The Detection of Current Filaments in Thin Amorphous Films

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Abstract
Switching and memory effects can be observed in many metal–insulator–metal structures. These phenomena are generally explained in terms of filamentary conduction through the insulator. The nonhomogeneous conduction causes a nonuniform potential in the top metal electrode. These small potential differences are detected with the aid of a scanning electron microscope. A special ac detection scheme is employed to improve the normal voltage contrast obtained in secondary electron micrographs. A fixed frequency ac bias is applied to the device and the secondary electron detector is narrowly tuned to this same frequency. This technique allows the suppression of normal topographical and compositional contrast and significantly improves the signal-to-noise ratio for voltage contrast. The presence of current filaments in Nb–Nb2O5–NiCr devices is experimentally verified.

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