Abstract
Accurate and continuous monitoring of eye movements using compact, low-power-consuming, and easily-wearable sensors is necessary in personal and public health and safety, selected medical diagnosis techniques (point-of-care diagnostics), and personal entertainment systems. In this study, a highly sensitive, noninvasive, and skin-attachable sensor made of a stable flexible piezoelectric thin film that is also free of hazardous elements to overcome the limitations of current computer-vision-based eye-tracking systems and piezoelectric strain sensors is developed. The sensor fabricated from single-crystalline III-N thin film by a layer-transfer technique is highly sensitive and can detect subtle movements of the eye. The flexible eye movement sensor converts the mechanical deformation (skin deflection by eye blinking and eyeball motion) with various frequencies and levels into electrical outputs. The sensor can detect abnormal eye flickering and conditions caused by fatigue and drowsiness, including overlong closure, hasty eye blinking, and half-closed eyes. The abnormal eyeball motions, which may be the sign of several brain-related diseases, can also be measured, as the sensor generates discernable output voltages from the direction of eyeball movements. This study provides a practical solution for continuous sensing of human eye blinking and eyeball motion as a critical part of personal healthcare, safety, and entertainment systems.