Evaluation of Imprint Properties in Sol-Gel Ferroelectric Pb(ZrTi)O3 Thin-Film Capacitors

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Abstract
Studies of imprint properties have been carried out by electrical evaluation with pulse switching response and circuit modeling on sol-gel lead zirconate titanate (PZT) ferroelectric thin-film capacitors. The imprint properties were evaluated by measuring the switched and nonswitched charges after three different operations at high temperature, which consist of (1) fatigue by cumulative bipolar pulses, (2) exposure to a large number of positive unipolar pulses, and (3) exposure to a large number of negative unipolar pulses. The nonswitched charge without polarization reversal after being exposed to a large number of unipolar pulses was increased to be greater than switched charge with polarization reversal. This causes the decrease of a noise margin when the memory cell is read. This phenomenon is enhanced by the sample temperature above 75°C, the pulse height, and the amount of cumulative fatigue cycles before imprint. This phenomenon is also found in the Nb-doped PZT capacitor, which is a candidate for fatigue-free materials.

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