Refractory Vertically Aligned Carbon Nanotube–Boron Nitride Nanocomposites for Scalable Electrical Anisotropic Interconnects

Abstract

Traditional metal interconnect technology faces several challenges when scaling down, such as electromigration and poisoning. Carbon nanotubes (CNTs) have been introduced in an attempt to solve these problems while providing on par performance. However, unexpected issues, such as great difficulty in manufacturing perfectly aligned CNTs and the undesired current 2 leakage caused by electron percolation, still exist. In this work, we present novel vertically aligned CNT (VACNT)-based nanocomposites utilizing hexagonal boron nitride (h-BN) as intertube insulating/shielding layers that can be prepared in a scalable and controllable fashion. This composite material inherits the full advantages of the directional conductivity of VACNTs which are strongly enhanced by the intertube h-BN layer and demonstrate excellent electrical anisotropy. This composite material achieves conductivities of 1060.43 and 4.43 Sm -1 along the directions parallel with and perpendicular to the VACNTs, respectively, while the previously reported electrical conductivity of CNT-polymer and CNT-ceramic counterparts are well below 10 -3 Sm -1 isotropically. Due to its refractory ability, the h-BN layer can also protect the prepared nanocomposites from harsh oxidation and erosion, showing ultrahigh stability up to 1400 °C.These results reflect a giant step toward a simple, turnkey solution to an advanced CNT-based composite material for future electrical interconnect applications.

Synthesis, characterisation and applications of core–shell carbon–hexagonal boron nitride nanotubes

“…27 The higher growth temperature (1200 C) is a likely contributing factor to this. Other studies tended to only observe the (002), ( 100) and (004) peaks for synthesis temperatures at 600 C, 39 900 C 34,38 or 1100 C, 37 indicating a more turbostratic h-BN structure. However, these crystallinity results cannot be solely associated with temperature, as other factors also inuence the h-BN crystallinity as discussed herein, including the CNT template surface crystallinity, h-BN deposition method etc.…”

“…Rough h-BN coatings are non-uniform and exhibit unevenness parallel to the surface of the underlying CNT. 27,30,35,37 Smooth h-BN coatings are uniform and can range from highly crystalline 20,29 to partially crystalline 31,32,39 to polycrystalline. 34,36,40 These two categories (rough vs. smooth) are visualised by transmission electron microscope (TEM) images of CNT@BN tubes synthesised by various deposition methods (Fig.…”

“…For CNTs that are individually separated on a substrate as part of an array, the problem of CNT agglomeration is no longer an issue. 21,22,31,36,37,41 36 When placed into the vacuum evacuated tubular furnace and heated to 900 C in argon, the B 2 O 3 melted, forming a molten coating that reacted with NH 3 to form smooth but polycrystalline h-BN on the CNT surface (Fig. 4k).…”

“…As their respective (002) peak positions are slightly displaced from one another, specically 2q ¼ 26.380 (JCPDS 41-1487) and 2q ¼ 26.748 (JCPDS 45-0896), one interpretation of XRD patterns for h-BN coated CNTs is that the (002) peak should be slightly upshied and asymmetric relative to that of the pristine CNT. 27,34,37,39 For a lamellar structure such as h-BN, a highly ordered crystal will have both two-and three-dimensional ordering. As the structure becomes more crystalline, the XRD pattern shows characteristic upshi and narrowing of the (002) peak, alongside the appearance of higher resolved peaks e.g.…”

“…However, in a small number of cases, it was possible to deconvolute the D + E 2g peaks to show the coreshell contributions made by carbon and boron nitride respectively. 27,37,38 2.2.2.1 Rate of h-BN deposition effects on crystallinity. A general observation on h-BN coating crystallinity variance is that methods which deposit h-BN at a high rate tend to produce polycrystalline or amorphous h-BN.…”