Phase Change Memory - The Memory Guy Blog

Extending the Write/Erase Lifetime of Phase Change Memory: Part 1- PCM Element Separation and Endurance

This is the first of a new line-up of Memory Guy posts by Ron Neale. In this 4-part series Ron takes a look at the recently-published analysis by a team from IBM and Yale University (Wiley: Communications of Advanced Materials, Volume 30, Issue 9, March 1, 2018 “Self-Healing of a Confined Phase Change Memory Device with a Metallic Surfactant Layer,” Xie et al) which has cast some new light on the complexity of the movement and element separation in phase change memory (PCM) device structures.

In this series of articles I will briefly review what I think is an important piece of work and its implications for the future of PCM write/erase (w/e) endurance in commercial PCM memory arrays. Today’s production Phase-Change Memory, the basis of the Intel/Micron 3D XPoint Memory, wears out faster than expected. This series will investigate some of the potential reasons for this discrepancy.

Back in 2016 a research team led by IBM claimed the world record for PCM w/e endurance of greater than 2 x 10E12 cycles (ALD-based Confined PCM with a Metallic Liner Toward Unlimited Endurance, Proc IEDM 2016 ). As of today commercially available PCM memory arrays offer w/e endurance of some six orders of magnitude less. The table below Continue reading “Extending the Write/Erase Lifetime of Phase Change Memory: Part 1- PCM Element Separation and Endurance”

Original PCM Article from 1970

For a number of years The Memory Guy has wanted to find a copy of the 1970 article, published in Electronics magazine, in which Intel’s Gordon Moore and two authors from Energy Conversion Devices, Ron Neale and D.L. Nelson, showed that PCM could be used as a memory device. After all, this is the technology behind Micron & Intel’s 3D XPoint Memory.

The cover of the magazine (this post’s graphic) has been used by Intel to promote its PCM or PRAM chips before those were spun off to Numonyx (now a part of Micron). Intel, though, didn’t appear to have anything to share but the cover photo.

Electronics magazine went out of business in 1995, and that makes the task of finding archive copies more challenging.

It recently occurred to me that the best person to ask might be the article’s lead author, Ron Neale, who has been a regular contributor to EE Times and who now also contributes blog posts to The Memory Guy.

I was astounded to discover that Continue reading “Original PCM Article from 1970”

IBM Jumps on the “New Memory” Bandwagon

At a technical conference hosted by the IEEE this week IBM announced the results of nearly a decade of research in which its scientists have been investigating the emerging technology known as “Phase Change Memory” (PCM). The scientists presented a means of successfully storing three bits per cell for the first time, while also addressing all of PCM’s challenging idiosyncrasies, including resistance drift and temperature drift.

Commonly referred to by the erroneous nickname “TLC” for Triple Level Cell, this technology squeezes three bits of data into the space of a single bit, essentially cutting the cost per gigabyte to about one third of that of a standard memory chip making it closer in cost to flash.

With this step IBM expects to help drive a new memory layer into existence, one that will fit between the cheap and slow NAND flash used in SSDs and the fast but expensive DRAM used for main memory. Such a layer would improve the cost/performance of all types of Continue reading “IBM Jumps on the “New Memory” Bandwagon”

Memory Issues in Space & Medical Applications

The Memory Guy was recently asked about using memories in a satellite. What would be a good technology to use in a space application?

The problem with space is that there is a lot of radiation. Radiation on the earth’s surface is lower because it is stopped by the atmosphere, but in space there is an abundance of radiation that interferes with most semiconductors. Radiation is also a concern in certain medical applications where a memory must maintain its contents while undergoing sterilization through irradiation. Experiments on conventional flash memories have shown data loss at only 2% of the Continue reading “Memory Issues in Space & Medical Applications”

Micron PCM Enters Mass Production

After years of prototyping Micron Technology claims to be the first to introduce production volumes of Phase-Change Memory, or PCM. This memory, also known as PRAM, has long been positioned as a contender to replace flash once flash reaches its scaling limit. Rather than use electrons to store a bit, PCM uses a type of glass that is conductive when in a crystalline state and resistive when amorphous, two states that are relatively easy to control. The size of the bits can shrink to a very small dimensions, allowing PCM to scale into the single-digit number of nanometers, which most folks today believe to be beyond the realm of flash.

This product began its life at Intel, then followed the Numonyx spin-off, and was taken over by Micron when it acquired Numonyx. In fact, Intel got into PCM very early on – this post’s graphic is the cover of an Electronics Magazine from September 1970 with an Intel story, written by Gordon Moore, telling about a 128-bit PCM research chip.

So far only three companies have produced samples Continue reading “Micron PCM Enters Mass Production”

A New Way to Build Phase-Change Memory (PCM)

An acquaintance recently brought to my attention an article in R&D Magazine about some pioneering research on phase-change memories or PCM. The researchers’ findings hold a lot of promise. (R&D Magazine’s article is based upon an original paper in the journal Science.)

A team led by Ritesh Agarwal, associate professor at the University of Pennsylvania, was trying to develop a better understanding of the mechanism behind the phase changes in PCM. The team found that existing programming algorithms that involve melting the material could be replaced with pulses of electrical current that not only would program the cell without heat, but provided an “On” to “Off” resistance ratio of 2-3 orders of magnitude, which renders the cell significantly easier to read, especially in the presence of noise. This effectively makes memory chip design Continue reading “A New Way to Build Phase-Change Memory (PCM)”

The End of Flash Scaling

Everyone knows that flash memory is about to hit its scaling limit – it’s right around the corner. We’re ready for it because it’s been right around the corner for more than a decade now. It’s so close we can taste it.

When will it happen?

One thing that is quite clear is that nobody knows when NAND flash will stop scaling. Everyone knows that it’s soon, but researchers continue to find ways to push the technology another couple of process nodes past where anyone thought it could possibly go, and they have been doing this since Continue reading “The End of Flash Scaling”

IEEE Spectrum: Did Bad Memory Chips Down Russia’s Mars Probe?

The IEEE Spectrum published an interesting article postulating that Russia’s recently-failed Mars probe may have suffered from bad memory chips. According to the Spectrum article the Russian government’s Official Accident Investigation Results faulted SRAMs:

The report blames the loss of the probe on memory chips that became fatally damaged by cosmic rays.

Both the main computer and the backup computer seem to have failed at the same time, Continue reading “IEEE Spectrum: Did Bad Memory Chips Down Russia’s Mars Probe?”