| AVS 54th International Symposium | |
| Electronic Materials and Processing | Wednesday Sessions |
| Session EM-WeA |
| Session: | Growth and Characterization of Complex Oxides |
| Presenter: | K.G. West, University of Virginia |
| Authors: | K.G. West, University of Virginia J. Lu, University of Virginia W. Chen, University of Virginia J. Yu, University of Virginia Y. Pei, University of Virginia S.A. Wolf, University of Virginia |
| Correspondent: | Click to Email |
Vanadium dioxide (VO2) undergoes a well known first order metal to semiconductor structural phase transformation just above room temperature at 341K. The abruptness of the phase transformation from its high temperature tetragonal phase to its low temperature monoclinic phase is accompanied by large changes in its electrical conductivity and infrared transmission characteristics, making it an excellent candidate for sensor and switching applications. Also recently it has been observed that an electric field can induce an abrupt transition and change in electrical conductivity below the phase transition temperature, owing even greater potential for its use in practical devices. The growth of high quality VO2 thin films can be problematic since several distinct oxide states exist. Growth conditions, such as O2 flow rate, process pressure, and substrate temperature can highly influence the phase of the growing film. Using a novel growth technique called reactive bias target deposition (RBTD), we have prepared highly oriented VO2 thin films on Al2O3 (0001) substrates at various growth temperatures ranging from 250C-550C. The influence of the growth parameters on the microstructure, and transport properties of VO2 thin films was systematically investigated. A change in electrical conductivity of 103 was measured at 341K associated with the well known structural phase transition (SPT). It was observed that the SPT temperature can be tuned to higher temperatures by mixing VO2 and other vanadium oxide phases. In addition a current/electric-field induced metal-insulator transition (MIT) was observed at room temperature with a change in electrical conductivity of 8x. The current densities required to induce the MIT in VO2 are on order of 6x104 A/cm2. The switching time of the MIT, as measured by high frequency current pulsed measurements, was determined to be roughly 10ns. RBTD utilizes a low energy broad beam ion source that reliably produces a very high density of low energy (5-50eV) inert gas ions. A large negative potential bias is applied to the metal sputtering target. The high density of low energy inert gas ions in front of the sputtering target, seeing a very large potential difference, are accelerated to the target surface at a near normal incidence angle at high enough energies to induce sputtering. A pulsed DC bias is used to avoid target poisoning during reactive processing.