Unexpected behavior of transient current in thin PZT films caused by grain-boundary conduction

Abstract

The behavior of the transient current at different preliminary polarizations has been studied in Pb(ZrTi)O3 (PZT) films with various grain structures. To affect the grain structure, PZT films were prepared by chemical solution deposition with a two-step crystallization process using combination of seed layers with a low Pb excess and the main layers with a 30 wt. % Pb excess. Some films were prepared with a fixed Pb excess in all the deposited layers. We found that the lead excess and the seed layer crystalline structure can affect the grain-boundary conduction which, in turn, influences the polarization dependence of the transient current and the appearance of current peaks which look like the so-called negative differential resistance region in the current-voltage curves. We show that the emergence of the current peaks in the PZT films depends on (i) whether the current flows inside the ferroelectric phase (grains) or outside, along grain boundaries and (ii) whether the applied bias direction is parallel or opposite to the polarization vector. A correlation between the grain-boundary conduction and current-polarization dependences is confirmed by the local current distribution measured by conductive atomic force microscopy. Possible mechanisms responsible for specific features of the transient current and appearance of the current peaks are discussed. The effect of grain-boundary conduction on the behavior of the current may be significant and should be taken into account in ferroelectric random access memory whose readout operation assumes registration of the magnitude of the polarization switching current under positive bias.

Superdomain dynamics in ferroelectric-ferroelastic films: Switching, jamming, and relaxation

“…It was found that fourfold vertex closure domains in this material are unstable, unlike those in BaTiO3 [32,101] or PZT, [13] in agreement with the clock-model predictions of Srolovitz and Scott. [51] When treating in the clock model the domain walls, rather than treating the polarization itself, [52] it is clear that bundle-domain switching, which can be described as correlated motion of defects, [86] so that the ferroelastic switching indeed dominates the polarization switching, in analogy to the Kosterlitz-Thouless dominancy in thin superconducting films..…”

“…We should note that our analysis is supported by a recent work by Sigov who suggested that defects in ferroelectrics can be correlated and comply with the KosterlitzThouless model. [52] In the Kosterlitz-Thouless framework, the energy of system is determined by the vortex-antivortex energy binding, . This energy represents also the superfluidic stiffness, i.e.…”

Влияние Кристаллической Структуры На Электрические Свойства Тонкопленочных PZT Структур

“…Подробное описание методики и полученных результатов даны в работе [21]. Для любого 2D изображения можно сравнить профили сигналов топографии и локального тока, протекающего вдоль выбранного профиля.…”

“…В отличие от этого, в пленках с непроводящими границами зерен ловушки расположены внутри зерна, и пик тока возникает при совпадении направлений сме-щения и поляризации. Перезарядка ловушек в данном случае контролируется влиянием поляризации как на внутреннее электрическое поле, так и на вероятность эмиссии носителя из примесного центра [21].…”

Peculiarities of the Process of Switching Polarization in Polycrystalline Thin Films of Lead Zirconate-Titanate

“…Было показано, что при переполяризации сохраняется подвижность доменных границ, а сами процессы связаны с выключением части переключаемого объема за счет закрепления зародышей обратных доменов заряженными дефектами. Однако авторы работы [5,6], изучая релаксацию тока при измерении вольт-амперных характеристик в отдельно взятом зерне пленок ЦТС методом атомно-силовой микроскопии, исключают вклад в релаксационные процессы доменного механизма, объясняя ее медленной [9]. Локальные процессы релаксации сигнала пьезоотклика исследовались на сканирующей зондовой нанолаборатории Ntegra Prima (НТ-МДТ, Россия) в режиме силовой микроскопии пьезоотклика.…”