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|TSV Modeling Considering Signal Integrity Issues|
|Keywords: TSV, electrical modeling, signal integrity|
|Due to the myriad of system-integration advantages offered by Through-Silicon Vias (TSVs), they are considered as one the key technologies needed for the development of future miniaturized and high-performance electronic products. However, the semi-conducting nature of silicon (Si) may cause signal integrity problems such as cross-talk, high insertion loss and electromagnetic interference, which may degrade the system performance. To prevent/minimize these problems, the impact of the conductivity of Si must be thoroughly investigated. In the early 70s, Hideki Hasagawa and his colleagues proved that depending on Si-resistivity and the frequency of operation, Si exhibits three modes (i.e., the dielectric, skin-effect and slow-wave mode). Since then, the impact of these modes on the signal integrity of planar transmission lines has been extensively investigated. In this work, we study the impact of these modes on the signal integrity behavior of TSVs for frequencies up to 60 GHz. For these investigations, two-conductor TSV (i.e., a signal and return-current TSV) were considered, each having a diameter of 40 microns and height of 200 µm. Our results reveal that in the presence of high-resistivity-Si, Si behaves just like isolating substrates (dielectric mode) at high frequencies. However, since high-resistivity-Si is expensive, either low-resistivity-Si or medium-resistivity-Si is commonly used. When low-resistivity-Si is used at high frequencies, the skin-effect mode occurs. The Si between the signal and return-TSV acts like a lossy ground, causing the return-current to flow on the surface of Si. Consequently, the signal and return TSV become disconnected. Huge insertion loss, delay, impedance mismatch and other signal integrity problems may occur. When medium-resistivity-Si is used at low frequencies, the slow-wave mode occurs, leading to large signal delays. From the results of our investigations, we derived design guidelines to minimize signal integrity problems issues which occur as a result of the conductivity of Si.|
|Dr. Ivan Ndip, Group Manager
Fraunhofer Institute for Reliability and Microintegration, IZM