Functionalization of suspended carbon nanotubes in silicon microsystems by Atomic Layer Deposition (ALD)

Carbon Nanotubes (CNTs) can be used as gas sensing elements when combined with electronic circuitry. The method of direct integration on free-standing microbridges allows CNT-to-silicon integration in a CMOS-compatible process that can be automated and scaled to wafer level. Sensitive gas sensors can thus be made in single chips containing both the electronics and the nanomaterial functionality. The present work explores functionalization of suspended CNTs from the direct integration method, using Atomic Layer Deposition (ALD), with the purpose of improving selectivity and sensitivity of gas sensors. Three wide-bandgap semiconducting oxides (ZnO, TiO₂ and Co₃O₄) are successfully deposited, where the resulting structures reflect the reactivity of the different ALD precursors. The work further demonstrates the potential this functionalization scheme has for greatly reducing the electrical resistance of the resulting Si-CNT-Si system.