Thermal rectification in thin films driven by gradient grain microstructure

Cheng, Zhe; Foley, Brian M.; Bougher, Thomas L.; Yates, Luke; Cola, Baratunde A.; Graham, Samuel

doi:10.1063/1.5021681

Cited by 10 publications

(8 citation statements)

References 37 publications

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“…where 𝜔 is the phonon frequency, ℏ is the reduced Planck constant, 𝑣 𝜆 is the modal phonon group velocity of phonon mode 𝜆, 𝜏 𝐶,𝜆 is the modal combined relaxation time, ∑ 𝑝 is over all phonon polarizations, and 𝐷 𝜆 is the modal phonon density of states, and 𝑓 𝐵𝐸 is the Bose-Einstein distribution function. The combined relaxation time 𝜏 𝐶,𝜆 of each phonon mode can be obtained from the Matthiessen's rule as 36,37 𝜏 𝐶,𝜆 = (…”

Section: Thermal Modelmentioning

confidence: 99%

Experimental observation of high intrinsic thermal conductivity of AlN

Cheng

Koh

Mamun

et al. 2020

Phys. Rev. Materials

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AlN is an ultra-wide bandgap semiconductor which has been developed for applications including power electronics and optoelectronics. Thermal management of these applications is the key for stable device performance and allowing for long lifetimes. AlN, with its potentially high thermal conductivity, can play an important role serving as a dielectric layer, growth substrate, and heat spreader to improve device performance. However, the intrinsic high thermal conductivity of bulk AlN predicted by theoretical calculations has not been experimentally observed because of the difficulty in producing materials with low vacancy and impurity levels, and other associated defect complexes in AlN which can decrease the thermal conductivity. This work reports the growth of thick (>15 m) AlN layers by metal-organic chemical vapor deposition with an air-pocketed AlN layer and the first experimental observation of intrinsic thermal conductivity from 130 K to 480 K that matches density-function-theory calculations for single crystal AlN, producing some of the highest values ever measured. Detailed material characterizations confirm the high quality of these AlN samples with one or two orders of magnitude lower impurity concentrations than seen in commercially available bulk AlN. Measurements of these commercially available bulk AlN substrates from 80 K to 480 K demonstrated a lower thermal conductivity, as expected. A theoretical thermal model is built to interpret the measured temperature dependent thermal conductivity. Our work demonstrates that it is possible to obtain theoretically high values of thermal conductivity in AlN and such films may impact the thermal management and reliability of future electronic and optoelectronics devices.

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Section: Thermal Modelmentioning

confidence: 99%

Experimental observation of high intrinsic thermal conductivity of AlN

Cheng

Koh

Mamun

et al. 2020

Phys. Rev. Materials

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“…The CVD diamond has been well-documented to have an inherent gradient microstructure through the thickness due to the columnar grain growth. [29][30][31] The through-plane thermal conductivity value used here was measured on a spot where the diamond is supported by the silicon substrate. The TDTR measurement was taken at 11.6 MHz with a 5x objective to induce near 1D heat transfer through the diamond.…”

Section: Resultsmentioning

confidence: 99%

Simultaneous Evaluation of Heat Capacity and In-plane Thermal Conductivity of Nanocrystalline Diamond Thin Films

Yates

Cheng

Bai

et al. 2021

Nanoscale and Microscale Thermophysical Engineering

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As wide bandgap electronic devices have continued to advance in both size reduction and power handling capabilities, heat dissipation has become a significant concern. To mitigate this, chemical vapor deposited (CVD) diamond has been demonstrated as an effective solution for thermal management of these devices by directly growing onto the transistor substrate. A key aspect of power and radio frequency (RF) electronic devices involves transient switching behavior, which highlights the importance of understanding the temperature dependence of a material's heat capacity and thermal conductivity when modeling and predicting device electro-thermal response. Due to the complicated microstructure near the interface between CVD diamond and electronics, it is difficult to measure both properties simultaneously.In this work, we use time-domain thermoreflectance (TDTR) to simultaneously measure the in-plane thermal conductivity and heat capacity of a 1-µm -thick CVD diamond film, and also use the pump as an effective heater to perform temperature dependent measurements. The results show that the in-plane thermal conductivity varied slightly with an average of 103 W/m-K over a temperature range of 302-327 K, while the specific heat capacity has a strong temperature dependence over the same range and matches with heat capacity data of natural diamond in literature.

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“…Cheng et al. [ 23 ] theoretically investigated the thermal transport in a diamond film with a gradient of material grains across the structure. This structure was showing large (growth side) versus small (nucleation side) grains from one side to the other.…”

Section: Thermal Diodesmentioning

confidence: 99%

“…Similarly, this type of thermal diode could be implemented in other grain gradient microstructures materials. [ 23 ]…”

Section: Thermal Diodesmentioning

confidence: 99%

See 1 more Smart Citation

Solid‐State Thermal Control Devices

Swoboda

Klinar

Yalamarthy

et al. 2020

Adv Elect Materials

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Over the past decade, solid‐state thermal control devices have emerged as potential candidates for enhanced thermal management and storage. They distinguish themselves from traditional passive thermal management devices in that their thermal properties have sharp, nonlinear dependencies on direction and operating temperature, and can lead to more efficient circuits and energy conversion systems than what is possible today. They also distinguish themselves from traditional active thermal management devices (e.g., fans) in that they have no moving parts and are compact and reliable. In this article, the recent progress in the four broad categories of solid‐state thermal control devices that are under active research is reviewed: diodes, switches, regulators, and transistors. For each class of device, the operation principle, material choices, as well as metrics to compare and contrast performance are discussed. New architectures that are explored theoretically, but not experimentally demonstrated, are also discussed.

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Thermal rectification in thin films driven by gradient grain microstructure

Cited by 10 publications

References 37 publications

Experimental observation of high intrinsic thermal conductivity of AlN

Experimental observation of high intrinsic thermal conductivity of AlN

Simultaneous Evaluation of Heat Capacity and In-plane Thermal Conductivity of Nanocrystalline Diamond Thin Films

Solid‐State Thermal Control Devices

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