Miniaturized Soft and Stretchable Multilayer Circuits through Laser-Defined High Aspect-Ratio Printing.

Stretchable electronics enable seamless integration of wearables with the human body, thereby creating new opportunities in biomedical applications. Miniaturized multilayer stretchable printed circuit boards are key for achieving high functional density circuits with minimal footprint. However, current microfabrication technologies struggle with simultaneously achieving tissue-like softness (<<1 MPa), high resolution and low sheet resistance. This study demonstrates a scalable printing method that enables ultra-soft (<0.4 MPa) stretchable conductors (>300% strain) with high-resolution (<2.5 µm width) and high aspect-ratio tracks (>1) connected by ultra-fine (20 µm) vertical-interconnect-access (VIA) for multi-layered configurations. The method is based on stencil printing into laser-defined bio-masks comprising the abundant biopolymer lignin, thereby achieving printing capabilities beyond conventional methods in a sustainable manner. Based on the unique capabilities, a miniaturized multilayer ultra-soft wireless near-field-communication temperature logger is developed. Laser-defined printing can pave the way for the next generation of ultra-soft miniaturized wearables.