Switchable Spontaneous Polarization Research Articles

Electron emission from ferroelectric ceramics with a special design patterned front electrode

Electron emission from a ceramic disk is due to spontaneous polarization switching induced by a high-voltage pulse applied to the surface electrodes. With a conventional front electrode, emission was erratic as a function of samples and decayed with shot number. On the contrary, when the front electrode consisted of a pattern of unconnected patches contained within a ring, emission was stable. The physics of the two configurations is investigated and a possible interpretation of the two different behaviors is given.

Nonlinear repolarization processes in ferroelectric liquid-crystal thin films

The dynamics of spontaneous polarization switching of the ferroelectric smectic C* in a variable electric field are examined theoretically and experimentally with the help of polarized light scattering. The observed effect of quasiresonant scattering both in freely suspended smectic films and in ordinary electro-optical cells is interpreted within the framework of the nonlinear model of isolated movable kinks in the director orientation distribution. It is shown that the maximum of the scattering intensity at the characteristic frequency of the applied electric field disappears at low temperatures and for small thicknesses of the smectic film. The dependence of the “resonant” frequency on the electric field amplitude, the proximity to the phase transition temperature, the film thickness and thickness of the ferroelectric domains, and also various material parameters is found. Estimates are made of such important characteristics as the dielectric anisotropy, viscosity, and elasticity of the smectic films. The effect of film thickness on the density distribution of the polar anisotropy energy in the film and on the corresponding shape of the moving orientation front within the film are discussed.

Surface discharge plasma induced by spontaneous polarization switching

A flashover plasma has been induced by spontaneous polarization switching on a polar surface of the ferroelectric crystal triglycine sulphate (TGS). The effect has not been observed in the paraelectric phase. The threshold switching voltage for a surface flashover ignition was as low as 100 V for pulsed and ac voltage. A mechanism of plasma initiation on a ferroelectric surface is proposed. It is assumed that the plasma is ignited by electron emission initiated by polarization switching. Subsequent electron avalanching occurs as a result of the high potential gradient along the ferroelectric surface caused by inhomogeneous polarization switching. Electrons and ions with energies up to several hundreds of eV were been recorded due to a high surface potential of the switched ferroelectric.

Ferroelectric electron emission flat panel display

Ferroelectric electron emission observed under periodic spontaneous polarization switching is the basis for the development of a new type of flat panel display. Electron emission occurs from individually operated ferroelectric domains. It is shown that ferroelectric displays may be fabricated in ‘‘plane-to-plane’’ geometry which is not possible for field emission displays.

Ferroelectric electron emission imaging of X-ray damage

X-ray irradiation of TGS crystals drastically suppresses ferroelectric electron emission excited during spontaneous polarization switching. Position sensitive electron detection made it possible to image a radiation damaged region by the use of continuous or pulsed X-ray flux.

Metal-ferroelectric-semiconductor characteristics of bismuth titanate films on silicon

Bismuth titanate (Bi4Ti3OI2) is one of the well known ferroelectrics which exhibits switchable spontaneous polarization in all directions.l,2 Because of its high Curie temperature of 675 °C and high breakdown strength, it has high potential for device applications. Some attempts have been reported regarding the integration of bismuth titanate into silicon MOSFETS for the implementation of non-volatile memories with limited success.3,4 In addition to this, bismuth titanate has a relatively high dielectric constant.5 Recently, there is tremendous interest in using these high dielectric constant materials for storage capacitors in dynamic random access memory applications (DRAM), and as gate insulators to increase the transconductance of MOSFETS.6-8 Therefore, in this paper we are presenting the results of metal—bismuth titanate- p—Si capacitors for device applications as a high dielectric constant material.

Structural phase transition in ferroelectric NH4103

Abstract The structural phase transformation between the ferroelectric and paraelectric form of NH4IO, near 83°C is dominated by tilt motions of IO6-octahedra within a perovskite-like framework. Simultaneously, small displacements of NH4 along the polar axis give rise to a switchable spontaneous polarization at low temperatures. As the transition mechanism is governed by the tilting of octahedra and not by the appearance of ferroelectricity, NH4IO3 is characterised as an improper ferroelectric material. Although the space group of the high-temperature β-phase is polar, the polarization moment is zero. Raman-active thermal soft modes appear in the ferroelectric phase. The phase transition is first order with anomalies of dielectric, piezoelectric and elastic constants.

Localized irreversible thermal switching of spontaneous polarization in ferroelectrics by laser

Abstract Irreversible thermal switching of spontaneous polarization which has been recently described1 for triglycine sulphate (TGS) is studied with a higher power laser (Argon ion laser), and a more efficient device to focus the light on a small area of the crystal (radius ≃ 1 μm). It is seen that an external depolarizing field is not needed to achieve irreversible switching. Laser pulses are sufficient if their duration is longer than a characteristic time t *. It is shown that laser flux φ * and time t* are related by an exponential law t* = BeA/φ. Such an exponential law had been found by G. W. Taylor for expressing some threshold time t * he defined, vs. electric field E.6 The most important difference is probably that Taylor's law is a macroscopic law where unipolar electric pulses E are uniformly applied to the whole crystal for time t * while the laser pulse is focused on a very small area to give an heterogeneous electric field leading to the reversal of a very thin domain. Thus, we have been able to find local variations of t* on the TGS surface, and an improved pyroelectric probe technique using a variable phase detection has allowed to see the effect of successive pulses of time duration t*. First appears an inner irreversible domain switching. Then a forward growth up to the illuminate surface is observed and finally a lateral growth.

Localized irreversible thermal switching in ferroelectric TGS by an argon laser

Irreversible thermal switching of spontaneous polarization, which has been recently described1 for triglycine sulphate (TGS), is studied with a higher power laser (Argon ion laser), and a more efficient device to focus the light on a small area of the crystal (radius ∼ 1 μm). It is seen that an external depolarizing field is not needed to achieve irreversible switching. Laser pulses are sufficient if their duration is longer than a characteristic time t+. It is shown that laser flux φ and time t+ are related by an exponential law t+ = BeA/φ A similar law had been found by G. W. Taylor for expressing a threshold time t* he defined, vs. electric field E(6). The most important difference is probably that Taylor's law is a macroscopic law where unipolar electric pulses E are uniformly applied to the whole crystal for time t+ while the laser pulse is focussed on a very small area to give an heterogeneous electric field leading to the reversal of one very thin domain. Thus, we have been able to find local varia...

Electrical properties of flash evaporated ferroelectric BaTiO3thin films

Flash evaporated, ferroelectric, barium titanate films have been prepared in the thickness range 0.04-2.0 mu m. They consist of oriental tetragonal crystallites having dimensions comparable with film thickness. Thickness dependent permittivity and other dielectric properties are interpreted in terms of Schottky barriers at the film-electrode interface. Switching is observed in films as thin as 0.08 mu m and loops and current transients are surprisingly similar to those from bulk ceramics. Switchable spontaneous polarization values are as high as 20% of the bulk single crystal value.