Magnetics and GaN for Integrated CMOS Voltage Regulators

The increased use of DC-consuming electronics in many applications relevant to everyday life, necessitates significant improvements to power conversion and distribution methodologies. The surge in mobile electronics created a new power application space where high efficiency, size, and reduced complexity are critical, and at the same time, many computational tasks are relegated to centralized cloud computing centers, which consume significant amounts of energy. In both those application spaces, conversion and distribution efficiency improvements of even a few-% proves to be more and more challenging. A lot of research and development efforts target each source of loss, in an attempt to improve power electronics such that it serves the advances in other fields of electronics. Non-isolated DC-DC converters are essential in every electronics system, and improvements to efficiency, volume, weight and cost are of utmost interest. In particular, increasing the operation frequency and the conversion ratio of such converters serves the purposes of reducing the number or required conversion steps, reducing converter size, and increasing efficiency. The aforementioned improvements can be achieved by using superior technologies for the components of the converter, and by implementing higher level of integration than most present-day converters exhibit. In this work, Gallium Nitride (GaN) high electron mobility transistors (HEMT) are utilized as switches in a half-bridge buck converter topology, in conjunction with fine-line 180nm complementary metal oxide semiconductor (CMOS) driver circuitry. The circuits are integrated through a face-to-face bonding technique which results in significant reduction in interconnects parasitics and allows faster, more efficient operation. This work shows that the use of GaN transistors for the converter gives an efficiency headroom that allow pairing converters with state-of-the-art thin-film inductors with magnetic material, a task that is currently usually relegated to air-core inductors. In addition, a new "core-clad" structure for thin-film magnetic integrated inductors is presented for the use with fully integrated voltage regulators (IVRs). The core-clad topology combines aspects from the two popular inductor topologies (solenoid and cladded) to achieve higher inductance density and improved high frequency performance.