You have to hand it to IBM’s engineers. They drag themselves into work after their company’s 100th birthday celebration , pop a number of Alka-Seltzers after which promptly announce another seismic invention. This time it is a new type of phase change memory (PCM) that reads and writes 100 times faster than flash, stays reliable for millions of write-cycles (in place of just thousands with flash), and is reasonable enough for use in anything from enterprise-level servers down to cellphones. PCM is predicated on a distinct alloy which might be nudged into different physical states, or phases, by controlled bursts of electricity. During the past, the technology suffered from the tendency of 1 of the states to chill and increase its electrical resistance over the years, resulting in read errors. Another limitation was that every alloy cell could only store a single little bit of data . But IBM employees burn through problems like these on their cigarette breaks: not just is their latest variant more reliable, it should also store four data bits per cell, which implies we will expect a knowledge storage “paradigm shift” throughout the next five years. Combine this with Intel’s promised 50Gbps interconnect , which has an analogous ETA, and knowledge will start flowing faster than booze from an open bar at the boss’s tab. There’s more detailed science inside the PR after the break, when you have a transparent head.
First Time
• Reliable multi-bit phase-change memory technology demonstrated
• Scientists achieved a 100 times performance increase in write latency
in comparison to Flash
• Enables a paradigm shift for enterprise IT and storage systems,
including cloud computing by 2016
ZURICH, June 30, 2011 – For the primary time, scientists at IBM Research have
demonstrated that a comparatively new memory technology, referred to as phase-change
memory (PCM), can reliably store multiple data bits per cell over extended
periods of time. This important improvement advances the construction of
low-cost, faster and tougher memory applications for consumer devices,
including cell phones and cloud storage, in addition to high-performance
applications, which includes enterprise data storage. With a mixture of
speed, endurance, non-volatility and density, PCM can enable a paradigm shift for enterprise IT and storage systems throughout the next five years.
Scientists have long been looking for a universal, non-volatile memory
technology with far superior performance than Flash – today’s most
ubiquitous non-volatile memory technology. Some great benefits of this sort of memory
technology would allow computers and servers as well instantaneously and
significantly enhance the whole performance of IT systems. A promising
contender is PCM that may write and retrieve data 100 times faster than
Flash, enable high storage capacities and never lose data when the ability is
turned off. Unlike Flash, PCM can be very durable and might endure at least
10 million write cycles, in comparison to current enterprise-class Flash at
30,000 cycles or consumer-class Flash at 3,000 cycles. While 3,000 cycles
will live longer than many consumer devices, 30,000 cycles are orders of magnitude
too low to be suitable for enterprise applications. (see chart for
comparisons).
“As organizations and consumers increasingly embrace cloud-computing models
and services, whereby some of the data is stored and processed in the
cloud, ever more powerful and efficient, yet affordable storage
technologies are needed,” states Dr. Haris Pozidis, Manager of Memory and
Probe Technologies at IBM Research – Zurich. “By demonstrating a multi-bit
phase-change memory technology which achieves for the primary time
reliability levels corresponding to those required for enterprise applications, we
made a gigantic step towards enabling practical memory devices based on
multi-bit PCM.”
Multi-level Phase Change Memory Breakthrough
To reach this breakthrough demonstration IBM scientists in Zurich used
advanced modulation coding techniques to mitigate the difficulty of short-term
drift in multi-bit PCM, which causes the stored resistance levels to shift
through the years, which in turn creates read errors. To this point, reliable retention
of information has only been shown for single bit-per-cell PCM, whereas no such
results on multi-bit PCM were reported.
PCM leverages the resistance change that happens within the material — an alloy
of numerous elements — when it changes its phase from crystalline –
featuring low resistance – to amorphous – featuring high resistance – to
store data bits. In a PCM cell, where a phase-change material is deposited
between a top and a bottom electrode, phase change can controllably be
induced by applying voltage or current pulses of various strengths.
These heat up the cloth and when distinct temperature thresholds are
reached cause the fabric to switch from crystalline to amorphous or vice
versa.
Moreover, reckoning on the voltage, roughly material between the
electrodes will undergo a phase change, which directly affects the cell’s
resistance. Scientists exploit that aspect to store not just one bit, but
multiple bits per cell. Inside the present work, IBM scientists used four
distinct resistance levels to store the bit combinations “00″, “01″ 10″ and
“11″.
To gain the demonstrated reliability, crucial technical advancements in
the “read” and “write” process were necessary. The scientists implemented
an iterative “write” process to conquer deviations within the resistance due
to inherent variability within the memory cells and the phase-change materials:
“We apply a voltage pulse according to the deviation from the specified level and
then measure the resistance. If the specified level of resistance is not
achieved, we apply another voltage pulse and measure again – until we
achieve the precise level,” explains Pozidis.
Despite using the iterative process, the scientists achieved a worst-case
write latency of about 10 microseconds, which represents a 100x performance
increase over even probably the most advanced Flash memory in the stores today.
For demonstrating reliable read-out of information bits, the scientists needed to
tackle the difficulty of resistance drift. As a result of structural relaxation
of the atoms within the amorphous state, the resistance increases over time
after the phase change, eventually causing errors within the read-out. To
overcome that issue, the IBM scientists applied a sophisticated modulation
coding technique that may be inherently drift-tolerant. The modulation coding
technique relies at the undeniable fact that, on average, the relative order of
programmed cells with different resistance levels would not change due to
drift.
Using that technique, the IBM scientists were capable of mitigate drift and
demonstrate long- term retention of bits stored in a subarray of 200,000
cells in their PCM test chip, fabricated in 90-nanometer CMOS technology.
The PCM test chip was designed and fabricated by scientists and engineers
located in Burlington, Vermont; Yorktown Heights, Ny and in Zurich.
This retention experiment have been under way for greater than five months,
indicating that multi-bit PCM can achieve a degree of reliability that is
suitable for practical applications.
The PCM research project at IBM Research – Zurich will continue to be
studied on the recently opened Binnig and Rohrer Nanotechnology Center.
The middle, that’s jointly operated by IBM and ETH Zurich as portion of a
strategic partnership in nanosciences, offers a cutting-edge
infrastructure, including a massive cleanroom for micro- and nanofabrication
in addition six “noise-free” labs, especially shielded laboratories for
highly sensitive experiments.
The paper “Drift-tolerant Multilevel Phase-Change Memory” by N. Papandreou,
H. Pozidis, T. Mittelholzer, G.F. Close, M. Breitwisch, C. Lam and E.
Eleftheriou, was recently presented by Haris Pozidis on the 3rd IEEE
International Memory Workshop in Monterey, CA.
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