Near-junction microfluidic thermal management of RF power amplifiers

Abstract

While gallium nitride (GaN) is attracting broad attention as the wide bandgap material of choice for both industrial and defense applications, thermal impediments present a significant barrier to full exploitation of its inherently high electron sheet charge density and electrical breakdown voltage. For the last four years, the Defense Advanced Research Projects Agency (DARPA) has pursued research focused on reduction of near-junction thermal resistance through use of diamond substrates and convective and evaporative microfluidics. The options, challenges, and techniques associated with the development of this embedded thermal management technology are described, with emphasis on the accomplishments and status of efforts related to GaN power am plifiers.

Applications and Impacts of Nanoscale Thermal Transport in Electronics Packaging

“…The goals of electronic materials development have primarily been focused in two directions: faster switching speed (i.e., higher frequency) [82][83][84] and higher power [85][86][87][88][89][90]. In communications [82][83][84]91,92] and computational electronics [11,[13][14][15], higher frequency is desirable, while higher power delivery is desired for electric vehicles [26,88,93], industrial and utilities [2,94,95], and military applications [96][97][98]. To move successfully in both directions, the industry must transition away from silicon, and to devices made from wide bandgap materials.…”

Challenges and opportunities in Gen3 embedded cooling with high-quality microgap flow

“…To overcome these limitations and remove a significant barrier to continued Moore's law progression in electronic components and systems, it is essential to "embed" aggressive thermal management in the chip, substrate, and/or package and directly cool the heat generation sites. The development of such "Gen3" thermal management technology, following on the Gen1 air-conditioning approaches of the early years and the decades-long commitment to the Gen2 "remote cooling" paradigm, has been spearheaded by the Defense Advanced Research Projects Agency (DARPA) [3][4][5] and embraced by many organizations [2,[6][7][8].…”

“…Through technology developed in this program, specifically the placement of GaN epitaxy on-or in close proximity to-high thermal conductivity diamond, the RF power handling capability of GaN high-electron-mobility transistor (HEMT) devices was increased by greater than a factor of 3 [9][10][11][12][13][14], to in excess of 500W/mm 2 of RF power and more than 400W/mm 2 of heat, as shown in Fig. 1 and described in greater detail in [8,15].…”

Efficient Microchannel Cooling of Multiple Power Devices With Compact Flow Distribution for High Power-Density Converters

“…Additionally, GaN high electron mobility transistors (HEMTs) can operate at higher frequencies, enabling the use of smaller passive components which further reduces the converter volume. However, the increased switching losses due to higher switching frequencies and reduced die sizes cause high heat fluxes, surpassing 1 kW/cm 2 [6], [7], which is far beyond the capabilities of conventional cooling methods [8]. Inadequate cooling of these devices causes high junction temperature which degrades their performance and reliability [9], [10].…”

“…For a given design and its corresponding thermal resistances (Rconv, Rint, Rj-c) and heat load, Qmax, the required flow rate to keep the junction temperature rise at ΔT max can be calculated using (7). The relationship between pressure drop and flow rate in the microchannel cold plate can be expressed in terms of a hydraulic resistance, rh.…”