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Tech Primer
Gold-Plastic Memory
 Taiwanese
researchers have been able to make a reliable and inexpensive nonvolatile memory
array, which is made out of a mix of plastic and gold nanoparticles. The array
is a 16-byte device called an organic nonvolatile bistable memory.
Attempts to make organic nonvolatile memory have been going on for a while now
and are continuing. The quest is to make devices from plastic and other carbon-based
chemicals as they can be manufactured cheaply using printing processes. But
these organic memory devices usually tend to break down in air and under the
stress of many read-write cycles whereas gold-plastic based memory can endure
more than 1,000 switches and retains its data for approximately 10 days even
when exposed to air. Yet, different researchers are pursuing organic nonvolatile
memory devices using either nanoparticals such as carbon-60 embedded in the
plastic or by using the plastic as part of an organic transistor structure.
Structure and workings
This new memory consists of gold nanoparticles, which are mixed into a polymer
material called PCm, which is sandwiched between two aluminum electrodes. In
order to read data bits from the device, one has to apply a small voltage and
measure the resulting current. In normal circumstances, the structure conducts
little current in the state in which it is storing a 0. Pushing the voltage
past two volts can increase the current flow 10,000 fold. Before this threshold,
a trickle of electrons is jumping from one gold nanoparticle to another. In
the process, some get trapped. Then at two volts there are enough trapped electrons
to form a highly conductive path through the device and at that point, smaller
voltages continue to produce the high current, and the device is considered
to be storing a 1. In order to erase a bit, a strong negative voltage needs
to be applied.
The small voltage involved in writing bits can be stressful for the plastic
and make a device unstable by causing the nanoparticles to clump together. In
order to avoid that, gold nanoparticles are connected directly to polymer chains,
which act as fingers that get intertwined with the host polymer. Due to this,
the stabilization of the structure of the organic memory can be ensured even
if high-voltage stress is applied.
An organic memory is considered essential to implement flexible electronics
such as radio-frequency identification (RFID), smart cards, e-paper, and flexible
displays.
For further information, visit: spectrum.ieee.org/dec07/5769
— Kushal Shah
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