Scalable Piezoelectric TFT Arrays on Flexible Substrates for Ultra-High Resolution 3D Force Imaging—From the Mechanism to Applications in Closed-Loop Robotics

Mechanoreceptors on the human hand allow us to perform sophisticated object manipulations, such as flipping pages, grasping an egg, or opening a door. The mechanoreceptors provide tactile feedback over a variety of physical parameters, which are accordingly manipulated to form a closed-loop network for error correction. In a similar manner, for robotics and neuroprosthetic applications, versatile manipulations of objects can only be achieved through high resolution spatiotemporal tactile sensing. However, multiple modalities which have been used so far do not meet the requirements for high fidelity and feasibility, since they indirectly infer tactile information rather than direct measurement.<br/>The difficulties can be overcome by developing tactile sensors which can simultaneously sense the tactile forces and multiplex signals. With no need for additional driving elements, this approach can circumvent the tradeoffs for density and performance. Engineering these sensors to sense both normal and shear forces at the required spatiotemporal resolution will ultimately allow human-like tactile perception for robotics and neuroprosthetic applications. Still, manufacturing challenges need to be addressed before implementing these multi-functional tactile sensors on flexible substrates with the desired integration density and accuracy in a scalable way.<br/>In this presentation, we report the fabrication of such a multi-functional tactile sensor and their array on flexible substrates by using the advanced piezoelectric zinc oxide (ZnO) thin film transistors (TFTs), leveraging the TFT based display technology. With millimeter scale spatial resolution, millisecond scale temporal resolution, and sensation of shear force distribution, it enabled grip adjustment for robotic android fingers by using closed-loop control. The benefits of scalable vacuum technology further allowed us to demonstrate ultra-high spatial resolution, mechanical flexibility, and waterproof operations. The detailed mechanism of force sensation in ZnO TFT is also discussed using an analytic model.