Embedded glass fan-out integration method for high-performance Ka-band RF microsystem

Heterogeneous radio-frequency (RF) microsystem integration is pivotal for overcoming the physical limitations of monolithic integration, enabling the low signal transmission loss and high operating frequencies demanded by next-generation communication networks. Glass interposers, characterized by inherently low dielectric loss, exceptional planarity, and highly tunable coefficient of thermal expansion, have emerged as an ideal platform for millimeter-wave (mmWave) RF microsystems. In this study, we propose a high-density, low-noise RF integration technology utilizing an embedded glass fan-out process. To address the challenges of glass micromachining, laser-induced deep etching (LIDE) was employed to fabricate high-precision cavities with superior verticality and minimal sidewall roughness for seamless die embedding. Subsequently, through an optimized chemical-mechanical polishing (CMP) process, the surface roughness of the redistribution layer (RDL) is reduced by 97%, successfully suppressing the transmission loss to below 0.25 dB/mm. A compact Ka-band microsystem integrating the low-noise amplifier and the antenna was designed and fabricated, featuring an optimized Chebyshev antenna array and a Klopfenstein taper transition for broadband impedance matching. Furthermore, we demonstrate a heterogeneously integrated Ka-band transceiver microsystem that combines high-performance GaN-based amplifiers with a cost-efficient silicon-based switch. The integrated transceiver exhibits a transmit gain of 26.08 dB and a receive noise figure of 2.73 dB at 28 GHz, within an ultra-compact footprint of 6 × 3 mm². This work provides a highly scalable and robust heterogeneous integration solution for high-performance, multi-functional mmWave microsystems in 5G-Advanced and future 6 G networks.