Study On Very High Frequency Multiple Phase On-chip Inductors With Magnetic Core

The development of on-chip power supply systems in the era of"beyond Moore's Law"is of great significance for portable electronic products,computers,servers,etc.to improve efficiency,reduce power consumption,and enrich functions.The fully integrated inductive voltage converters have the advantages of high working efficiency,large output current,and high voltage accuracy.However,the integration of on-chip magnetic core inductance is one of the current difficulties.In particular,the multi-phase inductor topology can not only improve the inductor's saturation current,but also effectively reduce the ripple current in the switching power supply.It is one of the effective ways to achieve high power efficiency and high output current switching power supply.This thesis studies multi-phase on-chip inductors based on a novel SU8 embedding process.On this basis,a multilayer magnetic core film material is introduced,and finally the inductance value L,the quality factor Q and the self-resonant frequency are greatly improved.First of all,in this thesis,a single-layer Ni₄₅Fe₅₅ soft magnetic alloy film with in-plane uniaxial anisotropy was prepared by applying an in-situ biasing magnetic field.The optimal process conditions were determined and the high-frequency performance were characterized.Its initial permeability,ferromagnetic resonance frequency,hard axis coercivity and resistivity are 730,1.6 GHz,3.25 Oe and 45(?)?·cm,respectively.Ni₄₅Fe₅₅ permalloy is finally selected as magnetic core,upon comparing the high-frequency performance of(Ni₄₅Fe₅₅/Si O₂)₂₀,(Ni₇₀Fe₃₀/Si O₂)₂₀ and(Ni₈₀Fe₂₀/Si O₂)₂₀multi-layer films.Secondly,Ansys HFSS is used to design the topological structure of the multiphase solenoid inductor,and the influence of coil turn,structural parameters and magnetic film topological structure on the inductance L,quality factor Q and resistance value is compared.The simulation results show that the inductance L of the single-phase inductor is around 130n H,the peak quality factor Q is 21,and the size of the ten-phase inductor is less than 5.29mm².Then,the preparation process of the micro-inductor was optimized,including the SU8 thick glue process and the stripping of the magnetic core,and the multiple rounds of micro-inductor samples were fabricated.All samples were tested.The results showed that the patterning has an important influence on the effective permeability of the multilayer magnetic core film.The inductance value of a single-phase inductor with an aspect ratio of 8.9:1 is only 5.8n H.The quality factor Q peak value is 4,and the inductance of the core film with the aspect ratio close to 1 generally exceeds 100n H,and the Q peak value exceeds 16.Finally,after fully considering the shape anisotropy,three batches of multiphase inductors were redesigned and processed,and the inductance density was increased to179.5n H/mm²,and the peak quality factor was increased to 16.6.The rationality of the design is verified by comparing the simulation value and the test value,the performance difference of each phase inductance of the same batch is analyzed statistically,which points out the direction for subsequent batch preparation.