Functional Electronic Screen Printing Electroluminescent Smart Fabric Watch

Functional Electronic Screen Printing – Electroluminescent Smart Fabric Watch Marc De Vos, Dr Russel Torah, Prof Steve Beeby and Dr John Tudor Smart Textiles Salon 6 th June 2013

Overview • Motivation for screen printed smart fabrics. • Introduce functional electronic screen printing on fabrics. • Printed smart fabric watch design. • Printing process for electroluminescent watch. • Demonstration video. • Conclusions and further work. • Examples of other screen printed smart fabrics. 2

Motivation for a printed watch • Digital watches are typically flexible straps with rigid displays. • Key Advantages of a printed smart fabric watch: – Increased comfort and flexibility through all fabric design. – Washable – greater sporting applications. – Can be easily integrated into other garments, furniture or curtains. • The technology can be used to demonstrate electroluminescent applications for visual displays. • Could be used alongside standard artwork for advertising displays. 3

Functional Electronic Screen Printing on Fabrics • Screen printing requires a screen, squeegee and a printable paste. • Key advantage: Any pattern can be printed, not restricted to warp and weft directions. • Key advantage: Printed on top of the fabric so the fabric properties next to the skin are not affected. • Key advantage: Roll to roll process so can be printed as part of the fabric manufacturing process. • It can be used to deposit standard materials such as conductors, resistors and dielectrics. • We have also developed more exotic printable materials such as piezoelectric, piezoresistive, thermochromic, sacrificial and electroluminescent. • Typical print thickness after drying is between 5 and 50µm depending on the materials. 4

Printed smart fabric watch design • Electroluminescence requires an electric field to be applied across a phosphor layer using. • A capacitor sandwich structure is used with a semitransparent top electrode layer to allow light emission. • The layers are printed directly on to the fabric with no further processing required. • Initial design is large to prove the concept. The design principle can be scaled up or down depending on application. 5

Printing process for EL watch on fabric • 6 individually printed and cured layers for the EL watch: – Interface layer: reduces surface roughness of the fabric. – Bottom electrode layer: provides the ground plane. – Dielectric layer: allows for a greater lamp brightness and reduced chance of short circuits. – Phosphor layer: provides the light producing layer, the phosphor emits light under the influence of an electric field. – Top/bus electrode layer: provides connection to the top electrode of the capacitor structure. – Semi-transparent electrode layer: provides an even distribution of charge across the phosphor layer for improved light distribution. 6

Electrical characteristics • Input voltage of 2. 7 -5. 5 v, 3 v used for testing. • If a standard “button cell” battery used, estimated lifetime of ~12 hours continuous use. • Lifetime could be significantly improved through use of touch sensors to turn display on/off. • Average resistance over a track of ~12 Ω – dependent on length and flexing. • Average resistance across top semi-transparent electrode of ~10 kΩ/cm. • Could implement a swipe feature to turn on. 7

Demonstration video 8

Photos of printed EL watch display prototype 9

Conclusions and further work • World’s first all screen printed EL watch display on fabric. • Can be printed on most fabrics. • First prototype stage demonstrated, future devices will be smaller and with more multi-layered PCB approach. • Integration of electronics possible into smaller packages on to fabric or as a detachable flexible circuit board. • Additional functions such as a swipe across the touch pads to turn on the display. • Smaller display and shorter wires would further increase the battery lifetime. 10

Examples of other Uo. S printed smart fabrics 11

Acknowledgments • University of Southampton – Electronics and Computer Science – www. ecs. soton. ac. uk • Smart Fabric Inks Ltd – www. fabinks. com 12