Aerosol-jet printing of interconnect and chip-level stiffness gradients for stretchable electronics

The need for stretchable electronics arises from the demand for flexible and deformable electronic devices that can conform to curved surfaces, withstand mechanical strain, and enable new applications in areas such as wearable technology, healthcare modeling, robotics, and electronic skins. Stretchable electronics offer the potential to enhance comfort, enable seamless integration with the human body, and open new avenues for innovation in electronic systems. Aerosol jet printing (AJP) offers advantages for the fabrication of stretchable electronics including conformal deposition, high resolution, design flexibility, and integration capabilities. 

This thesis work builds on ongoing efforts to make reliable additively manufactured stretchable devices. AJP is used to study two significant areas in the development of stretchable devices: (1) fabricating stretchable substrates with reliable circuitry and (2) creating stiffness gradients in the stretchable substrate (e.g. polydimethyldisiloxane (PDMS)) toward reliable mechanical connection of chips to the substrate. With the high resolution capabilities of AJP, one- and two-layer stretchable devices with embedded circuitry are achieved. These stretchable devices are thin (< 100 µm), biocompatible, and capable of surviving high strain. Additionally, multi-layered electrocardiogram (ECG) patches are successfully fabricated and demonstrated. Stiffness gradients are needed in the PDMS to prevent premature failure at the chip-PDMS interface to survive high strains needed in biomedical and robotics applications. Producing these stiffness gradients are explored by testing AJP to print PDMS curing agent and, alternatively, to print polyimide directly onto PDMS, with the latter technique showing promise. The utilization of the AJP to fabricate direct-customized multi-layered stretchable devices with embedded stiffness gradients surrounding rigid components will significantly enhance accessibility, enabling quick prototyping in diverse applications, especially in the biomedical field.