Abstract
We reported the basal-plane thermal conductivity in exfoliated bilayer hexagonal boron nitride h-BN that was measured using suspended prepatterned microstructures. The h-BN sample suitable for thermal measurements was fabricated by dry-transfer method, whose sample quality, due to less polymer residues on surfaces, is believed to be superior to that of PMMA-mediated samples. The measured room temperature thermal conductivity is around 484 Wm−1K−1(+141 Wm−1K−1/ −24 Wm−1K−1) which exceeds that in bulk h-BN, providing experimental observation of the thickness-dependent thermal conductivity in suspended few-layer h-BN.
Highlights
Hexagonal boron nitride (h-BN), analogous to graphene, is an one-atomic layer two dimensional (2D) material with honeycomb structures in which equal Boron and Nitrogen atoms bond compartmentally by sp[2] hybridization[1]
This is understandable that organic residues (e.g. PMMA) and functional groups which are introduced during PMMA-mediated wet-transfer process dominate thermal conduction in few-layer BN and reduce its value to below that of bulk h-BN4,18
The measured room temperature thermal conductivity reaches a high value of 484 Wm−1K−1(+ 141 Wm−1K−1/− 24 Wm−1K−1), exceeding that in bulk hexagonal boron nitride, indicating h-BN as a potential 2D material for efficient heat removal and thermal management in integrated electronic circuit with further miniaturization
Summary
We employed the standard prepatterned microstructures for thermal measurements[2,19,20,21], in which the two Pt/SiNx membranes, named Heater and Sensor in Fig. 1b, and their six supporting Pt/SiNx beams were released from silicon substrate by wet etching for 2.5 h to 3 h. The total measured thermal conductance of h-BN sample (σs) and the six supporting Pt/SiNx beams (σb) follows[21]: σb. A uniform temperature distribution was assumed and the average temperature rise Δ Th (Δ Ts) in Heater (Sensor) was used instead of the real temperature rise Δ TR,h (Δ TR,s) at the joint part of sample and Heater (Sensor) This assumption is valid when thermal conductance is low, e.g. σs < 0.1σb. The Finite Element Simulations (COMSOL Multiphysics 5.2, License No: 9400382) was carried out to simulate the temperature distribution in the suspended membranes, Heater and Sensor, at each temperature we measured. The two have been shown to be related as[18]
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