Heterogenous integration of Heatsinks with electronic devices

  • Daniel E Field

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)


Improved thermal management of power electronics is vital for improved device reliability and
performance. Devices used for applications in next-generation mobile communications and
internet of things, such as high-power high-frequency power amplifiers, and propulsion of
electric vehicles and space missions, such as power switches, must handle high power dissipation
with a large degree of Joule self-heating. To enable further development in these fields, improved
thermal management is a necessity. Near channel, heterogeneously integrated heatsinks and
spreaders are one aspect of the technology required to meet this challenge. In this thesis, the
mechanical and thermal properties of the semiconductor-heatsink interface have been studied.
This interface is key for determining the reliability of devices and accessing the heatsink’s benefits.
Various methods of integrating AlGaN/GaN high electron mobility transistors with diamond have
been investigated. In addition, the thermal properties of Si-on-SiC have been studied, aiming to
understand the thermal benefit of this material over silicon-on-insulator.
An improved analysis method has been developed to investigate the mechanical stability
of heterogeneously integrated thin films on stiff substrates, demonstrated in GaN-on-diamond.
This method has increased reliability and accuracy compared to previous analyses. In addition
to mechanical investigations, the thermal properties of novel GaN-on-diamond materials have
been studied. The use of crystalline Al₀.₃₂Ga₀.₆₈N and SiC interlayers have been demonstrated,
showing good promise for SiC layers with comparable effective thermal boundary resistance
(TBReff) to state-of-the-art GaN-on-diamond using SiNₓ (30±5 m² K GW⁻¹). A multi-step diamond
growth procedure has also been investigated and found to give record low TBReff of < 5 m² K
Finally, thermal characterisation of the heterointerface was undertaken on direct-bonded
Si-on-SiC. The interface of this material exhibited excellent thermal properties with TBReff < 10
m² K GW⁻¹. Simulations suggest this material could offer significant thermal improvements over
conventional silicon-on-insulator for power converters.
Date of Award12 May 2022
Original languageEnglish
Awarding Institution
  • The University of Bristol
SupervisorJames W Pomeroy (Supervisor) & Martin H H Kuball (Supervisor)

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