To achieve a package-level DC power grid for the next-generation power delivery to LSIs, multiple point-of-load (POL) buck DC-DC converters must be integrated into the package. We developed a 180 nm CMOS switch DC-DC buck converter for the POL DC power supply using a Zn-Fe ferrite core planar inductor embedded in an organic interposer. The embedded inductor had a 25 m thick copper spiral coil sandwiched by 10 m thick Zn-Fe ferrite thick film fabricated using the spin-spray method, which exhibited an inductance of 4.6 nH and a Q-factor of 11 at 50 MHz. A 180 nm CMOS switch was mounted using a flip-chip scheme on the organic interposer with the embedded inductor. The developed 50 MHz switching CMOS switch buck DC-DC converter exhibited a power conversion efficiency of about 68% when the input voltage was 2 V, the on-duty ratio was 0.5, the output voltage was 0.855 V, and the current was 1 A.
In order to establish the basic technology of package level DC power grid for next generation power delivery to LSIs, Zn-ferrite core planar power inductor embedded in an organic interposer, for power supply integrated in LSI package, has been fabricated and evaluated. Zn-ferrite core planar power inductor embedded in organic interposer had a footprint of 850×850 m 2 , 2-turn, 20 m thick copper spiral coil sandwiched by top and bottom Zn-ferrite film magnetic core. For a comparison, a 3-turn air core spiral inductor was also embedded in the same organic interposer, which exhibited a large degradation of inductance at high frequencies because of eddy current induced by widespread high frequency magnetic flux passing through the lower layer Cu metal plane. Zn-ferrite core planar inductor had a relative small decrease of inductance at high frequencies. From 3D electromagnetic field analysis, it was found that the magnetic core inductor embedded in interposer has a great advantage of a possible three dimensional layout of the inductor with small influence on the near signal-line and circuit ground.
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