Transparent and Flexible Graphene Pressure Sensor with Self-Assembled Topological Crystalline Ionic Gel
Kang Lib Kim, Sung Hwan Cho, Jaebok Lee, Gwangmook Kim, Kyuho Lee, Seung Won Lee, Han Sol Kang, Chanho Park, Chanho Park, Jong‐Hyun Ahn, Wooyoung Shim, Insung Bae, Cheolmin Park, Cheolmin Park
Abstract
This study demonstrates transparent and flexible capacitive pressure sensors using a high- k ionic gel composed of an insulating polymer (poly(vinylidene fluoride- co -trifluoroethylene- co -chlorofluoroethylene), P(VDF-TrFE-CFE)) blended with an ionic liquid (IL; 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) amide, [EMI][TFSA]). The thermal melt recrystallization of the P(VDF-TrFE-CFE):[EMI][TFSA] blend films develops the characteristic topological semicrystalline surface of the films, making them highly sensitive to pressure. Using optically transparent and mechanically flexible graphene electrodes, a novel pressure sensor is realized with the topological ionic gel. The sensor exhibits a sufficiently large air dielectric gap between graphene and the topological ionic gel, resulting in a large variation in capacitance before and after the application of various pressures owing to the pressure-sensitive reduction of the air gap. The developed graphene pressure sensor exhibits a high sensitivity of 10.14 kPa –1 at 20 kPa, rapid response times of <30 ms, and durable device operation with 4000 repeated ON/OFF cycles. Furthermore, broad-range detections from lightweight objects to human motion are successfully achieved, demonstrating that the developed pressure sensor with a self-assembled crystalline topology is potentially suitable for a variety of cost-effective wearable applications.