Read an article this week in Science Daily (Magnetic skyrmions: Not the only one of their class; …) about new magnetic structures that could lend themselves to creating a new type of moving, non-volatile storage. (There’s more information in the press release and the Nature paper [DOI: 10.1038/s41565-018-0093-3], behind a paywall).
Skyrmions and chiral bobbers are both considered magnetic solitons, types of magnetic structures only 10’s of nm wide, that can move around, in sort of a race track configuration.
Delay line memories
Early in computing history, there was a type of memory called a delay line memory which used various mechanisms (mercury, magneto-resistence, capacitors, etc.) arranged along a circular line such as a wire, and had moving pulses of memory that raced around it. .
One problem with delay line memory was that it was accessed sequentially rather than core which could be accessed randomly. When using delay lines to change a bit, one had to wait until the bit came under the read/write head . It usually took microseconds for a bit to rotate around the memory line and delay line memories had a capacity of a few thousand bits 256-512 bytes per line, in today’s vernacular.
Delay lines predate computers and had been used for decades to delay any electronic or acoustic signal before retransmission.
A new racetrack
Solitons are being investigated to be used in a new form of delay line memory, called racetrack memory. Skyrmions had been discovered a while ago but the existence of chiral bobbers was only theoretical until researchers discovered them in their lab.
Previously, the thought was that one would encode digital data with only skyrmions and spaces. But the discovery of chiral bobbers and the fact that they can co-exist with skyrmions, means that chiral bobbers and skyrmions can be used together in a racetrack fashion to record digital data. And the fact that both can move or migrate through a material makes them ideal for racetrack storage.
Unclear whether chiral bobbers and skyrmions only have two states or more but the more the merrier for storage. I am assuming that bit density or reliability is increased by having chiral bobbers in the chain rather than spaces.
Unlike disk devices with both rotating media and moving read-write heads, the motion of skyrmion-chiral bobber racetrack storage is controlled by a very weak pulse of current and requires no moving/mechanical parts prone to wear/tear. Moreover, as a solid state devices, racetrack memory is not sensitive to induced/organic vibration or shock, So, theoretically these devices should have higher reliability than disk devices.
There was no information comparing the new racetrack memory reliability to NAND or 3D Crosspoint/PCM SSDs, but there may be some advantage here as well. I suppose one would need to understand how to miniaturize the read-erase-write head to the right form factor for nm racetracks to understand how it compares.
And I didn’t see anything describing how long it takes to rotate through bits on a skyrmion-chiral bobber racetrack. Of course, this would depend on the number of bits on a racetrack, but some indication of how long it takes one bit to move, one postition on the racetrack would be helpful to see what its rotational latency might be.
At the moment, reading and writing skyrmions and the newly discovered chiral bobbers takes a lot of advanced equipment and is only done in major labs. As such, I don’t see a skyrmion-chiral bobber racetrack storage device arriving on my desktop anytime soon. But the fact that there’s a long way to go before, we run out of magnetic storage options, even if it is on a chip rather than magnetic media, is comforting to know. Even if we don’t ever come up with an economical way to produce it.
I wonder if you could synchronize rotational timing across a number of racetrack devices, at least that way you could be reading/erasing/writing a whole byte, word, double word etc, at a time, rather than a single bit.
Photo Credit(s): From Experimental observation of chiral magnetic bobbers in B20 Type FeGe paper