Publications de Enrico Colla | EPFL Graph Search

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The phenomenon of time-dependent polarization loss in poled ferroelectric capacitors, also known as retention, represents one of the most important reliability issues for ferroelectric nonvolatile memories. In a number of publications different ways to con ...

The new class of fully silicon-compatible hafnia-based ferroelectrics with high switchable polarization and good endurance and thickness scalability shows a strong promise for new generations of logic and memory devices. Among other factors, their competit ...

The switching of the sandwich structure ''ferroelectric+thin dielectric layer'' is theoretically studied. The behavior of the remanent polarization, P-r, coercive field, E(c), maximal polarization on the loop, P-s, and the slope of the hysteresis loop at E(c) as a function of both, the relative thickness of the layer (the thickness of the dielectric divided by the thickness of the ferroelectric) and the amplitude of the measuring field, is analyzed. It is shown that the effect of the layer on P-r and the sl

The region-by-region polarization switching in ferroelectric Pb(Zr,Ti)O-3 thin films sandwiched between Pt electrodes has been directly observed using piezoelectric scanning probe microscopy. A resolution improved by one order-of-magnitude compared to the ...

Ferroelectric capacitive devices for memory and MEMS applications require patterned ferroelectric thin films with high anisotropic etched features. In this paper, physical and chemical parameters during etching of Pb(Zr0.53Ti0.47)O-3 (PZT) by a dual frequency ECR/RF reactor have been investigated. The removal characteristics of blanket films and films with a patterned mask were investigated as a function of gas chemistry (Ar, halogen gases), substrate bias RF power and working pressure (from 5 x 10(-4) Pa t

Understanding of polarization reversal mechanisms in ferroelectric films is essential for evaluation and prediction of the properties of ferroelectric devices including nonvolatile memories. The widely accepted approach based on the domain wall motion kinetics describes correctly switching in single crystals but does not work properly for thin ferroelectric films used for memory applications. Recently an alternative approach based the on statistics of nucleation of the reversed polarization domain has been

Polarization reversal in BiFeO3 (BFO) thin films in a parallel-plate capacitor configuration has been explored using piezo-force microscopy (PFM). Through-electrode mapping of the local piezoresponse allows for direct observation of the domain growth, whic ...

Degradation of piezoelectric properties has been studied in ferroelectric PZT films by means of optical interferometry. The degradation under de bias and aging of poled films have been observed. The decay of piezoelectric coefficient with time is described by a logarithmic law with aging rates comparable to those of switching polarization. The aging rates are shown to be sensitive to poling conditions and to orientation of the poling field with respect to the direction of preferred polarization. The fatigue

Direct observation of polarization distribution at nanoscale by scanning force microscopy across partially etched Pb(Zr,Ti)O-3 film ferroelectric capacitors with size 2x3 mum and preferential orientation (111) has revealed an anomalous polarization pattern characterized by polarization inversion in the center of the capacitor. This self-structured pattern is reproducible and independent on the spontaneous polarization orientation, but strongly influenced by the film texture and capacitor size. In particular

In this communication we address two issues essential for low-voltage memory applications of ferroelectric thin films: the size effect on polarization switching, and polarization fatigue. According to the proposed concept, both of these phenomena are controlled by local injection of charge into the interfacial layers of the ferroelectric film. In the experimental part of this work, we show that the entrapped charge relaxation can be enhanced by introducing a thin RuO2 layer into the top interface of the Pt/

The piezoelectric properties of tetragonal BaTiO3 (BTO) crystals with a high density of 90° twin domain boundaries were experimentally investigated by Wada and Tsurumi (2004 Br. Ceram. Trans. 103 93). These crystals with engineered dense domain structures exhibit significantly larger intrinsic d33 and d31 coefficients than in mono-domain crystals. This phenomena was studied theoretically and several enhancement mechanisms (domain wall broadening, polarization tilting) were suggested in the past, but no sati

A unified approach for analysis of polarization fatigue and size effects on ferroelectric switching in relationship with injection and entrapment of charge at the interfacial layer of the ferroelectric film is developed. The proposed model suggests that an enhancement of the entrapped charge relaxation at the interfaces has a positive impact on both the polarization fatigue and size effects. This concept is implemented experimentally by introducing a thin conductive oxide (RuO2) layer into the top interface

The origin of a recently reported peculiar phenomenon-polarization reversal against the applied electric field in ferroelectric thin films [M. Aplanalp and P. Gunter, Ferroelectrics 258, 3 (2001), T. Morita and Y. Cho, Appl. Phys. Lett. 84, 257 (2004)]-has ...

Stress induced ferroelastic switching may represent an efficient toughening mechanism in piezoelectric-ferroelectric ceramics. During the crack propagation, the high tensional stresses at the crack tip can be partially released by the reorientation of 90 degree domains from along to perpendicular to the propagation direction. Compared to the phase transformation approach (inclusion of zirconia particles in the metastable tetragonal phase) this mechanism is not expected to reduce the piezoelectric properties

The manifestations of semiconductor depletion and depolarizing effects in switching and fatigue are studied and compared. It is shown that these effects play important but quite different roles in switching. The depletion effect strongly influences the values of the coercive field, E(c), and is responsible for its film-thickness dependence. The depolarizing effect influences significantly other parameters of the hysteresis loops. It is shown that the inverse thickness dependence of E(c) can not be attribute

Limited reliability of ferroelectric-based actuators restricts their use in high-performance applications, where stress-induced cracking of ferroelectric ceramics often leads to fatal failure. The main limiting factors are the relatively small fracture toughness and the brittle nature of ferroelectrics. However, ferroelectrics naturally exhibit fracture toughening (so called ferroelastic toughening) due to stress induced reorientation of non-180 degrees domains that inhibits crack propagation. Here we prese

A hydrothermal processing route was used to produce anisotropic submicrometer particles of potassium niobate-tantalates and pure potassium niobate. Piezoelectric activity, switching polarization, and piezoelectric hysteresis loops were observed in these ferroelectric perovskite nanorods by means of AFM assisted detection of induced piezoelectric vibrations. Both lattice and domain wall contributions to the piezoelectric response were evidenced.

The evolution of switching polarization (P-r(s)) suppression, in Pb(Zr,Ti)O-3 films, induced by two different electric treatments is addressed in terms of the nonlinear dielectric response. The ac electric field dependence of dielectric permittivity was collected at different fatigue states and the Rayleigh law was used to interpret the fatigue dependence of the nonlinear response. This approach has enabled us to distinguish between two fatigue stares induced by the different electric treatments.

Use of ferroelectric domain-walls in future electronics requires that they are stable, rewritable conducting channels. Here we demonstrate nontherrnally activated metallic-like conduction in nominally uncharged, bent, rewritable ferroelectric-ferroelastic ...

Enrico Colla

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Physical model of retention and temperature-dependent polarization reversal in ferroelectric films

Genuinely Ferroelectric Sub-1-Volt-Switchable Nanodomains in HfxZr(1-x)O2 Ultrathin Capacitors

Identification of Passive Layer in Ferroelectric Thin-Films from Their Switching Parameters

Microscopic aspects of the region-by-region polarization reversal kinetics of polycrystalline ferroelectric Pb(Zr,Ti)O-3 films

Mechanisms of Pb(Zr0.53Ti0.47)O-3 thin film etching with ECR/RF reactor

Kinetics of polarization reversal in ferroelectric films: role of domain nucleation and domain wall motion

Polarization Reversal in BiFeO3 Capacitors: Complex Behavior Revealed by PFM

Interferometric study of piezoelectric degradation in ferroelectric thin films

Unusual size effect on the polarization patterns in micron-size Pb(Zr,Ti)O-3 film capacitors

Downscaling of Pb(Zr,Ti)O-3 film thickness for low-voltage ferroelectric capacitors: Effect of charge relaxation at the interfaces

The stress-assisted enhancement of piezoelectric properties due to mechanically incompatible domain structures in BaTiO3

Charge relaxation at the interfaces of low-voltage ferroelectric film capacitors: Fatigue endurance and size effects

Polarization reversal due to charge injection in ferroelectric films

PFM investigation of stress induced ferroelastic switching in piezoelectric bulk ceramics

Depletion and Depolarizing Effects in Ferroelectric Thin-Films and Their Manifestations in Switching and Fatigue

Phase field simulations of ferroelastic toughening: The influence of phase boundaries and domain structures

Piezoelectric response and polarization switching in small anisotropic perovskite particles

Fatigue and nonlinear dielectric response in sol-gel derived lead zirconate titanate thin films

Bent Ferroelectric Domain Walls as Reconfigurable Metallic-Like Channels

Nonvolatile gate effect in a ferroelectric-semiconductor quantum well