Influence of Polymer Substrate Damage on the Time Dependent Cracking of SiNx Barrier Films

This work is concerned with the long-term behavior of environmentally-assisted subcritical cracking of PECVD SiNx barrier films on polyethylene terephthalate (PET) and polyimide (PI) substrates. While environmentally-assisted channel cracking in SiNx has been previously demonstrated, with constant crack growth rates over short periods of time (<1 hour) during which no substrate damage was observed, the present experiments over longer periods reveal a regime where cracking also develops in the polymer substrate. This time-dependent local cracking of the polymer underneath the channel crack is expected based on creep rupture or static fatigue. Our combined in-situ microscopy and finite-element modeling results highlight the combined effects of neighboring cracks and substrate cracking on the crack growth rate evolution in the film. In most cases, the subcritical crack growth rates decrease over time by up to two orders of magnitude until steady-state rates are reached. For SiNx on PI, crack growth rates were found to be more stable over time due to the lack of crack growth in the substrate as compared to SiNx on PET. These results provide a guideline to effectively improving the long-term reliability of flexible barriers by a substrate possessing high strength which limits substrate damage.  [Link to Research Article]

Direct Visualization of Thermal Conductivity Suppression Due to Enhanced Phonon Scattering Near Individual Grain Boundaries

Understanding the impact of lattice imperfections on nanoscale thermal transport is crucial for diverse applications ranging from thermal management to energy conversion. Grain boundaries (GBs) are ubiquitous defects in polycrystalline materials, which scatter phonons and reduce thermal conductivity (κ). Historically, their impact on heat conduction has been studied indirectly through spatially averaged measurements, that provide little information about phonon transport near asingle GB. Here, using spatially resolved time-domain thermoreflectance (TDTR) measurements in combination with electron backscatter diffraction (EBSD), we make localized measurements of κ within few μm of individual GBs in boron-doped polycrystalline diamond. We observe strongly suppressed thermal transport near GBs, a reduction in κ from ∼1000 W m−1 K−1 at the center of large grains to ∼400 W m−1 K−1 in the immediate vicinity of GBs. Furthermore, we show that this reduction in κ is measured up to ∼10 μm away from a GB. A theoretical model is proposed that captures the local reduction in phonon meanfree-pathsdue to strongly diffuse phonon scattering at the disordered grain boundaries. Our results provide a new framework for understanding phonon−defect interactions in nanomaterials, with implications for the use of high-κ polycrystalline materials as heat sinks in electronics thermal management. [Link to Research Article]

Low Thermal Boundary Resistance Interfaces for GaN-on-Diamond Devices

The development of GaN-on-diamond devices holds much promise for the creation of high-power density electronics. Inherent to the growth of these devices, a dielectric layer is placed between the GaN and diamond, which cancontribute significantly to the overall thermal resistance of the structure. In this work, we explore the role of different interfaces in contributing to the thermal resistance of the interface of GaN/diamond layers, specifically using 5 nm layers of AlN, SiN, or no interlayer at all. Using time-domain thermoreflectance along with electron energy loss spectroscopy, we were able to determine that a SiN interfacial layer provided the lowest thermal boundary resistance (<10 m2K/GW) because of the formation of an Si−C−N layer at the interface. The AlN and no interlayer samples were observed to have TBRs greater than 20 m2 K/GW as a result of a harsh growth environment that roughened the interface (enhancing phonon scattering) when the GaN was not properly protected. [Link to Research Article]

Progessing Thermal Metrology at Georgia Tech

In order to maintain prominence on campus, the Georgia Tech Heat Lab is undergoing a series of improvements starting in Fall 2018. These improvements will broadly improve equipment access and training, technical knowledge dissemination, community diversity, and organizational sustainability.

Sampath Kommandur and Shawn Gregory are leading these improvements. In the upcoming weeks, additional information will be provided and feedback will be solicited.

Precursory improvements include, but are not limited to:

  • Procuring new equipment
  • Developing new systems for user equipment access and training
  • Incorporating undergraduates and graduate communities
  • Broadening and engaging the Heat Lab community for sustainable growth and development
  • Being referenced in and disseminating state of the art research
  • Developing student technical skill sets
  • Reaching out to industry-sponsored projects


If you have any questions, comments, or concerns, please feel free to contact us at:

Heat Lab officially opens

Heat Lab Opens

Pictured: The Heat Lab’s newly renovated research lab in the Pettit Building

After renovating lab space in the Georgia Tech Institute of Electronics and Nanotechnology (IEN), the Heat Lab is now OPEN FOR BUSINESS! The Heat Lab specializes in working with industry to provide thermal measurements, simulations, and solutions leveraging the broad experimental and theoretical expertise of heat transfer faculty at Georgia Tech. The Heat Lab is a collaboration of 25 faculty comprising 30 different thermal tool sets and over 100 affiliated graduate students. Check out the tools page for a list our current equipment, with a number of new tools coming online in the next few months. To learn more about our services please contact us at