Oct 12, 2011
Non-destructive readout for complementary resistive switches
Non-volatile resistive switches are a promising alternative to Flash-based memory devices due to the prospect of high scalability and low power consumption. In this context, complementary resistive switches (CRS) were recently invented to prevent crosstalk of memory cells in a highly dense passive crossbar array. However, a drawback of complementary resistive switch (CRS) arrays results from the destructive readout that is needed to restore information. Readout is carried out by application of a read voltage, which is large enough to switch the cell from state 1 to 0 (identical to a write voltage) and is based on subsequent current pulse detection. Statistically, about 50% of cells read need a write back. Hence, 1.5 write pulses are needed for each read cycle on average, which results in high endurance requirements. Now, a novel non-destructive readout is presented, which makes use of an asymmetric set-up of a CRS cell.
The basic idea of the new approach is a CRS cell where both resistive switching cells have similar switching characteristics, but are distinguishable by different capacities. The concept was invented by a team of researchers from RWTH Aachen University and Forschungszentrum Jülich headed by Rainer Waser. Resistive switching memory cells were prepared by high-pressure sputtering of CMOS compatible TiO2 and SiO2.
In the work, theoretical calculations and circuit simulations are backed up by ultra short pulse measurements down to 50 ns and take advantage of the nonlinear switching kinetics.
The results of the study show that stored information can be read sufficiently by the new approach, which has the prospect of a fast and power-saving readout scheme for passive crossbar arrays without a read cycle limitation due to low endurances.
About the author
The study was conducted by the Electronic Materials Research Lab (EMRL), a collaboration of researchers at the RWTH Aachen University and Forschungszentrum Jülich. Both teams are headed by Prof. Rainer Waser, and are members of the section Fundamentals of Future Information Technology of the Jülich Aachen Research Alliance (JARA-FIT). Stefan Tappertzhofen and Eike Linn are PhD students in electronic engineering at RWTH Aachen University. They invented the concept, prepared the samples and made theoretical calculations. Lutz Nielen prepared the self-build sense amplifier and performed the measurements. Roland Rosezin and Florian Lentz conducted impedance measurements and contributed to theoretical modelling. Both are PhD students at Forschungszentrum Jülich. Dr Ilia Valov, Dr Rainer Bruchhaus, Dr Ulrich Böttger and Prof. Waser contributed to the work at all stages.