Effect of Buffer Layer on the Properties of Laser Ablated PZT Thin Films

Lead zirconate titanate (PbZr _x Ti_1?x O₃) or PZT ceramics are a class of piezoelectric materials that are currently experiencing widespread use in industry as electromechanical devices. PtSi/ZnO/PZT thin films were deposited by pulsed laser deposition at relatively low substrate temperature. The PZT thin films on PtSi substrates and on ZnO buffer layer were deposited at substrate temperature 300°C. The composition analysis shows that the film deposited at low temperature is stoichiometric. The films exhibit ferroelectric nature with coercive field of 19.6 kV/cm for 800 nm thick film. The leakage current density of the films shows a good insulating behavior.     

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.     

Miniature Microphone with Silicon-Based Ferroelectric Thin Films

A miniature microphone with silicon-based lead zirconate titanate (PZT) thin films has been fabricated and tested. The main structure of the device is composed of Al/Pt/PZT/Pt/Ti/SiO₂/Si₃N₄/SiO₂/Si multi-layer diaphragm. The PZT thin films have been prepared using an improved sol-gel method. Optimized fabrication process of the device has been developed, especially, RIE (reactive ion etching) and IBE (ion beam etching) processes have been used to etch the PZT thin film and electrode metal successfully. The sensitivity of microphone is 16 mV/Pa at 1 KHz and 158 mV/Pa at the resonant frequency of 17.3 KHz. The electrical and thermal reliability of the microphone is satisfactory. This miniature microphone can be widely used in hearing aids, mobile phones, and many other applications.     

Influence of the Lead Source Materials on the Microstructure and Ferroelectric Properties of PZT Films Sputter-Deposited Using Lead and Lead Oxide

In this investigation, PZT films were sputter-deposited on Si/SiO₂/Ti/Pt substrates using a dual-target system. The dual targets Pb/PZT(PbZr_0.54Ti_0.46O₃) and PbO/PZT(PbZr_0.54Ti_0.46O₃) were used to reveal the effects of various lead compensation source materials on the microstructure and ferroelectric properties of the films. The structures of the films were characterized by X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The chemical binding state was determined using X-ray photoelectron spectrometry (XPS). Ferroelectric polarizability was measured using a Radiant Technology RT66A tester. The influence of deposition temperatures on the microstructure and ferroelectric properties of the films was studied. Perovskite PZT films were successfully deposited using the Pb/PZT and the PbO/PZT dual target sputtering systems at a substrate temperature of between 500 and 580C. Structural change was elucidated as a function of deposition temperatures and the lead sources were correlated with the ferroelectric properties of the film. The ferroelectric characteristics of the PZT films deposited using the PbO/PZT dual target were better than those of films deposited using the Pb/PZT dual target, because the former films had a higher bonding energy.     

Effect of Solution Processing on PZT Thin Films Prepared by a Hybrid MOD Solution Deposition Route

Lead zirconate titanate, Pb(Zr_0.53Ti_0.47)O₃ (PZT), thin films were prepared by a hybrid metalorganic decomposition (MOD) solution deposition route; the effects of processing conditions on the film structure and properties were investigated. Solutions were synthesized by mixing and reacting Zr acetylacetonate and Pb acetate trihydrate with a solution prepared from Ti isopropoxide, acetic acid and water. Chemical changes in the solution during preparation and solution storage (i.e., aging) were investigated by visual observation and FTIR, and were evidenced by changes in phase content and properties of the final PZT films. Results suggest that Zr acetylacetonate and Pb acetate trihydrate react with a Ti oxoacetate-based precursor, and that this reaction continues during aging at room temperature. The PZT film quality and properties improved with aging time of the solution before deposition. To achieve good properties and design a convenient processing route, an accelerated aging scheme, including a brief aging at 60°C and freezing to prevent further reaction, was developed. PZT films prepared from these solutions had average dielectric constants of 1040, loss tangents of 0.05, remnant polarizations of 26 C/cm², and coercive fields of 39 kV/cm.     

Ferroelectric field effect in (La,Sr)CoO3/Pb(Zr,Ti)O3/(La,Sr)CoO3 heterostructures

Abstract

Epitaxial LaCoO₃/Pb(Zr,Ti)O₃/(La,Sr)CoO₃ (LSCO) heterostructures have been grown on LaAlO₃ by pulsed laser deposition for investigating ferroelectric field effect. In the heterostructure, semiconducting LaCoO₃ was used as a conducting channel layer, instead Si. The resistivity of the LaCoO₃ (LCO) channel layer was found to be dependent on an oxygen ambient, primarily the ambient oxygen pressure during deposition. The resistivity of the LCO layer varied in the range of 0.1 – 100 Ω cm. Ferroelectric field effect induced in LaCoO₃ layer was observed by measuring the resistance modulation of the LCO layer with respect to the polarized state of the PZT layer. The resistance modulation of 9% was obtained in the 680 Å thick LCO layer. Further the resistance modulation was improved up to 45% after applying dc bias. It is suggested that the LCO/PZT/LSCO heterostructure can be used as a ferroelectric field effect transistor.     

The dielectric response of ferroelectric films AT intermediate frequencies

Abstract

A technique is described for evaluating dielectric data on ferroelectric films using a Cole-Cole distribution function to separate film and electrode capacitance and resistance. The nature of the information obtained, and methods for validating the conclusions are discussed. The method is applied to lead zirconate titanate films on platinum and ruthenium oxide. Electrode capacitances are generally of the same order of magnitude as the film capacitance.     

Domains in ferroelectric VDF/TrFE copolymer thin films: Investigated by a new optical probe method

Abstract

A new optical probe method was developed by using electro-optic and piezoelectric effects and a phase sensitive detection to determine the polarization of domains in ferroelectric thin films. Ferroelectric domains within a region smaller than 1 μm were detected in annealed VDF(65)/TrFE(35) copolymer thin films. The switching dynamics of these individual domains were also investigated by using this method.     

Correlation between the sawyer-tower measured charge/area of a thin film PZT ferroelectric and the thickness mode piezoelectric coupling coefficient

Abstract

We have observed a 40% increase in the piezoelectrical coupling of a PZT layer upon application of a 10 μs pulse of 17 × 10⁴ V/cm, which generated a polarization of 2.2 μc/cm². A qualitative analysis of this data is given.     

Chemically derived seeding layer for {100}-textured PZT thin films

PZT thin films are used extensively in micro electromechanical systems (MEMS) due to its high piezoelectric coefficients. The electromechanical responses can be optimized by using textured films where the transverse coefficient e_31,f is of particular importance for MEMS structures such as cantilevers, bridges and membranes. It has been shown that {100}-textured PZT of morphotropic composition fabricated by chemical solution deposition (CSD) provides the highest transverse coefficient [1]. This specific texture can be obtained using a seeding layer of sputter deposited PbTiO₃ [2]. However, in a CSD process it is advantageous to also be able to produce the seed layer by chemical methods. The piezoelectric and dielectric properties of 2 μm PZT film seeded by CSD PbTiO₃ measured by a new 4-point bending setup are presented.     

Effect of Zr/Ti Ratio on Microstructure and Electrical Properties of Lead Zirconate Titanate Thin Films Derived by Pulsed Laser Deposition

PZT films were fabricated using various targets of Pb(Zr_xTi_{1 – x})O₃ with Zr/Ti ratios of 70/30, 58/42, 52/48, 45/55 and 30/70, and with excess PbO of 20 wt% on Pt/Ti/SiO₂/Si(100) substrates. The rosette structure was observed in the films derived from the target with a Zr/Ti ratio of 70/30 and disappeared with increasing titanium composition. The observations on surface and cross-sectional microstructure were consistent with a higher perovskite nucleation for the higher Ti content films. The PZT films derived from the target with a Zr/Ti ratio of 45/55 had a polycrystalline columnar microstructure extending throughout the thickness of the film and no pyrochlore phase on the surface was observed. The PZT films derived from the target with a Zr/Ti ratio of 45/55 exhibited better electric properties than those derived from the target with a Zr/Ti ratio of 52/48.     

Processing and Properties of Ferroelectric Pb(Zr,Ti)O3/Silicon Carbide Field-Effect Transistor

Metal-ferroelectric-(insulator)-semiconductor MF(I)S structures have been fabricated and the properties of pulsed laser-deposited PZT/Al₂O₃ gate stacks have been studied on n- and p-type 4H-SiC. Among several polytypes of SiC, 4H-SiC is considered as the most attractive one because of its wider bandgap (E _g ? 3.2 eV) as well as higher and more isotropic bulk mobility than other polytypes. Single PZT phase without a preferred orientation was confirmed by x-ray diffraction. The interface trap densities N _IT, fixed oxide charges Q _F, and trapped oxide charges Q _HY have been estimated by C-V curves with and without photo-illuminated measurements at room temperature. It is found that the charge injection from SiC is the dominant mechanism for C-V hysteresis. Importantly, with PZT/Al₂O₃ gate stacks, superior C-V characteristics with negligible sweep rate dependence and negligible time dependence under the applied bias were obtained compared to PZT directly deposited on SiC. The MFIS structures exhibited very stable capacitance-voltage C-V loops with low conductance (<0.1 mS/cm², tan δ ～ 0.0007 at 400 kHz) and memory window as wide as 10 V, when 5 nm-thick Al₂O₃ was used as a high bandgap (E _g ～ 9 eV) barrier buffer layer between PZT (E _g ～ 3.5 eV) and SiC (E _g ～ 3.2 eV). The structures have shown excellent electrical properties promising for the gate stacks as the SiC field-effect transistors (FETs). Depletion mode transistors were prepared by forming a Pb(Zr_0.52Ti_0.48)O₃/Al₂O₃ gate stack on 4H-SiC. Based on this structure, ferroelectric Pb(Zr,Ti)O₃ (PZT) thin films have been integrated on 4H-silicon carbide (SiC) in a SiC field-effect transistor process. Nonvolatile operation of ferroelectric-gate field-effect transistors in silicon carbide (SiC) is demonstrated.     

High quality lead zirconate titanate films grown by organometallic chemical vapour deposition

Abstract

Organometallic chemical vapour deposition is a suitable technique for the deposition of thin films of oxidic compounds such as lead zirconate titanate, PbZr_xTi_1?xO₃. Above a deposition temperature of about 600°C stoichiometric PbZr_xTi_1?xO₃ films can be grown on platinized silicon wafers within a large process window, independent of the precursor partial pressures and the deposition temperature. This is the result of a self-regulating mechanism. The PbZr_xTi_1?xO₃ films have excellent ferroelectric properties exhibiting high values, up to 60μC/cm², for the remanent polarisation. The value of the coercive field strength varies between 50 and 180 kV/cm, dependent on the composition. Layers with comparable properties can also be grown at lower temperatures, down to 500°C. In this case careful control of the gas-phase composition is required to obtain films with the correct stoichiometry.     

Effect of Rare Earth Europium Substitution on the Microstructure,Dielectric, Ferroelectric and Pyroelectric Properties of PZT Ceramics

Polycrystalline samples of Europium modified lead Zirconate titanate (Pb_{1 – x} Eu_x)(Zr_0.55Ti_0.45)_{(1 – x/4)}O₃ with x = 0.00, 0.02, 0.04, 0.06 has been prepared by mixed oxide (MO) method at sintering temperature of 1250C. The structural characterization of the samples investigated by X-ray diffraction technique exhibit tetragonal structure. PEZT (2/55/45) ceramics show single perovskite phase. Scanning electron micrographs depict uniform, densely packed structure. Dielectric, Pyroelectric and Ferroelectric studies have been performed and are reported and discussed in this paper. PEZT (2/55/45) show good current responsivity (F_i), voltage responsivity (F_v) and detectivity (F_d), in comparison to other compositions under study. Moreover its ferroelectric properties (high remanent polarization with low coercive field) make it suitable material for nonvolatile memory applications.     

Properties of PbZrxTi1−xO3/CeO2/SiO2/Si structure

Abstract

We report the crystalline quality and electrical properties of PbZr_xTi_1?xO₃ (PZT) films on n-type Si(100) substrates with CeO₂/SiO₂ dual buffer layers. PZT films and CeO₂ buffer layers were prepared by pulsed laser deposition technique, and SiO₂ buffer layers were formed by thermal dry oxidation. It was found that CeO₂/SiO₂ dual buffer layers effectively prevented Si and Pb interdiffusion between PZT and Si substrates. Furthermore, the capacitance-voltage (C-V) characteristics of the PZT/CeO₂/SiO₂/Si heterostructures demonstrated ferroelectric switching properties, showing a memory window as large as 2.7 V at 1 MHz.     

FERROELECTRIC GATE FET MEMORY BASED ON CONDUCTION OF FERROELECTRIC-INSULATOR INTERFACE

ABSTRACT

A new type of ferroelectric gate field effect transistor (FET) using ferroelectric-insulator interface conduction has been proposed. Drain current flows along the interface between ferroelectric and insulator layers and needs no semiconductor. This FET consists of source and drain electrodes on ferroelectric film (Pb(Zr_0.52Ti_0.48)O₃(PZT)) prepared on Pt/TiO₂/SiO₂/Si substrate, and gate electrode on HfO₂ insulator film on the PZT film between the source and the drain electrodes. Drain current flows through the interface of the ferroelectric and the insulator. Drain current versus gate voltage characteristics shows clockwise hysteresis loop similarly to the conventional p-channel FET with ferroelectric gate. The FET shows that the On/Off ratio of the conduction current is about 10⁵ and the Off state current is about 10^{? 10}A.     

Pulsed Laser Deposition of Ba0.6Sr0.4TiO3 Thin Films and Their Optical Properties

ABSTRACT

Barium strontium titanate [Ba_0.6Sr_0.4TiO₃ or BST (60/40)] thin films were deposited on MgO (100) substrates using pulsed laser deposition. X-ray diffraction (XRD) measurements revealed that the BST thin films had epitaxially grown on the MgO (100) substrates. The surface morphology of the thin films was observed using an atomic force microscope and the grain size was found to be about 100–150 nm. The surface roughness was around 4.9 nm for a 250 nm thick film. The optical transmittance of the BST thin film was measured using a transmission mode ellipsometer. The BST/MgO configuration was highly transparent in the visible region. The optical band gap energy of the BST film, calculated by applying the Tauc relation, was 3.56 eV. Optical waveguide characteristics of the BST (60/40) thin film were determined using a prism coupler. The electro-optic (E-O) properties were measured at 632.8 nm wavelength using a phase modulation detection method. The BST film exhibited a predominately quadratic E-O behavior and the quadratic E-O coefficient was found to be 0.58 × 10^{? 17} m²/V².     

Ferroelectric Properties of Pb(Zr1 − x,Tix)O3 Prepared by Modified Metallo-Organic-Decomposition Process

Beneficial effect of nano-sized PZT powder incorporation on modifying the characteristics of Pb(Zr_0.52Ti_0.48)O₃, PZT films was demonstrated. The amorphous phase derived from metallo-organic-decomposition (MOD) process started to crystallize at a post-annealing temperature as low as 500°C and can withstand 650°C post-annealing temperature process without inducing the PbO-loss phenomenon. However, 500°C post-annealed PZT films still exhibit paraelectric properties, which can be ascribed to the co-existence of large proportion of amorphous phase, surrounding the crystalline phase. It needs at least 650°C post-annealing process to fully developed the pervoskite structure for PZT films. The remnant polarization (Pr) of the PZT films increases with the proportion of crystalline phase, achieving Pr = 24.9 μC/cm² for 650°C annealed films, with coercive field (Hc) around Ec = 373 kV/cm.     

Mobile defect contribution to the dielectric non-linearity of PZT ferroelectric thin films

Abstract

Effect of the speed of bias voltage variation v on the dielectric non-linearity of metal-PZT-metal thin film capacitors has been studied. A distance ΔV between two maxima of C-V dependence on the voltage scale, characteristic for ferroelectric phase, as a function of the v value was investigated. It was established that decreasing vvalue led to ΔV decrease: ΔV = 1.8–2.0 V when v = 1.6x10⁴ V/s, and ΔV ? 1.0 V when v = 6.5x10^?2 V/s. The ΔV(v) dependence can be explained by the decreasing of the coercive field of the film due to the migration of charged mobile defects such as the doubly ionized oxygen vacancies, and the formation of space charge regions near the electrodes. Using the experimental data some parameters of the migration process were evaluated: the concentration of oxygen vacancies and their mobility were found to be about 10²⁴ m^?3 and 10^?11 m²/Vs, respectively. These values are close to the data published in the literature obtained using the alternative methods of investigation.     

Epitaxial La0.5Sr0.5CoO3 electrode films for ferroelectric device applications

Abstract

We have grown high quality La_0.5Sr_0.5CoO₃ thin films by Pulsed Laser Deposition. This material is a electrically conducting perovskite which can be used as structurally compatible electrodes for devices using ferroelectric materials such as Pb-La-Zr-Ti-O (PLZT). Oxygen stability was investigated under various annealing conditions. LSCO/PLZT/LSCO heterostructures were grown epitaxially on SrTiO₃ (STO) and MgO substrates. P-E hysteresis loop was observed with P_r = 20 μC/cm² and E_c = 24 kV/cm. Direct observation of the piezoelectric effect in PLZT was made by measuring the PLZT c-axis lattice constant under various electric fields. LSCO/STO superlattice was also grown by PLD. The superlattice showed excellent crystallinity with a Rutherford Backscattering (RBS) channeling minimum yield of only 3.6%.