Feiling Wang

Electro‐optic measurements of thin‐film materials by means of reflection differential ellipsometry

Electro‐optic properties of thin‐film materials grown on opaque substrates are determined utilizing the principles of reflection differential ellipsometry. The scheme of the measurement involves the detection of the field‐induced phase shift in a probing light beam reflected from thin‐film samples. To quantitatively determine the field‐induced indices change or birefringence and the field‐induced strain it is essential to model the differential ellipsometric process in the stratified structure. The modeling reveals that the field‐induced changes of the ordinary and the extraordinary indices contribute to the measured phase shift with different incident‐angle dependences. The field‐induced strain gives yet another unique incident‐angle distribution. By means of an incident‐angle‐varying technique, therefore, the field‐induced changes of ordinary index and extraordinary index in a thin‐film material may be determined separately. Detailed descriptions of the measuring technique and the modeling work are pres...

Birefringent bistability in (Pb,La)(Zr,Ti)O3 thin films with a ferroelectric‐semiconductor interface

We report a birefringent bistability exhibited in ferroelectric thin films with a ferroelectric‐semiconductor interface. Such birefringent bistability is observed in (Pb,La)(Zr,Ti)O3 (PLZT) thin films which are sandwiched between a platinum and a semiconducting indium‐tin oxide (ITO) electrode. The magnitude of the birefringence between the two remanent states is approximately 0.9×10−3. The Pt/PLZT/ITO structure features a nonvolatile electro‐optic memory operation, i.e., the switching between the two remanent birefringent states with bipolar electric pulses.

Transverse electro-optic effect of antiferroelectric lead zirconate thin films.

The transverse electro-optic effect in antiferroelectric lead zirconate thin films grown on fused quartz is observed. The birefringence shift as a function of the external electric field exhibits a characteristic response that is related to the electric-field-induced antiferroelectric-to-ferroelectric structural transition.

PLZT-based multilayer composite thin films, part I: Experimental investigation of composite film structures

Composite thin films produced by depositing alternating layers of various PLZT compositions were fabricated on Pt-coated Si wafer and Ag foil substrates. Films were prepared by MOD processes including automatic spin and dip coating from acetate precursors followed by annealing at 700°C. Ferroelectric (FE)/antiferroelectric (AFE), FE/relaxor and relaxor/AFE composites consisted of individual layer compositions including ferroelectric PLZT 2/55/45 and 7/65/35; AFE PLZT 0/100/0, 0/96/4 and 0/95/5; relaxor PLZT 9.5/65/35 and 12/65/35. The structural and electrical properties of the composite films were investigated. Composites were developed with 1) improved AFE-to-FE domain switching with decreased AFE-to-FE transition field and increased saturation polarization for materials with AFE-type properties, 2) increased induced polarization with decreased coercivity and polarization remanence for relaxor-type composites and 3) increased hysteresis loop squareness for ferroelectric memory materials compared with fi...

PLZT-based multilayer composite thin films, part II: Modeling of the dielectric and hysteresis properties

PLZT-based composite thin films with various compositions were fabricated and characterized in Part I of this study. Similarly to procedures reported in the literature, the low-field dielectric properties in Part II were modeled according to a series capacitor model based on the dielectric constants of the individual composite constituents. In order to model the FE high-field switching properties, AFE-to-FE phase transitions and non-uniform electric field distributions in the composite films, a new hysteresis modeling technique was developed based on a series capacitor model featuring the nonlinear polarizabilities of the individual components as evident from experimental data. The model predicts the behavior of any composite film structure provided the pure component properties are known.

Discrete electro-optic response in lead zirconate thin films from a field-induced phase transition.

A discrete transverse electro-optic response associated with a field-induced antiferroelectric–ferroelectric phase transition has been observed to exist in lead zirconate thin films grown on Pt/Ti-coated silicon substrates. The magnitude of the birefringence jump from the antiferroelectric to the ferroelectric state is approximately 2.5 × 10−2. Quantitative correlation between the field-induced birefringence and the polarization was also experimentally studied. The discrete birefringent change in the thin films may be a desirable property for applications in optical switches or other integrated-optical devices.

Effects of applied stress on the dielectric properties of PLZT thin films

The dielectric properties of electrooptic thin films were varied by altering the stresses placed upon the films. Selected thin films in the lanthanum-modified lead zirconate titanate system (PLZT) were produced by using the dip-coating process and applying various stresses. Comparisons were made among thin films under mechanically applied stresses of different magnitude. Properties measured were dielectric constant, saturation polarization, remanent polarization, coercive field and d-spacing. The effects of the applied stresses on the physical and electrical properties of the films are discussed.

Photoactivated birefringence in antiferroelectric thin films via a structural transition

A photoactivated birefringence has been observed in an antiferroelectric lead zirconate titanate (PZT) thin film material bounded by an indium‐tin oxide (ITO) electrode. This phenomenon stemmed from the ultraviolet (UV) assistance to an antiferroelectric‐to‐ferroelectric structural transition which otherwise was inhibited by an effect of the lead zirconate titanate (PZT)‐ITO interface. The UV‐assisted structural transition was accompanied by a significant change in the birefringence of the PZT thin films. Using this phenomenon, an UV‐addressed visible‐light modulation was demonstrated with an ITO/PZT/Pt thin film structure on silicon substrates.

A modification of the three‐point method of measuring contact resistivities of metal‐superconductor interfaces

Axisymmetric three‐point measurement of the contact resistance between a metal electrode and a superconductor substrate shows significant variation as a function of the placement of the voltage measuring probe on the metal electrode. This study explored this variation by the use of an analytical model simulating the voltage variation in the metal electrode. The model used a simplified scheme of mapping the electrode‐superconductor interface to an equivalent layer with the same resistivity as the metal electrode. The voltage in the electrode was obtained by solving Laplace’s equation. Using a numerical approximation process, three simplified equations for calculating the contact resistivities from the voltage measured from the three‐point method were developed. The contact resistivities calculated from the modified equations and those measured from the lap‐joint method were compared in order to show the validity of the modified equations. The radii of the electrode and current leads, and the ratio of the v...

Antiferroelectric/ferroelectric composite thin films

PLZT-based antiferroelectric (AFE)/ferroelectric (FE) composite thin films were fabricated by automatic spin coating and crystallized by rapid thermal processing. A computer-controlled automatic spin coat reactor was used to spin composite thin films from acetate precursors with successive layers of FE and AFE composition. Films were spun on platinum-coated silicon substrates and rapid thermal thermally processed at 700/spl deg/C. Composite thin films exhibited improved AFE-type properties including increased dielectric constant (K) and saturation polarization (P/sub sat/) and decreased FE switching field (E/sub F/) compared to typical AFE compositions. X-ray diffraction results indicated that the composite thin films consisted of distinct AFE and FE phases. Modeling of the dielectric properties revealed linear series capacitor behavior within the composite thin films for low electric field conditions; however, nonlinear effects were apparent at high electric fields.