A Coursebook in a Trilingual Classroom: To Use or not to Use

Coursebook use has proved to be a controversial issue in methodology. In this paper we refer to different writing on this subject, and take the argument a step further. As the way out, we look at an aspect of teaching English as a foreign language (EFL) that sooner or later every teacher comes up against – a need to write his/her materials. As our research has shown, this becomes of major importance in a trilingual classroom. Here, we also refer to some of the theoretical positions underlying third language acquisition (TLA)

Разработка алгоритма поэтапного совмещения перекрывающихся изображений для сравнительного анализа методов обнаружения ключевых точек

Memristive switches are promising devices for future nonvolatile nanocrossbar memory devices. In particular, complementary resistive switches (CRSs) are the key enabler for passive crossbar array implementation solving the sneak path obstacle. To provide logic along with memory functionality, "material implication" (IMP) was suggested as the basic logic operation for bipolar resistive switches. Here, we show that every bipolar resistive switch as well as CRSs can be considered as an elementary IMP logic unit and can systematically be understood in terms of finite-state machines, i.e., either a Moore or a Mealy machine. We prove our assumptions by measurements, which make the IMP capability evident. Local fusion of logic and memory functions in crossbar arrays becomes feasible for CRS arrays, particularly for the suggested stacked topology, which offers even more common Boolean logic operations such as AND and NOR

Stacked devices structures for resistive memory and logic

New memory technologies may penetrate the market only if they offer substantial improvements compared to existing concepts. Thus, new memory devices are required to consume less power, be non-volatile, have high scalability, be easy to fabricate under minimum area consumption. In this context resistive switching memory cells arranged in a passive crossbar architecture are especially promising. Resistive switching memory cells are simple two terminal metal-isolator-metal (MIM) structures and fulfill all these requirements. Integrating these structures into passive crossbar arrays a minimum area of 4F 2 per cell is consumed. A general challenge in these passive crossbar arrays is the existence of sneak paths, which results in constraints regarding the maximum array size. As resistive switching can be either unipolar or bipolar, different concepts for the alleviation of sneak paths are required. The scope of this thesis is to investigate stacked thin film devices based on the resistive switching effect for the application in passive crossbar array memory and logic. As unipolar switching material, Ag doped methylsilsesquioxane (MSQ) is investigated. MSQ, a spin-on glass, has previously shown very promising bipolar switching performance in conjunction with Ag electrodes and its planarization properties are extremely important for nanostructuring processes like nanoimprint lithography. When trying to increase integration density by sequential stacking of crossbar arrays, Ag electrodes are not stable enough. Thus, the active Ag was directly doped into the MSQ layer and inert Pt electrodes were used. The resistive switching behavior changed from bipolar (with Ag electrode) to unipolar (with Ag doped into the film). Using special test structures, the formation of Ag clusters could be identified to be responsible for the switching in these films. Single crosspoint junctions were characterized, revealing promising memory properties with moderate reset currents. The doping profiles were systematically investigated by ToF-SIMS. The insights gained were used to realize stacked arrays. Thus, an interesting unipolar switching material for the use in crossbar arrays in conjunction with a diode as select device has been proposed. For bipolar switching materials, a completely new concept for the alleviation of sneak paths in crossbar arrays, the complementary resistive switch (CRS), was proposed and has been experimentally realized for the first time. By arranging Cu-SiO$_{2}$ memristive elements in a fully vertical configuration, excellently quasi-statically switching CRS cells have been fabricated. Furthermore, dynamic measurements have been conducted over a large timescale. Apart from the fast electrical characterization in the nanosecond range, long measurements (in the range of minutes) with low voltages have been conducted. Using these measurements, the feasibility of voltage biasing schemes required for passive crossbar arrays was evaluated. The voltage schemes are necessary to properly address cells in these arrays and the bias leads to a defined voltage drop at each cell, which is below the switching voltage. It was found that these small voltages lead to a loss of information if applied repeatedly. A solution to this challenge is the application of appropriate oppositely biased recovery voltage pulses to these cells. Due to their high number of interconnections, crossbar arrays seem very well suited for next generation, reconfigurable and defect-tolerant logic applications. Thus, the realization of reconfigurable boolean logic operations with CRS cells as basic building blocks was investigated. With the help of phenomenological models which were obtained using the data from electrical characterization, several boolean logic functions could be demonstrated using a combination of specifically initialized CRS cells

Complementary resistive switches for passive nanocrossbar memories Published online: 18 April 2010

On the road towards higher memory density and computer performance, a significant improvement in energy efficiency constitutes the dominant goal in future information technology. Passive crossbar arrays of memristive elements were suggested a decade ago as non-volatile random access memories (RAM) and can also be used for reconfigurable logic circuits. As such they represent an interesting alternative to the conventional von Neumann based computer chip architectures. Crossbar architectures hold the promise of a significant reduction in energy consumption because of their ultimate scaling potential and because they allow for a local fusion of logic and memory, thus avoiding energy consumption by data transfer on the chip. However, the expected paradigm change has not yet taken place because the general problem of selecting a designated cell within a passive crossbar array without interference from sneak-path currents through neighbouring cells has not yet been solved satisfactorily. Here we introduce a complementary resistive switch. It consists of two antiserial memristive elements and allows for the construction of large passive crossbar arrays by solving the sneak path problem in combination with a drastic reduction of the power consumption

Electroforming and Resistance Switching Characteristics of Silver-Doped MSQ With Inert Electrodes

This paper reports on the resistance switching effect in silver-doped methylsilsesquioxane (MSQ) thin films with Pt top and bottom electrodes. Silver is thermally diffused into MSQ films for different times and the results prove that silver ions (or other oxidizable metal ions) are required in the system, but not necessarily as one of the two electrodes. SEM investigations at horizontal cells (gap width 15-100 nm) show the formation of metallic agglomerations in the gap. The forming process is found to be electric-field driven and the filament resistance is determined to be 30 Omega/nm. Under the assumption of conical-shaped filament growth, the diameter of a filament is calculated to 13.5 nm, which is in agreement with the SEM observations. Memory device related tests on 100 x 100 nm(2) cross junctions show unipolar switching up to 2000 times and retention at 85 degrees C for at least 6 x 10(4) s