Hui-Qin Ling

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.

Fatigue study of metalorganic-decomposition-derived SrBi2Ta2O9 thin films: The effect of partial switching

Fatigue characteristics of metalorganic-decomposition derived SrBi2Ta2O9 (SBT) ferroelectric thin films were investigated with varying film thickness, capacitor size, switching pulse amplitude, and pulse width. The effect of partial switching on fatigue was studied. An increase of nonvolatile polarization (Pnv) was observed over the initial period of fatigue when the capacitor was fully switched by the applied bipolar cycles. Fatigue increases with decreasing applied field and pulse width. These support the idea that fatigue in SBT may be viewed as a competition between domain-wall pinning and field-assisted unpinning. Partial switching caused by small field and short pulse width enhances charge trapping at domain walls, thus increasing fatigue.

Characterization of metalorganic decomposition-derived SrBi2Ta2O9 thin films with different thicknesses

Ferroelectric capacitors having sputtered Pt bottom and top electrodes and metalorganic decomposition derived ferroelectric thin films of SrBi2Ta2O9 (SBT) were prepared. The thickness effects on the structure, surface morphology, and electrical properties of SBT thin films were studied and discussed. Structure and surface morphology were analyzed by x-ray diffraction and atomic force microscope. The electrical properties were characterized by the measurements of hysteresis, capacitance, and pulse switching. The crystalline structure, grain size, and electrical properties do not depend on film thickness when films are less than 440 nm thick. A larger grain size is observed for films thicker than 440 nm, which results in a larger remnant polarization. The thickness dependence of the coercive voltage and reciprocal capacitance can be explained by an interfacial layer model. The thickness-independent coercive field and dielectric constant, calculated from the interfacial layer model, are around 19 kV/cm and 3...

PREPARATION OF (BA0.5SR0.5)TIO3 THIN FILMS BY SOL–GEL METHOD WITH RAPID THERMAL ANNEALING

Abstract (Ba 0.5 Sr 0.5 )TiO 3 (BST) thin films were deposited on Si and plantinized Si substrates using sol–gel method with rapid thermal annealing (RTA). The films were characterized by inductive coupled plasma (ICP) analysis, X-ray diffraction (XRD), atomic force microscope (AFM), scanning electron microscope (SEM) and electrical measurements. BST get well crystallized after RTA at 700°C for 5 min. Grain size, grain height, and thus, surface roughness and film density increase with the increase of annealing time. SEM cross-section results clearly demonstrate a better BST/substrate interface compared with conventional annealing. The dielectric constant and loss tangent of BST films at 10 kHz are 435 and 0.069, respectively. This good dielectric property is believed to arise from the better BST/substrate interface.

Effect of excess bismuth on the microstructures and electrical properties of strontium bismuth tantalate (SBT) thin films

Abstract Strontium bismuth tantalate (SBT) films with excess Bi contents were prepared on Pt/TiO2/SiO2/Si substrates by a metallorganic decomposition technique. Effect of excess Bi contents on the microstructure and electrical properties were investigated. A predominant layered perovskite structure could be formed when an excess Bi less than 30% was added. For films above 30% excess of Bi, secondary phases occurred. The remnant polarization and dielectric constant decreased with excess Bi content. This was attributed to a smaller grain size and the presence of secondary phases. The leakage current characteristics were also examined. Space charge limited mechanism was observed in SBT films. In summary, 10% excess Bi was found to be the optimum composition with respect to grain size, morphology, and electrical properties.

Different growth behavior of SrBi2Ta2O9 ferroelectric films under conventional and rapid annealing processing by metalorganic decomposition

Abstract SrBi 2 Ta 2 O 9 (SBT) thin films were prepared on Pt/TiO 2 /SiO 2 /Si substrates by metalorganic decomposition method. The grain growth behaviors of SBT films under conventional furnace annealing (CFA) and rapid thermal annealing (RTA) processing as functions of annealing temperature ( T ) and time ( t ) were investigated systematically. The grain size distribution with CFA and RTA basically conforms to Gaussian distribution, whereas the films annealed by RTA show higher nucleation rate than by CFA. Different grain growth kinetics of the films annealed at 750°C under CFA and RTA with varied anneal time was characterized. In Arrhenius curves, there were two distinct temperature regions corresponding to different growth activation energies. The value of growth activation energy under CFA is smaller than that under RTA.

Effects of processing on the characteristics of SrBi2Ta2O9 films prepared by metalorganic decomposition

SrBi2Ta2O9(SBT) films were prepared by metalorganic decomposition technique. The films were obtained by spin-on pyrolysis of the precursor solutions on various substrates and then annealed at 550–850 °C in dry oxygen, wet oxygen, or Ar. Effects of precursor solution concentration, anneal temperature, anneal atmosphere, substrate and Ar ion sputtering on the microstructure, morphology and electrical properties were investigated by means of x-ray diffraction, scanning electron microscope, atomic force microscope, x-ray photoelectron spectroscopy, and electrical measurements. The results indicated the grain size, and the remnant polarization (Pr) increased with increasing the anneal temperature up to 800 °C and the significant hysteresis loop could be obtained only after anneal above 700 °C. At 850 °C, the pyrochlore phase and other secondary phases were observed along with the SBT phase, leading to the decreasing Pr and dielectric constant. In addition, the development of crystalline phase and electrical pr...

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.

Fabrication and electrical properties of sol-gel derived (BaSr)TiO3 thin films with metallic LaNiO3 electrode

Abstract Metallic LaNiO 3 (LNO) films were prepared on LaAlO 3 (LAO) and Si substrates by metal-organic decomposition (MOD) and their application as the bottom electrode for sol-gel derived (BaSr)TiO 3 (BST) thin films was studied. X-ray diffraction, atomic force microscope and electrical measurements were used to characterize the multilayer films of BST/LNO/substrates. BST film on LNO-coated LAO substrate exhibited preferred (100) orientation. Smooth and dense surface with fine grains (∼50 nm) was observed. The electrical measurement results on BST films using LNO and stainless steel as the bottom electrodes, respectively, showed BST/LNO/substrates have higher dielectric constant, lower loss tangent, lower leakage current and higher breakdown voltage.

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.