Reference-Free Dual-Mode Cell-to-Cell Sensing for Area-Efficient Resistive Memory

Resistive Random Access Memory (RRAM) is a promising candidate due to its large R-ratio ($\mathrm{R}_{\mathrm{HRS}} / \mathrm{R}_{\mathrm{LrS}}$) in different switching states, low power consumption, excellent scalability, and compatibility with the manufacturing process. However, resistance shifts, process variations, and random mismatches restrict the practical use of RRAM applications. These challenges degrade the small sensing margin and increase read errors. Conventional sensing schemes using reference values are more affected by degradation. This paper proposes a novel reference-free cell-to-cell sensing scheme. Since the proposed novel sensing scheme directly compares only two unit cells, it requires no analog reference for sensing like the conventional sensing schemes. Furthermore, the proposed scheme produces 2-bit data through each sensing process and is applicable to dual-mode both voltage and current sensing modes. Comprehensive simulation in 40 nm CMOS technology demonstrates that the proposed sensing scheme reads 2-bit data without an analog reference compared to other sensing schemes. The proposed sensing scheme achieves an access time of $\lt 2 \mathrm{~ns}$ at 1.1 V in 40 nm CMOS.