Nonvolatile flash memory device using Ge nanocrystals embedded in HfAlO high-/spl kappa/tunneling and control oxides: Device fabrication and electrical performance

We fabricated a nonvolatile Flash memory device using Ge nanocrystals (NCs) floating-gate (FG)-embedded in HfAlO high-/spl kappa/ tunneling/control oxides. Process compatibility and memory operation of the device were investigated. Results show that Ge-NC have good thermal stability in the HfAlO matrix as indicated by the negative Gibbs free energy changes for both reactions of GeO/sub 2/+Hf/spl rarr/HfO/sub 2/+Ge and 3GeO/sub 2/+4Al/spl rarr/2Al/sub 2/O/sub 3/+3Ge. This stability implies that the fabricated structure can be compatible with the standard CMOS process with the ability to sustain source-drain activation anneal temperatures. Compared with Si-NC embedded in HfO/sub 2/, Ge-NC embedded in HfAlO can provide more electron traps, thereby enlarging the memory window. It is also shown that this structure can achieve a low programming voltage of 6-7 V for fast programming, a long charge retention time of ten years maintaining a 0.7-V memory window, and good endurance characteristics of up to 10/sup 6/ rewrite cycles. This paper shows that the Ge-NC embedded in HfAlO is a promising candidate for further scaling of FG Flash memory devices.     

Method of moments analysis of EM fields in a multilayered spheroid radiated by a thin circular loop antenna

This paper presents derivation and computation of electromagnetic (EM) fields inside a dielectric prolate spheroid radiated by a loop antenna. The dielectric spheroid is considered to be multilayered, and a thin circular loop antenna that is loaded by a voltage source radiates on the top of the prolate spheroid. The multiple interaction of transmitted and reflected waves with the spheroid is characterized by applying the method of moments (MoM) to both the circular loop antenna wire and the stratified spheroidal interfaces. The dyadic Green's function in the expansion form of eigenvector wave functions is used to derive the EM fields, so the formulation is quite compact. Different basis and weighting functions are used inside the method of moments procedure for obtaining in an efficient way the unknown current distributions along the antenna wire and the unknown expansion coefficients of their resulted EM fields. Current distributions and the transmitted fields inside the spheroidal model are computed numerically and the convergence issues are discussed.     

Aggregative and stochastic model of main path identification: a case study on graphene

This paper suggests a new method to search main path, as a knowledge trajectory, in the citation network. To enhance the performance and remedy the problems suggested by other researchers for main path analysis (Hummon and Doreian, Social Networks 11(1): 39–63, 1989), we applied two techniques, the aggregative approach and the stochastic approach. The first technique is used to offer improvement of link count methods, such as SPC, SPLC, SPNP, and NPPC, which have a potential problem of making a mistaken picture since they calculate link weights based on a individual topology of a citation link; the other technique, the second-order Markov chains, is used for path dependent search to improve the Hummon and Doreian’s priority first search method. The case study on graphene that tested the performance of our new method showed promising results, assuring us that our new method can be an improved alternative of main path analysis. Our method’s beneficial effects are summed up in eight aspects: (1) path dependent search, (2) basic research search rather than applied research, (3) path merge and split, (4) multiple main paths, (5) backward search for knowledge origin identification, (6) robustness for indiscriminately selected citations, (7) availability in an acyclic network, (8) completely automated search.     

Ultrafast switching in nanoscale phase-change random access memory with superlattice-like structures

Phase-change random access memory cells with superlattice-like (SLL) GeTe/Sb(2)Te(3) were demonstrated to have excellent scaling performance in terms of switching speed and operating voltage. In this study, the correlations between the cell size, switching speed and operating voltage of the SLL cells were identified and investigated. We found that small SLL cells can achieve faster switching speed and lower operating voltage compared to the large SLL cells. Fast amorphization and crystallization of 300 ps and 1 ns were achieved in the 40 nm SLL cells, respectively, both significantly faster than those observed in the Ge(2)Sb(2)Te(5) (GST) cells of the same cell size. 40 nm SLL cells were found to switch with low amorphization voltage of 0.9 V when pulse-widths of 5 ns were employed, which is much lower than the 1.6 V required by the GST cells of the same cell size. These effects can be attributed to the fast heterogeneous crystallization, low thermal conductivity and high resistivity of the SLL structures. Nanoscale PCRAM with SLL structure promises applications in high speed and low power memory devices.     

Paper-based microfluidic surface acoustic wave sample delivery and ionization source for rapid and sensitive ambient mass spectrometry

A surface acoustic wave-based sample delivery and ionization method that requires minimal to no sample pretreatment and that can operate under ambient conditions is described. This miniaturized technology enables real-time, rapid, and high-throughput analysis of trace compounds in complex mixtures, especially high ionic strength and viscous samples that can be challenging for conventional ionization techniques such as electrospray ionization. This technique takes advantage of high order surface acoustic wave (SAW) vibrations that both manipulate small volumes of liquid mixtures containing trace analyte compounds and seamlessly transfers analytes from the liquid sample into gas phase ions for mass spectrometry (MS) analysis. Drugs in human whole blood and plasma and heavy metals in tap water have been successfully detected at nanomolar concentrations by coupling a SAW atomization and ionization device with an inexpensive, paper-based sample delivery system and mass spectrometer. The miniaturized SAW ionization unit requires only a modest operating power of 3 to 4 W and, therefore, provides a viable and efficient ionization platform for the real-time analysis of a wide range of compounds.     

地板辐射供冷系统的热性能研究

实验比较了双位开关控制、变流量控制和室外温度补偿+室温反馈控制方式下地板辐射供冷系统室内温度稳定性、地板表面温度稳定性以及结露发生频率.研究结果表明,室外温度补偿控制方式的最低供水温度为15℃,室外温度补偿率为0.25;在运行初期,双位开关控制室温稳定性优于其他控制方式,随着系统运行时间延长,室外温度补偿+室温反馈控制...     

Computational study on aerodynamic mitigation of wind-induced, large-amplitude vibrations of stay cables with strakes

Modifications of circular cylinder surfaces, such as strakes and helical wires, effectively mitigate Kármán vortex-induced vibrations normal to flow and have been applied to the reduction of large-amplitude vibrations of stay cables in bridges, which occur under wind oblique to a cable with or without rainfall. This aerodynamic control method cannot be fully effective without understanding the behavior of the flow around and the associated forces on oblique cables. To address this issue, flow around a yawed cylinder with various strake patterns was studied using three-dimensional detached eddy simulation (DES) at Reynolds number of 1.4×10⁵. Results demonstrated that strake patterns strongly influence the development of flow structures around a yawed cylinder and therefore the associated forces on the cylinder. The results suggest that particular strake patterns can mitigate large-amplitude and low-frequency vibrations of stay cables induced by oblique wind.     

Evaluation of the control performance of hydronic radiant heating systems based on the emulation using hardware-in-the-loop simulation

This study presents an emulation method to evaluate the control performance of a hydronic radiant heating system. Since heat output in the system is dependent on the pressure loss and flow rate in the hydronic network, the interaction between thermal and hydronic models needs to be considered in the evaluation of the control performance. For this reason, many studies apply an integrated simulation to the evaluation; however, the analysis of the hydronic network sometimes leads to unreliable results due to the improper initial values for algebraic loops or the lack of modeling information on the hydronic components. In order to deal with this problem, this study suggests an emulation method, where the hydronic network is replaced by real hardware and the building physics is analyzed by a simulation. In the emulation, the pressure loss and flow rate in the hydronic network were represented by replacing the real pipe with equivalent hydraulic resistance. In addition, by using real control systems that connect the hydronic network and building simulation, the interaction between building physics and hydronic network could be considered in the evaluation. Based on the proposed emulation method, the performance of several control strategies was evaluated in terms of the accuracy and the rise time. The result shows that the individual control needs to be combined with hydronic balancing for more accurate control. Hydronic control devices such as a flow limit valve and a pressure differential control valve also proved to be helpful to the improvement of the control performance.