Silver Interdigitated Electrodes on Polyethylene Terephthalate Fabricated Using an Office Inkjet Printer for Flexible Electronics

Technical Summary: Silver Interdigitated Electrodes on Polyethylene Terephthalate Fabricated Using an Office Inkjet Printer for Flexible Electronics

Problem Statement
While industrial inkjet printing offers high-resolution fabrication for flexible electronics (FEs), the potential of consumer-grade office document printers as a cost-effective, rapid prototyping alternative remains underexplored. Current research often relies on specialized, expensive industrial printers (e.g., Fujifilm Dimatix) or complex lithography processes. There is a significant gap in the comprehensive characterization of regular desktop inkjet printers for fabricating functional electronic components, specifically regarding their repeatability, resolution limits, and suitability for creating interdigitated electrodes (IDEs) on flexible substrates like polyethylene terephthalate (PET).

Methodology
The study utilized a standard EPSON L130 office inkjet printer to fabricate silver (Ag) interdigitated electrodes on PET substrates. The methodology involved several critical stages:

• Design and Printing Optimization: IDEs were designed using Inkscape to ensure solid fills, avoiding scaling errors common in other file formats. The study systematically varied line widths (8 µm to 1000 µm), line spacing (100 µm to 500 µm), and orientation angles (0° to 180°) to determine optimal printing parameters. The printer was modified to load Novacentrix Metalon JS-B25P Ag nanoparticle ink into the black ink cartridge.
• Substrate Preparation: PET substrates (90 mm × 150 mm) were cleaned with isopropyl alcohol (IPA) and nitrogen gas. The printer components were similarly cleaned and dried to prevent contamination.
• Sintering and Sensing Material Deposition: Printed Ag-IDEs were sintered at 100°C for four hours. For sensing applications, a sensing layer of cuprous oxide (Cu₂O) was synthesized using a CuBr₂ precursor reduced by ascorbic acid. This material was deposited onto the IDEs via dip-coating. Two variants were tested: Cu₂O alone and Cu₂O mixed with polyvinylpyrrolidone (PVP) as a binder.
• Characterization: The printed electrodes were analyzed for line width accuracy, edge roughness, and resistance distribution. The sensing materials were characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Adhesion was tested via ASTM D3359 crosshatch tests, and mechanical reliability was assessed through 1000 bending cycles. Finally, sensor performance was evaluated for humidity and ethanol vapor detection (1–100 ppm) at room temperature (30°C).

Key Contributions

• Parameter Optimization for Consumer Printers: The study established that the EPSON L130 can reliably print Ag-IDEs with a minimum linewidth and spacing of 200 µm. It identified that lines narrower than 200 µm suffer from significant dimensional deviations due to bitmap rasterization artifacts.
• Orientation Dependence: The research demonstrated that print quality is orientation-dependent. Lines aligned at 0° and 90° relative to the print head movement exhibited minimal deviation (±5 µm) and reduced edge roughness, whereas diagonal orientations (30°–80°) showed greater inaccuracies.
• Binder Enhancement: The inclusion of PVP in the Cu₂O sensing layer significantly improved interfacial adhesion. The Cu₂O+PVP/Ag-IDE achieved a 4B adhesion rating (ASTM D3359), whereas the Cu₂O-only variant failed with a 0B rating. SEM analysis confirmed that PVP acted as a binder, enhancing particle clustering and connection between Cu₂O particles.
• Functional Sensor Fabrication: The study successfully fabricated a flexible ethanol sensor using these optimized parameters, demonstrating that office-grade printers can produce functional sensing components.

Results

• Electrical Performance: An array of 8 × 7 IDEs showed a high yield of 83%, with resistance values clustering around 2.30 ± 0.08 MΩ. The remaining electrodes fell within a usable range of 1.50 to 3.00 MΩ.
• Mechanical Reliability: The Ag-IDEs on PET demonstrated inherent durability, showing negligible resistance variation over 1000 bending cycles. However, the Cu₂O+PVP sensing layer exhibited microcracks after 300 cycles, limiting its mechanical robustness compared to the bare electrode, though the overall device remained functional.
• Sensing Capabilities:
  • Humidity: The sensor detected relative humidity in the 40% to 80% RH range at 30°C, with a recovery time of 30 seconds.
  • Ethanol: The sensor exhibited sensitivity to ethanol concentrations ranging from 1 ppm to 100 ppm. At 100 ppm, the average recovery time was 80 seconds.
  • Selectivity: The sensor showed a selective response to ethanol and water vapor, with negligible response to oxygen, carbon dioxide, nitrogen, and hydrogen.

Significance and Claims
The authors claim that this work bridges the gap between high-cost industrial fabrication and accessible rapid prototyping. By rigorously characterizing the limitations and capabilities of a standard office printer, the study demonstrates that consumer-grade inkjet printers are accessible and cost-effective platforms for developing flexible electronic sensors. The research validates that with optimized design parameters (specifically line width ≥200 µm and 0°/90° orientation) and appropriate material formulations (using PVP as a binder), reliable interdigitated electrodes and functional gas sensors can be produced without specialized equipment. The findings suggest a practical pathway for low-cost, scalable fabrication of flexible sensors for applications such as environmental monitoring and wearable health devices, provided the mechanical limitations of the sensing layer are accounted for.