Enhancing electrical performance of inkjet-printed flexible strain sensors through substrate surface coating and multiphysics simulation

Inkjet-printed piezoresistive sensors are gaining popularity due to process compatibility with flexible substrates and the possibility of rapid on-demand fabrication. However, several technical challenges are frequently encountered, such as the compatibility of commercial inks with non-standard substrate materials and the necessity to enhance sensor sensitivity for application-specific performance. This study introduces a novel approach for improving the sensitivity of Mitsubishi silver nanoparticle inks on non-standard substrates by utilizing a two-layer surface coating of polyvinyl alcohol (PVA) and potassium chloride (KCl). In this work, non-standard substrates such as standard paper, glossy inkjet paper, and polyimide were coated prior to silver nanoparticle ink deposition using an office inkjet printer. The baseline resistance of non-standard substrate was compared with the Mitsubishi special media. The baseline resistance measurements revealed the lowest values on Mitsubishi special media (4.74–6.43 Ω), while polyimide exhibited significantly higher resistance (426–894 Ω) with high variability (standard deviation of 170.10 Ω), indicating substrate-dependent conductive performance. Further multiphysics simulation studies investigating the influence of various design features on the sensitivity were performed. The results indicate that the unit cell of the meander pattern (Z-shape) enhances sensitivity of 96.1 in a confined area, making it an optimal design choice for strain sensor applications. Key findings revealed that both length and spacing width significantly influence sensor performance. The two-layer coating and design influence on sensitivity provides critical insights for enhancing the electrical conductivity and piezoresistivity.