The Netherlands’ Philips Research is set to publish details of a new phase-change memory, which has been targeted to hit the market in a 45 nanometer CMOS node in 2010, that should match the speed, density, low voltage and low power consumption requirements of future silicon chips. Unlike existing non-volatile memory technologies such as Flash memory, the performance of this new memory improves in virtually every respect the smaller you make it.
Phase-change materials, which change their physical properties depending on whether they are in their amorphous or crystalline phase, are widely used in optical storage media such as DVD Recordable and Rewritable discs. Philips' new solid-state memory cell uses an electric current to switch it between phases and to detect the resultant change in its electrical resistance.
Current DRAM switches at about 50 nanoseconds while the new phase-change memory from Phillips has a 30ns switch rate according to Phillip’s Koen Joosse in an interview with HostSearch.com. This is 100 to 200 times faster than the time required to program a Flash memory cell, making Philips' line-cell phase-change memory attractive as a DRAM replacement for certain applications. In addition, constructing the line-cell only requires one or two additional lithography steps, which suits it to low-cost chip production.
Previous memory cells based on phase-change materials have suffered from the fact that a relatively high voltage must be applied to the phase-change material in its high-resistance amorphous state in order to drive enough current through it to heat it. To overcome this problem, Philips developed a doped Antimony/Tellurium phase-change material in which threshold switching between the amorphous and crystalline phases occurs at a low electric field strength.
As silicon chips move to smaller feature sizes, a corresponding reduction in the length of the strip reduces the voltage needed for threshold switching, keeping it within the lower voltage ratings of these next-generation chips. For a 50-nm long strip of this material the required voltage is a mere 0.7V, which is well within the voltage that future silicon chips will be able to provide.
"The holy grail of the embedded memory industry is a so-called unified memory that replaces all other types, which combines the speed of SRAM with the memory density of DRAM and the non-volatility of Flash. Philips' new phase-change line-cell technology is a significant step towards this goal," said Dr. Karen Attenborough, project leader of the Scalable Unified Memory project at Philips Research.
