Optimizing Fragmentation of Metallic Film for Cracked-Based Strain Sensor

Crack-based strain sensors show promise for various applications, including structural health monitoring and human–machine interfaces, because of their high sensitivity. However, the sensing mechanism, which relies on the creation of nanocracks in a metallic thin film, makes the sensitivity and durability of the sensors difficult to control. This study focuses on optimizing the performance of crack-based sensors by studying the effect of metal film thickness on crack morphology and its relationship with the piezoresistivity of the functional layer. We conducted comprehensive electromechanical testing of sensors with different metal film thicknesses that were fabricated using microfabrication technologies. We also propose a patterning concept that enables the piezoresistivity of the functional layer to be tailored by specifying the crack distribution. This approach enables precise sensitivity control even at low strains (less than 3%). The experimental results also demonstrated the potential for enhancing the durability of a cracked sensor by selecting an appropriate Cr/Au ratio. We showcase the final performance and durability of such sensors by detecting hand–wrist movements over an extended period of time, as well as by monitoring signal stability during vibration tests.