High frequency characterization and analysis of through silicon vias and coplanar waveguides for silicon interposer

Abstract

A silicon interposer test vehicle with through silicon vias (TSVs) is evaluated under radio frequency (RF) application from DC to 10 GHz. TSVs with 30 μm diameter and 150 μm height were fabricated with one layer RDL of 20 μm line width. A group of coplanar waveguides (CPW) are designed and tested to analyze the electrical performance of the interposer under high frequency in both the time and frequency domains. Results show that the interposer cannot be used above 1 GHz because of excessive losses and high reflections. Based on the analysis of the test results and simulation results for different CPW (coplanar waveguides) structures, it is concluded that the poor performance was mainly caused by accumulated space-charge at the SiO2---Si interface and impedance mismatch of transmission lines. Solutions that were implemented included enhancing the thickness of the SiO2 insulation layer between the metal and silicon substrate and improving the design of the transmission line. Implementation of these changes led acceptable interposer performance up to 10 GHz.