This document discusses applications of low-cost conductive inks for flexible electronics. It summarizes several applications such as DC and RF interconnections, printed antennas for RFID and wireless sensing, chipless RFID, and hybrid systems integrating printed electronics with silicon chips. Requirements for conductive inks are discussed, such as printability, adhesion, conductivity, and low sintering temperatures. Experimental results on printed antennas, interconnections, and sensors show the potential of conductive inks for flexible and wearable electronics applications.

1. Applications with
Low-Cost Conductive Inks
iPack Center
Royal Institute of Technology (KTH)
Stockholm, Sweden

2. Outline
 Fundamental requirements for flexible
electronic applications
 Applications
DC and RF interconnections & reliability
Narrowband and wideband printed antennas
Printed chipless RFID
Printed wireless sensor
Hybrid system for flexible electronics
Masterclass Future of Conductive Printing Nov 27, 2012

3. Fundamental Requirements
of Low-cost Conductive Inks
 Good printability/wettability on different substrate
 Good adhesion/reliability to substrates
 High conductivity
 Typical sheet resistance < 0.1 Ohm/square for radio frequency
application
 Application-dependent (DC applications)
 Low sintering temperature: < 150-200℃ required for paper and
low-cost plastic substrate
 High printing resolution and line edge control
Masterclass Future of Conductive Printing Nov 27, 2012

4. DC and RF Interconnections
 Substrate-dependence: material, surface roughness, pore size
 Sintering temp and time strongly affect the sheet resistance
100°C Kordak Inkjet photo paper
Schoeller Inkjet photo paper
PEL Electronic grade paper for inkjet
UV Package paper from Korsnäs AB
PE Package paper from Korsnäs AB
4-point sheet resistance test
pattern printed on PEL paper
Masterclass Future of Conductive Printing Nov 27, 2012 [L. Xie et al., Mater. Lett. 2012]

5. DC and RF Interconnections
 Coplanar Wave Guides (CPW) as RF interconnections
 No double side printing needed
 Easy to adjust the RF characteristic impedance
 on both plastic and paper substrate
 Characterized by VNA and TDR
 50 impedance achieved, open the door for RF interconnection on paper
substrate
CPW CPS
g Ws Wg Wg Ws
t
G S G G S
H
(a) (b)
[Y. Feng et al., Digital Fabrication 2011]
Masterclass Future of Conductive Printing Nov 27, 2012

6. DC and RF Interconnections
 CPW as RF testing vehicles to measure
 Line resistance, inductance, conductance and capacitance at microwave frequencies
 Conductance and capacitance are related to substrate properties
Measured CPW parameters Extracted AC properties
Electrical properties
of the paper substrate
[B. Shao et al., ESTC, 2008] Masterclass Future of Conductive Printing Nov 27, 2012

7. Interconnection Reliability
 Interconnection reliability is always an important issue in
Printed lines initially sintered all at 90 ℃
applications

 Aging the printed lines in 85℃/ 85%RH environment up to 6 weeks
 Monitor the resistance change
 Resistances decreased after one week and kept stable afterwards
 Results show that UV package paper shows better reliability than inkjet paper in
the aging test
PEL paper UV package paper
Masterclass Future of Conductive Printing Nov 27, 2012 [L. Xie et al., Mater. Lett. 2012]

8. Printed Narrowband
UHF RFID Antennas
 UHF RFID Meander Line Antennas
(866-868 MHz)
 Simulated by HFSS
 Printed by inkjet & flexo
 Experimentally measured in “dark” room
 Results match well with design
 High robustness
 Low ink-consumption
[Y. Amin et al., J Electromagnet. Wave.
2012]
Masterclass Future of Conductive Printing Nov 27, 2012

9. Printed Narrowband
UHF RFID Antennas
 UHF RFID Bowetie Antennas (860-
960 MHz)
 Simulated by HFSS
 Printed by inkjet & screen
 Experimentally measured in “dark” room
 Results match well with design
 larger bandwidth
[Y. Amin et al., Prog. Electromagn. Res. 2012]
Measured Read Range Input Return Loss
Masterclass Future of Conductive Printing Nov 27, 2012

10. Printed Wideband Antennas
 Wideband Log-Spiral Antennas
 Log-spiral antennas inkjet printed on paper
 Experimentally measured in “dark” room
 Operational range of 0.8-3.0 GHz
 Accommodate several modules of wireless
sensing or other applications in addition to
an RFID tag [Y. Amin et al., J Electromagnet. Wave. 2012]
Input Return Loss 2D Radiation Pattern
Masterclass Future of Conductive Printing Nov 27, 2012

11. Printed Wideband Antennas
 Wideband Archimedean Spiral Antennas
 Archimedean spiral antennas inkjet printed on paper
 Experimentally measured in “dark” room
 Operational range of 0.8-3.0 GHz
 Simultaneously implementing a wide range of
different modules in addition to an RFID tag
[Y. Amin et al., Prog. Electromagn. Res. 2012]
Input Return Loss 2D Radiation Pattern
Masterclass Future of Conductive Printing Nov 27, 2012

12. Printed Chipless RFID
 Inkjet printed Chipless RFID on Paper
 Time doming reflection principle
 UWB impulse as interrogation signal
 1.67 Gbps data rate
 Tapered microstrip line to overcome the relative
higher series resistance of inkjet printed lines
[B. Shao et al., Micro. Opt. Techn. Let., 2011]
Masterclass Future of Conductive Printing Nov 27, 2012

13. Printed Chipless RFID
 Chipless RFID based on LC-tank
 Etched or Inkjet printed on plastic and paper substrate
 Sympathetic Oscillation Principle
 Possible to work for liquid-bearing applications
[B. Shao et al., Micro. Opt. Techn. Let., 2012]
Masterclass Future of Conductive Printing Nov 27, 2012 [Y. Feng et al., LOPE-C 2012]

14. Integration With Printed Sensors
for Wireless Sensing
 Printed Wireless Humidity Sensor
 f-MWCNTs as sensing material
 Passive sensor, fully-printable
 Design adapted for both UHF and UWB applications
[Y. Feng et al., IEEE Sens. J., 2012]
for UHF application, monitor return loss
for UWB application, monitor the reflected pulse energy
200
150
100
Voltage (mV)
50
0
-50
-100
-150
Interrogation UWB
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Time (ns)
impulse
Masterclass Future of Conductive Printing Nov 27, 2012
[Y. Feng et al., IEEE Sens. Conf., 2011]

15. Hybrid system integration
using Inkjet Printing
 Hybrid Interconnection Platform
 Using adhesive to form a smooth step transition
between substrate and packaged components
or bared Si IC dies
 This smooth ensures that printed metal lines will
not break when it crosses over the step
difference
To connect
bared
Si IC dies
To connect
packged
components [M. Mämtysalo et al., IEEE ECTC, 2012]
Masterclass Future of Conductive Printing Nov 27, 2012

16. Hybrid System
for Bio-Medical Applications
 Bio-patch Implemented with SoC
and Paper-based Inkjet Printing
 Bio-chip IC SoC
 Inkjet printed interconnection and electrodes
 Inkjet printed flexible cables
 Wearable Bio-patch on paper substrate
Printed
Interconnects
[G. Yang et al., IEEE T. Inf. Technol B., in Press]
Measured ECG signals and FFT
using Printed Bio-Patch
Masterclass Future of Conductive Printing Nov 27, 2012

17. Low Cost Conductive Ink for Flexible
Cables for Wearable ECG Monotoring
 Inkjet Printed Flexible Cable for ECG Monitoring
 Inkjet printed flexible cable on paper for wearable ECG
monitoring
 The cable consists of printed metal lines and a shielding line
in the middle
 The experimental results show that a reliable performance
with high quality ECG data is possible on the inkjet printed
cable on flexible cable
[Q. Wan et al., IEEE EPEPS, 2011]
Measured digitalized ECG Future of Conductive Printing Nov 27, 2012
Masterclass
signals @ 150 MHz

18. Acknowledgements
• Thank you for the financial support from
Vinnova (The Swedish Governmental
Agency for Innovation Systems) through
the Vinn Excellence centers program and
the EU Commission under the FP7 CLIP
(Conductive Low-cost Ink Project) project.
Masterclass Future of Conductive Printing Nov 27, 2012

19. Thank You!!
Questions?
Masterclass Future of Conductive Printing Nov 27, 2012