Abstract— This paper presents the first demonstration of a Gallium Nitride (GaN) -on-Si high-electron mobility transistor (HEMT) fully embedded in a glass package. AlGaN/GaN-on-Si HEMTs featuring n++ regrown contacts and a scaled Lg=90 nm copper t -gate are fabricated and thinned to 300μm. The fabricated HEMTs are singulated to a size of 350μm×540μm via femtosecond laser dicing. Using a 300μm AGC Inc. glass panel, the dielet is embedded and encapsulated with Ajinomoto Build-Up Film (ABF) GL102. For final back-end-of-line (BEOL) fabrication, two metal and two dielectric redistribution layers (RDL) are fabricated above the dielet. The effects of the RDL are analyzed and quantified through small-signal RF measurements of the integrated dielet. This integration scheme shows co-optimization from transistor to package-level design. This work lays the ground work for the future advanced packaging of such highly scaled GaN-on-Si dielets in a novel device-in-package platform for RF front ends.
Introduction— GaN HEMTs have become a leading candidate for RF, backside power, and harsh environment electronics [1]. These devices have excellent power amplification and high switching speeds while displaying high breakdown voltages. RF GaN HEMTs have mainly been fabricated in GaN-on-SiC [2], but recent advances in device engineering and scaling have allowed for the demonstration of excellent RF devices in GaN-on-Si epitaxy, which benefits from 200 mm and above wafer sizing [3]. To truly advance GaN circuit technology, a scalable, advanced packaging technology is required for the buildup of 3D-stacked dielets that leverage microvias and low-loss 3D-integrated circuit (3DIC) interconnects. Glass panel substrates provide a promising advanced packaging solution that has demonstrated low-loss at RF and mmWave frequencies when combined with low-loss ABF laminated film [4]. This glass platform allows for the buildup of a two-metal layer interposer for the embedding of chips [5]. The presented work demonstrates the integration of a highly scaled GaN dielet into such a glass interposer. Key insights have been made about the device performance after integration and encapsulation of the GaN dielet in the glass/ABF stack. Great care and novel fabrication flows were adopted for the fabrication of the scaled dielet.
Industry standard simulation platforms such as Silvaco TCAD, Keysight ADS, and Ansys HFSS were all used for the co-design of the GaN dielet in glass interposer circuit design and layout. In this paper, the focus will follow the dielet and interposer fabrication techniques, particularly the GaN device technology and its performance after integration into the glass interposer, and will conclude with an initial demonstration in RF amplifier performance. The presented work demonstrates only the first, of several future works related to the 3DIC design of GaN dielets in glass. A proposed glass device-in-package platform is illustrated in Fig. 1. Through the initial integration of a singulated GaN HEMT dielet, the path has been set for future integrated RF dielet-based front ends in glass.
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Tomas Palacios
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