Analysis of the Excellent Memory Disturb Characteristics of a Hourglass-Shaped Filament in Al2O3/Cu-Based CBRAM Devices

All resistive switching memory devices face a critical voltage-time dilemma, as they require fast write at moderate voltage together with disturb immunity at lower (read) voltage. In this paper, excellent voltage-time characteristics are demonstrated on a 90-nm CMOS-friendly W/Al2O3/TiW/Cu conductive-bridging memory cell. The switching voltage was evaluated in the large write pulsewidth range between 10 ns and 10 s, from which a very low slope of similar to 75 mV/decade was extracted. These characteristics allow, on the one hand, a fast switching (10 ns) at <3 V, and, on the other hand, excellent voltage-disturb immunity extrapolated to +/- 0.5 V for 10 years. Both constant-voltage-stress and read-endurance tests supported these predictions. By means of conductive-atomic-force microscopy tomography, the hourglass shape of the Cu filament was evidenced. Both the more distributed electrical field induced by this shape along the filament and the analysis of a charge-transfer (redox) reaction as rate-limiting mechanism in the switching process are discussed as the origins of this excellent disturb immunity.