Thin-Film Thermal Sensors on Chitosan Substrates for Sustainable Transient Electronics

Abstract

In recent years, transient (bio)electronics has witnessed a remarkable surge for their potential in sustainable and biocompatible electronic solutions. Here, chitosan-based films are demonstrated as versatile transient substrates for thin-film thermal sensors, merging sustainability with standard microfabrication. Two sensor types are fabricated: resistive temperature detectors (RTDs) via sputtering of a 100 nm molybdenum (Mo) layer, and thermistors through subsequent deposition of a 50 nm amorphous indium gallium zinc oxide (a-IGZO) semiconductor layer. Bi-directional thermal characterization in physiologically relevant ranges (25–55 ${}^{\circ }C$,  2.0% RH) reveals that both device types exhibited linear and reproducible responses. The thermistors show a significantly higher sensitivity (0.0184 ${}^{\circ }C$${}^{-1}$) more than an order of magnitude greater than the RTDs (0.0010 ${}^{\circ }C$${}^{-1}$), with minimal deviation during extended thermal cycling (standard deviations  $\sim$0.016 ${}^{\circ }C$${}^{-1}$ and  $\sim$0.0006${}^{\circ }C$${}^{-1}$, respectively). The sensors maintain full functionality under severe mechanical deformation, including twisting, folding, and bending to radii as small as 8 mm. Importantly, the devices are fully transient, dissolving completely in aqueous and mildly acidic environments within approximately 50 hours. This work establishes chitosan-based substrates as a promising platform for functional transient electronics leveraging existing thin-film technologies, paving the way for sustainable applications in soft robotics, agritech, and healthcare.