Design and fabrication of robust tunnel junctions for gas sensing

There is still a strong need for more selective gas sensors, and although previous work has suggested that inelastic electron tunneling spectroscopy (IETS) based gas sensing is a promising approach, poor yield and failure of the sensors prevent these devices from being used commercially. The objective of this work was to develop a robust tunnel junction design along with the fabrication methods for IETS based room temperature gas sensors. Four tunnel junction designs were studied: (1) Gold-zinc oxide (Au-ZnO) Schottky junctions created mechanically; (2) tunneling gaps created by electromigration; (3) aluminum-aluminum oxide-aluminum (Al-Al2O3-Al) tunnel junctions created by electric-field enhanced oxidation, thermal oxidation, and glow discharge oxidation; and (4) gold-silicon dioxide-gold (Au-SiO 2-Au) tunnel junctions using sputter deposited SiO2. This is the first report of IETS of any gas above 4 K. The crossover glow discharge design was found to be the most robust design. IETS peaks were broader than at 4 K due to temperature. Temperature broadening is prominent at room temperature. The broadening of IETS peaks is the major concern to be addressed for using these sensors commercially. Peak detection and identification using pattern recognition technique appears to be a promising approach. Future work should address these effects along with mechanisms for increasing robustness of tunnel junctions and the rate of infusion of gas molecules from the top electrode to the tunnel junctions.