Single-Step Fabrication of Monolithic Flexible Capacitive Pressure Sensors With Enhanced Sensitivity via Femtosecond Laser Direct Writing and Microhole Structuring

Abstract

Flexible capacitive pressure sensors (CPSs) have attracted a lot of interest due to their potential applications in wearable electronics. Manufacturing flexible CPSs involves multiple steps to fabricate sensitive layers, electrode layers, and various sensitivity-amplifying microstructures. Despite significant advancements, there remains a critical need to simplify the fabrication processes, enhance the sensitivity, and create more compact pressure sensors. In this study, a single-step fabrication of a flexible CPSs in a gelatin matrix mixed with silver nitrate is reported. A seamless monolithic design is achieved by using a femtosecond laser-based direct writing technique to pattern silver electrodes in gelatin. This approach offers high-precision 3D fabrication of metallic silver in a single step. To increase sensitivity, microholes are fabricated in the gelatin layer using an amplified laser beam with the same fabrication setup. The microholes filled with air instigate a large variation in dielectric permittivity of a medium between two electrodes under applied pressure, resulting in enhanced sensitivity ≈2.44 kPa−1 in the range of 0–0.5 kPa. This work highlights the potential of femtosecond laser-based direct writing of flexible sensors in next-generation wearable technologies, providing a pathway for high-performance solutions and a streamlined fabrication approach.