13.4 A 22nm 1Mb 1024b-Read and Near-Memory-Computing Dual-Mode STT-MRAM Macro with 42.6GB/s Read Bandwidth for Security-Aware Mobile Devices

Many security-aware mobile devices, using the secure hash algorithm (SHA) or the advanced encryption standard (AES) for data encryption, require short read-access time (t
AC
) and wide-IO from nonvolatile memory (NVM) for high-read bandwidth and SHA/AES shift/rotate functions. STT-MRAM is the major on-chip NVM for advanced process nodes [2]–[6]; however, it requires small-offset sense amplifiers (SAs) for robust reads, against a small TMR-ratio, at the expense of large area overhead and read energy (E
RD
). As Fig. 13.4.1 shows, designing STT-MRAM macros for security-related applications imposes three main challenges. (1) Using a large number of SAs for wide parallel-IO readout to achieve a short t
AC
, but this results in a high peak current l
PEAK
and a large area overhead. Using fewer SAs for sequential wide-IO readout reduces l
PEAK
and area overhead, but imposes long t
AC
and a low read bandwidth (BW
R
). (2) MRAM macros with a high l
PEAK
degrade the supply (V
DD
) integrity of the chip, often leading to failure in noise-sensitive blocks on the same chip. (3) A conventional memory-logic-separated scheme imposes a long latency (2 cycles: wide-IO memory read + flip-flop (FF) shift/rotate) for NVM-based security logic operations. This paper presents a multibit current-mode SA (MB-CSA) for a high BW
R
with a short t
AC
and a low l
PEAK
. Also presented is a near-memory computing (NMC) unit with a 1-cycle access, to speed up computing for security applications. This work resulted in a 22nm 1 Mb STT-MRAM macro with dual-mode operations: wide-IO memory and NMC. The proposed 1 Mb macro demonstrates the largest number of data-out operations (1024b) with a t
AC
of 275ns using a 0.85V supply. In memory mode, this device outperformed all reported NVM macros in terms of BW
R
(42.67GB/s) and E
RD
(0.23pJ/b. This work also presents the first MRAM macro with NMC functionality, a 33.3% reduction in logic area, and only a 170ps latency, after NVM access, for 1 b shift/rotate operations.