Experimental investigation on 3D metal interconnection for HySiF(hybrid system in flexible) devices using electrohydrodynamic(EHD) system

Abstract

For many years, it has been accepted that the flexible applications can not show high device performance and efficiency due to its inherent material issues while the Si based chips present a totally different aspect (high performance but low flexibility). However, recently, this conventional stereotype is being challenged because the new concept called HySiF (hybrid system in flexible) devices merges two different aspect of the benefits such as high device performance and high mechanical flexibility. In addition, the HySiF devices can also be applied to various applications such as wearable devices, sweat sensors, flexible displays, smart cards, etc which is why this new technical trend starts drawing tremendous attention from many people and research fields. However, while there are diverse technical challenges to commercialize the HySiF devices, we are trying to focus on the fabrication of producing Ag based 3D step-covered metal interconnection using a electrohydrodynamic (EHD) system targeting for the electrical connection between any types of functional Si based chips on a flexible substrate. In order to create 3D step-covered metal interconnection, we control the line width (10∼50 μm) hy optimizing the EHD parameters (flow rate:μl/min, working height: μm, applied voltage: kV, velocity: mm/s, acceleration: mm/s2) that covers various step heights (0 μm ∼ 10 μm) utilizing the Ag nanoparticle based metal ink with a control of the sintering temperature less than 200 °C. As a specific application, 5 μm thick micro-LED chips with a 4×4 array were roll-transferred on the PI substrate and were successfully interconnected using the Ag metal ink sintered at 150 °C maintaining its electrical device performance even under the bending condition (diameter=5mm). As a result, we expect that our work can create lots of opportunities for any kinds of future HySiF applications by eliminating the face-up 3D interconnection issues.