Thick-Copper-Buried Inductors Using Anodized Aluminum Package Substrates

Spiral inductors were fabricated by burying thick metals in radio frequency (RF) package substrates. The inductors consist of a 40-μm-thick copper spiral buried in an anodized aluminum substrate and an overpass supported by a benzocyclobutene layer on top of the substrate. Due to their low ohmic loss, significantly high Q factors were obtained at 2 GHz: a Q factor of over 100 with 4.2-nH inductance (2.5-turn spiral) and a Q of 60 with 7.8-nH inductance (3.5-turn). The results demonstrate that the substrate-buried thick metal process can be a viable technique to meet the demands on cost-effective high-Q inductors compatible with conventional thin-film processes for RF integrated circuits.