Ferroelectric Sensors Research Articles

Influence of grain boundary, defect and internal stress states on properties of ferroelectric materials

Abstract Performance characteristics in ferroelectric based components, sensors and thin films for memory and storage applications are significantly influenced by aging instability in these perovskite materials. The aging changes can be attributed both to dc electrochemical effects, where migration of ionic charges lead to degradation in permittivity, loss and resistance, and to changes in domain structure and mobility. This latter reflects the presence within the microstructure of defect states, diffuse grain boundary structures and internal stresses. Aging in these materials is also dependent on microstructure, impurities, dopants and stoichiometry, as well as on ambient temperature and applied dc field stresses. Significant improvements in aging and performance characteristics have been achieved with selected dopant additions to BaTiO3, such as ZrO2, which control grain morphology, resulting in structural modifications and decreased domain mobility. Permittivity has been found to be highly dependent on internal stress and this dependence has been mathematically modeled and related to the aging instability. Similarly, a model has been developed which explains the changes in grain morphology, resistivity, aging and PTC effects in terms of site occupancy of the dopants in the BaTiO3 lattice. Properties of ferroelectric films are also significantly influenced by structure, dopant incorporation and grain size, but understanding of these interrelationships is less advanced.

Ferroelectric temperature sensors for thermometric titrations and enthalpimetric analysis

The capabilities of commercially available barium titanate ferroelectric ceramics with switching points of 25 and 0°C were tested for use in thermometric titrations. Temperature ( T) versus resistance ( R) data taken from 24 to 26°C for seven ferroelectrics and from −1 to +1°C for three others were fitted to an exponential equation of the form R = Aexp( CT), where A is a scaling factor and C is the temperature coefficient of resistance. A ferroelectric sensor (FES) was wired in a Wheatstone bridge in place of the thermistor customarily used in conventional instrumentation. Calculations substantiated that the bridge imbalance potential response approximated linearity within any 1°C interval, provided that the bridge was balanced in the middle of the span. The response of the FES bridge showed a fourfold enhancement for a given temperature change compared with the thermistor bridge and a concomitant reduction in baseline noise. Analytical capabilities are illustrated by thermometric redox titrations in the concentration range between 3 × 10 −5 and 2 × 10 −3 M.

Detection of fluid velocity and hydroacoustic particle velocity using a temperature autostabilized nonlinear dielectric element (TANDEL)

A ferroelectric sensor operated in the temperature autostabilized mode was developed for the measurement of the particle motion in hydroacoustic fields. The sensor is a capacitorlike element constructed from antimony sulfur iodide (SbSI) single crystals and SbSI–polymer composites. The device is operated slightly above the Curie point of SbSI, which is approximately 20 °C. Using a Schering bridge, the element is heated by driving it through the hysteresis cycle. The heat transferred to the surrounding fluid is related to the motion of the fluid. The technique was applied to the measurement of a constant velocity flow field and to a low-frequency acoustic field. In the case of the constant velocity flow field, an exponential relationship between fluid velocity and sensor voltage was observed. For acoustic fields, the response of the sensor decreased sharply with frequency above 100 Hz. The acoustic particle velocity could be measured to a frequency around 1 kHz.

TANDEL measurement of hydroacoustical particle motion

A new ferroelectric sensor for measuring the particle motion in hydroacoustic fields has been developed. The sensor is a capacitor constructed by adding conducting end plates to single crystals or polymer composites of antimony sulfur iodide (SbSI). The device is operated above the Curie point of about 20 °C. The heating is accomplished through the hysteresis cycle driven by a Sawyer-Tower-type bridge. In the temperature region slightly above the Curie point, both the real part ε′ and the imaginary part ε″ of the dielectric permittivity have a large negative slope as a function of temperature. The negative slope in ε″ causes the Temperature Autostabiling feature of the Nonlinear Delectric ELement (TANDEL). Cooling the sensor by a fluid flow changes the temperature of the sensor, and consequently ε′ and ε″. The change of ε′ unbalances the bridge, producing a detectable signal. The output for steady flow shows the characteristic exponential dependence on fluid speed. The sensor displays directional sensitivity. The response to low-frequency acoustic fields is discussed and related to the heat transfer properties of horizontal cylinders. [Work supported by the ONR.]

A one-dimensional ferroelectric image sensor using an organic photoconductor

Abstract A scanning one-dimensional image sensor fabricated from a gadolinium molybdate crystal is reported. The ease of motion of a domain wall in the crystal is perturbed by conductivity variations in a polymeric photocon-ductor layer coated on one of the crystal's faces. These perturbations in turn are sensed as alterations of the voltage-current relationship of the device as seen by an external circuit. No mask, photolithography or electrode patterning was employed in the fabrication of the device. The optical resolution in the direction of scanning was measured to be 20 to 25μm.

A Self-Scanned Ferroelectric Image Sensor

A prototype imaging system consisting of a monolithic sensor array of pyroelectric elements has been constructed which is capable of imaging visible, infrared and x-radiation. The image sensor is a true flat-panel, self-scanned device which generates a video picture of radiation intensity patterns at the usual television rate of 30 frames per second. The detector material is ceramic lead-zirconatc-titanate. which has an individual spot responsivity of 1 ViW. The video Information is extracted from the sensor mosaic by digital scanning and video coupling circuits which are connected to the array by row and column address electrodes. The electronic circuitry consists of low cost. low power integrated circuits. The initial prototype system incorporates a 5 x 5 element sensor matrix and a large scale device composed of' an array of 2500 spots is currently under construction.

A self-scanned ferroelectric image sensor

A prototype imaging system consisting of a monolithic sensor array of pyroelectric elements has been constructed which is capable of imaging visible, infrared and x-radiation. The image sensor is a true flat-panel, self-scanned device which generates a video picture of radiation intensity patterns at the usual television rate of 30 frames per second. The detector material is ceramic lead-zirconatc-titanate which has an individual spot responsivity of 1 V/W. The video information is extracted from the sensor mosaic by digital scanning and video coupling circuits which are connected to the array by row and column address electrodes. The electronic circuitry consists of low cost, low power integrated circuits. The initial prototype system incorporates a 5 × 5 element sensor matrix and a large scale device composed of an array of 2500 spots is currently under construction.