Ultra thin electronics could thin out the wearables herd

Posted by Lee Chantrey | 18.09.2018

At present wearables face a difficult balancing act between two features that will be critical to their success – function and form.

Enhancing the capabilities of a device means building in more processors, more sensors and generally more electronics. But for consumers to warm to the idea of wearables designers need to pay attention to the ergonomics, which puts limits on how much technology you can cram in. This has given rise to new challenges in the field of ultra-thin electronics.

While still very much at the experimental stage, the field of ultra-thin electronics promises a potential shortcut by allowing gadgets to be worn directly on the skin or integrated into clothes. Commercial products are still some way off, but university laboratories have made some significant breakthroughs in recent months.

In May, a team from the University of Wisconsin-Madison created what they claim is the fastest stretchable electronic circuit, which can be applied to the skin like a tattoo. In a paper in the journal Advanced Functional Materials, the researchers describe how the wires of their ultra-thin electronics are fashioned into repeating S-bends made from two interlaced wires.

The design borrows from the ‘twisted-pair cabling’ approach invented by father of the telephone Alexander Graham Bell to cancel out electromagnetic interference in telephone cables. The team says this contains the electromagnetic waves running through the circuit, which prevents almost all current loss and allows it operate at frequencies of up to 40GHz.

The shape of the circuits also allows them to be stretched without hampering performance, while at 25 micrometres thick these ultra-thin electronics are much less bulky than other stretchable circuits. They say this flexibility and sleek form factor make them ideal for wearable electronics and their high frequency operation could make them suitable for future super-fast 5G wireless communication technologies.

Just last month [June] engineers from Korea University and the University of Illinois at Chicago created an electrically conductive material so ultra-thin it’s transparent. The team claim it has a world-record combination of high transparency and low electrical resistance that is at least 10-times better than the previous record.

In a paper in journal Advanced Materials the team describes how the material is fabricated using a process called electrospinning to create nanofibers of polyacrylonitrile one-hundredth the diameter of a human hair. These are deposited on to a surface so that they criss-cross over each other millions of times to create a mat.

To make it conducive the mat is then spatter-coated with a metal so that it can attract metal ions and then electroplated with copper, silver, nickel or gold. The resulting material is 92% transparent, bendable and stretchable and both the electrospinning and electroplating take mere seconds meaning the process should be relatively high-throughput and commercially viable.

But ultra-thin electronics and circuits are no use unless the components they connect are equally sleek. Thankfully in April scientists from the University of Tokyo recently unveiled an ultrathin “e-skin” made from organic electronics that they used to create flexible displays and a light detector that could monitor blood oxygen concentration.

Crucially the research reported in journal Science Advances overcame a major limitation of organic electronics – they normally require bulky protective coatings to prevent them from degrading when they come in contact with air. The Japanese engineers managed to create a protective layer so thin that the entire device is just 3 micrometres thick.

The approach uses materials and processes already found in the manufacture of OLED displays, so the researchers think their work should transition smoothly to large-scale production. So it may not be too long before your smartphone is replaced by an electronic display laminated to the back of your hand!