Micromachined substrate integrated waveguides with electroplated copper vias in reflowed glass substrate for millimeter-wave applications

•Fully micromachined SIW and HMSIW for millimeter-wave applications are demonstrated.•Reflowed glass substrate with copper vias are used for mechanically stable SIW.•Fabricated SIW and HMSIW devices show good insertion losses from 25 to 40 GHz.

Substrate integrated waveguide (SIW) technology has been studied as a solution to overcome high cost, high fabrication complexity and low integrity with planar circuits of classical rectangular waveguides. In this paper, a micromachined SIW with electroplated copper vias embedded in a glass dielectric substrate for millimeter-wave applications have been proposed and demonstrated. In the proposed SIW, borosilicate glass filled into the silicon trench using a glass reflow process is used as a dielectric material of the waveguide, and copper electroplating process is performed to realize metal via structures required for the electrical sidewall of the waveguide. The proposed SIW structure can be fabricated by micromachining batch processes while maintaining high power handling capability and low loss property of the waveguide, and provides a mechanically stable, process temperature-insensitive platform for direct integration of the SIW with tunable RF MEMS (radio-frequency micro electro mechanical systems) devices. The insertion loss of the fabricated 10-mm-long SIW is measured to be lower than 0.95 dB in a frequency range from 20 to 45 GHz. More compact 10-mm-long half-mode SIW (HMSIW) is also fabricated, and its insertion loss is measured to be lower than 1.3 dB in the same frequency region.

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