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Gallium nitride (GaN) high electron mobility transistors (HEMTs) are key components of modern radio frequency (RF) power amplifiers. However, device self-heating negatively impacts both the performance and reliability of GaN HEMTs. Accordingly, laser-based pump-probe methods have been used to characterize the thermal resistance network of epitaxial material stacks that are used to fabricate HEMT structures. However, validation studies of these measurement results at the device level are lacking. In the present work, a GaN-on-SiC wafer was characterized using frequency-domain thermoreflectance and steady-state thermoreflectance techniques. The thermal conductivity of the GaN channel/buffer layer, SiC substrate, and the interfacial thermal boundary resistance at the GaN/SiC interface were determined. Results were validated by performing thermal imaging and modeling of a transmission line measurement (TLM) structure fabricated on the GaN-on-SiC wafer.
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Experimental Probing of the Bias Dependent Self-Heating in AlGaN/GaN HEMTs With a Transparent Indium Tin Oxide Gate
The demand for high power and high-frequency radio frequency (RF) power amplifiers makes AlGaN/GaN high electron mobility transistors (HEMTs) an attractive option due to their large critical field, high saturation velocity, and reduced device footprint as compared to Si-based counterparts. However, due to the high operating power densities, intense device self-heating occurs, which degrades the electrical performance and compromises the device’s reliability. The self-heating behavior of AlGaN/GaN HEMTs is known to be not solely a function of the dissipated power but is highly bias-dependent. As the operation of RF power amplifiers involves alteration of the device operation from fully-open to pinched-off channel conditions, it is critical to experimentally map the full channel temperature profile as a function of bias conditions. However, such measurement is difficult using optical thermography techniques due to the lack of optical access underneath the gate electrode, where the peak temperature is expected to occur. To address this challenge, an AlGaN/GaN HEMT employing a transparent gate made of indium tin oxide (ITO) was fabricated, which enables full channel temperature mapping using Raman spectroscopy. It was found that the maximum channel temperature rise under a partially pinched-off condition is more than ∼93% higher than that for an open channel condition, although both conditions would lead to an identical power dissipation level. The channel peak temperature probed in an ITO-gated device (underneath the gate) is ∼33% higher than the highest channel temperature that can be measured for a standard metal-gated AlGaN/GaN HEMT (i.e., next to the metal gate structure) operating under an identical bias condition. This indicates that one may significantly underestimate the device’s thermal resistance when solely relying on performing thermal characterization on the optically accessible region of a standard AlGaN/GaN HEMT. The outcomes of this study are important in terms of conducting a more accurate lifetime prediction of the device lifetime and designing thermal management solutions.
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- Award ID(s):
- 1934482
- PAR ID:
- 10390516
- Date Published:
- Journal Name:
- ASME 2022 International Technical Conference and Exhibition on Packaging and Integration of Electronic and Photonic Microsystems
- Page Range / eLocation ID:
- 1 - 8
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1115/IPACK2022-98800
