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In this work, the piezoelectric properties of chemical solution deposition derived ferroelectric HfO2–CeO2 thin films deposited on platinized silicon substrates are investigated. Large-signal strain-field measurements show an effective piezoelectric coefficient of approximately d 33 , eff = 12.7 pm / V for 17 mol. % cerium under bipolar excitation and d 33 , eff = 8 pm / V under unipolar excitation. Progressive bipolar electric field cycling leads to a reduction in the overall field induced strain although no fatigue with regards to the polarization is observed. To explain this, we propose a model explanation based on changes in the polarization reversal pathway from a primarily ferroelastic, i.e., 90 ° domain wall mediated switching, to a 180 ° type switching. Furthermore, unipolar strain-field measurements reveal a negative intrinsic piezoelectric coefficient in the absence of any ferroelastic contribution, confirming theoretical predictions. The results suggest that the ferroelastic contribution to the field-induced strain needs to be stabilized in Hafnia-based ferroelectric materials to make them more feasible for micro-electromechanical systems. [ABSTRACT FROM AUTHOR]

While the influence of various fabrication parameters during deposition on the ferroelectricity of hafnium oxide has been extensively studied, the effect of different atmospheres on the actual switching process has not yet been investigated. In this work, we characterized the ferroelectric properties of undoped hafnium oxide prepared by reactive sputtering under three different atmospheres: dry oxygen/nitrogen, wet nitrogen, and vacuum conditions. We found a significant correlation between dry and wet atmospheres and resulting polarization. Specifically, we observed a direct effect on ferroelectric switching when the film was exposed to dry atmospheres and vacuum, resulting in a higher electric field necessary to initialize the wake-up effect due to an initial imprint effect. Increasing the amount of wet nitrogen during switching decreased the imprint and lowered the necessary voltage required for the wake up. We present a simple model that explains and discusses the incorporation of moisture and its resulting consequences on the ferroelectric properties of hafnium oxide. Additionally, kinetic Monte Carlo simulations showed that the addition of protons to the oxide thin film leads to a lowering of the potential and to a redistribution of protons and oxygen vacancies, which reduces the initial imprint. [ABSTRACT FROM AUTHOR]

During dynamic random access memory (DRAM) capacitor scaling, a lot of effort was put searching for new material stacks to overcome the scaling limitations of the current material stack, such as leakage and sufficient capacitance. In this study, very promising results for a SrTiO3 based capacitor with a record low capacitance equivalent thickness value of 0.2 nm at target leakage current are presented. Due to the material properties of SrTiO3 films (high vacancy concentration and low band gap), which are leading to an increased leakage current, a physical thickness of at least 8 nm is required at target leakage specifications. However, this physical thickness would not fit into an 18 nm DRAM structure. Therefore, two different new approaches to develop a new ZrO2 based DRAM capacitor stack by changing the inter-layer material from Al2O3 to SrO and the exchange of the top electrode material from TiN to Pt are presented. A combination of these two approaches leads to a capacitance equivalent thickness value of 0.47 nm. Most importantly, the physical thickness of <5 nm for the dielectric stack is in accordance with the target specifications. Detailed evaluation of the leakage current characteristics leads to a capacitor model which allows the prediction of the electrical behavior with thickness scaling. [ABSTRACT FROM AUTHOR]

We report on a simulation model for bipolar resistive switching in cation-migration based memristive devices. The model is based on the electrochemical driven growth and dissolution of a metallic filament. The origin of multilevel switching is proposed to be direct tunneling between the growing filament and the counter electrode. An important result of our parameter simulation studies is that different materials show the same experimental multilevel behavior. Our model fully reproduces the experimental data and allows for an explanation of the transition from bipolar to nonpolar switching. [ABSTRACT FROM AUTHOR]

Effects of the thermal treatment and the fabrication process of Pb(Zr0.3Ti0.7)O3 (PZT) thin films using chemical solution deposition on Pt/TiOx electrode stacks were investigated using complementary analytical techniques including atomic force microscopy (AFM), x-ray photoelectron spectroscopy, high-resolution transmission electron microscopy, and grazing incidence x-ray reflectivity of synchrotron radiation. The surface and interface structures of the Pt/TiOx electrode stacks with different thermal treatments, and the PZT/Pt/TiOx sample were examined. The propagation of Pt hillocks on the bare Pt/TiOx electrode stacks upon the annealing was observed. AFM observations also revealed that the upper surface of the Pt bottom electrode under PZT thin film became rougher than that of the bare Pt electrode with the same thermal history. Global structural information including the density, surface or interface root-mean-square roughness, and thickness of each constituent layer in the samples were determined using x-ray reflectivity. A density decrease of the Pt layer upon the annealing or during the fabrication of PZT thin films was found from fitting the specular reflectivity, and further confirmed by the negative shift of the Yoneda peak of Pt in the diffuse reflectivity. The formation of Pt hillocks on the bare Pt electrodes was attributed to the compressive stress during the high-temperature annealing caused by the limited incorporation of Ti and O into the Pt layer. Roughening of the PZT/Pt interface was ascribed to the interaction between the compressive stress in Pt and the indentation by the PZT crystallization and grain growth during the annealing. [ABSTRACT FROM AUTHOR]

The pressure dependence of pentacene (C22H14) transistors with solution-processed polyvinylphenol gate dielectric on glass substrates is investigated by applying uniaxial mechanical pressure with a needle. We found that organic thin-film transistors are sensitive to applied pressure inherently. The measurements reveal a reversible current dependence of the transfer characteristics where the drain current is switching between two states. Experimental and simulation results suggest that switch-on voltage and interface resistance are affected. The change takes seconds, hinting at trap states being responsible for the effect. [ABSTRACT FROM AUTHOR]

The authors report the study of polarization fatigue in Pb(Zr,Ti)O3 (PZT) ferroelectric thin films using in situ high-resolution grazing incidence x-ray specular reflectivity of synchrotron radiation. The results demonstrate that there is no formation of a region of different electron densities in the film growth direction with subnanometer depth resolution during fatigue. The upper bounds on the theoretically predicted interfacial accumulation of oxygen vacancies at the interfaces between PZT and Pt electrodes are determined by the comparison of experimental results and theoretical simulations. [ABSTRACT FROM AUTHOR]

Structural investigations of Pb(Zr,Ti)O3 (PZT) ferroelectric thin films derived by chemical solution deposition on Pt/TiOx electrode stacks were performed using grazing incidence x-ray specular reflectivity of synchrotron radiation and transmission electron microscopy. A density inhomogeneity, i.e., a sublayer structure, in the PZT thin films was observed; the upper PZT sublayer had a lower density and the lower sublayer had a higher density. The influence of the density inhomogeneity, as a possible extrinsic contribution to size effects in ferroelectric thin films, was discussed. [ABSTRACT FROM AUTHOR]

In this letter, Monte Carlo simulation methods were used to investigate the influence of the defect orientation and concentration on the hysteresis loop in ferroelectric thin films. The hysteresis loops were calculated by an existing Monte Carlo model. For a certain type of defect orientation, the simulations revealed an asymmetric hysteresis loop behavior, similar to hysteresis curves recorded by imprint measurements. Though these results may not directly offer a new explanation for the imprint mechanism in ferroelectric thin films, they still provide insight information about the often observed phenomenon of imprinted hysteresis loops of as-prepared thin-film capacitors. [ABSTRACT FROM AUTHOR]