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.     

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.     

Epitaxial Pb(Zr,Ti)O<Subscript>3</Subscript> Capacitors on Si by Liquid Delivery Metalorganic Chemical Vapor Deposition

La_0.5Sr_0.5CoO₃/Pb(Zr_xTi_1–x)O₃/La_0.5Sr_0.5CoO₃ capacitors have been successfully fabricated by liquid delivery metalorganic chemical vapor deposition on Si wafers using SrTiO₃ thin layer (20 nm) as a template. Zr(dmhd)₄ in tetrahydrofuran was used as Zr precursor for compatible thermal behavior with Pb(thd)₂ and Ti(OiPr)₂(thd)₂ precursors. The dependence of the ferroelectric film composition on the precursor mixing ratio and growth temperature has been systematically studied by Rutherford Backscattering (RBS). Ferroelectric and piezoelectric properties at the composition close to morphotropic phase boundary region (Pb(Zr_0.5Ti_0.5)O₃) have been investigated for application in nonvolatile ferroelectric random access memories and microelectromechanical system (MEMS). These capacitors show desirable ferroelectric properties, which proves that this approach is very promising for both fundamental study and potential applications. The changes of spontaneous polarization (P_s) and piezoelectric coefficient (d₃₃) with Ti/(Zr + Ti) ratio are also presented and compared with theoretical values.     

Fabrication of sub 50-nm direct-patterned Pb(Zr,Ti)O<Subscript>3</Subscript> films by electron beam-induced metal-organic deposition

Direct-patterned lead zirconate titanate (PZT) films prepared from an electron beam sensitive stock solution were investigated for advanced stage applications in sub 50-nm patterned systems. The required electron beam dose for the direct-patterning of PZT precursor films was 4.5 mC/cm². The PZT precursor films with pattern size of 500 × 500 μm² were exposed to an electron beam for 2 h and annealed at 400°C for 30 min under an O₂ ambient. After exposure and annealing, values of the remnant polarization and coercive field were 7.0 μC/cm² and 97 kV/cm at 10 V, respectively. These results suggest a possible application of PZT films in micro- or nano-electromechanical systems.     

Textured-Ba(Zr,Ti)O<Subscript>3</Subscript> piezoelectric ceramics fabricated by templated grain growth (TGG)

Ba(Zr_0.085Ti_0.915)O₃ (BZT) ceramics were grain-oriented (textured) in the <001>-orientation using the Templated Grain Growth (TGG) process. The piezoelectric response of the textured samples was enhanced when poled and measured in the <001>-textured direction. The d₃₃-coefficients for samples measured with a low drive field (<5 kV/cm) displayed values as high as ∼975 pC/N. These d₃₃-coefficients were at least three times greater than randomly-oriented BZT ceramics and equally greater than many lead-free piezoelectric ceramics reported in literature. This work successfully demonstrated that grain-oriented BZT ceramics display piezoelectric coefficients (d₃₃-coefficients) that are similar to currently used lead-based materials. This strategy may allow these ceramics to potentially replace some of the lead-based ceramics that are currently being used in various low-temperature and low-drive piezoelectric applications.     

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.     

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.     

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.     

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.     

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 investigation of key processing parameters in fabrication of Pb(Zr<Subscript><Emphasis Type="Bold">x</Emphasis></Subscript>Ti<Subscript>1−<Emphasis Type="Bold">x</Emphasis></Subscript>)O<Subscript>3</Subscript> thick films for MEMS applications

It has always been a big challenge to deposit dense and crack-free Pb(Zr _x Ti_1−x )O₃ (PZT) thick films through Chemical Solution Deposition (CSD). In this study, a sol with higher concentration (≥0.6 M) was spun onto a platinised silicon substrate. The single layer thickness of a dense, crack-free film with several tenths of nanometres up to 350 nm could be obtained. It was found that the key factor in obtaining thick crack-free films was to choose an appropriate heating profile. In this study, the deflection of a single layer at various stages of heating was analysed through the measurement of the wafer curvature using the Dektak profilometer. As a result three characteristic changes of deflection were found, happening at 300, 450 and 500 °C. These obvious changes in wafer deflection closely relate to the transformations of sol-to-gel, gel-to-amorphous solid and amorphous solid-to-solid crystals. Furthermore, using these temperatures to thermally treat each single layer, it was possible to obtain thick crack-free films by repeatedly spin coating. The dielectric and piezoelectric properties, such as d_33,f and e_31,f, of the films with different thicknesses and orientations were measured and compared.     

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.     

Incorporation of Pb,Ti, and Zr into MOCVD grown PbZrxTi1-xO3 thin films

Abstract

Metal Organic Chemical Vapour Deposition was used to grow PbTiO₃ and PbZr_xTi_1-xO₃ thin films on Pt/Ti/SiO₂/Si substrates. Incorporation of Pb and Ti into PbTiO₃ was studied as a function of the growth temperature, gas phase composition, and reactor pressure, keeping the other deposition parameters constant. The stoichiometric homogeneity in lateral and in vertical direction was measured on optimised PbTiO₃ and PbZr_xTi_1-xO₃ layers using Inductive Coupled Plasma – Atomic Emission Spectroscopy.     

Slow Dielectric Relaxation in Pb(Zr,Ti)O3 and (Ba,Sr)TiO3 Ferroelectric Thin Films

An impedance analysis of Ni/Pb(Zr,Ti)O₃/Pt thin-film structures based on measurements at the frequencies from 100 Hz to 100 MHz, along with the data of Grazing Angles XRD, TEM and photo-electric study, is used to obtain electronic structure of the PZT thin films deposited by sol-gel method on silicone substrates. Both slow capacitance relaxation and charging/discharging currents versus time under step-voltage excitation have been studied in (Ba,Sr)TiO₃ thin films between SrRuO₃ electrodes.     

Preparation and evaluation of sub-100 nm Pb(Zr,Ti)O3 films derived from modified sol-gel solutions for low-voltage operation of feram

Abstract

Sub-100 nm PbZr_0.3Ti_0.7O₃ (PZT) films were prepared on Pt/SiO₂/Si substrates from modified sol-gel solutions without using any seeding layers. Firstly, we studied Pb content [Pb/(Zr+Ti)] dependence of 90-nm-thick films. In the wide Pb content region of 108 – 125%, the films had perovskite-single-phase fine columnar grains with (111)-orientation and no voids. Electric properties were dependent on Pb content. The film with good microstructure, rectangular hysteresis, high remanent polarization (P_r), and low leakage current was gained for Pb content of 116%. Secondly, we studied film thickness dependence of PZT(116/30/70) films. Films from 90 down to 61 nm in thickness were prepared. We found that the sub-100 nm films with good microstructures could be prepared from the modified solutions. The sub-100 nm films had saturation voltage of 1.25 V and high P_r even at 1 V or less. In particular, a 61-nm-thick film had high.P_r of 17 μC/cm2 at 0.75 V.     

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.     

Multiferroic,magnetoelectric and magneto-impedance properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/(Pb,Sr) TiO<Subscript>3</Subscript> bilayer films

We prepared NiFe₂O₄/(Pb, Sr)TiO₃ (NFO/PST) bilayer films by the chemical solution method and investigated their multiferroic, magnetoelectric and magneto-impedance properties. Multiferroic properties have been observed at room temperature. The bilayer films exhibit saturation polarization P _s ? 26.6 μC/cm² and saturation magnetization M _s ? 134 emu/cm³. With increasing Sr content, M _s. and P _s values of the NFO/PST bilayer films decrease. The variation may be ascribed to the influence of interfacial strain and decrease in tetragonality. High magnetoelectric coupling effect has been observed in the NFO/PST bilayer films with maximum value of α _E  = 6.35 Vcm^?1 Oe^?1 measured at H _DC  ~ 1 kOe and f ~ 10 kHz for Sr ~ 10% (NFO/PST10). The magneto-impedance measurements establish a strong dependence on magnetic field, further confirming magnetoelectric response in NFO/PST bilayer films. An alternative approach for impedance analysis of NFO/PST10 bilayer film provides direct evidence of strain mediated magnetoelectric coupling at room temperature. The results indicate that NFO/PST bilayer films can be considered as a potential multiferroic magnetoelectric material.     

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.     

Pb(Mg1/3Nb2/3)0.97Ti0.03O3 Ferroelectric Thin Films, Deposited by Laser Ablation on TiN Bottom Electrodes

Pb(Mg_1/3Nb_2/3)_0.97Ti_0.03O₃ (PMNT) polycrystalline thin films were deposited on Titanium Nitride electrode at different temperatures by laser ablation, using a wavelength of 248 nm. The morphology of the films was analyzed by scanning electron microscopy (SEM). The nature of the ferroelectric layer-electrode interface is studied by transmission electron microscopy (TEM) as well as the effect of its characteristics in the performance of the multilayer system. The influence of the annealing temperature on the dielectric properties was studied by hysteresis and fatigue measurements.     

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.