Henrik Sandberg is the business developer for flexible and wearable applications (http://graphene-flagship.eu/material/GrapheneApplicationAreas/Pages/Flexible-and-Wearables.aspx) for the Graphene Flagship. He is a principal scientist at the centre for Printable and Hybrid Functionalities at VTT Technical Research Centre in Finland. His work is currently focused on printed electronic devices and circuits, polymer device physics, printing technology and printing ink formulation as well as heterogeneous and monolithic integration for flexible electronics. He offers his insights on graphene applications in flexible and wearable devices.
Q: What is the current state of graphene for flexible and wearable applications?
Graphene and other layered materials have been particularly effective in the production of many different sensors required for wearable applications. Physical sensors can be incredibly sensitive and can be monolithically integrated in printed electronics, for example, without the need for any metals or other environmentally problematic materials. The exceptional properties of graphene also allow for extremely sensitive chemical sensors and, in the case of biosensors, can be very selective as well. In addition to sensors and conductors, high performance devices based on CVD graphene are maturing. Layered materials can be used for integrated circuits, amplifiers and more.
For printed electronics applications the flake-based layered materials provide a family of easily processable materials which retain their exceptional properties. Graphene, for example is an environmentally friendly material with an electrical conductivity higher than graphite. In addition, typical low-cost, large-area applications may not need the high electrical conductivity provided by metal-based inks.
The current flexible and wearable market presents a promising area for fast adaptation of layered materials. This is particularly true for low-cost, environmentally-friendly applications such as printed matter (posters, packages, etc.) and textiles with sensing capabilities.
Transferred CVD-based devices with higher performance, allowing integrated circuits and backplane/frontplane electronics for sensors and displays, and even for RF devices and circuits, are even more promising but will take longer to reach the market.
For wearable applications, the flexibility of graphene--both grown CVD and exfoliated flakes--is a particularly enabling property, as graphene has proved to be less sensitive to bending cycles than current metal-based solutions.
Q: What challenges does graphene face in becoming integrated in flexible and wearables?
Graphene and other layered materials are most suitable for applications like sensors. Physical sensors can be based on graphene only, but most other sensors will require functionalization of the graphene for a specific purpose. The production of consistent materials and devices is not yet mature enough for integration into circuits and applications, but there has been great progress in recent years.
The integration of CVD graphene into flexibles and wearables applications with current processes (e.g. CMOS) require further development and acceptance by the industry, especially for production line development and alterations. Layered materials are typically transferred from a production sheet/wafer at this time, and the reliable and reproducible transfer of the material has not been established
There are currently graphene formulations that can be reliably printed, for example for conductors or electrodes for applications not required to carry large currents. The target could be low-cost products with a short life-span, e.g. disposable items, where graphene would not introduce any recycling issues. The electrical resistance level is still a challenge for many applications where current metal-based solutions are acceptable.
Q: What flexible and wearable products or prototypes containing graphene are currently available?
Wearable and flexible electronics are currently not a standardized and established technology, thus there are not many applications even for non-graphene solutions, except for the smart watch-type applications. With layered materials we target much more integrated and unobtrusive solutions, even if they offer fewer functions and lower performance. For structural, thermal and ESD applications there are already solutions on or very close to market. For the electronics applications there are still reliability and reproducibility issues that must be sorted out, but there is active IPR activity, and Europe with the Graphene Flagship in the lead, is on the forefront of this development.