[FoRK] advances in spintronics

Eugen Leitl eugen at leitl.org
Fri Nov 23 07:05:34 PST 2012


http://semiaccurate.com/2012/11/16/everspin-makes-st-mram-a-reality/

Everspin makes ST-MRAM a reality

LSI AIS 2012: Non-volatile memory with DDR3 speeds

Nov 16, 2012 in Storage

by Charlie Demerjian

logo everspin 63x17 Everspin makes ST MRAM a realityEverspin has introduced a
production ST-MRAM memory that combines high speeds, high density, and
non-volatile storage. Best of all, it can be produced on normal semiconductor
lines at bleeding edge geometries.

MRAM is short for Magnetoresistive RAM, and up until this anouncement was
only available in Toggle form. Now Everspin has announced ST-MRAM or Spin
Torque MRAM, and sample boards are available now. ST-MRAM takes less power to
switch, to run, and the cells can shrink with smaller processes just like
transistors.

The ST-MRAM shown today is built on a standard 90nm process, and from that
you get a 64Mb chip that is pin compatible with a DDR3 DRAM. That means for a
comparable size device, you can get the DIMM pictured below but it doesn’t
lose data when powered off. Densities start off at 64MB, remember this is a
90nm product, and the speeds are comparable to current DDR3/1600MHz.

Everspin ST MRAM DIMM Everspin makes ST MRAM a reality

64MB Everspin ST-MRAM in DDR3 DIMM format

Timings are also comparable to DDR3/1600, but not exactly the same. This
isn’t marketing-speak to hide a flaw, the CAS latency is the same, but the
other timings are different due to how MRAM works.  This means higher access
granularity and no needed refresh, so accesses can be done quite differently.
Since ST-MRAM does not need to be refreshed, that changes how bits can be
accessed and patterns are optimal to read it with. All of the old DRAM tricks
for banks, accesses, and block reads are not necessarily beneficial for this
technology, and that changes just about everything. This is not to say it is
worse, more granular and faster without refresh related rules is a very good
thing.

Current DDR3 controllers, if they follow the spec fully, should be able to
work with ST-MRAM. They will undoubtedly need a firmware update to make them
aware of the non-volatile nature of the memory, but that is understandable.
These updates should also let you do a lot more tricks with access, the old
handcuffs are not there any more. The short story is that with very little
work, it should work with many modern memory controllers.

Looking forward a bit, if you can get 64Mb chips out of a 90nm process, think
about what happens when you move to a modern process. Process steps are 90nm,
65nm, 45nm, 32nm, and now down to 22nm. That means the 64Mb parts are built
on a -4 process, or to put it another way, would get 16x the density moving
to a bleeding edge process. I will let you do the math, but a 20/22nm MRAM
will hold a bit less than current DRAMs on the same process and not lose it
when you pull the plug. Everspin assures SemiAccurate that it does shrink to
those geometries and that dies sizes are roughly the same as DRAM for the
same capacity chip.

Better yet, switching a bit cell is determined by current density, so energy
used goes down with the square of the process size, but not exactly. There
are a few other factors to take in to account, but each shrink should bring a
large power savings with it like you might typically expect from
semiconductors. Normal DRAMs don’t shrink nearly as well, and flash is at the
point of decreasing performance as process get smaller too.

Everspin ST MRAM in LSI card Everspin makes ST MRAM a reality

ST-MRAM working in an LSI RAID card

Everspin is saying that the pricing of MRAMs now is comparable to SRAMs, that
would be very high to you and me. With the advent of ST-MRAM, when volume
goes up prices should drop to that of standard DRAMs. For non-volatile memory
that is in the ballpark of current alternatives for energy use all while on a
90nm process. Impending shrinks mean ST-MRAM has a pretty good outlook. Once
this technology goes mainstream it will change things, count on it.S|A


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