US team create carbon nanotube ultra-memory
Chips to last a billion years, hold trillion bits/sq in
US researchers have demonstrated a form of nanotube archival memory that can store a memory bit for a billion years, and has a theoretical trillion bits/square inch density.
The researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) Berkeley were led by physicist Alex Zettl. They built a prototype device based on a nanoscale iron particle, about 1/50,000th the width of a human hair, moving along a carbon nanotube like a shuttle.
The nano-structure was created in a single step by pyrolysis of ferrocene in argon at 1,000 degreees C. The created nanotube elements are dispersed in isopropanol ultrasonically and deposited on a substrate with electrical contacts applied to the ends of the nanotube. The researchers say these steps are compatible with common semiconductor manufacturing techniques.
By applying an electric current, the iron particle shuttle could be made to move inside the nanotube either away from or towards the current source. When the current was turned off the particle was, as it were, frozen in position. By applying the current in a timed pulse the particle could be made to move a fixed 3nm distance in steps. The speed of movement could be altered by varying the applied bias voltage.
The researchers say that placing the shuttle either side of the mid-point along the length of the nanotube can constitute a digital one or zero. A transmission electron microscope showed the shuttle moving - there is a video showing this accessible here . In a practical device the shuttle position could be read via detecting the axial electrical resistance of the nanotube by small voltage pulses. This is sensitive to the physical location of the enclosed nanoparticle shuttle and the pulses do not alter the state of the shuttle.
Calculations were made based on how far the shuttle would have to move at room temperature, with no applied voltage, before its position altered sufficiently for the data value to be changed, and how long this would take. The researchers calculated it would take 3.3 × 10 to the power 17 seconds and conclude that they have demonstrated the feasibility of an archival storage memory element with a billion year lifespan.
Other calculations suggest a complete archival chip could store a trillion bits in a square inch in this way. Fascinating stuff, but any practical usage is still many, many years away.
The research is described in a publication called Nano Letters, in a paper called Nanoscale Reversible Mass Transport for Archival Memory . ®