(347e) Low-Temperature (180°C) Chemical Vapor Deposition of Crystalline Vanadia for Electronics Applications

Thin films of semiconducting vanadium pentoxide, (i.e., vanadia, V₂O₅) find uses in electronics applications such as gas and humidity sensors, solid-state batteries, electronic and optical switches, electrochromic windows, information storage/display devices and color memory devices. The method of deposition influences the microstructure of the films, which in turn propagates into the structural, electrical and optical properties. Most applications of thin film V₂O₅ employ the crystalline form, although amorphous material has demonstrated advantages in some cases such as batteries. Deposition of vanadia has been demonstrated by a variety of means, including chemical vapor deposition (CVD) from the metalorganic precursor Vanadium Oxide Tri-iso-Propoxide (VOTP). Atomic layer deposition (ALD) has also been demonstrated with VOTP and water. Curiously, however, the deposition of crystalline V₂O₅ by CVD using these two precursors has not been examined in its own right. The present work fills that gap, and specifically examines the transition from amorphous to crystalline form when the deposition temperature increases from 100 to 300°C. The transition is essentially complete within the temperature window 180-200°C. By contrast, ALD requires a post-annealing step to 400-500°C to achieve such crystallinity, and CVD with VOTP alone requires similar temperatures. When grown by CVD at about 1.5 Torr to thickness between 30 and 200 nm, the V₂O₅ films (from VOTP + water) also exhibit grain microstructure and orientation, chemical composition, and surface smoothness appropriate for use in electronic devices. The low temperature deposition of crystalline films opens up new possibilities for using vanadia on polymer substrates for applications in transparent and flexible electronics.