Unveiling Viscoelastic Response of Capacitive-type Pressure Sensor by Controlling Cross-Linking Density and Surface Structure of Elastomer

Research on pressure sensors using elastic materials is actively underway to develop next-generation devices for applications in healthcare monitoring, haptic sensors, and electronic skin. Capacitive-type pressure sensors have several advantages among various types of pressure sensors because they can be manufactured in a small size, and their sensitivity is superior to other types of pressure sensors. Capacitive-type pressure sensors consist of two electrodes and an intermediate active layer, typically made up of elastomer such as polydimethylsiloxane (PDMS). Because a change in thickness of the elastomer upon applied pressure is a key operating mechanism, viscoelastic properties of elastomer should be considered when optimizing sensor performance. In this study, we examined viscoelastic properties of PDMS by controlling its cross-linking density. Effects of cross-linking density on performances of pressure sensors were also analyzed. Dynamic mechanical analysis and swelling method were employed to measure an accurate cross-linking density which significantly affected sensitivity, hysteresis, and recovery rate of pressure sensors. Performances of pressure sensors were also studied according to surface patterns (i.e., dome, square) of PDMS and surface treatment (i.e., UV/ozone, perfluordecyltrichlorosilane). Pressure sensing characteristics were optimized by incorporating dome structure and appropriate surface treatment on PDMS. Results of this study demonstrate that viscoelastic response of elastomer is vital for optimizing properties of capacitive-type pressure sensors.