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

Materials, technologies, and circuit concepts for nanocrossbar-based bipolar RRAM

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO2, WO3, GeSe, SiO2 and MSQ thin films were integrated into nanojunctions of 100x100 nm(2). The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10(10) bit

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

Observation of unipolar resistance switching in silver doped methyl-silsesquioxane

Resistive switching materials attract high scientific interest as a candidate for potential next-generation non-volatile memories. Nano crossbar structures and single junctions down to 60 x 60 nm(2) with integrated silver doped methyl-silsesquioxane (MSQ) as switching material are fabricated using UV nano imprint. Here silver doped MSQ with platinum top and bottom electrodes replaces the formerly used material stack with undoped MSQ between platinum bottom and silver top electrodes. The new material system yields advantages regarding the process temperature budget and therefore multiple crossbar arrays and electrode layers are possible in order to multiply the integration density by the number of crossbar layers. (C) 2009 Elsevier B.V. All rights reserved