Ultrahigh Sensitivity to Strain of Cracked Thin Films Based on Metallic Nanoparticles in a Dielectric Matrix

Platinum nanoparticle-based strain gauges are elaborated by means of atomic layer deposition on flexible polyimide substrates. Their electromechanical response is tested under mechanical bending at strain levels up to 1%. Sudden changes in electrical resistance are observed above 0.6% strain when straight cracks are formed in the nanostructured thin film. Scanning electron microscope (SEM) experiments reveal that these cracks are preferentially formed next to the interface with aluminum top electrodes. After crack formation, a giant gauge factor of 2 × 10
⁴
is measured at a strain level of 0.3%. This high sensitivity to strain is attributed to the gradual opening (or closing) of the cracks when mechanical strain is applied. Finally, we demonstrate the feasibility of a flexible heart rate monitor, which integrates a cracked Pt nanoparticle-based strain gauge.