Wearable and Transparent Capacitive Strain Sensor with High Sensitivity Based on Patterned Ag Nanowire Networks

In this study, a transparent and stretchable thin-film capacitive strain sensor based on patterned Ag nanowire networks (AgNWs) was successfully fabricated. The AgNWs were patterned using a capillary force lithography (CFL) method and were embedded onto the surface of the polydimethylsiloxane substrate. The strain (ϵ) sensitivity of the capacitive strain sensor was controlled and enhanced by patterning the AgNWs into electrodes with an interdigitated shape. The interdigitated capacitive strain sensor (ICSS) is expected to have -1.57 gauge factor (GF) at 30% ϵ by calculation, which is much higher than the sensitivity of typical parallel-plate-type capacitive strain sensors. Because of the interdigitated pattern of the electrodes, the GF of the ICSS was increased up to -2.0. The ICSS had no hysteresis behavior up to ϵ values of 15% and showed stable ϵ sensing performance during the repeated stretching test at ϵ values of 10% for 1000 cycles. Furthermore, there was no cross talk between ϵ and pressure sensing in the AgNW-based ICSS, which was found to be insensitive to externally applied pressure. The ICSS was then used to detect the finger and wrist muscle motions of the human body to simulate its application to large and small ϵ sensing.