High Density Crossbar Structure for Memory Application.

[摘要] In this thesis study, we utilized two-terminal resistive devices to construct high-density crossbar arrays for memory and logic applications. The performance advantages of the devices using a-Si as the resistance switching layer have been confirmed in this thesis study in terms of switching speed ( < 50ns), high on/off current ratio ( > 106), good data retention ( > 6years), and programming endurance ( > 105). The resistive memory was further engineered so that the devices can exhibit intrinsic diode-like I-V characteristics at on-state with reverse bias current suppressed to below 10−13 A and providing rectifying ratio > 106. The intrinsic diode behavior can be explained by the motion of Ag ions inside the a-Si matrix and are robust during device operation by surviving > 108 programming and erasing cycles. The intrinsic rectifying behavior is critical to solving the ;;sneak path” problem that has hindered high-density crossbardevelopment. Based on these developments, we successfully demonstrated vertical integration of nanoscale crossbar arrays on CMOS circuits. The integrated crossbar/CMOS devices preserved all desired functionalities including low programming current, high on/off current ratio, excellent device uniformity, and the intrinsic rectifying characteristics. Integrated systems composed of a 40 × 40 crossbar array with 50 nm half-pitch have been fabricated on 180 nm technology node CMOS. For the first time, complex data patterns including binary 40 × 40 images and ;;color” 40 × 40 images can be stored and retrieved in the integrated crossbar/CMOS system without having to use transistors as current steering elements at each crosspoint inside the array.We further developed a framework for modeling the resistive switching devices. The modeling involves identifying and solving the filament growth equations together with the metal/insulator/semiconductor tunneling equation that can correctly predict the dynamic resistive switching characteristics including the apparent threshold effect, the dependence of switching time on voltage, and multiple level storage capability. The governing equations were further incorporated into conventional SPICE package and were used to successfully demonstrate several simple circuit operations.

[发布机构] University of Michigan

[效力级别] Resistance Random Access Memory

[关键词] Crossbar Memory Array;Resistance Random Access Memory;Electrical Engineering;Engineering;Electrical Engineering