Microfabrication Technology Of Planar Microinductor With Magnetic Film For DC-DC Integration

The portable electronic products have been rapidly developed in recent years and all of them become lighter and smaller in size.So the internal integrated power management chip shows more essentiality in this system.However,the monolithic DC-DC converter in current application is only the power supply chips integration,and the passive components such as inductors,resistors and capacitors are external devices.The inductance and quality factor of an thin-film inductor,when used in high frequency circuit to realize the function of filtering,tuning and matching,could directly influence the performance of the circuit system.Therefore,it is very significant to realize the miniaturization and high sensitivity of micro-inductor for integrating the passive devices to power management chip and improving the performance of this system.The micro-inductors fabricated by MEMS technology and thin-film technology have technological superiority of small volume,low resistance,high inductance,low loss and batch production.So MEMS technology was used to fabricate the planar microinductors with different structures,materials and thickness of magnetic film in this paper.The loss mechanics of micro-inductor are deeply analyzed for establishing the inductor model.On this basis,the planar models are simulated by COMSOL software,and the properties of the materials parameters and some parameters of the inductor on the inductance and quality factor are calculated.The magnetic thin-film was introduced into the planar micro-inductor and a patterned film is proposed to improve the inductance and reduce the loss of the magnetic material at high frequency.Finally,we propose four kinds of planar inductor models: double planar spiral inductor,the no pattern on Ni film double-layer planar spiral inductor,the no pattern on NiFe film double-layer planar spiral inductor and patterned NiFe film double planar spiral inductor.Finite element analysis software also helps to analyze the influence of magnetic thin-film on planar microinductor.The result shows that the magnetic thin-film is helpful to improve the inductance of the inductor and the patterned magnetic thin-film can decrease vortex loss effectively.Based on simulation and theoretical analysis,four models of planar micro-inductors were fabricated by MEMS process.The tape-out process which is suitable for planar micro-inductor were developed in the experiment.Then,the inductance and quality factor of these micro-inductors in the frequency of 10k-10 MHz are fully characterized by Agilent E4294 A Impedance Analyzer.The results show that the inductance of microinductor with patterned NiFe thin-film is 2.17?H and quality factor is 2.8 at 1.5MHz;the quality factor is 1.6 times of micro-inductor with no pattern on NiFe thin-film and the inductance is 3 times of micro-inductor without magnetic thin-film.The inductance increased along with the increase of film thickness of NiFe film appropriately.So the micro-inductor with patterned NiFe thin-film has better performance for DC-DC converter.At last,the synchronous DC-DC conversion detection circuit was designed and made the corresponding PCB board to detect the conversion efficiency of the prepared micro-inductors.The experimental results show that the micro-inductor with patterned NiFe thin-film has the highest efficiency(67%),higher than other three fabricated microinductors.Although it is lower than the conversion efficiency was obtained by commercially available wire-wound magnetic-core inductor conversion(90%),the area of micro-inductor is only 1/8 of the wire-wound magnetic-core inductor.All in all,it has significant potential in future DC-DC integration.