PLZT Film Research Articles

Evaluation of Lead Zirconate–Titanate Ceramic Target for Sputter Deposition of Films for Use in Ferroelectric Capacitors

A high‐density 3 in. diameter (Pb,La)(Zr,Ti)O3 [PLZT] ceramic target containing 20% excess PbO was sputtered by radio‐frequency magnetron sputtering to deposit films containing excess Pb and evaluated with respect to target stability for use in the mass production of ferroelectric memories on Si wafers. The results indicated that PLZT film deposition rate increased with power but the excess PbO content correspondingly decreased. The Pb loss in the films was attributed to secondary preferential sputtering of film substrate in the plasma. Regardless of this difference, excess PbO containing 12 in. diameter PLZT ceramic targets were evaluated in a commercial sputtering system over a period of 7 months and the film Pb content was stable within ±1%.

Field-induced strain of (Pb, La)(Zr, Ti)O 3 epitaxial films grown by metal organic chemical vapor deposition

Two micrometers thick (Pb, La)(Zr, Ti)O 3 [PLZT] films with wide composition range were epitaxially grown on (1 0 0)SrRuO 3 bottom electrode layers epitaxially grown (1 0 0) SrTiO 3 substrates by metal organic chemical vapor deposition. Constituent phase of the films were found to be almost the same with the reported phase diagram for the sintered body except for the wider coexistence region of tetragonal and rhombohedral phases. The change of the measured field-induced strain with the electric field was almost respond to the square of the polarization of the films except the negative strain region, but the magnitude was different. This is due to the increase of the electrostatic coefficient of the film with increasing the La/(Pb + La) ratio. As a results, field induced strain of the PLZT film was found to be controlled by adjusting the composition of PLZT films.

Development of Sol-Gel Precursor System for Direct-Patternable PZT Ferroelectric Films Containing La as a Dopant

ABSTRACTDirect-patternable lanthanum substituted lead zirconate titanate (PLZT) films were prepared by sol-gel technique using orth-nitrobenzaldehyde as a photosensitive agent. PLZT films with various La concentration were formed on Pt(111)/Ti/SiO2/Si(100) substrate for direct-patterning of PLZT films and ferroelectric properties measurement. A well-defined and direct-patterned PLZT film was obtained and the improvement of leakage current density, fatigue resistance and dielectric constant with increased substitution of La in PLZT film were observed especially with 4 mol% La doped PLZT film. From this result, we confirmed that direct-patternable PLZT film is suitable for application in micro device.

Preparation and properties of two-dimensional PLZT photonic crystals using a sol–gel method

Lead lanthanum zirconate titanate (PLZT) film with an array of air-holes was successfully fabricated on a platinum-deposited (0 0 1) magnesium oxide substrate using a sol–gel method with a resist mold. A PLZT precursor solution was cast into a mold with resist pillars patterned using electron-beam lithography. After removing the resist pillars and applying a firing process, a PLZT ceramic film with air-holes was obtained. The patterned PLZT film was grown epitaxially on the substrate. Reflection peaks were also observed by optical measurement of PLZT film with a hexagonal array of air-holes. The frequency range of the reflection peaks coincided with that of the calculated photonic band structures. We consider that this periodic structure and process are suitable for preparing tunable photonic crystals.

Characteristics of Photovoltaic Lead Lanthanum Zirconate Titanate Ceramics in a Layered Film Structure Design

This paper reports on the formation of a new layered film structure and the highly improved photovoltaic output of PLZT. The photovoltaic current of the PLZT film was more than 102 times of magnitude higher than that of bulk PLZT. The improved photovoltaic effect of layered film structure is good for the power sources of wireless transducers and ultraviolet sensing systems.

Preparation and photo-induced properties of lead lanthanum zirconate titanate multilayers

This paper reports on the formation of multilayer structures and the highly improved photo-induced output current of the lead lanthanum zirconate titanate (PLZT) employed. The photo-induced effect of ferroelectrics has the advantage of simple mechanisms of non-bias applications, which are indispensable for semiconductor p-n junctions. But the output current of PLZT bulk is too low for it to be used as a device current source. The new design is described using an upper transparent indium tin oxide electrode. The PLZT film structure exhibited an output current of the order of microamperes upon light illumination. The photo-induced current of the PLZT film was more than 102 times that of bulk PLZT. These differences are due to the characteristics of the design of the multilayers including the configuration of the electrode. The PLZT film also has the advantage of easy output control and suitability for use on Si. A simple model is used for an illustratative explanation of the improved photo-induced effect in the PLZT film. Results show that the photo-induced effect of the ferroelectric multilayer is useful as the current source for micro-electro-mechanical systems.

Effect of Electrode Configuration on Phase Retardation of PLZT Films Grown on Glass Substrate

Lead lanthanum zirconate titanate (PLZT) thick films were deposited on a glass substrate using a methoxyethanol-based sol–gel multicoating method. Two types of electrodes, a coplanar surface electrode and an embedded electrode, were deposited on the films to measure the phase retardation of the PLZT films by the Senarmont method. The quadratic electrooptic properties were measured as a function of the film thickness, for thicknesses ranging from 1 to 4 μm. The PLZT film with the embedded electrode structure showed a higher phase retardation value and enhanced electric breakdown resistance.

Photovoltaic effect of lead lanthanum zirconate titanate in a layered film structure design

This letter reports on the formation of a layered film structure and the highly improved photovoltaic output of the lead lanthanum zirconate titanate (PLZT) employed. The photovoltaic current of the PLZT film per unit width was more than 102 times larger than that of bulk PLZT, while the photovoltaic voltage per unit thickness in the layered film structure was almost the same as that in bulk ceramics. These differences are due to the characteristics of the film structure and configuration of the electrode. A simple model is used for the phenomenological explanation of the improved photovoltaic effect of the PLZT film.

Photovoltaic properties of lead lanthanum zirconate titanate ceramics in a layered film structure design

This paper reports on the formation of a new layered film structure and the highly improved photovoltaic output of the lead lanthanum zirconate titanate (PLZT) employed. The new structure design is described using a top transparent indium tin oxide (ITO) electrode. The PLZT film structure exhibited V and mA output. This means that the photovoltaic current of the PLZT film per unit width was more than 10 2 times larger than that of bulk PLZT, while the photovoltaic voltage per unit thickness in the layered film structure was almost the same as that in bulk ceramics and single crystal. These differences are due to the characteristics of the film structure and configuration of the electrode. PLZT film also has the advantage of its easily controllable parameters: film thickness, illuminated area, and illumination intensity. A simple model is used for the phenomenological explanation of the improved photovoltaic effect of the PLZT film.

Electro-Optical Properties of (Pb, La)(Zr, Ti)O3 Films Prepared by Aerosol Deposition Method

Electro-optically active and highly transparent lanthanum-modified lead zirconate titanate [PLZT, Pb0.91La0.09(Zr0.65Ti0.35)O3] films over 1 µm thick were deposited directly on glass substrates using an aerosol deposition method. An optical transmittance of 70% at the wavelength of 800 nm was obtained for a 4.5-µm-thick PLZT film with a reflection loss of 20% at the film and substrate surfaces. A quadratic electro-optical response with a slim loop was observed, consistent with the expected bulk response. The quadratic electro-optical coefficient was 2.5×10-18 m2/V2, comparable to that of films deposited on buffer layers using a sol-gel method. These results indicate that aerosol deposition provides a superior method for depositing the layers of optical devices.

Modification of (Pb,La)(Zr,Ti)O3 thin films during pulsed laser liftoff from MgO substrates

Pulsed excimer laser irradiation of an absorbing thin film through a transparent substrate has been employed to separate epitaxial (Pb,La)(Zr,Ti)O3 (PLZT) thin films from their MgO growth substrates. The morphology, microstructure, and dielectric properties of the laser-modified PLZT layer generated at the original PLZT/MgO interface by this laser liftoff (LLO) process was investigated. Atomic force microscopy measurements of the film surface after LLO indicated average surface roughness on the order of 90–100 nm, complementing previously reported scanning electron microscopy studies that revealed what appeared to be a rough glassy layer. The surface roughness is thought to form as the original growth substrate is ejected from the films transferred towards the end of the 38 ns pulse, pulling the molten near-interfacial portion of the PLZT film via surface tension, and followed by quenching of the liquid phase. Transmission electron microscopy of PLZT films transferred to Si wafers showed the surface layer consists of an irregular amorphous layer ranging in thickness from 50 to 100 nm, although some surface features protruded as far as 300 nm. Enhanced levels of lead were found to be present in the amorphous phase by Rutherford backscattering spectrometry, implying PbO evaporation and subsequent condensation during LLO. Electrical measurements determined the relative dielectric constant of the surface layer to be in the range of 40 – 70. Subsequent ion milling of the layer demonstrated that the ferroelectric and dielectric properties of the original PLZT films were largely recovered, while the surface roughness was reduced to below 40 nm. The observed differences between the dielectric and ferroelectric properties of the film transferred after complete removal of the amorphous layer compared to those of the film on the original MgO substrate are attributed to the removal of substrate clamping.

Compositional homogeneity of ferroelectric (Pb,La)(Ti,Zr)O3thick films

Quantified wavelength dispersive spectroscopy (WDS) x-ray element maps were used to characterize active (Pb,La)(Ti,Zr)O3(PLZT) layers on Pt/PLZT/Al2O3substrates, one fired at 1050 °C and the other at 1150 °C. In the layer fired at 1050 °C, randomly distributed micrometer-sized compositional irregularities were observed as La-rich regions that were in most cases enriched also with Ti and deficient in Pb and Zr compared to the matrix. Such compositional imperfections were not observed in the PLZT layer fired for the same duration at 1150 °C. The level of microheterogeneity for all elements in the specimen fired at 1150 °C and for Pb, Ti, and Zr in the specimen fired at 1050 °C was below 1% relative at confidence level of 99% while for La it was as much as 2.5% relative. In point-beam line profiles across the active layer starting from the Pt electrode toward the outer surface of the cross-section of the PLZT film, the Pb concentration decreased continuously in both samples, confirming the importance of providing a properly equilibrated partial pressure of Pb around the sample during the entire firing process. Better dielectric and ferroelectric characteristics of the specimen fired at 1150 °C compared to the sample fired at 1050 °C were attributed to the differences in compositional heterogeneity between these samples. The study of the micro-compositional characteristics of these ceramic materials with quantitative WDS mapping has contributed to the optimization of processing parameters and hence to the understanding of the properties of ferroelectric PLZT materials.

Characterization of D2 Gas Interaction with (Pb, La)(Zr, Ti)O3 Film on Pt and Ti at Elevated Temperature

The interaction of poly-crystalline (Pb, La)(Zr, Ti)O3 [PLZT] films deposited on Pt and Ti films with D2 gas was evaluated by baking at 200°C in 3% D2/N2 gas at 4.5 Torr for up to 30 min. Secondary ion mass-spectroscopy (SIMS) of the D2 gas baked PLZT films on Pt revealed that the PLZT contained a D concentration of 1×1019 atoms/cm3. In contrast, the PLZT film which was deposited on Ti contained virtually no D after D2 gas baking. The incorporation of D into the PLZT film on Pt was attributed to deuterium dissociation into D+ ions on the Pt film and then diffusion of D+ into the PLZT film. These results indicate that although the PLZT covered the Pt, the Pt film was catalytically active.

Phase transformation and paired-plate precipitate formation in Pb 0.91La 0.09Zr 0.65Ti 0.35O 3 films grown on sapphire substrates

We report on the phase transformation behavior of Pb 0.91La 0.09Zr 0.65Ti 0.35O 3 (9/65/35) PLZT films grown on r-sapphire substrates via rf-magnetron sputtering. A complex microstructure results in these films depending on deposition and annealing conditions. A random equiaxed polycrystalline grain morphology was observed after rapid thermal annealing or furnace annealing when the as-deposited films were predominantly pyrochlore. Precipitate formation (100–150 nm) was observed in PLZT films that were deposited at temperatures in excess of 490°C with a perovskite structure, after furnace annealing at 700°C. We believe that this is related to internal stresses in the films due to both the lattice mismatch and the thermal expansion mismatch between the PLZT film and the sapphire substrate.

Preparation and characterization of antiferroelectric PLZT2/95/5 thin films via a sol–gel process

Antiferroelectric (AFE) Pb 0.98La 0.02(Zr 0.95Ti 0.05)O 3 (PLZT2/95/5) thin films with thickness of 0.7 μm were successfully deposited on Pt/Ti/SiO 2/Si substrate via a modified sol–gel process. The lead lanthanum zirconate titanate (PLZT) thin films were characterized by X-ray diffractometer (XRD), SEM, dielectric and ferroelectric (FE) measurements. Single phase of perovskite PLZT was obtained for the samples annealed at temperature from 550 to 700 °C. Double P– E hysteresis loops indicating a phase transformation from antiferroelectric to ferroelectric phase were observed for the PLZT thin films at room temperature. The dielectric constant and dielectric loss of the PLZT film annealed at 700 °C are 510 and 0.016, respectively. A saturated polarization as high as 36 μC/cm 2 was observed for the same PLZT thin film. The forward switching field ( E AFE–FE) and backward switching field ( E FE–AFE) of the 700 °C annealed PLZT thin film at room temperature are estimated to be 96 and 31 kV/cm from P– E hysteresis loop, and 91 and 38 kV/cm from dielectric constant dc bias field characteristic, respectively. The variations of the dielectric and ferroelectric properties of the PLZT thin films as a function of annealing temperature were explained in terms of grain size variation.

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.

Relationship between PB content, crystallographic texture and ferroelectric properties of plzt thin films for FRAM® applications

In order to have better control of ferroelectric properties and fast PLZT thin film quality control monitoring during FRAM processing, a correlation between ferroelectric performance, Pb content and crystallographic texture needs to be established for RF magnetron sputtered PLZT thin films. The ferroelectric performance of 200 nm PLZT thin films that contain different levels of Pb excess and different volume fractions of {100} textured materials were investigated. It was found that a higher Pb excess in the as-sputtered PLZT film leads to a higher volume fraction of {100} textured crystallites after annealing. Highly {111} textured PZT thin films show a relatively high Qsw (≈2Pr), however the fatigue and the aging performance is not optimized. The optimized range for the volume fraction of {100} textured material was identified. PLZT thin films, of which the {100} volume fraction is in die optimized range, exhibit improved fatigue and aging performance, better suited for FRAM application.

Chemical solution technique to prepare perovskite PZT and PLZT thin films and powders

PbZr0.65Ti0.35O3 and Pb0.91La0.09Zr0.65Ti0.35O3 thin films with thickness of around 100 nm were prepared by the chemical solution deposition technique on Si (100) substrate. Complex metal alkoxide precursors were synthesized by alcoholisis and alcohol exchange reactions starting from metallorganics compounds. NMR spectroscopic techniques, 1H and 13C, and FTIR analysis were used to study the arrangement of the metals and oxygen in the precursor molecules. The films were deposited on Si (100) by spin coating technique and thermal treated by Rapid Thermal Processing for film crystallization. The thermal evolution and structural characterization were performed by DTA-TG/FTIR and by glazing incidence XRD and XRD powder. A PLZT powder with a well-crystallized perovskite structure was obtained at 700°C free of pyrochlore phase whereas the PLZT film exhibits a distorted perovskite structure and residual pyrochlore. The PZT films were less crystallized. The silicon substrate affects the crystal structure of the film. The residual acetylacetonate groups in the precursor of PLZT, would reduce the clustering of Zirconium species.

Characterization of Metal-Ferroelectric-(Metal-)Insulator-Semiconductor (MF(M)IS) Structures Using (Pb, La)(Zr, Ti)O3 and Y2O3 Films

Metal-ferroelectric-(metal-)insulator-semiconductor (MF(M)IS) structures are fabricated and characterized using (Pb, La)(Zr0.3Ti0.7)O3 (PLZT) and Y2O3 films. Y2O3 buffer layers are epitaxially grown on Si(111) substrates by molecular beam epitaxy and ferroelectric PLZT films are formed on (Pt/)Y2O3/Si by the sol-gel technique. It was found that the Al/Y2O3/Si MIS structure has a low leakage current of less than 10-8 A/cm2. The capacitance–voltage (C–V) characteristics of the PLZT/Y2O3/Si MFIS structure exhibit a hysteresis loop due to the ferroelectricity of the PLZT film with a memory window of 1 V. On the other hand, the memory window of the Pt/PLZT/Pt/Y2O3/Si MFMIS structures is significantly improved.