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.     

Preparation and properties of Pb(Zr, Ti)O3 ferroelectric thin films and compositionally graded thin films on LaNiO3/Si substrates

LaNiO₃ (LNO) thin films were prepared on Si (100) wafer by MOD method. Pb(Zr, Ti)O₃ ferroelectric thin films and their compositionally graded thin films were prepared on LNO/Si (100) substrates by a modified sol–gel method. The composition depth profile of a graded film was determined by using a combination of Auger electron spectroscopy and Ar ion etching. The results confirmed that the processing method produces graded composition change. XRD analysis showed that the graded thin film possessed a composite structure of tetragonal and rhombohedral. The dielectric constant of the graded thin films was higher than that of each thin film unit, but the loss tangent was near to each other at 10 kHz. The temperature characteristics of the dielectric constant of the graded thin films at different frequencies showed three peaks and ferroelectric relaxor feature to some extent. Hysteresis loops showed that graded thin film had higher remanent polarization, smaller coercive field than each thin film unit. The pyroelectric coefficient of the graded thin films increased gradually with temperature, and was higher than that of each thin film unit.     

Growth and electrical properties of (211) BaTiO3 thin films on Pt-coated Si(100) substrates

Abstract

Barium titanate (BaTiO₃) thin films with high (211) orientation have been prepared on Pt(111)/Si(100) substrates by R. F. magnetron sputtering at a substrate temperature between 550°C and 580°C in an Ar/O₂ atmosphere. The I-V curve of a thin film capacitor (Ag-BaTiO_3-Pt) has been measured and the C-V curves are obtained for frequencies between 100Hz and 1MHz. Neither the I-V curve nor the C-V curves are symmetrical and a very large change in the slope of all curves is found to occur at ～+0.5v.     

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.     

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.     

Correlation between electrical properties and crystalline phases for ZnO-Bi2O3 based varistor ceramics with rare earth additives

In this study, the correlation between the electrical properties and crystalline phases of ZnO-Bi₂O₃ based varistor ceramics with rare earth additives was investigated. The additives used were in the form R₂O₃, where R represents Eu, Ho, Y, Er, Yb, or Lu. It was found that the incorporation of rare earth additives led to an increase in the varistor voltage in the nonlinear region, an increase in the leakage current in the pre-breakdown region, and a reduction in the limiting voltage in the upturn region. In the sample with added Y₂O₃, a phase referred to as the R-phase, which contained Y, Bi, Sb, Zn, Mn, and O, was observed to be homogeneously distributed at ZnO grain boundaries. X-ray diffraction analysis revealed that the amount of the Zn-Sb-O spinel and Bi-Cr-O phases present was reduced by the rare earth addition, and that rare earth elements were incorporated into a common crystalline phase. It is suggested that the formation of the R-phase at ZnO grain boundaries and the reduction in the Bi₂O₃ liquid phase during the sintering process might be responsible for suppressing ZnO grain growth, thus leading to an increase in the varistor voltage.     

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.     

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.     

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.     

Structural and electrical properties of Sb-doped p-type ZnO thin films fabricated by RF magnetron sputtering

We investigated the Sb-doping effects on ZnO thin film using RF (radio frequency) magnetron sputtering and RTA (rapid thermal annealing). The structural and electrical properties of the thin films were measured by X-ray diffraction, SEM (scanning electron microscope), and Hall effect measurement. Thin films were deposited at a high temperature of 800°C in order to improve the crystal quality and were annealed for a short time of only 3 min. The structural properties of undoped and Sb-doped films were considerably improved by increasing oxygen content in the Ar-O₂ gas mixture. Sb-doping also significantly decreased the electron concentration, making the films p-type. However, the crystallinity and surface roughness of the films degraded and the mobility decreased while increasing Sb-doping content, likely as a result of the formation of smaller grain size. From this study, we observed the transition to the p-type behavior at 1.5 at.% of Sb. The thin film deposited with this doping level showed a hole concentration of 4.412?×?10¹⁷ cm^?3 and thus is considered applicable to p-type ZnO thin film.     

Chemical processing and properties of Sr2(Ta,Nb)2O7 thin films

Abstract

The crystallographic orientation, microstructure and electrical properties of Sr₂(Ta, Nb)₂O₇ thin films strongly depended on the composition (Ta:Nb). Post-annealing at 850°C was effective for the improvement of some properties. The thin films with relatively Nb-rich compositions, such as Sr₂(Ta_0.6Nb_0.4)₂O₇ and Sr₂(Ta_0.5Nb_0.5)₂O₇, showed the (0k0) preferred orientation. The Sr₂(Ta_0.5Nb_0.5)₂O₇ thin film had a lamination layer structure after the post-annealing at 850°C for 6 min in oxygen. The characteristic microstructure originated in the crystallographic orientation of (0k0), which is the cleavage plane, and influenced electrical properties. The dielectric constant little change with the composition, however, the P-E hysteresis properties improved with the Nb content.     

Structural and electrical properties of sol-gel synthesized PLZTthin films

Thin films of PLZT with PbTiO₃ interlayers have been fabricated by using a sol-gel spin-on process. Three compositions of PLZT, namely 8/65/35, 15/40/60 and 18/30/70, have been deposited on platinum and quartz substrates and heat treated at 650°C. All three compositions have crystallized in the perovskite phase. The 8/65/35 composition, which has been investigated in greater detail exhibits a low value of leakage current. It also exhibits polarization hysteresis, with E_c=20 kV/cm and P_r=25 μC/cm²     

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.     

稀土永磁电机的开发与应用(二)

(续上期) 5 稀土永磁电机的开发方向 近年来,随着永磁材料性能的不断提高和完善,特别是钕铁硼磁体的热稳定性和耐腐蚀性的改善以及电力电子元件的进一步发展和改进,加上永磁电机研究和开发经验的逐步成熟,除了大力推广和应用已有研究成果外,稀土永磁电机的应用和开发进入一个新阶段,目前正向大功率化(超高速、高转矩)、高功能化、微型化和环境适应性方向发展[7,11,13].     

Growth of MgTiO3 thin films by pulsed laser deposition and their electrical properties

Abstract

MgTiO₃ thin films have been grown on various substrates by pulsed laser deposition (PLD) to investigate the application for microwave dielectrics and optical devices. Highly oriented MgTiO₃ thin films were obtained on sapphire (c-plane Al₂O₃). MgTiO₃ thin films deposited on SiO₂/Si and platinized silicon (Pt/Ti/SiO₂/Si) substrates were polycrystalline nature. MgTiO₃thin films grown on sapphire were transparent in the visible and had a sharp absorption edge at 280 nm. These MgTiO₃ thin films had extremely fine feature of surface morphology, i.e., rms roughness of 0.87 nm. Dielectric constant and loss of MgTiO₃ thin films deposited by PLD were about 24 and 1.5% at 1MHz, respectively. These MgTiO₃ thin films also exhibited little dielectric dispersion.     

Synthesis and properties of ferroelectric Si-doped (Bi, Nd)4Ti3O12 thin films by chemical solution deposition

Ferroelectric Si-doped (Bi,Nd)₄Ti₃O₁₂ thin films have been prepared on Pt/TiO_x/SiO₂/Si substrates through metal-organic compounds by the chemical solution deposition. The Bi_3.25Nd_0.75Ti_2.9Si_0.1O₁₂ (BNTS) precursor films were found to crystallize into the Bi-layered perovskite Bi₄Ti₃O₁₂ single-phase above 600^∘C. The synthesized BNTS films revealed a random orientation having a strong 117 reflection. The BNTS thin films prepared between 600^∘C and 700^∘C showed well-saturated P-E hysteresis loops with P _r of 13–14 μ C/cm² and E _c of 100–110 kV/cm at an applied voltage of 5 V. The surface roughness of the BNTS thin films was improved by Si doping compared with that of undoped Bi_3.35Nd_0.75Ti₃O₁₂ films.     

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%.     

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.     

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.     

Effect of seed layers on dielectric properties of Ba(Zr0.3Ti0.7)O3 thin films

The Barium zirconium titanate Ba(Zr_0.3Ti_0.7)O₃ thin films were prepared on Pt/Ti/SiO₂/Si substrates with seed layers at the BZT/Pt interface by sol–gel process. Microstructure and structure of thin films were examined. Dielectric properties of thin films with various seed layers thicknesses were investigated as a function of frequency and direct current electric field. The tunability and dielectric constant of BZT thin films increased with increasing seed layer thickness from 0 to 20 nm, while it decreased with a further increase in thickness above 20 nm, meanwhile, the leakage current showed the similar tendency at applied electric field of 250 kV/cm. The optimized seed layer thickness for BZT thin films plays an important role in maintaining the high tunability and low leakage current, which are suitable for microwave device applications.