An integrated passive balun on Si, SiGe, and GaAs substrates

This paper reports the design of a low loss, small size, and low cost dual balun for quad band GSM application. The balun was initially designed on a GaAs substrate for wirebond applications [1], and further design optimizations were conducted on a typical SiGe substrate and on high resistivity Si substrates to implement the balun fabrication in a conventional Si fab. The finalized balun using high resistivity Si substrates fabricated in Si fab, was used on a quad band GSM/EDGE transceiver module and on a WCDMA/EDGE transceiver module. These baluns on 8 inch Si wafers were bumped and flip chip assembled to the module substrates, which eliminated the conventional die attach and wirebond process. Flip chip assembly further decreases the form factor of the module. The designed flip chip balun on Si has comparable performance as the balun designed on GaAs substrate [1], with further size reduction by flip chip assembly.