High-Q embedded inductors in fan-out eWLB for 6 GHz CMOS VCO

We investigate high-quality (high-Q) inductors realized in the fan-in area and in the fan-out area of the embedded wafer level ball grid array (eWLB) package. We show that the inductors realized in the fan-out area have negligible substrate losses and lower parasitic capacitances compared to the inductors in the fan-in area. As a result, the fan-out inductors offer significantly higher quality factors and higher self-resonance frequencies (SRFs). We also investigate effects of the chip-to-package interconnection. We demonstrate the advantages of fan-out eWLB inductors on the example of a 6 GHz voltage controlled oscillator (VCO) chip manufactured in a 65 nm complementary metal-oxide-semiconductor (CMOS) technology and assembled in an eWLB package. We use a 1.1 nH high-Q differential coupled fan-out eWLB inductor for the LC tank to reduce the phase noise. We use a VCO fabricated with a standard on-chip inductor and assembled in the identical eWLB package as a reference. Measurement results demonstrate lower phase noise and higher output power of all VCOs with embedded eWLB inductors. The measured phase noise for the VCO with the fan-out eWLB inductor is in best case 9 dB lower than that of the reference VCO with the on-chip inductor. The results prove the integration concept and demonstrate excellent potential of inductors realized in the fan-out area of eWLB.