March
16, 2005---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 Recordable and 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, a so-called
unified memory that replaces all other types, 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.
For
further information please contact:
Philips Research/Public Relations
Koen Joosse
Tel.: +314027 43703
E-mail: koen.joosse@philips.com
About
Royal Philips Electronics
Royal Philips Electronics of the Netherlands (NYSE:
PHG, AEX: PHI) is one of the world's biggest electronics
companies and Europe's largest, with sales of EUR
30.3 billion in 2004. With activities in the three
interlocking domains of healthcare, lifestyle and
technology and 161,500 employees in more than 60
countries, it has market leadership positions in
medical diagnostic imaging and patient monitoring,
color television sets, electric shavers, lighting
and silicon system solutions. News from Philips
is located at www.philips.com/newscenter
