Silicon transformer balun

A transformer balun fabricated by an integrated circuit silicon fabrication process, said balun comprising:

• a substrate;
• a series of alternating metal layers and dielectric layers provided on the substrate and being configured to define a first rectangular outer conductor and a second rectangular outer conductor that are part of a coaxial structure and that are spaced apart from each other to define a gap therebetween, wherein each dielectric layer includes a plurality of conductive vias extending through the dielectric layer to make electrical contact between opposing metal layers, and wherein a top metal layer forms a top wall of the outer conductors and a bottom metal layer forms a bottom wall of the outer conductors and the other metal layers and dielectric layers define sidewalls of the outer conductors;
• a first inner conductor extending down the first outer conductor and a second inner conductor extending down the second outer conductor where the first and second inner conductors are electrically coupled in the gap, wherein the first and second inner conductors and the gap define a balun junction;
• a coplanar waveguide (CPW) feed structure formed as part of one of the metal layers, said CPW feed structure including a center conductor electrically separated from opposing reference conductors, where the center conductor is electrically coupled to the first inner conductor through a conductive via extending through one of the dielectric layers;
• and
• first and second output lines where the first output line is electrically coupled to the sidewall of the first outer conductor and the second output line is electrically coupled to the sidewall of the second outer conductor proximate the balun junction.

A method for fabricating a transformer balun comprising:

• providing a substrate;
• depositing a series of alternating metal layers and dielectric layers on the substrate in a configuration to define a first outer conductor and a second outer conductor that are part of a coaxial structure and that are spaced apart from each other to define a gap therebetween, wherein each dielectric layer includes a plurality of conductive vias extending through the dielectric layer to provide electrical contact between opposing metal layers, and wherein a top metal layer forms a top wall of each outer conductor and a bottom metal layer forms a bottom wall of each outer conductor and the other metal layers and dielectric layers define sidewalls of the outer conductor;
• configuring a first inner conductor extending down the first outer conductor and a second inner conductor extending down the second outer conductor where the first and second inner conductors are electrically coupled in the gap, wherein the first and second inner conductors and the gap define a balun junction;
• and
• configuring first and second output lines so that the first output line is electrically coupled to a sidewall of the first conductor and the second output line is electrically coupled to a sidewall of the second conductor proximate the balun junction.