Electrical conductivity and dynamics of electroforming in AlSiO xAl thin film sandwich structures

Abstract

Recent work has established that in evaporated SiO x thin film sandwich structures with gold electrodes, which show the Poole–Frenkel effect (enhanced conductivity at high electric fields due to the lowering of the potential barrier at donor-like centres), the value of the Poole–Frenkel field-lowering coefficient β increases with voltage cycling prior to the onset of electroforming. These enhanced β values were associated with the establishment of a high-field region during the electroforming process. In the present work, aluminium electrodes were used in order to explore the characteristics of contrasting system. Electroforming occurred in some samples, but with a maximum current value of less than 1 mA, considerably less than with the gold electrodes. Poole–Frenkel conductivity was observed in the initial voltage cycles, with a β value of typically 4.5×10 −5 eV m 1/2 V −1/2, moderately exceeding the theoretical value. Electroforming normally took place after several voltage cycles, but was not permanent, with a reversion to Poole–Frenkel conduction during some cycles. As for the case with gold electrodes, the value of β increased in the first few cycles, but after further voltage cycling, the behaviour became less stable with varying values of β. After further voltage cycling, electroforming disappeared and β reduced to the order of 2×10 −5 eV m 1/2 V −1/2. This behaviour can be understood in terms of a filamentary conduction model, in which the stability of samples with aluminium electrodes is inferior to those with gold electrodes, as a consequence of the lower melting point.