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High-Frequency On-Chip Inductors with Patterned CoZrTa Films
Keywords: On-chip Inductors, Magnetic Materials, High Frequency
There is an increasing demand for improving the chip-area efficiency of on-chip inductors. Prior researches have shown modest improvements in the inductance (L) and quality factor (Q) above 1 GHz by integrating on-chip inductors with ferromagnetic materials. In this work, enhancements of 3.5X in inductance and 3X for the quality factor at frequencies as high as 3 GHz have been successfully demonstrated by using a continuous CoZrTa-ring structure in spiral inductors at the 100 µm scale. Further improvement of the frequency response of L up to 6 GHz was achieved by micro-patterning the magnetic film. This work demonstrates significantly larger increases in L and Q above 1 GHz as compared to prior efforts thereby making the added processing cost worthwhile. Inductors with magnetic material were fabricated on quartz substrates using electron beam lithography (EBL) and magnetron sputtering for pattern definition and metallization, respectively. Three types of magnetic thin film structures including single-ring, double-ring and sandwich structures are designed to optimize the frequency response. Besides spiral inductors, stripline inductors with different thickness of CoZrTa films were also fabricated to better evaluate the thickness-dependent inductor performance. Measurements show that inductors with thicker CoZrTa films have 5X increase of inductance which is significantly larger than the increase of inductors with thin CoZrTa layers. However, the frequency response is limited to 300MHz because thicker magnetic films result in more severe eddy current and larger induced energy loss especially in magnetic via regions, which degrade the performance of the inductors. Hence, a clear trade-off between enhancement of inductance and the frequency response is observed.
Hao Wu, Student
Arizona State University
Tempe, AZ

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