CMOS RFIC Inductors Incorporated with Domain Patterned Permalloy Films and Investigation of Domain Dynamics therein

Abstract

Inductors are one of the major constraints in the design of RFICs. This is because they consume large area and the quality factor is very low. Low quality factor is attributed to the parasitic losses at the higher frequencies. Substrate eddy current losses is one among the contributing parasitic losses. To improve the inductance density and quality factor of on-chip spiral inductors in RFICs employment of magnetic materials is one of the popular approaches. In cases where bulk magnetic material is used around inductors, eddy current losses become significant at higher frequencies restricting their usage to lower frequencies. Patterning the magnetic material has shown to reduce these drawbacks. For magnetic materials, formation of magnetic domains and their dynamics may play a major role in defining their properties at higher frequencies. In this thesis, effect of size and shape of Permalloy patterns in the formation of magnetic domains, their dynamics, and the influence of these domain controlled patterns on properties of spiral inductor are investigated. It is shown experimentally that the shape and size induced domain patterns in Permalloy play a varied role in the improvement of inductance. Micromagnetic simulations with OOMMF are used to determine the domain patterns. Secondly, 60 nm thick domain-patterned-Permalloy have given more improvement in inductance and quality factor compared to 96 nm thick patterns. OOMMF simulations show the same trend that 60 nm patterns which contain cross tie walls perform better than 96 nm patterns which contain asymmetric Bloch wall. Permalloy domain-controlled patterns have also been incorporated as magnetic shield and an improvement in the performance of the inductors is observed. All the experimental observations confirm the necessity of incorporation of proper magnetic patterns whose shape and size could be controlled to form appropriate domain patterns for high frequency applications like inductors in RFICs.