A Combined Spin Coating and Lift-Off Process (CSLOP) to Realize Thick Silver Microstructures with a High Aspect Ratio for IoT Applications

Abstract

This paper presents a new manufacturing technology, i.e., combined spin coating and lift-off process (CSLOP), for the fabrication of Ag interconnects and microstructures such as interconnect lines, interdigitated capacitors and spiral inductors with a high aspect ratio of thickness vs. width. For the interconnect fabrication using the thin film CSLOP, Ag lines with a width range from 10 to $100\ \mu \mathrm{m}$ can be realized with an electrical resistivity of $\sim 2.36\ \mu\Omega\cdot \text{cm}$, only 1.48 times higher than that of bulk silver ($1.59\ \mu\Omega\cdot \text{cm}$), which is the lowest resistive Ag line ever reported. For high performance on-chip flexible passive fabrication using the thick film CSLOP, the interdigitated capacitors with an electrode thickness of $70\ \mu \mathrm{m}$ can exhibit a capacitance of 0.502pF@10 kHz and the 5-turn, $70\ \mu \mathrm{m}$ thick spiral inductor can have high $Q$ performance with a highest inductance density up to 9.7 nH/mm2. Because the process scheme can be applied using other metal/metal oxide nanoparticles, the CSLOP can facilitate the realization of highly sensitive sensors and excellent heterogeneous integration for IOT applications.