An Ultra-Thin Flexible CMOS Stress Sensor Demonstrated on an Adaptive Robotic Gripper

An ultra-thin (20 μm), flexible CMOS stress sensor for hybrid systems-in-foil (HySiF) is presented. The system is designed for Fin Ray® grippers in order to measure the emerging stress on the gripper in operation, enabling the extraction of object shape and operation status. In-plane stress is linearly converted to electrical signals proportional to shear stress and normal stress difference using two sensing elements. Each stress signal is processed and digitized by an integrator and a 10-bit SAR ADC. In contrast to rigid chips, the stress cannot be avoided in the sensitive blocks, such as the signal processing chain and digital controller, when an ultra-thin chip is under deformation. The influence of stress levels, up to 350 MPa, is minimized by using stress-insensitive components, design measures, and layout techniques. This work represents the first demonstration of stress-aware top-to-bottom CMOS design on an ultra-thin chip.