Multi‐layer microstrip antennas on quartz substrates: Technological considerations and performances at 60 GHz

This paper describes the thin‐film fabrication process and the performance of 60‐GHz aperture‐coupled microstrip patch antennas printed on fused quartz substrates. It is shown that their characteristics (input impedance, axial ratio) are strongly modified by residual air gaps located between the two substrates of the antenna. In particular, FDTD simulations demonstrate that these parasitic effects can be minimized by using two ground/reflecting planes and by keeping the thickness of the air layer thinner than λ0/250, where λ0 is the free‐space wavelength. To face this technological problem, two intermediate metal and adhesive (low‐temperature) wafer bonding techniques, respectively based on indium and polymer layers, have been developed and validated experimentally for linear and circular polarization patch antennas and arrays. The lift‐off fabrication process is also described.