Investigation of the reliability behavior of conductive-bridging memory cells

Conductive-bridging memory can store information as different resistance states even when not powered. In order to check reliability challenges for nonvolatile-memory applications, the data retention has to be tested carefully. This letter describes a new test scheme using electrical bias for acceleration and enables the fast recording of such detailed information. Experimental data for memory devices based on Ag:GeS2 as the active-matrix material are presented. Excellent stability and reproducibility of the resistance states for more than 300 cycles are demonstrated in the temperature range from 25 degrees C to 85 degrees C. Based on the calculated activation energy, ten years of data retention is extrapolated

Selection of optimized materials for CBRAM based on HT-XRD and electrical test results

Among emerging memory technologies that rely on the bistable change of a resistor, the conductive bridging random access memory (CBRAM) is of particular interest due to its excellent scaling potential into the sub-20 nm range and low power operation. This technology utilizes electrochemical redox reactions to form nanoscale metallic filaments in an isolating amorphous solid electrolyte. Ge chalcogenides are candidate materials for high performance solid electrolytes in combination with Ag as the preferred metal showing high mobility and switching speed. Due to the thermal budget for a back end of the line (BEOL) processing, the layer stack materials must withstand temperatures in the range of 300-450 degrees C. Pure GeS was stable up to 450 degrees C without crystallization. For GeSe, deleterious crystallization was observed. High temperature X-ray diffraction (HT-XRD) and electrical characterization with stepwise annealing were applied to characterize the thermal stability of Ag/GeSe and Ag/GeS material systems. The higher onset temperature for solid-state reactions found with HT-XRD in the Ag/GeS system is the key for the better electrical performance compared to the Ag/GeSe system. Even after thermal annealing with a peak temperature of 300 degrees C, excellent and stable yield numbers of more than 90% for memory elements were achieved for the sulfide, which qualifies this material system for a low temperature BEOL process

Study on the dynamic resistance switching properties of NiO thin films

The resistive switching properties of NiO-based memory cells were investigated utilizing test structures with a Storage contact size of 150 nm in diameter. Two well defined stable resistance states with high OFF/ON ratios were achieved by unipolar operation. Detailed electrical characterizations with respect to nonvolatile memory applications reveal fast (1000cycles) and retention tests up to 110 degrees C show excellent stability and indicate the competitive potential with respect to established nonvolatile memory devices. (C) 2009 Elsevier B.V. All rights reserved