Inkjet printing in manufacturing of stretchable interconnects

Abstract

Stretchable circuits have the potential to enable integrating electronics in everyday objects, but also skin-like, imperceptible electronic applications. However, manufacturing stretchable electronics requires developing novel manufacturing methods and using novel materials at least as substrate. Since the elastic materials for stretchable electronics are relatively soft, using traditional manufacturing methods becomes more problematic, whereas contactless material deposition by inkjet-printing is unaffected by such material properties. This study concentrates on feasibility analysis of using inkjet printing in manufacturing of stretchable electronics. First, printing related challenges are evaluated by manufacturing test structures with inkjet-printer using silver nanoparticle ink on elastic thermoplastic polyurethane substrate and sintering structures in convection oven. Adhesion between ink and substrate, but also sheet resistance, is evaluated. A minimum sheet resistance approx. of 26 m was obtained, and peak strains of inkjet-printed conductors are found to be between 1.0 % and 1.5 %, but conductivity is observed to be almost fully reversible when strain is released.

Soft Inkjet Circuits

“…The resistance change ratio within each stayed fairly constant, from initially 4.2-fold to 3.8-fold after 1000 cycles. According to these results, the stretchability of the traces is considerably better than reported in prior work on inkjet printed circuits [29].…”

Experimental Characterization of Inkjet-Printed Stretchable Circuits for Wearable Sensor Applications

“…Pulse oximeters use optical photoplethysmography (PPG) to estimate oxygenated and de-oxygenated blood components based on their distinct light absorption coefficients. Pulse oximetry also detects photoplethysmographic (PPG) signals produced by variations in the amount of arterial blood related to the periodic contractions and relaxations of the heart [17]. …”

“…In previous research, the main focus has been dedicated to solving problems which prevented the fabrication of conductive patterns on stretchable substrates [16,17,18]. This includes adhesion issues, and optimization of printing parameters using various types of inks and substrates.…”

Screen-Printing Fabrication and Characterization of Stretchable Electronics

“…Conductive traces can be embedded in elastomer substrates in various ways. Conductive patterns have been fabricated, e.g., by etching 17 , screen-printing and stencil printing 18 , and inkjet printing 19 . Intrinsically stretchable materials, such as polymers (e.g., PEDOT:PSS 20 ) and CNT compounds 21 , generally permit high elongations but suffer from high resistance, whereas metal interconnects are less resistant yet usually not suitable for high elongation.…”