A statistical study of magnetic tunnel junctions for high-density spin torque transfer-MRAM (STT-MRAM)

Abstract

We have demonstrated a robust magnetic tunnel junction (MTJ) with a resistance-area product RA=8 Ω−µm 2 that simultaneously satisfies the statistical requirements of high tunneling magnetoresistance TMR > 15σ(R p ), write threshold spread σ(Vw)/<Vw> <7.1%, breakdown-to-write voltage margin over 0.5V, readinduced disturbance rate below 10 -9 , and sufficient write endurance, and is free of unwanted write-induced magnetic reversal. The statistics suggest that a 64Mb chip at the 90-nm node is feasible. IntroductionThe density of STT-RAM [1] can be as competitive with that of embedded DRAM. It is more scalable and consumes less power than the conventional field-MRAM [2]. This paper describes an STT-MRAM with 70x210 nm 2 MTJ devices. This MTJ provides sufficient statistical margins among read-and writeoperation and satisfies the junction long-term reliability requirements.

Proposal for Switching Current Reduction Using Reference Layer With Tilted Magnetic Anisotropy in Magnetic Tunnel Junctions for Spin-Transfer Torque (STT) MRAM

“…In conclusion, we summarize the potential benefits of the proposed TMA MRAM and compare it with the conventional STT MRAM with PMA in terms of crucial memory design attributes (see Table 1). The ratio of the read current density (while reading data "zero") to the critical switching current density corresponding to the write frequency same as the read frequency has been designated as (J READ /J DISTURB ) [34], [35].…”

Investigation of in-situ doping profile for N+/P/N+ bidirectional switching device using Si_1−xGe_x/Si/Si_1−xGe_x structure

“…As shown in Fig. 2a, the group with a length of 20 nm showed the best performance with a current density of 1 MA/cm 2 and an I on /I off ratio of $10 4 , which is acceptable for an STT-MRAM [4]. Moreover, after adjusting the slope of the doping profile in the Si 0.8 Ge 0.2 and Si interface, it was found that a steeper slope gives better performance, as shown in Fig.…”

“…Essential characteristics of a selective device include simple structure and high performance. In an STT-MRAM, a bidirectional current flow and high current drivability of more than 10 6 A/cm 2 should be achieved for device operation [4].…”

Spin-transfer torque in nanoscale magnetic devices

“…Here, we will not attempt to provide a global view, but will focus on three recent projects from our nanomagnetics group at Cornell University, Ithaca, New York: (i) progress in reducing the critical current for spin-transfer-driven magnetic switching [5], (ii) measurements of the bias dependence of the spin torque in magnetic tunnel junctions using spin-torque-driven ferromagnetic resonance (ST-FMR) [6], and (iii) single-shot measurements of the magnetic dynamics during the process of spin-torque switching [7]. [8][9][10][11]. The primary remaining challenges for commercialization of this technology are to minimize the current required for switching while maintaining sufficient thermal stability for the memory devices and while maximizing the switching speed, demonstrating that the magnetic tunnel junctions used as memory elements can withstand the relatively large current densities needed for spintorque switching without damage during extended use, and demonstrating sufficient reproducibility in the switching characteristics of the magnetic elements.…”