Sputtered lead scandium tantalate thin films: a microstructural study

Lead scandium tantalate (PST) thin films have been deposited on a platinized silicon substrate with and without a buffer layer of MgO at the temperature of 525°C. It was found that PST films on the substrate without a buffer layer were strongly (1 1 1) oriented perovskite, whilst films on the substrate with a buffer layer showed the presence of second-phase pyrochlore, and the films were (1 1 1) and (1 1 0) oriented. These structural differences were believed to result from the structural differences between the platinum layers immediately below the respective PST layers. The lines which divide PST into network of islands were found to be no more than wider grain boundaries, rather than cracks as believed previously. Micro-beam diffraction and energy dispersive X-ray analysis showed that grain boundaries were tantalum-rich and lead-deficient compared to perovskite grain centres. Electrical properties, such as relative permittivity and dielectric loss, for the films were also measured.     

Infrared television: performance of pyroelectric vidicon at 8 to 14 ?m

The performance of a television camera using the 2.54cm pyroelectric vidicon has been measured and compared with an analysis that attempts to identify the factors limiting the performance of the system.     

High temperature processing of ferroelectric thin films using interconnect wafer technology

Abstract

There is interest in ferroelectric thin films for uncooled IR detector applications. Currently the processing of these devices takes a fully integrated approach where the thin films are deposited directly onto underlying CMOS readout circuitry, thereby imposing severe limits on the thermal budget available for the crystallisation of the ferroelectric material. This is incommensurate with obtaining the best ferroelectric properties from materials such as lead scandium tantalate (PST) which requires elevated temperature processing to attain the highest merit figures for IR detection. In this paper thin film PST processed within the CMOS survivability envelope will be compared to that processed at temperatures up to 850°C. A novel interconnect wafer technology will be outlined which enables processing to be extended to such temperatures. It will be shown that elevated temperature processing of the PST film can result in dramatic improvement of the materials merit figure for IR detection     

Hard-vacuum pyroelectric vidicon: suitable materials

A new mode of operation of the pyroelectric Vidicon is reported. This mode does not require a soft vacuum and the tube is operated hard. Requirements for suitable pyroelectric materials are discussed and the results of experiments operating in this mode are presented.     

Microbeam analysis studies of the copper-silver interface

Copper-silver bimetallic samples have been examined by microbeam analytical techniques. Composition studies have concentrated on the interface region between the two metals. In this region two distinct phases characteristic of a eutectic structure were observed by backscatter electron imaging in the SEM. X-ray microanalysis has shown that the eutectic is composed of a copper-rich and a silver-rich phase. The crystal structure and composition of the constituent phases of the eutectic material have been confirmed by electron diffraction studies of a thinned foil of the eutectic composition. The surface structure of ion-beam etched eutectic material has been examined at high resolution. The silver-rich constituent of the eutectic is found to etch preferentially. The surface composition of the eutectic has been explained in terms of this ion-beam-induced surface structure.     

Ferroelectric materials and IR bolometer arrays: From hybrid arrays towards integration

Abstract

Large arrays of bolometer elements offer uncooled and simple operation, and a thermal imaging performance which challenges the cooled semiconductor (photon) detectors. A hybrid array technology, exploiting the pyroelectric property of ferroelectric ceramic materials in the bolometer elements, is the basis of a successful range of linear and 2-D arrays. However, other technologies will compete for cost effectiveness in large area devices. Direct integration of ferroelectric thin films onto suitable thermal microstructures on the silicon readout IC is attractive if deposition processes which are compatible with the silicon IC are established. Deposited lead based perovskite films show considerable potential. Thin film resistance bolometers will also compete, and have some advantages of compatibility in fabrication.     

Epitaxy and interfacial phase in thin films of lead scandium tantalate deposited by reactive sputtering on a platinum interlayer

Abstract

Lead scandium tantalate (PST) films with a lead-rich composition were deposited at 500°C by RF sputtering on sapphire substrates coated with Pt and were investigated by cross-sectional transmission electron microscopy. The films consisted almost entirely of the perovskite phase. The grains of perovskite PST had a crystallographic orientation almost parallel to that of the underlying Pt. Some elongated voids were observed. The presence of an interfacial phase, with interplanar spacings consistent with a pyrochlore phase, was demonstrated by electron diffraction and dark-field imaging. The crystallographic orientation of this phase is also nearly parallel to that of the Pt. Energy-dispersive X-ray microanalysis showed that the interfacial phase is lead-deficient. The interfacial phase is irregular in thickness. A reduction in the Pb content of the film leads to a thicker interfacial layer. The implications for the mechanism of growth of PST on Pt and for improvement of the film quality are discussed.     

Studies on the effects of sewage effluent on gastropod populations in experimental streams

Population density, biomass, growth and reproduction rate of the gastropods Lymnaea peregra (Müller) and Potamopyrgus jenkinsi (Smith) were monitored over a 21 month period in three experimental earth channels, one carrying clean river water and the others 25 and 50% treated sewage effluent mixed with river water. Each channel was divided into riffle and pool stretches; the abundance and biomass of both species were higher in the riffles. The abundance and biomass of L. peregra were significantly greater (P < 0.01) in the riffle in the presence of effluent. Concentration of effluent did not have a significant effect on abundance or biomass. The abundance and biomass of P. jenkinsi were significantly greater (P < 0.001) in riffle and pool in the absence of effluent. In addition, the abundance and biomass of P. jenkinsi were significantly greater (P < 0.05) in the 25% effluent channel than in 50% effluent. No significant differences in the growth of L. peregra between channels were observed. The average number of eggs and of egg masses laid by L. peregra was significantly greater (P < 0.01) in riffle and pool in the presence of effluent. In the riffle, significantly more masses (P < 0.05) and more eggs per adult (P < 0.01) were laid in the 25% effluent channel than in 50% effluent. No differences were observed in the reproduction rate per adult of P. jenkinsi between the 0 and 25% effluent channels. It is concluded that population differences between channels are probably largely the result of differing mortality rates.     

Leakage and Groove Pressure of an Axial Piston Pump Slipper with Multiple Lands

This article presents a new analytical model, based on Reynolds equation of lubrication, to evaluate the leakage and pressure distribution for an axial piston pump slipper taking into account the effect of nonvented grooves. The equations consider slipper spin and tilt and are extended to be used for a generic slipper with any number of grooves. A test rig has been designed and used to check experimentally the applicability of the theoretical equations and comparisons between theoretical and experimental results show a good agreement. The new theory can predict slipper leakage and pressure inside the groove with a high level of accuracy, especially at the very low slipper tilts that exist in practice. Experimentally, it is demonstrated that although a groove maintains a constant pressure along its path, under abnormal conditions the pressure differential can exist inside the groove. The effect of tangential velocity on groove pressure and slipper leakage is then studied experimentally, showing that as the rotational speed increases, there is a small decrease in leakage and a small increase in the average pressure inside the groove.