High power gallium nitride micro-electronics: thermal management using microfluidics

Zhang, Gan (2021). High power gallium nitride micro-electronics: thermal management using microfluidics. University of Birmingham. Ph.D.

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Abstract

Last four decades have seen unprecedented development in communication, defence, electronics, and computing technologies. The increased power density plus the miniaturisation of the device present challenges in managing the high heat flux in the microchip level. Besides, the highly heterogeneous heat flux in electronic devices presents more challenges to thermal management (TM). This calls for the development of more efficient cooling technologies for these high-power microelectronic devices. This PhD study aims to address this challenge by developing the high performance of heat transfer fluids (HTFs) and compact cooling devices. Gallium Nitride (GaN) based transistors which acted as inhomogeneous high heat flux output were targeted in this work.
The work involves formulating, characterisation and performance measurements of various heat transfer fluids (including base fluids and nanofluids), design, fabrication and assemble, and package and experiments of microfluidics including foam metal, micro-jet impingement. Both experimental work and modelling were performed and the following main conclusions were obtained.
• Heat transfer fluids study
Two types of nanofluids were formulated and investigated for the application in room temperature and the low temperature. The BN/DI water nanofluids used in the room temperature shows 5.2 % enhancement in the thermal conductivity compared to the base fluid for the 0.5 wt.%. The other material rGO/EG+DW nanofluids used for the temperature as low as -50 ℃ has 17 % thermal conductivity increase with the concentration of 2.0 wt.%. This suggests that the nanofluids can have a better thermal performance for the microfluidic channel than the base fluids.
• Performance of the microfluidics
With the experimental comparison of the copper-foam based microfluidic channel and the micro-jet channel, the micro-jet channel was chosen due to a higher heat transfer coefficient. Both base fluids and nanofluids were experimental tests and the numerical simulation was validated with the micro-jet channel. The test showed that the BN/DI water nanofluids with a concentration of 0.5 wt.% can increase the heat transfer coefficient 5 % compared to the DI water. Meanwhile, the 2.0 wt.% rGO/EG+DW nanofluids showed a similar trend with an 11% increase in the heat transfer coefficient compared to EG+DW base fluid.
The direct measurement of the temperature with Raman thermography was used to measure the temperature in the finger of the die. The experiment test suggests that with the target power density of 5 W/mm in the finger (1×10⁷ W/mm² in the finger), the peak temperature in the devices was 120 °C far below 200 °C. The thermal resistance for the jetting channel was 19.76 °C/W. The device used in the experiment was GaN-on-SiC. For the GaN-on-Diamond, a higher power density can be obtained.
Thus, for the thermal management of the GaN devices, the nanofluids, material selection for the devices thermal package and micro-jet channel play important roles once the specific GaN transistors are selected.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):