3 nanospheres

Gallium oxide thin films were prepared by thermal evaporation and deposition of Ga₂O₃ on NaCl(001) cleavage planes at varying substrate temperatures, oxygen pressures and deposition rates. The structure of the so-prepared thin films was checked by Transmission Electron Microscopy and Selected Area Diffraction and also characterized by X-ray Photoelectron Spectroscopy and Atomic Force Microscopy, both in the as-deposited state and after different oxidative and reductive treatments. The substrate temperature proved to be most crucial for the structure of the gallium oxide films, ranging from low-contrast amorphous structures at low substrate temperatures (298 K) to nanosphere structures at higher temperatures (580 K). The stability of the films was found to be mainly determined by the interaction of substrate temperature and deposition rate. Crystalline β-Ga₂O₃ structures were obtained after oxidative, reductive and annealing treatments at and beyond 773 K suggesting that the crystallization is mainly a thermal annealing effect.     

纳米SiO2/低密度聚乙烯复合材料的陷阱特性与电击穿机制

以低密度聚乙烯（LDPE）为聚合物基体,通过熔融共混的方式填充不同粒径的纳米SiO₂无机颗粒,制备纳米SiO₂/LDPE复合材料,研究提高聚乙烯电绝缘性能的纳米改性方法和机制。利用SEM表征纳米SiO₂在LDPE基体中的微观形态和分散程度,采用DSC和偏光显微镜（PLM）分析纳米SiO₂对LDPE基体结晶度和结晶形态的影响,通过热刺激电流法（TSC）分析纳米SiO₂/LDPE复合材料的陷阱密度和陷阱能级,并结合电击穿的Weibull分布研究纳米复合材料的击穿机制。研究结果表明:纳米SiO₂填充可以改变复合材料结晶度,进而增加LDPE基体本征结构缺陷和陷阱密度,同时填充纳米SiO₂颗粒可引入比LDPE基体本征陷阱更深的陷阱能级,纳米SiO₂填充颗粒引入的陷阱能级深度随着复合材料结晶度的增加而先增大后减小,填充浓度3wt%时可最有效地通过俘获载流子而抑制电击穿过程,纳米SiO₂/LDPE复合材料的击穿场强达到最高值。与60 nm SiO₂颗粒相比,30 nm SiO₂填充颗粒具有更高的比表面积,界面电极化导致更高的介电常数,更高密度的纳米界面深陷阱态对于提高电击穿场强更有效。当填充浓度为5wt%时,纳米颗粒的团聚作用导致纳米复合材料的击穿强度降低。基于电双层理论提出了电子捕捉模型和界面结构模型,合理阐释了纳米SiO₂/LDPE复合材料的微观陷阱特性及宏观电击穿机制。      

Growth of SiOx nanofibers using FeSi and β-FeSi2 substrates with Ga droplets

The growth of SiO_x nanofibers on iron silicide substrates with Ga droplets was examined. It is found that well-aligned, highly oriented nanofibers were grown in an orderly fashion with a high density from FeSi substrates. Though the length of the nanofibers depends on the growth time and the growth temperature, their diameters were about 20 nm throughout the nanofibers grown under the examined growth conditions. On the other hand, although the evidence of the growth of highly oriented, dense and well-aligned nanofibers was not obtained, the growth of small piece of nanofibers was evident, for the use of β-FeSi₂ substrates.     

Growth and structural investigations of epitaxial hexagonal YMnO3 thin films deposited on wurtzite GaN(001) substrates

Epitaxial hexagonal YMnO₃ (h-YMnO₃) films having sharp (00l) X-ray diffraction peaks were grown above 700 °C in 5 mTorr O₂ via pulsed laser deposition both on as-received wurtzite GaN/AlN/6H-SiC(001) (w-GaN) substrates as well as on w-GaN surfaces that were etched in 50% HF solution. High-resolution transmission electron microscopy revealed an interfacial layer between film and the unetched substrate; this layer was absent in those samples wherein an etched substrate was used. However, the substrate treatment did not affect the epitaxial arrangement between the h-YMnO₃ film and w-GaN substrate. The epitaxial relationships of the h-YMnO₃ films with the w-GaN(001) substrate was determined via X-ray diffraction to be (001)_YMnO3 ‖ (001)_GaN : [11¯0]_YMnO3 ‖ [110]_GaN; in other words, the basal planes of the film and the substrate are aligned parallel to one another, as are the most densely packed directions in planes of the film and the substrate. Interestingly, this arrangement has a larger lattice mismatch than if the principal axes of the unit cells were aligned.     

Al2O3/TiO2复配改性环氧树脂的绝缘特性

为了满足高压直流输电体系对绝缘子性能的特殊要求,使用三氧化二铝(Al₂O₃)和二氧化钛(TiO₂)复配掺杂的方法改性环氧树脂基底,对复合物表面结构以及绝缘特性进行了分析。绝缘性能测试结果表明,相比于Al₂O₃或者TiO₂单独掺杂,共掺杂可以更显著降低复合物表面电阻率并且增加电气强度。将2种纳米材料的质量调到合适比例时,纳米粉体/树脂基底界面上会形成一定的导电通道,载流子可以沿着通道被传导出去,从而改善表面电阻率。而适当量Al₂O₃的引入可以进一步改善材料的电气强度。优化后复合物的表面电阻率为8.62×10¹³Ω,电气强度可达到29.01 kV/mm,共掺杂的协同效应对于树脂绝缘性能的提升十分有意义。     

Bi2O3助熔剂对CaO-B2O3-SiO2/Al2O3玻璃陶瓷复合材料性能的影响

以CaO-B₂O₃-SiO₂(CBS)玻璃粉体和Al₂O₃陶瓷粉体为原料,通过在CBS与Al₂O₃的质量比固定为50:50的玻璃-陶瓷复合材料中添加适量的Bi₂O₃作为烧结助熔剂,探讨了Bi₂O₃助熔剂对CBS/Al₂O₃复合材料的烧结性能、介电性能、抗弯强度和热膨胀系数的影响规律.研究表明:Bi₂O₃助熔剂能通过降低CBS玻璃的转变温度和黏度促进CBS/Al₂O₃复合材料的致密化进程,于880 ℃下烧结即能获得结构较致密、气孔较少的CBS/Al₂O₃复合材料.然而,过量添加Bi₂O₃将使玻璃的黏度过低,从而恶化CBS/Al₂O₃复合材料的烧结性能、介电性能及抗弯强度.当Bi₂O₃的添加量为CBS/Al₂O₃复合材料的1.5wt%时,于880 ℃下烧结即能获得最为致密的CBS/Al₂O₃复合材料,密度为2.82 g·cm^-3,这一材料具有良好的介电性能(介电常数为7.21,介电损耗为1.06×10^-3),抗弯强度为190.34 MPa,0~300 ℃的热膨胀系数为3.52×10^-6 K^-1.