Optimizing Write Current and Power Dissipation in MRAMs by Using an Astroid Curve

Optimizing Write Current and Write Power Consumption in Magnetoresistive Random Access Memories by Using Generalized Asteroid Curves

“…The write current is large in comparison with, for example, ferroelectric RAM (FeRAM) and with read current of MRAM itself. 3) The write current is also a critical limiting factor in future scalability of MRAM memory cells, because the magnetic field to switch the magnetization increases as the width of MTJ device decreases. 4) Another problem is cell selectivity.…”

“…On the other hand, it is reported that MTJ devices with newly devised shapes exhibit thinner star-shaped curves of the switching fields than conventional MTJ devices, and thus better cell selectivity and smaller switching fields suitable for denser memories to sub-100 nm MTJ widths. 8,9) Theoretical expressions and methods for optimizing MRAM write current and write power consumption were developed in a previous work 3) for conventional MTJ cells whose switching characteristics can be described by the asteroid curve. If the expressions can be extended to include a parameter related to the thinner switching characteristics curves of MTJs with the newly devised shapes as above, the expressions should be able to predict to what extent the writing current can be lowered with the new MTJ shape design approach.…”

“…The previous paper 3) discussed variations and margins related to actual memory cells in an LSI chip whose MTJ switching characteristics theoretically follow the asteroid curve. The paper then defined an asteroid curve that should be used for the MRAM LSI design with some design margins, and the limited ranges of the magnitudes of the easy-axis and hard-axis magnetic fields that are needed to avoid mis-selection of half-selected cells.…”

“…The other assumptions such as those related to the structures of MRAM cell and cell arrays are the same as in the previous work. 3) Since the purpose of this paper is to generalize the previous results based on the generalized asteroid curves, the points different from the previous work will be focused on. The notation, definitions, and equations in the previous paper 3) are used here.…”

“…3) Since the purpose of this paper is to generalize the previous results based on the generalized asteroid curves, the points different from the previous work will be focused on. The notation, definitions, and equations in the previous paper 3) are used here.…”