Atomic layer deposition of titanium oxide and nitride on vertically aligned carbon nanotubes for energy dense 3D microsupercapacitors

摘要

This work demonstrates the use of ALD coatings in a full-cell 3D microsupercapacitor (MSC) device for the first time. The novel device design described herein has potential to be exploited for rapid and scalable manufacturing of on-chip MSCs integrated with other electronic devices in standard semiconductor fabs or foundries. In this study, atomic layer deposition (ALD) was used to deposit conformal pseudocapacitive coatings of titanium oxide (TiO_2) and titanium nitride (TiN) onto CVD-grown vertically aligned carbon nanotubes (VACNTs) to increase the area-specific capacitance (by 240 × and 74 × at 0.1 Vs~(-1) versus the as-deposited VACNT electrode and full-cell VACNT device, respectively) and thus energy density for microscale energy storage applications. The study indicated that combining TiO_2 and TiN ALD layers resulted in a multilayered composite coating rich in oxygen vacancies with enhanced capacitance relative to a single TiO_2 or TiN layer due to a dynamic surface chemistry that developed during charge-discharge cycling. A key component of this multilayered coating was the formation of titanium oxynitride (TiON) which we attributed to the improved performance. Further, we demonstrated that controlling the thickness and stoichiometric ratio of the TiN-TiO_2 composite coating was key to enabling functionality and optimizing the symmetric 3D MSC device performance.