(Invited) Resistive Random Access Memory for Storage Class Applications

Resistive RAM (RRAM) is one of the most promising emerging nonvolatile memory technologies thanks to fast operation, superior scalability, low power consumption and potential for 3D stacking. From an architectural point of view, 1T1R architecture is suitable for embedded memory applications while 1S1R based cross-point architecture is suited to high density memory applications. In the 1S1R based cross-point integration, however, the suppression of sneak current paths has been the major technical barrier for the high density RRAM.

We show that the sneak path challenge has been overcome by utilizing a Field Assisted Superlinear Threshold (FAST) selector [1]. The FAST selector device uses an insulating amorphous material which provides volatile switching at critical electric field. Excellent selector performance is presented, including high selectivity of > 10⁷, sharp switching slope of < 5mV/dec., and large endurance of > 10¹¹. The low fabrication temperature (≤300°C) of the FAST selector allows 3D stacking of 1S1R memory layers. It is also demonstrated that a volatile switch based selector has inherent benefits such as low voltage overhead for 1S1R integration and high read voltage margin.  

For the 1S1R demonstration, electrochemical metallization RRAM with a sub-5nm filament is utilized. The RRAM device offers a self-current-limiting feature during the program operation [2]. The self-limited program obviates the need for external current compliance, which can increase the number of concurrent programs in the 1S1R cross-point architecture with reduced power consumption and increased reliability benefits. Furthermore, the hold voltage property (snap-back behavior) of a FAST selector allows novel sensing techniques such as Resistance Ratio Amplification (RRA) which amplifies the intrinsic ON/OFF ratio of RRAM by a factor of > 10⁴ [2]. Besides the direct advantage of increased memory ON/OFF ratio, the RRA technique also reduces BER and increases read bandwidth of the RRAM array. The integrated self-current-limited RRAM with FAST selector enables the high density and high performance 1S1R RRAM technology.

References

[1] S. H. Jo, T. Kumar, S. Narayanan, W. D. Lu and H. Nazarian, “3D-stackable crossbar resistive memory based on field assisted superlinear threshold (FAST) selector,” IEDM, 2014.

[2] S. H. Jo, T. Kumar, C. Zitlaw and H. Nazarian, “Self-limited RRAM with ON/OFF resistance ratio amplification,” VLSI Tech. Symp. 2015.