Printed Electronics

Team:
Li Yang, Amin Rida, Rushi Vyas, Vasileios Lakafosis, Giulia Orecchini

Organic Substrate - LCP

Why consider LCP as a substrate?

  • Liquid Crystal Polymer (LCP) can be used as a high performance multilayer substrate
  • Excellent electrical properties (εr ~ 3.10 and tanδ=0.002)
  • Flexible (WSN nodes can be rolled or molded into desired shape)
  • Good performance: mechanical integration compatibility and economic viability

Wideband (9%) UHF RFID tag on LCP to cover the global 860-930 MHz band

Antennas fabricated on 12"x12" in LCP Film

back to top

Organic Substrate - Paper

Why Consider Paper as a Substrate?

  • Environmental Friendly and low cost (lowest material made by humankind)
  • Large Reel to Reel Processing
  • Low surface profile with appropriate coating
  • Compatible for printing circuitry by direct write methodologies
  • Host nano-scale additives (e.g. fire retardant textiles)
  • Can be made hydrophobic
  • Dielectric constant εr (~3) close to air's, allowing EM waves to penetrate substrate easily with minimum (5-6%) power reflection

Coated paper

Drop of water on hydrophobic paper

back to top

Paper Dielectric Properties Characterization

The down shifted TEmnp mode resonant frequency between an empty and a loaded cavity gives the information of the sample dielectric constant.


back to top

Inkjet-printing Technology - Printer

Characteristics:
  • Piezo-driven jetting device to preserve polymeric properties of ink
  • 10 pL drops give ~ 21 μm resolution
  • Drop placement accuracy ±10 μm gives a resolution of 5080 dpi
  • Drop repeatability about 0.5%
  • Printability on organic substrates (LCP, paper ...)
High resolution inkjet printed copper (50 μm)








back to top

Inkjet-printing Technology - Ink

Ink:

  • Consisting of nano-spheres melting and sintering at low temperatures (150 °C)
  • After melting a good percolation channel is created for electron flow
  • Provides a better result than traditional polymer thick film material approach which uses metal flakes
Nano-sized silver ink.
Particle size = 30 nm



SEM Images of a Layer of Printed ink, Beore and After a 15 Minute Cure at 150°C

back to top

Carbon Nanotubes as Gas Sensor

  • CNTs structure can be conceptualized by wrapping a one-atom-thick layer of graphite into a seamless cylinder
  • Single-walled CNTs and Multi-walled CNTs
  • A diameter of close to 1 nanometer, with a tube length that can be many thousands of times longer
  • CNTs composites have electrical conductance highly sensitive to extremely small quantities of gases, such as ammonia (NH3) and nitrogen oxide (NOx)
  • The conductance change can be explained by the charge transfer of reactive gas molecules with semiconducting CNTs

CNT Particles: Single Walled CNT
Solvent: Dimethylformamide (DMF)



  • Particle size < 215um
  • Viscosity 10-13 cps
  • Surface tension 28 dynes/cm



back to top

Inkjet-printed SWCNT Films

Formulation:

  • P2 sample from purified SWCNT by air oxidation and catalyst removing (aggregated at the concentration of 0.1mg/ml)
  • P3 sample from purified SWCNT after nitric acid processing (go up to 0.4mg/ml)
  • 0.4mg/ml P3 sample dispersed in DMF
  • 12 hours sonication to prevent aggregations of large particle residues

  • Silver electrodes were patterned before depositing the SWCNT film, followed by a 140°C sintering
  • The electrode finger is 2mm by 10mm with a gap of 0.8mm. SWCNT film was 2mm by 3mm
  • 1.1mm overlapping zone to ensure the good contact between the SWCNT film and the electrodes

back to top

Gas Chamber Measurement

  • Gas chamber: gas inlet, outlet and exhaust hood
  • 4% Ammonia gas for 30 minutes
  • SWCNT stable response up to 1GHz
  • 25L was used for future steps




back to top

Antenna Design and Performance

  • Conductive ink has become the major cost of an RFID tag after introducing the paper-based substrate
  • Minimizing the amount of ink used per antenna will save thousands of dollars in the mass production
  • Bandwidth 810MHz - 890MHz
  • When bended 814MHz - 891MHz
  • 2.01dBi Directivity with 94.2% efficiency

back to top

Gas Detection

  • Power reflection coefficient changes from -18.4dB to -7.6dB. At reader's side, this means 10.8dBi increase of the received power level
  • By detecting this backscattered power differnce, the sensing function is fulfilled

back to top