Eugene Furman

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...

An investigation of the resonance properties of rainbow devices

In the last fifteen years considerable progress has been made in developing novel materials and devices for electromechanical actuator applications based on a variety of ferroelectric materials. Recently a novel type of high displacement actuator was developed. It is a monolithic, domed, stress-biased wafer consisting of oxide and reduced layers. These actuators are envisioned to be used in a variety of applications for which the knowledge of the resonance modes is essential. In this paper measurements of the resonant modes are compared to the predictions of the finite-element model. A number of low frequency modes were observed and identified as the bending modes. A higher frequency radial mode was determined to be less dependent on the sample dimensions than the bending modes. Effects of the boundary conditions on the resonant modes were modeled and investigated experimentally. For the modeling aspect of the study it was necessary to measure elastic constants, thermal expansion coefficients, and bulk de...

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.

Composition and microstructure of chemically reduced PLZT ceramics

Abstract Hot-pressed PLZT ceramic wafers were chemically reduced by a special processing technique on one of the major surfaces to form oxide-reduced layer composite structures. Devices based on such structures have promising characteristics for actuator use. The composition and microstructure of the reduced layer from several PLZT ceramics of different compositions as well as the oxide-reduced layer interface were examined and analyzed by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM). A variety of the oxide phases, such as PbO, ZrO2, ZrTiO4 and LaTiO3, were revealed in the reduced PLZT samples by XRD in addition to the anticipated metallic lead phase. SEM micrographs showed that the reduced PLZT ceramics were composed of various fine-grained particles, and the metallic lead formed a continuous phase. It was found that the oxide-reduced layer interface region was composed of a mixture of unreduced and reduced phases. The thickness of the mixed phase region was primarily associate...

Fabrication and proprerties of PSZT antiferroelectric rainbow actuators

Abstract A new type of high-displacement actuator called Rainbow (Reduced And INternally Biased Oxide Wafer) was recently developed, and it shows promising characteristics in a variety of potential applications. The fabrication and propertites of Rainbow actuators from PSZT antiferroelectric ceramic with compositions near the antiferroelectric-ferroelectric (AFE-FE) phase boundary were investigated.It was found that the chemical reduction reaction proceeded much more rapidly in PSZT than in PLZT ceramics. The optimum conditions for the processing of PSZT Rainbows were determined to be 850°C for 2–3 hours. Large axial displacements ranging from 102 to 273 μm were obtained from the PSZT Rainbow samples by application of electrif fields greater than the AFE-to-FE phase switching levels. The characteristics of the field-induced displacements of the Rainbow samples were dependent on the manner of applying mechanical load on the samples. At room temperature, the antiferroelectric PSZT Rainbows exhibited a conca...

Electromechanical properties of Rainbow devices

A stress-biased, domed, electromechanical bender called a Rainbow was recently developed. Displacement characteristics for Rainbow devices based on piezoelectric PLZT compositions were studied in the frequency range far below the fundamental resonant mode frequency. Experimentally obtained field-induced displacements were compared with those predicted by a finite element model. The model underestimated the observed displacements. Low frequency relaxation of the displacements was observed experimentally.

Finite Element Analysis of Rainbow Ceramics

The finite element method has been utilized to analyze the processing and performance of the newly developed Rainbow (Reduced And INternally Biased Oxide Wafer) ceramic actuators. A Rainbow is produced by a special chemical reduction process to form a dome-shaped, stress-biased structure which delivers a large field-induced displacement while attaining moderate load-bearing capability. The creation of the domed structure and accompanying internal stress by the reduction process is simulated by considering a Rainbow as a two-layer heterogeneous circular plate and allowing it to cool down from the reduction temperature to room temperature. Based on the derived domed structure, the Rainbow performance including electric field-induced displacements and resonant characteristics is modeled. Modeled dome curvature, internal stress, and electromechanical characteristics of the Rainbow ceramic are discussed with respect to material properties and geometrical parameters. Comparisons between the modeling results and the experimental data obtained from the Rainbow samples made with PLZT ceramics are presented. A good agreement was exhibited between the modeling predictions and the experimental measurements for the dome curvature and internal stress distribution, but appreciable disparities were observed in the electromechanical properties. The results imply that the internal stress should have a strong influence on the Rainbows electromechanical performance.

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.

Dielectric breakdown in PLZT 9.5/65/35 ceramics

There is currently a trend to reduce the thickness of the dielectrics and to operate them at higher field levels. Understanding and controlling the breakdown strength will permit higher operating fields. The main goal of this work was to establish the breakdown mechanism in PLZT ceramics. The breakdown experiments were conducted with both hot-pressed and conventional ceramics. The breakdown strength was studied as a function of electrode material, voltage polarity, ramp rate, and temperature. All of the results were consistent with electromechanical breakdown being the dominant mechanism.