Highly Ordered 3D Microstructure-Based Electronic Skin Capable of Differentiating Pressure, Temperature, and Proximity

Abstract

Electronic skin are devices that mimic the functionalities of human skin, which require high sensitivity, large dynamic range, high spatial uniformity, lowcost and large-area processability, and the capacity to differentiate various external inputs. We herein introduce a versatile droplet-based microfluidic-assisted emulsion self-assembly process to generate three-dimensional microstructure-based highperformance capacitive and piezoresistive pressure sensors for electronic skin applications. Our technique can generate uniformly sized micropores that are selfassembled in an orderly close-packed manner over a large area, which results in high spatial uniformity. The size of the micropores can easily be tuned from 100 to 500 μm, through which sensitivity and dynamic range were controlled as high as 0.86 kPa −1 and up to 100 kPa. Our device can be printed on curvilinear surfaces and be molded into various shapes. We furthermore demonstrate that by simultaneously utilizing capacitive and piezoresistive pressure sensors, we can distinguish between pressure and temperature, or between pressure and proximity. These demonstrations make our process and sensors highly useful for a wide variety of electronic skin applications.

Highly Uniform and Low Hysteresis Piezoresistive Pressure Sensors Based on Chemical Grafting of Polypyrrole on Elastomer Template with Uniform Pore Size

“…Such a phenomenon can be attributed to the lower critical buckling load of the longer columns between the larger pores (i.e., F c ∝ L −2 , where F c is the critical buckling load, E is the elastic modulus, I is the moment of inertia, and L is the length of the column) . The sample with lower F c is expected to undergo a larger strain at a given pressure . This will increase the sensitivity of the sensor since larger compressive strain at a given pressure signifies a larger relative change in resistance.…”

“…Various works have been reported to improve the performance of piezoresistive pressure sensors, most of which have been focused on increasing the sensitivity 3a,7. For instance, microstructuring of the piezoresistive element into porous structure,4b,8 pyramids,7a,9 microdomes3d,10 have been demonstrated to improve the sensitivity, which has been attributed to the decrease in the compressive modulus 7a,11. Porous structures, in particular, was utilized in various pressure sensors due to their facile fabrication process and scalability.…”

“…In this work, we have fabricated piezoresistive pressure sensors by chemically grafting polypyrrole (PPy, a conductive polymer) on the surface of porous PDMS (polydimethylsiloxane) elastomer, which exhibited high uniformity and negligible hysteresis. The porous PDMS elastomer was made using microfluidic emulsion droplet self‐assembly technique, which generates uniformly sized pores assembled in a highly ordered close‐packed manner. The sensors had much lower coefficient of variance (2.43%) in relative resistance change compared to that of sensors made with randomly shaped pores (69.65%), which implies that uniform porosity is of great importance to achieve uniform sensor performance.…”

Mechanically transformative electronics, sensors, and implantable devices

“…Recent research trends in e-skins (29) and wearable electronics (30,31) have focused on the development of highly sensitive pressure sensors to achieve human skin-like sophisticated sensing. Although advances in materials and micro-/nanofabrication have shown impressive accomplishments toward this goal, pressure sensors with high sensitivity are limited because of their small dynamic ranges [e.g., 0 to 10 kPa in piezoresistive or piezoelectric devices (32,33) and 0 to 100 kPa in capacitive devices (34,35)], therefore substantially restricting the spectrum of applications. A tunable pressure sensor built on a transformative platform may resolve this issue.…”

A novel, stretchable, silver‐coated polyolefin elastomer nanofiber membrane for strain sensor applications

“…Meanwhile, the flexibility and conductivity, also key points that affect the sensitivity, sensing range, and response–recovery speeds of a pressure or strain sensor . Therefore, a great diversity of structures have been designed and studied to optimize the flexibility and conductivity of sensing materials, for example, via a combination of conductive materials, such as carbon nanotubes, graphene, silver nanowires, or poly(3,4‐ethylene dioxythiophene)–poly(styrene sulfonate) with the flexible microstructured substrates of Polydimethylsiloxane (PDMS), polyurethane (PU), or fabrics, or the construction of flexible structures with intrinsically rigid conductive materials, such as foam, gradient film, or networks . In addition to so many efforts, the pursuit of perfect flexibility and conductivity remain urgent for improving the performance of pressure and strain sensors.…”