ELECTROFORMING AND SWITCHING IN OXIDES OF TRANSITION-METALS - THE ROLE OF METAL-INSULATOR-TRANSITION IN THE SWITCHING MECHANISM

Electroforming and switching effects in sandwich structures based on a nodic films of transition metal oxides (V, Nb, Ti, Fe, Ta, W, Zr, Hf, Mo) have been studied. After being electroformed, some materials exhib ited current-controlled negative resistance with S-shaped V-I characte ristics. For V, Fe, Ti, and Nb oxides, the temperature dependences of the threshold voltage have been measured. As the temperature increased , V-th decreased to zero at a critical temperature T-0, which depended on the film material. Comparison of the T-0 values with the temperatu res of metal-insulator phase transition for some compounds (T-t = 120 K for Fe3O4, 340 K for VO2, similar to 500 K for Ti2O3, and 1070 K for NbO2) showed that switching was related to the transition in the appl ied electric held. Channels consisting of the above-mentioned lower ox ides were formed in the initial anodic films during the electroforming . The possibility of formation of these oxides with a metal-insulator transition was confirmed by thermodynamic calculations. (C) 1996 Acade mic Press, Inc.