3 March 2005óGiven the rapidly increasing data volumes
that are downloaded onto mobile devices such as cell
phones and PDAs, there is a growing demand for suitable
storage media with more and more capacity. At CeBIT,
IBM will for the first time show the prototype of
the MEMS*- assembly of a nanomechanical storage system
known internally as the "millipede" project.
Using revolutionary nanotechnology, scientists at
the IBM Zurich Research Laboratory, Switzerland, have
made it to the millionths of a millimeter range, achieving
data storage densities of more than one terabit (1000
gigabit) per square inch, equivalent to storing the
content of 25 DVDs on an area the size of a postage
of extremely fine tips "write" tiny pits
representing individual bits into a thin film of highly
specific polymer. The principle is comparable with
the old punch cards, but now with structural dimensions
in the nanometer scale and the ability to erase data
and rewrite the medium.
high storage density of more than a terabit was achieved
by using individual silicon tips to create pits approximately
10 nanometers in diameter, i.e. 50,000 times smaller
than the period at the end of this sentence. Experimental
chips have been designed comprising more than 4,000
of these tips arrayed in a small 6.4 mm x 6.4 mm².
These dimensions make it possible to pack an entire
high-capacity storage system into the SD flash memory
product feasibility in terms of storage density, performance
and reliability was demonstrated in recent experiments
using the prototype on display. While current storage
technologies are gradually approaching fundamental
limits, the nanomechanical approach has enormous development
potential: storage densities which correspond to the
size of molecular structures may even be possible.
Moreover, the nanomechanical data medium has been
optimized to use a minimum amount of energy. Thus,
it is ideally suited for use in mobile devices such
as digital cameras, cell phones and USB sticks. Other
possible applications include lithography on the nanometer
scale, as well as atomic and molecular manipulation.
CeBIT, a video microscope provides a look inside the
storage unit that reveals, for example, how the polymer
surface is moved across the tips with the help of
a micromechanism (MEMS). An animated illustration
shows how the parallel tips of the read and write
array operate and how the individual tips work, and
thus explains what is happening on the nanometer scale.
the heart of the "millipede" technology
is a two-dimensional array of V-shaped silicon cantilevers,
each 70 micrometers (thousandths of a millimeter)
long. At the end of each cantilever there is apart
from the tip a micrometer-sized sensor for reading
as well as a heating resistor above the tip, which
is needed for writing. The cone shaped tip is just
under one micrometer in length and has a radius of
a few nanometers at its apex. The cantilever cells
are arranged in the form of an array on a 10 mm x
10 mm chip. One of the recent array designs comprises
a total of 4,096 (64 x 64) cantilevers. The MEMS elements
are etched out of a silicon single crystal using existing
technologies. The actual data medium is a thin polymer
film coated on a silicon substrate. The tips can independently
read, write or erase the bits.
sophisticated design ensures that the tips are held
level above the storage medium with high precision
and that external vibrations and impacts are absorbed.
To increase the data rate, read- and write-electronics
are used that allow the operation of multiple tips
in parallel. Electromagnetic actuation moves the storage
medium very precisely in the x and the y-direction
so that each tip can read and write within its storage
field of 100 micrometers on a side. These short distances
are crucial for achieving fast access times.
For the device to perform its reading, writing, erasing
or overwriting functions, the tips are brought into
contact with the polymer. Bits are written by heating
the tip to a temperature above the glass transition
temperature of the polymer by means of the heating
resistor integrated in the cantilever. The polymer
in close proximity to the tip is heated and becomes
softer allowing the tip to indent a few nanometers
into the film mechanically stressing the material.
For reading, the cantilever's reading sensor, which
is separate from the tip, is heated slightly. As the
polymer film is scanned under the tip, the tip moves
in and out of the written indentations. When the tip
moves into an indent, it cools down because of the
reduced distance to the substrate. This cooling results
in a measurable change in electrical conductivity
of the sensor. To overwrite data thermo-mechanical
effects are used. They cause the stressed polymer
material closely around a newly created bit to relax.
Thus, existing pits can be erased by creating very
close new ones. More than 10,000 writing and overwriting
cycles have proved the concept's suitability as a
reusable storage medium.
Micro-electro mechanical system.