High-Resolution Printing-Based Vertical Interconnects for Flexible Hybrid Electronics

Flexible hybrid electronics (FHE) is an emerging area that combines printed electronics and ultra-thin chip (UTC) technology to deliver high performance needed in applications such as wearables, robotics, and internet-of-things etc. The integration of UTCs on flexible substrates and the access to devices on them requires high resolution interconnects, which is a challenging task as thermal and mechanical mismatches do not allow conventional bonding methods to work. To address this challenge, the resource-efficient, area-efficient, and low-cost printing routes for obtaining vertical interconnection accesses (VIAs) are demonstrated here. It is demonstrated how high-resolution printers (electrohydrodynamic and extrusion-based direct-ink writing printers) can be used for patterning of high-resolution, freeform, vertical conductive structures. To access the transistors on UTCs, the VIAs, obtained using conventional photolithography and plasma etching steps, are filled with conductive silver nanoparticle-based ink/paste using high-resolution printers. Comprehensive studies are performed to compare and benchmark in terms of: i) the printing speed and throughput of the printers, ii) the electrical performance of vertically connected transistors in UTCs, and iii) the electrical performance stability of FHE system (interconnects and UTCs) under mechanical bending conditions. This in-depth study shows the potential use of printing technologies for development of high-density 3D integrated FHE systems.