Antenna-Integrated and PA-Embedded Glass Substrates for D-Band InP Power Amplifier Modules

Abstract

This article presents an innovative antenna-in-package (AiP) solution designed for 140-GHz indium phosphide (InP) power amplifier (PA) front-end modules. In this design, InP PAs are strategically embedded at the center of a glass substrate (AGC EN-A1) sandwiched by low-loss dielectric layers (ABF-GL102) on both sides. This arrangement facilitates ultrashort die-to-package interconnects through 20- $\mu $ m dielectric vias, achieving a remarkably low simulated loss of 0.2–0.3 dB at 140 GHz and an impressive $S11$ / $S22$ of less than −15 dB across a wide frequency range from 110 to 170 GHz. We conducted a thorough evaluation of various PA designs with two-stage and three-stage amplifying circuits embedded within this package. The findings reveal that the embedded InP PAs deliver consistent small signal gains of 11.1 dB for the two-stage and 15.8 dB for the three-stage PAs at 140 GHz, comparable with their bare die performance and other existing packaging technologies. A key feature of this design is the integration of a 5- $\mu $ m-thick copper heat spreader on the PA backside, which significantly enhances thermal management. In addition, the design accommodates the seamless integration of a $1\times 8$ microstrip patch antenna array. Directly connected to the PA output, this array achieves maximum broadside gains of 12.9, 25.3, and 29.7 dB for the standalone antenna, and the PA-antenna modules with two-stage and three-stage PAs at 139 GHz, respectively, over a 3-dB bandwidth of 5 GHz (136–141 GHz). Moreover, the radiation pattern of the PA-antenna module has been meticulously characterized, showcasing a $13^{\circ } ~3$ -dB E-plane beamwidth and $64^{\circ } ~3$ -dB H-plane beamwidth from the broadside. With its superior electrical and thermal performance, scalability, and cost-effectiveness, this package presents a promising solution for developing D-band beamforming arrays in next-generation communication systems.