On-package magnetic materials for embedded inductor applications

Emerging applications in microwave communication, RFIC, and power delivery system are driving the need for the miniaturization, cost-reduction and quality optimization of inductors. In our prior work, high-quality-factor and low-resistance embedded inductors were fabricated on low-cost printed circuit board (PCB) for system-on-package applications. The inductor with a CoFeHfO magnetic core patterned by sand-blasting experimentally produced an inductance gain of ∼12% over the air-core inductor. In order to further improve the inductance gain, we looked at alternative processes and materials to use in the fabrication of magnetic cores. In this paper, we investigated and compared the magnetic properties of CoFeHfO magnetic cores on the PCB substrate patterned by both wet-etching and sandblasting. The magnetic domain images by Kerr microscopy, hysteresis loops and permeability spectra clearly showed that the CoFeHfO core patterned by wet-etching had a 3x larger permeability value and softer magnetic properties than the core patterned by sand-blasting. With the implementation of the CoFeHfO core by wet-etching, the theoretic calculation predicted an inductance gain of 32% for our embedded inductor. Besides CoFeHfO, we also explored the magnetic properties of CoTaZr film deposited on the same PCB substrate and measured its permeability value to be ∼600, which theoretically indicated a gain of 128% for the inductor we designed.