Monolithic implementation of air-buried microstrip lines for high-density microwave and millimeter wave ICs

This paper introduces a new type of monolithic transmission line structure for high-density microwave and millimeter wave integrated circuits. An air-buried microstrip line (ABMSL) has been monolithically fabricated on glass substrates using a new multi-layer process. The ABMSL has the advantages of low insertion loss and high isolation between transmission lines compared to conventional planar transmission lines such as microstrip lines and coplanar waveguides (CPWs), because of its geometric structure that has air as a dielectric medium and ground conductor walls formed to surround the strip conductor. Over a high frequency range (from 5 GHz to 40 GHz), the ABMSL has very low insertion loss below 0.08 dB/mm. The isolation between two ABMSLs that have 2 mm coupling length and are separated by a 60 μm distance is less than -43 dB.