Jin-Bo Cheng

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.

Quantitative theory for laser-generated Lamb waves in orthotropic thin plates

A quantitative theory for modeling the laser-generated transient ultrasonic Lamb waves propagating along arbitrary directions in orthotropic thin plates is presented by employing an expansion method of the generalized Lamb wave modes. The displacement is expressed by a summation of the symmetric and antisymmetric modes in the surface stress-free orthotropic plate, and it is particularly appropriate for wave form analyses of Lamb wave in thin plates because one needs only to evaluate a few of the lowest order modes. The transient wave forms are analyzed in the thermoelastic regime and the oil coating generation method for a transversely isotropic plate. The results show that the theory provides a quantitative analysis to characterize anisotropic properties and elastic stiffness properties of the orthotropic plates by the laser-generated Lamb wave detection.

Effects of applied electric field during postannealing on the tunable properties of (Ba,Sr)TiO3 thin films

The impact of postannealing in electric field on the structure, tunability, and dielectric behavior of rf magnetron sputtering derived (Ba,Sr)TiO3 films has been studied. It has been demonstrated that postannealing in the proper electric field can increase the dielectric constant and the tunability remarkably and destroy the symmetry of capacitance-voltage characteristics of the films. The increased out-of-plane lattice constant and the appearance of the hysteresis loops in the electric-annealed films indicated the formation of small polar regions with tetragonal structure, which are responsible for the increased dielectric constant and tunability. It was proposed that the segregation of Ti3+ ions caused by electric annealing could induce the formation of BaTiO3-like regions, which are ferroelectric at room temperature.

SYNTHESIS AND CHARACTERIZATION OF FERROELECTRIC NANOCRYSTAL POWDERS OF SrBi2Ta2O9 BY A POLYMERIZABLE COMPLEX METHOD

Ferroelectric nanocrystal powders of SrBi2Ta2O9 (SBT) have been first prepared by a polymerizable complex (PC) route. The bismuth powder, strontium carbonate, and water-soluble tantalum oxalate solution were used as starting materials. Thermal analyses (TGA and DSC), x-ray diffraction (XRD), transmission electron microscopy (TEM), and conventional BET method were explored to characterize the structure, morphology, and specific surface area of PC-derived SBT powders calcined at 500-850 °C. As control samples, SBT powders were also fabricated by metalorganic decomposition (MOD) method. The XRD and TEM results indicate that high pure and well crystalline powders can be obtained at 650 °C with a average size of 50 nm. The PC-derived powder has much larger surface area than MOD-derived powder. The BET value of PC and MOD powder at 750 °C for 2h is 6.7 and 1.5m2/g, respectively. The specific surface area of powder prepared by conventional solid-state reaction is quite low, typically less than 1.5m2/g. Therefore...

PREPARATION AND CHARACTERIZATION OF POLED NANOCRYSTALS AND POLYMER COMPOSITE SrBi2Ta2O9/PC FILMS

ABSTRACT SrBi2Ta2O9/polycarbonate (SBT/PC) composite thin films were prepared by spin coating method. Ultra-fine SrBi2Ta2O9(SBT) (∼ 40–50 nm) nanocrystals with pure layered-perovskite phase were synthesized by a polymerizable complex route. The structure and morphology of SBT nanocrystals and composite films were studied by means of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The frequency and temperature dependence on dielectric properties of SBT/PC composite thin films were evaluated. The orientation degree of nanocrystals in PC polymer was estimated by measuring the transparency spectra of unpoled and poled composite thin films. The poling relaxation properties after corona poling were examined.

WELL-BEHAVED METAL-OXIDE-SEMICONDUCTOR CAPACITOR CHARACTERISTICS OF ZIRCONIUM OXIDE FILMS FABRICATED BY SURFACE SOL-GEL PROCESS

ABSTRACT The surface sol-gel (SSG), a solution-based and stepwise film growth technique, was developed to produce ultrathin zirconium oxide (ZrO2) films for high-k gate dielectric application. X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) measurements confirm the successful deposition of ultrathin polycrystalline ZrO2 films on Si substrate by the SSG method. Electrical measurements show that a large effective oxide thickness (EOT) of 2.4 nm with high leakage current was obtained, and a hysteresis in C-V curves and large fix charge density in ZrO2 films was observed, which related to the formation of substoichiometric silicon oxide in the interface. Surface nitridation of Si substrate by NH3 plasma can effectively reduce the leakage current and fixed or trapping charge density, as well as improve the interface properties. EOT of 2.21 nm with JA = 30.4 mA/cm2 at Vg = +1 V was demonstrated in ZrO2 films with a Si nitride barrier layer.

Nonlinear Photoacoustic Effect in Semiconductors: Second Harmonic Wave Behavior

The nonlinear photoacoustic (PA) and photothermal (PT) phenomena have attracted considerable attention in recent years. Balk et al [1] reported the nonlinear effects observed in Scanning Electron Acoustic Microscopy (SEAM), and pointed out that comparing with the fundamental wave imaging, the second harmonic imaging displayed different structures of materials. Wetsel et al [2] investigated the nonlinear phenomena in PhotothermalOptical-Beam-Deflection (POBD) imaging, and presented a nonlinear thermal resistance model. We have studied [3] the nonlinear piezoelectric PA effect of silicon wafers in an applied dc electric field. The dependences of the fundamental frequency PA amplitude and phase on laser power have been measured and explained by considering the nonlinear surface and bulk Auger recombinations of the photogenerated carriers (PGC). Now, both experimental and theoretical investigations on the second harmonic wave behavior of the nonlinear piezoelectric PA effect in semiconductor silicon wafer are reported. The “subsurface approximation” method presented by Cheng et al [3] is extended to calculate a second harmonic component. A good agreement between the experiment and the theory is obtained.

Topography of Integrated Circuits Detected by Phase Selection in Modulated Optical Reflectance Microscopy

The development of semiconductor industry has promoted the improvement of the inspection techniques which can be used for evaluating semiconductor materials and devices. In recent years, the modulated optical reflectance (MOR) technique has attracted great interest because it is a simple, direct and sensitive evaluation method in addition to its noncontact, nondestructive and non-invasive mode.