Thermal imaging characterization for high frequency and high power devices

Abstract

We present the thermoreflectance thermal imaging method and the equipment for transient thermal characterization with a time resolution of 100 ns and a submicron spatial resolution for high speed RF and communication devices. Thermoreflectance is a non-invasive and non-contact imaging method. Our unique approach interlocks the timing of image acquisition and the device biasing such that a high speed thermal response is captured both in a temperature profile and a 2D image. Following the description of the thermoreflectance technology, some examples are shown from recent transient thermal characterizations of RF devices including: gallium nitride (GaN) or gallium Arsenide (GaAs) multi finger high electron mobility transistors (HEMT), GaN heterojunction bipolar transistors (HBT) and transistor arrays on a chip. Features of these devices are in the sub-micron range.

Advances in thermal conductivity for energy applications: a review

“…Finding the right chemical composition is the starting point for understanding a low-k material. For inorganic crystalline materials, which cover the vast majority of TBCs and thermoelectrics, heavy elements, soft and highly anharmonic bonds, complex unit cells, and large mass contrast of constituent atoms all typically lead to low k. Note that these requirements are exactly the opposite of those for high-k materials as discussed earlier around equation (9). Heavy elements and soft bonds result in low v and thus low θ D .…”

“…Although the high intrinsic k of low-dimensional materials, especially carbon allotropes (often with k > 1000 W m -1 K -1 ), motivated research on their thermal transport properties [299][300][301][302][303][304], their actual k is influenced by the geometric size of the materials. For an ideal sample with characteristic lateral size L, a power law divergence, k ∝ L ς , was predicted in 1D systems 9 , while for 2D systems k ∝ ln(L) is predicted according to the Fermi-Pasta-Ulam model [312,313]. Practically, k of 1D and 2D systems is limited by higher-order phonon scattering [314,315], defects and impurities, and boundary scattering [316][317][318].…”

“…Based on equation ( 9) and a survey of adamantine compounds, Slack [248] summarized four now-classic rules to identify non-metallic materials with high k ph : (a) low atomic mass, (b) strong inter-atomic bonding, (c) simple crystal structure, and (d) low anharmonicity. Rules (a) and (b) are often quantified in terms of a high Debye temperature, which dominates the numerator in equation (9). Rule (c) implies small number of optical phonon branches which contribute little to heat transport but provide channels for anharmonic scattering.…”

“…Image reprinted from [7], Copyright (2020), with permission from Elsevier. Images from [8,9] Copyright © 2015, IEEE. of thermal conductivity in materials for thermal management and energy applications.…”

“…For isotope-controlled c-BP and c-BAs, the measured P ≈ 22% and ~8%, respectively. For reference, P ≈ 10% for Si, 20% for Ge, 15% for GaN, 43% for hBN, 50% for diamond, and 58% for graphene according to prior experimental literatures[280] 9. Mingo and Broido pointed out that ς is between 1/3 and 1/2 in quasi-1D for simple 3ph scattering in carbon nanotubes and should converge to finite values at long L ~1 cm if more rigorous 2nd order 3ph scattering is considered[314].…”