High-Density SOT-MRAM Based on Shared Bitline Structure

• Published in: IEEE transactions on very large scale integration (VLSI) systems 2018-08, Vol.26 (8), p.1600-1603
• Main Authors: Seo, Yeongkyo, Roy, Kaushik
• Format: Article
• Language: English
• Subjects: Bitline sharing; Columns (structural); Density; Energy dissipation; heavy metal (HM); high density; Integrated circuit modeling; magnetic random access memory (MRAM); Mathematical model; Metals; Random access memory; Resistance; spin-orbit torque (SOT); spin-transfer torque (STT); Switches; Torque; Transistors; Tunnel junctions
• ISSN: 1063-8210; 1557-9999
• DOI: 10.1109/TVLSI.2018.2822841

This brief proposes a new design technique for spin-orbit torque magnetic random access memory (SOT-MRAM), suitable for high-density and low-power on-chip cache applications. A bitline of the proposed memory bit cell is shared with that of an adjacent bit cell leading to a reduction in the number of metals along the column direction. This results in higher integration density due to improved metal pitch limited region. The proposed memory can optimize the bit-cell area by aggressively reducing the size of write access transistor, since SOT-based switching operation of SOT devices translates to smaller size of write access transistor. Furthermore, the proposed SOT-MRAM still retains the advantages of SOT-MRAM such as low write energy dissipation, high read-disturb margin, and improved reliability of magnetic tunnel junction. In comparison with the conventional SOT-MRAM bit cells, our proposed MRAM bit cell can have 20% less bit-cell area. Even compared with the standard STT-MRAM, our proposed bit cell still achieves higher integration density. Moreover, the shared bitline SOT-MRAM achieves > 6\times lower write power and higher read-disturb margin than does the STT-MRAM.