Multi-length scale hierarchical architecture overcoming pressure sensing range-speed tradeoff for skin electronics

Pressure sensing electronics have gained significant attention in human-machine interface, soft robotics, and wearable biomedical applications. However, the existing sensor architectures are inadequate in overcoming the classical tradeoff among sensing range, sensitivity, and speed. Herein, a contact architecture combining a unique microstructure and hierarchical scheme is presented to overcome the pressure sensing range-speed tradeoff in flexible pressure sensors. A sensitive piezoresistive pressure sensor capable of simultaneously achieving a wide three orders-of-magnitude sensing range and tens of milliseconds fast response is demonstrated. This sensor consists of 3D porous laser-induced graphene (LIG) electrodes contacted with a rough layer of silver microflowers (AgMFs), where silver nanoflakes (AgNFs) were grown on polystyrene (PS) spheres. Sensing is hierarchically performed via various mechanisms across different length scales, i.e. , on the nanoscale by the contact change among AgNFs and that between AgNFs and LIG and on the microscale by the deformation-induced resistance change in the AgMFs and 3D porous LIG. The multi-length scale contact architecture featuring a combination of the unique AgMF microstructure and the hierarchical scheme opens a new avenue for advanced flexible pressure sensors requiring a wide range operation without compromising their sensitivity and speed. Ultra-sensitive pressure sensing is provided hierarchically, on the nanoscale by contact between silver nanoflakes and LIG nanosheets, and on the microscale by contact between AgMFs and LIG.