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

AM Evans and A Giri and VK Sangwan and SN Xun and M Bartnof and CG Torres-Castanedo and HB Balch and MS Rahn and NP Bradshaw and E Vitaku and DW Burke and H Li and MJ Bedzyk and F Wang and JL Bredas and JA Malen and AJH McGaughey and MC Hersam and WR Dichtel and PE Hopkins, NATURE MATERIALS, 20, 1142-+ (2021).

DOI: 10.1038/s41563-021-00934-3

Low-k dielectric materials are essential to allow continued electronics miniaturization, but their low thermal conductivity limits performance. Here, two-dimensional covalent organic frameworks are shown to combine high thermal conductivity with a low dielectric constant. 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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