Polarization Switching Process Research Articles

Ferroelectric Domain Dynamics in PMN-PT Ceramics

The polarization switching process was investigated in PMN-PT ceramics through the frequency dependence of the hysteresis loops and the electric field induced-strain measurements. In order to investigate the influence of the ferroelectric phase on the domain reorientation process, PMN-PT ceramics with rhombohedral and tetragonal symmetries were studied. The higher coercive field observed in the tetragonal composition was associated with a higher lattice distortion. The results suggested that the ceramic with rhombohedral symmetry presents a higher collective reorientation of the domains than the tetragonal one. The reorientation of the domains was modeled as occurring in a viscous medium where several resistance forces such as viscous force and restoring forces act on them. The coercive field was interpreted as an effective field necessary to overcome these resistance forces.

Investigation of Domain Switching and Retention in Oriented PbZr0.3Ti0.7O3 Thin Film by Scanning Force Microscopy

The polarization switching and retention in oriented tetragonal lead zirconate titanate films have been investigated by piezoresponse scanning force microscopy (SFM) on the nanoscale level. We observed the processes of polarization switching by choosing suitable poling conditions. It was found that the domain nucleated from the surface under the applied field and grew via both forward and sideways growth. This switching process was different from the conventional model in which sideways growth occurs after the forward growth reaches the opposite surface. Successive sideways and forward growth was observed with the stimulation of the applied field. We also studied the retention behavior of a single domain with a diameter of about 270 nm. Simultaneous forward and sideways backswitching of polarization led to the lowering of the piezoresponse of the retained domain together with the decrease of the domain area. The temporal dependence of the retained domain area was found to fit the stretched exponential law. This study demonstrates that the SFM technique is a powerful tool providing insight into the complicated behaviors of ferroelectric domains.

Investigation of Polarization Switching Processes in Pb(Zr,Ti)O 3 Capacitors Using Piezoresponse Imaging

Polarization switching processes in ferroelectric capacitors with epitaxial Pb(Zr,Ti)O 3 (PZT) thin films grown on SrRuO 3 /SrTiO 3 (100) were investigated using piezoresponse imaging technique with and on the top electrodes using atomic force microscopy. PZT thin films had only 180° domains because of a tetragonal structure and completely (001)-orientations. Piezoresponse measurements revealed that the polarization switching process changed as the switching pulse voltage increased. At lower switching pulse voltage regions (∼1.4 V c ), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2 V c ), the new nucleations during switching period were observed. Activation field can be also estimated 310-370 kV/cm.

半導体エレクトロニクス 圧電応答顕微鏡による強誘電体Ｐｂ（Ｚｒ，Ｔｉ）Ｏ３薄膜の分極反転過程の観察

Polarization switching processes in epitaxial Pb (Zr, Ti) O3 (PZT) thin films grown on SrRuO3/SrTiO3 (100) were observed using piezoresponse scanning force microscopy (PFM). PFM observations were carried out directly on the PZT surface and with and on Pt top electrodes. XRD patterns exhibited that PZT thin film had only 180° domains because of a tetragonal structure and completely (001)-orientation. From PFM observations directly on PZT film, it was found that domain wall velocity in the vertical direction was estimated 89m/s. PFM observations with and on the top electrode revealed that the polarization switching processes were dependent on the switching pulse voltage. At lower switching pulse voltage regions (-1.5Vc), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2Vc), the new nucleations during switching period were observed.

Investigation of Polarization Switching Processes in Pb(Zr,Ti)O 3 Capacitors Using Piezoresponse Imaging

Polarization switching processes in ferroelectric capacitors with epitaxial Pb(Zr,Ti)O 3 (PZT) thin films grown on SrRuO 3 /SrTiO 3 (100) were investigated using piezoresponse imaging technique with and on the top electrodes using atomic force microscopy. PZT thin films had only 180° domains because of a tetragonal structure and completely (001)-orientations. Piezoresponse measurements revealed that the polarization switching process changed as the switching pulse voltage increased. At lower switching pulse voltage regions (∼1.4 V c ), the polarization switching occurred from only the latent nuclei. On the other hand, at higher switching pulse voltage (>2 V c ), the new nucleations during switching period were observed. Activation field can be also estimated 310-370 kV/cm.

DC Biased Dielectric Property of MPB PZT Ceramics with Monoclinic Distortion at Low Temperatures

Complex dielectric properties of PbZr 1 m x Ti x O 3 ceramics with compositions in the vicinity of the morphotropic phase boundary (x=0.46, 0.48, and 0.51), as a function of dc bias fields, were measured under small ac signal conditions. In monoclinic phase, dielectric permittivity shows hysteresis behavior and decreases with increasing bias field when E bias >E c . For compositions of tetragonal phase and near the on-set of the monoclinic phase transitions, dielectric permittivity increases with increasing bias electric field, indicating a continued polarization switching process. Such anomalous behavior is attributed to the E-field induced monoclinic phase, which allows polarization rotation without domain reversal. Temperature dependence of the dc biased dielectric property between 12K and 300K is also reported. Dielectric dispersion is mostly clamped out for both PZT 54:46 and PZT 52:48 as temperatures approaching 12K; however, remains significant in PZT 49:51.

Influence of Excitation Frequency and Amplitude on the Switching Properties of SBT and PZT Thin Films at 10 MHZ Hysteresis Frequency

For development and optimization of high density ferroelectric random access memory (FeRAM) devices, it is highly important to understand the polarization switching process. As demands on measurement hardware for these nonlinear devices rise with falling cycle time, the development of faster measurement equipment is desired for observation. We report on the direct investigation of the switching behaviour near device operation frequency of chemical solution deposition (CSD) prepared thin films of perovskite materials such as strontium bismuth tantalate SrBi 2 Ta 2 O 9 (SBT) and lead zirconate titanate Pb(Zr 0.3 ,T 0.7 )O 3 (PZT) with a newly developed measurement setup. In this work, high speed dynamic hysteresis measurements are performed to further explore the dynamic behaviour of polarization switching into the frequency domain. Virtual Ground measurements down to 100 ns cycle time of excitation signal were achieved, providing additional insight into device operation. A rise of Vc with a factor of 0.065 kV/decade between measurements at 10 Hz and 10 MHz of excitation frequency was confirmed.

Influence of Metal Electrodes on the Ferroelectric Responses of Poly(vinylidene fluoride-trifluoroethylene) Copolymer Thin Films

ABSTRACTFerroelectric polymer thin films have been investigated for applications such as sensors, MEMS, and memory devices, just name a few. In these thin film devices, it is anticipated that the interface effect will play an important role in determining the device performance. In this paper, we present the results of a recent study on the influence of metal electrodes on ferroelectric switching behavior of poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) polymer thin films. The results show that the influence of metal electrodes on the polarization response can be divided into two effects, the bulk effect and interface effect. The bulk effect manifests itself as the built-in bias field when metal electrodes with different work functions were used on the two surfaces of the P(VDF-TrFE) film. The interface effect is more complicated but is directly related to the metal work function. For a metal I/insulator (ferroelectric film)/metal II (MIM) sandwich structure in which the metal I and metal II possess different work functions, the low frequency polarization hysteresis loop shows asymmetric response (different switching fields). The polarization switching time also depends on whether the applied voltage is in parallel or anti-parallel to the built-in bias field. In the fast polarization switching process, it was observed that the interface effect plays a dominating role and the switching time is mainly limited by the charge injection from metal electrodes to the polymer film. For metal electrodes with higher work function, higher injection currents and hence faster polarization switching were observed. The results from I-V studies also show that the charge injection process is a Schottky type and the barrier height estimated from the temperature dependence of the I-V curves is consistent with the metal work functions used.

Polarization Switching Studies in Ferroelectric Glycine Phosphite Single Crystals

Glycine Phosphite [NH 3 CH 2 COOH 3 PO 3 ], abbreviated as GPI, undergoes a para-ferroelectric phase transition from the monoclinic symmetry P2 1 /a to P2 1 at 224.7 K. We report here a systematic study of the polarization switching process in this crystal. Growth of these crystals from aqueous solution has been undertaken employing both solvent evaporation and slow cooling methods. Hysteresis loop measurements along the polar b -axis yielded a spontaneous polarization value of 0.5 w C/cm 2 and a coercive field of 2.5 kV/cm. Conventional Merz technique was employed for polarization switching studies, wherein bipolar square pulses were applied to the sample to induce domain reversal. The transient switching pulse that flows through the sample on application of the field was recorded. The maximum switching time required for domain switching was measured both as a function of electric field and temperature. The experimentally observed switching curves were fitted with the model based on the Pulvari-Kuebler theory of nucleation and growth of domains. From the experimental data, the values of mobility and activation field were obtained. It was observed that switching process in this crystal is predominantly governed by the forward growth of domain walls in the high field region. However, switching process in GPI crystal was found to be slower than that found in other glycine based ferroelectric crystals.

Transient Behavior of the Polarization in Ferroelectric Thin Film Capacitors

AbstractThe understanding of the polarization switching process of ferroelectric capacitors is highly relevant for the development and optimization of FeRAM devices. We report on the characterization of Pb(Zr,Ti)O3 thin films which have been studied by means of dedicated rectangle pulse measurements. Decreasing the voltage level of the excitation pulses decelerates the polarization switching significantly to the range of milliseconds and reduces the switchable polarization. In this work the influence of niobium (Nb) doping on the switching properties of PZT thin films prepared by CSD are investigated to reach the aspired conditions of low voltage operation, read and write access pulses in the range of nanoseconds. For the implementation of the transient behavior of ferroelectric capacitors in circuit design and simulation tools it is necessary to develop a model which precisely describes the polarization hysteresis, the pulse switching behavior as well as the small signal capacitance. The fundamental considerations for this model are presented, based on an ideal ferroelectric capacitor, taking into account the Curie-von Schweidler behavior. The latter is observed in non-ferroelectric high-K materials as well as in ferroelectric thin films.

Sn2P2S6films for memory devices with nondestructive readout

Abstract The polarization switching processes of ferroelectric polycrystalline Sn2P2S6 films on Al substrates were studied. The effect of full reverse spontaneous switching after the influence of a repolarizing pulse on the prepoled sample was investigated. This opens the way for making the ferroelectric memory devices with rapid nondestructive readout.

Switching studies and the effect of irradiation on ferroelectric properties of TAAP and DTAAP

Polarization switching processes in TAAP and DTAAP have been studied by the Merz method. The switching process in DTAAP is slower than in TAAP. The temperature dependence of switching time indicates that the crystal might contain groups of domain nuclei with different activation energies. X-ray irradiation causes an increase in the threshold field below which switching could not occur and decrease in the mobility of domain walls. Irradiation decreases the peak value of dielectric constant, Tc and increases the value of coercive field. Domain structure studies on TAAP crystals have shown that the crystals grow as both predominantly single domain and multi domains, depending on which the internal bias increases or remains unaffected upon irradiation.

Polarization switching in radiation damaged ferroelectric crystals

The polarization switching processes in radiation damaged ferroelectrics were studied by the Merz method. In irradiated triglycine sulphate and sodium nitrite, the switching time depends exponentially on the applied electric field. Irradiation increases the importance of nucleation and sideways motion of the domain walls in polarization switching.

Ultrasonic Measurement of Polarization Switching Processes in Barium-Titanate Single Crystal

A previously developed nondestructive piezoelectric method for studying the state of polarization of ferroelectric crystals is applied to study polarization switching in barium titanate single crystals. We propose three polarization processes. The first and second processes were designated nucleation and growth by Merz. The third process cannot be measured by conventional pulse methods, and has a very slow polarizing velocity. This indicates the existence of layers which lie between the surface layer and inner layer. Switching time results are considered in the light of the above experiments.