Chip-Less Wireless Electronic Skin Sensors Enabled by Epitaxial Freestanding Compound Semiconductors

Electronic skin (e-skin) has been developed with a goal to obtain a non-invasive human health monitoring electronic system with its imperceptibility. So far, one of the major shortcomings in this field is the bulky wireless communication system that severely affects its wearability. In this work, we introduce a single-crystalline non-Si-based e-skin system where fully conformable, ultrathin, piezoelectric, compound semiconductor membranes are incorporated as power-efficient wireless communication modules and extremely high sensitivity sensors without needing for bulky chips and batteries. The developed GaN surface acoustic wave-based device successfully measured wirelessly three different inputs including strain, ultraviolet light, and ion concentrations. The consistency and accuracy of the measured heart rate and pulse waveforms over a 7-day period, during which the e-skin was re-attached 7 times, strongly demonstrate the reusability and long-term wearability of our device. This study will change the paradigm of e-skins by providing versatile wireless platforms for fully imperceptible e-skins with very high sensitivity and low power consumption.