The exciting field of stretchable electronics (SE) promises numerous novel applications, particularly in-body and medical diagnostics devices. However, future advanced SE miniature devices will require high-density, extremely stretchable interconnects with micron-scale footprints, which calls for proven standardized (complementary metal-oxide semiconductor (CMOS)-type) process recipes using bulk integrated circuit (IC) microfabrication tools and fine-pitch photolithography patterning. Here, we address this combined challenge of microfabrication with extreme stretchability for high-density SE devices by introducing CMOS-enabled, free-standing, miniaturized interconnect structures that fully exploit their 3D kinematic freedom through an interplay of buckling, torsion, and bending to maximize stretchability. Integration with standard CMOS-type batch processing is assured by utilizing the Flex-to-Rigid (F2R) post-processing technology to make the back-end-of-line interconnect structures free-standing, thus enabling the routine microfabrication of highly-stretchable interconnects. The performance and reproducibility of these free-standing structures is promising: an elastic stretch beyond 2000% and ultimate (plastic) stretch beyond 3000%, with 10 million cycles at 1000% stretch with <1% resistance change. This generic technology provides a new route to exciting highly-stretchable miniature devices.

This paper focuses on the implementation of a new technique for the fabrication of stretchable electronic patches that can be used for medical applications. The technique is based on the Electronics on Plastics by Laser Release (EPlaR) technology which enables a one-step release of a stack of flexible/stretchable layers incorporating the active layers like interconnects and embedded devices. As a proof of concept meander shaped polyimide (PI) structures are fabricated on top of a glass substrate and then transferred to a PDMS substrate with the use of this technology. The stretchability in the device is enhanced by fabricating these meander shaped structures free from the PDMS substrate hence giving them the freedom to move out of plane.

A method for fabricating stretchable sensor arrays consisting of rigid islands attached to a stretchable membrane is proposed. The method utilizes a CMOS compatible post processing approach, where the sensor elements and the underlying electronics are fabricated first, followed by a sequence of etching steps and polymer spin coating that result in the formation of the stretchable array. The elements of the array are connected by free-standing interconnects that are prefabricated in the metal stack of the CMOS. The presented fabrication results demonstrate the feasibility of manufacturing of fine-pitch, high density arrays where the interconnects are completely separated from the stretchable substrate allowing for high stretchability.

A platform for the batch fabrication of pneumatically actuated Stretchable Micro-Electrode Arrays (SMEAs) by using state-of-the-art micro-fabrication techniques and materials is demonstrated. The proposed fabrication process avoids the problems normally associated with processing of thin film structures on polydimethylsiloxane (PDMS), by first fabricating the electrodes and electrical interconnects on the silicon wafer using fine-pitched stepper lithography, and afterwards transferring the structures to the elastomer. Stretchability is achieved by a novel spiral design for the interconnects. Experiments demonstrate the biocompatibility of the fabricated devices for in vitro cell culturing