A Sensor Array Using Multi-functional Field-effect Transistors with Ultrahigh Sensitivity and Precision for Bio-monitoring

Abstract

Mechanically adaptive electronic skins (e-skins) emulate tactition and thermoception by cutaneous mechanoreceptors and thermoreceptors in human skin, respectively. When exposed to multiple stimuli including mechanical and thermal stimuli, discerning and quantifying precise sensing signals from sensors embedded in e-skins are critical. In addition, different detection modes for mechanical stimuli, rapidly adapting (RA) and slowly adapting (SA) mechanoreceptors in human skin are simultaneously required. Herein, we demonstrate the fabrication of a highly sensitive, pressure-responsive organic field-effect transistor (OFET) array enabling both RA- and SA- mode detection by adopting easily deformable, mechano-electrically coupled, microstructured ferroelectric gate dielectrics and an organic semiconductor channel. We also demonstrate that the OFET array can separate out thermal stimuli for thermoreception during quantification of SA-type static pressure, by decoupling the input signals of pressure and temperature. Specifically, we adopt piezoelectric-pyroelectric coupling of highly crystalline, microstructured poly(vinylidene fluoride-trifluoroethylene) gate dielectric in OFETs with stimuli to allow monitoring of RA- and SA-mode responses to dynamic and static forcing conditions, respectively. This approach enables us to apply the sensor array to e-skins for bio-monitoring of humans and robotics.

Flexible and Stretchable Physical Sensor Integrated Platforms for Wearable Human‐Activity Monitoringand Personal Healthcare

“…Therefore, the direct integration of a piezoelectric polymer as a gate dielectric layer into the transistor is another approach for pressure sensors based on a piezo electric polymer. Tien and co-workers, [ 46,107 ] Trung et al, [ 77 ] and Kim et al [ 61 ] directly integrated a P(VDF-TrFE)/BaTiO 3 nanocomposite and P(VDF-TrFE) as gate dielectric layers with an OFET. The sensing mechanism of these devices based on the direct piezoelectric effect can be explained by the change of the remnant polarization ( P r ) or equivalent voltage ( V 0 ) inside the piezoelectric polymer under the external pressure that modulates the intensity of the charge accumulated at the semiconductor/dielectric interface leading to a changing source-drain read-out current.…”

“…The sensing mechanism of these devices based on the direct piezoelectric effect can be explained by the change of the remnant polarization ( P r ) or equivalent voltage ( V 0 ) inside the piezoelectric polymer under the external pressure that modulates the intensity of the charge accumulated at the semiconductor/dielectric interface leading to a changing source-drain read-out current. Furthermore, Tien et al [ 46 ] and Kim et al [ 61 ] demonstrated that a piezoelectric pressure sensor based on the P(VDF-TrFE)/BaTiO 3 nanocomposite can be used to measure static and dynamic pressure. Meanwhile, a piezoelectric pressure sensor is usually used to measure dynamic pressure only.…”

“…By using the AC gate-bias technique, they were able to elaborate the precise and quantitative separation of unknown, simultaneously applied stimuli of pressure-temperature or strain-temperature by decoupling the output signal from the bimodal sensor (Figure 13 b,c). To improve the responsivity of bimodal sensing to pressure and the rapidly adapting detection of dynamic pressure, Kim et al [ 61 ] used the microstructure of a functional gate dielectric (P(VDF-TrFE)), which greatly improved the pressure responsivity of the OFET sensor due to the larger fl exoelectricity-enhanced piezoelectric effect in pyramidalshaped microstructures; a minute pressure of as low as 20 Pa was detectable. The sensors could be applicable for extremely precise and sensitive detection of the heart-beat rate and skin temperature for human biomonitoring (Figure 13 d,e).…”

“…Flexible pressure sensors based on P(VDF-TrFE) fi lm have been demonstrated. [ 46,47,49,61 ] Although inorganic materials possess inferior fl exibility when compared to their organic counterparts, many inorganic materials with ultrathin fi lms or nanowires (NWs) can exhibit good mechanical fl exibility. Therefore, ultrathin fi lm or NW inorganic piezoelectric materials have also been extensively investigated for fl exible and stretchable pressure-sensing devices.…”

Wearable high-performance pressure sensors based on three-dimensional electrospun conductive nanofibers

“…Three-dimensional (3D) structured conductive polymeric materials are promising for achieving highly flexible pressure sensors. In the last few years, various structures and materials have been developed to fabricate ultrasensitive pressure sensors that can effectively collect pressure stimuli in the low-pressure regime (<10 kPa) [11][12][13][14][15][16] . However, several obstacles limit the practical application of such sensors.…”