Giant Tunneling Piezoresistance of Composite Elastomers with Interlocked Microdome Arrays for Ultrasensitive and Multimodal Electronic Skins

Abstract

The development of flexible electronic skins with high sensitivities and multimodal sensing capabilities is of great interest for applications ranging from human healthcare monitoring to robotic skins to prosthetic limbs. Although piezoresistive composite elastomers have shown great promise in this area of research, typically poor sensitivities and low response times, as well as signal drifts with temperature, have prevented further development of these materials in electronic skin applications. Here, we introduce and demonstrate a design of flexible electronic skins based on composite elastomer films that contain interlocked microdome arrays and display giant tunneling piezoresistance. Our design substantially increases the change in contact area upon loading and enables an extreme resistance-switching behavior (ROFF/RON of ∼10(5)). This translates into high sensitivity to pressure (-15.1 kPa(-1), ∼0.2 Pa minimum detection) and rapid response/relaxation times (∼0.04 s), with a minimal dependence on temperature variation. We show that our sensors can sensitively monitor human breathing flows and voice vibrations, highlighting their potential use in wearable human-health monitoring systems.

Tailoring force sensitivity and selectivity by microstructure engineering of multidirectional electronic skins

“…, where V is the applied voltage, J is the current density, and A CNT is the electrical contact area between MWNTs, which is in turn proportional to the physical contact area (A C ) between interlocked microstructures 25 . Therefore, the contact-area change critically affects contact resistance.…”

“…1e). For interlocked composite microstructures, high surface conductivity is preferred for enhancing pressure sensitivity due to the drastic R C change with changing contact area under proper loading pressure 25 . In this study, interlocked composite microstructures having 8 wt% CNTs were utilized.…”

“…In particular, the sensing performance of piezoresistive e-skins with microstructure arrays critically depends on the localized stress distribution of microstructures and the resulting contact area change when external mechanical forces are applied in different directions. Although the interlocked microdome structures have been reported to exhibit high pressure sensitivity 25,26 , indepth investigation of the effects of microstructures on the multidirectional sensing performances has not been done. A systematic and in-depth analysis of geometrical effects on sensing performance is important to enable the design of tunable e-skins having high force sensitivity and selectivity, which can be customized for diverse applications.…”

“…To facilitate comparison of the geometrical shape effect on the stress sensing properties, an interlocked geometry of the different microstructure arrays was employed. This has been reported to enhance the variation in contact area and localized stress in the microstructures, thereby improving the stress sensitivity and multidirectional force sensing capabilities of eskins [25][26][27][28] . For the fundamental understanding of the sensing mechanisms, experimental piezoresistive properties were compared to the finite-element simulation of contact-area change and the localized stress distribution of microstructured e-skins.…”

Nanomaterial‐Enabled Wearable Sensors for Healthcare

“…[6,138] Numerous materials and configurations have been reported for resistive pressure sensing. Pressure sensitive pathways can be formed using interlocked structures, [139][140][141][142][143][144] percolative networks of nanomaterials, [57,145,146] microfabricated structures (e.g., micropyramids, micropillars), [147][148][149] porous structures (e.g., sponges, foams, porous rubbers) [26,150,151] and so forth. For example, Figure 5a presents the working principle of a pressure sensor using interlocked microdome array.…”