In this paper, a three-dimensional heterogenous-integrated (3DHI) wafer-level packaging (WLP) process is proposed, and a radio frequency (RF) front-end module with two independent ultra-high frequency (UHF) receiving channels are designed and implemented, which covers 400 MHz–600 MHz and 2050 MHz–2200 MHz respectively for unmanned aerial vehicle (UAV) applications. The module is formed by wafer-to-wafer (W2W) bonding of two high-resistivity silicon (HR-Si) interposers with embedded bare dies and through silicon via (TSV) interconnections. Double-sided deep reactive ion etching (DRIE) and conformal electroplating process are introduced to realize the high-aspect-ratio TSV connection within 290 µm-thick cap interposer. Co-plane waveguide (CPW) transmission lines are fabricated as the process control monitor (PCM), the measured insertion loss of which is less than 0.18 dB/mm at 35 GHz. The designed RF front-end module is fabricated and measured. The measured return loss and gain of each RF channel is better than 13 dB and 21 dB, and the noise figure is less than 1.5 dB. In order to evaluate the capability of the 3DHI process for multi-layer interposers, the module is re-designed and fabricated with four stacked high-resistivity silicon interposers. After W2W bonding of two pairs of interposers and wafer slicing, chip-to chip (C2C) bonding is applied to form a four-layer module with operable temperature gradient.
RF System-on-Package (SOP) Development for Compact Low Cost Wireless Front-End Systems