Ferroelectric effect in spin coated Ba0.9Sr0.1TiO3 thin films

Abstract

The achievement of excellent growth of lead zirconium titanate (PZT) films by various techniques for use as ferroelectric memories has generated an extensive research interest in the synthesis of various other perovskite and layered oxides. Ba_xSr_1?xTiO₃ thin films have also been deposited by various methods to study their dielectric behavior. We report the synthesis of Ba_xSr_1?xTiO₃ (where x ' 0.9, 0.1) by a solution method using hydroxides, acetates, and nitrate salts as precursors for barium and strontium, and titanium isopropoxide for titanium. The films deposited by spin coating on ITO coated glass substrates showed ferroelectric behavior.     

Effect of alloying platinum bottom electrode with silver: In relation to CSD processing of PZT thin films

Abstract

A quantity of silver was evaporated onto platinised-silicon (Pt/Ti/SiO₂/Si) and then annealed in air to form a silver-platinum alloy. The lattice spacing of the alloy matched that of the composition of lead zirconate titanate (PZT) used. The surface of the silver-platinum alloy was covered in hillocks. It was found that after PZT was deposited by chemical solution deposition (CSD) these hillocks had disappeared. The presence of mobile Pb and the formation of a transient intermetallic phase (Pt₃Pb) was taken as the cause for this planarisation. Nucleation of perovskite PZT occurred earlier on silver-platinum compared to a film deposited onto platinised-silicon. The degree of preferred orientation developed for the film on the alloyed electrode was not as good as that found on platinised-silicon.     

Sol-gel PZT thin films on nickel alloy electrodes

Abstract

The Ni alloy electrode was used for a bottom electrode of PZT thin films prepared by sol-gel process. Although PZT films were crystallized on soda–lime glass substrates with the alloy electrodes at a relatively low temperature of 500°C, second phases of Pb₃O₄ and ZrTiO₄ were produced on the electrode in addition to the perovskite PZT phase. In order to prevent the second phases forming, the heat treatment time of the electrode was increased to obtain the thicker Al₂O₃ layer on the alloy electrode. The second phases decreased with increasing the heat treatment time; however, the phases did not disappear. When BaTiO₃ films were inserted between the electrodes and PZT films, the PZT single phase was obtained. The tan δ of the films decreased with decreasing the amount of the second phases, finally it became 3.9%, the film of which possessed a remanent polarization of 20 μC/cm².     

Effect of seed layer on electrical properties of Pb(Zr,Ti)O3 films grown by metalorganic chemical vapor deposition

Abstract

Pb(Zr_xTi_1?x)O₃ (PZT) ferroelectric thin films were prepared by metalorganic chemical vapor deposition (MOCVD) on Pt/Ti/SiO₂/Si substrate. Very thin PZT films, which were deposited at a lower temperature and post-annealed at higher temperature for crystallization, were used as a seed layer. PZT films grown on the seed layer exhibited superior characteristics in the crystalline structure and electrical properties, compared to those deposited without seed layer. Depending on the deposition conditions of PZT seed layer, a wide variation of surface morphology and stoichiometry was found between samples, whereas chemical composition was found to be very similar.     

Pt/TiN electrodes for stacked memory with polysilicon plug utilizing PZT films

Abstract

The mechanism of TiN barrier metal oxidation of Pt/TiN electrodes are investigated for planarized stacked memory utilizing lead zirconate titanate (PZT). Thinner (<100 nm) and highly oriented platinum films are required in gigabit scale ferroelectric nonvolatile memories whose capacitor size is comparable to PZT grain size. Oxygen diffusivity to oxidize TiN is found to depend on the Pt film thickness. In cross-sectional TEM images of PZT/Pt/TiN/Si, titanium oxide is observed beneath the Pt grain boundary. The oxygen is diffused through the Pt grain boundary under heat treatment in an oxygen atmosphere for crystallization of PZT films, and oxidizes the underlying TiN barrier metal.     

Enhancement of Ferroelectric Properties of Pb(Zr,Ti)O3 Films Grown by Metal-Organic Chemical Vapor Deposition on Noble-Alloy Bottom Electrodes

Pb(Zr,Ti)O₃ (PZT) films grown on Ir electrodes by a metal-organic chemical vapor deposition (MOCVD) have suffered from high leakage and rough surface. We sputtered Pt and Ir simultaneously onto Ti/SiO₂/Si substrates and formed Ir-Pt alloy bottom electrodes with various compositions. With an optimal composition of Ir and Pt, PZT films grown by MOCVD on this substrate showed smoother surface and suppressed leakage via the bottom interface. At the specific composition of Ir and Pt, two different phases seemed to be acquired. They constituted the electrodes and affected the PZT grain nucleation independently so that the grains with different origins grew and restrained the vicinal grains, and finally soothed the faceted-grain-formation. No fatigue was observed even in PZT on Ir-Pt alloy with much Pt content.     

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.     

Preparation and characterization of PZT ferroelectric thin films by plasma enhanced metalorganic chemical vapor deposition

Abstract

PZT thin films with a uniform distribution of components were prepared by plasma enhanced chemical vapor deposition (PECVD) using Pb(C₂H₅)₄, Z (O-i-C₄H₉)₄, Ti(O-i-C₃H₇)₄, and oxygen. The crystallization of films was occure after annealing in the temperature range between 450 and 550°C under O₂ ambient for 1 hr. The significant change of Pb concentration in PECVD PZT thin films was not observed in the relation to annealing temperature and time. The dielectric constant PECVD PZT thin films increased with the Ti content, showed the maximum value in the vicinity of morphotropic phase boundary (MPB) composition of PZT material, and decreased with the Ti content. The leakage current density of PZT (65/35) thin film of 180 nm in thickness was 3·37 × 10^?7 A/cm² at the applied voltage of 3 V. Remanent polarization increased with increasing of Zr content in the film and coercive field was nearly independent of the composition. The typical values of electrical properties were ε_r = 570, E_c = 90 kV/cm, and P_r = 19 μC/cm² in the PECVD PZT (54/46) thin film of 220 nm in thickness.     

Pulsed excimer laser deposition of ferroelectric thin films

Abstract

Pulsed UV excimer laser ablation was employed to deposit multi-axial, bi-axial and uni-axial ferroelectric compositions of PZT, bismuth titanate and lead germanate respectively. In general, a fluence lower than 2 J/cm² caused a preferential evaporation of volatile components, resulting in stoichiometric imbalance. However, the fluences beyond 2 J/cm² enabled the deposition of stoichiometric thin films of multi-component oxide systems. The intrinsic bombardment due to the energetic ablated species during the thin film deposition seemed to influence the composition, structure, orientation and the electrical properties. The electrical characterization of ferroelectric films indicated a dielectric constant of 800–1000, a P_r of 32μC/cm² and E_c of 130KV/cm for polycrystalline PZT films and the corresponding quantities were measured to be 150, 7 μC/cm² and 20 KV/cm for in-situ crystallized c-axis preferred oriented bismuth titanate films. Lead germanate thin films oriented along c-axis (003) showed a dielectric constant of 30, a P_r of 2.5 μC/cm² and E_c of 55 KV/cm.     

LARGE AREA PIEZOELECTRIC ACTUATORS USING METAL FOIL SUBSTRATES WITH Pb(Zrx,Ti1 - x)O3 THIN FILMS

ABSTRACT

We report on the deposition of Pb(Zr_x,Ti_{1 - x})O₃ (PZT) thin films by chemical solution deposition (CSD) on stainless steel foils. The electrical characterization proves good ferroelectric properties with a remnant polarization of 38 μ C/cm². Since PZT is also piezoelectric the 35 μ m and 50 μ m thick metal foils are used to make piezoelectric actuated cantilever beams of several millimeter lengths. Actuated with 10–30 V a displacement up to 32 μ m was measured in quasi-static mode. In resonance mode the displacement increases several times at the same driving voltage.     

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.     

An aqueous,low temperature process for synthesizing PZT(53,47) thin films

Abstract

The Deposition by Aqueous Acetate Solution (DAAS) technique has been developed for the preparation of thin films of Pb(Zr_0.53Ti_0.47)O₃[PZT(53,47)] perovskites. This process, which employs titanium acetate, tends to establish a chemically bound network in the pre-annealed phase and facilitates the crystallization of ferroelectric lead perovskites at a relatively low temperature. The addition of surface wetting reagents and oxidants and the action of ultrasonic waves were shown to affect the crystallinity and film quality of PZT(53, 47) perovskites on Pt<111>/Ti/SiO₂/Si<100> substrates. The band structure analysis of the FTIR spectrum is illustrated to be a simple way of monitoring the crystallization of PZT(53, 47) perovskites. Physical and electrical characterization of the resultant thin films were performed. The advantages of the DAAS process for fabricating thin ferroelectric films are examined.     

MFIS and MFMIS structures using Pb(Zr,Ti)O3 films for nonvolatile memory devices

Abstract

In this work, metal / ferroelectric / insulator / semiconductor (MFIS) and metal / ferroelectric / metal / insulator / semiconductor (MFMIS) structures using Pb(Zr, Ti)O₃ (PZT) films were fabricated and characterized for nonvolatile NDRO memory device. 300nm-thick PZT films were deposited by reactive RF magnetron sputtering method on ZrTiO₄(ZT)/Si and Pt/ZT/Si substrates. C-V hysteresis were measured in both MFIS and MFMIS structures. By using a small-size MFM capacitor on a large-size MIS structure, it was found that the memory window of MFMIS structure was larger than that of the MFIS structure. There is a critical area ratio (S_MIS/S_MFM) in MFMIS structure. When an area ratio in MFMIS structure is below 12, the memory window increased with increasing area ratio. We could obtain that the memory window of MFMIS structure with a S_MIS/S_MFM of 11.8 was 2.1 V and 3.2 V with an applied voltage at 3 V and 5 V.     

Fatigue and retention of Pb(Zr0.53Ti0.47)O3 thin film capacitors with Pt and RuO2 electrodes

Abstract

Pb(Zr_0.53Ti_0.47)O₃ (PZT) thin films were deposited on Pt and RuO₂ coated Si and MgO substrates using the sol-gel process. Fatigue and retention tests were performed on these samples. The films grown on RuO₂ electrodes are fatigue-free up to nearly 10¹¹ cycles. Their retention life-time extrapolates to more than 10¹⁰ seconds. The fatigue behavior of films grown on Pt electrodes depends on the PZT film orientation. Highly oriented (001) PZT films maintain 50% of their initial P?r-P?r value after 10¹¹ cycles. The randomly oriented films maintain less than 3% of the initial P?r-P?r value after 10¹¹ cycles. However, the retention life-time of both highly oriented and randomly oriented PZT films grown on Pt electrodes extrapolates to higher than 10¹¹ seconds. It appears that fatigue of films grown on RuO₂ is mainly controlled by the film/electrode interface. On the other hand, fatigue of films grown on Pt appears to depend on both the film/electrode interface as well as on bulk effects.     

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.     

Device effects of various Zr/Ti ratios of PZT thin-films prepared by sol-gel method

Abstract

PZT, PbZr_xTI_1?xO₃, thin-films with various Zr/Ti ratios, 100/0 (lead zirconate) to 0/100 (lead titanate), were prepared by the sol-gel method. Basic electric properties, dielectric constant, tan σ, P-E hysteresis curve, switching properties were measured respectively as a function of composition. Dielectric constant indicated a specific peak value (～1100) around the morphotropic phase boundary between tetragonal and rhombohedral phase. Satisfactory low-voltage saturated hysteresis curves were observed for the compositions of PZT(90/10) through PZT(20/80). The remanent polarization and the coercive field increased as the titanium content decreased. The result of X-ray measurement showed that the lattice constants of thin-Film PZT are different from bulk ceramics for compatible compositionsS. The boundary, on which the c/a ratio must be 1 (rhombohedral phase), was slightly shifted to PbTiO₃ side. This distortion in crystal structure is considered to be due to the thin-film effect, which the lattice mismatch between the platinum substrate and the PZT layer, restricted the ions to position into proper cites.     

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.     

Pyroelectric properties of sol-gel derived PZT thin films with various Zr/Ti ratios

Abstract

Integrated pyroelectric arrays are receiving serious attention for the next generation of room temperature uncooled IR cameras. Such pyroelectric arrays are based on monolithic ferroelectric(FE) thin films. FE films with large values of reported pyroelectric coefficients include PbTiO₃, Ca-doped PbTiO₃, La-doped PbTiO₃, PZT 53/47 and Pb(Sc_0.5Ta_0.5)O₃. The present paper reports a systematic study of the compositional dependence of PZT thin films on their pyroelectric properties. A series of sol-gel derived PZT (lead zirconate titanate) thin films with various Zr/Ti ratios, namely, PbTiO₃, PZT 20/80, PZT 35/65, PZT 53/47, PZT 65/35, PZT 92/8 and PbZrO₃, were prepared on platinized Si substrates. The films were fired to 650 – 700°C to crystallize them into single-phase perovskite. The degree of preferred orientation, grain size and firing temperature affect the pyroelectric responses. Pyroelectric coefficients as large as 2.5 × 10^?8 C/cm²-K were obtained, making such PZT thin films attractive in pyroelectric arrays.     

Fundamental characteristics of DRAM capacitor application of PLZT ultrathin films prepared by MOCVD

Lanthanum-modified lead zirconate titanate (PLZT) thin films (50 nm to 200 nm) were deposited on Pt/SiO₂/Si substrate by metal-organic chemical vapor deposition (MOCVD). The electrical properties of the films were investigated as a function of the La content or the substrate temperature. Ferroelectric PZT(0/50/50) films were obtained at substrate temperatures as low as 500 °C; their electrical characteristics improved with increasing substrate temperature. La exhibited adequate solid solution in the PZT above 650 °C. PLZT(15/45/55) films with a thickness of 100 nm were found to have good properties for application to the capacitors of dynamic random access memory (DRAM), namely, an effective charge density of 80 fF/μm², a permittivity of 1000, an SiO₂ equivalent thickness of 0.4 nm, and a leakage current density of 5 × 10⁻⁸ A/cm. Addition of La to PZT was effective in reducing the leakage current with an increase in the registration rate. RuO₂ and/or IrO₂ bottom electrodes for ferroelectric PLZT films were also investigated. The RuO₂ films were found effective as diffusion barriers for PLZT and MgO. Significant interdiffusion at RuO₂/Si and RuO₂/SiO₂ interfaces occurred during the deposition of PLZT films. Annealing of the RuO₂ film considerably depressed interface reactions. © 1998 Scripta Technica. Electr Eng Jpn, 122(1): 25–36, 1998     

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.