Tunneling conduction in virgin and fatigued states of PZT films

Fatigued state of the Pt-PZT-Pt system is studied by means of low-temperature conduction measurements. It is shown that the conduction in the temperature interval of 100-140 degrees K is determined by the cold field emission of electrons (tunneling conduction mechanism). The Fowler-Nordheim equation describes well the observed current-voltage relations for reasonable values of the system parameters. The conduction measurements in this regime show that the strong fatigue of the switching polarization provokes a substantial increase of the cold-field-emission-controlled current. The decrease of the switching polarization from 60 to 15 mu C/cm(2) due to fatigue results in a shift of the I-V characteristic towards the lower fields by some 500 kV/cm. Partial. rejuvenation of the sample by short-time beating to 490 degrees K results in a complete restoring of the initial current-voltage characteristic. It is shown that the fatigue-induced increase of the conduction can be modeled by the charging of the interfacial layers of thickness comparable with the tunneling length. This interpretation is consistent with the fatigue scenario related to the space charge-assisted blocking of the centers of the domain nucleation suggested earlier.