Figure 4
(a) Lumped element model describing the electrical characteristics of the EAP actuators. Charge on the capacitor C represents ionic charge responsible for the actuator deflection. Rp and Rs are parasitic resistances that reduce the charge and voltage on the capacitor. (b) Calculated final voltage on the capacitor in the lumped model as a function of the transistor on-current. With increasing transistor on-current, the capacitor voltage increases because the transistor channel resistance ceases to be the limiting factor. For high transistor currents, the actuator response becomes limited by the actuator’s parasitic resistances and is independent of the drive current. The measured actuator deflection rate follows the same trend for different supply current limits, confirming the importance of the drive current up to the point where deflection saturates. The applied voltage was in both cases 2 V. (c) The large capacitance of the Nafion gate dielectric enables very large on-currents on the order of 10 mA for printed ion gel OTFTs. VDS=−2 V. W/L=836.5. (d) These high-current OTFTs can drive an EAP actuator. The actuator deflection rate corresponds to the transistor on-current when they are connected in series. Toward the end of the sweep, the current and deflection rate both decrease as the actuator becomes fully charged. The supply voltage across the actuator and the transistor channel in series was 2 V. EAP, electroactive polymer; OTFT, organic thin film transistors.
