Cold-field-emission test of the fatigued state of Pb(ZrxTi1−x)O3films

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Abstract
Fatigue phenomena occurring in Pb(ZrxTi1−x)O3 ferroelectric thin-film capacitors (FECAP) with Pt electrodes are studied by means of conduction measurements in the cold-field-emission (tunneling) regime. We have determined that conduction in virgin FECAPs is controlled by tunneling at temperatures 100–140 K and electric fields (2.3–3.0 MV/cm). The Fowler–Nordheim equation successfully describes observed current–voltage relations for reasonable values of the semiconductor parameters of the system. Fatigue of the switching polarization induced by bipolar voltage cycling provokes a substantial increase in tunneling conduction, shifting the I–V curve to lower fields by some 0.5 MV/cm. The partial restoration of the switching polarization produced by heating of the sample up to 490 K results in a complete restoration of the initial current–voltage characteristic. It is shown that the fatigue-induced increase in conduction can be modeled by the charging of an interfacial layer of a thickness comparable with the tunneling length. This interpretation is consistent with a fatigue scenario related to the space-charge-assisted blocking of near-by-electrode centers of domain nucleation.