High RF performance TSV silicon carrier for high frequency application

Three dimensional system-in-package (3D SiP) based on silicon carriers or interposer is a fast emerging technology that offers system design flexibility and integration of heterogeneous technologies. One of the key technologies enabler for silicon carrier is through silicon via (TSV). The development of 3D SiP will require the devices with different functionality operating at high frequency to be densely packed on the silicon substrate. However, silicon substrate is usually of low resistivity, when a high frequency signal is transmitted vertically through the substrate via, significant signal attenuation can occur that leads to poor RF performance. In this paper, a coaxial TSV structure in silicon carrier is presented for high frequency applications. The coaxial TSV is able to suppress undesirable substrate loss as well as provide good impedance matching. Electrical modeling of coaxial TSV structure was carried out to obtain the required geometries for impedance matching. Three different types of test vehicles were fabricated; Cu-plug TSV in both low (~10 Omega-cm) and high resistivity (~4000 Omega-cm) silicon substrate, and coaxial TSV in low resistivity silicon substrate. The S-parameters of the via structure of the test vehicles were measured from 100 MHz to 10 GHz. The measured results show that the coaxial TSV structure is able to suppress silicon substrate loss and provide good RF performance compared to Cu-plug TSV structure.