Scientific Reports (Jan 2021)

Ratio-based multi-level resistive memory cells

  • Miguel Angel Lastras-Montaño,
  • Osvaldo Del Pozo-Zamudio,
  • Lev Glebsky,
  • Meiran Zhao,
  • Huaqiang Wu,
  • Kwang-Ting Cheng

DOI
https://doi.org/10.1038/s41598-020-80121-7
Journal volume & issue
Vol. 11, no. 1
pp. 1 – 12

Abstract

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Abstract Ratio-based encoding has recently been proposed for single-level resistive memory cells, in which the resistance ratio of a pair of resistance-switching devices, rather than the resistance of a single device (i.e. resistance-based encoding), is used for encoding single-bit information, which significantly reduces the bit error probability. Generalizing this concept for multi-level cells, we propose a ratio-based information encoding mechanism and demonstrate its advantages over the resistance-based encoding for designing multi-level memory systems. We derive a closed-form expression for the bit error probability of ratio-based and resistance-based encodings as a function of the number of levels of the memory cell, the variance of the distribution of the resistive states, and the ON/OFF ratio of the resistive device, from which we prove that for a multi-level memory system using resistance-based encoding with bit error probability x, its corresponding bit error probability using ratio-based encoding will be reduced to $$x^2$$ x 2 at the best case and $$x^{\sqrt{2}}$$ x 2 at the worst case. We experimentally validated these findings on multiple resistance-switching devices and show that, compared to the resistance-based encoding on the same resistive devices, our approach achieves up to 3 orders of magnitude lower bit error probability, or alternatively it could reduce the cell’s programming time and programming energy by up 5–10 $$\times$$ × , while achieving the same bit error probability.