Fabrication and Characterization of PEDOT:PSS Strain Sensors on Polyimide Substrates via Intaglio Microcontact Printing
Hiroshi Yamauchi, Ryosuke YamadaIntroduction/Objective:
Organic flexible electronics have attracted considerable attention for wearable human sensing applications, including sensors integrated onto fingernails. However, conventional film-based strain gauges often exhibit poor conformal contact when attached to curved nail surfaces. The objective of this study was to develop a direct patterning method for PEDOT: PSS strain sensors on curved substrates using intaglio microcontact printing (μCP) and to evaluate their electrical and strain-sensing characteristics.
Methods:
A flexible UV-curable acrylate resin stamp was fabricated from a laser-machined aluminum master mold and used for intaglio μCP. PEDOT:PSS films were directly patterned onto flexible polyimide substrates by controlling ink transfer within recessed grooves of the stamp. Strain gauges were fabricated by forming PEDOT:PSS films between sputtered Au electrodes. The patterned films were characterized by dimensional analysis, current-voltage (I-V) measurements, bending tests, and hysteresis evaluation.
Results:
The intaglio μCP process enabled controlled pattern transfer with a final line width of approximately 1030 mm, corresponding to only a 3% deviation from the design value. The patterned PEDOT:PSS films exhibited linear I-V characteristics, indicating stable ohmic conduction. The electrical resistance increased with increasing curvature, demonstrating effective strain-sensing behavior. Based on the resistance-curvature relationship, the gauge factor was estimated to be approximately 180, which is significantly higher than that of conventional metallic strain gauges. The tested intaglio-patterned film exhibited approximately linear electrical behavior with only minor hysteresis during a single forward-and-reverse voltage-sweep cycle.
Discussion:
The recessed-groove structure of the intaglio stamp effectively suppressed ink spreading and improved dimensional accuracy on curved surfaces. The high gauge factor obtained in this study suggests that PEDOT:PSS films are highly sensitive to mechanical deformation. Furthermore, the low-temperature, solution-based fabrication process is compatible with direct patterning on naillike surfaces and may facilitate the future development of wearable nail-mounted sensors.
Conclusion:
This study demonstrated a direct fabrication method for PEDOT:PSS strain sensors on curved surfaces using intaglio microcontact printing. The fabricated sensors exhibited stable electrical characteristics, high strain sensitivity, and good pattern fidelity. The proposed approach provides a promising route toward lightweight, minimally invasive, and potentially fully organic nailmounted wearable sensing systems for continuous human monitoring.