Philips Research Press Release

Philips Research team publishes details of a non-volatile memory that scales in size and performance in line with deep sub-micron silicon chip technology

Eindhoven, The Netherlands -- In the April issue of Nature Materials, scientists at Philips Research will publish details of an innovative phase-change memory that promises to match the speed, density, low voltage and low power consumption requirements of future deep sub-micron 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 Rewritable discs. In these discs it is the reflectivity of the material that changes, with a laser being used both to heat the material to the required temperature in order to switch it between its amorphous and crystalline phases and to detect the resultant change in its reflectivity. Philips' new solid-state memory cell employs similar phase-change materials deposited as an ultra-thin film on the surface of a silicon chip, and uses an electric current to switch it between phases and to detect the resultant change in its electrical resistance. Although similar memory devices have been investigated before, Philips' new 'line-cell' phase-change memory has the potential to meet both the performance and scaling requirements of future nano-electronic silicon chips.

The secret of Philips' memory cell lies in the structure and materials used. 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. For silicon chips produced in advanced CMOS process technologies these voltages are not practical. 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 of around 14V/μm.

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 phase-change element in Philips' line-cell is surrounded by relatively low thermal conductivity silicon dioxide, avoiding interface reactions and providing an extra degree of freedom in the choice of electrode material. Phase changes occur extremely quickly, typically within 30 ns in Philips' prototype devices, with the added advantage that symmetrical programming pulses can be used. 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.

"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.

Demonstration of this new memory cell puts Philips in the same leading-edge position for nanoelectronic phase-change memory development that it has enjoyed for many years in the development of phase-change technology for optical storage.
 

Measurement of the performance of a phase change memory chip

High-resolution picture is available from:

+ www.research.philips.com/newscenter/pictures/
050316-phchmem.html
 

For further information please contact:
 

Ellen de Vries
Philips Research
Tel.: +31 40 27 42321
Mobile: +31 6 53243037
Email: ellen.de.vries@philips.com

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Royal Philips Electronics of the Netherlands (NYSE: PHG, AEX: PHI) is a global leader in healthcare, lighting and consumer lifestyle, delivering people-centric, innovative products, services and solutions through the brand promise of “sense and simplicity”. Headquartered in the Netherlands, Philips employs approximately 134,200 employees in more than 60 countries worldwide. With sales of EUR 27 billion in 2007, the company is a market leader in medical diagnostic imaging and patient monitoring systems, energy efficient lighting solutions, as well as lifestyle solutions for personal wellbeing. News from Philips is located at www.philips.com/newscenter.