Fabrication of CNT-Based Planar Micro-Coils on Silicon Substrate

Micro-coils are the most popular inductor structures. It is desirable to have high aspect ratio (HAR) planar micro-coils where the “planar” structure ensures less fabrication process steps compared to their 3-D counterparts, and HAR ensures that a lesser area is occupied by the micro-coil as well as low resistance due to larger conductor cross section. Such HAR planar micro-coils are generally realized through electrochemical-deposition (ECD) of metals, generally copper, inside blind HAR trenches in a substrate. However, such an ECD process into HAR trenches is very challenging, resulting into voids and the process is required to be optimized for different aspect ratios, which makes it time consuming and complex. In this paper, we present a novel way of realizing planar micro-coils in silicon using carbon nanotubes (CNTs). The issue of poor electrical conduction between two adjacent CNT bundle is resolved through graphene-deposition and this allows the electrical conduction along the length of the micro-coil (in the plane of the coil), which is necessary for a planar micro-coil structure. Planar micro-coils of an aspect ratio (AR) 3:1 is realized using such graphenic-CNTs and their electrical characterization is reported here. DC and low-frequency electrical characterization of these coils are performed, which shows the micro-coils have a high inductance value compared to the other micro-coils reported in the literature. The process of obtaining such planar micro-coils, using the CNT-graphenic heterostructure reported here, is less complex compared to the conventionally used ECD of Cu, and unlike ECD of Cu inside trenches of different AR will not require any optimization.