Thick metal integrated transmission line fabrication

Abstract

A method for fabricating thick metal integrated transmission lines and circuit topologies for microwave integrated circuits. Microstrip or coplanar waveguide (CPW) transmission line and circuit topologies may be fabricated on semiconductor or dielectric substrates. For microstrip transmission line topologies, a metal ground plane is applied to the opposite side of the substrate from the thick metal transmission line conductor structures. To fabricate a thick metal transmission line topology, a metal plating base is applied to a substrate surface. A photoresist layer, which may include a preformed photoresist sheet, is then applied over the plating base layer. The photoresist layer is exposed to X-rays, such as from a synchrotron, through a mask having an X-ray absorber pattern that defines the desired transmission line or circuit topology. The photoresist layer is then developed to remove sections of the photoresist layer corresponding to the mask pattern and to expose portions of the plating base layer. Thick metal transmission line circuit structures are then electroplated onto the plating base, into the wells formed by the developed photoresist layer. Transmission line thicknesses of approximately 5 .mu.m-1 mm, may thereby be formed, having highly vertical side walls. The method may be used to fabricate various microstrip and CWT transmission line and tightly coupled circuit topologies, including couplers, low-pass and band-pass filters, and resonators.