Fabrication Of Pressure Sensor Research Articles

Advancing the pressure sensing performance of conductive CNT/PDMS composite film by constructing a hierarchical-structured surface

Flexible pressure sensors have attracted wide attention due to their applications to electronic skin, health monitoring, and human-machine interaction. However, the tradeoff between their high sensitivity and wide response range remains a challenge. Inspired by human skin, we select commercial silicon carbide sandpaper as a template to fabricate carbon nanotube (CNT)/polydimethylsiloxane (PDMS) composite film with a hierarchical structured surface (h-CNT/PDMS) through solution blending and blade coating and then assemble the h-CNT/PDMS composite film with interdigitated electrodes and polyurethane (PU) scotch tape to obtain an h-CNT/PDMS-based flexible pressure sensor. Based on in-situ optical images and finite element analysis, the significant compressive contact effect between the hierarchical structured surface of h-CNT/PDMS and the interdigitated electrode leads to enhanced pressure sensitivity and a wider response range (0.1661 ​kPa−1, 0.4574 ​kPa−1 and 0.0989 ​kPa−1 in the pressure range of 0–18 ​kPa, 18–133 ​kPa and 133–300 ​kPa) compared with planar CNT/PDMS composite film (0.0066 ​kPa−1 in the pressure range of 0–240 ​kPa). The prepared pressure sensor displays rapid response/recovery time, excellent stability, durability, and stable response to different loading modes (bending and torsion). In addition, our pressure sensor can be utilized to accurately monitor and discriminate various stimuli ranging from human motions to pressure magnitude and spatial distribution. This study supplies important guidance for the fabrication of flexible pressure sensors with superior sensing performance in next-generation wearable electronic devices.

Vapor-Phase Polymerization of PEDOT for Wearable Fabric Pressure Sensors

Vapor-Phase Polymerization of PEDOT for Wearable Fabric Pressure Sensors

A carbon nanotube-based textile pressure sensor with high-temperature resistance.

Textile pressure sensors capable of withstanding high temperatures have attracted increasing interest due to their potential applications in harsh conditions. In this work, a textile pressure sensor with high-temperature resistance was realized based on multi-wall carbon nanotubes (MWCNTs) and quartz fabrics. The textile pressure sensors exhibited low fatigue over 20 000 cyclic loadings. Owing to the high-temperature resistance of MWCNTs and quartz fabrics, the textile sensor can work at temperatures up to 300 °C and can maintain good sensitivity after calcination at 900 °C in N2 for 30 min. This work provides a simple, facile, and inexpensive method for fabricating textile pressure sensors with high-temperature resistance.

Design and fabrication of a novel on-chip pressure sensor for microchannels

Design and fabrication of a novel on-chip pressure sensor for microchannels

Design and fabrication of a novel on-chip pressure sensor for microchannels.

Pressure is important in virtually all problems in fluid dynamics from macro-scale to micro/nano-scale flows. Although technologies are well developed for its measurement at the macroscopic scale, pressure quantification at the microscopic scale is still not trivial. This study reports the design and fabrication of an on-chip sensor that enables quantification of pressure in microfluidic devices based on a novel technique called astigmatic particle tracking. With this technique, thin membranes that sense pressure variations in the fluid flow can be characterized conveniently by imaging the shapes of the particles embedded in the membranes. This innovative design only relies on the reflected light from the back of the microchannel, rendering the sensor to be separate and noninvasive to the flow of interest. This sensor was then applied to characterize the pressure drop in single-phase flows with an accuracy of ∼70 Pa and good agreement was achieved between the sensor, a commercial pressure transducer and numerical simulation results. Additionally, the sensor successfully measured the capillary pressure across an air-water interface with a 7% deviation from the theoretical value. To the best of our knowledge, this pore-scale capillary pressure quantification is achieved for the first time using an on-chip pressure sensor of this kind. This study provides a novel method for in situ quantification of local pressure and thus opens the door to a renewed understanding of pore-scale physics of local pressure in multi-phase flow in porous media.

A High-Performance Textile Pressure Sensor Based on Carbon Black/Carbon Nanotube-Polyurethane Coated Fabrics with Porous Structure for Monitoring Human Motion

A High-Performance Textile Pressure Sensor Based on Carbon Black/Carbon Nanotube-Polyurethane Coated Fabrics with Porous Structure for Monitoring Human Motion

Track-Etch Membranes as Tools for Template Synthesis of Highly Sensitive Pressure Sensors.

Flexible pressure sensors with high sensitivity are highly desired in wearable electronics and human-machine interaction. Introducing the surface microstructures to the capacitive-type sensors can improve sensitivity and reduce response time. However, conventional techniques for the fabrication of highly sensitive and large-area pressure sensors still remain challenging. Here, a template synthesis approach is reported for fabrication of a large-area and low-cost ionic micropillar array templated from track-etch membranes. The pressure sensors based on the ionic micropillars gel dielectric layers exhibit a low limit of detection (∼0.5 Pa) and high sensitivity (14.83 kPa-1) in the low-pressure regime (0-5 kPa) and linear sensitivity (1.96 kPa-1) over a wide pressure range of 24-230 kPa. The versatility of the sensors is demonstrated in various human physiological signal detection scenarios and spatial pressure distribution. Furthermore, a real-time pressure mapping insole was fabricated on the basis of a large-area micropillared ionic gel dielectric layer combined with the screen-printing technique. The scalable and low-cost fabrication of pressure sensors with micropillars templated from a track-etch membrane provides new insights into the future development of health monitoring and human-machine interaction.

Inkjet-Printed, Nanofiber-Based Soft Capacitive Pressure Sensors for Tactile Sensing

The development of soft electronics is critical to the realization of artificial intelligence that comes into direct contact with humans, such as wearable devices, and robotics. Furthermore, rapid prototyping and inexpensive processes are essential for the development of these applications. We demonstrate here an additive, low-cost method for fabricating polydimethylsiloxane based soft electronics by inkjet printing. Herein, a novel approach using a water-soluble polyvinyl alcohol layer as the substrate, inexpensive, fully digital fabrication of capacitive pressure sensors is enabled by sandwiching mesh-like conductive layers and microstructured dielectric in a straightforward, convenient manner. These sensors exhibit improved sensitivity (4 MPa^−1) at low pressures (< 1 kPa) in contrast to sensors with a flat elastomer dielectric and can still detect large pressures around 50 kPa, having excellent long-term repeatability over 2000 cycles, without significant hysteresis (≤ 8.5 %). The tactile sensing ability of the fabricated devices was demonstrated in a practical application. Moreover, sensor characteristics are easily adjustable, simply by changing printing parameters or tuning the ink solution. The proposed approach provides scalable solution for fabricating high-sensitivity printed sensors for e-skin and human-machine interfaces.

A new strategy for the fabrication of a flexible and highly sensitive capacitive pressure sensor

The development of flexible capacitive pressure sensors has wide application prospects in the fields of electronic skin and intelligent wearable electronic devices, but it is still a great challenge to fabricate capacitive sensors with high sensitivity. Few reports have considered the use of interdigital electrode structures to improve the sensitivity of capacitive pressure sensors. In this work, a new strategy for the fabrication of a high-performance capacitive flexible pressure sensor based on MXene/polyvinylpyrrolidone (PVP) by an interdigital electrode is reported. By increasing the number of interdigital electrodes and selecting the appropriate dielectric layer, the sensitivity of the capacitive sensor can be improved. The capacitive sensor based on MXene/PVP here has a high sensitivity (~1.25 kPa−1), low detection limit (~0.6 Pa), wide sensing range (up to 294 kPa), fast response and recovery times (~30/15 ms) and mechanical stability of 10000 cycles. The presented sensor here can be used for various pressure detection applications, such as finger pressing, wrist pulse measuring, breathing, swallowing and speech recognition. This work provides a new method of using interdigital electrodes to fabricate a highly sensitive capacitive sensor with very promising application prospects in flexible sensors and wearable electronics.

A waterproof and breathable textile pressure sensor with high sensitivity based on PVDF/ZnO hierarchical structure

Smart wearable devices based on piezoelectric effect are widely used, but it is a great challenge to ensure the breathability and waterproof of piezoelectric devices. Therefore, we use conductive fabric (CF) as electrode material. ZnO nanorods (NRs) were grown on one side of one CF, and electrospun PVDF nanofiber membrane was sandwiched between the CF with ZnO NRs and the other CF. Attributed to this structure, the pressure sensor has waterproof property and maintains good breathability. Furthermore, the sensor with the ZnO NRs/PVDF hierarchical structure piezoelectric layer can generate an output voltage of 1.60 ± 0.08 V at 150 kPa, which is more than 10 times higher than that of pure PVDF nanofiber membrane, and has a sensitive linear response in the wide range of 3–150 kPa (11.07 mV kPa−1). Moreover, after the sensor had experienced 3600 cycles of pressing, the output voltage basically remained unchanged. In addition, sliding on the sensor at a certain pressure can produce regular fluctuating signals, and the FEM is used to explain the principle of this process. Benefiting from the unique properties, the sensor can be installed on clothes to monitor the environment in real time like wind or rainfall.

Fabrication and Performance of Graphene Flexible Pressure Sensor with Micro/Nano Structure.

Laser-induced graphene (LIG) has been widely used in flexible sensors due to its excellent mechanical properties and high conductivity. In this paper, a flexible pressure sensor prepared by bionic micro/nanostructure design and LIG mass fraction regulation is reported. First, prepared LIG and conductive carbon paste (CCP) solutions were mixed to obtain a conductive polymer. After the taro leaf structure was etched on the surface of the aluminum alloy plate by Nd:YAG laser processing, the conductive polymer was evenly coated on the template. Pressure sensors were packaged with a stencil transfer printing combined with an Ecoflex flexible substrate. Finally, the effects of different laser flux and the proportion of LIG in the composite on the sensitivity of the sensor are discussed. The results show that when the laser flux is 71.66 J·cm−2 and the mass fraction of LIG is 5%, the sensor has the best response characteristics, with a response time and a recovery time of 86 ms and 101 ms, respectively, with a sensitivity of 1.2 kPa−1 over a pressure range of 0–6 kPa, and stability of 650 cycle tests. The LIG/CCP sensor with a bionic structure demonstrates its potential in wearable devices.

Conductive and room-temperature self-healable polydimethylsiloxane-based elastomer film with ridge-like microstructure for piezoresistive pressure sensor

The fabrication of piezoresistive pressure sensor with self-healing function has attracted worldwide attention for its great prospects in intelligent robots, remote health monitoring and electronic skin. In this work, a conductive and self-healable elastomer (CSE) film with ridge-like microstructure was designed for flexible piezoresistive pressure sensor. Firstly, self-healable polydimethylsiloxane (PDMS)-based elastomer with ureido and imine groups was synthesized via a simple one-pot two-step polycondensation reaction with aminopropyl-terminated PDMS, isophorone diisocyanate and 1, 3, 5-triformylbenzene as monomers. Secondly, the synthesized PDMS-based elastomer solution was casted onto a sandpaper pre-sprayed with ureido pyrimidinone grafted carbon nanotubes/polyurea mixed solution, and the CSE film was obtained after drying and peeling off from the sandpaper. The piezoresistive pressure sensor fabricated with two single-electrode CSE films exhibited high sensitivity of 8.7 kPa−1 (0–6.1 kPa), low detection limit (50 Pa), fast response capability (response/relaxation time of 40/117 ms) and repeatability for 10,000 loading–unloading tests. Moreover, the sensor was able to fully recover to normal work after healing for 36 h at room temperature or even 200 s under the irradiation of near infrared (NIR) light. Importantly, the sensor was successfully applied for not only detecting human motions including radial pulse, speech recognitions and joint movements but also monitoring health status wirelessly through Bluetooth transmission. Our findings put forward a novel method to fabricate a high-performance self-healable piezoresistive sensor for wearable electronics, healthcare monitoring and electronic skin.

Fabrication and characterization of piezoresistive flexible pressure sensors based on poly(vinylidene fluoride)/thermoplastic polyurethane filled with carbon black‐polypyrrole

AbstractElectrically conductive composites of thermoplastic polyurethane (TPU), poly(vinylidene fluoride) (PVDF), and carbon black‐polypyrrole (CB‐PPy) were prepared by melt compounding followed by compression molding or by filament production followed by fused filament fabrication (FFF). The storage modulus (G′) and complex viscosity (η*) of the composites increased with the addition of CB‐PPy leading to a more rigid material. The electrical and rheological percolation threshold of composites were 5 and 3 wt%, respectively. In fact, composites with 5 wt% or more CB‐PPy content display G′ higher than G″ indicating a solid‐like behavior. Furthermore, the addition of CB‐PPy increased the electrical conductivity of all composites. However, the electrical conductivity values of composites containing 5 and 6 wt% of CB‐PPy produced by compression molding are one and seven order of magnitude higher than those of FFF composites with same composition. Compression molded and 3D printed composites with 6 wt% of CB‐PPy displayed high sensitivity/gauge factor, large measurement range and reproducible piezoresistive response during 100 loading‐unloading cycles for both processing methods. The results presented in this study demonstrated the potential use of FFF for producing piezoresistive flexible sensors based on PVDF/TPU/CB‐PPy composites.

Local metal segregation as root cause for electrical shorts in highly doped pressure sensor devices

The fabrication of pressure sensor dies for precise and stable industrial applications requires a critical high dose implantation process strongly affecting the manufacturing yield of these devices. This paper describes a specific critical process related failure mechanism caused by this implantation process generating local electrical shorts within the piezo resistive structures in-built in the doped silicon substrate surface. The defect signature was investigated by applying site specific localization, advanced target preparation strategy and high-resolution electron microscopy to understand its process related root cause. The electrical shorts could be localized by Lock-in Thermography (LIT) and then were prepared by advanced laser and focused ion beam (FIB) based preparation in both cross-section and plan-view direction for in-depth investigation of the crystal defect signature by high resolution transmission electron microscopy (TEM) analysis in combination with energy dispersive X-ray spectroscopy (EDXS). As a result, the defect mechanism could be identified as segregation of embedded metal residues caused by Fe and Ni contamination from the high dose implantation equipment.

Effects of Ag-coated twisted-yarns and equivalent circuits on textile pressure sensors

Wearable sensors have become an indispensable part of life because they reflect different aspects of human interactions and surroundings. However, the complex technologies, materials, and structures still limit their applicability. Herein, we propose an adjustable pressure sensor by designing the structure of the e-textiles. Through the tilt of the conductive yarns on the spacer fabrics, the resistance behavior can be analyzed by an equivalent circuit. These sensors show high sensitivity (gauge factor ~ 16.7) under slight pressure. In addition, the effects of conductive yarns (Ag-coated twisted yarns) are evaluated in detail based on the difference of spacer fabrics, the sensing yarns, the buckling of the conductive spun yarns, as well as the conductive twisted yarns. The technique and the analyzing method from the equivalent circuits are expected to bring great contributions to analyze the wearable pressure-touch sensors in the future.

Design, fabrication and performance of flexible pressure sensors based on microstructures

With the rapid development of science and technology, electronic skin and flexible wearable devices have attracted wide attention because of their important applications in human motion, health monitoring, intelligent robots and other fields. The traditional pressure sensors based on noble metal or metal oxide semiconductor have high cost or poor flexibility, while the flexible pressure sensors based on microstructures have the advantages of high sensitivity, wide strain range, low cost, low power consumption and fast response, which play an important role in electronic skin and flexible wearable devices and have become one of the main research hotspots of materials and devices in flexible electronics. This review systematically summarizes the important progress made in the material selection, structural design, preparation methods and sensing performance of flexible pressure sensors based on different flexible substrate microstructures such as pyramid, microsphere, micro-column, bionic structure and fold and porous conductive polymer materials. Finally, the future development of flexible pressure sensors is prospected.

Anodically bondable Low Temperature Co-Fired Ceramic (LTCC) based Fabry-Pérot Interferometer (FPI) pressure sensor design

In this study, effect of anodic bonding temperature on the sensitivity, frequency response, Q factor and frequency bandwidth of Fabry–Pérot Interferometer (FPI) pressure sensor was studied by considering anodically bonded low temperature cofired ceramic (LTCC)-Si substrates. Using LTCC subsrate rather than glass for FPI pressure sensor fabrication makes this study different from the available studies in the literature. Four sensors design were studied under different bonding temperature between the 320 °C − 520 °C. Thickness of Si diaphragms were 5 μm, 10 μm, 15 μm and 20 μm with the radius of 300 μm, 400 μm, 500 μm, 600 μm, 700 μm, respectively. It was found that the sensitivity, frequency response and Q factors were influced by anodic bonding temperature induced stress on Si diaphragms although frequency bandwidth is not correlated with the bonding temperature induced stress. In this study, it was concluded that anodic bonding temperature is a useful parameter for tuning the sensitivity, frequency response and Q factor of micro electro-mechanical system (MEMS) based FPI pressure sensor.

Deep Eutectic Solvent Induced Porous Conductive Composite for Fully Printed Piezoresistive Pressure Sensor

AbstractManufacturing flexible pressure sensor using scalable and straightforward process is highly desired for next‐generation wearable electronics and intelligent robots. Here, a fully printed pressure sensor is proposed using a newly developed porous conductive composite. The composite ink is prepared by simply mixing the polydimethylsiloxane (PDMS), carbon black (CB), and a deep eutectic solvent (DES). The DES induces phase segregation between the PDMS and CB and serves as a liquid template to form the porous structure during the annealing process. This spontaneously formed conductive architecture that has not been previously reported in a printable ink endows superior electrical–mechanical performance to the composites, and significantly simplifies the device fabrication of flexible pressure sensors. The developed pressure sensors exhibit comprehensive performance capabilities appropriate for the wearable device, human–machine interfaces, and robot tactile.

Highly sensitive and flexible pressure sensors using position- and dimension-controlled ZnO nanotube arrays grown on graphene films

A facile and novel technique for the fabrication of pressure sensors is reported based on the hybridization of one-dimensional nanomaterials and two-dimensional graphene film. In particular, piezoelectric pressure sensors are fabricated by using vertically aligned and position- and dimension-controlled ZnO nanotube arrays grown on graphene layers. Graphene layers act not only as substrates for catalyst-free growth of high-quality ZnO nanotubes but also as flexible conduction channels connecting ZnO nanotubes and metal electrodes. Freestanding and flexible sensors have been efficiently obtained via mechanical lift-off of hybrid ZnO nanotube/graphene film structures and by exploiting the weak van der Waals forces existing between the graphene film and the original substrates. A prototype of such devices shows a high pressure sensitivity (−4.4 kPa−1), which would enable the detection of weak flows of inert gas. The relatively low wall thickness and large length of the ZnO nanotubes suggest a relatively high sensitivity to external pressures. The obtained nanotube sensors are attached to the philtrum and wrist of a volunteer and used to monitor his breath and heart rate. Overall, the prototype hybrid sensing device has great potential as wearable technology, especially in the sector of advanced healthcare devices.

3D-printed liquid metal-based stretchable conductors and pressure sensors

Microfluidic devices control fluids on the micrometer-scale and are commonly used for lab-on-chip applications, such as sensors, micropumps and biological analyzers. Commonly reported fabrication methods for achieving flexible microfluidic structures are labor-intensive, require many cumbersome steps, and have limited options for materials. This paper presents a rapid-manufacturing technique using a PolyJet 3D-printer for creating soft microfluidic substrates embedded with liquid metals to fabricate stretchable conductors and pressure sensors. By using this novel method, several spiral-shaped soft pressure sensors with multimaterial-based substrates are 3D-printed simultaneously in less than six minutes. Microfluidic channels with cross-sections ranging from 150 × 150 to 350 × 350 µm are successfully achieved in a soft substrate. This 3D-printing method allows fabrication of complex, enclosed channels without any photocurable support material, thus minimizing post-processing time. Simulation and experiments are conducted to characterize the quasi-static and dynamic properties of the fabricated pressure sensor. In particular, experimental results show that these 3D-printed microfluidic pressure sensors are robust, capable of withstanding high pressures up to 1 MPa.