Inkjet printing techniques for wearable/stretchable electronics in healthcare

Abstract

Inkjet printing techniques, a good alternative of the traditional MEMS techniques, can be utilized to fabricate flexible and stretchable electronics, which can be used for healthcare applications. Therefore, the objectives of this study are 1) Providing proof of concept for the inkjet printing parameters for silver (Ag) and polyimide (PI) inks, 2) understanding the relationship between the dynamics of inkjet-printed patterns and surface energies of the substrate, and 3) demonstrating printing a flexible circuit on a PI coated substrate. During experiments, the effects of the printing parameters including jetting voltages, cartridge temperatures, and drop spacings of both the Ag and PI inks via the drop size and line width measurements were explored. The surface energies were manipulated by applying $O_2$ and $CF_4$ plasma for different durations using Reactive Ion Etching (RIE) that were measured by the means of contact angle measurements and ink drop size and line width measurements. Our results indicated that 1) the drop sizes increase as jetting voltages and cartridge temperatures increase, respectively, 2) the line widths decrease with increasing drop spacings, and 3) the $CF_4$ plasma increases the hydrophobicity of the surface while $O_2$ increases the hydrophilicity of the surface. Collectively, we successfully demonstrated accurate printing of multi-layered ECG circuit with a drop size of 40 $\mu{m}$ for the Ag ink and PI ink. The next goal will be to demonstrate wireless continuous monitoring of reliable ECG signals using the printed ECG circuit.