Plasma Treatment of Composite Piezoelectric Thin Films for Good Adhesion of Printed Conductive Ink
Kiran Kumar Sappati, Bishakh Rout, Pierre‐Luc Girard‐Lauriault, Sharmistha Bhadra
Abstract
Lead zirconate titanate and polydimethylsiloxane (PZT–PDMS) thin films are an attractive choice for a flexible piezoelectric substrate. In this work, the surface modification of the PZT–PDMS composite with plasma treatment is developed to fabricate flexible conductor patterns or devices directly on the composite surface. Optimized plasma treatment conditions are achieved by varying plasma parameters such as the pressure of treatment, type of gas, gas flow, and time of treatment. Plasma polymerization is carried out using C2H4–CO2, and argon (Ar) is used for the surface ablation effect in low-pressure conditions. Atmospheric pressure plasma (APP) is performed in a N2 atmosphere which has a surface etching effect. All the treatments create a hydrophilic layer, which is confirmed with water contact angle measurements, X-ray photoelectron spectroscopy, and Fourier transform infrared analysis. Silver conductive ink was printed on the plasma-treated films to fabricate flexible conductive patterns, and the bonding strength was tested by performing adhesive tests such as tape, ultrasonic, and soak tests. APP treatment under a N2 environment with a 300 V input voltage, 21.5 kHz frequency, and 2 min deposition time proves to be the most efficient surface modification technique. This treatment produces a silica-like layer on the composite surface and results in better wettability. It reduces the contact angle from 108 to 20° immediately after the treatment and shows strong adhesion during several rigorous adhesion tests. The printed conductive patterns on the N2-treated film show strong mechanical stability and exhibit great electric conductivity under bending and releasing. The APP treatment under N2 environment can overcome the adhesion issue of the printed conductive layer on the hydrophobic composite surfaces. Moreover, all the above plasma treatments have a negligible effect on the piezoelectric properties of PZT–PDMS films.