High Thermal Conductivity and Ultra-Low-K Dielectric Constants in Two-Dimensional Polymers

To limit electronic crosstalks in miniaturized microprocessors, low-dielectric-constant (low-k) materials are necessary to limit charge build-up and signal propagation delay. However, lowering the dielectric constant also comes with low thermal conductivities in materials, which complicates heat dissipation in high-power-density chips. Two-dimensional (2D) covalent organic frameworks (COFs) combine high surface-to-volume ratios, which lead to low dielectric permittivities, and periodic layered geometries, which result in high thermal conductivities. Here, we report the measurement of high-quality COF thin films with thermoreflectance spectroscopy to reveal that 2D COFs have high thermal conductivities (1 W m⁻¹ K⁻¹) with ultra-low dielectric permittivities (k = 1.6). Our results pave way for highly oriented, layered 2D polymers are promising next-generation dielectric layers.<br/>Through systematic atomistic simulations, we also demonstrate that these porous polymers possess tunable mechanical and thermal properties that arise from their singular layered architecture comprising strongly bonded light atoms and periodic laminar pores. For example, the negative Poisson’s ratio arises from the weak van der Waals interactions between the two-dimensional layers along with the strong covalent bonds that act as hinges along the layers, which facilitate the twisting and swiveling motion of the phenyl rings relative to the tensile plane. The mechanical and thermal properties of two-dimensional covalent organic frameworks can be tailored through structural modularities such as control over the pore size and/or interlayer separation.