Effects of post-deposition annealing ambient on the electrical characteristics and phase transformation kinetics of sputtered lead zirconate titanate (65/35) thin film capacitors

Abstract

The fabrication of high dielectric constant lead zirconate titanate thin films for dynamic random access memory application involves post-deposition annealing to convert the low dielectric constant pyrochlore phase to the desired high dielectric constant perovskite phase. The results of our experiments detailing the dielectric characteristics such as degradation field (the electric field at which a sudden increase in leakage takes place), leakage current density, time-dependent dielectric breakdown characteristics, charge storage density, coercive field, and charge storage density are reported. The charge storage density was measured using both double-bipolar pulses and quasistatic capacitance-voltage techniques. The results of these two measurement techniques are discussed for oxygen and nitrogen annealed films. Additionally, a comparative study of the phase transformation kinetics when the post-deposition annealing is carried out in a nonoxidizing ambient such as nitrogen, as against an oxidizing ambient (pure oxygen), is detailed.

Why do antiferroelectrics show higher fatigue resistance than ferroelectrics under bipolar electrical cycling?

“…Interestingly, it has been found that the features of etch grooves are more severe in fatigued ferroelectrics than in fatigued antiferroelectrics. 7,18 Although our model predicts that unipolar pulses lead to no or little fatigue in ferroelectrics, as confirmed by the experimental observations in the literature, 19,20 it indicates that AFE materials should show evident fatigue under unipolar electrical cycling, at least in one of the two hysteretic branches ͓i.e., the upper or the lower, see Fig. 1͑a͔͒.…”

Unipolar and bipolar fatigue in antiferroelectric lead zirconate thin films and evidences for switching-induced charge injection inducing fatigue

“…The same phenomenon has also been reported for ferroelectric materials. 3,[20][21][22] The less severity of unipolar fatigue in comparison with bipolar fatigue in antiferroelectrics can also be clearly seen from Figs. 2͑a͒ and 2͑b͒; both the less significant increase in P r ͑N͒ / P r ͑0͒ as a function of N in Fig.…”

Bipolar and unipolar electrical fatigue in ferroelectric lead zirconate titanate thin films: An experimental comparison study

“…7, one can see that under the same cycling voltage unipolar fatigue is indeed less severe than bipolar fatigue, consistent with experimental results reported previously. [3][4][5] For instance, we see that the polarization loss is only less than 4% after 10 9 unipolar cycles at 3 V ͓Figs. 6͑a͒ and 6͑e͔͒ while ϳ35% of P r ͑0͒ is lost after 10 9 bipolar cycles at the same voltage ͓Figs.…”

“…1,2 Many publications in the past deal with bipolar electrical fatigue in ferroelectric thin films, 2 and fewer deal with unipolar fatigue in both thin-film and bulk ceramic ferroelectrics. [3][4][5] This is probably because of the potential applications of ferroelectric memories (FeRAM) in future non-volatile memory devices, where each cell is driven by bipolar pulses. However, it should be noted that in case of the devices made from ceramic ferroelectrics the driving pulses used are usually unipolar.…”