The dynamics of the magnetization switching in magnetic tunnel junctions (MTJs) designed for spin-transfer-torque (STT) magnetoresistive random access memory (MRAM) was investigated using micromagnetic simulations. It was found that for short pulses (< approx 10 ns), the switching current threshold does not correlate with the switching field threshold and it is, therefore, essentially insensitive to MTJ shape (aspect ratio) and edge roughness. However, if the magnetization reversal is thermally activated for longer pulses, the switching current and the switching field are directly correlated. For a relatively large MTJ, the distribution is wide due to the excitation of high-order spin wave modes.
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