P. Gutruf, S. Walia, E. Zeller, H. Nili, S. Sriram, M. Bhaskaran
Keywords: stretchable electronics, wearable devices, sensors, gas, UV, microfabrication
Summary:Electronics and sensors pervade all aspects of life, needing solutions to make them less obtrusive, which is where fully transparent electronics come into play. Our research focus has been to realise stretchable electronic devices with highly functional characteristics while being optically transparent. This new class of electronics is promising for designing novel systems, such as in vitro pH sensors, transient and printable electronic devices, sensory robotic skin, and wearable electronic devices. Challenge: All electronic devices rely on oxide materials – these are in the form of ultra-thin coatings, often prepared at high temperatures. Integration of multifunctional oxide thin layers in flexible devices would create enhanced functionality and performance. This integration has been limited by the brittle nature of oxides and high temperature processing requirements. The research and technology challenge lies in effectively combining the two diverse materials together – functional oxides processed at >250 °C and flexible polymers and plastics which disintegrate above 120 °C. Innovation: Our research has addressed this key bottleneck with a ubiquitous transfer process. This process utilised the naturally weak adhesion of platinum to silicon, and this allows us to create electronics on a rigid substrate such as silicon and then peel off the layers to transfer onto a flexible substrate. This process also results in a unique ‘micro-tectonic’ surface, creating opportunities to explore new stretchable device applications. This process has been successfully demonstrated using transparent indium tin oxide and zinc oxide thin films (both deposited at high temperatures) with stretchability of up to 15% which is exceptionally high for a brittle oxide. This process allows the creation of transparent stretchable electronics with nanometre resolution as well as large-area functional devices without the need of tailoring the production process to the design. An overlapping plate-like thin film microstructure contributes to the enhanced strain performance; where this unique microstructure also offers increased surface area which is very advantageous for sensing applications. Results: We have demonstrated a unique transfer process which would help overcome this challenge [published in Nature (NPG) Asia Materials]. With this process, we have also demonstrated room temperature gas and UV sensors [published in Small], which retain their functionality when stretched. More details in attached abstract. Impact: The ability to combine any functional oxide with biocompatible substrate material creates the potential for consumer electronics applications in wearable electronics. Gas sensors can monitor toxic gases and be used as low-cost sensors in mines, while the UV sensors can monitor UV radiation and be utilized as a preventive measure for skin cancer. These devices have major implications for economic impact through widespread market adoption, social impact through health applications, and environmental impact through gas monitoring.