Over the last 30 years, there has been increasing
interest in the use of plastic polymers as conductors or semiconductors.
Polymers that have semiconducting characteristics are called
"conjugated" polymers and they behave as semiconductors for reasons that are
different to those of inorganic devices.
Despite this, semiconductor polymers are engineered using many
of the lessons learned with traditional semiconductors. As a result, progress in
the use of semiconducting polymers has been quite rapid.
How it started
This prototype light emitting polymer display screen has been developed by Cambridge Display Technology.
Polymer semiconductor technology was invented in 1989 at the
Cavendish Laboratory at Cambridge University in the UK. It began when physicist
Richard Friend and chemist Andrew Holmes were experimenting with organic
polymers. Quoted in the Cambridge "Alumni Magazine", Holmes says: "we started
with a plastic material called PPV, made by a process that allows it to be
coated in thin films over large surface areas. If the material is chemically
'doped', it can conduct electricity nearly as well as a good metallic
conductor".
However, the two scientists were interested in seeing how good
the 'undoped' material was as an insulator. "We sandwiched a thin film between
metal electrodes and subjected it to a high voltage. What happened next was pure
serendipity. Someone switched out the lights by mistake and the plastic was seen
to emit a yellow-green light. We had discovered the plastic version of a
light-emitting diode."
In 1992, a company called Cambridge Display Technology was
formed to develop commercial applications for light-emitting polymers (LEP),
sometimes also called organic light emitting diodes (OLED). Joint ventures have
since been signed with Seiko-Epson, Philips, DuPont, Hoechst and UNIAX.
