Facile Fabrication of Ultraflexible Transparent Electrodes Using Embedded Copper Networks for Wearable Pressure Sensors

Pressure sensors are in urgent need due to the explosive demands in electronic skins. However, current resistive-type pressure sensors require electrode materials with complex multilevel microstructures or low opacity. Herein, a Cu network transparent electrode (TE) embedded in the polydimethylsiloxane (PDMS) substrate is designed to realize wearable pressure sensor. The Cu network is fabricated by oxygen plasma treatment-assisted crack template and electroplating. The oxygen plasma treatment improves the surface adhesion force of the substrate, which suppresses uneven template cracking and prevents the electroplating solution from seeping under the templates, thereby resulting in 20 times figure-of-merit improvement in optoelectronic performance. Sandwiching the Cu network between PDMS layers provides the best flexibility reported for such a low-cost transparent conducting material. The embedded Cu network TE-based pressure sensors are capable of detecting a pressure of 1.1 Pa with a sensitivity of 76.1 kPa(-1), surpassing the subtle pressure sensing properties of natural skin. In situ observations indicate that such a high performance originates from the reversibly structural deformation-dependent resistance of the Cu network during repeated pressing-release thanks to the constraining effect of the PDMS. This work opens a new strategy to fabricate transparent and flexible pressure sensors in a simple yet efficient matter.