Technology showcase

What could flexible electronics ever do for us?

Stuart Cherry

A lot! Ceilings that are lights and tablet computers that fit in your pocket for starters. But think about medical applications and things get really interesting: faster wound healing, more convenient treatment for skin conditions and improved cancer therapies are all possible.

And how about helping new parents bond and enjoy a cuddle with their jaundiced baby? Allowing the baby to continue its potentially life-saving treatment without having to spend hours a day isolated in a phototherapy chamber.

What is flexible electronics?

So what is this technology that can do everything from lighting and displays to helping sick babies? Ultimately, flexible electronics is exactly what it sounds like: electronic devices that you can bend and stretch into any shape, time and again.

That means creating electronic circuits that can withstand the stresses of being flexed, and that can be printed directly onto flexible, stretchable substrates capable of protecting the delicate circuitry.

These totally flexible circuits are the ultimate goal. But like any technology, the journey to it will progress in a number of steps. According to Herman Schoo of Holst Centre – an open innovation R&D centre investigating flexible electronics – the first step will most likely be large sheet electronic devices made using sheet-to-sheet manufacturing processes. Roll-to-roll manufacturing could then provide a route to scale up production volumes further.

Preformed curved applications such as lights that can be embedded into furniture will be next. Step three is likely to be applications that can be bent by the user, ideal for creating tablet computer displays that can be rolled up to fit in your pocket. Finally, we'll see electronic devices that can be bent and stretched in any direction.

Why do we need flexible electronics?

But the question is, why do we need another form of electronics? Standard silicon-chip-based electronics is making great strides in miniaturization, cramming more functionality into smaller chips. Couldn't we just embed these chips into flexible materials to create flexible applications?

Schoo says not. New applications like organic light emitting diodes (OLEDs) and organic photovoltaics (OPVs) need big areas. “With silicon-based circuits, you would need huge numbers of embedded chips to get the necessary intensity and uniformity. That would be prohibitively expensive and would generate so much heat locally, you would melt the substrate!”

Printed circuitry is spread over a wider area. For example, OLEDs intrinsically emit light from an entire surface. Because of this larger active area, heat dissipation is less concentrated and temperatures lower. Moreover, it is significantly cheaper to produce a sheet of printed electronics than countless embedded ICs, especially if you use roll-to-roll processes.

What no other technology can do

Roll-to-roll processes are cheap, and a major step on the road to flexible electronics. But when Holst Centre talked to the people likely to use flexible electronics, it soon became clear that stretchable, free-form applications were what really caught their imagination.

They caught the imagination of Holst Centre's researchers too. Printable electronics reduces costs, and rollable electronics can make familiar electronic devices more convenient. “But stretchable electronics opens up completely new applications,” says Holst Centre's Margreet de Kok. “And the option to combine flexible electronics with additional carriers is really interesting and could allow us, for example, to integrate electronics into fabrics.”

This could lead to applications like wearable medical sensors such as heart monitors. These don't need ultra-high performance, but they do need to be sterile for each patient. That means the sensors themselves have to be disposable. “Being light and relatively cheap to produce, printed electronics is ideal for this and could lead to throwaway sensors quite quickly,” de Kok adds.

Flexible electronics could also revolutionise phototherapy. Light is already used to treat pain and skin conditions such as psoriasis. And of course, potentially fatal neonatal jaundice. Plus exciting new applications are emerging all the time, like making wounds heal faster or activating chemotherapy drugs at the site of a tumour to reduce the side-effects of treating skin cancers.

All these therapies require extended exposure to appropriate light. With the conventional lamps used in today's therapies, the patient has to stay immobile and isolated for hours. Embed the phototherapy equipment into clothes, blankets or bandages, and people could undergo their treatment while carrying on with their lives. Those ill babies could come out of the incubator for a cuddle.

For that, the phototherapy circuitry has to be spread over a wide area and completely flexible and stretchable. In other words, it needs to be flexible electronics.

Coming soon?

Flexible electronics is very much a work in progress. According to Schoo and de Kok, Holst Centre has developed device structures that can be flexed many times and created proof-of-concept demonstrators of many applications.

The challenge now is to scale that up to high volumes and develop techniques for integrating the circuits into carriers such as textiles. For healthcare applications that come into contact with our skin, there are also specific challenges related to avoiding allergic responses, bio-compatibility and sterilisation.

So there is still some way to go. But the pair believes the first bendable lighting applications could appear within five to eight years. Co-development is key. And Holst Centre is working with leading research institutes and companies, such as Philips, in the EU-funded PLACE-it programme