  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 <0.3% resistance change, and >10
million cycles at 1000% stretch with <1% resistance change. This generic
technology provides a new route to exciting highly-stretchable miniature
devices.
