FLIP CHIP ASSEMBLED HIGH-Q MICRO-INDUCTORS FOR RF-IC APPLICATIONS
J. ZENG, C. H. WANGTP, A. J. SANGSTER

Abstract. This paper presents the development of high-Q micro-inductors for multi-GHz RF-IC applications. The suspended inductor devices were produced using flip chip assembly approach. The inductor structures with supporting pillars were fabricated on a flexible polyimide carrier and then assembled onto silicon substrates using flip chip bonding. Individual and 2×2 arrays of suspended inductors have been successfully produced on silicon substrates. Maximum Q-factors of ~15 and ~13 have been achieved for meander and spiral inductor devices at ~1GHz before pad deembedding. It is shown that the optimal air gap between the inductor and substrate surface is ~15 μm beyond which no further enhancement in Q-factor can be obtained. The polyimide carrier has negligible effect on the RF performance of the inductors. The measured results are in good agreement with that of theoretical simulation using Ansoft HFSS software package. Encapsulation of the free-standing inductors has been investigated using glass cover and SU8 epoxy as sealing material. It is shown that the cap and sealing ring have no noticeable effect on the Q-factor of the devices at the frequency of above 1 GHz.