Electrical performance and reliability assessment of silver inkjet printed circuits on flexible substrates

Abstract

Inkjet printing has proven to be a promising alternative method in the fabrication of printed electronics, besides screen printing and photolithography etching. In this work, we characterize the electrical performance of inkjet printed circuits on flexible PET and glossy photo paper. The electrical circuits were printed using a commercial Epson L310 piezoelectric printer, and the NB series silver ink and chemical-sintering PET substrate from Mitsubishi Paper Mills. This method allows rapid prototyping of electronic circuits (~\u200930 min design,\u2009~\u20095 s fabrication) and quick iteration of prototypes. The system has a resolution of 250 µm electrodes and 300 µm electrical gaps, and on average, 1.5\u2009±\u20090.2 µm in thickness. The effect of printing on different substrates, geometry and overprinting on sheet resistance was also studied. It was found that double printing produced better electrodes with lower resistances. A stable conducting circuit has a sheet resistivity of\u2009<\u2009150 mΩ/sq for high aspect ratio features such as wires, and horizontal patterns have higher conductivities compared to vertical patterns. Optimum gap between conducting lines was found to be 300 µm with smaller gaps creating stray ink blotches that cause short circuits. The printed lines are tolerant against common solvents and conduct reliably when operating under 100 °C. For bending tests, a serpentine flexion sensor was printed and bent at angles from\u2009−\u200990° to 90°. It was found that at reverse bending, the resistivity increases 0.9% for every 1° bent while for forward bending, the resistivity decreases by the sum of 0.4% for every 1° bent. The printed circuits are resistant to the Scotch tape test, immersion in deionized water, acetone and ethyl alcohol with line resistance still within less than 10 Ω/cm after treatment. This study shows that silver inkjet printed electrodes can be reliably printed using a commercial printer to produce low-cost flexible and wearable electronics.