Optimization of organic field-effect transistor-based mechanical sensors to anisotropic and isotropic deformation detection for wearable and e-skin applications

Flexible electronics represent a viable technology for the development of innovative mechanical sensors. This paper reports a detailed study of electro-mechanical performances of Organic Field-Effect Transistor-based sensor, investigating the role of source-drain electrodes layout in combination with organic semiconductor morphology obtained by different patterning methods. Two different sensor structures, with interdigitated and spiral-shaped source and drain electrodes, are employed together with solution-processed organic semiconductors deposited by drop-casting or patterned by means of meniscus-guided printing. This technique allows the orientation of crystalline domains to specific directions, and was employed to provide anisotropic or isotropic semiconductor patterns onto the transistor's channel area. The different device configurations are tested as strain gauges and tactile sensors, by imposing anisotropic surface strain or complex deformations by means of custommade, 3D-printed indenters. A wise choice of device structure and semiconductor patterning allows optimizing sensing performances as a response to specific deformations: interdigitated devices with crystalline domains aligned along the channel length direction are ideal strain gauges, while sensors with spiral-shaped electrodes in combination with isotropic semiconductor patterning are preferential for reproducing the sense of touch, which deals with the transduction of more complex deformation patterns. These results pave the way to the development of innovative sensors in the field of flexible bioengineering, in particular for the development of wearable and e-skin applications for joint motion monitoring and tactile sensing.