Magnetic-Assisted Transparent and Flexible Percolative Composite for Highly Sensitive Piezoresistive Sensor via Hot Embossing Technology

Abstract

A highly transparent and flexible percolative composite with magnetic reduced graphene oxide@nickel nanowire (mGN) fillers in EcoFlex matrix is proposed as a sensing layer to fabricate high-performance flexible piezoresistive sensors. Large excluded volume and alignment of mGN fillers contribute to low percolation threshold (0.27 vol %) of mGN-EcoFlex composites, leading to high electrical conductivity of 0.003 S m–1, optical transmittance of 71.8%, and low Young’s modulus of 122.8 kPa. Large-scale microdome templates for sensors are prepared by hot embossing technology cost-effectively and COMSOL Multiphysics is utilized to optimize the sensor performances. Piezoresistive sensors fabricated experimentally show superior average sensitivity of 1302.1 kPa–1 with a low device-to-device variation of 3.74%, which provides a new way to achieve transparent, highly sensitive, and large-scale electronic skin.

Hot Embossing Process Technology Forming Arbitrary Patterns in Real Time

“…For these reasons, hot embossing technology, which has high productivity and cost‐saving advantages for making micropatterns on flexible materials such as polymer films, has received attention recently. [ 8–12 ] The hot embossing process is a method for generating ultrafine patterns using a patterned mold. The user‐defined pattern can be engraved on the patterned mold through a lithography process or a mechanical process method.…”

“…The user‐defined pattern can be engraved on the patterned mold through a lithography process or a mechanical process method. [ 8–12 ] After making the patterned mold, a polymer film is heated above the glass transition temperature, which changes the molecular structure of the film to a soft state. [ 8–10 ] The hot embossing process can perform micropatterning on various types of polymer films with a lower glass transition temperature than the heat plate temperature.…”

“…However, in the case of a polymer film having a higher glass transition temperature than heat plate temperature, there is a limitation in the hot embossing process. [ 9–12 ] After the polymer film changes to a soft state, a microscale pattern is created by applying pressure and heat to the polymer film using a patterned mold and heat plate. [ 8 ]…”

“…In 2019, a research group fabricated a soft mold using the R2R method and applied the mold to the P2P process to create an ultrafine pattern that has a pattern width of 35 µm and a pattern depth of 13.429 µm. [ 11 ] In addition, studies have been conducted to fabricate various miniature sensors such as piezoresistive sensors and pressure sensors using the processed ultrafine patterns. [ 11,12 ] Furthermore, research was also conducted to create an embossed polymer sheet with 14 µm width and 6.8 µm depth by using the R2R process after making a polyimide mold using a lithographic patterning method.…”

“…[ 11 ] In addition, studies have been conducted to fabricate various miniature sensors such as piezoresistive sensors and pressure sensors using the processed ultrafine patterns. [ 11,12 ] Furthermore, research was also conducted to create an embossed polymer sheet with 14 µm width and 6.8 µm depth by using the R2R process after making a polyimide mold using a lithographic patterning method. [ 11 ] In addition, in 2020, a research group created a microchannel of 200 µm × 150 µm on a polymethyl methacrylate (PMMA) film using a P2P process.…”