Name: Fabrication of the Capacitive Pressure Sensor
Uploaded: 2023-03-17T14:35:00
Description: Watch this Scientific Journal Video about Fabrication of the Capacitive Pressure Sensor at JoVE.com

The video demonstrates the fabrication process of a capacitive pressure sensor using platinum silicone foam and an interdigitated fringe effect design. It details mixing components, curing in a 3D mold, and the impact of varying ratios on sensitivity. A cyclic test confirms the sensor's durability and repeatability.

fabrication of the capacitive pressure sensor

Microfluidic Channel-Based Soft Electrodes for Capacitive Pressure Sensing

Soft pressure sensors have been widely explored in applications such as pneumatic robotic grippers1, wearable electronics2, human-machine interface systems3, etc. In such applications, the sensory system requires flexibility and stretchability to ensure conformal contact with arbitrary curvilinear surfaces. Therefore, it requires all the essential components, including the substrate, the transducing element, and the electrode, to provide consistent functionality under extreme deformation conditions4. Moreover, to maintain high sensing performance, it is essential to keep the changes in the soft electrodes to the minimum level to avoid interference in the electrical sensing signals5.
As one of the core components in soft pressure sensors, stretchable electrodes capable of sustaining high stress and strain levels are crucial for the device to preserve stable conductive pathways and impedance characteristics6,7. Soft electrodes with excellent performance usually possess 1) high spatial resolution at the micrometer scale and 2) high stretchability with strong bonding to the substrate, and these are indispensable characteristics to enable highly integrated soft electronics in a wearable size8. Therefore, various strategies have been proposed recently to develop soft electrodes with the above properties, such as ink-jet printing, screen printing, spray printing, and transfer printing, etc.9. The ink-jet printing method6&#160;has been widely used due to its advantages of simple fabrication, no masking requirement, and a low amount of material waste, but it is hard to achieve high-resolution patterning due to limitations in terms of the ink viscosity. Screen printing10&#160;and spray printing11&#160;are simple and cost-effective patterning methods that require a shadow mask on the substrate. However, the operation of placing or removing the mask can reduce the clarity of the patterning. Although transfer printing4 has been reported to be a promising way to achieve high-resolution printing, this method suffers from a complicated procedure and a time-consuming printing process. Furthermore, most of the soft electrodes produced by these patterning methods have other disadvantages, such as delamination from the substrate.
Herein, we present a novel printing method for the rapid fabrication of cost-effective and high-resolution soft electrodes based on microfluidic channel configurations. Compared to other conventional fabrication methods, the proposed strategy utilizes elastic conductive polymer composites (ECPCs) as the conductive material and lithographically embossed microfluidic channels to pattern the electrode traces. The ECPCs slurry is prepared by the solvent evaporation method and consists of 7 wt.% carbon nanotubes (CNTs) well-dispersed in a polydimethylsiloxane (PDMS) matrix. By scraping the ECPCs slurry into the microfluidic channel, high-resolution electrodes defined by lithographic patterning can be produced. In addition, since the electrode is mainly based on PDMS, strong bonding is created at the interface between the ECPCs-based electrode and the PDMS substrate. Thus, the electrode can sustain a stretch level as high as the PDMS substrate. The experimental results confirm that the proposed stretchable electrode can respond linearly to axial strains up to 30% and exhibit excellent stability in a high-pressure range of 0-400 kPa, indicating the great potential of this method for fabricating soft electrodes in capacitive pressure sensors, which is also demonstrated in this work.

Author Spotlight: Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing  

Microfluidic Channel-Based Soft Electrodes and Their Application in Capacitive Pressure Sensing

Our research really focuses on flexible and stretchable electronics for sensing applications, while trying to develop innovative materials and manufacturing precisely for flexible electronic systems. Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most electrodes are either restricted by the patterning resolution or the capability of inkjet printing, high-viscosity super-elastic materials.In this protocol, we have demonstrated a novel microfluidic channel-based printing method for stretchable electrodes. The conducting material of the electrode, the ECPC flooring, can be scraped into the microchannel, thus forming a conductive polymer that exhibits a stretchability as high as the PDMS substrate. Compared with the actions produced by existing fabrication methods, such as inkjet printing, scrape printing, spray printing, and transfer printing, the proposed microfluidic channel-based soft electrons have the advantages of a high printing resolution and high stretchability, with the strong binding to the substrate.The protocol presented in this research combines marriage of stretchable materials and microfluidic channels, enabling a low-cost and rapid application method for producing high-resolution, stretchable electrons for soft robotic tactile sensing applications.

Watch this Scientific Journal Video about Fabrication of the Capacitive Pressure Sensor at JoVE.com

Fabrication of the Capacitive Pressure Sensor  

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Transient Stability and System Controls

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Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most electrodes are either restricted by the patterning resolution or the capability of inkjet printing with high-viscosity super-elastic materials. In this paper, we present a simple strategy to fabricate microchannel-based stretchable composite electrodes, which can be achieved by scraping elastic conductive polymer composites (ECPCs) into lithographically embossed microfluidic channels. The ECPCs were prepared by a volatile solvent evaporation method, which achieves a uniform dispersion of carbon nanotubes (CNTs) in a polydimethylsiloxane (PDMS) matrix. Compared to conventional fabrication methods, the proposed technique can facilitate the rapid fabrication of well-defined stretchable electrodes with high-viscosity slurry. Since the electrodes in this work were made up of all-elastomeric materials, strong interlinks can be formed between the ECPCs-based electrodes and the PDMS-based substrate at the interfaces of the microchannel walls, which allows the electrodes to exhibit mechanical robustness under high tensile strains. In addition, the mechanical-electric response of the electrodes was also systematically studied. Finally, a soft pressure sensor was developed by combining a dielectric silicone foam and an interdigitated electrodes (IDE) layer, and this demonstrated great potential for pressure sensors in soft robotic tactile sensing applications.

Flexible electrodes have a wide range of applications in soft robotics and wearable electronics. The present protocol demonstrates a new strategy to fabricate highly stretchable electrodes with high resolution via lithographically defined microfluidic channels, which paves the way for future high-performance soft pressure sensors.

Flexible and stretchable electrodes are essential components in soft artificial sensory systems. Despite recent advances in flexible electronics, most ...

Elastic Conductive Polymer Composite (ECPCs) Slurry Synthesis and Fabrication of Stretchable Electrodes

To begin, disperse the carbon nanotubes, or CNTs, into a toluene solvent at a one-to-30 weight ratio, and dilute the PDMS base with toluene at an equal weight ratio. Magnetically stir the CNT toluene suspension and PDMS toluene solution at room temperature for one hour. Mix the prepared suspension and solution to form a liquid CNT PDMS toluene mixture, and magnetically stir on a hot plate at 80 degrees Celsius to evaporate the toluene.Then add the PDMS curing agent into the mixture at a 10-to-one weight ratio to complete the synthesis of the ECPCs slurry. To fabricate the microfluidic channel-based stretchable electrodes, mix the PDMS-based solution and the curing agent at a 10-to-one weight ratio, and place the uncured PDMS mixture in a vacuum desiccater until all air bubbles disappear. Prepare the SU8-based mold with different microfluidic channel patterns using the conventional lithography technique on a silicone wafer.Then pour the degassed mixture onto the fabricated mold, and place the mold on a hot plate at 85 degrees Celsius for one hour to cure the PDMS and transfer the SU8 mold pattern on the cured PDMS film. Then peel off the PDMS layer. Next, cast a small amount of the synthesized ECPCs slurry onto the PDMS surface, and using a razor blade, carefully scrape the slurry along the embossed microfluidic channel.Then heat the slurry at 70 degrees Celsius for two hours. Finally, connect a copper wire to each end of the prepared electrodes, using conductive silver paste, and seal the connection with an adhesive rubber sealant. Soft electrodes with different trace designs and printing resolutions can be fabricated through this protocol.The resistance of the electrodes increased with decreasing line width, and the serpentine electrodes exhibited higher resistance than the line structure electrodes, due to their longer effective length. The resistance of the electrodes increased linearly, with the tensile strain caused by the geometric effect. The sensitivity of the serpentine electrodes was lower than the line structure electrode, due to the strained releasing effect.