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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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Thermophysical property measurement of GaN/SiC, GaN/AlN, and AlN/SiC epitaxial wafers using multi-frequency/spot-size time-domain thermoreflectance
Gallium nitride (GaN)-based high electron mobility transistors (HEMTs) are essential components in modern radio frequency power amplifiers. In order to improve both the device electrical and thermal performance (e.g., higher current density operation and better heat dissipation), researchers are introducing AlN into the GaN HEMT structure. The knowledge of thermal properties of the constituent layers, substrates, and interfaces is crucial for designing and optimizing GaN HEMTs that incorporate AlN into the device structure as the barrier layer, buffer layer, and/or the substrate material. This study employs a multi-frequency/spot-size time-domain thermoreflectance approach to measure the anisotropic thermal conductivity of (i) AlN and GaN epitaxial films, (ii) AlN and SiC substrates, and (iii) the thermal boundary conductance for GaN/AlN, AlN/SiC, and GaN/SiC interfaces (as a function of temperature) by characterizing GaN-on-SiC, GaN-on-AlN, and AlN-on-SiC epitaxial wafers. The thermal conductivity of both AlN and GaN films exhibits an anisotropy ratio of ∼1.3, where the in-plane thermal conductivity of a ∼1.35 μm thick high quality GaN layer (∼223 W m−1 K−1) is comparable to that of bulk GaN. A ∼1 μm thick AlN film grown by metalorganic chemical vapor deposition possesses a higher thermal conductivity than a thicker (∼1.4 μm) GaN film. The thermal boundary conductance values for a GaN/AlN interface (∼490 MW m-2 K−1) and AlN/SiC interface (∼470 MW m−2 K−1) are found to be higher than that of a GaN/SiC interface (∼305 MW m−2 K−1). This work provides thermophysical property data that are essential for optimizing the thermal design of AlN-incorporated GaN HEMT devices.
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- Award ID(s):
- 2234479
- PAR ID:
- 10632533
- Publisher / Repository:
- AIP Publishing
- Date Published:
- Journal Name:
- Journal of Applied Physics
- Volume:
- 137
- Issue:
- 9
- ISSN:
- 0021-8979
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Gallium nitride (GaN) high electron mobility transistors (HEMTs) are key components enabling today’s wireless communication systems. However, overheating concerns hinder today’s commercial GaN HEMTs from reaching their full potential. Therefore, it is necessary to characterize the respective thermally resistive components that comprise the device’s thermal resistance and determine their contributions to the channel temperature rise. In this work, the thermal conductivity of the GaN channel/buffer layer and the effective thermal boundary resistance (TBR) of the GaN/substrate interface of a GaN-on-SiC wafer were measured using a frequency-domain thermoreflectance technique. The results were validated by both experiments and modeling of a transmission line measurement (TLM) structure fabricated on the GaN-on-SiC wafer. The limiting GaN/substrate thermal boundary conductance (TBC) beyond which there is no influence on the device temperature rise was then quantified for different device configurations. It was determined that this limiting TBC is a function of the substrate material, the direction in which heat primarily flows, and the channel temperature. The outcomes of this work provide device engineers with guidance in the design of epitaxial GaN wafers that will help minimize the device’s thermal resistance.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1063/5.0245381
