IBM scientists achieve storage memory breakthrough

May 17, 2016
For the first time, scientists at IBM Research have demonstrated reliably storing 3 bits of data per cell using a relatively new memory technology known as phase-change memory (PCM). In this photo, the experimental multi-bit PCM chip used by IBM scientists is connected to a standard integrated circuit board. The chip consists of a 2 × 2 Mcell array with a 4- bank interleaved architecture. The memory array size is 2 × 1000 μm × 800 μm. The PCM cells are based on doped-chalcogenide alloy and were integrated into the prototype chip serving as a characterization vehicle in 90 nm CMOS baseline technology. Credit: IBM Research

For the first time, scientists at IBM Research have demonstrated reliably storing 3 bits of data per cell using a relatively new memory technology known as phase-change memory (PCM).

The current landscape spans from venerable DRAM to hard disk drives to ubiquitous flash. But in the last several years PCM has attracted the industry's attention as a potential universal memory technology based on its combination of read/write speed, endurance, non-volatility and density. For example, PCM doesn't lose data when powered off, unlike DRAM, and the technology can endure at least 10 million write cycles, compared to an average flash USB stick, which tops out at 3,000 write cycles.

This research breakthrough provides fast and easy storage to capture the exponential growth of data from mobile devices and the Internet of Things.

Applications

IBM scientists envision standalone PCM as well as hybrid applications, which combine PCM and flash storage together, with PCM as an extremely fast cache. For example, a mobile phone's operating system could be stored in PCM, enabling the phone to launch in a few seconds. In the enterprise space, entire databases could be stored in PCM for blazing fast query processing for time-critical online applications, such as financial transactions.

Machine learning algorithms using large datasets will also see a speed boost by reducing the latency overhead when reading the data between iterations.

How PCM Works

PCM materials exhibit two stable states, the amorphous (without a clearly defined structure) and crystalline (with structure) phases, of low and high electrical conductivity, respectively.

To store a '0' or a '1', known as bits, on a PCM cell, a high or medium electrical current is applied to the material. A '0' can be programmed to be written in the amorphous phase or a '1' in the crystalline phase, or vice versa. Then to read the bit back, a low voltage is applied. This is how re-writable Blue-ray Discs store videos.

Previously scientists at IBM and other institutes have successfully demonstrated the ability to store 1 bit per cell in PCM, but today at the IEEE International Memory Workshop in Paris, IBM scientists are presenting, for the first time, successfully storing 3 bits per cell in a 64k-cell array at elevated temperatures and after 1 million endurance cycles.

"Phase change memory is the first instantiation of a universal memory with properties of both DRAM and flash, thus answering one of the grand challenges of our industry," said Dr. Haris Pozidis, an author of the paper and the manager of non-volatile memory research at IBM Research - Zurich. "Reaching three bits per cell is a significant milestone because at this density the cost of PCM will be significantly less than DRAM and closer to flash."

To achieve multi-bit storage IBM scientists have developed two innovative enabling technologies: a set of drift-immune cell-state metrics and drift-tolerant coding and detection schemes.

More specifically, the new cell-state metrics measure a physical property of the PCM cell that remains stable over time, and are thus insensitive to drift, which affects the stability of the cell's electrical conductivity with time. To provide additional robustness of the stored data in a cell over ambient temperature fluctuations a novel coding and detection scheme is employed. This scheme adaptively modifies the level thresholds that are used to detect the cell's stored data so that they follow variations due to temperature change. As a result, the cell state can be read reliably over long time periods after the memory is programmed, thus offering non-volatility.

"Combined these advancements address the key challenges of multi-bit PCM, including drift, variability, temperature sensitivity and endurance cycling," said Dr. Evangelos Eleftheriou, IBM Fellow.

The experimental multi-bit PCM chip used by IBM scientists is connected to a standard integrated circuit board. The chip consists of a 2 × 2 Mcell array with a 4- bank interleaved architecture. The memory array size is 2 × 1000 μm × 800 μm. The PCM cells are based on doped-chalcogenide alloy and were integrated into the prototype chip serving as a characterization vehicle in 90 nm CMOS baseline technology.

Explore further: IBM scientists demonstrate computer memory breakthrough

More information: Aravinthan Athmanathan et al. Multilevel-Cell Phase-Change Memory: A Viable Technology, IEEE Journal on Emerging and Selected Topics in Circuits and Systems (2016). DOI: 10.1109/JETCAS.2016.2528598

M. Stanisavljevic, H. Pozidis, A. Athmanathan, N. Papandreou, T. Mittelholzer, and E. Eleftheriou,"Demonstration of Reliable Triple-Level-Cell (TLC) Phase-Change Memory,'' in Proc. International Memory Workshop, Paris, France, May 16-18, 2016

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13 comments

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ab3a
5 / 5 (5) May 17, 2016
Nice. I wonder what the read and write times to each storage node are. It can be slower and still be very competitive. Keep in mind that each cell is three bits, not one.
BartV
2 / 5 (4) May 17, 2016
This new Flash can endur at least 10 million write cycles, but that is way too low to be a DRAM replacement, because DRAM read/write cycles are basically unlimited.

Pooua
5 / 5 (5) May 17, 2016
"To store a '0' or a '1' ... a high or medium electrical current is applied ... to read the bit back, a low voltage is applied. This is how re-writable Blue-ray Discs store videos."

Optical disks, such as CD, DVD or Blu-ray (there is no "Blue-ray") use lasers to read and write bits, rather than electrical current, but, yes, crystalline/amorphous phase change is one way of encoding data on these disks.

I'm still unclear how this new PCM memory achieves three bits per cell.
compose
May 17, 2016
This comment has been removed by a moderator.
compose
May 17, 2016
This comment has been removed by a moderator.
Da Schneib
not rated yet May 18, 2016
We can go a lot smaller than 90nm. But even ten million write cycles is not going to revolutionize computing; this stuff is not usable for general-purpose RAM. On the other hand, it may easily replace hard disks with SSDs that operate at flash speeds, but last orders of magnitude longer than flash.
compose
May 18, 2016
This comment has been removed by a moderator.
Da Schneib
not rated yet May 18, 2016
For such a smart person, @compose, who knows a fair bit of electronics, you have some pretty weird ideas about physics. You might want to think about that. Maybe all those physicists know something you haven't figured out yet.
compose
May 18, 2016
This comment has been removed by a moderator.
Da Schneib
not rated yet May 18, 2016
It would be rather improbable, don't you think?
Yep. You vs. 50,000 physicists, sorry you lose. Get over it.
Ojorf
not rated yet May 18, 2016
Who knows how much compose knows or understands, his comments are just bits copied and pasted (with a word changed here and there) off of the press release from the IBM News room : https://www-03.ib...4949.wss

for example from the above link:

IBM scientists used four distinct resistance levels to store the bit combinations "00", "01" 10" and "11".

and
The scientists implemented an iterative "write" process to overcome deviations in the resistance due to inherent variability in the memory cells and the phase-change materials: "We apply a voltage pulse based on the deviation from the desired level and then measure the resistance

and
In addition, depending on the voltage, more or less material between the electrodes will undergo a phase change, which directly affects the cell's resistance.


etc. etc.
Da Schneib
not rated yet May 18, 2016
Err, actually that's 3 bits, which is 000, 001, 010, ... 101, 110, 111. Eight levels FTW.
compose
May 18, 2016
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