Polarization-electric Field Hysteresis Loops Research Articles

Crystal Orientation Dependence on Electrical Properties of Pb(Zr,Ti)O3 Thick Films Grown on Si Substrates by Metalorganic Chemical Vapor Deposition

(111)c- and (100)c-oriented SrRuO3 films were successfully grown on (111)Pt/TiO2/SiO2/(100)Si and (100)LaNiO3/(111)Pt/TiO2/SiO2/(100)Si substrates, respectively, by RF-magnetron sputtering method. On these (111)c- and (100)c-oriented SuRuO3 films, (111)- and (001)/(100)-oriented fiber-textured Pb(Zr0.35Ti0.65)O3 films with 2.0 µm in thickness were grown by metalorganic chemical vapor deposition (MOCVD). Well-saturated polarization-electric field (P-E) hysteresis loops were observed for both films. The remanent polarization (Pr) values of (111)- and (001)/(100)-oriented 2.0 µm-thick Pb(Zr,Ti)O3 (PZT) films were almost the same at approximately 45 µC/cm2 at 200 kV/cm, while the coercive field (Ec) values of these films were slight different at 61 kV/cm and 71 kV/cm, respectively. Moreover, the field-induced strains measured by scanning probe microscopy were also almost the same at approximately 0.2% up to 100 kV/cm. These data show the crystal orientation independence of the remanent polarization and field-induced strain of Pb(Zr0.35Ti0.65)O3 films.

Effect of lattice-misfit strain on the process-induced imprint behavior in epitaxial Pb(Zr0.52Ti0.48)O3 thin films

The effect of lattice-misfit strain on the process-induced imprint behavior in Pb(Zr0.52Ti0.48)O3 (PZT) capacitors with Pt (top), and SrRuO3, La0.7Sr0.3MnO3 or LaNiO3 (bottom) electrodes has been studied. With the different oxide electrodes and by changing the deposition oxygen pressure, various lattice-misfit strains in the epitaxial PZT films have been produced. It was found that after in situ annealing at reduced oxygen pressures, the capacitors showed an increased voltage offset in the polarization-electric field hysteresis loops with increasing the misfit strain, irrelevant to the oxide electrodes employed, while lattice disorder at the bottom interface can effectively eliminate the voltage shift. Our results suggest that the imprint behavior is caused by oxygen loss via dislocations generated by the misfit strain relaxation at the growth temperature.

Effects of uniaxial prestress on the ferroelectric hysteretic response of soft PZT

This paper deals with the influence of preload stress on the ferroelectric hysteretic behavior of piezoelectric ceramics. The polarization and strain versus electric field hysteresis loops were measured for soft lead zirconate titanate (PZT) piezoceramic material under various uniaxial compressive stress preloads of up to −400 MPa. The investigation revealed that the superimposed compression load reduced the remnant polarization, decreased the coercive field, and also had a significant impact on the dielectric and piezoelectric properties. With increasing mechanical load, dielectric hysteresis and butterfly hysteresis became less and less pronounced, as the compressive stress prevented full alignment of the domains and induced mechanical depolarization. The slopes of the polarization and strain curves at zero electric field were measured to evaluate the dependence of permittivity and piezoelectric coefficients on the prestress. The experimental results were interpreted in terms of the non-180° domain switching process under combined electromechanical loading.

Deep level transient spectroscopy of lead zirconate titanate grown on La0.5Sr0.5CoO3/LaAlO3 substrate

Epitaxial lead zirconate titanate thin films were grown by pulsed laser deposition method on LaAlO3 substrate using La0.5Sr0.5CoO3 (LSCO) as the bottom electrode. Two different top electrode systems were studied: a single platinum layer and a platinum/LSCO bi-layer. The as-grown, post-annealed and fatigued samples were subsequently investigated via polarization-electric field hysteresis loops measurement and deep level transient spectroscopy. It was found that polarization fatigue occurs only for films with single platinum layer top electrode but not with Pt/LSCO electrode bi-layer ones. Hole traps with activation energy 0.209 eV were detected in the fatigued samples with single Platinum top electrode. This is the first observation of fatigue-related deep levels in PZT films and provides new insight into the switching fatigue mechanisms.

Sol-gel derived la modified PZT thin films: structure and properties

Lanthanum modified PZT thin films with compositions, namely 8/60/40, 8/70/30, 10/70/30 and 12/70/30 were deposited on platinized silicon substrates by sol-gel spin coating technique. Characterization of these films by XRD and SEM show that the films possess perovskite phase with submicron crystallite size. The saturation polarization (Ps), remnant polarization (PR) and coercive field (Ec) of polarization-electric field hysteresis loop are presented for all compositions. The 8/60/40 composition shows hysteresis loop with P/sub R/ = 11 /spl mu/C/cm/sup 2/. The temperature dependence of dielectric constant and dielectric loss of these films are also studied. Leakage current densities for these thin films are found to be in the range of 10/sup -/-10/sup -/ A/cm/sup 2/. To show the possible application of these thin films for micro electromechanical system (MEMS), a device incorporating an 8/60/40 PLZT thin film has been fabricated using silicon micromachining technology. This device functions satisfactorily as a vibration sensor with a resonance frequency of approximately 8.45 MHz.

Deep level transient spectroscopy of lead zirconate titanate grown on La 0.5Sr 0.5CoO 3/LaAlO 3 substrate

Epitaxial lead zirconate titanate thin films were grown by pulsed laser deposition method on LaAlO 3 substrate using La 0.5Sr 0.5CoO 3 (LSCO) as the bottom electrode. Two different top electrode systems were studied: a single platinum layer and a platinum/LSCO bi-layer. The as-grown, post-annealed and fatigued samples were subsequently investigated via polarization-electric field hysteresis loops measurement and deep level transient spectroscopy. It was found that polarization fatigue occurs only for films with single platinum layer top electrode but not with Pt/LSCO electrode bi-layer ones. Hole traps with activation energy 0.209 eV were detected in the fatigued samples with single Platinum top electrode. This is the first observation of fatigue-related deep levels in PZT films and provides new insight into the switching fatigue mechanisms.

Comparison of the Ferroelectricity for 70–80 nm Thick Pb(Zr,Ti)O3 Films Deposited on (111)Ir Bottom Electrodes at Different Temperatures by MOCVD

70–80 nm-thick Pb(Zr,Ti)O3 (PZT) films were deposited on (111)Ir/TiO2/SiO2/Si substrates at 415 and 540°C by metalorganic chemical vapor deposition (MOCVD). The remanent polarization (P r) value showed 22 μ C/cm2 at an applied voltage of 3 V, even for the film deposited at 415°C. However, this value was almost 40% of that for the film deposited at the higher temperature. P r value was enhanced up to 40 μ C/cm2 and the squareness of the polarization-electric field (P-E) hysteresis loop was also improved by the post-annealing at 500°C, even though a noticeable change was not detected on the x-ray diffraction pattern. Moreover, both of the P r and coercive field (E c) values of the film annealed at 500°C after 415°C-deposition were almost saturated below 2 V, as same as the as-deposited films at 540°C.

Crystallization behavior and ferroelectric properties of PbTiO3/Ba0.85Sr0.15TiO3/PbTiO3 sandwich thin film on Pt/Ti/SiO2/Si substrates

A PbTiO3/Ba0.85Sr0.15TiO3/PbTiO3 (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO2/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO3 layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10−6 Acm−2, 2.46 µCcm−2, and 41 kVcm−1, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.

Origin and implications of the observed rhombohedral phase in nominally tetragonal Pb(Zr0.35Ti0.65)O3 thin films

The structural and electrical properties of Pb(Zr0.35Ti0.65)O3 (PZT) thin films ranging in thickness from 700 to 4000 Å have been investigated. These (001)/(100)-textured films were grown by metalorganic chemical vapor deposition on (111)-textured Ir bottom electrodes. It was observed that, in the as-deposited state, the thinnest PZT films are rhombohedral even though bulk PZT of this composition should be tetragonal. Thicker films have a layered structure with tetragonal PZT at the surface and rhombohedral PZT at the bottom electrode interface. In this article we investigate the origin of this structure and its effect of the ferroelectric and dielectric properties of PZT capacitors. It has been suggested that thin films stresses can affect the phase stability regions of single domain PZT. This possibility has been investigated by piezoresponse microscopy and thin film stress measurements. In the as-deposited state the majority of PZT grains contain a single ferroelastic domain, whereas after a high temperature anneal, a large fraction of the grains contain several ferroelastic domains. Wafer curvature measurements in combination with x-ray diffraction stress measurements in the Ir bottom electrode showed that the as-deposited PZT films are, within experimental error, stress free at room temperature. Landau–Ginbzurg–Devonshire formalism was used to explain the origin of the rhombohedral phase as a result of substrate constraint on single domain PZT grains. Annealing was found to affect the relative volume fractions of the rhombohedral and tetragonal phases and the electrical properties of PZT films. Intermediate temperature anneals increased the volume fraction of the rhombohedral phase and the coercive field extracted from the polarization-electric field hysteresis loops. After a high temperature anneal (650 °C) the majority of the grains transformed into a polydomain state, decreasing the volume fraction of the rhombohedral phase and the coercive field. If the high temperature anneal was performed after deposition of the top electrode, the coercive field became independent of the PZT thickness.

Dielectric and piezoelectric properties of relaxor Pb(Sc1/2Nb1/2)O3 thin films

Pure perovskite Pb(Sc1/2Nb1/2)O3 thin films without pyrochlore phase were prepared by the sol–gel method on TiO2/Pt/TiO2/SiO2/Si substrates. Films exhibited (111) preferred orientation and columnar microstructure. Diffuse phase transitions with permittivity maximum decreasing in value and shifting toward higher temperature with increasing frequency and slim polarization-electric field hysteresis loops typical for relaxors were observed. The maximum field-induced piezoelectric d33 coefficient measured with ac electric field of 14 kV/cm was 58 pm/V. The d33–dc electric field relation is virtually hysteresis free.

Large remanent polarization of 100% polar-axis-oriented epitaxial tetragonal Pb(Zr0.35Ti0.65)O3 thin films

100% polar-axis (c-axis)-oriented epitaxial Pb(Zr0.35Ti0.65)O3 (PZT) thin films were grown and their large remanent polarization (Pr) was directly measured. Perfectly c-axis-oriented epitaxial PZT thin films were obtained on (100)cSrRuO3//(100)SrTiO3 substrates when the deposition temperature increased to 540 °C together with a decrease in the film thickness down to 50 nm. Polarization–electric-field hysteresis loops were well saturated and had a square shape. The Pr of a 50 nm thick film saturated at 0.9 V, and its value was over 90 μC/cm2; almost independent of the measurement frequency within the range from 20 Hz to 1 kHz. This value was in good agreement with the estimated one from the a- and c-axes mixture-oriented epitaxial PZT film having the same composition taking into account the fact that only the c-axis-oriented domain contributed to the polarization. On the other hand, the coercive field value of a perfectly c-axis-oriented film was 140 kV/cm and almost the same as that of the mixture-oriented one having the same film thickness. These results show that PZT has a large Pr applicable for high-density ferroelectric random access memory.

Influence of Temperature on the Microstructure and Electrical Properties of BBT Thin Films

The BBT films were prepared by a spin-coating process from the polymeric precursor method (Pechini process). In order to study the influence of the temperature on the BBT microstructure and electrical properties, the films were deposited on platinum coated silicon substrates and annealed from 700@C to 800°C for 2 hours in oxygen atmosphere. The crystallinity of the films was examined by X-ray diffraction while the surface morphology was analysed by atomic force microscope. The dielectric properties and dissipation factor of BaBi 2 Ta 2 O 9 films at 1 MHz were observed. The polarization-electric field hysteresis loops revealed the ferroelectric characteristics of BaBi 2 Ta 2 O 9 thin films.

Dielectric Behaviour and Polarization Response of Proton Irradiated Ba0.65Sr0.35TiO3/P(VDF-TrFE) Composites

Ba0.65Sr0.35TiO3/P(VDF-TrFE)70/30 composites have been prepared by dispersing Ba0.65Sr0.35TiO3 powder in a vinylidene fluoride-trifluoroethylene copolymer (with 70 mol% vinylidene fluoride) matrix. The effects of irradiation with 3 MeV protons on the dielectric properties and polarization response of the composites have been investigated. At a dosage of 100 Mrad, both the copolymer and the composites exhibit a broad peak in the relative permittivity whose location shifts upwards in temperature with increasing frequency. This result implies that the proton irradiation breaks up the coherent polarization domains in the normal ferroelectric copolymer phase into nanopolar regions, thereby converting the material to a relaxor ferroelectric. The polarization-electric field hysteresis loop becomes slimmer after irradiation, particularly for the composites with low ceramic volume fraction. For the unirrdiated samples, the slight increase of remnant polarization with ceramic volume fraction indicates that the remnant polarization of the ceramic phase is not much higher than that of the copolymer phase. After irradiation, the remnant polarization of the copolymer drops sharply. The remnant polarization of the irradiated composites rises steeply with increasing ceramic volume fraction and is only 20% lower than that of the unirradiated composites at a ceramic volume fraction of about 0.5.

Characterisation of proton irradiated Ba 0.65Sr 0.35TiO 3/P(VDF-TrFE) ceramic–polymer composites

Barium strontium titanate/poly (vinylidene fluoride-trifluoroethylene)70/30 (Ba 0.65Sr 0.35TiO 3/P(VDF-TrFE) 70/30) composite with high dielectric permittivity was developed by integrating high dielectric permittivity ceramic powder with proton irradiated polymer matrix. The composite after irradiation behaves as a relaxor ferroelectric material and this behaviour is similar to that of irradiated P(VDF-TrFE) 70/30 co-polymer. Due to the irradiation, dielectric peaks broadened and moved towards the lower temperature, creating high relative permittivity values in a broad temperature range. Ba 0.65Sr 0.35TiO 3/P(VDF-TrFE) composite with 0.5 ceramic volume fraction with a dosage of 80 Mrad can reach a relative permittivity of ∼160 at room temperature (at 1 kHz), which is about 14 times higher than that of pure copolymer. Polarization-electric field hysteresis loops of composites are strongly depended on the ceramic powder volume fraction and the effects of irradiation is less apparent in composites with higher ceramic powder volume fraction.

Thermally Activated Low Frequency Dielectric Dispersion of Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 Thin Film

Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films on Pt/Ti/SiO 2 /Si substrate have been fabricated by pulsed laser deposition technique. The temperature dependent dielectric constant and polarization-electric field (P-E) hysteresis loops of PLZT film demonstrate the phase transition from antiferroelectric to ferroelectric. The Curie temperature (T c ) and dielectric constant at T c are 196C and 2065, respectively. The maximum saturated polarization reaches nearly 50 w C/cm 2 , corresponding to a maximum induced charge of 12.5 nC. The complex dielectric constants and ac conductivities of PLZT thin film are measured as a function of frequency (0.01Hz∼1 MHz) and temperature (25∼200C) in order to investigate dielectric dispersions and conduction mechanisms. We also observe the strong low-frequency dielectric dispersion at high temperature above 125C due to the migration of thermally activated oxygen vacancies. The estimated activation energy for conduction is 0.76 eV. The conduction mechanism seems more complicated than simple hopping model. Consequently, understanding of oxygen vacancy transfer in the antiferroelectric PLZT thin film is important for practical applications in high charge storage and actuator devices.

Thermally Activated Low Frequency Dielectric Dispersion of Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 Thin Film

Antiferroelectric Pb 1.075 La 0.025 Zr 0.95 Ti 0.05 O 3 (PLZT) thin films on Pt/Ti/SiO 2 /Si substrate have been fabricated by pulsed laser deposition technique. The temperature dependent dielectric constant and polarization-electric field (P-E) hysteresis loops of PLZT film demonstrate the phase transition from antiferroelectric to ferroelectric. The Curie temperature (T c ) and dielectric constant at T c are 196C and 2065, respectively. The maximum saturated polarization reaches nearly 50 w C/cm 2 , corresponding to a maximum induced charge of 12.5 nC. The complex dielectric constants and ac conductivities of PLZT thin film are measured as a function of frequency (0.01Hz∼1 MHz) and temperature (25∼200C) in order to investigate dielectric dispersions and conduction mechanisms. We also observe the strong low-frequency dielectric dispersion at high temperature above 125C due to the migration of thermally activated oxygen vacancies. The estimated activation energy for conduction is 0.76 eV. The conduction mechanism seems more complicated than simple hopping model. Consequently, understanding of oxygen vacancy transfer in the antiferroelectric PLZT thin film is important for practical applications in high charge storage and actuator devices.

Dry etching of SrBi2Ta2O9 thin films in Cl2/NF3/O2/Ar inductively coupled plasmas

A parametric study of high density plasma etching of SrBi2Ta2O9 (SBT) thin films was carried out in a planar type inductively coupled plasma (ICP) etcher with different chemistries of Cl2/Ar, Cl2/NF3/Ar, and Cl2/NF3/O2/Ar. The etch rate was a strong function of gas concentration, ICP source power, and rf chuck power. Both Cl2/NF3/Ar and Cl2/NF3/O2/Ar plasmas showed maximum etch rates of ∼1600 Å/min at 5 mTorr, 700 W ICP power, and 150 W rf chuck power. The addition of NF3 and O2 into the Cl2/Ar mixture played an important role in not only enhancing the etch rate, but also smoothing the etched surface by reducing the kinetic energy of ions. Electrical properties of the SBT films were quite dependent of plasma chemistries: Cl2/NF3/O2/Ar showed the least damage in the films and resulted in overall the best polarization-electric field hysteresis loop compared to other chemistries.

Dielectric, hypersonic, and domain anomalies of (PbMg1/3Nb2/3O3)1−x(PbTiO3)x single crystals

Dielectric permittivities, Brillouin backscattering spectra, polarization-electric field hysteresis loops, and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystals (PbMg1/3Nb2/3O3)1−x(PbTiO3)x(PMN-xPT) for x=0.24 and 0.34. For PMN-24%PT, a diffuse phase transition which is associated with a broad frequency-dependent dielectric maximum was observed near 380 K. As the temperature increases, the PMN-24%PT crystal gradually develops cubic regions and is fully converted into the cubic state near 375 K. An extra dielectric anomaly appears at 370 K, possibly due to the percolating polar cluster induced by an external electric field. PMN-34%PT exhibits a nearly normal ferroelectric phase transition near 445 K from the tetragonal to the cubic phase. In addition, a weak diffuse phase transition observed near 280 K may result from partial conversion of rhombohedral phase to tetragonal phase. The dielectric thermal hysteresis confirms that the transitions near 280 and 445 K are diffuse first order and first order, respectively. The dielectric permittivities of PMN-24%PT and PMN-34%PT obey the relation, εm′/ε′(f,T)=1+[T−Tm(f )]γ/2δγ2, above the temperature of permittivity maximum Tm.

Phase transitions and domain structures in relaxor-based ferroelectric (PbZn1/3Nb2/3O3)0.915(PbTiO3)0.085 single crystal

Polarization-electric field (P-E) hysteresis loops and domain structures have been measured as a function of temperature in relaxor-based ferroelectric single crystal (PbZn1/3Nb2/3O3)0.915(PbTiO3)0.085 (PZN-8.5%PT). In order of increasing temperature, PZN-8.5%PT undergoes successive phase transitions: rhombohedra1 phase (below ∼375 K) → coexistence of rhombohedral and tetragonal phases (between ∼375 and ∼390 K) → tetragonal phase (between ∼390 and ∼420 K) → coexistence of tetragonal and cubic phases (between ∼420 and ∼460 K) → cubic phase (above ∼460 K). Phase coexistence suggests an inhomogeneous distribution of Ti4+ concentration in the PZN-8.5%PT crystal.

Dielectric properties of relaxor ferroelectric (PbMg1/3Nb2/3O3)1−x(PbTiO3)x single crystals

Successive phase transitions have been observed in relaxor ferroelectric single crystals (PbMg1/3Nb2/3)1−x(PbTiO3)x (PMN-xPT) for x=0.24. 0.31 and 0.33, by using dielectric measurements and polarization-electric field (P-E) hysteresis loops. Phase coexistence that is characterized by broad dielectric maximum and gradual-evolution of remanent polarization, has been observed in these crystals. The field-cooled-zero-field-heated dielectric permittivity shows that the dc bias field induces a long-range ferroelectric phase transition.