Write/erase cycling endurance of memory cells with SiO/sub 2//HfO/sub 2/ tunnel dielectric

The write/erase cycling endurance of low voltage floating-gate memory cells programmed and erased by tunneling through a SiO/sub 2//HfO/sub 2/ dual layer tunnel dielectric stack is investigated. The use of fixed single pulse program and erase conditions leads to fast shifting (after /spl sim/1000 cycles) of the threshold voltage window, so that only a limited number of write/erase cycles can be achieved. Increasing the write and erase duration quickly leads to an excessive erase time so that a different erase method has to be used. Improvement of the erase behavior and cycling endurance has been obtained by a combination of two methods. Inclusion of soft write pulses between the erase pulses reduces the amount of charge trapped in the tunnel dielectric and therefore limits the increase in erase time. Also, the erase voltage can progressively be raised in order to further limit the erase time, leading to an endurance of 10 000 cycles on the considered cells. When combining the SiO/sub 2//HfO/sub 2/ stack with channel hot electron injection so that tunneling is only required in one direction, 100 000 write/erase cycles are demonstrated with minimal change of the memory window.     

Impulse partial discharge characteristics and their mechanisms under non-uniform electric field in N/sub 2//SF/sub 6/ gas mixtures

We have investigated impulse partial discharge (PD) and breakdown (BD) characteristics of a needle-plane gap in N/sub 2//SF/sub 6/ gas mixtures under positive lightning impulse voltage application, and discussed their physical mechanisms. The 50% probability PD inception voltage (PDIV/sub 50/), leader discharge onset voltage (LOV) and BD voltage (BDV/sub 50/) were measured and analyzed as a function of gas pressure and SF/sub 6/ content. Experimental results revealed the stepwise propagation process of the impulse PD and enabled us to classify the impulse PD in N/sub 2//SF/sub 6/ gas mixtures into two types, the streamer discharge and the leader discharge. We also discussed the impulse PD propagation mechanisms in terms of PD parameters such as propagation length, time interval and current pulse magnitude, and suggested a sequential relationship in the PD propagation process under non-uniform electric field.     

Widely tunable Al/sub 2/O/sub 3/-GaAs DBR filters with variable tuning characteristics

We demonstrate an optical tunable filter using Al/sub 2/O/sub 3/-GaAs layers as the top distributed Bragg reflector mirror. The mechanical properties and spectral response versus voltage are characterized. The tuning characteristics can be changed by removing the tensile-stressed Si/sub 3/N/sub 4/ on the mirror and legs. An integrated optical-mechanical model is used to analyze the result. Axial nitride and initial residual stress are incorporated into the model to obtain accurate fit. A 64-nm tuning range with 12-V tuning voltage is measured, a significant improvement over previous designs.     

Simultaneous removal of NO/sub x/, SO/sub x/, and CO/sub 2/ at elevated temperature using a plasma-chemical hybrid process

In previous studies, the authors confirmed that the plasma-chemical combined hybrid process for controlling NO flue gas emission was extremely effective and economical in comparison with the conventional selective catalytic reduction (SCR) system and other technologies. In the present study, we carried out experiments on the simultaneous removal of NO/sub x/ and SO/sub x/ at elevated temperature using the plasma-chemical hybrid process. A series of experiments was performed to quantify all the reaction byproducts such as N/sub 2/O, CO, HNO/sub 2/, HNO/sub 3/, NO/sub 3//sup -/, and SO/sub 4//sup -/ to evaluate the simultaneous NO/sub x/ and SO/sub x/ removal efficiency. The oxidation from NO to NO/sub 2/ without decreasing NO/sub x/ concentration (i.e., minimum reaction byproducts) and with least power consumption is the key for the optimum operation of the plasma reactor. The produced NO/sub 2/ was totally converted to N/sub 2/ and Na/sub 2/SO/sub 4/ with Na/sub 2/SO/sub 3/ or Na/sub 2/S with and without NaOH using the barrier-type packed-bed plasma reactor followed by the packed-column chemical reactor. The NO/sub 2/ reduction was more effective for Na/sub 2/S than Na/sub 2/SO/sub 3/ but produces H/sub 2/S with Na/sub 2/S. For both cases at least five times the stoichiometric amount of chemicals were required for complete NO/sub 2/ reduction. Nearly 100% of NO/sub x/ and SO /sub 2/ and 40% Of CO/sub 2/ simultaneous removal were achieved with less than 5 ppm of N/sub 2/O and CO. The operating cost was less than 1/4 the SCR process. The additional SO/sub 2/ treatment system can be eliminated.     

Impact of high-/spl kappa/ dielectric HfO/sub 2/ on the mobility and device performance of sub-100-nm nMOSFETs

Scaling of Si MOSFETs beyond the 90-nm technology node requires performance boosters in order to satisfy the International Technology Roadmap for Semiconductors requirements for drive current in high-performance transistors. Amongst the preferred near term solutions are transport enhanced FETs utilizing strained Si (SSi) channels. Additionally, high-/spl kappa/ dielectrics are expected to replace SiO/sub 2/ around or after the 45-nm node to reduce the gate leakage current problem, facilitating further scaling. However, aside from the many technological issues such as trapped charge and partial crystallization of the dielectric, both of which are major issues limiting the reliability and device performance of devices employing high-/spl kappa/ gate stacks, a fundamental drawback of MOSFETs with high-/spl kappa/ dielectrics is the mobility degradation due to strong soft optical phonon scattering. In this work we study the impact of soft optical phonon scattering on the mobility and device performance of conventional and strained Si n-MOSFETs with high-/spl kappa/ dielectrics using a self-consistent Poisson Ensemble Monte Carlo device simulator, with effective gate lengths of 67 and 25-nm. Additionally we have also briefly investigated the effect (the percentage change) that a trapped charge within the gate oxide will have on the drive current for both a SiO/sub 2/ oxide and an equivalent oxide thickness of high-/spl kappa/ dielectric.     

Impulse partial discharge and breakdown characteristics of rod-plane gaps in N/sub 2//SF/sub 6/ gas mixtures

Impulse partial discharge (PD) and breakdown (BD) characteristics of rod-plane gaps in N/sub 2//SF/sub 6/ gas mixtures were investigated for different gap geometry, gas pressure and SF/sub 6/ gas content. Experimental results revealed that the 50% probability breakdown voltage increased with gas pressure, which agreed with the theoretical values with consideration of discharge time lag for impulse voltage application. For the calculation of discharge inception voltage, the volume-time theory was successfully applied to the N/sub 2//SF/sub 6/ gas mixture. Furthermore, impulse PD light emission image was observed together with PD current pulse and light intensity waveforms. The long discharge with stepwise propagation and double-peak PD pulses could be observed, which corresponded to the streamer/leader transition leading to breakdown.     

Imaging breakdown spots in SiO/sub 2/ films and MOS devices with a conductive atomic force microscope

Conductive atomic force microscopy (C-AFM) was used to study the dielectric breakdown of SiO/sub 2/ layers at a nanometric scale. First, bare oxide regions were stressed and broken down using the tip as the metal electrode of a MOS structure. The results show that the initial breakdown is electrically propagated to neighbor regions, affecting their dielectric strength. Moreover, the area affected by the initial breakdown depends on the breakdown hardness. In particular, it is shown that this area is smaller when the current through the structure is limited during the experiments. The effect of the current limitation is analyzed in detail. Based on the results, a qualitative picture of the breakdown process is presented, which accounts for this effect. Finally, for the first time, the breakdown spots in standard MOS devices (with poly-Si gate) are electrically imaged with C-AFM. The areas of the observed spots are in agreement with those obtained on bare oxides.     

Comparative study on the spectroscopic properties of Nd:GdVO/sub 4/ and Nd:YVO/sub 4/ with hybrid process

We have proposed a hybrid procedure for determining spectroscopic parameters for uniaxial solid-state laser crystals. Using our procedure, the spectroscopic properties of Nd:GdVO/sub 4/ were evaluated and compared to those of Nd:YVO/sub 4/. As a result, the peaks of absorption and stimulated emission cross sections of Nd:GdVO/sub 4/ in /spl pi/-polarization were determined to be 2.6 and 10.3/spl times/10/sup -19/ cm/sup 2/, respectively, and were smaller than those of Nd:YVO/sub 4/. On the other hand, the fluorescence lifetime of 1 at% Nd:GdVO/sub 4/ was evaluated to be 83.4 /spl mu/s, and was similar to 84.1 /spl mu/s of 1 at% Nd:YVO/sub 4/. Therefore, the product of stimulated emission cross section and fluorescence lifetime (/spl sigma//sub em//spl tau//sub f/ product) of Nd:GdVO/sub 4/ was smaller than that of Nd:YVO/sub 4/ under 1 at% of Nd/sup 3+/ doping concentration. The radiative lifetime of spontaneous emission of Nd:GdVO/sub 4/ was 168 /spl mu/s and was 1.9 times longer than that of Nd:YVO/sub 4/. Because of the low value of radiative quantum efficiency of Nd:GdVO/sub 4/ (50%), careful cavity design is required for creating a well performing solid-state laser with Nd:GdVO/sub 4/, based on the larger /spl sigma//sub em//spl tau//sub f/ product rather than the /spl sigma//sub em//spl tau//sub f/ product of Nd:YAG.     

Plasma reforming of aliphatic hydrocarbons with CO/sub 2/

CO/sub 2/ reforming of methane, propane, and neopentane was investigated with a ferroelectric packed-bed reactor (FPR) in N/sub 2/ at temperatures ranging from 298 K to 433 K. The reaction behavior of the hydrocarbons was greatly affected by their chemical structures and reaction temperature. At ambient temperature, hydrocarbon conversion decreased in the following order: neopentane/spl Gt/propane>methane. With an increase in reaction temperature, hydrocarbon reactivity was enhanced with only a slight difference in the conversions of the above hydrocarbons. CO/sub 2/ deoxygenation was a clean reaction irrespective of reaction temperature, but CO was formed not only from CO/sub 2/ but also from hydrocarbons. No chemical interaction between CO/sub 2/ and the hydrocarbons in nonthermal plasma was observed. Temperature effect on the H/sub 2/ yield depended on the hydrocarbon structure. Higher H/sub 2/ yields were obtained for neopentane and propane than for methane. Product composition and carbon balance were also affected by the hydrocarbon structure, relative concentrations of hydrocarbons to CO/sub 2/, and temperature.     

WO3/BTO heterostructures based NO2 sensor with enhanced response characteristics

Abstract

In the present work, an efficient NO₂ gas sensor has been realised using single phase Barium titanate, BaTiO₃, (BTO) thin film, grown by chemical solution deposition technique (CSD). The gas sensing characteristics of BTO thin film were enhanced by integrating WO₃ modifier in the form of uniformly distributed circular nano-clusters and continuous overlayer. The WO₃ nanoclusters/BTO sensing element exhibited enhanced sensor response (～156) with fast response speed (16?s) at a relatively low operating temperature (140?°C) towards 50?ppm NO₂ gas. An attempt has been made to explain the sensing mechanism involving the twin effect of “Fermi-level exchange mechanism” and “spill over mechanism” upon interaction with target NO₂ gas. The obtained results in the present work are encouraging for the realization of hand-held NO₂ gas sensor.     

Influence of Cr/sub 2/O/sub 3/ and MnO additives on the surface properties of alumina insulators

Alumina insulators containing 95wt% Al/sub 2/O/sub 3/ were doped with Cr/sub 2/O/sub 3/ and MnO(MnCO/sub 3/). The properties of the doped samples were measured and compared with those of the original alumina insulators. Better surface performances of the samples doped with proper Cr/sub 2/O/sub 3/ and MnO were obtained while the bulk properties have hardly been changed. After doping the sample showed a lower SEE (secondary electron emission) coefficient, a lower surface resistivity and a higher surface flashover voltage in vacuum. Meanwhile, some points regarding the effects of manganese and chromium doping on the properties of alumina insulators were also briefly discussed.     

Electrical Characteristics and Thermal Stability of Pt/HfO 2 /Si Metal-Insulatror-Semiconductror Capacitors

The HfO 2 thin films for use in gate dielectric applications were deposited at 300 onto p-type Si (100) substratee using Hf[OC(CH 3 ) 3 ] 4 as the precursor in the absence of oxygen by plasma-enhanced chemical vapor deposition. The HfO 2 films deposited in the absence of O 2 show excellent electrical properties such as low capacitance equivalent thickness (CET), good thermal stability and low charge trapping. The as-deposited films have an interfacial layer of approximately 1 nm in thickness, resulting in a decrease in the thickness of the interfacial layer by about 50% compared to films deposited in the presence of oxygen. The leakage current density of HfO 2 films was approximately 3 orders of magnitude lower than an electrically comparable SiO 2 at the same CET. The improvement of electrical properties can be attributed to the decrease in the SiO 2 interfacial layer. The thickness of the interfacial layer can be contolled by the deposition in the absence of oxygen after evacuation of the reaction chamber by means of an ultra-high vacuum.     

Corona and breakdown characteristics between sphere electrode with a protrusion and plane electrode under negative pulse voltage in N/sub 2/ gas

Corona and breakdown characteristics for a configuration of a sphere with a needle and a plane in N/sub 2/ gas are studied. The protrusion was used to simulate a metallic particle attached to a high voltage conductor surface in power apparatus. The corona and breakdown characteristics depend on the vertical distance between the needle tip and the bottom sphere. It was observed that the breakdown path changed from needle-to-plane to sphere-to-plane while increasing the vertical distance of the needle from the plane. Although corona was generated at the needle-tip at first and developed in the direction of the plane, both the needle-plane and the sphere-plane breakdown occurred at some short vertical distances. The sphere-plane breakdown in that distance was triggered by corona from the needle.     

The behavior of N/sub 2/+SF/sub 6/ gas mixtures subjected to orthogonal electric and magnetic fields

The limiting equivalent electric fields in N/sub 2/+SF/sub 6/ binary gas mixtures due to Townsend discharges are evaluated directly from a Monte-Carlo simulation when the mixture is subjected to orthogonal electric and magnetic fields. Along with the limiting equivalent electric fields, transverse and perpendicular drift velocities, electron mean energies and collision frequencies are also determined within the scope of the Monte-Carlo simulation. The equivalent reduced electric field (EREF) concept for the corresponding limiting electric fields is also investigated for the calculated mean energy levels and collision frequencies. The EREF values are found to be in good agreement with the previously published limiting electric field data.     

Fabrication of amorphous bulk and multi-phase ceramics by melting method in the HfO2-Al2O3-Gd2O3-Eu2O3system

Ceramics have generally been fabricated from powders by shape forming & sintering methods except for glasses and glass ceramics. Glasses and glass ceramics can be fabricated by melting methods. The melting method has not only higher productivity but also higher shape forming ability than powder processes via forming & sintering methods. Thus we have reinvestigated melting methods in binary and ternary oxides systems to fabricate amorphous bulk ceramics and bulk nano composites. We have successfully fabricated amorphous phases by simple melt solidification methods in ternary eutectic melts in the HfO₂-Al₂O₃-Gd₂O₃system. The present study demonstrates the formation of the amorphous phases in quaternary systems HfO₂-Al₂O₃-Gd₂O₃-Eu₂O₃. Furthermore, we have also succeeded to fabricate nano-structured bulk ceramics, which consisted of constituent oxide grains with 20–100 nm in size, by post annealing of the amorphous phase.     

Power frequency dependence of space charge behavior and partial discharge characteristics in SF/sub 6/ gas

The partial discharge (PD) and breakdown (BD) characteristics in SF/sub 6/ gas under commercial and higher frequency (/spl sim/600 Hz) ac voltage applications were investigated using high-speed electrical and optical measuring techniques with phase gate control method. Experimental results revealed that 400 Hz BD voltage at a certain gas pressure range was higher than that for 60 Hz and PD characteristics especially at the positive PD inception phase were much influenced by the applied power frequency. From these results, we clarified the dependence of space charge behavior on the applied power frequency and discussed the physical mechanism of PD and BD in SF/sub 6/ gas with consideration of the space charge behavior generated by PD in the previous half cycle of ac voltage.     

Influence of process conditions on the ferroelectric characteristics of SrBi2Ta2O9 films prepared by rf magnetron sputtering

Abstract

The effects of sputtering conditions on the SrBi₂Ta₂O₉ films deposited via a single-target RF-sputtering process were investigated in this study. It was found that the composition of targets significantly affected the phases and the composition of the deposited films. When the target contained high bismuth content, SrBi₂Ta₂O₉ and a secondary Bi₂O₃ phase were formed. When the bismuth content in the targets was insufficient, a pyrochlore phase was produced. SEM images revealed that the composition of the targets also affected the surface morphology of the obtained films. When the target-to-substrate distance was increased, bismuth oxide was formed, which resulted in an increase in the leakage current. By optimizing the deposition conditions, the ferroelectric properties of SrBi₂Ta₂O₉ films were improved.     

Partial discharge inception characteristics of LN/sub 2//polypropylene laminated paper composite insulation system for high temperature superconducting cables

Partial discharge (PD) inception characteristics of liquid nitrogen (LN₂)/polypropylene (PP) laminated paper composite insulation system for high temperature superconducting (HTS) cables were investigated in terms of the volume effect and the V-t characteristics. The electrical and optical measurements of PD inception characteristics showed that initial PD could be generated between PP laminated paper layers, as well as in a butt gap. Using a parameter called statistically stressed liquid volume (SSLV) based on the discharge probability in both butt gaps and LN₂-filled thin layers between PP laminated papers, we could systematically analyze and evaluate the volume effect on PD inception stress (PDIE). Furthermore, experimental results revealed that n values of V-t characteristics at PD inception were as high as 80-110. On the other hand, the lower n values obtained at breakdown were interpreted by the intensified PD development in thermal bubbles generated after the PD inception     

一种2/4线话音接口的设计与实现

文章介绍了一种2/4线话音接口和回波抵消器的设计与实现方案,该方案实现了2/4线的话音接口,包括A/D、D/A变换,ADPCM编解码,自适应回波抵消等。其中,ADPCM编解码和回波抵消器是基于FPGA使用VHDL语言编写实现的。测试表明,该接口电路以较小的资源消耗,提供了优异的话音通信质量,在电力系统话音通信中具有重要的实用价值。