Sub-nanosecond spin-torque switching of perpendicular magnetic tunnel junction nanopillars at cryogenic temperatures

Abstract

Spin-transfer magnetic random access memory is of significant interest for cryogenic applications where a persistent, fast, low-energy consumption and high device density is needed. Here we report the low-temperature nanosecond duration spin-transfer switching characteristics of perpendicular magnetic tunnel junction (pMTJ) nanopillar devices (40 to 60 nm in diameter) and contrast them to their room temperature properties. Interestingly, at fixed pulse voltage overdrive the characteristic switching time decreases with temperature, in contrast to macrospin model predictions, with the largest reduction in switching time occurring between room temperature and 150 K. The switching energy increases with decreasing temperature, but still compares very favorably to other types of spin-transfer devices at 4 K, with < 300 fJ required per switch. Write error rate (WER) measurements show highly reliable (WER ≤ 5×10 -5 with 4 ns pulses at 4 K) demonstrating the promise of pMTJ devices for cryogenic applications and routes to further device optimization.

Adjusting Thermal Stability in Double-Barrier MTJ for Energy Improvement in Cryogenic STT-MRAMs

“…3 the temperature of such parameters with emphasis on corresponding values at 300 K and 77 K. As the temperature decreases, all three parameters increase, thus resulting in higher values at 77 K with respect to room temperature. This is in line with experimental results reported in [26,27].…”

Embedded Memories for Cryogenic Applications

“…When cooling down to 77 K, we can observe a penalty of about 1.45× and 2.1× in terms of t p for SMTJ-and DMTJ-based bitcells. This is because the critical switching current dramatically increases as temperature goes down to cryogenic levels [16,17,32], with an adverse impact on energy and latency for write operation. This can be counterbalanced by increasing the width of the access transistor.…”

“…Figure 7 shows the statistical distribution of the bitline voltages for SMTJ-and DMTJ-based STT-MRAM bitcells operating at 300 K and 77 K. From the two sensing operations, V BL(P) and V BL(AP) , the voltage sensing margin (V SM ) is defined as: V SM = V BL(AP) − V BL(P) . Due to the rise in the TMR, V SM increases at cryogenic temperatures as compared to 300 K [14,32]. In particular, from Figure 7, we can observe V SM improvements by about 36% and 48% for the SMTJ-and DMTJ-based STT-MRAMs.…”

Thermal effects in spin torque switching of perpendicular magnetic tunnel junctions at cryogenic temperatures

“…Perpendicularly magnetized magnetic tunnel junction (pMTJ) are currently the most promising and extensively studied STT device for commercialization because of their high switching efficiency and scaling properties [7,8]. Although commercial operating temperature are between -40 and 150 • C, pMTJs have also been recently explored for use as memory elements for a cryogenic computer operating at 4 K [9][10][11]. Interest in these devices is associated with the need for a high density low temperature memory that can be tightly integrated with superconducting logic [12].…”

“…In this article, we use the thermally activated spintransfer torque switching model [14][15][16][17] to determine the * laura.rehm@nyu.edu † andy.kent@nyu.edu -0.4 -0. effective switching temperature T eff -the sample temperature at the switching voltage-and the voltage switching threshold from room temperature down to 4 K. Two different methods are used, one based on measurements of the read disturb rate and the other on the measurements of the switching voltage versus pulse duration. These are applied to 40 to 60 nm diameter pMTJs with relatively low resistance products (RA ≈ 3 Ωµm 2 ), junctions that exhibit low energy (< 300 fJ/switch) and fast (sub-ns) switching at 4 K as reported in [10]. We find that the switching temperature T eff versus bath temperature sat-urates below about 75 K. Our findings show that junction heating is significant below this temperature and that spin torque switching remains stochastic at cryogenic temperatures.…”