Ultrasensitive Hierarchical Piezoresistive Pressure Sensor for Wide‐Range Pressure Detection

Abstract

Pressure sensitivity and wide range are two crucial features of flexible electromechanical sensors for applications in the next‐generation of intelligent electronics, such as wearable healthcare monitors and soft human–machine interfaces. Conventional pressure sensors have a narrow pressure range (<10 kPa) and complex fabrication processes, which significantly hinder their extensive applications. A facile laser‐engraving method is proposed to fabricate a flexible multiwalled‐carbon‐nanotube (MWCNTs)/poly(dimethylsiloxane) (PDMS) composite‐based piezoresistive sensor with hierarchical microstructures. Herein, the nonstandard‐circular feature and Gaussian distributed facula of a laser spot are utilized to produce the middle‐level porous microdome upon the bottom‐level cylinder microcolumn array, while the top‐level tentacle‐like conical micropillars are produced by vertically rotating the acrylic mold during the laser engraving process. This novel hierarchical microstructure endows the proposed piezoresistive sensor with orders‐of‐magnitude of higher sensitivity (≈35.51 kPa−1) than that of other reported electromechanical sensors and a more extensive pressure sensing range up to 23 kPa. Moreover, the detection limit of the sensor is down to 2 Pa, which makes it a desirable candidate for monitoring subtle pressure. The sensor is successfully applied to distinguish the syllables of each pronounced word, detect movements of the human wrist, and monitor radial arterial pulse, thus demonstrating its promising applications in wearable electronics.

Flexible Pressure Sensors with Combined Spraying and Self-Diffusion of Carbon Nanotubes

“…As summarized in Figure , most of the research on pressure sensors focus on obtaining high sensitivity under small pressure. ,,,− While some pressure sensors have not achieved high sensitivity and measurement range is relatively small, ,,, very few sensor studies have achieved ultrawide range measurement but did not achieve a high full-scale sensitivity. In this work, the SPC sensor employs a simple process to achieve ultrahigh sensitivity covering an ultrawide range and excellent durability.…”

“…The performance of the piezoresistive pressure sensor directly depends on the action mode of the microstructure of the active layer and the electromechanical properties of the materials used in the active layer. ,, On one hand, a variety of materials including carbon materials (carbon nanotubes, carbon black, graphene), − metal materials (gold nanowires, gold nanoparticles), , conductive polymers (PEDOT:PSS), , and compound materials (MoS 2 , MXene) ,− have been widely utilized as the active layers of sensors. MXene is prone to oxidative failure; its properties are not as stable as carbon nanotubes (CNTs), and the bonding force between metal materials and polymer matrix is difficult to control, which often results in a large change in the elasticity of the polymer matrix.…”

“…Therefore, the difference in the microstructure of the active site of the sensor can largely influence the performance of the sensor, such as sensitivity. At present, the microstructures of the active layer that has been reported include hollow microstructures, microcapsules, snail tentacles, DNA-like double helix, hemispheres, pyramids, ,, bionic fingerprint, microporous, leaf patterns, surface concave–convex, sea-urchin, etc. Among them, the leaf-like layered pressure sensor reported by Jian et al used the natural leaf surface as the mold and the ACNT/G hybrid film as the conductive layer, achieving a high sensitivity of 19.8 kPa –1 , but the measurement range was only 6 kPa.…”

Bioinspired Hierarchical Structure for an Ultrawide‐Range Multifunctional Flexible Sensor Using Porous Expandable Polyethylene/Loofah‐Like Polyurethane Sponge Material

“…Next, to further compare the performance of this double-layer sensor with other reported literature, including those using the sponge-like structure, [52,61,[64][65][66][67] as well as some representative works [60,68,69] with an ultrawide detection range, as shown in Figure 3g, we focused on the maximum sensitivity and the detection range of the sensor, represented by the red bar on the right and the black bar on the left, respectively. For the blue bar (called performance insufficiency) in the figure, the closer it was to the middle, the more balanced the sensor's performance was, while the shorter its length, the more excellent the sensor's comprehensive performance (considering that the sensitivity and detection range of the sensor are equally important).…”

Highly Scalable, Sensitive and Ultraflexible Graphene‐Based Wearable E‐Textiles Sensor for Bio‐Signal Detection

“…[ 17–18 ] However, the sensitivity of the piezoelectric, triboelectric, and capacitive pressure sensors are limited due to their intrinsic disadvantages. [ 19 ] For example, the piezoelectric sensors suffer from a lack of accuracy originating from the intrinsic hysteresis and creep phenomenon of the piezoelectric materials. [ 20 ] The output signals generated from triboelectric sensors can easily be influenced by environmental conditions, such as temperature and humidity.…”