IIIT Hyderabad Publications
CMOS RFIC Inductors Incorporated with Domain Patterned Permalloy Films and Investigation of Domain Dynamics therein
Author: Vasu Pulijala
Report no: IIIT/TH/2016/28
Inductors are one of the major constraints in the design of Radio Frequency Integrated Circuits (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. Research in this area is towards fabrication of 3D-MEMS inductors and synthesis of new magnetic materials. 3D MEMS inductors are difficult to implement in monolithic RFICs due to packaging and stability issues. Patterned electrical ground or amorphous magnetic ground planes beneath the inductor are employed to reduce the eddy current 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. Permalloy, which is known for its soft magnetic properties and compatibility with CMOS process, has been used widely for enhancement of inductance of spiral inductors but the frequency is restricted to <1GHz. When patterned as magnetic bars and square dots, improvement in the performance of inductors has been observed at frequencies >1 GHz and in such cases Ferromagnetic Resonance(FMR) of the patterned material has set the limitations to employment at further higher frequencies. 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 Object Oriented Micro-Magnetic Framework (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.
Full thesis: pdf
Centre for VLSI and Embeded Systems Technology
Copyright © 2009 - IIIT Hyderabad. All Rights Reserved.