Using an innovative nanotechnology, IBM scientists have demonstrated a data storage density of a trillion bits per square inch — 20 times higher than the densest magnetic storage available today.
IBM achieved this remarkable density — enough to store 25 million printed textbook pages on a surface the size of a postage stamp — in a research project code-named “Millipede”.
Rather than using traditional magnetic or electronic means to store data, Millipede uses thousands of nano-sharp tips to punch indentations representing individual bits into a thin plastic film. The result is akin to a nanotech version of the venerable data processing ‘punch card’ developed more than 110 years ago, but with two crucial differences: the ‘Millipede’ technology is re-writeable (meaning it can be used over and over again), and may be able to store more than 3 billion bits of data in the space occupied by just one hole in a standard punch card.
Although this unique approach is smaller than today’s traditional technologies and can be operated at lower power, IBM scientists believe still higher levels of storage density are possible. “Since a nanometer-scale tip can address individual atoms, we anticipate further improvements far beyond even this fantastic terabit milestone,” said Nobel laureate Gerd Binnig, an IBM Fellow and one of the drivers of the Millipede project. “While current storage technologies may be approaching their fundamental limits, this nanomechanical approach is potentially valid for a thousand-fold increase in data storage density.”
The terabit demonstration employed a single “nano-tip” making indentations only 10 nanometers (millionth of a millimeter) in diameter — each mark being 50,000 times smaller than the period at the end of this sentence. While the concept has been proven with an experimental setup using more than 1,000 tips, the research team is now building a prototype, due to be completed early next year, which deploys more than 4,000 tips working simultaneously over a 7 mm-square field. Such dimensions would enable a complete high-capacity data storage system to be packed into the smallest format used now for flash memory.
While flash memory is not expected to surpass 1-2 gigabytes of capacity in the near term, Millipede technology could pack 10 – 15 gigabytes of data into the same tiny format, without requiring more power for device operation.
“The Millipede project could bring tremendous data capacity to mobile devices such as personal digital assistants, cellular phones, and multifunctional watches,” says Peter Vettiger, Millipede project leader. “In addition, we are also exploring the use of this concept in a variety of other applications, such as large-area microscopic imaging, nanoscale lithography or atomic and molecular manipulation.”
The core of the Millipede project is a two-dimensional array of v-shaped silicon cantilevers that are 0.5 micrometers thick and 70 micrometers long. At the end of each cantilever is a downward-pointing tip less than 2 micrometers long. The current experimental setup contains a 3 mm by 3 mm array of 1,024 (32 x32) cantilevers, which are created by silicon surface micromachining. A sophisticated design ensures accurate leveling of the tip array with respect to the storage medium and dampens vibrations and external impulses. Time-multiplexed electronics, similar to that used in DRAM chips, address each tip individually for parallel operation. Electromagnetic actuation precisely moves the storage medium beneath the array in both the x- and y-directions, enabling each tip to read and write within its own storage field of 100 micrometers on a side. The short distances to be covered help ensure low power consumption.
For the operation of the device — i.e. reading, writing, erasing and overwriting — the tips are brought into contact with a thin polymer film coating a silicon substrate only a few nanometers thick. Bits are written by heating a resistor built into the cantilever to a temperature of typically 400 degrees Celsius. The hot tip softens the polymer and briefly sinks into it, generating an indentation. For reading, the resistor is operated at lower temperature, typically 300 degrees Celsius, which does not soften the polymer. When the tip drops into an indentation, the resistor is cooled by the resulting better heat transport, and a measurable change in resistance occurs.
To over-write data, the tip makes a series of offset pits that overlap so closely their edges fill in the old pits, effectively erasing the unwanted data. More than 100,000 write/over-write cycles have demonstrated the re-write capability of this concept.
While current data rates of individual tips are limited to the kilobits-per-second range, which amounts to a few megabits for an entire array, faster electronics will allow the levers to be operated at considerably higher rates. Initial nanomechanical experiments done at IBM’s Almaden Research Center showed that individual tips could support data rates as high as 1 – 2 megabits per second.
Power consumption greatly depends on the data rate at which the device is operated. When operated at data rates of a few megabits per second, Millipede is expected to consume about 100 milliwatts, which is in the range of flash memory technology and considerably below magnetic recording.
The 1,024-tip experiment achieved an areal density of 200 gigabits (billion bits, Gb) per square inch, which translates to a potential capacity of about 0.5 gigabytes (billion bytes, GB) in an area of 3 mm-square. The next-generation Millipede prototype will have four times more tips: 4,096 in a 7 mm-square (64 by 64) array.
The most recent technical report on the Millipede project is published in the June 2002 inaugural issue of IEEE Transactions on Nanotechnology.