On-chip spiral inductors find numerous applications in analog integrated circuits, power delivery and RF circuits for wireless communications. Currently most on-chip inductors have inductance densities of up to 200 nH/ mm² with absolute values in the range of 1--15 nH. This directly translates to chip areas of square of a few hundred micrometers. With extensive scaling of active devices, it is important to reduce the area of passive devices such as on-chip inductors while maintaining high inductance values. Integrating magnetic material with on-chip inductors is one of the most common approaches used to enhance the inductance value. Magnetic material with high permeability confines and amplifies the induced magnetic flux inside it and thus contributes to the increase of inductance. However, at high frequencies, inductors with high permeability magnetic materials exhibit losses mainly due to eddy currents and ferromagnetic resonance. In this dissertation, an extensive study and discussion of different approaches were presented for integrating magnetic materials with inductors such as choice of structure, materials, loss mechanisms and design trade-offs with potential applications. Through experiments and simulations, it is demonstrated that spiral inductors with patterned NiFe rings at 100 mum scale can achieve enhancements of 6X in inductance and 3X in quality factor at frequencies as high as 200 MHz, with corresponding inductance density up to 770 nH/mm². Furthermore, inductors with Co-Zr-Ta ring structures can obtain 3.5X increase of inductance up to 3 GHz with the peak quality factor around 3, which is very attractive for RFIC applications. Finally, a possible additional optimization method was proposed and the preliminary results showing promising improvement of the inductor performance was demonstrated in simulation.
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