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Thermo-Mechanical Study of AlN Thin-Films As Heat Spreaders in III-V Photonic Devices

[+] Author Affiliations
Shenghui Lei, Ryan Enright

Nokia Bell Labs, Dublin, Ireland

Ertugrul Kardemir, David McCloskey, John F. Donegan

Trinity College Dublin, Dublin, Ireland

Paper No. IPACK2017-74184, pp. V001T02A010; 8 pages
  • ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems collocated with the ASME 2017 Conference on Information Storage and Processing Systems
  • ASME 2017 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems
  • San Francisco, California, USA, August 29–September 1, 2017
  • Conference Sponsors: Electronic and Photonic Packaging Division
  • ISBN: 978-0-7918-5809-7
  • Copyright © 2017 by ASME


Ridge-type hybrid III-V active waveguides on silicon-on-insulator (SOI) substrates demonstrate poor thermal performance due to several factors. One aspect of their typical design that leads to large thermal resistance is the use of polymer-based optical cladding around the waveguide. To address this issue, we have been exploring the use of deposited aluminium nitride (AlN) as an alternative optical cladding material. AlN is an excellent dielectric with optical properties making it suitable as a cladding around III-V waveguides. Crucially, this material can demonstrate thermal conductivities ∼100 times larger than current polymer cladding materials such as benzocyclobutene (BCB). Electro-thermo simulation results suggest that replacing BCB with AlN could reduce device thermal resistance by ∼2 times. However, our previous linear elastic mechanical modelling indicates that mismatched thermal expansion has the potential to cause mechanical tensile failure in the III-V waveguide when cooled from the processing temperature to room temperature if AlN is deposited in a neutral residual stress state.

Here, to facilitate the design of encapsulated reliable hybrid semiconductor lasers, we extend our finite element, electro-thermo-mechanical model to include a residual stress in the deposited AlN. Using the Christensen criterion to define the maximum allowable stress in the device, our simulations indicate that there is a window of residual compressive stress in the AlN where mechanical failure may be avoided. To assess the feasibility of accessing this region of compressive residual stress while maintaining suitable thermal properties in the deposited AlN, we measure the thermal conductivity of AlN thin films (∼1.6 μm thick) deposited on silicon using a time-domain thermo reflectance (TDTR) setup. Stress measurements demonstrate compressive residual stresses ranging from ∼0 to −0.5 GPa. The TDTR measurement results reveal a similar thermal conductivity of ∼155 Wm−1K−1 over the entire range of compressive residual stress. These results strengthen the promise of encapsulating III-V active waveguides with AlN that simultaneously satisfy both thermal and mechanical requirements.

Copyright © 2017 by ASME



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