Ultrasensitive Interfacial Capacitive Pressure Sensor Based on a Randomly Distributed Microstructured Iontronic Film for Wearable Applications

Abstract

The rapid development of pressure sensors with distinct functionalities, notably, with increased sensitivity, fast response time, conformability, and a high degree of deformability, has increased the demand for wearable electronics. In particular, pressure sensors with an excellent sensitivity in the low-pressure range (<2 kPa) and a large working range simultaneously are strongly demanded for practical applications in wearable electronics. Here, we demonstrate an emerging class of solid polymer electrolyte obtained by incorporating a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis­(trifluoromethylsulfonyl)­imide with poly­(vinylidene fluoride-co-hexafluoropropylene) as a high-capacitance dielectric layer for interfacial capacitive pressure sensing applications. The solid polymer electrolyte exhibits a very high interfacial capacitance by virtue of mobile ions that serve as an electrical double layer in response to an electric field. The randomly distributed microstructures created on the solid electrolyte help the material to elastically deform under pressure. Moreover, the interfacial capacitance is improved by utilizing a highly conductive porous percolated network of silver nanowires reinforced with poly­(dimethylsiloxane) as the electrodes. An ultrahigh-pressure sensitivity of 131.5 kPa–1, a low dynamic response time of ∼43 ms, a low limit of detection of 1.12 Pa, and a high stability for over 7000 cycles are achieved. Finally, we demonstrate the application of the sensor for international Morse code detection, artery pulse detection, and eye blinking. Owing to the ultrahigh sensitivity, the as-fabricated sensor will have great potential for wearable devices in health status monitoring, motion detection, and electronic skin.

Enhanced Sensitivity of Iontronic Graphene Tactile Sensors Facilitated by Spreading of Ionic Liquid Pinned on Graphene Grid

“…In this case, the sensitivity is calculated to be 31.1 kPa −1 , which is one of the highest values reported in the medium‐pressure range (> a few kPa) so far (see Table S1 in the Supporting Information) . Although higher sensitivities have been reported in the previous reports, these values are typically obtained in extremely low pressure regimes (below 1 kPa) . For instance, the use of pyramidal ionic gels exhibited extremely high sensitivity of 41 kPa −1 at the low pressure below 0.4 kPa .…”

“…[9,[28][29][30][31][32] Although higher sensitivities have been reported in the previous reports, these values are typically obtained in extremely low pressure regimes (below 1 kPa). [33,34] For instance, the use of pyramidal ionic gels exhibited extremely high sensitivity of 41 kPa −1 at the low pressure below 0.4 kPa. [35] On the other hand, the sensitivity in the i-GTS can be improved by decreasing the gap between the ionic liquid droplet and graphene top electrode.…”

Ionic Tactile Sensors for Emerging Human‐Interactive Technologies: A Review of Recent Progress

“…Conductive liquid materials (e.g., eutectic gallium–indium (EGaIn), electrolytes and ionic liquid (IL))‐based microfluidic strain sensors have been investigated extensively as piezoresistive ITS. These sensors are commonly made up of elastomeric matrices, i.e., elastomeric silicon, PDMS, and Ecoflex with embedded microchannels filled with conductive liquids. External force induces change in length and the cross‐sectional areas of the ion‐conducting channels ( Figure a), that change the impedance of the channel, which can be measured by the AC impedance measurements .…”

“…Remarkably different from the conventional electronic conductors, ionic materials can be used in two different ways to fabricate two different supercapacitive ITS device architectures: i) in first type, stretchable ionic conductors are utilized as electrodes with a stretchable dielectric sandwiched between two ionic conductors and ii) second type includes ionic materials as dielectrics, which are sandwiched between two stretchable electrodes (including noble metals, conducting polymers, carbon nanotubes (CNTs), and silver nanowires deposited on various flexible polymer substrates such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), and polyurethane (PU). The second type of supercapacitive ITS are more common, due to their high pressure sensitivity and fast response …”

“…Second, as shown in Figure , microstructures within human skin such as intermediate ridges, which is regarded as a crucial enhancer in human skin sensation under mechanical stimuli, have been mimicked in the ITS via topologically patterned array of micro‐ or nanostructured ionic materials. For instances, the ITS with high performance have been developed using novel structural engineering of ionic deformable polymeric materials . Similar to the structural features of human skin such as fingertip and interlocked ridges that can amplify the tactile stimuli to cutaneous mechanoreceptors, structural engineering of ionic materials plays a significant role in enhancing the performance of the ITS under tactile stimuli.…”