Imec researchers create simple plastic microprocessor

A group from Imec in Belgium succeeded in integrating 4,000 organic transistors to create the microprocessor, which measures 2cm² and is built on top of flexible plastic foil.

Although plastic electronics have been used in some prototype LED displays and radio-frequency identification (RFID) tags, they have been limited to a handful of organic transistors performing simple control logic.

Wide-scale adoption of plastic electronics promises devices that are cheaper, lighter, more robust and flexible compared with their silicon counterparts.

However, they can never compete with silicon in terms of performance, because the organic materials fundamentally limit the mobility of electrons and thus the speed of operation.

Nevertheless, project lead Jan Genoe of Imec believes plastic electronics have huge potential for a range of applications where silicon is simply not cost effective or robust enough.

‘Silicon processors have become very advanced but they are expensive — there’s a minimum unit cost, somewhere around €1 [£0.88]. You could envisage using a simple processor working at low speed, where you would not be able to use silicon,’ he told The Engineer.

Key to this is the fabrication process. The team starts with a sheet of flexible plastic around 25um in thickness, then deposit alternating layers of gold electrodes and insulating plastic layers.

The transistors are made by spinning the foil to spread a drop of organic liquid into a thin, even layer, which when heated transforms into solid pentacene — an organic semiconductor. The layers are then etched using photolithography to make the final pattern.

Genoe said plastic electronics could feature on all manner of consumer products, performing simple calculations, such as on a cereal box where they would work out the exact nutritional values of a serving. But there could also be industrial applications, exploiting niches where silicon is not considered due to cost or inflexibility.

‘Assume you have a few million very cheap sensors on a foil that you can wrap around a gas pipe where you want to detect leaks. If you want to read out from all the sensors, even with a high-performing silicon processor, it will be difficult.

’But if you have a plastic microprocessor attached to each sensor that takes an average value and cancels out noise — false spikes — then connects to a local higher-performing silicon unit, this could work.’

The challenge now will be to scale up the fabrication process, although Genoe said the team can borrow certain techniques from the production of organic LEDs (OLEDs), which are a step ahead in terms of development.

‘The organics are rather similar, the way you treat them is similar, but an OLED pixel is still pretty large with respect to a transistor, so you need greater accuracy. But the roadmaps for upscaling are similar,’ Genoe said, adding that the ultimate goal will be printed plastic electronics.