High-efficiency Double-side Embedded Inductor For Fully Integrated Power Management

The popularization and development of various electronic devices have put forward higher requirements for the stable power supply of devices in different applications.Com-pared with LDOs（low-dropout regulators）,switching power supplies are widely used in various power electronic devices because of their higher efficiency and rich topology.Magnetic devices such as inductors and transformers are the key components of switch-ing power supplies.The requirements of small size,high power density,and low cost bring high challenges to the design and manufacture of magnetic devices.Among the existing magnetic devices,the discrete magnetic devices usually occupy a large volume,and it is difficult to meet the requirements of miniaturized electronic devices.Most magnetic devices based on PCB（printed circuit board）technology are limited by the low inductance density of the line size.The introduction of magnetic materials through a special process and the use of multi-layer metal wiring can improve the performance of the PCB to a certain extent,but increase the manufacturing cost.On-chip magnetic devices are easier to meet the miniaturization requirements,but most on-chip magnetic devices are limited by technologies such as thick-resist lithography,and the thickness of metal is small,which usually leads to large resistance and high loss,reducing the overall system performance.The large area/volume and low efficiency of these magnetic devices affect and limit the performance of the power system.Therefore,this thesis proposes a miniature power inductor to achieve high inductor efficiency in a small area for use in a fully integrated power management system.The miniature power inductor proposed in this thesis is based on a silicon-based em-bedded wiring process.Two planar spiral metal coils with a thickness close to half the thickness of the substrate are embedded into the silicon substrate from the front and back,respectively,and are connected through silicon vias to connect the two coils in parallel,so that the effective metal thickness similar to the substrate thickness is realized,and the DC resistance of the inductor is greatly reduced.On the other hand,the double-sided embed-ded structure weakens the limitation of the aspect ratio on the coil line width and spacing.With a larger effective metal thickness of the inductance,a smaller metal width and spac-ing can still be achieved,ensuring the inductance density.This thesis uses HFSS to carry out a systematic simulation study of the proposed double-sided embedded inductor,and on this basis,the process design and experimental preparation are carried out.The double-sided embedded inductor designed and fabricated in this thesis achieves an effective metal thickness of 300μm,a metal width of 25μm and a spacing of 15μm on a 350μm thick silicon substrate.The double-sided embedded inductor with an area of 0.8 mm~2prepared in this thesis has only a DC resistance of 42 mΩ,and the inductance value reaches 16.1n H,thus achieving a large inductance-to-DC resistance ratio of 0.4 n H/mΩ.The high in-ductance to DC resistance ratio guarantees inductive performance,and the double-sided embedded inductor can achieve 96.1%efficiency in integrated DC-DC converter applica-tions from 1.8 V to 0.85 V,100 MHz.Compared with other related studies,the inductor has the highest efficiency when the output current is in the range of 0.16 A to 1.2 A.