Hydrogen insertion compounds of transition metal oxides

Polycrystalline tungstic acid, WO₃.H₂O, has been examined as an electrode material. Hydrogen insertion occurs on electrochemical reduction to give a blue product, formulated as H_xWO₃.H₂O, which is topotactically related to the parent material. Proton diffusion rates in the reduced product were measured by an electrochemical relaxation technique and shown to be much higher than in polycrystalline WO₃.     

Intrinsic defects in silicon

A review is given of what has been learned from electron paramagnetic resonance (EPR) and localized vibrational mode (LVM) spectroscopy concerning isolated lattice vacancies and self-interstitials, and their interactions with other defects in silicon. This information can supply the basic tools with which to help unravel much of the complex processes and structures involved in crystal growth, device processing, and radiation damage.     

Intrinsic defects in high-purity SiC

Intrinsic defects are of importance for different applications of SiC such as: the semi-insulating (SI) properties of SI substrates, the carrier lifetime of high-voltage, bipolar power devices and the colour of gemstones (Moissanites). In order to tailor the properties of the material, we need to understand the properties of the intrinsic defects, their energy positions in the bandgap, their ability to capture carriers from the bands, their formation and annealing as well as their interplay with other defects.High-purity SiC materials (doping less than 10¹⁶ cm⁻³) grown by high temperature chemical vapour deposition (HTCVD), physical vapour transport (PVT) and chemical vapour deposition (CVD) have been investigated by electron paramagnetic resonance (EPR), photoluminescence (PL), absorption and electrical techniques. Vacancies , divacancies and antisite-related defects are found to be common. The present knowledge of intrinsic defects in SiC based on both experiments and on calculations will be presented as well as their influence on mainly the semi-insulating properties.     

掺杂过渡金属氧化物对ZnO-B_2O_3-SiO_2玻璃的改性研究

采用高温熔融和过渡金属氧化物掺杂的方法,制备了掺杂不同过渡金属氧化物(Sb2O3、TiO2、CeO2、MnO2)的ZnO-B2O3-SiO2无铅玻璃。研究了所制玻璃的物理化学性能。结果表明:掺杂过渡金属氧化物后,ZnO-B2O3-SiO2玻璃的结构和封接性能得到较大改善,玻璃的耐水性提高1.5～2.0倍,线膨胀系数从60×10–7/℃降至40×10–7/℃。     

Metal-insulator phase transition in vanadium oxides films

Vanadium oxide films (VO₂) are of a typical phase transition ranging between metal phase to a semi-conducting phase. The theoretical metamorphose temperature of VO₂ is around 340 K (67 °C). This transition temperature is mostly governed by the deposition method in which the film was made, and the film's composition. Optical and electrical properties of VO₂ films are dramatically changed during this phase transition, thus making it useful in many microelectronics and optoelectronics applications. In this work we evaluate several deposition methods of VO₂ and their relations to the electro-optics properties of such films. The examined VO₂ films consisted of various phases of the material. Best films to demonstrate a metal-insulator transition were made in vacuum evaporation of V powder in a tungsten boat, treated in argon-oxygen flow (10:1), at 400 °C. The temperature range of phase transitions was found at 16-80 °C. Resistivity changes and colors of the films were studied as well.     

Photoconductivity of Hf-based binary metal oxides

In order to explore the possibility of bandgap engineering in binary oxide insulators we studied photoconductivity of nanometer-thin Hf oxide layers containing different fractions of cations of another sort (Si, Al, Sr, or Ce) deposited on (1 0 0)Si. The smallest bandgaps of the Hf:Al and Hf:Ce oxides are close to the values found in elemental Al₂O₃ (6-6.2 eV) and HfO₂ (5.6 eV), respectively, and show little sensitivity to the concentration of Al or Ce. This result suggests that the oxide sub-network with the largest bandgap preserves its gap energy, while development of a narrower gap is prevented, likely, by dilution of the second cation sub-network. In Hf:Si oxide samples photoconductivity thresholds of 5.6-5.9 eV, corresponding to the bandgap of HfO₂, were observed for all studied Si concentrations, suggesting phaseseparation to occur during deposition. Photoconductivity of SrHfO₃ exhibits two thresholds, at 4.4 and 5.7 eV, which are close to the bandgaps of elemental SrO₂ and HfO₂, respectively. These gap values indicate the phase separation also to occur in this binary oxide. Through this work photoconductivity is demonstrated to be a feasible method to trace phase separation in binary oxides, even in nanometer-thin layers.     

Transition metal oxides on organic semiconductors

Transition metal oxides (TMOs) on organic semiconductors (OSs) structure has been widely used in inverted organic optoelectronic devices, including inverted organic light-emitting diodes (OLEDs) and inverted organic solar cells (OSCs), which can improve the stability of such devices as a result of improved protection of air sensitive cathode. However, most of these reports are focused on the anode modification effect of TMO and the nature of TMO-on-OS is not fully understood. Here we show that the OS on TMO forms a two-layer structure, where the interface mixing is minimized, while for TMO-on-OS, due to the obvious diffusion of TMO into the OS, a doping-layer structure is formed. This is evidenced by a series of optical and electrical studies. By studying the TMO diffusion depth in different OS, we found that this process is governed by the thermal property of the OS. The TMO tends to diffuse deeper into the OS with a lower evaporation temperature. It is shown that the TMO can diffuse more than 20 nm into the OS, depending on the thermal property of the OS. We also show that the TMO-on-OS structure can replace the commonly used OS with TMO doping structure, which is a big step toward in simplifying the fabrication process of the organic optoelectronic devices.     

Thermosonic bonding of lead-free solder with metal bump for flip-chip bonding

While extensive research on the lead-free solder has been conducted, the high melting temperature of the lead-free solder has detrimental effects on the packages. Thermosonic bonding between metal bumps and lead-free solder using the longitudinal ultrasonic is investigated through numerical analysis and experiments for low-temperature soldering. The results of numerical calculation and measured viscoelastic properties show that a substantial amount of heat is generated in the solder bump due to viscoelastic heating. When the Au bump is thermosonically bonded to the lead-free solder bump (Sn-3%Ag-0.5%Cu), the entire Au bump is dissolved rapidly into the solder within 1 sec, which is caused by the scrubbing action of the ultrasonic. More reliable solder joints are obtained using the Cu/Ni/Au bump, which can be applied to flip-chip bonding.     

P-type doping of organic wide band gap materials by transition metal oxides: A case-study on Molybdenum trioxide

A study on p-doping of organic wide band gap materials with Molybdenum trioxide using current transport measurements, ultraviolet photoelectron spectroscopy and inverse photoelectron spectroscopy is presented. When MoO₃ is co-evaporated with 4,4′-Bis(N-carbazolyl)-1,1′-biphenyl (CBP), a significant increase in conductivity is observed, compared to intrinsic CBP thin films. This increase in conductivity is due to electron transfer from the highest occupied molecular orbital of the host molecules to very low lying unfilled states of embedded Mo₃O₉ clusters. The energy levels of these clusters are estimated by the energy levels of a neat MoO₃ thin film with a work function of 6.86 eV, an electron affinity of 6.7 eV and an ionization energy of 9.68 eV. The Fermi level of MoO₃-doped CBP and N,N′-bis(1-naphtyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (α-NPD) thin films rapidly shifts with increasing doping concentration towards the occupied states. Pinning of the Fermi level several 100 meV above the HOMO edge is observed for doping concentrations higher than 2 mol% and is explained in terms of a Gaussian density of HOMO states. We determine a relatively low dopant activation of ～0.5%, which is due to Coulomb-trapping of hole carriers at the ionized dopant sites.     

晶态介孔金属氧化物的研究进展

用氧化硅介孔分子筛SBA-15,KIT-6,FDU-12和SBA-16作为模板,在其孔道中生长各种过渡金属氧化物,最终产物是晶态的介孔金属氧化物.这种材料具有广泛的应用前景.电子显微镜是研究这些新型纳米材料不可或缺的手段.本文简述介孔金属氧化物的合成和结构鉴定,以及该研究领域的最新进展.     

Surface treatment of wire bonding metal pads

The random formation of micrometric crystals on Al bonding pads can be an issue affecting wire bonding metal pad quality. The dry etch chemistry used to remove final passivation dielectric layers from the top of the bonding Al pad area is in fact based mainly on fluorine-containing gases (such as CF₄, CHF₃, etc.) which can leave fluorine as a residual on the metal pad surface as bonded or “free” AlF₃, especially in the metal grain boundary zones. Fluorine contamination on the Al wire bonding pads, under particular temperature and humidity conditions, causes the formation of Al(OH)₃ and Al/fluorine compound crystallites, not allowing, as a consequence, growth of the superficial and homogeneous natural Al₂O₃ layer. This paper concerns the analytical methods used to reveal the formation of such crystal defects and the operative solutions effective in preventing them, leaving the metal pad surface in the optimal condition for subsequent wire bonding operations.     

Point defects generated by direct-wafer bonding of silicon

High-purity float zone (FZ) silicon p- and n-type wafers were directly bonded hydrophobically at 700°C and 1050°C. Electrical I-V and capacitance-voltage (C-V) characterization was performed on p-n junctions of 2-mm square chips cut out from properly bonded areas of the wafers. The point defects were investigated by Deep Level Transient Spectroscopy (DLTS). As expected, annealing at 700°C resulted in high void density, while at 1050°C void-free bonded structures were formed. The I-V characteristics were dominated by recombination at the bonded interface and by the resistance of the n-type wafer. The point defects identified by DLTS are divacancy, vacancy-phosphor, and vacancy-oxygen complexes. These defects explain qualitatively the observed characteristics of the samples.     

金属材料的激光诱导等离子体光谱法成分分析的实验研究

以波长1064nm的Nd：YAG调Q激光束为激发光源,对铜、镁铝合金和钢等金属材料的激光诱导等离子体光谱（Lips）进行了实验探测,并分析了延迟时间、环境气体等因素对元素光谱特性的影响。适当的延迟时间和氩气环境能显著地改善谱线的信噪比,从而提高元素含量分析的精度。     

Group IVB metal oxides high permittivity gate insulators depositedfrom anhydrous metal nitrates

The electrical performance of column IVB metal oxide thin films deposited from their respective anhydrous metal nitrate precursors show significant differences. Titanium dioxide has a high permittivity, but shows a large positive fixed charge and low inversion layer mobility. The amorphous interfacial layer is compositionally graded and contains a high concentration of Si-Ti bonds. In contrast, ZrO₂ and HfO ₂ form well defined oxynitride interfacial layers and a good interface with silicon with much less fixed charge. The electron inversion layer mobility for an HfO₂/SiO_xN_y /Si stack appears comparable to that of a conventional SiO₂ /Si interface     

Investigation of defects in deposited oxides with a frequencyresolved capacitance technique

In this paper we propose a new tool to investigate defective oxides. The technique measures the differential capacitance of MOS devices under substrate accumulation as a function of the small-signal frequency. In off-stochiometric oxides deposited by plasma-enhanced CVD we measure a consistent increase of capacitance while decreasing frequency. An analytical model of capacitance is developed, starting from the hypothesis that trapped charge hops between defect sites around the Fermi level via a phonon-assisted mechanism. The hopping characteristic time depends on the energy difference and distance between defects and is compared with the inverse frequency. This gives rise to the observed dispersive behavior of the capacitance. Experimental results are successfully reproduced by the proposed model. Defect densities up to 10²⁰ cm^-3 were extracted, with an energy span as low as 0.1 eV and hopping distance around 25 Å     

铁系氧化物对Bi_2O_3-ZnO-B_2O_3封接玻璃性能的影响

采用熔融淬冷法制备了铁系氧化物(Fe_2O_3、Co_2O_3、Ni_2O_3)掺杂Bi_2O_3-ZnO-B_2O_3(BiZnB)系玻璃。分别采用差热分析法(DTA)、X射线衍射分析(XRD)、热膨胀仪等测试手段,研究各铁系氧化物对基础玻璃体系结构与性能的影响。结果表明,掺杂铁系氧化物后,BiZnB系玻璃的特征温度有所下降。玻璃转变温度(t_g)从416℃降低至406℃,软化温度(t_f)从464℃降至456℃,开始析晶温度(t_x)从633℃最低降至609℃,其中Ni_2O_3的降低作用最为显著。铁系氧化物的掺杂使玻璃的线膨胀系数(α)从99×10~(-7)/℃~(-1)增大至108×10~(-7)/℃~(-1)。BiZnB系玻璃掺杂铁系氧化物后,仍具有良好的化学稳定性。     

Ab initio study of point defects in dielectrics based on Pr oxides

We discuss the influence of band structures and point defects (oxygen vacancies and interstitials, and praseodymium vacancies) in Pr₂O₃, PrO₂, and PrSiO_3.5 on the electrical properties of high-K gate dielectrics for the application in CMOS technology. In particular, we consider the origin of fixed charges and leakage currents. We address these issues mostly from the perspective of ab initio calculations for formation energies, electronic structures, and band alignment between the film and the silicon substrate.     

利用金属键合和激光剥离技术制备GaN/metal /Si异质结构的研究

利用金属键合和激光剥离将生长在蓝宝石衬底上的GaN薄膜转移到Si衬底上。键合后采用波长为248nm的准分子脉冲激光辐照蓝宝石衬底,低温处理去除蓝宝石衬底。系统地研究不同键合温度和激光能量密度对GaN结构和光学特性的影响。AFM、XRD和PL测试表明：键合温度和激光剥离的能量密度较低,转移衬底后GaN的质量较好;激光剥离的阈值能量密度为300mJ/cm2;键合温度400℃的样品均方根粗糙度（RMS）约为50nm。     

GaN/metal/Si heterostructure fabricated by metal bonding and laser lift-off

A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF (248 nm) excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photolumi-nescence measurements showed that (1) the quality of the GaN film was higher at a lower bonding temperature and lower energy density; (2) the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm~2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.