Qi-Yue Shao

Characteristics of LaAlO3 gate dielectrics on Si grown by metalorganic chemical vapor deposition

Amorphous LaAlO3 (LAO) gate dielectric thin films have been deposited on Si substrates using La(dpm)3 and Al(acac)3 sources by low-pressure metalorganic chemical vapor deposition. The growth mechanism, interfacial structure, and electrical properties have been investigated by various techniques. The ultrathin films show smaller roughness of ∼0.3 nm, larger band gap of 6.47 eV, and good thermal stability. The growth follows a chemical dynamic control mechanism. High-resolution transmission electron microscopy confirms there exists no interfacial layer, or only thinner ones, between LAO and Si. X-ray photoelectron spectroscopy analyses reveal that the thinner interfacial layer is compositionally graded La–Al–Si–O silicate and Al element is deficient in the interfacial layer. The reliable value of equivalent oxide thickness around 1.2 nm of LAO/Si has been achieved.

Enhanced fatigue-endurance of ferroelectric Pb1−xSrx(Zr0.52Ti0.48)O3 thin films prepared by sol-gel method

The polarization fatigue behaviors of ferroelectric Pb1-xSrx(Zr0.52Ti0.48)O-3 (PSZT) thin films deposited on Pt-coated silicon wafers are investigated. Significantly enhanced fatigue endurance with increasing Sr doping and decreasing temperature is observed, and the almost fatigue-free performance up to 10(10) switching cycles for PSZT (x=0.2) thin films at room temperature is identified. The dc-conductivity measurements suggest almost 20 times decreasing of the oxygen vacancy density as the Sr doping increases from x=0 to x=0.2. It is believed that the Sr-doping enhances the stability of oxygen ions and suppresses oxygen vacancies, consequently resulting in the improved fatigue endurance. (c) 2006 American Institute of Physics.

Structure and electrical properties of strontium barium niobate ceramics

Abstract SBN, x =0.25, 0.35, 0.50, 0.60 and 0.75 series of ceramics prepared by traditional sintering method have been studied systematically. The impact of composition and sintering temperature on structures, microstructures, and electrical properties of SBN ceramics was characterized of X-ray diffraction, scanning electron microscopy, and electrical measurements. It is found that the composition and temperature play an important role on the fabrication of single phase tetragonal TTB SBN ceramics. At x =0.5, TTB SBN ceramics can be obtained at 1200°C. For x 2 O 6 even at 1300°C; TTB structure SBN and orthorhombic phase SrNb 2 O 6 for x >0.5. The complete TTB phase is produced at 1350°C. With Sr content increasing, the electrical performances show a regular change, strongly conforming to the reducing of the Curie temperature. SBN with the Sr composition of x =0.60–0.75 is a promising candidate for electro-optics device applications.

Temperature-dependent fatigue behaviors of ferroelectric ABO3-type and layered perovskite oxide thin films

The temperature-dependent dielectric and ferroelectric fatigue behaviors of ABO(3)-type perovskite thin films Pb(Zr0.52Ti0.48)O-3 (PZT) and Pb0.75La0.25TiO3 (PLT) and layered Aurivillius thin films SrBi2Ta2O9 (SBT) and Bi3.25La0.75Ti3O12 (BLT) with Pt electrodes are studied. The improved fatigue resistance of PZT and PLT at a low temperature can be explained by the defect-induced suppression of domain switch/nucleation near the film/electrode interface, which requires a long-range diffusion of defects and charges. It is argued that the fatigue effect of SBT and BLT is attributed to the competition between domain-wall pinning and depinning. The perovskitelike slabs and/or (Bi2O2)(2+) layers act as barriers for long-range diffusion of defects and charges, resulting in localization of the defects and charges. Thus, the fatigued SBT and BLT can be easily rejuvenated by a high electric field over a wide temperature range

Growth and characterization of Al 2 O 3 gate dielectric films by low-pressure metalorganic chemical vapor deposition

Ultrathin Al2O3 films have been deposited on n-Si substrates by low-pressure metalorganic chemical vapor deposition (MOCVD) as gate dielectrics for next generation MOSFET applications. Al(acac)3 was used as metalorganic precursor. Impacts of substrate temperature and post-annealing in O2 or N2 on equivalent oxide thickness (EOT), leakage current density (JA) and carbon residue of Al2O3 films have been studied. It is found that post-annealing is necessary for ultrathin Al2O3 films to obtain good electrical properties. The EOT shows slight deposition temperature dependence and the lowest EOT value with ∼0.8 nm is obtained at 600 °C. Typical Al2O3 ultrathin films have larger frequency dependence and EOT of ∼ 1.2 nm with JA of 36 mA/cm2 at Vg = + 1 V. AES depth profiles demonstrate that post-annealing in an O2 atmosphere could effectively eliminate the carbon contamination of Al2O3 films. Meanwhile, further post-annealing in N2 could decrease the JA of Al2O3 films to 8 mA/cm2.

Strontium-modified lead zirconate titanate thin films for electrically tunable device applications

Strontium-modified lead zirconate titanate Pb1−xSrxZr0.52Ti0.48O3 [(PSZT) x=0.2–0.8] thin films were prepared on Pt∕TiO2∕SiO2∕Si substrates by the sol-gel method. The Curie temperature of PSZT films decreases with the increase of Sr contents and paraelectric PSZT films at room temperature are demonstrated as x approaches 0.4. The increase of Sr contents also leads to the simultaneous decrease of dielectric constant, tunability, and dielectric loss. The composition dependence of Curie temperature and tunability can be attributed to the shrinkage of crystal lattice due to a Sr addition. PSZT films with x=0.6 show the largest figure of merit of 24 with a moderate tunability of 48% and a dielectric loss of 0.02. This suggests that Sr-modified PZT is a potential candidate for voltage tunable applications.

Preparation of composite coating particles of α-Al2O3–SiO2 by heterogeneous nucleation-and-growth processing

In order to solve the difficult problem of heterogeneity of different components in the procedure of ceramic preparation, heterogeneous nucleation-and-growth processing is used to prepare the homogeneous distribution powders. Composite coating particles consisting of alpha alumina cores (average particle size 0.57 μm) with an outer amorphous silica layer are prepared by the heterogeneous nucleation-and-growth processing. The amorphous silica layer on cores is confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM) and zeta-potential measurement. Effects of silica content in composite coating particles versus concentration of tetraethylorthosilicate (TEOS), pH value, reaction time and reaction temperature are studied.

Growth and ferroelectric properties of sol-gel derived Pb(Zr,Ti)O3 using inorganic zirconium precursor

Abstract Pb(Zr 0.52 Ti 0.48 )O 3 (PZT) thin films were prepared by sol-gel methods using zirconium nitrate hydrate as the starting zirconium precursor. X-ray diffraction (XRD), atomic force microscopy (AFM) and electrical measurement were used to characterize PZT thin films. The effect of various heat treatment processing of rapid thermal anneal (RTA) and conventional thermal anneal (CFA) on structure and ferroelectric properties of PZT thin films has been investigated. RTA-annealed PZT films show better structure and electrical properties than CFA-annealed ones. The RTA-treated PZT thin films at 650°C show a remanent polarization of 19.7 μC/cm 2 and coercive field of 18.4 kV/cm, and exhibit high fatigue resistance against 4×10 9 switching cycles, all of which can match PZT thin films obtained using zirconium alkoxide. Meanwhile, the use of inorganic zirconium salt greatly increases the shelf life of the precursor solution.

Structure and tuning properties of sol–gel-derived Pb0.4Sr0.6Zr0.52Ti0.48O3 (PSZT) thin films

Pb0.4Sr0.6Zr0.52Ti0.48O3 (PSZT60) thin films were successfully prepared on platinized silicon (Pt/Si) and Nb-doped SrTiO3 (STO) substrates by the sol–gel method. X-ray diffraction characteristics show that the films on STO exhibit highly (0 0 1) oriented structure and the films on Pt/Si have polycrystalline structure. Dielectric properties of PSZT films aimed at electrically tunable applications were investigated as a function of temperature and electric field. The films on STO show higher Curie temperature, larger dielectric constant and higher tunability, due to a highly c-axis orientation and larger grain size. Both the PSZT films on STO or Pt/Si substrates show a weakly temperature-dependent tunability in the temperature range from 25 to 150 °C, implying favourable temperature stability for practical application. These results suggest that the PSZT60 film may be a potential candidate material for further investigation of electrically tunable applications.

Epitaxial growth of (PbZr)TiO3 films on LaAlO3 by sol-gel method using inorganic zirconium source

Abstract Epitaxial ferroelectric Pb(Zr 0.52 Ti 0.48) O 3 (PZT) thin films were successfully fabricated on LaAlO 3 substrates using an inorganic zirconium source by the sol-gel method. Single-phase perovskite formation was achieved by rapid thermal anneal at 650°C. Temperature dependence of the structural and morphological characteristics of sol-gel-derived PZT films were investigated by means of X-ray diffraction θ-2θ scan, rocking curve, and ϕ-scan, scanning electron microscopy, and atomic force microscopy. The films showed better epitaxy and density with smaller roughness. In addition, the characteristic of sol-gel-derived PZT thin films using the mixed PZT powder/precursor solution was also studied.