IBM scientists make workable, speedier memory alternative

Researchers at IBM labs are working on a new memory technology which they claim is faster and cheaper than Flash.

It’s known as phase-change memory (PCM) and is said to hold the potential for giving users non-volatile and high-density data storage.

And it could leave Flash memory in the dust, with claims that it is 100 times faster and far more durable. Apparently it can endure 10 million write cycles, compared to Flash, which is only good for 30,000.

IBM says that while 3,000 cycles will outlive many consumer devices, they are not so good with the business enterprise side of the market as they are too slow.  

With speed as its strength PCM would allow computers and servers to boot instantaneously as well as improving the overall performance of IT systems.

The researchers also claim that it could be instrumental in helping to develop low-cost, speedier and “more durable” memory for mobiles, cloud storage and date storage.

Scientists in Zurich used advanced modulation coding techniques to mitigate the problem of short-term drift in multi-bit PCM. They said this combination caused the stored resistance levels to shift over time, which in turn created read errors. 

They said PCM works by leveraging the resistance change that occurred in a material made up of various elements.

When the material changed from a low resistance crystalline to a high resistance amorphous the magic occurred.  

In a PCM cell, where a phase-change material is deposited between a top and a bottom electrode, phase change can be controlled and then induced through applying different strengths of voltage.

The team says that these heat up the material, and when distinct temperature thresholds are reached cause the material to change from crystalline to amorphous or vice versa.

Apparently depending on which voltage is pushed, more or less material between the electrodes will undergo a phase change. This phase change directly affects the cell’s resistance, which the scientists use to store not only one bit, but multiple bits per cell.  

Currently researchers are using four distinct resistance levels to store the bit combinations “00”, “01” 10” and “11”.

IBM explains that in order to achieve the reliability, “crucial technical advancements in the “read” and “write” process were necessary.”

To do this, the scientists implemented an iterative “write” process to overcome deviations in the resistance, which was caused by an “inherent variability in the memory cells and the phase-change materials.”

They then applied a voltage pulse based on the deviation from the desired level, then measured the resistance.  

If the desired level of resistance is not achieved, then another voltage pulse was fired and the scientists measured it again.

The process was repeated until they got the exact level they wanted. Despite some wrong footings they claimed that they had done well, with the worst process marking out a write latency of around 10 microseconds, which still represented “100x performance increase over even the most advanced Flash memory on the market today.”

The reliable read-out of data bits challenge required the scientists to tackle the  problem of resistance drift.  

The challenge here was that because of structural relaxation of the atoms in the amorphous state, the resistance increased over time after the phase change. This eventually caused errors in the read-out.  

To overcome this the scientists used an advanced modulation coding technique, which they described as “inherently drift-tolerant”.  The modulation coding technique is based on the fact that, on average, the relative order of programmed cells with different resistance levels does not change due to drift.

And it seemed to have worked, as by using this technique, IBM was able to mitigate drift and demonstrate long- term retention of bits stored in a subarray of 200,000 cells of their PCM test chip, fabricated in 90-nanometer CMOS technology.  

You can take your white coats off now. 

IBM thinks the technology will be available within the next five years.