Fast-switching plastic circuit mimics CMOS function

The printed circuit is believed to be the fastest-operating and lowest-power plastic logic oscillator created to date.

The full commercial potential of plastic electronic circuits has been hampered by their lower speed and by the requirement of high supply voltage (of the order of 100V), which means that they are unable to compete with conventional silicon-based electronics especially in off-the-grid applications, which are the most attractive for this technology.

‘Performance advances in organic electronics are driven by a better understanding of the motion of charges in these materials, and also exploring a wider range of structures,’ said Prof Henning Sirringhaus of Cambridge University and co-founder and chief scientist of Plastic Logic, which took part in the research.

‘One of the strengths of this field is that organic chemistry gives you access to a whole plethora of molecular structures and there’s now a better understanding of where to look, and that’s been driving improvements in performance.’

So far in the field of plastic electronics there have been two classes of materials: polymers and small molecules; and two broad types of operation: positive charge material with holes and negative charge with electrons (p-type and n-type).

‘We have a material now that operates as both p-type and n-type, which gives you a number of options for making complementary circuits — or CMOS-type structures,’ said Sirringhaus, adding that this was achieved by working with a new class of ambipolar organic materials developed by a team at Imperial College London.

CMOS — complementary metal-oxide semiconductor — has become the pervasive technology in consumer electronics because its sharp threshold switching allows relatively complex logic circuits with low power consumption. It also allows easy integration as part of larger circuits.

The device developed by Sirringhaus and team exhibits carrier mobility in excess of 1cm²/Vs. This opens up a range of possibilities for integrating flexible robust plastic electronics with quite advanced functionality across large distributed surfaces.

‘If you want to functionalise some surface with silicon, you have to pick and place a silicon chip onto that surface and bond it with some kind of bonding technology,’ said Sirringhaus.

One application he discussed was interactive packaging on medicines that ensures correct doses are taken at the right time.