Yeongin Kim1,2,Jun Min Suh1,Jiho Shin1,Yunpeng Liu1,Hanwool Yeon1,3,Kuan Qiao1,Hyunseong Kum1,4,Chansoo Kim1,Han Eol Lee1,5,Chanyeol Choi1,Hyunseok Kim1,Doyoon Lee1,Jaeyong Lee1,Jihoon Kang1,Sungsu Kang6,Jihoon Kim6,Sungkyu Kim7,Joshua Perozek1,Kejia Wang1,Yongmo Park1,Kumar Kishen1,Lingping Kong1,Tomas Palacios1,Jungwon Park6,Min-Chul Park8,Hyung-jun Kim8,Yun Seog Lee6,Kyusang Lee9,Jiyeon Han10,Jeehwan Kim1
Massachusetts Institute of Technology1,University of Cincinnati2,Gwangju Institute of Science and Technology3,Yonsei University4,Jeonbuk National University5,Seoul National University6,Sejong University7,Korea Institute of Science and Technology8,University of Virginia9,Amorepacific R&D Center10
Yeongin Kim1,2,Jun Min Suh1,Jiho Shin1,Yunpeng Liu1,Hanwool Yeon1,3,Kuan Qiao1,Hyunseong Kum1,4,Chansoo Kim1,Han Eol Lee1,5,Chanyeol Choi1,Hyunseok Kim1,Doyoon Lee1,Jaeyong Lee1,Jihoon Kang1,Sungsu Kang6,Jihoon Kim6,Sungkyu Kim7,Joshua Perozek1,Kejia Wang1,Yongmo Park1,Kumar Kishen1,Lingping Kong1,Tomas Palacios1,Jungwon Park6,Min-Chul Park8,Hyung-jun Kim8,Yun Seog Lee6,Kyusang Lee9,Jiyeon Han10,Jeehwan Kim1
Massachusetts Institute of Technology1,University of Cincinnati2,Gwangju Institute of Science and Technology3,Yonsei University4,Jeonbuk National University5,Seoul National University6,Sejong University7,Korea Institute of Science and Technology8,University of Virginia9,Amorepacific R&D Center10
Health monitoring platforms based on electronic skins have included flexible/stretchable sensors, electronic circuits, and skin-compatible adhesive patches. They have applications in biophysical tracking of fitness and wellness, and clinical management. The broader use of e-skins in our daily lives can be boosted by the capability to communicate data wirelessly. A major shortcoming of conventional wireless e-skins is rigid integrated circuit (IC) chips, such as near-field communication (NFC) and radio frequency identification (RFID) chips. Those IC chips compromise overall flexibility. Also, the data accuracy of analog-to-digital converters (ADCs) in IC chips are dependent on power consumption. The power constraint in wireless e-skin systems often leads to reduced sensitivity of sensing data converted by ADCs. Thousands of transistors in IC chips generate a lot of heat and consume significant power, leading to reduced wireless distance. Chip-less wireless e-skin sensors based on inductor-capacitor (LC) resonators have been reported, but their applications are limited to pressure and strain sensing with relatively low sensitivity because of the limitations of capacitive sensor designs.<br/><br/>We report a chip-less wireless e-skin technology based on surface acoustic wave (SAW) sensors. Our wireless SAW e-skin shows high strain sensitivity (the minimum detectable strain of 0.048 %); low energy consumption (3.7 nJ/measurement); versatility as a sensing platform for strain, UV, and ion concentrations in sweat; and long-term wearability of one week. The excellent piezoelectricity and single-crystallinity of our ultrathin freestanding membrane of gallium nitride (GaN) on soft patch enable wireless communication without IC chips. The ultrathin GaN epitaxial layers are grown on graphene-coated GaN substrates by remote homoepitaxy and are easily released from the weak graphene-GaN interface by 2D material-based layer transfer (2DLT) process. These results present routes to cheap, low-power, high-sensitivity, and versatile platforms for wireless health monitoring devices.