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.     

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.     

The bulk photovoltaic effect in ferroelectric Pb(Zr,Ti)O3 thin films

Abstract

The bulk photovoltaic effect (BPE) has been investigated in lead zirconate titanate (PZT) thin films. Measurements of the kinetics, spectral distribution and photocurrent hysteresis loops have been made. In the extrinsic spectral region, the steady-state photocurrent is primarily due to the BPE, where the photovoltaic tensor component has been determined to be G₃₁ = 10_?9 cm/V. However, in the intrinsic region, the BPE has not been determined due to the strong contribution from photoinjection currents. Finally, it is shown that the BPE may be the driving force for photoinduced hysteresis changes in PZT thin films, particularly in the extrinsic spectral region.     

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.     

Epitaxial growth of multilayered (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 ferroelectric thin films with different orientations

Epitaxial (Bi,La)₄Ti₃O₁₂ (BLT) thin films, epitaxial Pb(Zr,Ti)O₃ (PZT) thin films, and epitaxial multilayered BLT/PZT ferroelectric thin films with different orientations were prepared on SrTiO₃ (STO) single crystal substrates by pulsed laser deposition. From X-ray pole-figures and electron diffraction patterns, the epitaxial orientation relationships between BLT layers, PZT layers, and STO substrates were identified to be (1) BLT(001)//PZT(001)//STO(001), and BLT[110]//PZT[100]//STO[100] for the multilayered thin films on (001)-oriented STO substrates, and (2) BLT(118)//PZT(011)//STO(011), and $ {\text{BLT}}{\left[ {\overline{1} \overline{1} 0} \right]}//{\text{PZT}}{\left[ {100} \right]}//{\text{SrTiO}}_{3} {\left[ {100} \right]} $ for the multilayered films on (011)-oriented STO substrates. Tri-layered films of the same compositions showed well-defined hysteresis loops as well as a high fatigue resistance up to 1?×?10¹⁰ switching cycles.     

Pb(Zr,Ti)O3 thin film growth on yttrium-treated Si(100)

Abstract

Pulsed laser ablation has been used to deposit ferroelectric Pb(Zr, Ti)O₃ (PZT) thin films on Si(100) and on yttrium-treated Si(100) substrates. The yttrium (Y) treatment of a Si surface followed by oxidation resulted in formation of a very thin, Y-enhanced SiO₂ antidiffusion barrier layer, thereby suppressing the undesirable PZT/Si interdiffusion. The best PZT film grown on Y-treated Si(100) had a breakdown voltage of 0.6 MV/cm, a coercive field of 71 KV/cm, and a remanent polarization of 18 μC/cm².     

Bilayered Pb(Zr,Ti)O3/(Bi,Nd)4Ti3O12 thin films

Bilayered ferroelectric thin films consisting of Pb(Zr_0.52Ti_0.48)O₃ (PZT) and (Bi_3.15Nd_0.85)Ti₃O₁₂ (BNT) have been successfully synthesized on Pt/Ti/SiO₂/Si substrates, via a combined sol–gel and rf-sputtering route. Their ferroelectric and dielectric properties are critically dependent on the phases present, film texture and in particular layer and film thicknesses. Due to the coupling of PZT and BNT bilayers, there requires an optimized thickness combination of the two ferroelectric layers, in order to give rise to the wanted ferroelectric and dielectric properties, while the phenomenon can not be accounted for by the simple series connection model.     

Bilayered Pb(Zr,Ti)O3/(Bi,Nd)4Ti3O12 thin films

Bilayered thin films consisting of Pb(Zr_0.52Ti_0.48) O₃ (PZT) and (Bi_3.15Nd_0.85)Ti₃O₁₂ (BNT) layers are successfully deposited on Si(100)/SiO₂/Ti/Pt substrate by a combined process involving sol-gel and RF-sputtering. Their dielectric properties cannot be described by the simple rule of mixture on the basis of the series connection model. There occurs a dielectric layer of lower dielectric permittivity in the bilayered thin film, which degrades the polarization behaviors. The bilayered film gives rise to an improvement in fatigue resistance up to 10¹⁰ switching cycles. Moreover, the domain pinning effect after polarization switching is reduced greatly as compared to that of single layered PZT and BNT thin films.     

Dielectric and relaxor ferroelectric properties of Ba-doped Pb(Zr,Ti)O3 ceramics

(Pb,Ba)(Zr,Ti)O₃ is a relaxor ferroelectric material. Dielectric and ferroelectric properties of (Pb_1-x Ba _x )(Zr_0.70Ti_0.30)O₃ ceramics have been investigated for compositions varying in the range of 0.20?≤?x?≤?0.30. Reagent grade PbO, ZrO₂, TiO₂ and BaCO₃ raw powders were used, ceramics were fabricated by convenient solid state reaction. The experimental results show that the substitution of Ba for Pb can enhance the ferroelectric relaxor characteristics. With the Ba content increasing, the electric hysteresis was narrowed and the polarization was reduced. Meanwhile the temperature T _m that corresponding to the maximal dielectric constant was decreased. It has also been found that the hydrostatic pressure may cause the phase transition more diffuse and move T _m to higher temperature.     

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.     

Growth and electrical properties of Pb(Zr,Ti)O3 thin films by sputtering using an alloy target

Abstract

Pb(Zr_x,Ti_1?x)O₃ thin films were deposited on Pt/SiO₂/Si substrates by the rf magnetron sputtering using an alloy target consisting of Zr-Ti alloy and Pb metal. The dependence of electrical properties on film thickness and sputtering gas pressure was investigated. The dielectric constant and the remanent polarization decreased and the coercive field increased with the decrease of the film thickness. In the dependence of gas pressure, the relative dielectric constant of the film with only a perovskite phase were in the range of 235–280, which were higher than those of the film with only a pyrochlore phase, 20. The asymmetry of hysteresis loops increased with the decrease of the gas pressure.     

Low-temperature sintering of ferroelectric Pb(Zr,Ti)O3 thick films derived from stable sol-gel solutions

Abstract

We have studied sintering and densification of PbZr_0.52Ti_0.48O₃ (PZT) films derived from diol-based sol-gel solutions. We found that densification by sintering began at below 750°C and completed at 850°C in 5 min. Initially, 0.83- μm-thick PZT single-coated films were prepared on Pt/Ti/SiO₂/Si substrates from stable propylene-glycol (l,2-propanediol)-based solutions by crystallization at 700°C. The crystallized films consisted of fine perovskite grains and voids. We studied the firing temperature dependence of various properties such as microstructure, crystallinity, and ferroelectric properties for the single-coated films. Finally, 0.54- μm-thick PZT single-coated dense films were prepared by firing at 850°C for 5 min. In order to prepare thicker PZT dense films, we studied low-temperature sintering of PZT multicoated thick films. Using this approach, 1.7- μm-thick PZT dense films were prepared by firing at 850°C for 5 min.     

Pulse width dependent polarizations of ferroelectric (Pb,La)(Zr,Ti)O3 thin film capacitors

Abstract

We report the measurements of pulse polarizations of (Pb, La)(Zr, Ti)O₃ ferroelectric capacitors as a function of pulse width. Pulse polarizations were measured from the switching current responses in the pulse width range from 1 μs to 1 s. The relation between pulse polarizations(switched(P?) and non-switched polarization(P?)) and hysteresis loop parameters was studied. In the case of all write/read pulse widths are same, P? increased but P? decreased with increasing pulse width. These results are explained by poling effects and confirmed by measuring pulse width dependencies with different patterns of pulse trains.     

Characterization of Pb(Zr,Ti)O3 thin films on SOI prepared by excimer laser deposition

Abstract

Ferroelectric Pb(Zr,Ti)O₃ (PZT) thin films were prepared by pulsed excimer laser deposition on Silicon-on-Insulator (SOI) substrates with and without an electrode. Their properties can be improved by rapid thermal annealing, based on the structural and interfacial characteristics analysis by X-ray diffraction, Rutherford backscattering spectroscopy and automatic spreading resistance measurements. The thin films were revealed of to be polycrystalline perovskite structure with mainly ?100? and ?110? orientations; the crystallite size and the structure are dependent on the annealing time. The PZT thin films did not interact with the top silicon layers of SOI, and the composition was on the tetragonal side of the morphotropic phase boundary in the PbTiO₃-PbZrO₃ phase diagram.     

Solution chemistry effects in Pb(Zr,Ti)O3 thin film processing

Ferroelectric thin films in the PZT compositional family were prepared by two different solution deposition methodologies. The approaches were based on the use of carboxylate and alkoxide precursors, and acetic acid. Solution aging and mixing order effects on thin film microstructure and ferroelectric properties were studied. Films prepared from 15 day old solutions had a lower remanent polarization (1.4 μC/cm2) and higher coercive field (256 kV/cm) than films prepared from 1 day old solutions (Pr = 18.7 μC/cm2; Ec = 55.2 kV/cm). Raman, FTIR, and NMR spectroscopies were employed to confirm the role of acetic acid in the process, and to begin to understand why changes in solution chemistry can so dramatically affect the resulting film microstructure and properties. FTIR spectroscopy indicated that in addition to acting as a solvent, acetic acid also serves as a chemical modifier in the two processes. That is, it reacts with the alkoxide precursors on a molecular level, replacing the alkoxy ligands. Ester formation was also observed by both FTIR and NMR spectroscopy. The formation of this by-product implies the simultaneous formation of water, and therefore, in-situ hydrolysis and condensation of the precursors.     

Influence of rapid thermal annealing on pyrochlore/perovskite phase formation in laser ablated Pb(Zr,Ti)O3 thin films

Abstract

Pb(Zr,Ti)O₃ thin films were prepared by ArF excimer laser deposition on silicon and Pt-coated silicon substrates, and then were treated by rapid thermal annealing. The dependence of perovskite/pyrochlore phase formation on annealing conditions was investigated. The results show that the formation of perovskite phase or pyrochlore phase in the films was not only dependent on the heat treatment temperature, but also dependent on the heat treatment time. A wide range operational window of heat treatment time and temperature for obtaining single phase perovskite Pb(Zr,Ti)O₃ thin films was given, and the films were analyzed by Rutherford backscattering spectroscopy to explain this phase transition.     

Investigation on the electrical characteristics of sol-gel derived Pb1.05(Zr0.53Ti0.47)O3 thin films

Abstract

Lead zirconate titanate (PZT) thin films with composition Zr/Ti ～ 0.53/0.47 were deposited by the sol-gel technique. The films were characterized in terms of its polarization relaxation, fatigue and imprint characteristics. We have found that the polarization relaxation is due to the presence of a depolarization field which increases dramatically with the rise in temperature. Improved fatigue performance was observed when the film was fatigued with higher frequency. The direction of imprint depends on the state of polarization. With the increase in net polarization, the trapped charge density at the film-electrode interface increases which leads to imprint characteristics. Also the imprint increases considerably with the rise in temperature. Finally, we have made an attempt to correlate simultaneously fatigue, polarization relaxation, and imprint characteristics with the presence of mobile charge defects (viz. V_o) and defect dipoles (viz. V_Pb – V_o) in the film.     

Dielectric characteristics investigation of (Ba0.7Sr0.3)(Ti0.9Zr0.1)O3 ferroelectric thin films

By the radio frequency (RF) magnetron sputtering methods, (Ba_0.7Sr_0.3)(Ti_0.9Zr_0.1)O₃ (BSTZ) ferroelectric thin films were deposited on the Pt/Ti/SiO₂/Si(100) substrates. The crystal structural and microstructure of these thin films were analyzed by means of the XRD, SEM, and AFM. Moreover, the dielectric characteristics were also investigated by the C-V and J-E analyses. The optimal deposition parameters for these BSTZ thin films were: RF power is 160 W, oxygen concentration is 25%, substrate temperature is 580°C, and chamber pressure is 0.075 mPa. Under these optimal deposition conditions, the (111) and (110) oriented polycrystalline of the BSTZ thin films grow easily. And under a bias voltage of 0.5 MV/cm, the dielectric constant and leakage current density of the BSTZ thin films are 191 and 3×10^?8 A/cm², respectively. In addition, under various measured temperatures (0 ～ 80°C) and frequencies (100 kHz ～ 1 MHz), all the dielectric constants remain almost unchanged. Compared to BSTZ thin films reported previously, in this study, the deposited thin films have the advantage of lower leakage current and hence are suitable for the applications of dynamic random access memory.     

Structure and properties of sol-gel processed (Pb,La)TiO3 ferroelectric thin films

Abstract

The influence of heat treatment and substrate materials on PLT thin films by sol-gel processing has been researched. Epitaxial growth PLT thin films with perovskite-type structure on sapphire, SrTiO₃ and MgO single crystal substrates have been prepared. The epitaxial relations are (100)PLT28/(100)SrTiO₃, (111)PLT28//(0001)sapphire and (100)PLT14//(100)MgO. The PLT polycrystal thin films with perovskite-type structure on Si single crystal and quartz glass substrates have been prepared. The remanent polarization Pr and the coercive field Ec of PLT15 ceramic thin films are 7.7 μc/cm² and 34 kv/cm at 4 KHz respectively. The optical transmittance of PLT28 ceramic thin films within the wavelength range of λ = 500–1000 nm is approximately 80%.     

Preparation of Textured Growth Pb(Zr,Ti)O3 Thin Films on Si Substrate Using SrTiO3 as Buffer Layers

PZT thin films are deposited on SiO₂/Si substrate by metallo-organic decomposition (MOD) process, using SrTiO₃ (STO) as buffer layer for textured growth. The STO layers deposited on SiO₂/Si substrate by pulsed laser deposition process show (100)/(200) preferred orientation, whereas the STO buffer layer deposited on silica substrate using spin-coating technique show random orientation behavior. The use of STO as buffer layers enhanced the crystallization and the preferred orientations of the PZT films. The PZT on STO buffered SiO₂/Si substrates thus obtained possess high refractive index, (n)_PZT/STO = 2.1159, and are of good enough quality for optical waveguide applications.