Download Thick film area - ePrints Soton

Functional Electronic Screen
Printing – Electroluminescent
Smart Fabric Watch
Marc De Vos, Dr Russel Torah, Prof Steve Beeby and Dr John Tudor
Smart Textiles Salon
6th 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 2.7-5.5v, 3v 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 UoS 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