Abstract
In spin-transfer torque magnetoresistive random access memory, the magnetization dynamics of a free layer is usually assumed to be determined by the torque created via a position-independent current density. In circuits, however, it is the voltage, not the current density, which stays fixed during switching. Therefore, the approximate evaluation of the torque based on a fixed current density becomes questionable in modern magnetic tunnel junctions with a tunneling magnetoresistance ratio of about 200%, where the current density across the structure can vary by a factor of three. In this work, we compare the switching times obtained within a fixed voltage assumption with those from the approximate fixed current density assumption. We demonstrate that the assumption of a fixed current can reproduce the correct switching if the current is appropriately adjusted. It is shown that the correction to the current is not universal and depends on various factors such as TMR, temperature, the size of the structure and resistance area.
Highlights
The latest advancements in the development of computer memory have been based on the down-scaling of semiconductor components
We compare switching times obtained within the approach with a fixed voltage across the magnetic tunnel junction (MTJ) and the one with constant current density described by (2) to the reference model [17] generalized to perpendicularly magnetized MTJs (p-MTJs), in which the total current is fixed but redistributed over time according to the local resistance value
In order to compensate the effect of the varying resistance, the current value I under the assumption of a fixed current must be increased by ∼9% for anti-parallel one (AP) to P and decreased by ∼4% for P to AP switching, for a tunneling magnetoresistance ratio (TMR) of 200%
Summary
The latest advancements in the development of computer memory have been based on the down-scaling of semiconductor components. We show that a correction of the current value allows the fixed current approach to correctly reproduce the switching time distribution obtained using a fixed voltage, and that the correction depends on system parameters such as TMR, temperature, size of the structure and resistance area.
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