Fabrication and Characterization of Through-glass vias (TGV) based 3D Spiral and Toroidal Inductors by Cost-effective ECDM Process

Abstract

Fabrication of 3-dimensional (3D) spiral and toroidal inductors in non-conductive fused silica substrate by electrochemical discharge machining (ECDM) method is reported for the first time in this article. Through-holes having an average diameter of 580 μm are first etched by the ECDM and then completely filled by using a bottom-up electrodeposition technique. Later, front and back-side redistribution lines were formed by through-resist electroplating. The toroidal inductors had a total of 5 turns. The spiral inductors had different coil widths, i.e., 100 μm, 150 μm and 200 μm with a variable number of turns ranging from 3 to 6 turns. Due to the superior insulation characteristics of fused silica, the insulation and barrier layer were not required. Substrate losses are also expected to be lower as compared to the conventional silicon substrate. The simulation of the designed inductors was performed in ANSYS highfrequency simulation software (HFSS) to indicate the inductor characteristics. The simulated inductance and quality factor (Q-factor) at the self-resonant frequency of 0.75 GHz were observed to be 26.1 nH, and 136.8, respectively. Electrical resistances of the fabricated toroidal and spiral inductors were experimentally measured to be 168 mΩ and 338 mΩ, respectively.