Perpendicular spin transfer torque magnetic random access memories with high spin torque efficiency and thermal stability for embedded applications (invited)

Abstract

Magnetic random access memories based on the spin transfer torque phenomenon (STT-MRAMs) have become one of the leading candidates for next generation memory applications. Among the many attractive features of this technology are its potential for high speed and endurance, read signal margin, low power consumption, scalability, and non-volatility. In this paper, we discuss our recent results on perpendicular STT-MRAM stack designs that show STT efficiency higher than 5 kBT/μA, energy barriers higher than 100 kBT at room temperature for sub-40 nm diameter devices, and tunnel magnetoresistance higher than 150%. We use both single device data and results from 8 Mb array to demonstrate data retention sufficient for automotive applications. Moreover, we also demonstrate for the first time thermal stability up to 400 °C exceeding the requirement of Si CMOS back-end processing, thus opening the realm of non-volatile embedded memory to STT-MRAM technology.

Estimation of thermal stability factor and intrinsic switching current from switching distributions in spin-transfer-torque devices with out-of-plane magnetic anisotropy

“…Pinna et al 13 reported that, in a system with uniaxial anisotropy, n = 2 is a much better fit to the data at long time scales than n = 1, and the crossover regime between deterministic and thermal effects could span very large switching timescales. However, Liu et al 14 used n = 1 following the effective temperature argument, while Thomas et al 15 argued that n = 1 provides a better fit to their experimental data than n = 2. Fitting experimental data with equations (3) and (4) using n = 1 or n = 2 leads to large discrepancies in the values of ∆ as discussed below.…”

Role of CoFeB thickness in electric field controlled sub-100 nm sized magnetic tunnel junctions

“…1(b Next, we determine the values of H K using simple thermal activation model for single domain particles. 32,33 According to this model, by fitting the switching probability, P as a function of field H, one can estimate the values of the anisotropy field H K and the thermal stability ∆. The switching probability is given by…”

Dual referenced composite free layer design optimization for improving switching efficiency of spin-transfer torque RAM

“…Magnetostatic interaction between layers is largely offset by the exchange and not included here. The objective of this design is to maximize the switching efficiency ξ-the existing figure of merit: [8][9][10] …”