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Thermal stress modelling of diamond on GaN/III-Nitride membranes

Cuenca, Jerome A., Smith, Matthew D., Field, Daniel E., C-P. Massabuau, Fabien, Mandal, Soumen, Pomeroy, James, Wallis, David J., Oliver, Rachel A., Thayne, Iain, Kuball, Martin and Williams, Oliver A. 2020. Thermal stress modelling of diamond on GaN/III-Nitride membranes. Carbon 10.1016/j.carbon.2020.11.067
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Diamond heat-spreaders for gallium nitride (GaN) devices currently depend upon a robust wafer bonding process. Bonding-free membrane methods demonstrate potential, however, chemical vapour deposition (CVD) of diamond directly onto a III-nitride (III-N) heterostructure membrane induces significant thermal stresses. In this work, these thermal stresses are investigated using an analytical approach, a numerical model and experimental validation. The thermal stresses are caused by the mismatch in the coefficient of thermal expansion (CTE) between the GaN/III-N stack, silicon (Si) and the diamond from room temperature to CVD growth temperatures. Simplified analytical wafer bow models underestimate the membrane bow for small sizes while numerical models replicate the stresses and bows with increased accuracy using temperature gradients. The largest tensile stress measured using Raman spectroscopy at room temperature was approximately 1.0 GPa while surface profilometry shows membrane bows as large as 58. This large bow is caused by additional stresses from the Si frame in the initial heating phase which are held in place by the diamond and highlights challenges for any device fabrication using contact lithography. However, the bow can be reduced if the membrane is pre-stressed to become flat at CVD temperatures. In this way, a sufficient platform to grow diamond on GaN/III-N structures without wafer bonding can be realised.

Item Type: Article
Date Type: Published Online
Status: In Press
Schools: Physics and Astronomy
Publisher: Elsevier
ISSN: 0008-6223
Date of First Compliant Deposit: 2 December 2020
Date of Acceptance: 22 November 2020
Last Modified: 07 Dec 2020 17:59

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