phase change memory

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phase change memory

A non-volatile, random access memory (RAM) technology that was designed to replace flash memory and, ultimately, DRAM memory. Developed by Stanford Ovshinsky, reknowned for his inventions in memories and solar panels, "phase change RAM" (PRAM, PCRAM) and "chalcogenide RAM" (C-RAM) are other names for phase change memory (PCM).

Electrical vs. Optical Phase Change
Phase change memory employs the same principle as rewritable optical discs (CD-RWs, DVD-RWs, etc.), in which the bit cell is either in an unstructured "amorphous" state or highly structured "crystalline" state, both of which are extremely stable. However, phase change memory uses electrical pulses to change the bit rather than the heat from a laser, and it is read by measuring the electrical resistance through the cell, not the reflection of the laser light (see phase change disc).

In addition, phase change memory cells are denser than optical disc cells, and they can hold more than one bit. Prototypes with several dozen bits per cell have been demonstrated.

Phase Change vs. Flash
Phase change memory eliminates many disadvantages of flash memory. Like DRAM and SRAM memory, any byte in phase change memory can be written; whereas, flash requires an entire block to be written. As the flash cell's elements (feature sizes) become smaller, its floating gate architecture becomes more problematic. However, the smaller the phase change cell, the denser and faster the phase change chip becomes. In addition, phase change memory handles millions of rewrites compared to hundreds of thousands for flash. See PCMS, phase change disc, chalcogenide glass and future memory chips.


Change the Phase of the Bit
A long, medium-amplitude pulse creates a highly conductive crystalline bit in the memory cell. A short, high-amplitude pulse resets the bit back to an amorphous state, which is a poor conductor.







Automatically Radiation Hardened
Based on the Ovonyx phase change memory cell, this 4 megabit C-RAM (Chalcogenide RAM) memory chip from BAE Systems is shown in its package before it is covered and the leads are cut. Due to the huge resistance difference between a 1 and 0 in the memory cell (5K and 100K ohms), the chip is automatically "rad hard." External radiation cannot change the phase sufficiently enough to alter the value of the cell. (Image courtesy of BAE Systems, www.baesystems.com)
References in periodicals archive ?
Summary: TEHRAN (FNA)- A team of scientists now has an explanation of how a particular phase-change memory (PCM) material can work one thousand times faster than current flash computer memory, while being significantly more durable with respect to the number of daily read-writes.
Phase-change memory due to read and write with fast speed, high-density storage capacity, and compatible with complementary metal-oxide-semiconductor (CMOS), which regarded as the most promising alternative flash memory, becomes the mainstream of the next generation of nonvolatile storage technology [5, 6].
As a result of the advances, the Singapore researcher has now created a version of phase-change memory that is as fast as RAM chips and packs in many times more storage capacity than flash drives.
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.
The technology, dubbed Phase-Change Memory (PCM) is a type of non-volatile
India, May 18 -- Scientists at IBM have achieved a breakthrough in developing the storage capabilities of phase-change memory (PCM).
Nanotechnology specialists from the US and Korea cover nanowire growth and integration; high performance, low power electronic devices; nanowire phase-change memory; biosensors; metal silicide nanowires and their spintronic and renewable energy applications; optoelectronic devices; and energy devices like photovoltaics, mechanical nanogenerators, thermoelectric harvesters, and lithium-ion batteries.
In 2014, Micron, the main phase-change memory (PCM) promoter for standalone memory, stopped actively selling PCM chips following the collapse of sales targeting the shrinking entry-level mobile phone market.
Popescu, "Phase-change memory: science and applications," Physica Status Solidi (b), vol.
Phase-change memory is being actively pursued as an alternative to the flash memory, as flash memory is limited in its storage density and phase-change memory can operate much faster.