Investigation of On-Chip Inductors for Fully Integrated DC-DC Converters

TL;DR

This paper designs and tests on-chip inductors in a 0.18 μm CMOS process, integrating them into buck converters to evaluate their performance and efficiency in a fully integrated DC-DC conversion system.

Contribution

It demonstrates the fabrication and measurement of on-chip inductors with high inductance and quality factors, and compares their performance in integrated buck converters with different diode implementations.

Findings

Inductors achieved over 250 nH with validated simulation.

Buck converters operated at 30 MHz with 69.1% efficiency.

On-chip inductors are viable for integrated DC-DC converters.

Abstract

On-silicon inductors using a bulk 0.18 {\mu}m CMOS process have been designed. By shunting different metal layers in parallel, inductor values and quality factors were simulated. Selected inductors were then employed in two open-loop buck converters for comparison: the first used an off-chip discrete diode, and the second used an on-chip active diode. All inductors and converters were sent for fabrication. The fabricated inductors were then measured to have values more than 250 nH over a wide range of frequency, validating the simulation results. The buck converters were switched at 30 MHz with a fixed duty ratio of 0.5, to generate an output voltage of 1.2 V from an input voltage of 2.4 V. The peak efficiency was measured to be 69.1% for a light load current of 12.9 mA.