As the features of microprocessors are miniaturized, low-dielectric-constant (low-k) materials are necessary to limit electronic crosstalk, charge build-up, and signal propagation delay. However, all known low-k dielectrics exhibit low thermal conductivities, which complicate heat dissipation in high-power-density chips. Two-dimensional (2D) covalent organic frameworks (COFs) combine immense permanent porosities, which lead to low dielectric permittivities, and periodic layered structures, which grant relatively high thermal conductivities. However, conventional synthetic routes produce 2D COFs that are unsuitable for the evaluation of these properties and integration into devices. Here, we report the fabrication of high-quality COF thin films, which enable thermoreflectance and impedance spectroscopy measurements. These measurements reveal that 2D COFs have high thermal conductivities (1 W m−1 K−1) with ultra-low dielectric permittivities (k = 1.6). These results show that oriented, layered 2D polymers are promising next-generation dielectric layers and that these molecularly precise materials offer tunable combinations of useful properties.
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W.R.D., J.-L.B. and F.W. thank the Army Research Office of the United States for a Multidisciplinary University Research Initiatives (MURI) award under grant no. W911NF-15-1-0447. A.M.E. is supported by a National Science Foundation (NSF) Graduate Research Fellowship under grant no. DGE-1324585. N.P.B. also acknowledges an NSF Graduate Research Fellowship. A.G. and P.E.H. appreciate support from the Office of Naval Research (grant no. N00014-20-1-2686). M.B., J.A.M. and A.J.H.M. gratefully acknowledge support from the Army Research Office, grant W911NF-17-1-0397. The electron microscopy work was supported by the United States Department of Energy (DOE DE-SC0019356), and the impedance spectroscopy work was supported by the NSF (DMR-1720139). This study made use of the Integrated Molecular Structure Education and Research Center (IMSERC) and the Electron Probe Instrumentation Center (EPIC) at Northwestern University, both of which have received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205 and NSF ECCS1542205, respectively), the Materials Research Science and Engineering Center (NSF DMR-1720139), the State of Illinois, and the International Institute for Nanotechnology. Portions of this work were performed at the DuPont–Northwestern–Dow Collaborative Access Team (DND-CAT) located at Sector 5 and Sector 8 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co. and the Dow Chemical Company. This research used resources of the Advanced Photon Source and Center for Nanoscale Materials, both of which are DOE Office of Science User Facilities operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. Resources at the Advanced Photon Source were funded by the NSF under award no. 0960140. This research used resources of the Advanced Light Source, a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231.
Northwestern University and the University of Virginia have filed a preliminary patent application (provisional application no. 6314014) related to the discoveries disclosed here.
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Evans, A.M., Giri, A., Sangwan, V.K. et al. Thermally conductive ultra-low-k dielectric layers based on two-dimensional covalent organic frameworks. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-00934-3