Development of a through wafer 3D vertical micro-coaxial probe

Abstract

A through wafer 3D vertical micro-coaxial probe flushed in a silicon substrate has been designed and fabricated. As a result of using silicon as a dielectric, the probe's compatibility with commercial applications has significantly increased. The probe has been designed using radio frequency (RF) calculations and consists of 100 µm inner diameter and 300 µm outer diameter vias, which corresponds to a 1:3 inner/outer conductor ratio. Fabrication results indicate that the probe through holes can be formed using standard photolithography techniques and Bosch's process for deep reactive ion etching. The probe vias were successfully metalized with a diluted silver paste using a novel filling method. Measured results demonstrate that the probe has good signal transmission with a reflection coefficient less than −10 dB from 15 to 57 GHz. By developing an RF based three-dimensional micro-coaxial probe, its use as vertical interconnects in high frequency system-in-package technologies have considerably improved.