Summary of IBM scientists achieve storage memory breakthrough
This article details a breakthrough by IBM scientists in Phase-Change Memory (PCM), achieving 3 bits per cell for the first time. This advancement enhances density and reduces costs, positioning PCM as a potential universal memory combining DRAM speed with flash non-volatility. The technology utilizes drift-immune metrics and adaptive coding to ensure data stability against temperature changes and time drift, enabling faster mobile device launches and efficient enterprise database processing.
Parts used in the Phase-Change Memory Project:
- Phase-change memory cells
- Amorphous phase material
- Crystalline phase material
- Electrical current source
- Low voltage read mechanism
- Drift-immune cell-state metrics
- Drift-tolerant coding scheme
- Adaptive detection thresholds
The current memory 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.
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).
- What is the primary advantage of PCM over DRAM?
PCM does not lose data when powered off, unlike DRAM. - How many write cycles can PCM endure compared to a USB stick?
PCM can endure at least 10 million write cycles, while a USB stick tops out at 3,000. - Can PCM be used in hybrid applications with flash storage?
Yes, IBM envisions hybrid applications where PCM acts as an extremely fast cache combined with flash storage. - How does PCM store a bit of data?
A high or medium electrical current is applied to place the material in either an amorphous or crystalline phase to represent a 0 or 1. - What significant milestone did IBM achieve at the IEEE International Memory Workshop?
IBM scientists successfully stored 3 bits per cell in a 64k-cell array at elevated temperatures after 1 million endurance cycles. - How do the new cell-state metrics improve reliability?
These metrics measure a physical property that remains stable over time, making them insensitive to drift caused by electrical conductivity changes. - What role does the adaptive coding and detection scheme play?
This scheme adaptively modifies level thresholds to follow variations due to temperature changes, ensuring reliable data reading over long periods. - Why is storing 3 bits per cell considered a significant milestone?
At this density, the cost of PCM becomes significantly less than DRAM and closer to flash.
