phase change memory

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phase change memory

A non-volatile, random access memory technology that is designed to initially replace flash memory and, eventually, DRAM memory. Invented by Stanford Ovshinsky, who founded Energy Conversion Devices (ECD) in 1960, the vendors of phase change memory products are licensees of Ovonyx Unified Memory (OUM) from Ovonyx, Inc. (, an ECD spin-off. "Phase change RAM" (PRAM and 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" 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 as with optical discs. In addition, the bit in phase change memory 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 considerably denser than optical disc cells, and they can be made to hold more than one bit. In fact, prototypes with several dozen bits per cell have been demonstrated.

Phase Change Vs. Flash
Phase change memory eliminates many of the 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 memory 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,
References in periodicals archive ?
Numonyx also unveiled a new brand name for its phase change memory products created for embedded applications - Numonyx[R] Omneo[TM] PCM.
Phase Change Memory - Fundamentals and Measurement Techniques is recommended primarily for test engineers and test engineering managers who are new to making PRAM measurements, but it will be useful for the experienced user, as well.
The paper, "Phase-transition characteristics of Al-Sb phase change materials for phase change memory application," by Xilin Zhou, Liangcai Wu, Zhitang Song, Feng Rao, Kun Ren, Cheng Peng, Sannian Song, Bo Liu, Ling Xu, and Songlin Feng appears in the journal Applied Physics Letters.
Various technologies including phase change memory, charge trap memory, nanocrystal memory, PMC, RRAM and 3D memory are potential candidates to replace flash memory.
His research has focussed on fabrication of ultra-high capacitance density capacitors for DRAM, high-k gate dielectric research, resistance switching memory, phase change memory, cross-bar arrays and thin film transistors for their applications in future 3D stacked memories.
researchers will present their latest findings on phase change memory (PCM) next week at the 2009 International Electron Devices Meeting (IEDM), the world's main forum for reporting breakthroughs in technology, physics and the modeling of semiconductors and other electronic devices.
New Research Discovery Paves Way for Scalable, Higher Density Phase Change Memory Products
Phase Change Memory - or PCM - has the potential to enable the next wave of innovation.
Reportlinker Adds Phase Change Memory Enters a New Phase 2nd ed.
2, 2010 /PRNewswire/ -- UBM TechInsights, the preeminent provider of services for companies seeking to leverage and protect their technology and intellectual property assets, announces the first commercial design win of a Phase Change memory component in a downstream product application.