A Study on Graphene Structure Control Using Ammonia Gas for a Highly Sensitive Pressure Sensor

Graphene has been used in various fields because of its excellent mechanical, optical, electrical, and thermal properties. However, its intrinsic low sensitivity to pressure limits its sensor applications. To overcome this drawback, many researchers have tried to improve the sensitivity by controlling the defects on the graphene, but have yet to report a significant increase in sensitivity compared to the pristine graphene. Herein, we fabricated a graphene-based highly sensitive pressure sensor by flowing ammonia gas during chemical vapor deposition. The ammonia gas assisted the generation of nano-sized defects due to nitrogen doping in the graphene lattice, as well as macro-sized cracks in the graphene layer, due to the corrosion of the Cu surface. We regulated the concentration ratio of ammonia gas and methane gas during the graphene synthesis, which controlled the crack generation. These cracks weakened the in-plane force of the networks in the geometric structure of the graphene, thereby allowing them to deform more easily under external force, and changing the resistance of the sensor dramatically. As a result, the sensitivity of the pressure sensor increased about 10,000 times higher than that of the pristine graphene. These results suggest that controlling defects to improve graphene's mechanical sensitivity provides a promising route to pressure sensor applications.