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Four-Valued Magnetic Random Access Memory Based on Magneto Tunnel Junction and Resonant Tunneling Diode
Tetsuya Uemura and Masafumi Yamamoto

We proposed a novel four-valued magnetic random access memory (MRAM), that uses a double barrier magneto tunnel junction (MTJ) and a resonant tunneling diode (RTD) connected in series. The double barrier MTJ in the form FM1/I/FM2/I/FM1, where FM1 and FM2 represent ferromagnetic materials with different coercive forces and I represents an insulator, respectively, can take four distinct resistance values, depending on the direction of magnetization of each ferromagnetic layer. The RTD can increase the magneto-resistance (MR) ratio of the MTJ without area penalty due to the NDR characteristics and compactness. The circuit simulation showed that the GaAs/AlAs-based triple barrier RTD with its peak-to-valley current ratio of 20 increased the effective MR ratio from 15% to more than1700%. The cell area per bit is 2F2/bit, which is suitable for a ultra-high density memory.

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