Freestanding Functional Structures by Aerosol‐Jet Printing for Stretchable Electronics and Sensing Applications

Abstract

Modern electronic devices, particularly those intended for wearable or human health monitoring applications, require high levels of flexibility and stretchability. Hence devices, as well as interconnects, need to be capable of retaining functionality even when being mechanically deformed. Most approaches towards achieving this rely on printing or transferring structures onto elastomeric substrates that can withstand stretching. However, the processing involved can often be cumbersome, and the structures themselves tend to suffer from poor fatigue and/or are limited by the mechanical properties of the underlying substrate. Here, we have developed a novel aerosol jet printing technique capable of building fully freestanding functional structures layer by layer, which are robust and reliable upon thousands of stretching cycles. The process involves printing a combination of layers of different materials with the desired functionality, onto a substrate coated with a sacrificial film that is subsequently dissolved to release the printed structure. Using this method, we demonstrate freestanding conductive wires that can be used as stretchable interconnects/electrodes, and that also function as strain‐sensors. Additionally, we show that a freestanding capacitive structure functions as a robust, stretchable humidity sensor, paving the way for the development of other multilayer, multifunctional stretchable devices and sensors.

Fully Printed, Wireless, Stretchable Implantable Biosystem toward Batteryless, Real‐Time Monitoring of Cerebral Aneurysm Hemodynamics

“…The combination of additional passes and thinner ink resulted in spreading during deposition and loss of features, as shown in Figure 2B for the 1:1 ink from 1 pass to 5 passes (further details in Figure S3, Supporting Information). The previously reported AJP-enabled structure [21] relied on a thick layer deposition for preventing shorting between conductive layers, but lowered sensitivity. Stage temperature did not have any significant effect on line width or thickness for the 4:1 ink.…”

“…The previously reported AJP-enabled structure [21] relied on a thick layer deposition for preventing shorting between conductive layers, but lowered sensitivity. [21] The resistance remained higher due to the use of a composite layer of PI and AgNP as the conductive paths. [23] Prior to optimization, the two electrode layers were consistently and frequently electrically connected despite depositing PI between the layers.…”

“…[1][2][3] Some recent works with rigid electronics have attempted the integration of the inductive coupling method with medical stents. [21] However, conductive traces were fabricated as a mixed polyimide (PI) and silver nanoparticle (AgNP) composite that resulted in resistances still too high for use in wireless devices despite an overall thickness near 30 µm. Cerebral aneurysm detection often is required to reach arteries over 5 cm from the skin.…”

Structural Innovations in Printed, Flexible, and Stretchable Electronics

“…Reproduced with permission. [ 89 ] Copyright 2019, Wiley‐VCH. K) Comparison of stretchability between well‐bonded (strong) and weakly bonded (weak)indium tin oxide (ITO) serpentine ribbons with different arc angle (top) and length‐to‐radius ratio (bottom).…”

“…[ 77,88 ] Printed‐then‐transferred tortuous 2D structures exhibit superior stretchability (Figure 3K) while showing minor conductivity change during stretching (Figure 3J). [ 77,89 ] The overall fabrication complexity of printed rigid, freestanding structure is comparable with that of its photolithographic or laser‐ablation counterparts, therefore considered less advantageous compared to the direct planar printing methods.…”