Highly Sensitive and Flexible Strain-Pressure Sensors with Cracked Paddy-Shaped MoS₂/Graphene Foam/Ecoflex Hybrid Nanostructures

Three-dimensional graphene porous networks (GPNs) have received considerable attention as a nanomaterial for wearable touch sensor applications because of their outstanding electrical conductivity and mechanical stability. Herein, we demonstrate a strain-pressure sensor with high sensitivity and durability by combining molybdenum disulfide (MoS₂) and Ecoflex with a GPN. The planar sheets of MoS₂ bonded to the GPN were conformally arranged with a cracked paddy shape, and the MoS₂ nanoflakes were formed on the planar sheet. The size and density of the MoS₂ nanoflakes were gradually increased by raising the concentration of (NH₄)₂MoS₄. We found that this conformal nanostructure of MoS₂ on the GPN surface can produce improved resistance variation against external strain and pressure. Consequently, our MoS₂/GPN/Ecoflex sensors exhibited noticeably improved sensitivity compared to previously reported GPN/polydimethylsiloxane sensors in a pressure test because of the existence of the conformal planar sheet of MoS₂. In particular, the MoS₂/GPN/Ecoflex sensor showed a high sensitivity of 6.06 kPa^-1 at a (NH₄)₂MoS₄ content of 1.25 wt %. At the same time, it displayed excellent durability even under repeated loading-unloading pressure and bending over 4000 cycles. When the sensor was attached on a human temple and neck, it worked correctly as a drowsiness detector in response to motion signals such as neck bending and eye blinking. Finally, a 3 × 3 tactile sensor array showed precise touch sensing capability with complete isolation of electrodes from each other for application to touch electronic applications.