Design And Fabrication Of On-chip Integrated Power Inductor

Power supply is indispensable for electronic products,where switched-mode power supplies is widely used in all kinds of power converters because of its excellent performance.With the rapid development of integrated circuit technology and the ever-increasing demand of miniaturization of electronic products in the market,the disadvantages of off-chip inductors(transformers)used by traditional switching power supply products are becoming increasingly obvious.Compared with the traditional discrete passive devices,the integrated power inductors have better high frequency performance,higher inductance density and can improve the dynamic response of circuits.Also,it can be miniaturized and on-chip,so as to achieve a single chip switching converter or Pwr So C(“Power Supply on Chip”).In this paper a racetrack microinductor with Ni45Fe55 core for integrated DC-DC converter was designed and manufactured based on MEMS technology.Analytical models including the inductance model,the resistance model,the winding AC/DC loss model and the core loss model were presented based on electromagnetic field theories,also,the FEM simulation was employed by ANSYS Maxwell.A racetrack microinductor was fabricated by MEMS technology,including photolithography,physical vapor deposition,wet etching et.al.The small-signal measurements for the micro-inductor were conducted using an LCR Meter for a frequency range of 1 to 100 MHz,the measured inductance of the fabricated micro-inductor shows a flat inductance value of 214 nH up to a frequency of at least50 MHz with less than 10%drop,the maximum Q factor is 9.23 at 9.2 MHz,and the measured DC resistance is 470 mΩ.The test circuit of microinductor was designed based on a commercially available 20 MHz buck converter from Semtech.Compare to efficiency of 84.93%of a PCB integrated air-core inductor,the measured efficiency of the buck converter using the micro-inductor is 80.27%,when the input voltage 2.7 V,output voltage 1.8V,output current 200 m A.while the air-core inductor occupies an area of 32 mm~2 with inductance density only of 7.16 nH/mm~2.But the area of the integrated inductor is only 2.9 mm~2,and the inductance density of microinductor is 73.8nH/mm~2,which shows great area and inductance density advantages than the PCB air-core inductor.At the end of the paper,the power loss of the converter was analyzed in detail,if the power loss of PCB board is ignored,the inductor can achieve peak efficiency of 92.71%.