In recent years, spin-transfer torque random access memory (STT-RAM)
has been considered as a potential candidate to replace SRAM in
cache design. Compared with SRAM, STT-RAM has advantages of high
data density, nearly zero leakage power, and non-volatility. In
order to further increase data density, multi-level-cell (MLC)
STT-RAM has been proposed. However, write disturbance of MLC STT-RAM
incurs the two-step transition (TT) problem. The TT problem is
resulted from its hard domain and soft domain cannot be flipped to
the opposite magnetization direction at the same time. Therefore,
the soft domain has to be flipped twice to flip to the opposite
magnetization direction of the hard domain. The TT problem will hurt
the lifetime of MLC STT-RAM due to the redundant flips on soft
domains. In order to mitigate the TT problem of MLC STT-RAM, we
propose an alternative encoding scheme (AES) to reduce the
occurances of TTs. AES utilizes the encoding method to eliminate
most TTs and takes a balance distribution of unavoidable TTs among
cells to improve the lifetime of MLC STT-RAM. The experiment results
showed that the proposed scheme achieved a great lifetime
improvement than conventional MLC STT-RAM scheme and the related
work.

In recent years, spin-transfer torque random access memory (STT-RAM)
has been considered as a potential candidate to replace SRAM in
cache design. Compared with SRAM, STT-RAM has advantages of high
data density, nearly zero leakage power, and non-volatility. In
order to further increase data density, multi-level-cell (MLC)
STT-RAM has been proposed. However, write disturbance of MLC STT-RAM
incurs the two-step transition (TT) problem. The TT problem is
resulted from its hard domain and soft domain cannot be flipped to
the opposite magnetization direction at the same time. Therefore,
the soft domain has to be flipped twice to flip to the opposite
magnetization direction of the hard domain. The TT problem will hurt
the lifetime of MLC STT-RAM due to the redundant flips on soft
domains. In order to mitigate the TT problem of MLC STT-RAM, we
propose an alternative encoding scheme (AES) to reduce the
occurances of TTs. AES utilizes the encoding method to eliminate
most TTs and takes a balance distribution of unavoidable TTs among
cells to improve the lifetime of MLC STT-RAM. The experiment results
showed that the proposed scheme achieved a great lifetime
improvement than conventional MLC STT-RAM scheme and the related
work.

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