Pattern-Aware Encoding for MLC PCM Storage Density, Energy Efficiency, and Performance Enhancement

Taehyun Kwon, Muhammad Imran, Joon Sung Yang

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)


With the scaling limitations and increasing leakage power of the existing charge-based memories, next-generation memory technologies to overcome the issues are in development. Among the various emerging memories, phase change memory (PCM) is considered as a promising candidate due to its scalability potential and negligible leakage power. For enhanced storage density, the multilevel cell (MLC) operation has been proposed for PCM. This, however, comes at cost of poor reliability, write energy increase and performance degradation. Unlike DRAM, the MLC PCM has a much higher soft error rate due to the resistance drift phenomenon. Error correction code (ECC) schemes can be utilized to improve the MLC PCM reliability, however, this would lead to a lower storage density and an increase in write energy and latency. The iterative programming required for the MLC PCM also degrades its energy efficiency and performance. This paper introduces a simple yet effective encoding scheme to mitigate the problems of the MLC PCM. By using a simple XOR-based encoding, the proposed architecture minimizes the most drift-prone state in the data. The method divides the original data into several encoding blocks and analyzes initial pattern frequencies for each 2-bit pattern. Based on the initial pattern frequencies, the inputs for the XOR encoding are selected that result in minimal frequency of the drift-prone state. This considerably enhances the MLC PCM reliability, leading to a high storage density with a reduced ECC overhead. The energy efficiency and performance are also improved due to reduction in iterative current pulses and ECC overhead. The simulation results show a reduction of about $10^{5}$ X in soft error rate. The improvements in energy efficiency and performance over the conventional 4-level cell (4LC) PCM are 11.5% and 31.9%, respectively.

Original languageEnglish
Article number8758189
Pages (from-to)1855-1865
Number of pages11
JournalIEEE Transactions on Computer-Aided Design of Integrated Circuits and Systems
Issue number9
Publication statusPublished - 2020 Sept

Bibliographical note

Funding Information:
Manuscript received January 20, 2019; revised April 1, 2019; accepted May 2, 2019. Date of publication July 9, 2019; date of current version August 20, 2020. This work was supported in part by the Basic Science Research Program through the National Research Foundation of Korea by the Ministry of Education under Grant NRF-2018R1D1A1B07049842 and Grant 2015R1D1A1A01058856, and in part by the Ministry of Trade, Industry Energy (MOTIE) under Grant 10080594 and Korea Semiconductor Research Consortium (KSRC) support program for the development of the future semiconductor device. This paper was recommended by Associate Editor Z. Shao.

Publisher Copyright:
© 1982-2012 IEEE.

All Science Journal Classification (ASJC) codes

  • Software
  • Computer Graphics and Computer-Aided Design
  • Electrical and Electronic Engineering


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