Through Silicon Via interposer for millimetre wave applications

A novel Through Silicon Via (TSV) structure to mitigate the high electrical loss at high frequency is presented here. At low frequency, the loss for the TSV is caused mainly by the material loss of the Silicon (Si) substrate due to its low resistivity. However, at millimetre wave (mmWave) frequency range, especially above 50GHz, in addition to the insertion loss, the return loss due to impedance mismatched becomes significant. These losses become a serious setback for the Si Interposer for the mmWave applications. To overcome these losses, polymer cavity formed in the Si substrate with TSV is developed. The polymer has lower loss tangent and lower dielectric constant than Si. These properties can help to reduce the insertion loss and the return loss. Depending on the requirement, multiple set of TSV can be formed on the polymer cavity to provide higher interconnect density. From the simulation results, the new polymer cavity TSV at 100GHz have an insertion loss and return loss of ~0.2dB and less than -25dB, respectively. On the other hand, conventional high resistivity TSV has an insertion loss and return loss of ~1.4dB and more than -10dB, respectively, at the same frequency. For higher frequency range, the performance of the polymer cavity TSV is approximately consistent, but the conventional TSV deteriorated drastically. In this paper, the design, fabrication process and the measurement results are presented. The prototype polymer cavity TSV via-line-via test vehicle has a measured insertion loss of less than 1dB and a return loss of better than -10dB through the frequency range up to 110Gz.