Non-Linear Imprint Behavior of PZT Thin Films

Ferroelectric thin film capacitors are promising candidates for non-volatile ferroelectric Random Access Memories (FeRAM's) as they exhibit a switchable polarization. There are three important failure-mechanisms influencing the performance of these capacitors and disturbing the long-term stability and reliability under operation conditions fatigue, retention, and imprint. The imprint effect of lead zirconate titanate (PZT) thin films was investigated in this paper. Establishing and maintaining a polarization state leads to a shift of the hysteresis loop on the voltage axis and also to a loss of polarization. The voltage shift as well as the loss of polarization can cause a failure of the ferroelectric memory cell (read and write failure). The experimental results obtained on PZT films are discussed in view of the predictions of imprint models proposed in the literature.     

Influence of Stress on the Performance of PZT Thin Films for Microphone Application

ABSTRACT

A series of microphone cells based on integrated PZT thin films were fabricated by typical MEMS process. The thickness of back silicon as a load of the vibrating diaphragm was controlled by changing ICP (Inductive Coupling Plasma) etching time and power. Concaved diaphragms with different radius were formed due to the balanced tensile stress among the multi-layer films structure. The remnent and saturated polarization strength of microphone cells decreased with the increased deformation of diaphragm. The phenomenon was explained as the weakening of mechanical-electrical coupling in piezoelectric thin films in stressed state.     

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.     

Thickness Dependence of Piezoelectric Properties for PZT Thin Films with Regard to MEMS Applications

In this work we report on the investigation of the piezoelectric and ferroelectric properties of Pb(Zr,Ti)O₃ (PZT) thin films with a composition of 45% zirconium and 55% titanium prepared by chemical solution deposition (CSD) regarding the major properties required in MEMS applications. Therefore we have measured the polarization and the piezoelectric coefficient d ₃₃ and strain using a high-resolution double beam laser interferometer. We found that d ₃₃ alike the strain is nearly independent of the sample thickness. To estimate the lifetime of MEMS we stressed the samples by applying switching and non-switching voltage pulses. In the non-switching case, no change of the material properties was observed whereas the use of switching voltage pulses resulted in a strong decrease of the piezoelectric properties and the polarization. Here we found a linear behavior between the material properties in the fatigued state and the sample thickness.     

Preparation of PZT Thin Films by Liquid-Source MOCVD Using of Cyclohexane Solvent

Pb(Zr, Ti)O₃ thin films were grown on 8-inch Ir(111)/SiO₂/Si substrate by a MOCVD system aiming at application utilizing high-density ferroelectric memory (FRAM). Two types of solvents, THF and cyclohexane were used for liquid source delivery. It was found that the ferroelectric properties of the MOCVD-PZT films using cyclohexane solvent were better than them using THF solvent. By choosing cyclohexane as solvent, the MOCVD-PZT thin films showed strong ?111? preferred orientation and the Pt/PZT/Ir capacitors exhibited promising ferroelectric performances, for instance, large switching charge (Qsw) of 56.4 uC/cm².     

Ultrasonic Micromotors Based on PZT Thin Films

The integration of piezoelectric Pb(Zr,Ti)O₃ thin films on silicon substrates for ultrasonic motor applications is reviewed. With suitable buffer and bottom electrode layers the problems due to high processing temperatures in oxygen ambient can be handled. Reproducibility can be increased by stabilized electrode systems and seeding layers for PZT nucleation. Elastic fin micromotors of millimeter size have been fabricated. They achieve the necessary torques, low speeds, and battery voltage operation for applications in wristwatches. However, their efficiency needs to be improved. Better figure of merits of the material still can be achieved. Better designs with larger coupling factors are desirable.     

Microstructure and Properties of Solution Deposited, Nb-Doped PZT Thin Films

Nb doped PZT films with Nb concentrations of 0, 5, 8 and 12 mol% are being processed via chemical solution deposition on platinized Silicon substrates. An original processing route including seed layer and additional PbO coating is presented whereby homogeneous, pyrochlore free microstructures with 111/100 texture are obtained. The temperature dependence of the dielectric constant shows diffuse peaks corresponding to the paraelectric to ferroelectric transition. The transition temperature is found to decrease from 325°C to 220°C with increasing Nb content. Nb is however found to lead to a substantial increase in the dielectric constant in comparison to non-doped PZT. The dependence of the dielectric constant on DC bias field is also reported. Strong asymmetries towards positive values both in the values of the dielectric constant and coercive fields are obtained at room temperature, and become replenished at 100°C. This is interpreted in terms of space charge effects on the pinning of domain walls. Furthermore, the loss tangent shows a relaxation peak which shifts to higher frequencies with increasing Nb content, and suggests that Nb-doping affects the dielectric properties of the interfacial layer. Finally, Nb addition is found to lead to slant hysteresis loops with lower remnant polarization and coercive field.     

Effect of Pyrolytic Film Thickness on the Texture Evolution of PZT Thin Films

This paper describes the effects of pyrolysis temperature and film thickness before annealing on the orientation and microstructure of the lead zirconate titanate (PZT) thin films prepared by chemical solution deposition method (CSD). Different thickness of the pyrolytic films were obtained by repeating deposition and pyrolysis with different times. The orientation and microstructures of the PZT thin films were characterized by X-ray diffractometry (XRD) and field-emission scanning electron microscope (SEM). The results show that the thickness of the pyrolytic films was the principal factor that affects the crystalline structures in PZT thin films.     

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.     

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.     

Improvement of Capacitive Behavior on Gradient-Free PZT Thin Films

PbZr_0,52Ti_0,48O₃ thin films were synthetized by sol-gel techniques on large scale Pt(111)/TiO_x/SiO₂/Si substrates (200 mm in diameter). The Zr/Ti ratio gradient – that appears through the thickness of the layer with standard processing – can be reduced using an optimized “gradient-compensated” approach. Capacitance measurements revealed an augmentation of the effective permittivity from 5 to 15% using “gradient-free” PZT (reaching 1700 for 2μm). Large scale breakdown voltage analysis revealed an increase of 20% for the breakdown field for low thicknesses (1.25MV/cm for 240 nm-thick layer) suitable for capacitor integration.     

Optimized PZT Thin Films for Pyroelectric IR Detector Arrays

A planar multi target sputtering technology was used to deposit highly (111) oriented Pb(Zr _x Ti_1–x )O₃ (PZT) thin films with x ranging from 0–0.6. The preparation of a stable Pt/ZrO₂ electrode is described and analyzed in terms of stress and stress-temperature behavior. The PZT films with low Zr content are under compressive stress after deposition. The dielectric constant and loss peaks occur at a composition close to the morphotropic phase boundary. Films on the tetragonal side of the phase diagram with a Zr content up to about 25% exhibited a strong self polarization and strong voltage shifts in the C(V) curves. High pyroelectric coefficients of >2×10^–4 C/(m²K) have been measured on these films without additional poling. The self polarization fades out with increasing Zr content. The low values of the pyroelectric coefficient for the PZT film with 60% Zr is discussed in terms of the possible crystallographic variants after distortion and the tensile stress state during the phase transition. Based on the systematic study of stress and electrical properties of PZT films with a wide range of composition presented in this paper, films with a Zr content up to about 25% turned out to give the best properties for the use in pyroelectric detector arrays.     

Studies on piezo coefficients of PLD and sol-gel grown PZT thin film for devices

Abstract

The effect of electrical (DC) contact poling processes on the ferroelectric and piezoelectric properties of sol–gel and pulsed laser-deposited PZT thin films has been investigated as a function of the poling field, temperature and time. The remnant polarization and piezoelectric coefficient are found to increase with and saturate at dc-poling field of 100- 300?kV/cm, temperature of 100–120?°C and poling time of 10–20?min. as compared with un-poled PZT thin films. The P-E hysteresis loops of poled PLD grown PZT films shows sharper switching behaviour as compared to imbalanced loop in sol-gel grown films. An improvement of piezoelectric and ferroelectric properties of sol–gel PZT thin films is found, as compared to those deposited using pulsed laser deposition (PLD), indicating that a poling process is required for sol–gel PZT thin films.     

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.     

Fabrication of PZT Thick Films on Silicon Substrates for Piezoelectric Actuator

In recent years, there has been an increased interest in ferroelectric lead zirconate titanate (PZT) films for applications in piezoelectric devices. Many potential applications require a film thickness of about 10 m for higher force, better sensitivity and stability. In this study we fabricate lead zirconate titanate (PZT) thick films by screen printing on silicon substrates with a platinum bottom electrode. Various substrates were studied. The longitudinal piezoelectric coefficient, d₃₃, was measured by the normal load testing method. Breakdown voltage, tan , P-E hysteresis loop and permittivity were measured on the PZT thick films. The results are promising for the use of PZT thick films in various applications, for example, in silicon micromachined micro-pump.     

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.     

Pyroelectric Properties of PZT/PMNZTU Composite Thick Films

Lead zirconate titanate/uranium doped lead magnesium niobate—lead zirconate titanate (PZT/PMNZTU) composite thick films have been fabricated on silicon substrates at 710°C using a composite sol gel technique. A slurry, made up of PMNZTU powder and PZT sol, was spun onto a silicon substrate and fired to yield a porous skeletal ceramic structure. Subsequent sol infiltration and pyrolysis was used to modify the density of the films prior to final sintering at 710°C.Pyroelectric and dielectric properties have been measured as a function of sol infiltration. The pyroelectric coefficients (p _max = 2.41 × 10^–4 Cm^–2 K^–1) of the composite thick films were found to be comparable to the tape cast and monolithic ceramics of similar composition (2.8 and 3.0 × 10^–4 Cm^–2 K^–1 respectively).Maximum figures of merit (F _V = 2.23 × 10^–2 m² C^–1, F _D = 0.89 × 10^–5 Pa^–1/2), calculated using the electrical properties of the thick films, can be compared with those of screen printed thick films (F _V = 2.7–3.9 × 10^–2 m² C^–1, F _D = 0.8–1.1 × 10^–5 Pa^–1/2) processed at temperatures of ca 1100°C. The ability to directly integrate thick pyroelectric films onto substrates at temperatures as low as 710°C, while maintaining competitive figures-of-merit is of considerable interest for future device applications.     

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.     

Growth and Studies of Calcium Doped Laser Ablated Barium Titanate Thin Films

Ba_{1 ? x}Ca_xTiO₃ targets were prepared by conventional solid state reaction with varied amounts of the calcium content (5 at.%, 10 at.%) and the thin films were deposited on Pt(111) coated Si substrate using pulsed laser ablation technique. The thin films were deposited at different pressures and temperatures, so as to determine the optimized growth parameter for the good quality BCT thin films. The pressure variation on the growth parameters made a dramatic impact in tailoring the dielectric constant and phase transition. The phase evolution of the BCT thin films evolves from 450°C and at higher substrate temperatures (～700°C) for different partial pressures of oxygen, the preferred orientation of the thin films were observed. The SIMS analysis reveals a sharp interface exist at the bottom electrode (Pt)–BCT thin films indicating no interdiffusion taking place which might lead to the degradation of devices. The BCT thin films deposited at higher pressures (>60 mtorr) exhibited higher Ba content indicating the possibility of the Ca occupying the Ti site and is reflected in the decrease of the dielectric phase transition temperature. The ferroelectric hysteresis and Capacitance voltage measurement shows the signature of ferroelectricity.     

The Effect of Sintering Processes on the Properties of Mn-F Doped PZT Ceramics

Fluoridated PZT ceramics were produced by solid-state and liquid-phase sintering methods, according to the formula Pb(Zr_0.52Ti_0.48)_1-xMn_xO_3-yF_y, where 0 < x < 0.015 and 0 < y < 0.1. The effects of sintering processes on the phase development and microstructure of Mn-F doped PZT ceramics have been investigated using XRD and FEGSEM. In solid-state sintering, the fluoride additive enhanced the densification of PZT ceramics, enabling densification to >95% relative density at a temperature as low as 1000°C. However, fluoride loss at high temperatures was found to be a significant problem. Alternatively, ceramics with a density >92% were prepared by sintering at a temperature of 850°C by incorporating a eutectic mixture of PbO and V₂O₅ as sintering aid. Problems associated with volatilization of fluoride compounds during sintering could be alleviated using this approach. EPMA was employed to analyze the distribution of the additives in the calcined powders and sintered ceramics. The nonlinear dielectric properties were determined by measuring P-E loops, using an AC electric field in the range 0.1 to 2.0 kV mm^?1.