Analysis of microinductor performance in a 20-100 MHz DC/DC converter

This paper presents a low-profile thin-film microfabricated inductor on silicon and its performance in a high-frequency low-power dc/dc converter. The design of the inductors has focused on maximizing efficiency while maintaining a relatively flat frequency response up to 30 MHz. The inductance at 20 MHz is approximately 150 nH with a resistance of 1.8 Ω. The performance of the microinductor has been compared to two conventional commercially available 150-nH chip inductors. One of the chip inductors has a magnetic-material core and the other is an air core. The maximum efficiency of the microinductor, which relates the power loss of the microinductor to output power loss of the converter, is measured to be approximately 93% at 20 MHz. The low-power dc/dc converter operates in the tens of milliwatts output power range, with an input voltage of 1.8 V and an output voltage programmable between 0 and 1.8 V. The converter maximumefficiencywhen using themicroinductor on silicon is 78.5% at 20 MHz, which is approximately2%lower than the efficiency using the conventional chip inductors.