Porous flexible piezoresistive sensor using liquid metal for low pressure detection

Abstract

Gallium-based liquid metals with the superiority of exceptional metallic conductivity, fluidity at room temperature, and nontoxicity are showing promising perspectives in flexible sensors and electronics. However, the limited particle size that serves as one of the intrinsic properties of the materials may induce poor charge transfer, thus further weakening their application performance. This paper presents a flexible pressure sensor using a simple and low-cost method of integrating gallium-based liquid metal and multi-walled carbon nanotubes (MWCNTs), which have the merit of forming numerous conductive pathways due to the exceptional aspect ratio. Meanwhile, liquid metal particles can deform flexibly under pressure, which enables them to serve as conductive links between the nanotubes, greatly strengthening the inner conductive network, and thus exhibiting a desirable piezoresistive performance when functioning as sensor material. Benefitting from the proposed porous structure, the developed sensor shows excellent mechanical softness which is a critical merit in detecting low pressure. Our experimental results indicate that the sensor has a fast response/recovery time of 400/1200 ms and high sensitivity of signal output (normalized resistance change of 84 %) under a low pressure (2.4 kPa). Our proposed design and sensor prototype exhibit significant potential in human motion detection including the counting of walking steps as a demonstration of the application.