In this study, we compared the transient self-heating behavior of a homoepitaxial β-Ga2O3 MOSFET and a GaN-on-Si HEMT using nanoparticle-assisted Raman thermometry and thermoreflectance thermal imaging. The effectiveness of bottom-side and double-side cooling schemes using a polycrystalline diamond substrate and a diamond passivation layer were studied via transient thermal modeling. Because of the low thermal diffusivity of β-Ga2O3, the use of a β-Ga2O3 composite substrate (bottom-side cooling) must be augmented by a diamond passivation layer (top-side cooling) to effectively cool the device active region under both steady-state and transient operating conditions. Without no proper cooling applied, the steady-state device-to-package thermal resistance of a homoepitaxial β-Ga2O3 MOSFET is 2.6 times higher than that for a GaN-on-Si HEMT. Replacing the substrate with polycrystalline diamond (under a 6.5 μm-thick β-Ga2O3 layer) could reduce the steady-state temperature rise by 65% compared to that for a homoepitaxial β-Ga2O3 MOSFET. However, for high frequency power switching applications beyond the ~102 kHz range, bottom-side cooling (integration with a high thermal conductivity substrate) does not improve the transient thermal response of the device. Adding a diamond passivation over layer diamond not only suppresses the steadystate temperature rise, but also drastically reduces the transient temperature rise under high frequency operating conditions.
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Transient Heat Release During Mitochondrial Proton Uncoupling
Non-shivering thermogenesis through mitochondrial proton uncoupling is one of the dominant thermoregulatory mechanisms crucial for normal cellular functions. The metabolic pathway for intracellular temperature rise has widely been considered as steady-state substrate oxidation. Here, we show that a transient proton motive force (pmf) dissipation is more dominant than steady-state substrate oxidation in stimulated thermogenesis. Using transient intracellular thermometry during stimulated proton uncoupling in neurons of Aplysia californica, we observe temperature spikes of ~7.5 K that decay over two time scales: a rapid decay of ~4.8 K over ~1 s followed by a slower decay over ~17 s. The rapid decay correlates well in time with transient electrical heating from proton transport across the mitochondrial inner membrane. Beyond ~33 s, we do not observe any heating from intracellular sources, including substrate oxidation and pmf dissipation. Our measurements demonstrate the utility of transient thermometry in better understanding the thermochemistry of mitochondrial metabolism.
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- Award ID(s):
- 1706854
- NSF-PAR ID:
- 10175169
- Date Published:
- Journal Name:
- Communications biology
- Volume:
- 2
- ISSN:
- 2399-3642
- Page Range / eLocation ID:
- 279
- 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
- Journal Article:
- https://doi.org/10.1038/s42003-019-0535-y
