Sensitive Piezoresistive Pressure Sensor Research Articles

Room-temperature self-healing polysiloxane networks for highly sensitive piezoresistive pressure sensor with microdome structures

Soft piezoresistive pressure sensor is an important component for next generation flexible electronics. Micropatterning of such sensors significantly improves the pressure sensitivity, however, the short device lifetime due to scratches and motions limits the translation to industrial applications. Herein, we report a novel poly(ODMS-co-MAA) for self-healing piezoresistive sensor to effectively overcoming such shortcoming. Self-healing capability was achieved by incorporating dynamic Fe(III)-carboxylate linkages in the polymer networks. These linkages work as sacrificial bonds and dissipate energy caused by mechanical damage. The bonds subsequently reform and functionality of the sensor can be restored. The poly(ODMS-co-MAA)-based self-healing polymer networks (SPN) were effectively healed from damages showing the recovery of electrical resistance (>95%) within 10 hrs. SPN was fabricated with microdome structures and exhibited a superior pressure sensitivity (2 kPa−1) as well as stability compared to planar features (9.13 × 10−3 kPa−1), demonstrating its excellent potential as pressure sensor. Combined results demonstrate the potential of the self-healing networks for next generation piezoresistive pressure sensors.

Mechanical buckling assisted formation of 3D conductive composite meso-structure for highly sensitive piezoresistive pressure sensor

With the advancement of robotics and wearable devices related research fields, enhancing the sensitivity of piezoresistive pressure sensor is the first demand of the related research to sense the subtle stimuli. To improve sensitivity, a material tailoring approach using the nature of different materials and an introduction of novel structures made by processing existing materials have been studied. Such latter mechanical exploration has the unique advantage of obtaining performance beyond the nature of the material. This study introduces a 3D meso-structured piezoresistive pressure sensor, which exhibits remarkably improved sensitivity of 450 times compared with that of a conventional 2D sensor, manufactured through simple mechanical buckling assisted 3D structure formation. The principle of sensitivity improvement is related to the developed tensile strain in the sensor and both numerical and experimental analyses show that the maximum principal strain plays a crucial role as a governing parameter to determine the sensitivity. Classical mechanics-based analyses further show that performances can be easily tuned by adjusting its thickness. The present sensor has excellent durability and reliability (stable over 10,000 operating cycles). Consequently, the use of a highly sensitive sensor with a digital twin application is demonstrated for real-time and virtual stress monitoring in a cantilever.

Sensitive piezoresistive pressure sensor based on micropyramid patterned tough hydrogel

Microstructures are decisive factors of hydrogel-based piezoresistive pressure sensors for excellent performances in flexible electronics. However, the desirable microstructures are still difficult to be completely engineered on the surface of hydrogel, owing to limitations concerning to comprehensive mechanical performances of hydrogels. Herein, we prepared a type of piezoresistive pressure sensor by decorating pyramid microarrays on the surface of a tough and ionically conductive polyacrylamide (PAAm)/poly(vinyl alcohol) (PVA) hydrogel. To achieve high sensing behaviors, sizes and topologies of the recessed pyramid microarrays molded by three-dimensional (3D) printing photosensitive resin were investigated for elaborate fabrication of pyramid microarray hydrogel. The ionically conductive PAAm/PVA hydrogel of excellent comprehensive mechanical performances decorated with pyramid microarrays was able to generate large contact resistance variation to respond to external pressure, achieving a maximum sensitivity to 2.27 kPa−1, low detection limit of 9.0 Pa, as well as good recoverability and stability. Such tough and sensitive device based on micropyramid patterned tough hydrogel have potential applications in the fields of flexible electronics.

Highly Sensitive Piezoresistive Pressure Sensor Based on Super-Elastic 3D Buckling Carbon Nanofibers for Human Physiological Signals' Monitoring.

The three-dimensional (3D) carbon nanostructures/foams are commonly used as active materials for the high-performance flexible piezoresistive sensors due to their superior properties. However, the intrinsic brittleness and poor sensing properties of monolithic carbon material still limits its application. Rational design of the microstructure is an attractive approach to achieve piezoresistive material with superior mechanical and sensing properties, simultaneously. Herein, we introduce novel three-dimensional buckling carbon nanofibers (3D BCNFs) that feature a unique serpentine-buckling microstructure. The obtained 3D BCNFs exhibit superior mechanical properties, including super-elasticity (recovery speed up to 950 mm s−1), excellent flexibility (multiple folds), high compressibility (compressed by 90%), and high fatigue resistance (10,000 bending cycles). The pressure sensor fabricated by the 3D BCNFs shows a high sensitivity of 714.4 kPa−1, a fast response time of 23 ms, and a broad measuring range of 120 kPa. The pressure sensor is further applied to monitor the physiological signals of humans, and is capable of detecting the characteristic pulse waves from the radial artery, fingertip artery, and human-breath, respectively.

Design Rules for a Wearable Micro-Fabricated Piezo-Resistive Pressure Sensor.

Wearable flexible piezo-resistive pressure sensors hold a wide-ranging potential in human health monitoring, electronic skin, robotic limbs, and other human–machine interfaces. Out of the most successful recent efforts for arterial pulse monitoring are sensors with micro-patterned conductive elastomers. However, a low-current output signal (typically in the range of nano-amperes) and bulky and expensive measurement equipment for useful signal acquisition inhibits their wearability. Herein, through a finite element analysis we establish the design rules for a highly sensitive piezo-resistive pressure sensor with an output that is high enough to be detectable by simple and inexpensive circuits and therefore ensure wearability. We also show that, out of four frequently reported micro-feature shapes in micro-patterned piezo-resistive sensors, the micro-dome and micro-pyramid yield the highest sensitivity. Furthermore, investigations of different conductivity values of micro-patterned elastomers found that coating the elastomer with a conductive material (usually metallic) leads to higher current response when compared to composited conductive elastomers. Finally, the geometric parameters and spatial configurations of micro-pyramid design of piezo-resistive sensors were optimized. The results show that an enhanced sensitivity and higher current output is achieved by the lower spatial density configuration of three micro-features per millimeter length, a smaller feature size of around 100 μm, and a 60–50 degrees pyramid angle.

Highly Sensitive Piezoresistive Pressure Sensor Based on Micropyramid Patterned Tough Hydrogel

Highly Sensitive Piezoresistive Pressure Sensor Based on Micropyramid Patterned Tough Hydrogel

Highly sensitive piezoresistive pressure sensors based on laser-induced graphene with molybdenum disulfide nanoparticles

Wearable pressure sensors have drawn significant attention because of their extensive applications in motion detection, tactile sensing, and health monitoring. However, the complex manufacturing process and high cost of active materials make low-cost, large-scale production elusive. In this work, we report a flexible piezoresistive pressure sensor assembled with two 3D laser-induced graphene (LIG) foam electrodes on a polyimide thin film from a simple laser scribing process in the ambient environment. The design of the air gap between the two foam electrodes allows the sensor to showcase a low limit of detection of 0.274 Pa, which provides favorable sensing performance in motion detection and wrist pulse monitoring. The addition of spherical MoS2 nanoparticles between the two foam electrodes further enhances the sensitivity to 88 kPa−1 and increases the sensing range to significantly outperform the previous literature reports. The demonstrated LIG pressure sensors also exhibit fast response/recovery rates and excellent durability/repeatability.

Solvodynamically Printed Silver Nanowire/Ethylene-co-vinyl Acetate Composite Films as Sensitive Piezoresistive Pressure Sensors

Pressure sensing is an important aspect of many processes and has a wide range of applications such as robotics and health monitoring. With the shift toward flexible and wearable technology, it is essential to develop high-performance flexible pressure sensors. In this study, we use solvodynamic printing to fabricate highly conductive piezoresistive composite films consisting of silver nanowires embedded in an ethylene-co-vinyl acetate matrix. The performance of the pressure sensor is tunable based on the composition and patterning of the film. The films can operate under a low input voltage (∼0.1 mV) with power consumption of <5 nW and show a low detection limit (12.9 ± 0.37 Pa), fast response time (11–22 ± 2.9 ms), and high sensitivity (67.3 ± 5.9 kPa–1) in the low-pressure regime, which is on par with commercially available pressure sensors. We further demonstrate the successful application of the film as a pulse-monitoring device.

Binary Spiky/Spherical Nanoparticle Films with Hierarchical Micro/Nanostructures for High-Performance Flexible Pressure Sensors.

Flexible pressure sensors have been widely explored for their versatile applications in electronic skins, wearable healthcare monitoring devices, and robotics. However, fabrication of sensors with characteristics such as high sensitivity, linearity, and simple fabrication process remains a challenge. Therefore, we propose herein a highly flexible and sensitive pressure sensor based on a conductive binary spiky/spherical nanoparticle film that can be fabricated by a simple spray-coating method. The sea-urchin-shaped spiky nanoparticles are based on the core-shell structures of spherical silica nanoparticles decorated with conductive polyaniline spiky shells. The simple spray coating of binary spiky/spherical nanoparticles enables the formation of uniform conductive nanoparticle-based films with hierarchical nano/microstructures. The two differently shaped particles-based films (namely sea-urchin-shaped and spherical) when interlocked face-to-face to form a bilayer structure can be used as a highly sensitive piezoresistive pressure sensor. Our optimized pressure sensor exhibits high sensitivity (17.5 kPa-1) and linear responsivity over a wide pressure range (0.008-120 kPa), owing to the effects of stress concentration and gradual deformation of the hierarchical microporous structures with sharp nanoscale tips. Moreover, the sensor exhibits high durability over 6000 repeated cycles and practical applicability in wearable devices that can be used for healthcare monitoring and subtle airflow detection (1 L/min).

Piezoresistive Pressure Sensors: Synergistic Resistance Modulation toward Ultrahighly Sensitive Piezoresistive Pressure Sensors (Adv. Mater. Technol. 4/2020)

Piezoresistive Pressure Sensors: Synergistic Resistance Modulation toward Ultrahighly Sensitive Piezoresistive Pressure Sensors (Adv. Mater. Technol. 4/2020)

Hydrophobic and Stable MXene-Polymer Pressure Sensors for Wearable Electronics.

Ti3C2Tx MXene has exhibited great potential for use in wearable devices, especially as pressure sensors, due to its lamellar structure, which changes its resistance as a function of interlayer distance. Despite the good performance of the reported pure MXene pressure sensors, their practical applications are limited by moderate flexibility, excessively high MXene conductivity, and environmental effects. To address the above challenges, we incorporated multilayer MXene particles into hydrophobic poly(vinylidene fluoride) trifluoroethylene (P(VDF-TrFE)) and prepared freestanding, flexible, and stable films via spin-coating. These films were assembled into highly sensitive piezoresistive pressure sensors, which show a fast response time of 16 ms in addition to excellent long-term stability with no obvious responsivity attenuation when the sensor is exposed to air, even after 20 weeks. Moreover, the fabricated sensors could monitor human physiological signals such as knee bending and cheek bulging and could be used for speech recognition. The mapping spatial pressure distribution function was also demonstrated by the designed 10 × 10 integrated pressure sensor array platform.

Synergistic Resistance Modulation toward Ultrahighly Sensitive Piezoresistive Pressure Sensors

AbstractImprovement of sensitivity of electrical piezoresistive sensors is critical for high‐precision and ultrasensitive detection, which mainly depends on the modulation ability of total resistance of sensor under applied pressure. However, in most of the reported sensor devices, the contact resistance and body resistance (the key parts of total resistance of sensor) generally cannot be modulated simultaneously, which results in the limited sensitivity. In this work, an ultrahighly sensitive piezoresistive pressure sensor with an exquisitely designed structure is demonstrated, providing an uncomparable advantage of synergistic modulation of contact resistance and body resistance under applied pressure. As a result, the sensor shows excellent sensing performance, with the highest sensitivity up to 11 668.6 kPa−1, the detection limit as low as 0.425 Pa, and the great stability over 20 000 cycle measurements. In respect of practical application, the high sensitivity endows the sensor with high‐precision recognition ability for detecting the weak pressure signals such as sound wave of ringtone and fluctuation of breath or pulse. These results suggest the synergistic resistance modulation to be an effective method toward piezoresistive pressure sensors with ultrahigh sensitivity and offer a new strategy for the achievement of high‐performance pressure sensors.

A Highly Sensitive Piezoresistive Pressure Sensor Based on Graphene Oxide/Polypyrrole@Polyurethane Sponge.

In this work, polyurethane sponge is employed as the structural substrate of the sensor. Graphene oxide (GO) and polypyrrole (PPy) are alternately coated on the sponge fiber skeleton by charge layer-by-layer assembly (LBL) to form a multilayer composite conductive layer to prepare the piezoresistive sensors. The 2D GO sheet is helpful for the formation of the GO layers, and separating the PPy layer. The prepared GO/PPy@PU (polyurethane) conductive sponges still had high compressibility. The unique fragmental microstructure and synergistic effect made the sensor reach a high sensitivity of 0.79 kPa−1. The sensor could detect as low as 75 Pa, exhibited response time less than 70 ms and reproducibility over 10,000 cycles, and could be used for different types of motion detection. This work opens up new opportunities for high-performance piezoresistive sensors and other electronic devices for GO/PPy composites.

Compressible AgNWs/Ti3C2Tx MXene aerogel-based highly sensitive piezoresistive pressure sensor as versatile electronic skins

AgNWs/Ti3C2Tx MXene aerogel with well-aligned layer structure was prepared by a directional freezing strategy, and applied to fabricate piezoresistive pressure sensor, which has ultrahigh sensitivity (645.69 kPa−1) and low detection limit (1.25 Pa).

Flexible and Highly Sensitive Piezoresistive Pressure Sensor with Sandpaper as a Mold

Flexible pressure sensors based on piezoresistive induction have recently become a research hotspot due to the simple device structure, low energy consumption, easy readout mechanism and excellent performance. For practical applications, flexible pressure sensors with both high sensitivity and low-cost mass production are highly desirable. Herein, this paper presents a high-sensitivity piezoresistive pressure sensor based on a micro-structured elastic electrode, which is low cost and can be mass-produced by a simple method of sandpaper molding. The micro-structure of the electrode surface under external pressure causes a change in the effective contact area and the distance between the electrodes, which exhibits great pressure sensitivity. The test results show that the surface structure is twice as sensitive as the planar structure under low pressure conditions. This is because of the special morphology of silver nanowires (AgNWs), which exhibits the tip of nanostructures on the surface and realizes the quantum tunneling mechanism. The sensor has high sensitivity for transmitting signals in real time and it can also be used to detect various contact actions. The low cost mass production and high sensitivity of flexible pressure sensors pave the way for electronic skin, wearable healthcare monitors and contact inspection applications.

P‐138: A High Sensitive Resistive Pressure Sensor with NH4HCO3‐induced Porous Structure Active Layer

A facile approach to achieve high sensitive piezoresistive pressure sensor is proposed. By introducing NH4HCO3 to produce porous structures in the PSR‐layer (Pressure sensor rubber), sensor shows high flexibility and elasticity. The resistance increases with external stress. Sensitivity reaches 0.8kPa‐1 under the pressure of 0–25kPa, with high linearity and stability.

A Flexible and Highly Sensitive Pressure Sensor Based on a PDMS Foam Coated with Graphene Nanoplatelets.

The demand for high performance multifunctional wearable devices is more and more pushing towards the development of novel low-cost, soft and flexible sensors with high sensitivity. In the present work, we describe the fabrication process and the properties of new polydimethylsiloxane (PDMS) foams loaded with multilayer graphene nanoplatelets (MLGs) for application as high sensitive piezoresistive pressure sensors. The effective DC conductivity of the produced foams is measured as a function of MLG loading. The piezoresistive response of the MLG-PDMS foam-based sensor at different strain rates is assessed through quasi-static pressure tests. The results of the experimental investigations demonstrated that sensor loaded with 0.96 wt.% of MLGs is characterized by a highly repeatable pressure-dependent conductance after a few stabilization cycles and it is suitable for detecting compressive stresses as low as 10 kPa, with a sensitivity of 0.23 kPa−1, corresponding to an applied pressure of 70 kPa. Moreover, it is estimated that the sensor is able to detect pressure variations of ~1 Pa. Therefore, the new graphene-PDMS composite foam is a lightweight cost-effective material, suitable for sensing applications in the subtle or low and medium pressure ranges.

A Flexible and Highly Sensitive Piezoresistive Pressure Sensor Based on Micropatterned Films Coated with Carbon Nanotubes

Excellent flexibility, high sensitivity, and low consumption are essential characteristics in flexible microtube pressure sensing occasion, for example, implantable medical devices, industrial pipeline, and microfluidic chip. This paper reports a flexible, highly sensitive, and ultrathin piezoresistive pressure sensor for fluid pressure sensing, whose sensing element is micropatterned films with conductive carbon nanotube layer. The flexible pressure sensor, the thickness of which is 40 ± 10 μm, could be economically fabricated by using biocompatible polydimethylsiloxane (PDMS). Experimental results show that the flexible pressure sensor has high sensitivity (0.047 kPa−1in gas sensing and 5.6 × 10−3 kPa−1in liquid sensing) and low consumption (&lt;180 μW), and the sensor could be used to measure the pressure in curved microtubes.