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Thermally conductive ultra-low-k dielectric layers based on two-dimensional covalent organic frameworks

Abstract

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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Fig. 1: Templated colloidal polymerization of boronate ester-linked COF films.
Fig. 2: Optoelectronic properties of COF films.
Fig. 3: COF-5 dielectric layer impedance measurements.
Fig. 4: Thermal properties of 2D COF thin films.
Fig. 5: Meta-analysis of thermal conductivities in low-k dielectrics.

Data availability

Source data are provided with this paper. Additional data are available from the corresponding authors upon request.

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Acknowledgements

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.

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Contributions

A.M.E. prepared and characterized all COF films. A.G. performed all thermal property characterization and simulations. V.K.S. prepared COF-5 devices and performed impedance spectroscopy. S.X. and H.L. performed and interpreted density functional theory calculations. M.B. performed thermal property characterization. C.G.T.-C. performed and interpreted the X-ray reflectivity experiments. H.B.B. performed synchrotron X-ray scattering experiments. M.S.R. prepared EG/SiC substrates used for COF devices. N.P.B. imaged the COF devices using scanning electron microscopy. E.V. assisted with monomer syntheses. D.W.B. assisted with synchrotron X-ray characterization. V.K.S., H.L., M.J.B., F.W., J.-L.B., J.A.M., A.J.H.M., M.C.H., W.R.D. and P.E.H. supervised this work. All authors contributed to the conception of the study, data interpretation and manuscript preparation.

Corresponding authors

Correspondence to William R. Dichtel or Patrick E. Hopkins.

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Competing interests

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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Peer review information Nature Materials thanks the anonymous reviewers for their contribution to the peer review of this work.

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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

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