Optimizing Diamond Heat Spreaders for Thermal Management of Hotspots for GaN Devices

Abstract

As devices become smaller while still requiring high reliability in the presence of extreme power densities, new thermal management solutions are needed. Nowhere is this more evident than with the use of Gallium Nitride (GaN) transistors, where engineers struggle with the thermal barriers limiting the ability to achieve the intrinsic performance potential of GaN semiconductor devices. Emerging as a common solution to this GaN thermal management challenge are metallized diamond heat spreaders. In this paper, a diamond heat spreader has been applied with a hybrid Si micro-cooler for to cool GaN devices. Several different grades and thicknesses of microwave CVD diamond heat spreaders, as well as various bonding layers, are characterized for their thermal effects. The heat spreader is bonded through a TCB (thermal compression bonding) process to a Si thermal test chip designed to mimic the hotspots of 8 GaN units. The heat dissipation capabilities were compared through experimental tests and fluid-solid coupling simulations, both showing consistent results. In one configuration, using a diamond heat spreader 400μm thick with a thermal conductivity > 2000W/mK, to dissipate 70W heating power, the maximum chip temperature can be reduced by 40.4%, for test chips 100μm thick. And 10kW/cm2 hotspot heat flux can be dissipated while maintaining the maximum hotspot temperature under 160ºC. The concentrated heat flux has been effectively reduced by the diamond heat spreader, and much better cooling capability of the Si micro-cooler has been achieved for high power GaN devices.

Embedded Two-Phase Cooling of High Flux Electronics Via Press-Fit and Bonded FEEDS Coolers

“…The temperature dependence of thermal conductivity of the substrates was accounted for by assuming the following relationship [22]:…”

“…where T is in C, and a ¼ 3:037 Â 10 5 (W/m K) and n ¼ 1:334 for silicon [22,23]. For SiC, a constant value of k ¼ 390 W/m K given by the manufacturer data sheet was used due to the lack of reliable temperature dependent data on 4H-SiC.…”

Heterogeneous Integration of Diamond Heat Spreaders for Power Electronics Application

“…With miniaturization and increasing chip density, the heat generation is concentrated within a small area, leading to thermal hot spots. For instance, the gate-to-gate spacing in Gallium Nitride (GaN) High Electron Mobility Transistors (HEMTs) is typically less than 50μm, which creates concentrated thermal regions [7]. Heat sinks alone are insufficient to dissipate highly concentrated heat flux.…”

“…Despite considerable research interests, incorporating diamonds in power electronics suffers from complex processing, high temperatures, and cost. Recent advancements in fabricating diamonds through Chemical Vapor Deposition (CVD) process have reduced the cost to ∼$1/mm 2 [7]. The most common method of creating passive heat spreaders on active devices is growing synthetic diamond films on silicon substrates.…”

Pushing the limits of microfocus X-ray sealed-tube sources for crystallography

“…The brightness of an X-ray tube is mainly limited by the thermal conductivity of the bulk anode material. As the thermal conductivity of diamond is up to about 5 times higher than that of copper and the highest known conductivity of all bulk materials [1], industrial diamond is increasingly replacing traditional materials for the thermal management in challenging applications [2], in which a high local heat load needs to be dissipated, such as in heat sinks for high-power microelectronic devices [3,4]. In X-ray sources, diamond can be used as a heat sink directly coupled to the anode material, resulting in a significantly higher thermal conductivity compared to a conventional metallic anode and, hence, allowing for an increase in tube brilliance by applying a higher power load on the anode [5].…”