Fabrication process of integrated inductors on flexible substrate for radio frequency and microwave applications

Abstract

This paper presents a fabrication process for integrated inductors on a flexible substrate using a simple and cost effective method. Kapton was the choice for the substrate due to its attractive characteristics such as thermal stability and electrical insulation. Metal layers were formed by the deposition of a thin Ni film onto the substrate as a seed for Au electroplating deposition and to improve the adhesion between the metal and the substrate. Au lines were patterned by lift-off and served as a mask for Ni wet etching. SiO2 was selected as the dielectric, also patterned by lift-off and preceded by a Cr e-beam deposition step to enhance adhesion. Inductor structures were formed by a conventional photolithography process. There was no need for substrate modification to improve metal adhesion with the use of an Ni intermediate layer. Using this process, it was possible to fabricate integrated inductors appropriate for radio frequency and microwave circuits on a flexible substrate with values compatible with those from the simulation and the literature.