The stability of conductance in electropolymerized insulating polypyrr
ole under application of a high voltage was investigated using a metal
-insulator-metal-type diode device. The conductance varied over time d
ue to application of the voltage, and the current-time profiles were c
lassified into three types according to the level of the applied volta
ge. In the very low voltage region the conductance was stable; in the
middle voltage region the conductance increased to a stable value; and
in the high voltage region the conductance first increased and then d
ecreased. The mechanism of the change in conductance, the W-Vis absorp
tion spectra and the photo-radiated current behaviour are dismissed.