Sensitive NH3OH and HCl Gas Sensors Using Self-Aligned and Self-Welded Multi-Walled Carbon Nanotubes

Self-aligned and self-welded multi-walled carbon nanotubes were grown for the first time using a metal-catalyzed chemical vapor deposition technique between 18 mum-high silicon posts with 2-6 mum gaps with excellent ohmic electrical contacts and mechanical bonding strengths in excess of 0.1 muN/CNT. The electrical conductivity of 5-10 MWCNTs spanning the gap between adjacent silicon posts changed drastically upon exposure to ammonia and hydrochloric gases at room temperature. In devices reported here the electrical contact between both sides of the MWCNTs and the silicon posts are intimately formed during the growth process. Thus, the gas sensitivity of these self-welded MWCNT devices are less affected by the contact barrier changes. Moreover, since the MWCNTs are self- aligned and self-welded during the growth, the only post processing steps that are needed are dicing and wire-bonding to a chip carrier (package), making these devices inherently more reliable and cost effective