Low-Current High-Speed Spin-Transfer Switching in a Perpendicular Magnetic Tunnel Junction for Cache Memory in Mobile Processors

The efficiency of the power reduction in a normally off mobile processor employing spin-transfer torque magnetoresistive random access memory-based cache memory strongly depends on the write charge, which is the value of the write pulsewidth multiplied by the write current. We studied the spin-transfer switching probability (P_sw) in a perpendicular magnetic tunnel junction (p-MTJ) with the aim of achieving high-speed switching of less than a few nanoseconds at a low current below 100 μA. High-speed switching faster than 1 ns was observed at a write current below 100 μA. To understand the observed pulsewidth dependence of P_sw, analysis using a macrospin model based on a dynamic switching was carried out. The analysis reproduced the nature of the P_sw distributions quantitatively. In addition, the developed analysis suggested the effectiveness of miniaturizing the storage layer to reduce the switching current. The p-MTJ operated continuously without any error at a write pulsewidth of 2 ns and current of 49 μA.