Inkjet Printed Antennas for NFC systems

1. Inkjet Printed Antennas for NFC systems Jordi Mujal, Eloi Ramon, Elkin Díaz, Jordi Carrabina Microelectronic and Electronic Systems Dpt. CEPHIS Group Universitat Autònoma de Barcelona Bellaterra, Barcelona Jordi.Mujal@uab.cat Álvaro Calleja, Ricardo Martínez, Lluís Terés Integrated Circuits And Systems, ICAS Group Institut de Microelectrònica de Barcelona – IMB-CNM (CSIC) Campus UAB - Bellaterra, Barcelona Alvaro.Calleja@imb-cnm.csic.es ICECS 2010 Athenes, Greece

2. Introduction What is printed electronics? • Fast path to flexible components. • Less expensive and faster than wafer-based fabrication • Investments for facilities are not so costly as a wafer foundry. • Electronics integration in other printed media and/or other electronic systems (assembly not required). • Large electronics. (e.g. Large displays) • Environmentally friendly. • New devices-new applications S/D electrodes LC resonator Diode bridge resistor UHF antenna

3. Introduction Why inkjet? • Fast prototyping • Low cost lab tool • Non contact deposition • Min wasting material • Customisation, small series • Easy to integrate with existing production lines But? • Low speed • Ink development challenging • Complex ink-substrate interaction • Pattern control • Uniformity? It is one of the most promising printing techniques, but there is along path to explore

4. Organic Circuits State of the Art • Limits on operation frequency: • Organic semiconductors: poor mobility and need high voltages • Printing resolutions restrict patterning to larger dimensions. Research on organic electronics for RFID tags is focusing on low frequency (HF) 64 bit (414 OTFT’s) and 128 bit (1286 OTFT’s) plastic transponder for RFID on 13,56MHz (2010): K. Myny, S. Steudel, P. Vicca, M.J. Beenhakkers, N.A.J.M. van Aerle, G. H. Gelinck, J. Genoe, W. Dehaene, P. Heremans. “Plastic circuits and tags for 13.56 MHz radio-frequency communication”. Solid-State Electronics 53 (2009) 1220-1226.

5. Work Motivations Low cost Organic RFID systems → Antenna should be printed making an entirely printed system. Low frequency RFID devices requires antennas with Q>40 → Such antenna is not easy to achieve with inkjet printing. Conductive inks have high resistivity. Near Field Communications (NFC) is a recent wireless technology working only at 13.56 MHz that enables data exchange in a short range, not more than 10 cm. NFC short distance range, allows smaller Q factor antennas than typically HF RFID tags → This encouraged us to explore its inkjet printing feasibility.

6. Inkjet Printing Process • Characterized by: • Discrete drop printing • Printhead-ink-substrate interaction • Printer Dimatix DMP 2831 • Substrate: Katpon • Sunchemical silver ink U5603 (20% silver) • Dielectric ink (CETEMMSA) Inkjet platform: Printer & Substrate & Inks

7. Characterization of Conductive Tracks Test Vehicles: Cross Bridge ressonator test vehicle (5x5mm pads, 200um track width, 1-2 layers) Van der Pauw measurement

8. Measurement Discrepances Differences → Cross Bridge section uniformity!

9. Thickness Measurement 1 layer => 860nm 2 layers => 1060nm

10. Introduction:What is NFC? • Contactless data exchange based on magnetic field induction. • Short-range operation (<10 cm). • 13.56MHz carrier with ASK modulation. • 106, 212 or 412 kbps. • Active and passive modes. • Peer to peer mode and compatible with existing passive proximity cards. • Multiple applications: Payment, ticketing, advertisement, electronic keys, identification, smart posters,… a) Inductive coupling for data transmission NFC Chip b) NFC RF frontend c) Active NFC mode

11. NFC Antenna Requirements • NFC communication => Inductive link (similar to RFID) • Antenna requirements (according to chip manufacturer): • L= 0.3 to 3 uH • C= 3..30 pF • Self-resonance > 35MHz • R => Q<40 (target Q=35) ↓Q => ↑B, ↓tr, ↓tf, ↑ Losses

12. Antenna Design & Simulation Test Inductor Design Simulation software: Agilent ADS momentum Symmetric Circular Spiral Dimensions: Outer edge → 35mm Track width → 650um Lines space → 550um Num turns → 6 Simulation Results • No bandwith limitations. • Inductive coupling distance? • with thickness estimations and maesured conductivity: • Q < 7 Experiments

13. Antenna Fabrication Printing conditions before bulging: Substrate temperature room temp. 3 layers 8 layers 60ºC • ↑ Temp. Higher solvent evaporation rate: • ↑ Thickness • ↑ Coffee drop effect enhancement

14. Electrical Characterization • Q factor increases proportionally to the number of printed layers

15. Test Results (TX-RX Distance) NFC antenna in testbench for range measurements. Communication Range Results (cm) in Active and Passive Modes (424kbps): • NXP NFC chip PN532. • Best results for printed antennas: • 3.5cm (active mode) • 2.0cm (passive mode) • a) in blue passive mode results, in pink active mode. • b) outer dimensions: 52x33mm, 6 turns, line width: 500 um.

16. Conclusions • Printed passive components are crucial for the development of low cost, flexible and printed systems like RFID or NFC. • Commercial conductive ink was characterized with different methods obtaining a (best result) conductivity of 1.25·e7 S/m ± 10%. • NFC Antenna was designed, simulated and fabricated, with a best Q factor of 5. • Tested Antennas under NFC operation with a range up to 3.5 cm between NFC printed coupled antennas. • Inkjet technology is capable to process antennas for NFC systems.

17. Future Work • Remaining challenge is to improve conductivity of inkjet printed patterns in order to achieve optimum performance, which is still far from RFID but functional enough for NFC requirements. • The conductivity of conductive inks needs to increase, and the inkjet process should increase its thickness deposition capacity. • Printing other passive components for antenna matching circuits: capacitors, resistors and inductors.

18. Thanks for your attention • Any question now? • Questions later on? Jordi.Mujal@uab.cat Alvaro.Calleja@imb-cnm.csic.es