Reliability and Lifetime of Chemically Sintered Printed Zinc for Highly-Conductive Biodegradable Antennas

Biodegradable or transient electronics are a class of electronics that break down under physiological or environmental conditions into harmless components, offering a solution to the problem of electronic waste generation. Biodegradable electronic devices need conductors to serve as interconnects as well as antennas or inductive loops for wireless power transfer and data communication. In these antennas, conductivity is crucial for functionality, but the majority of biodegradable conductors are significantly less conductive (on the order of 10³ S/m or less) than their non-degradable counterparts like evaporated copper or printed silver. Additionally, many existing printed biodegradable conductors have functional lifetimes measured in minutes or days, which can be useful in some applications, but is insufficient for applications in which weeks' or months' of data is desired. Higher conductivity, longer-lasting biodegradable conductors are needed.<br/>In recent years, printed zinc treated with acetic acid solution has emerged as a promising biodegradable, highly conductive material, with conductivity greater than 10⁵ S/m possible. The low-temperature nature of this process makes it compatible with many biodegradable substrates, which cannot withstand thermal sintering processes. The acid treatment conditions—concentration, exposure time, drying temperature, and drying time—needed to achieve high conductivity are very precise. Small deviations from optimal conditions can cause conductivity to fall by more than four orders of magnitude, rendering devices unusable. These optimal acid treatment conditions also depend on which polymer is used as the ink’s binder and on the substrate. Here, we present the optimization of chemically sintered zinc traces, taking binder and substrate material into account. The resulting traces maintain their conductivity for a few weeks.