快猫短视频

THE 19th century idea of storing data on punched cards could make a comeback
in the next generation of memory chips, say researchers at IBM in Zurich. They
believe a cellphone containing one of their new super-dense chips will be able
to store two full-length movies, more than 150 hours of MP3 music, or all the
information on a stack of printed paper more than 200 metres tall.

Called Millipede, the electromechanical data store uses microscopic probes to
make indentations in a polymer film. The dents represent data and are erased by
simply warming the polymer. It was far from clear whether the experimental
technology had a future
(快猫短视频, 27 March 1999, p 46).
But recent breakthroughs make IBM confident of commercialisation within five
years鈥攁round the time magnetic disc drive technology will probably reach
its storage limit, says Peter Vettiger, the IBM scientist who heads the
Millipede project.

Today鈥檚 magnetic discs store around 15 gigabits of data per square inch of
surface area, and read it at around 200 megabits per second. Optical discs store
less than magnetic discs, but are cheaper. Transistor-based microchip memory can
be read faster, but it stores less, costs more and usually loses data when the
power is switched off.

In the mid-1990s, Vettiger and Gerd Binnig looked into the technology behind
scanning tunnelling microscopes to store data. STMs have probes with tips only
nanometres across, which the researchers used to make indents in a smooth
surface. They experimented with a spinning polycarbonate disc, like a CD, coated
with polymethylmethacrylate (PMMA).

Instead of a spinning disc, IBM now uses a flat silicon base, spin-coated
with PMMA. The probes, fixed to platforms on the end of cantilevered arms, are
arrayed in 32 rows of 32 probes on a silicon chip. The arms are chemically doped
to make them flex and conduct electricity. This heats the arms while moving them
towards the plate to penetrate the coating right down to the substrate
(see Diagram).
The polymer is moved step by step past the array chip while the probes
write data line by line.

To read data, the probes are lightly warmed and their temperature measured.
The extra heat loss from contact with the substrate registers as a bit. Data is
erased by heating targeted areas more strongly.

A single tip can already store 500 gigabits per square inch, write data at 50
kilobits per second and read 1 megabit per second. When all the probes in a line
are working together, data speeds increase in proportion. There is a trade-off
between speed and power consumption, however, so battery-powered portables and
phones will run at slower speeds than desktop hardware plugged into the mains.