Fabrication of Cavity-Backed Serial-Fed Microstrip Patch Antenna Array for D-Band (140 Ghz) Using Quartz Glass on Silicon Hybrid Bonded Wafer

In this paper, quartz glass hybrid bonded wafer for antenna circuit substrates at D-band frequencies is presented. The structure of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$75 \mu \mathrm{m}$</tex> thickness quartz glass layer directly bonded onto single crystal silicon base substrate having air-filled cavity allows to realize low-loss, high gain and broad bandwidth antenna. This configuration doesn't contain organic material at all, therefore, it is expected to have better reliability against harsh environment and moisture. A prototype of the cavity-backed <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1 \times 4$</tex> serial-fed microstrip patch antenna array was fabricated using this hybrid bonded wafer and achieved 13 dB antenna gain and 30 GHz bandwidth at center frequency of around 140 GHz. The realization of a large cavity enclosing the entire patch array enables much better characteristics than with a single patch. These results proved its high potential for next generation automotive radar application, etc.