New non-volatile technology that is expected to replace flash memory-phase change memory

Phase Change Memory (PCM) is a new type of non-volatile technology pioneered by Intel, Numonys and Samsung, which can become a low-cost, more reliable, faster and better alternative to flash memory technology.

Some industry insiders even believe that phase change memory has the potential to accelerate the data storage market's transition from hard drives to solid state drives. One of them is Ed Doller, chief technology officer of Numonyx. Numonyx is a joint venture company created by Intel and ST Microelectronics.

Doller said: "PCM is a very promising alternative flash memory technology that will allow the entire industry to continue to confidently transition from HDD to SSD."

PCM is still in its infancy

However, PCM is still in the stage of trial wafer production, and this technology still faces a series of problems. When can Numonyx and Samsung (Samsung is developing market specifications for Numonyx's PCM products) when can it deliver commercially valuable products? Can the cost of this product be comparable to flash memory in terms of price?

Richard Tomaszewski, HP industry standard server product manager, said: "PCM has high read and write speeds, low volatility and high storage density, which can make up for the shortcomings of NAND flash and the limitations of traditional hard drives. Therefore, some people think that PCM will Next-generation technology after NAND flash. "

But Tomaszewski said that there are some other non-volatile memory technologies-including resistive memory (RRAM) and spin-polarized random access memory (STTRAM)-may become viable alternative technologies.

Tomaszewski said: "These technologies still need further testing and development to prove whether they are reliable. High volume and high output rate are the keys to a successful technological transformation."

He said that in order to replace the existing technology, the new technology must be equal to or better than the existing technology in terms of reliability, durability and service life.

He said that a new technology may take several years from trial wafer production to production in order to obtain sufficient output to achieve scale feasibility and meet reliability and durability expectations.

What is phase change memory?

Doller said that PCM provides high performance and low energy consumption, combining the best features of NOR, NAND and RAM on a chip, including: bit variability, non-volatile, high read speed, high write / erase Speed ​​and good scalability.

Bit variability: PCM, like RAM or EEPROM, is bit-variable-that is, the stored information can be switched from 1 to 0, or from 0 to 1, and no additional erasing steps are required. Flash memory technology generally requires an erase step to change the information.

Non-volatile: PCM is non-volatile, just like NOR flash and NAND flash. PCM does not require continuous power supply to retain information, while RAM is required.

Reading performance: Like RAM and NOR flash memory, PCM also has the characteristics of high-speed random reading. In this way, the code can be executed directly from the storage, without copying to RAM and then executed. The read delay of PCM is close to one word per cell of NOR flash memory, and the read bandwidth is close to DRAM.

Write / erase performance: The write throughput rate of PCM is higher than that of NAND flash memory, and the latency is lower. These features, coupled with the absence of an erase step (bit variability), make PCM significantly outperform NOR and NAND flash memory.

Scalability: Scalability is another unique aspect of PCM. Both NOR and NAND flash memory rely on floating gate memory structures, and these structures are difficult to reduce. As the number of memory cells in flash memory continues to shrink, the number of electrons stored on the floating gate also decreases. Because PCM does not save electronics, it does not need to face the problem of electronic preservation expansion.

Recently, Intel and Numonyx researchers demonstrated a 64MB test chip stacked with multiple PCM arrays. These array layers provide scalability to achieve higher memory density while preserving higher performance.

So far, due to the use of cutting-edge lithography technology, the cost of NAND flash memory technology has dropped to a very low level, but what level it can still be reduced, this remains to be concerned. This is why many people are looking for alternative technologies.

Price is currently one of the advantages of NAND flash

Tomaszewski said: "HP believes that it is too early to say who is the final winner. From the perspective of development progress, PCM seems to be ahead of other technologies. But can PCM be mass-produced and continue to expand while meeting energy, capacity, Requirements for reliability and durability are still to be investigated. "

ObjecTIve Analysis solid-state disk analyst Jim Handy said that PCM may become a strong competitor to flash memory because it has the same advantages as flash memory at higher speeds.

Although the growth momentum of PCM has become more apparent, Handy believes that the mass production and implementation of this technology will wait a few years, perhaps ten years.

He said: "At present, the memory process has reached 34nm, and now needs to further reach 10 ~ 12nm."

Handy said that the biggest challenge facing PCM is cost.

He said that due to insufficient economic scale and research and development limitations, the first generation of PCM chips may be twice as expensive as existing DRAM and flash memory chips.

Handy pointed out that Toshiba recently showed a prototype of NAND flash memory based on 10nm process technology.

He said that as the chip size becomes smaller, NAND flash memory will be able to match PCM. He said: "Perhaps sometime in the future, NAND flash memory will reach its own limit, this will also be the time when PCM or other competitive technologies take off."

PCM's promise: better data retention

Doller said that PCM carries many expectations, mainly because its data retention and durability are not mutually restrictive.

He said: "This means that no matter whether we recycle the PCM memory device 1 million times or only once, the data retention is the same."

Another phenomenon that makes PCM easier to use in system-level designs is that PCM "failures" always occur during the writing process.

Doller said: "So if we write data to the PCM memory device, the write verification function shows that the data is not there, then the data will be immediately rewritten to another location. Unlike NAND flash, PCM will not It is inherently affected by the read interference mechanism. "

Because PCM has excellent reliability, Doller believes that this technology will be the first to be used in applications with the most critical requirements.

Harry Yoon, senior marketing manager at Samsung PRAM, said that Samsung expects their own version of PCM, which will become phase change random access memory (PRAM), to replace NOR flash in a range of mobile applications.