Physical Characterization of Two-Terminal SOT-MRAM Cell

Due to its non-volatility, fast operation, and high endurance, magnetoresistive random access memory (MRAM) based on current-induced switching originating from spin-transfer torque (STT) is one of the most credible candidates to succeed present random access memory technologies. However, the STT-MRAM technology has many limitations, including high critical switching current and stochastic nature of STT-switching, which are unsuitable for ultrafast operation of memory device at nanosecond (ns) and sub-ns regimes. A relatively new switching concept, based on the spin-orbit torque (SOT) effect, is an excitation of torque induced by an in-plane current, typically in a heavy-metal layer, showing potential to overcome these limitations. On the flip side, all the SOT-MRAM cells studied so far require a three-terminal structure to apply the in-plane current, which increases the cell size because of two additional isolated contacts and associated interconnects. In this paper, we designed, fabricated, and analyzed the world first two-terminal SOT-MRAM cell, in which an in-plane current and out-of-plane current are simultaneously generated upon the application of a voltage. We have further confirmed that the switching mechanism is SOT-dominant, and moreover, compared to STT technology, the critical write current is reduced by more than 70% under the same MRAM architecture with 110 nm-diameter magnetic tunnel junctions (MTJs).