  A new genre of Spin-Transfer Torque (STT) MRAM is proposed, in which
bi-directional writing is achieved using thermoelectrically controlled magnonic
current as an alternative to conventional electric current. The device uses a
magnetic tunnel junction (MTJ), which is adjacent to a non-magnetic metallic
and a ferrite film. This film stack is heated or cooled by a Peltier element
which creates a bi-directional magnonic pulse in the ferrite film. Conversion
of magnons to spin current occurs at the ferrite-metal interface, and the
resulting spin-transfer torque is used to achieve sub-nanosecond precessional
switching of the ferromagnetic free layer in the MTJ. Compared to electric
current driven STT-MRAM with perpendicular magnetic anisotropy (PMA),
thermoelectric STT-MRAM reduces the overall magnetization switching energy by
more than 40% for nano-second switching, combined with a write error rate (WER)
of less than 10-9 and a lifetime of 10 years or higher. The combination of
higher thermal activation energy, sub-nanosecond read/write speed, improved
tunneling magneto-resistance (TMR) and tunnel barrier reliability make
thermoelectric STT-MRAM a promising choice for future non-volatile memory
applications.
