Controllable Graphene Wrinkle for a High-Performance Flexible Pressure Sensor

Abstract

Flexible pressure sensors have aroused tremendous attention, owing to their broad applications in healthcare, robotics, and prosthetics. So far, it remains a critical challenge to develop low-cost and controllable microstructures for flexible pressure sensors. Herein, a high-sensitivity and low-cost flexible piezoresistive sensor was developed by combining a controllable graphene-nanowalls (GNWs) wrinkle and a polydimethylsiloxane (PDMS) elastomer. For the GNWs–PDMS bilayer, the vertically grown GNWs film can effectively improve the interface strength and form delamination-free conformal wrinkles. More importantly, a controllable microstructure can be easily tuned through the thermal wrinkling method. The wrinkled graphene-nanowalls (WG) piezoresistive sensor has a high sensitivity (S = 59.0 kPa–1 for the 0–2 kPa region and S = 4.8 kPa–1 for the 2–20 kPa region), a fast response speed (<6.9 ms), and a low limit of detection (LOD) of 2 mg (∼0.2 Pa). The finite element method was used to analyze the working mechanism of the sensor, which revealed that the periods of the wrinkles play a dominant role in the performances of the sensors. These prominent merits enable wrinkled graphene sensors to successfully detect various signals from a weak stimulus to large pressures, for example, the detection of weak gas and plantar pressure. Furthermore, object manipulation, tactile imaging, and braille recognition applications have been demonstrated, showing their great potential in prosthetics limbs and intelligent robotics.

Force-Sensitive Interface Engineering in Flexible Pressure Sensors: A Review

“…By calculating the ratio of the increase in the rate of change of the output electrical signal to the increase in the input pressure, the sensitivity dimension can be unified to kPa −1 , thereby avoiding the difficult comparison between pressure sensors with different sensing principles due to different units. The sensitivity of a flexible piezoresistive sensor can be governed by Equation (3) [ 32 , 39 ]: where I is the current, Δ I is the change in current, and I 0 is the initial current, or Equation (4) [ 32 ]: where R is the resistance, R 0 is the initial resistance, and the sensitivity formula of the flexible capacitive pressure sensor is Equation (5) [ 32 , 40 ]: where C is the capacitance and C 0 is the initial capacitance.…”

“…In order to ensure the flexibility of the flexible pressure sensor, the materials used are all inherently flexible or are made into low-dimensional materials to achieve the purpose of flexibility. The commonly used flexible substrate materials are PDMS [ 13 , 42 , 43 ], PI [ 38 , 44 ], PU [ 45 ], PET [ 39 , 46 ], and other polymer materials. This is due to the fact that these polymer materials have stable performance and long polymer chains making the material tough and strong while ensuring flexibility.…”

“…In addition, Yang et al used a simpler thermally induced wrinkle method ( Figure 2 e), only changing the heating temperature required for the transfer of GNWs to PDMS elastomers to prepare GNWs/PDMS films. Then, the GNWs film and the interdigital electrode are integrated into a flexible pressure sensor with good performance (a high sensitivity: 59.0 kPa −1 ) [ 39 ]. The size of wrinkles prepared by stretching, in situ growth, or heat treatment can be changed by controlling the corresponding parameters, but the structure mode obtained is relatively simple.…”

“…Copyright © 2019, American Chemical Society. Copyright © 2018 WILEY-VCH Verlag GmbH & Co., KGaA, Weinheim), disorder, [ 38 , 39 , 82 , 91 ] (Copyright © 2020, the author(s). Copyright © 2021, American Chemical Society.…”

Microdome-Tunable Graphene/Carbon Nanotubes Pressure Sensors Based on Polystyrene Array for Wearable Electronics

“…On the other hand, the microstructure of resistive pressure sensors is critical in improving the sensitivity [ 3 , 17 ]. Among sensing materials, graphene/CNTs exhibit some special advantages, including high electrical conductivity, inherent and structural flexibility, chemical and thermal stability [ 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ]. These materials demonstrate outstanding mechanical and electrical characteristics, which make them viable candidates for wearing strain/pressure sensors.…”