High-Q SU8 based above-IC inductors for RF power devices

This paper discusses quality factor Q enhancement of inductors integrated above very low resistivity substrates (under 0.1 Ω.cm). The impact of such resistivity on the performance and the ineffectiveness of patterned ground shields are presented. Consequently, for high Q purpose, we investigate solid ground shield, additional dielectric thickness, metallic ribbon section including its aspect ratio. Q values as high as 55 at 5 GHz for a total inductance value of 0.8 nH can be achieved with only 60 μm thick dielectric layer. A low cost process has been developed to integrate these inductors above RF power LDMOS devices using the SU8 photoresist as dielectric.