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.     

Self-polarization effect in Pb(Zr,Ti)O3 thin films

Abstract

The self-polarization effect is investigated in Pb(Zr,Ti)O₃ (PZT) thin films deposited by sol-gel and magnetron sputtering techniques. The effective piezoelectric coefficient of as-grown films, which is proportional to their initial polarization (self-polarization), is measured by a sensitive interferometric technique as a function of the annealing temperature, PZT composition, film thickness and bottom electrode material. The results indicate that the films are self-polarized by an internal bias field upon cooling through the phase transition temperature. It is suggested that a built-in field of a Schottky barrier between the PZT film and the bottom electrode is responsible for the observed effect. Self-polarization of the films is found to be very stable and in some cases to be as high as 90% of that produced by the subsequent room temperature poling. This property is very useful for piezoelectric and pyroelectric applications of PZT films since the poling procedure can be avoided. The properties of self-polarization are found to be similar for the films produced by sol-gel and sputtering techniques, suggesting that the same mechanism is operative in both cases.     

Raman,X-ray and electrical properties of MOD PZT/PLZT thin films

Abstract

Ferroelectric PZT/PLZT thin films have been fabricated using the metallo-organic precursor compounds. The structural development, spectroscopic and dielectric properties of these films have been investigated using atomic force microscopy (AFM), X-ray diffraction, Raman scattering and dielectric measurements. Experimental results show that Raman spectroscopy is an effective tool of monitoring the structural development of the small sized PZT films in the tetragonal phase field. Dielectric characteristics have been improved by the rapid thermal processing approach. A rosette growth model is proposed to explain the observation of the tri-intersection of the perovskite phase in PZT films.     

Crystallization of rapid thermal processed PZT

Abstract

The influence of substrate materials on the crystallization kinetics of thin film PZT is presented. Structure and orientation of electrodes affect the nucleation and growth processes of PZT as it transforms from pyrochlore to perovskite. These determine the final film structure and ferroelectric and dielectric properties. Rapid thermal processed sol gel PZT was fabricated on ruthenium oxide (RuO₂) and on platinum electrodes. A study of oriented RuO₂ electrodes was carried out using glancing angle XRD and transmission electron microscopy (TEM). These techniques were used to assess types and locations of phases present in the films, grain size, crystal orientation and morphology.     

PIEZOELECTRIC RESPONSE OF PZT NANOSTRUCTURES OBTAINED BY FOCUSED ION BEAM

ABSTRACT

Pb(Zr_x,Ti_{1 - x})O₃ (PZT) microscale island (1μ m～ 100 nm) was fabricated by Focused Ion Beam (FIB) before and after its crystallization. In the first case the FIB etching is realized on amorphous films and a post annealing treatment, at the crystallization temperature of the PZT films, is necessary to cristallize the film in the perovskite phase. In the second case the etching are made on crystallized films. Local electrical properties were evaluated by piezoresponse force microscopy (PFM) technique and the degradations induce in the films are studies by Raman spectroscopy. Compared to the PZT island fabricated after crystallization, the result shows that there is noticeable enhancement in nanoscale electrical properties of PZT island fabricated before crystallization, especially when the island size decreases.     

MOCVD PBZRxti1−xo3 thin films on platinized silicon wafers and srtio3 crystals

Abstract

PbZr_xTi_1-xO₃ (PZT) thin films were grown on 6” platinized silicon substrates (Pt / Si) and SrTiO₃ (STO) crystals by Metal-Organic Chemical Vapor Deposition (MOCVD) as a function of the Zr / (Zr+Ti) ratio in the gas phase. Morphology, optical properties, and crystal structure were investigated by scanning electron microscopy, atomic force microscopy, ellipsometry, and X-ray diffraction. The morphology, structure, and optical properties of the polycrystalline and epitaxial films were compared. The determination of the refractive index by ellipsometry (from 550 nm to 2000 nm) was not sensible for the films grown on (Pt / Si) but successful for the films grown on SrTiO₃.     

Modification of PZT nucleation and growth using oxide layer in multi-layered electrodes

Abstract

The ferroelectric properties of PZT on RuO₂ electrodes were compared to those on RuO₂/Pt electrodes. The better hysteretic properties were obtained from Pt/RuO₂/PZT/RuO₂/Pt ferroelectric capacitors. The enhancement of ferroelectric properties is likely attributed to the modification in the microstructure of PZT film. The interfacial modification would be affected by the factors such as surface roughness, stress, and porosity of RuO₂ film. As the result of the interfacial modification, better quality PZT films are produced, thereby resulting in better ferroelectric properties. We made an effort to understand the relationship between the grain size and the coercive voltage in terms of the domain formation and the domain pinning in connection with defects like grain boundaries.     

Characteristics of ferroelectric gate mos and mosfets

Abstract

Electrical characteristics of metal-insulator-semiconductor (MIS) capacitors of a variety of ferroelectric materials like lead zirconate titanate (PZT), lead titanate (PT) and barium magnesium fluoride (BMF) on p-silicon have been studied. PZT was deposited by r.f. magnetron sputtering from a composite target and PT from co-evaporation. The films were annealed in oxygen atmosphere in the temperature range 550–700°C for various times. PZT and PT films which are directly deposited on silicon showed low effective dielectric constant.¹⁰ For normal applied bias voltages (±5 V), the C-V curves did not show significant hysteresis. The effective dielectric constant was improved significantly by the incorporation of a buffer layer. BMF film was deposited in ultra high vacuum on a heated substrate and the film was encapsulated by a zirconium oxide layer. The C-V curves for these MIS capacitors shows hysteresis and the direction of hysteresis corresponds to ferroelectric polarization.     

Basic investigations on a piezoelectric bending actuator for micro-electro-mechanical applications

Abstract

This article deals with basic investigations into the development and manufacturing process of a piezoelectric animated micro actuator. The concept of the fabrication of a piezoelectric microactuator will be introduced and first fundamental investigations on materials characterization and process technology for the Pt bottom electrode and piezoelectric PZT layer will be presented. PZT thin film have been deposited with the chemical solution deposition (CSD) technique and have been characterized with dielectric and ferroelectric measurements. For optimization of actuator properties an analytical approach and a simulation with finite element method was carried out. This shows that the cantilever must have a length above 300 μm to reach a tip deflection higher than 10 μm at voltages comparable to those used in integrated circuits (IC). Additionally, stress measurements of each layer have been used to characterize the films mechanically.     

Conducting oxide electrodes for ferroelectric films

Abstract

Suitability of oxide electronic conductors [e.g. ruthenium oxide (RuO_x) and indium-tin-oxide (ITO)] as contact metallization for ferroelectric films (e.g. PbZr_xTi_1?xO₃) was investigated using techniques such as Rutherford backscattering spectrometry, x-ray diffraction and electron spectroscopy for chemical analysis. Thin films of RuO_x and ITO were deposited on Si substrates by reactive sputtering. Either PbO or PZT (x = 0.53) films were deposited onto the conducting oxides and the specimens were annealed at various temperatures between 400°C and 700°C. Less intermixing was found in Si/RuO_x/ PZT films when compared to Si/ITO/PZT under similar processing conditions. The ferroelectric properties of PZT films on RuO_x electrodes are compared to those on Pt electrodes. The PZT films show improved fatigue properties on RuO_x electrodes.     

Ferroelectric memory programs in Canada

Abstract

Thin film PZT ferroelectrics have been fabricated in Canada since 1976 by magnetron sputtering and more recently by acetate-based sol gel processing and are now being considered for implementation into commercial communications systems. Processing based on rapid thermal annealing has shown marked advantages for crystallization into the required perovskite phase. Applications based on the piezoelectric properties of PZT films are shown to have an interesting potential for a range of devices.     

Metalorganic chemical vapor deposition of ferroelectric Pb(Zr,Ti)O3 thin films

Abstract

The controllability of PZT film properties and the possibility of the scaling up the MOCVD to the commercial based production were briefly reviewed. The film composition and crystalline phase of the PZT films were easily controlled using the MOCVD process. The electrical properties were also controlled by changing the growth parameters. A low processing temperature was achieved using a new Pb precursor, tryethyl n-pentoxy lead. Large area growth of PZT and PLZT films on a 6–8 inch wafer was also achieved.     

A study of phase transformations in rapid thermal processed sol gel PZT using glancing angle x-ray diffraction

Abstract

A technique is established for depth profiling of thin film PZT using glancing angle x-ray diffraction. The transformation of PZT from the pyrochlore to perovskite phase is monitored throughout the thickness of the films. Thin film PZT was deposited using the sol gel technique. The effects of substrate, linear ramp rate, hold temperature and hold time on crystal nucleation and growth were investigated using rapid thermal annealing. The films crystallized on platinum into the perovskite phase through a highly textured interfacial region to a non-textured region at the surface, while films on ITO showed a random texture. Transforming the PZT films to perovskite and limiting the texture to the interfacial region was achieved using a ramp rate of 50°C/s and a hold time of 650°C/30s.     

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.     

Dielectric and Pyroelectric Properties of Lead Zirconate Titanate Composite Films

A new sol-gel approach has been established to prepare dense and crack-free lead zirconate titanate (PZT)/PZT composite films. This new process combines the modified sol-gel method for preparing ceramic/ceramic composite films and the infiltration technique. In the modified sol-gel method, sintered PZT powder is dispersed in a PZT precursor solution to form a slurry which is then spin-coated on a substrate. However, the resulting composite film usually contains a considerable amount of pores, and thus resulting in serious degradation of the mechanical, ferroelectric and piezoelectric properties of the films. In the present work, an additional step, infiltration, has been included in the method. A diluted PZT precursor solution is deposited on the composite film to infiltrate and fill-up the pores, and hence a dense composite film is obtained. The dielectric, ferroelectric and pyroelectric properties of the resulting PZT/PZT composite film are comparable to those of a sol-gel derived PZT film; showing the values of 1200, 0.04, 21 μC/cm² and 180 μC/m² K for relative permittivity, dielectric loss, remanent polarization and pyroelectric coefficient, respectively.     

Study on property variation due to the interface between PZT and electrode

Abstract

The ferroelectric capacitors are fabricated using RuO₂/Pt electrode to examine the electrode effect on ferroelectric properties. PZT films are prepared by metalorganic decomposition (MOD) on sputter deposited electrodes. In particular, inductively coupled plasma(ICP) etcher is used to minimize the etching damage. In addition, TiO₂ reaction barrier layer is also employed to retard the degradation of ferroelectric properties due to the reaction between a passivation layer and PZT film. The better hysteretic properties were obtained from Pt/RuO₂/PZT/RuO₂/Pt ferroelectric capacitors. The enhancement of ferroelectric properties is likely attributed to the modification in the microstructure of PZT film. The interfacial modification would be affected by the factors such as surface roughness, stress, and porosity of RuO₂ film. The result implies RuO₂/Pt would be a good electrode for a nonvolatile memory application.     

Improvement on ferroelectric properties of metal-organic decomposited PZT thin film prepared by using prenucleation layer

Abstract

Perovskite SrRuO₃ (SRO) layer was, for the first time, been successfully synthesized by using metal-organic decomposition (MOD) process. The presence of SRO buffer layer on Pt(Si) substrates has significantly enhanced the crystallization and densification behavior of the subsequently deposited Pb(Zr_0.52Ti_0.48)O₃ films. The pyrochlore free perovskite phase can be obtained by post-annealing the PZT/SRO/Pt(Si) films at 500°C, which is 50°C lower than that needed in PZT/Pt(Si) films. The fine grain (～0.3 μm) microstructure can be attained by post-annealing at 650°C for PZT/SRO/Pt(Si) films and 700°C for PZT/Pt(Si) films. The ferroelectric hysteresis properties of the two PZT films are comparable to each other. The leakage current properties of PZT/SRO/Pt(Si) films increased pronouncedly with post-annealing temperature, resulting in inferriar leakage behavior to PZT/Pt(Si) films.     

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.     

Characterization of dielectric and acoustic properties of CSD PZT thin films at high frequencies

In this study, the microwave dielectric and the acoustic properties of Pb(Zr _x ,Ti_1-x )O₃ (PZT) thin films deposited using chemical solution deposition (CSD) were investigated using the same measurement setup. High dielectric constants in the range of ~280–540 and loss tangents less than 0.1 at 4 GHz were measured, where the value depends on the thickness of the PZT film. The voltage tunability of the 340 nm and 440 nm thick PZT thin films was ~34% and 5% for the 140 nm thick PZT film at 120 kV/cm and 4 GHz. The acoustic parameters of the PZT thin films under DC bias voltages were determined using a one-dimensional acoustic wave resonator model. For the PZT films of thicknesses 340 nm and 440 nm, the acoustic resonance frequency shift was about 15 MHz and the electromechanical coupling coefficient was ~10% at an electric field of 160 kV/cm. The large dielectric constant and high tunability suggest that the characterized PZT thin films may be suitable for radio frequency (RF) applications such as high-density RF MIM capacitors and other tunable devices.     

Low temperature sintering of screen-printed Pb(ZrTi)O3 thick films

Abstract

There has been increasing interest in ferroelectric lead zirconate titanate (PZT) films for the applications in piezoelectric and pyroelectric devices. Many potential applications require a film thickness of above 10 μm for higher force, better sensitivity and stability. But it is very difficult to fabricate the PZT thick film on the silicon substrate because of the volatility of PbO and the interdiffusion of the Pb and Si through the bottom electrode during the sintering at normal temperatures (such as above 1200°C). We speculated densification and reaction mechanism of the PZT thick films fabricated at relatively low temperature (under 1000°C) without sintering aids. The PZT thick films were screen-printed on Pt / Al₂O₃ substrate using a paste of PbO, ZrO₂ and TiO₂ powder mixture. Highly densified PZT thick films could be fabricated on Pt / Al₂O₃ substrate at 1000°C, and we achieved the density, remanent polarization, coercive field, dielectric permittivity, dissipation factor and breakdown field of 98%, 10 μC/cm² and 20 kV/cm, 540, 0.009 and 15 MV/m, respectively. The results show the possibility of densification of the PZT thick film at relatively low temperature without sintering aids, and the results are promising for the use of PZT thick films in various applications.