In this work, we describe a new approach for compact and energy-efficient cooling of converters where multiple miniaturized microfluidic cold-plates are attached to transistors providing local heat extraction. The high pressure drop associated with microchannels was minimized by connecting these cold-plates in parallel using a compact 3D-printed flow distribution manifold. We present the modeling, design, fabrication and experimental evaluation of this microfluidic cooling system and provide a design strategy for achieving energy-efficient cooling with minimized pumping power. An integrated cooling system is experimentally demonstrated on a 2.5 kW switched capacitor DC-DC converter, cooling down 20 GaN transistors. A thermal resistance of 0.2 K/W was measured at a flow rate of 1.2 ml/s and a pressure drop of 600 mbar, enabling the cooling of a total of 300 W of losses in the converter using only 75 mW of pumping power, which can be realized with small micropumps. Experimental results show a 10-fold increase in power density compared to conventional cooling, potentially up to 30 kW/l. This proposed cooling approach offers a new way of co-engineering the cooling and the electronics together to achieve more compact and efficient power converters.

In this work we demonstrate high-performance lateral GaN power Schottky barrier diodes (SBDs) based on a novel multi-channel tri-gate architecture. A significant reduction in ONresistance (RON) of 50%, down to 7.2 ± 0.4 Ω·mm, along with a much smaller forward voltage (VF) of 1.57 ± 0.06 V, were achieved with multiple 2DEG channels (multi-channels) formed by periodic AlGaN/GaN heterostructures. We used a tri-anode structure to form Schottky contact to the multi-channels through the fin sidewalls, leading to a small turn-ON voltage (VON) of 0.67 ± 0.04 V. To simultaneously control the multi-channels and effectively spread the electric field in OFF state, a tri-gate structure was integrated in the anode, resulting in an ultra-low leakage current (IR) of ~1 nA/mm at -600 V and a high breakdown voltage (VBR) of -900 V at 1 μA/mm with grounded substrate. In addition, the devices presented promising switching performance, due to the small product of RON and reverse charge (Q), thanks to the optimized tri-gate geometry, and the high effective mobility (μe) of 2063 ± 123 cm2·V-1s-1 despite the small fin width (w) of 50 nm. Our approach combines in a unique way the excellent electrostatic control of the tri-gate structure with the high conductivity of multi-channels, offering a promising platform for future advances in GaN power devices.

GaN transistors are being employed in an increasing number of applications thanks to their excellent performance and competitive price. Yet, GaN diodes are not commercially available and little is known about their performance and potential impact on power circuit design. In this work, we demonstrate scaled-up GaN-on-Si Tri-Anode Schottky Barrier Diodes (SBDs), whose excellent DC and switching performance are compared to commercial Si fast recovery diodes and SiC SBDs. Moreover, the advantageous lateral GaN-on-Si architecture enables to integrate several devices on the same chip, paving the way to power integrated circuit. This is demonstrated by realizing a diode-multiplier Integrated Circuit (IC), which includes up to 8 monolithically-integrated SBDs on the same chip. The IC was integrated on a DC-DC magnetic-less boost converter able to operate at a frequency of 1 MHz. The IC performance and footprint are compared to the same circuit realized with discrete Si and SiC vertical devices, showing the potential of GaN power ICs for efficient and compact power converters.

In an era where high-frequency flying capacitor (FC) multilevel inverters (MLIs) are increasingly gaining attention in energy conversion systems that push the boundaries of power density, the need for a compact, fast, and accurate FC voltage monitoring system is also increasing. In this article, we designed and developed a new FC measurement system, based on precise sampling of the inverter switching node voltage, through a bidirectional clamping circuit. The deviation of FC voltages from their nominal values is extracted by solving a set of linear equations. With a single sensor per phase and no isolation requirements, as opposed to dozens of sensors in traditional FC monitoring, our approach results in significantly lower cost, complexity, and circuit size. Detailed device-level simulations in LTspice and system-scale simulations in MATLAB validate the accuracy and speed of the proposed measurement system and the balancing strategy in steady-state, abrupt load change, and imbalance conditions. Experiments carried out in a three-phase gallium nitride five-level inverter prototype reveal a gain in precision and bandwidth that is more than 30 times that of conventional methods, at a fraction of their cost and footprint. The recorded performance renders the developed sensor an ideal solution for fast MLIs based on wide-bandgap technology.