PCM

Monatomic PCMs: A New Direction

Ron NealeUntil now designers of PCM devices have tried to make PCM meet their expectations by experimenting with an almost infinite number of possible multi-element glass compositions, in order to tinker with or emphasise a particular composition-related device characteristic. The apparent advantage of this great variety of materials comes with the baggage of reliability and performance-compromising element separation, driven by the forces of electro-migration, electrostatic effects and phase separation.

Is it possible to cast aside the problems of the multi-element PCM compositions and look at the possibility of monatomic PCMs?  For a team at IBM, Zurich and Aachen University the answer is an unequivocal “Yes!” and recently they have published details of the remarkable progress they have made with amorphous antimony (Sb), as an initial candidate element. This research was published in a June 2018 paper in Nature Materials Letters titled: Monatomic phase change memory, by Martin Salinga et al, IBM and Aachen University).

A difficulty faces those venturing in this new direction: While it is possible to bring many elements to the amorphous state, they very quickly crystallize at room temperature and higher.  The IBM researchers used simulations to find that the keys to obtaining a stable amorphous state is to control the quenching rate and the volume of the sample. That part of the antimony research is underpinned by some very impressive simulations that use only about 200 atoms.

Here’s the issue that this approach Continue reading

Extending the Write/Erase Lifetime of Phase Change Memory: Part 3 – Failure Modes for the Threshold Switch

Ron NealeThis is Part 3 of a short Memory Guy series which continues to explore the possible future impact on PCM memory performance, especially write/erase endurance, building on the results of the IBM/Yale University analysis outlined in Part 1 and Part 2.


Part 3 of this series of articles triggered by the recently published PCM device analysis by a team from IBM/Yale University, moves to a look at its possible implications for the arsenic doped GST threshold switch.  Although the threshold switch was not part of the IBM/Yale work, the implementation of the call for bipolar operation of PCMs means there will be a requirement for a threshold switch whose durability matches that of the memory with which it will be associated in a memory array.

If the study’s finding for PCM can be applied to the arsenic-doped GST threshold switch which is used in today’s commercially-available PCM arrays then the threshold switch might just be the weak link that accounts for the poor endurance of commercial PCM memory arrays.

One little conundrum we must address is: Which Continue reading

Extending the Write/Erase Lifetime of Phase Change Memory: Part 2 – A More Complete View of Element Separation

Ron NealeThis is Part 2 of a short Memory Guy series which will continue to explore the possible future impact on PCM memory performance, especially write/erase endurance, building on the results of the IBM/Yale University analysis outlined in Part 1.


After, in Part 1, summarizing the methodology my next step was to try to bring together in another simple diagram all the detail of the complexity of  the movement of the different elements of the phase change memory material at different locations within the memory cell which the IBM/Yale work has disclosed. Movement which leads to the conclusion that bi-polar operation would be means of extending PCM endurance.

In this post’s first diagram (below) the central region provides illustration of the paper’s unique PCM device structure: A high aspect ratio tapered cell lined with a metal conductor. With the two-state memory switching region located (red coloured) roughly at the centre of the taper.  This means that, Continue reading

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

Ron NealeThis 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

Latest White Paper: New Memories for Efficient Computing

A Potpourri of Emerging MemoriesThere has been a lot of discussion in the trade press lately about new memory technologies.  This is with good reason: Existing memory technologies are approaching a limit after which bits can’t be shrunk any smaller, and that limit would put an end to Moore’s Law.

But there are even more compelling reasons for certain applications to convert from today’s leading technologies (like NAND flash, DRAM, NOR flash, SRAM, and EEPROM) to one of these new technologies, and that is the fact that the newer technologies all provide considerable energy savings in computing environments.

Objective Analysis has just published a white paper that can be downloaded for free which addresses a number of these technologies.  The white paper explains why energy is wasted with today’s technologies and how these new memory types can dramatically reduce energy consumption.

It also provides a Continue reading

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 is a regular contributor to EE Times.

I was astounded to discover that Continue reading

IBM Jumps on the “New Memory” Bandwagon

IBM's 3-Bit PCM Read AlgorithmAt 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

Memory Issues in Space & Medical Applications

How an alpha particle disrupts a memory bitThe 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

Fundamentals of Memory – Free Online Course

Fundamentals of Memory Course - EE TimesSome time ago The Memory Guy was asked by Numonyx (later acquired by Micron) to put together an online course for EE Times on memory technologies, explaining how each one works and where it is used.

Although the course was very well received, I never posted a link to it on The Memory Guy blog.  This post is intended to correct that error.

The course runs 75 minutes and covers the basics of DRAM, non-volatile RAM, SRAM, NAND flash, NOR flash, mask ROM, and EEPROM.  It explains each technology’s advances in size, cost and performance, leading up to the development of Continue reading

Macronix Solves Flash Wear Problem

Macronix Headquarters, Hsinchu TaiwanThe December issue of the IEEE Spectrum includes a fascinating article about a 100 million cycle flash memory developed by Macronix.  The company will present this design at at IEDM this month.

In brief: Macronix’ researchers buried a heater in the array to heat the tunnel dielectric, annealing out the disruptions & traps that might cause a bit to fail.

A prototype has so far been tested more than 100 million cycles and it shows no sign of impending failure.  Researchers believe that it is likely to reach one billion or more cycles, but such testing will take several months.  This just may be able to Continue reading