Electromechanical evaluation of sub-micron NiCr-carbon thin films as highly conductive and compliant electrodes for dielectric elastomers

Abstract

This paper focuses on the electromechanical evaluation of combinations of novel sub-micron metal and carbon thin film electrodes for dielectric elastomers. The thin film electrodes are sputtered either onto 37.5 % biaxially pre-stretched polydimethylsiloxane (PDMS)-foils or on 57.5 % pre-stretched foils under pure shear conditions. The electrodes are wrinkled after relaxing the pre-stretch. The wrinkles in combination with the innovative sputtered sandwich-layers of nickel-chromium and carbon, with a total thin film thickness of 10 nm–40 nm, lead to exceptional electromechanical properties. With an initial resistance of only 500 Ω/square, some electrode configurations tolerate high strain up to 100 % without losing conductivity. 10 million cycles of mechanical load do not cause any major degradation of the thin films and their resistances. The capacitance-strain function is linear as long as the test strain is kept below the previously applied pre-stretch. During all the experiments, no delamination of these compliant thin film electrodes was observed. The force-displacement characteristics of the dielectric elastomer can be altered by applying high voltages on the electrodes, and thus, the actuator working principle is demonstrated. Depending on the kind of pre-stretch, some layer sequences are advantageous and others are disadvantageous when a low resistance at high strain is favored. In general, biaxially pre-stretched membranes with a metallic electrode configuration provide the best properties. Hence, this work proves, that sub-micron sandwich-layers of nickel-chromium and carbon are suitable for electrodes of dielectric elastomer actuators and sensors.