Antennas in Glass Interposer For sub-THz Applications

The development of next generation (6G) wireless communications is expanding new spectrum bands into sub-terahertz (sub-THz) frequencies above 100 GHz, and the antenna is a key component in RF front-end modules (FEM) for such frequency bands. This paper demonstrates integrated packaging solutions for antenna components in D-band by using glass-based package. With the assistance of full-wave simulation in HFSS software, we design sub-THz patch antennas operating at 140 GHz frequency band, and form arrays of such patch antennas for 5G+/6G (sub-THz) wireless communication applications. The patch antennas and feeding networks are implemented by microstrip structures on the top of the glass interposer, with ground planes beneath. Build-up layers of polymer dry films are laminated on a glass core substrate for multi-layer copper metallization, and copper structures are patterned on the polymer layers. For precise fabrication of the antenna and feeding structures in package, we utilise the semi-additive patterning process to deposit the copper structures. By forming patch antenna arrays, we obtain 10.6 dBi gain using a 4-element linear array and 16.2 dBi gain using a 4-by-4 2-D rectangular array. The feeding methods of patch arrays are also discussed in the paper. The bandwidths achieved for these arrays are 7% (10 GHz) and 5% (7 GHz), respectively, based on return loss measurements. The measurement results present good match to simulation models, considering the uncertainties at such high frequencies. We believe that this is the first demonstration of glass-based antenna-in-package solution in D-band frequencies. Antenna structures on glass substrates illustrated in this paper represent one of the basic building blocks for the heterogeneous integration of sub-THz FEM in glass-based packages.