Dashboard

Now you are in the subtree of TECHNOLOGY and MARKETS public knowledge tree. 

ON/OFF ratio of MRAM

access device page 12 of Xiao-Bennett

The on/off ratio of access devices: if this ratio is insufficient, then
the crossbar suffers from large power dissipation during programming and potentially also from write disturb. A reasonable
limit on crossbar size is the point when the total leakage in all
the unselected and half-selected devices matches the current
flowing through the selected device. For example, with an On/
Off ratio of $10^6$ , the limit on crossbar size is roughly $1000 x 1000$

2014 Burr et al.: Access devices for 3D crosspoint memory IBM

Access device OFF-state leakage currents that are several orders of magnitude lower than the ON-state current allow the use of large arrays which are desirable to increase overall area efficiency. For instance, assuming that a single bit is being written in a $1000 x1000$ array, an access device ON/OFF current ratio of $10^6$ is needed in order to keep the

aggregate unselected cell leakage current to the same order of magnitude as the write current

2020 A Variation Robust Inference Engine Based on STT-MRAM with Parallel Read-Out Yandong Luo

Due to its limited on/off ratio, STT-MRAM is often used as digital memory that only allows row-by-row read-out for near-memory computing.

We propose three techniques
1) a 2T-2MTJ bit-cell design with high on/off ratio,
2) redundancy for MSB weights to mitigate the impact of MTJ conductance variations, and
3) a hybrid-layer mapping scheme to reduce column current thus mitigating CSA offset effect

2016 Resistive Memory Device Requirements for a Neural Algorithm Accelerator Sapan Agarwal

ON/OFF ratio of MRAM is not very high, this will limit the size of the crossbar - did you estimate the limiting size?

  • This is actually a good point. No, we did not estimate it specifically.

If he meant a task of discerning a single ON against a background
of many OFFs, then indeed, 10000 OFFs might well be enough to
drown a few ONs in noise (or even 1000 OFFs would suffice). But
if we talk of general BNN performance based on the crossbar, we
saw it taking up to 10% of noise or so without much deterioration,
so the hopes there are much higher. But yes, we did not measure.

example - lets say $ R_{on} = 4 * R_{off} $ and say 5 ONs is among 10k OFFs, so the signal is $ 3* 5 $.
The relative signal is $ 15/10k $ which is 0.15 percent, and this relative signal should be higher than the level of electrical Johnson (or etc) noise.