Comparison of compact on-chip inductors embedded in wafer-level package

On-chip high-Q spiral inductors on Si substrate embedded in WLP have been fabricated. These inductors consisted of a thick Cu electroplated rerouting to reduce electrical resistance and a thick resin layer to separate the inductors typically 20 μm from Si substrate. The inductance L of 5.0 and 4.9 nH with the quality factor Q of 28.4 and 42.9 were obtained for a 3.5 turn rectangle spiral inductor at 2 GHz on the Si substrate, which had a resistivity of 4-6, 1kΩcm, respectively. The R_Si in the assignment parameters for lumped RLC equivalent circuit by ADS denoted more than 5 kΩ in a 3.5 turn. In addition, the measured results of Q, L and f_res corresponded well with the simulated values by HFSS and Sonnet. This technology realizes embedded high quality inductors in WLP.