A stretchable and conformable thin-film transistor (TFT) driven LED display that can be incorporated into clothing has been demonstrated by European researchers. Unlike many current wearable technologies, the display does not require a separate device to provide feedback, making it more comfortable and less invasive for the user.
The research was carried out by the Holst Centre, an independent R&D centre in The Netherlands that develops sensor technologies and flexible electronics, which was set up in 2005 by nanoelectronics research centre, Imec and the Netherlands Organisation for Applied Scientific Research (TNO).
Wearable devices such as healthcare monitors and activity trackers are designed for people to monitor their fitness and health. However, many of today’s wearables are separate devices that users must remember to wear.
The next step forward will be to integrate these devices into clothing, and in doing so will make wearable devices less obtrusive and more comfortable, encouraging people to use them more regularly and, hence, increase the quality of data collected.
A key step towards realising wearable devices in clothing is creating displays that can be integrated into textiles to allow interaction with the wearer.
The new conformable display is very thin and mechanically stretchable. A fine-grain version of the proven meander interconnect technology was developed by the CMST lab at Ghent University, Belgium and Holst Centre to link standard, rigid LEDs into a flexible and stretchable display. The LED displays are fabricated on a polyimide substrate and encapsulated in rubber, allowing them to be sealed into textiles that can be washed.
Importantly, the technology uses fabrication steps that are known to the manufacturing industry, enabling rapid industrialisation.
Last year, UK-based company Cambridge Consultants developed a ‘smart’ material that transforms clothing into active motion sensors. The XelfieX material uses lightweight and durable fibre-optic thread to act as the sensor, along with a small electronics pack which clips on to the fibre − in a pocket, for example – and communicates with a smartphone.
In the newer device which integrates the display into the clothing rather than on a separate accessory, small LEDs are mounted on an amorphous indium-gallium-zinc oxide (a-IGZO) TFT backplane that employs a two-transistor and one capacitor (2T-1C) pixel engine to drive the LEDs. The displays offer higher pitch and increased, average brightness compared to earlier versions.
‘To maximise the benefits wearables can offer, they need to be able to provide feedback on what users are doing as well as measuring it,’ said Edsger Smits, senior research scientist at the Holst Centre. ‘By combining Imec’s patented stretch technology with our expertise in active-matrix backplanes and integrating electronics into fabrics, we’ve taken a giant step towards that possibility.’