# Miniaturized Soft and Stretchable Multilayer Circuits through Laser‐Defined High Aspect‐Ratio Printing

## TL;DR

A new printing method creates ultra-soft, stretchable circuits with high precision, enabling miniaturized wearable electronics for biomedical use.

## Contribution

A scalable, sustainable method for ultra-soft, high-resolution stretchable multilayer circuits using lignin-based bio-masks.

## Key findings

- Ultra-soft stretchable conductors with <0.4 MPa softness and >300% strain are achieved.
- High-resolution (<2.5 µm) and high aspect-ratio tracks are connected via ultra-fine (20 µm) VIAs.
- A miniaturized ultra-soft wireless NFC temperature logger is demonstrated using the method.

## Abstract

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.

A scalable printing method is developed that enables ultra‐soft stretchable conductors with high‐resolution and high aspect‐ratio tracks connected by ultra‐fine VIAs for multi‐layered configurations. The method uses stencil printing into laser‐defined bio‐masks comprising the abundant biopolymer lignin, thereby achieving printing capabilities beyond conventional methods in a sustainable manner. A miniaturized multilayer ultra‐soft wireless NFC temperature logger is developed as demonstration.