Graphene Based Low Voltage Field Effect Transistor Coupled with Biodegradable Piezoelectric Material Based Dynamic Pressure Sensor.

Pressure sensors form the basic building block for realization of an electronic or tactile skin used in prothesis, robotics, and other similar applications. This paper presents a device consisting of biodegradable piezoelectric material based dynamic pressure sensor coupled with a graphene field-effect-transistor (GFET) operated at very low voltage (50 mV). The device has a biodegradable ß-glycine/chitosan composite based metal-insulator-metal (MIM) structure connected with GFET in an extended gate configuration. The developed device shows a sensitivity of 2.70 × 10-4 kPa-1 for a pressure range of 5-20 kPa and 7.56 × 10-4 kPa-1 for a pressure range between 20 and 35 kPa. A distinctive feature of the presented device is its very low operation voltage, which offers a significant advantage toward the development of energy efficient large-area electronic skin. Further, the biodegradability of piezoelectric material makes the presented sensors useful in terms of reduced electronic waste, which is currently another growing area of interest.

A Wearable Supercapacitor Based on Conductive PEDOT:PSS-Coated Cloth and a Sweat Electrolyte.

A sweat-based flexible supercapacitor (SC) for self-powered smart textiles and wearable systems is presented. The developed SC uses sweat as the electrolyte and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the active electrode. With PEDOT:PSS coated onto cellulose/polyester cloth, the SC shows specific capacitance of 8.94 F g-1 (10 mF cm-2 ) at 1 mV s-1 . With artificial sweat, the energy and power densities of the SC are 1.36 Wh kg-1 and 329.70 W kg-1 , respectively for 1.31 V and its specific capacitance is 5.65 F g-1 . With real human sweat the observed energy and power densities are 0.25 Wh kg-1 , and 30.62 W kg-1 , respectively. The SC performance is evaluated with different volumes of sweat (20, 50, and 100 µL), bending radii (10, 15, 20 mm), charging/discharging stability (4000 cycles), and washability. With successful on-body testing, the first demonstration of the suitability of a sweat-based SC for self-powered cloth-based sensors to monitor sweat salinity is presented. With attractive performance and the use of body fluids, the presented approach is a safe and sustainable route to meet the power requirements in wearable systems.

van der Waals Contact Engineering of Graphene Field-Effect Transistors for Large-Area Flexible Electronics.

Graphene has great potential for high-performance flexible electronics. Although studied for more than a decade, contacting graphene efficiently, especially for large-area, flexible electronics, is still a challenge. Here, by engineering the graphene-metal van der Waals (vdW) contact, we demonstrate that ultralow contact resistance is achievable via a bottom-contact strategy incorporating a simple transfer process without any harsh thermal treatment (>150 °C). The majority of the fabricated devices show contact resistances below 200 Ω·µm with values as low as 65 Ω·µm achievable. This is on par with the state-of-the-art top- and edge-contacted graphene field-effect transistors. Further, our study reveals that these contacts, despite the presumed weak nature of the vdW interaction, are stable under various bending conditions, thus guaranteeing compatibility with flexible electronics with improved performance. This work illustrates the potential of the previously underestimated vdW contact approach for large-area flexible electronics.

Textile-Based Potentiometric Electrochemical pH Sensor for Wearable Applications.

In this work, we present a potentiometric pH sensor on textile substrate for wearable applications. The sensitive (thick film graphite composite) and reference electrodes (Ag/AgCl) are printed on cellulose-polyester blend cloth. An excellent adhesion between printed electrodes allow the textile-based sensor to be washed with a reliable pH response. The developed textile-based pH sensor works on the basis of electrochemical reaction, as observed through the potentiometric, cyclic voltammetry (100 mV/s) and electrochemical impedance spectroscopic (10 mHz to 1 MHz) analysis. The electrochemical double layer formation and the ionic exchanges of the sensitive electrode-pH solution interaction are observed through the electrochemical impedance spectroscopic analysis. Potentiometric analysis reveals that the fabricated textile-based sensor exhibits a sensitivity (slope factor) of 4 mV/pH with a response time of 5 s in the pH range 6⁻9. The presented sensor shows stable response with a potential of 47 ± 2 mV for long time (2000 s) even after it was washed in tap water. These results indicate that the sensor can be used for wearable applications.