A Cost-Effective 1T-4MTJ Embedded MRAM Architecture with Voltage Offset Self-Reference Sensing Scheme for IoT Applications

Masanori HAYASHIKOSHI  Hiroaki TANIZAKI  Yasumitsu MURAI  Takaharu TSUJI  Kiyoshi KAWABATA  Koji NII  Hideyuki NODA  Hiroyuki KONDO  Yoshio MATSUDA  Hideto HIDAKA  

IEICE TRANSACTIONS on Electronics   Vol.E102-C   No.4   pp.287-295
Publication Date: 2019/04/01
Online ISSN: 1745-1353
DOI: 10.1587/transele.2018CDP0007
Type of Manuscript: Special Section PAPER (Special Section on Solid-State Circuit Design — Architecture, Circuit, Device and Design Methodology)
nonvolatile memory,  magnetic memory,  memory architecture,  

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A 1-Transistor 4-Magnetic Tunnel Junction (1T-4MTJ) memory cell has been proposed for field type of Magnetic Random Access Memory (MRAM). Proposed 1T-4MTJ memory cell array is achieved 44% higher density than that of conventional 1T-1MTJ thanks to the common access transistor structure in a 4-bit memory cell. A self-reference sensing scheme which can read out with write-back in four clock cycles has been also proposed. Furthermore, we add to estimate with considering sense amplifier variation and show 1T-4MTJ cell configuration is the best solution in IoT applications. A 1-Mbit MRAM test chip is designed and fabricated successfully using 130-nm CMOS process. By applying 1T-4MTJ high density cell and partially embedded wordline driver peripheral into the cell array, the 1-Mbit macro size is 4.04 mm2 which is 35.7% smaller than the conventional one. Measured data shows that the read access is 55 ns at 1.5 V typical supply voltage and 25C. Combining with conventional high-speed 1T-1MTJ caches and proposed high-density 1T-4MTJ user memories is an effective on-chip hierarchical non-volatile memory solution, being implemented for low-power MCUs and SoCs of IoT applications.