A low loss, 5.5 GHz-20 GHz monolithic balun

A low-loss monolithic Marchand balun has been designed and fabricated using polyimide as the inter-metal dielectric. The measured return loss is less than -10 dB from 5.5 GHz to 28 GHz. The balun loss is less than 0.7 dB over the 6 GHz to 21 GHz operating band. This is the lowest loss ever reported for such a balun. The excellent loss is the result of using a relatively thick polyimide layer (10 /spl mu/m) as the inter-metal dielectric. This balun has been applied to HBT and pHEMT amplifiers with second harmonic components suppressed >40 dB, even in compression, demonstrating very good push-pull operation.