Charge screening strategy for domain pattern control in nano-scale ferroelectric systems.

Strain engineering is a widespread strategy used to enhance performance of devices based on semiconductor thin films. In ferroelectrics strain engineering is used to control the domain pattern: When an epitaxial film is biaxially compressed, e.g.

Controlled Charging of Ferroelastic Domain Walls in Oxide Ferroelectrics.

Conductive domain walls (DWs) in ferroic oxides as device elements are a highly attractive research topic because of their robust and agile response to electric field. Charged DWs possessing metallic-type conductivity hold the highest promises in this aspect. However, their intricate creation, low stability, and interference with nonconductive DWs hinder their investigation and the progress toward future applications.

Free-Carrier-Compensated Charged Domain Walls Produced with Super-Bandgap Illumination in Insulating Ferroelectrics.

Charged domain walls in ferroelectrics are movable and electronically conducting interfaces inside insulating materials. A simple and reliable method for their artificial production with ultraviolet (UV) light is described. The UV illumination produces free carriers in ferroelectric bulk, which simultaneously promotes the formation of charged domain walls and provides charge for their compensation.

Néel-like domain walls in ferroelectric Pb(Zr,Ti)O3 single crystals.

In contrast to the flexible rotation of magnetization direction in ferromagnets, the spontaneous polarization in ferroelectric materials is highly confined along the symmetry-allowed directions. Accordingly, chirality at ferroelectric domain walls was treated only at the theoretical level and its real appearance is still a mystery. Here we report a Néel-like domain wall imaged by atom-resolved transmission electron microscopy in Ti-rich ferroelectric Pb(Zr1-xTix)O3 crystals, where nanometre-scale monoclinic order coexists with the tetragonal order.

Piezoelectric enhancement under negative pressure.

Enhancement of ferroelectric properties, both spontaneous polarization and Curie temperature under negative pressure had been predicted in the past from first principles and recently confirmed experimentally. In contrast, piezoelectric properties are expected to increase by positive pressure, through polarization rotation. Here we investigate the piezoelectric response of the classical PbTiO3, Pb(Zr,Ti)O3 and BaTiO3 perovskite ferroelectrics under negative pressure from first principles and find significant enhancement.

Bent Ferroelectric Domain Walls as Reconfigurable Metallic-Like Channels.

Use of ferroelectric domain-walls in future electronics requires that they are stable, rewritable conducting channels. Here we demonstrate nonthermally activated metallic-like conduction in nominally uncharged, bent, rewritable ferroelectric-ferroelastic domain-walls of the ubiquitous ferroelectric Pb(Zr,Ti)O3 using scanning force microscopy down to a temperature of 4 K. New walls created at 4 K by pressure exhibit similar robust and intrinsic conductivity.

Formation of charged ferroelectric domain walls with controlled periodicity.

Charged domain walls in proper ferroelectrics were shown recently to possess metallic-like conductivity. Unlike conventional heterointerfaces, these walls can be displaced inside a dielectric by an electric field, which is of interest for future electronic circuitry. In addition, theory predicts that charged domain walls may influence the electromechanical response of ferroelectrics, with strong enhancement upon increased charged domain wall density.

Negative-pressure-induced enhancement in a freestanding ferroelectric.

Ferroelectrics are widespread in technology, being used in electronics and communications, medical diagnostics and industrial automation. However, extension of their operational temperature range and useful properties is desired. Recent developments have exploited ultrathin epitaxial films on lattice-mismatched substrates, imposing tensile or compressive biaxial strain, to enhance ferroelectric properties.

Polarization charge as a reconfigurable quasi-dopant in ferroelectric thin films.

Impurity elements used as dopants are essential to semiconductor technology for controlling the concentration of charge carriers. Their location in the semiconductor crystal is determined during the fabrication process and remains fixed. However, another possibility exists whereby the concentration of charge carriers is modified using polarization charge as a quasi-dopant, which implies the possibility to write, displace, erase and re-create channels having a metallic-type conductivity inside a wide-bandgap semiconductor matrix.

Controlled stripes of ultrafine ferroelectric domains.

In the pursuit of ferroic-based (nano)electronics, it is essential to minutely control domain patterns and domain switching. The ability to control domain width, orientation and position is a prerequisite for circuitry based on fine domains. Here, we develop the underlying theory towards growth of ultra-fine domain patterns, substantiate the theory by numerical modelling of practical situations and implement the gained understanding using the most widely applied ferroelectric, Pb(Zr,Ti)O3, demonstrating controlled stripes of 10 nm wide domains that extend in one direction along tens of micrometres.

Ferroelectric translational antiphase boundaries in nonpolar materials.

Ferroelectric materials are heavily used in electro-mechanics and electronics. Inside the ferroelectric, domain walls separate regions in which the spontaneous polarization is differently oriented. Properties of ferroelectric domain walls can differ from those of the domains themselves, leading to new exploitable phenomena.

Free-electron gas at charged domain walls in insulating BaTiO₃.

Hetero interfaces between metal-oxides display pronounced phenomena such as semiconductor-metal transitions, magnetoresistance, the quantum hall effect and superconductivity. Similar effects at compositionally homogeneous interfaces including ferroic domain walls are expected. Unlike hetero interfaces, domain walls can be created, displaced, annihilated and recreated inside a functioning device.

Cold-field switching in PVDF-TrFE ferroelectric polymer nanomesas.

Polarization reversal in ferroelectric nanomesas of polyvinylidene fluoride with trifluoroethylene has been probed by ultrahigh vacuum piezoresponse force microscopy in a wide temperature range from 89 to 326 K. In dramatic contrast to the macroscopic data, the piezoresponse force microscopy local switching was nonthermally activated and, at the same time, occurring at electric fields significantly lower than the intrinsic switching threshold. A "cold-field" defect-mediated extrinsic switching is shown to be an adequate scenario describing this peculiar switching behavior.

Thermally induced cooperative molecular reorientation and nanoscale polarization switching behaviors of ultrathin poly(vinylidene fluoride-trifluoroethylene) films.

Ultrathin films of the ferroelectric polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] have recently attracted intensive research interest due to their potential applications in emerging organic devices. As special geometry confinement systems, many aspects about their processing, microstructure, and performance are far from being well understood. Here, the cooperative molecular orientation, macroscopic ferroelectric properties, and nanoscale polarization switching behaviors of thermally crystallized ultrathin P(VDF-TrFE) films were investigated.

Improved screening ability of ferroelectric-semiconductor interface.

Recent progress in integrating ferroelectrics directly on silicon opens the exciting possibility of implementing ferroelectric-semiconductor devices. One of the major problems for such integration is the instability of the ferroelectric state in very thin films, which is mainly controlled by the screening ability of the ferroelectric-semiconductor interface. We show here that the presence of built-in potential in the semiconductor can strongly influence the screening ability of the interface.

Tunable thin film bulk acoustic wave resonator based on Ba(x)Sr(1-x)TiO3 thin film.

A tunable membrane-type thin film bulk acoustic wave resonator (TFBAR) based on a Ba(0.3)Sr(0.7)TiO(3)(BST) thin film has been fabricated.

Large-scale fabrication of titanium-rich perovskite PZT submicro/nano wires and their electromechanical properties.

We report a 2-step approach to prepare tetragonal perovskite PbZr(0.1)Ti(0.9)O(3) submicro/nano wires in gram scale and with over 95% wire content.

DC bias-dependent shift of the resonance frequencies in BST thin film membranes.

Direct current (DC) bias-dependent acoustic resonance phenomena have been observed in micromachined tunable thin film capacitors based on Ba(0.3)Sr(0.7)TiO3 (BST) thin films.

Nonvolatile gate effect in a ferroelectric-semiconductor quantum well.

Field effect transistors with ferroelectric gates would make ideal rewritable nonvolatile memories were it not for the severe problems in integrating the ferroelectric oxide directly on the semiconductor channel. We propose a powerful way to avoid these problems using a gate material that is ferroelectric and semiconducting simultaneously. First, ferroelectricity in semiconductor (Cd,Zn)Te films is proven and studied using modified piezoforce scanning probe microscopy.

Piezoelectric micromachined ultrasonic transducers based on PZT thin films.

This paper describes fabrication and characterization results of piezoelectric micromachined ultrasonic transducers (pMUTs) based on 2-microm-thick Pb(Zr0.53Ti0.47O3) (PZT) thin films.

Analytical modeling of the apparent d33 piezoelectric coefficient determined by the direct quasistatic method for different boundary conditions.

The longitudinal piezoelectric coefficient d33 measured by the quasistatic (Berlincourt-type) method is strongly dependent on the sample aspect ratio (thickness/lateral dimension) and the type of contacts used to collect the charge and apply the pressure on the sample. In this study, we present an analytical model in which apparent (measured) d33 is a function of the aspect ratio, the mechanical properties of contacts, and the properties of piezoelectric material. Using derived relations, it is possible to obtain the true value of d33 in the wide range of boundary conditions.

The effect of boundary conditions and sample aspect ratio on apparent d33 piezoelectric coefficient determined by direct quasistatic method.

The effect of boundary conditions (e.g., type of metal contacts) and sample geometry (e.