Epitaxial thin film heterostructures of relaxor ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3

Abstract

We have grown stoichiometric pure perovskite phase Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) thin films and PMN-PT/SrRuO₃ heterostructures on miscut (100) SrTiO₃ substrates by pulsed laser deposition. X-ray diffraction θ–2θ scans show that the PMN-PT films are purely c-axis oriented. The off-axis Φ scans show that the heterostructures grow “cube-on-cube” with an in-plane epitaxial arrangement of PMN-PT[100], [010] // SrRuO₃[001] // SrTiO₃[100] and PMN-PT[010], [100] // SrRuO₃[110] // SrTiO₃[010]. The crystalline quality of the films found to be comparable to that of bulk single crystals. The AFM images show that the SrRuO₃ and PMN-PT layers have smooth surfaces with root mean square roughness of 9Å. These epitaxial heterostructures can be used for the fabrication of piezoelectric devices.     

EFFECTS OF DEPOSITION PARAMETERS AND FILM THICKNESS ON THE PHASES AND ELECTRICAL PROPERTIES OF Pb(Mg1/3Nb2/3)O3 THIN FILMS MADE BY MOCVD USING ULTRASONIC NEBULIZATION

ABSTRACT

PMN thin films were deposited by MOCVD using ultrasonic nebulization and the effects of deposition parameters and film thickness on the phases and electrical properties of the PMN films were investigated. The low deposition temperature and RTA treatment were favorable to deposit the PMN films with a low content of pyrochlore phase. Excess Mg enhanced the formation of perovskite phase of PMN films also. As the film thickness was increased, the portion of pyrochlore phase in PMN films was decreased. The dielectric constant of PMN films increased with the film thickness and showed the value of 25–230.     

Substituent Effects in 0.65Pb(Mg1/3Nb2/3O30.35PbTiO3 Piezoelectric Ceramics

Pb(Mg_1/3Nb_2/3O₃–-PbTiO₃ (PMN-PT) ceramics with base compositions close to the morphotropic phase boundary are potential materials for many applications such as transducers and actuators due to their high dielectric constants and electromechanical coupling factors. However, their dielectrical and mechanical losses are too high for high-power applications. In this paper, the dielectric and electromechanical properties of piezoelectric PMN-PT ceramics were investigated in specimens containing various A-site and B-site substituents with the goal of developing lower loss materials for wider applications. Emphasis was placed on various transition metal cation substituents of both lower and higher valences. Mn substituent was found to be the most promising substituent investigated for developing high power low loss piezoelectric PMN-PT ceramics.     

Epitaxial ferroelectric Pb(Mg1/3Nb2/3)O3-PbTiO3 thin films on La0.7Sr0.3MnO3 bottom electrode

Epitaxial (001)-oriented 0.7Pb(Mg_0.33Nb_0.67)O₃-0.3PbTiO₃ (PMN-PT) thin films were deposited by pulsed laser deposition on vicinal SrTiO₃ (001) substrates using La_0.7Sr_0.3MnO₃ as bottom electrode. Detailed microstructural investigations of these films were carried out using X-ray diffraction (XRD), atomic force microscopy (AFM) and transmission electron microscopy (TEM). Polarization-field hysteresis curves were measured at room temperature. Spontaneous polarization P _s , remnant polarization P _r and coercive voltage V _c were found to be 25 μC/cm², 15 μC/cm² and 0.81 V, respectively. Field dependent dielectric constant measurements exhibited butterfly shaped curves, indicating the true ferroelectric nature of these films at room temperature. The dielectric constant and the dielectric loss at 100 kHz were found to be 238 and 0.14, respectively. The local piezoelectric properties of PMN-PT films were investigated by piezoelectric force microscopy and were found to exhibit a local piezoelectric coefficient of 7.8 pm/V.     

Piezoelectric properties of the Pb(Sc1/2Nb1/2) O3-Pb(Mg1/3Nb2/3) O3-PbTiO3 ternary ceramic materials near the morphotropic phase boundary

Abstract

The physical and electrical properties of xPb(Sc_1/2Nb_1/2)O₃-yPb(Mg_1/3Nb_2/3)O₃-zPbTiO₃(PSMNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows on almost linear region between the PSMNT 58/00/42 and PSMNT 00/68/32 MPB compositions of the binary systems. The maximum piezoelectric constant, d ₃₃ = 680 pC/N, were found at PSMNT 29/33/38, where ε^T ₃₃/ε₀ = 3,800, and electromechanical coupling factors, (k _p = 70%, k₃₁ = 43%, and k ₃₃ = 76%) and T _c = 207°C were obtained. The maximum electromechanical coupling factors, (k _p = 72%, k ₃₁ = 45%, and k ₃₃ = 77%) were found at PSMNT 29/34/37, where ε^T ₃₃/ε₀ = 3,000, d ₃₃ = 640 pC/N, and T _c = 205°C were obtained. These values are better than those of PZT.     

Field-induced successive phase transitions of Pb(Zn1/3Nb2/3)O3-x%PbTiO3 crystals

The field-induced structural phase transitions of Pb[(Zn_1/3Nb_2/3)_1−x Tix]O₃ (PZN-x%PT) with x = 0.09 and 0.045 were investigated by the high-resolution micro-Brillouin scattering. PZN-9%PT crystals undergo two first order phase transitions, while PZN-4.5%PT undergo a second order phase transition under the zero-field cooling. Under the field-cooling, the higher phase transition of PZN-9%PT changed into a second order phase transition and the temperature range of a tetragonal phase was widened. Whereas a lower phase transition kept the nature of a first order phase transition. On the other hand, elastic anomaly was appeared on phase transition of PZN-4.5%PT under the field cooling.     

MOCVD of Pb(Zr x Ti1-x )O3 thin films on MgTiO3/Si substrates and their electrical properties

Abstract

Pb(Zh _x , Ti_1-x )O₃(PZT) thin films were deposited on Si substrates using MgTiO₃ as the buffer layer and the electrical properties of those MFIS structures were investigated. PZT and MgTiO₃ films were made by MOCVD using ultrasonic spraying technique. Perovskite PZT films have been succesfully made at the substrate temperature of 550 to 600°C only when using MgTiO₃ buffer layer. AES depth profile analysis and RBS analysis revealed that there is no remarkable interdiffusion and no formation of reaction layer between PZT and MgTiO₃ and/or between MgTiO₃ and Si substrate. The capacitance-voltage (C-V) curves of the MFIS structure which were made with PZT and MgTiO₃buffer layer have shown the hysteresis resulted from the ferroelectric switching of the PZT films.     

Preparation of (PbxBa1-x)TiO3 thin films by MOCVD using an aerosol-assisted liquid delivery system

Abstract

Thin films of PbTiO₃, BaTiO₃ and (Pb_xBa_1-x)TiO₃ (PBT) have been prepared by metal-organic chemical vapor deposition using a horizontal reactor with an aerosol-assisted liquid delivery system. Structural and electrical properties have been investigated as a function of the lead content x. First results on PBT thin films grown on platinized silicon substrates show, for x < 0.8, an increasing tetragonal distortion of the lattice cell (c/a >1), and accompanying ferroelectric behavior which is similar to the bulk material. For smaller lead content (x < 0.8) no ferroelectric behavior is established and a small tetragonal distortion of opposite type (c/a <1) is observed. This distortion is attributed to a thermally induced tensile film stress and may be responsible for the suppression of the ferroelectric phase transition.     

IR detectors using Pb(Mg1/3Nb2/3)O3 and Pb(Sc1/2Ta1/2)O3 ceramics under DC bias

Recently, one type of thermal-type IR detector, the pyroelectric sensor, has become of great interest in commercial applications, because of its ability to operate without cooling, its constant detectivity independent of wavelength, and its low cost. The conventional pyroelectric materials are usually normal ferroelectric materials with a first and second phase transition. The working temperatures are sufficiently below the Curie temperature T_c for stable responsivity to temperature. Electric field induced-type pyroelectric sensors have also been proposed. Relaxor ferroelectric materials such as Pb(Mg_1/3Nb_2/3)O₃ (PMN) and Pb(Sc_1/2Ta_1/2)O₃ (PST), which have a glassy Curie temperature near room temperature, are used in this type of sensor. This paper describes the sensor properties of electric field induced-type pyroelectric sensors prepared by using PMN and PST ceramics as compared with the conventional type sensors. Material evaluations of PMN and PST ceramics were made to determine their dielectric and pyroelectric properties. PMN shows excellent induced pyroelectric properties for the sensors over a wide range of temperatures. On the other hand, PST seems to be inadequate for an IR detector because of a very narrow high-response temperature range. The sensors with PMN and PST ceramics show enhanced pyroelectric activities under dc bias field. The measured sensor voltage responsivities agree with the calculated values for the PMN case. The electric field induced-type infrared sensor with thick or thin film materials seems to be satisfactory as linear array IR detectors for thermal imaging, with application of a higher electric field.     

Preparation and electrical properties of 0.4Pb(Zn1/3Nb2/3)O3-0.6Pb(Zr0.4Ti0.6)O3 thin films by 2-step annealing method

Films of (1−x)Pb(Zn_1/3Nb_2/3)O₃-xPb(Zr_0.4Ti_0.6) O₃ (x = 0.6, 40PZN-60PZT) were deposited on Pt/TiO₂/ SiO₂/Si substrate through spin coating. Using a combination of homogeneous precursor solution preparation and two-step pyrolysis process, we were able to obtain the 40PZN-60PZT thin films of perovskite phase virtually without pyrochlore phase precipitation after annealing above 650^∘C. But since annealing done at the high temperatures for extended time can cause diffusion of Pt, TiO₂ and Si, and precipitation of nonstoichiometric PbO, we adopted 2-step annealing method to circumvent these problems. The 2-step annealed films show dense microstructure than the 1-step films annealed at higher temperature. Furthermore, the root-mean-square surface roughness of 220 nm thick films which are annealed at 720^∘C for 1 min and then annealed at 650^∘C for 5 min was found to be 3.9 nm by atomic force microscopy as compared to the 12 nm surface roughness of the film annealed only at 720^∘C for 5 min. The electrical properties of 2-step annealed films are virtually same and those of the 1-step annealed films annealed at high temperature. The film 2-step annealed at 720^∘C for brief 1 min and with subsequent annealing at 650^∘C for 5 min showed a saturated hysteresis loop at an applied voltage of 5 V with remanent polarization (P _r) and coercive voltage (V _c) of 25.3 μC/cm² and 0.66 V respectively. The leakage current density was lower than 10⁻⁵A/cm² at an applied voltage of 5 V.     

Solid state crystal growth of BiScO3-Pb(Mg1/3Nb2/3)O3-PbTiO3

Single crystals 0.26BiScO₃-0.25Pb(Mg_1/3Nb_2/3)O₃-0.49PbTiO₃ [BSPMNT] have been grown for the first time by the solid-state crystal growth (SSCG) method. A <110> oriented Ba(Zr,Ti)O₃ crystal seed was embedded in a matrix of BSPMNT compact which was annealed at high temperatures to induce the single crystal growth. Various fluxes, including Bi₂O₃, LiBiO₂, PbO/LiBiO₂, and PbO/Bi₂O₃, were used and their effects on the microstructure of the annealed compacts and the single crystal growth behavior were investigated. In the annealed samples with PbO/Bi₂O₃ flux, a considerable single crystal growth occurred at 1050?°C (with thickness on the order of 500?C1000???m), without the formation of abnormally large grains in the matrix. The results were explained in terms of the effect of various fluxes, based on the grain growth theory.     

Phase Development and Electrical Properties of Pb(Yb 1/2 Nb 1/2 )O 3 -PbTiO 3 Epitaxial Films

The growth and electrical properties of Pb(Yb 1/2 Nb 1/2 )O 3 -PbTiO 3 (PYbN-PT) epitaxial films were investigated. PYbN-PT epitaxial films with SrRuO 3 bottom electrodes were grown by pulsed laser deposition. Optimization of the growth conditions for the PYbN-PT epitaxial films was carried out on (100) SrRuO 3 /(100) LaAlO 3 substrates using the (50/50) composition target. It was found that formation of pyrochlore phase could be caused not only by low growth temperatures or lead deficiency, but also by poor surface condition of the SrRuO 3 bottom electrodes. (001) PYbN-PT epitaxial films with good crystalline quality were obtained for a range of deposition rates (60-100 nm/min) and temperatures (620-680 °C) after vacuum annealing the SrRuO 3 bottom electrodes. The ferroelectric and piezoelectric properties of 1 w m-thick PYbN-PT epitaxial films with (50/50) and (60/40) compositions and with (001) and (111) orientations were investigated using (100) LaAlO 3 , (100) SrTiO 3 , and (111) SrTiO 3 substrates with SrRuO 3 bottom electrodes. The highest remanent polarization (29 w C/cm 2 ) and effective piezoelectric coefficient e 31.f ( m 14 C/m 2 ) were observed in the (001) PYbN-PT (50/50) film. The transition temperature of the (001) PYbN-PT (50/50) film was about 380 °C. Because of the degradation of the target during the deposition, a 3 w m-thick film was prepared by three depositions (1 w m each layer). The 3 w m-thick film exhibited a higher e 31.f coefficient of m 19 C/m 2.     

Ferroelectric Pb5Ge3O11 MFMOS capacitor for one transistor memory applications

Abstract

The basic mechanism for an one transistor memory device has been studied. Many ferroelectric materials such PbZr_xTi_1?xO₃ (PZT), SrBi₂Ta₂O₉ (SBT), Pb₅Ge₃O₁₁ (PGO) etc. were analyzed for this application. Because of its low remanent polarization and low dielectric constant, the c-oriented Pb₅Ge₃O₁₁ thin film was selected for one-transistor memory applications. Pb₅Ge₃O₁₁ thin films have been prepared using MOCVD and RTP (Rapid Thermal Process) post-annealing. Lead bis-tetramethylheptadione [Pb(thd)₂] and germanium ethoxide [Ge(OC₂H₅)₄] were used as the precursors. The Pb₅Ge₃O₁₁thin films were deposited onto Ir/Ti/SiO₂/Si wafers to measure their compositions, phase formation, microstructure and ferroelectric properties. The extremely highly c-oriented Pb₅Ge₃O₁₁ thin films showed good ferroelectric and electrical properties. A 300 nm thick PGO thin film exhibited a square and saturated hysteresis loop with 2Pr of 3.98 μC/cm², 2Ec of 128 KV/cm at an applied voltage 5V, leakage current of 5.1×10^?7 A/cm² at 100 KV/cm, and dielectric constant of close to 36. The c-axis oriented Pb₅Ge₃O₁₁ thin film also exhibited very good retention properties. The experimental results showed that a Pb₅Ge₃O₁₁ MFMOS gate stack is suitable for one-transistor memory applications.     

Ferroelectric SrBi2Ta2O9 thin films deposited by liquid injection MOCVD using novel bimetallic alkoxide precursor

Abstract

The ferroelectric SBT films were deposited on Pt/Ti/SiO₂/Si substrates by liquid injection metalorganic chemical vapor deposition (MOCVD) with single-mixture solution of Sr[Ta(OEt)₅(dmae)]₂ and Bi(C₆H₅)₃. The Sr/Ta and Bi/Ta ratio in SBT films depended on deposition temperature and mol ratio of precursor in the single-mixture solution. At the substrate temperature of 400°C, Sr/Ta and Bi/Ta ratio were close to 0.4 and 1 at precursor mol ratio of 0.5～1.0. As-deposited film was amorphous. However, after annealing at 750°C for 30 min in oxygen atmosphere, the diffraction patterns indicated polycrystalline SBT phase. The remanent polarization (Pr) and coercive field (Ec) of SBT film annealed at 750°C were 4.7 μC/cm²and 115.7 kV/cm at an applied voltage of 5 V, respectively. The SBT films annealed at 750°C showed practically no polarization fatigue up to 10¹⁰ switching cycles.     

Relaxor behavior of piezoelectric Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics sintered at low temperature

A (100-x)Pb(Yb_1/2Nb_1/2)O₃-xPbTiO₃ [PYN-PTx] solid solution system with 49.0????×????51.0 was prepared using a conventional ceramics process and sintered at low temperature. When excess PbO was added into the PYN-PTx system, all samples were sintered at temperatures as low as 800°C with good dielectric and piezoelectric properties. It is suggested that a liquid phase with excess PbO was formed during the sintering and improved the densification of PYN-PTx ceramics at low temperatures. For the PYN-PTx binary system, it was found that the temperature dependence of the relative permittivity follows a Curie?CWeiss Law above the deviation temperature (T_D) at high temperatures. Good piezoelectric properties of d ₃₃ ?=?510 pC/N, ?? _r ?=?2800 at RT, k _p?=?0.57, and k _t?=?0.42 with T_c?=?373°C were obtained for PYN-PT49.5 ceramics sintered at 800°C for 8 h.     

Structure and Properties of Hot-Pressed Pb(Lu1/2Nb1/2)O3-PbTiO3 Binary System Ceramics*

Solid solution series of the (1 - x)Pb(Lu_1/2Nb_1/2)O₃ - x PbTiO₃ binary system ceramics (PLuNT) were synthesized and hot-pressed (temperature 950°C to 1130°C, pressure 25 MPa); its structure, dielectric and piezoelectric properties were studied. Pure lutecium niobate PLuN (x = 0) has a pronounced long-range order in the B-sublattice and an antiferroelectric to paraelectric phase transition at ～258°C. The phase structure of the PLuNT system, at room temperature, changes from a pseudomonoclinic (psd-M, space group Bmm2) to tetragonal (T, space group P4mm). The pseudomonoclinic phase extends over the 0 ≤ x ≤ 0.38 interval within which the monoclinic angle β proceeds a minimum near to 90° at x ? 0.2. The morphotropic region covers the interval x = 0.38 - 0.49, the concentration ratio psd-M:T? 1 (the morphotropic phase boundary—MPB) corresponds to x = 0.41. Within the morphotropic region, a rather strong distortion of the unit cell—(c/a - 1)≥ 0.02, β ≥ 90.37º, characteristic of “hard” piezoelectrics is maintained. Dielectric dispersion and broadening of the phase transition, features typical to relaxors, are observed within the concentration interval of 0.1 ≤ x ≤ 0.3. The highest electromechanical coupling coefficients: k_p = 0.66, k_t = 0.48, k₃₁ = 0.34 of (1 - x) PLuN?xPT ceramics are attained in compositions near the MPB at x ≈ 0.41. Non-isovalent doping of PLuNT with La³⁺ in Pb sublattice shifts the MPB to lower values of x.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Switching Current Measurements in Pb(Zn1/3 Nb2/3)O3-PbTiO3 Relaxor Ferroelectric Single Crystals

Switching current measurements have been carried out on relaxor ferroelectric single crystal-PZN, and the solid solution 0.86PZN-0.04PT and 0.91PZN-0.09PT for crystallographic directions [001] and [111]. The experiments showed the presence of two maximum points in the switching current for 0.86PZN-0.04PT and 0.91PZN-0.09PT that can be attributed to the co-existence of two phases. The switching time inverse shows a two-fold linear dependence on applied field for both [001] and [111]. This suggests that the polarization reversal in the relaxor systems is related to the mobility of the domains. The switching time in relaxor ferroelectric is long (millisecs) compared to the reported data on normal ferroelectric Barium titanate (microsecs). The switching time is dependent on the composition of the crystal along both [001] and [111]. Along [111], the switching time decreases as the PT component increases in the crystal while along [001], the switching time increases as the PT increases.     

Incorporation of Pb,Ti, and Zr into MOCVD grown PbZrxTi1-xO3 thin films

Abstract

Metal Organic Chemical Vapour Deposition was used to grow PbTiO₃ and PbZr_xTi_1-xO₃ thin films on Pt/Ti/SiO₂/Si substrates. Incorporation of Pb and Ti into PbTiO₃ was studied as a function of the growth temperature, gas phase composition, and reactor pressure, keeping the other deposition parameters constant. The stoichiometric homogeneity in lateral and in vertical direction was measured on optimised PbTiO₃ and PbZr_xTi_1-xO₃ layers using Inductive Coupled Plasma – Atomic Emission Spectroscopy.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.