In-house manufactured thin film circuits are used by Lucas Aerospace in gas turbine engine fuel control systems where stability and reliability in a harsh environment are required.The construction of a complex active thin film circuit is reviewed with emphasis on some less obvious aspects of production. Where component attachment and engineering techniques used are thought to be of special interest a more detailed explanation is given.As is normal in the avionics industry a high degree of system integrity is required so that quality control is essential. Therefore, the role of Quality Engineering in the production plan is described.

V.  Needham

The Production of Complex Thin Film Circuits

D. S. Campbell

Editorial

Book Reviews

The failure mechanism of solid tantalum and aluminium capacitors have been investigated using a combination of electrical measurements and electron microscopy. The capacitor dielectric was examined before and after life testing and changes correlated with electrical measurements.The basic mechanism of failure of solid tantalum capacitors is found to be field crystallisation of the essentially amorphous dielectric oxide. The growth of higher conductivity crystalline oxide during operation of the capacitors causes an increase in leakage current and may result in catastrophic failure. The effect of field crystallisation can be minimised by using high purity tantalum to reduce the number of crystallisation nucleation sites. Since crystalline growth is primarily dependant on applied voltage, high voltage capacitors are much more susceptible to failure than low voltage units.There appears to be no long term failure mechanism in solid aluminium capacitors. However, a particular problem with these units is that they are difficult to make. This is because the anodic layer is chemically less stable in the case of aluminium than in the case of tantalum. The attack is initiated during the deposition of manganese oxide by pyrolysis from manganese nitrate solution and developed by the reform process. Solid aluminium capacitors often have a lower capacitance and higher initial leakage current than comparable solid tantalum units; however, the leakage current decreases on life tests and their reliability is high.

J. Brettle

N. F. Jackson

Failure Mechanisms in Solid Electrolytic Capacitors

This paper describes the preparation and properties of Langmuir (long-chain fatty-acid) films, for use as optical waveguides. It is shown how the refractive index and molecular thickness can be estimated by probing the films with a guided wave, and how such layers may be utilised to modify the propagation characteristics of pre-fabricated guiding structures. Cases of isotropic and anisotropic guides formed from such films are discussed, together with further uses of such films as cladding to guides and other materials.

C. W. Pitt

L. M. Walpita

Applications of Langmuir Films in Integrated Optics

R.  Hurditch

Electrochromic Displays

To compare the properties of anodized aluminium oxide layers an easy thickness determination method is wanted. Crevecoeur and De Wit used a method expressing the thickness in terms of peak voltages obtained by forming again after annealing. The aim of the work described here is to relate the value of the peak voltage to the thickness of the layer measured by ellipsometry.On specimens formed in an aqueous solution of b oric acid and ammonium hydroxide the following relation is found between the thickness d (nm) and peak voltage <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mi>p</mml:mi></mml:msub></mml:mrow></mml:math> (volt):d &#61; 1.020 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mi>p</mml:mi></mml:msub></mml:mrow></mml:math> + (0.00044 &#177; 0.00011) <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mi>V</mml:mi><mml:mi>p</mml:mi><mml:mn>2</mml:mn></mml:msubsup></mml:math>. On specimens formed in a solution of ammonium pentaborate in ethylene glycol the squared <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mi>p</mml:mi></mml:msub></mml:mrow></mml:math> term is of a lower value. however when <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>V</mml:mi><mml:mi>p</mml:mi></mml:msub></mml:mrow></mml:math> is less than 150 V the above relation holds for layers formed in both electrolytes, the systematic error then being less than 1&#37;.

R.  Van Schuur

The Determination of the Thickness of Anodic Al2O3 Film

Recently a greater understanding of the physics and chemistry of anodic oxide growth on III-V compound semiconductors has become available. These details are reviewed and critically assessed. With the data avilable now new device applications can be considered.

H. L. Hartnagel

Electrolytic Oxidation of Semiconductor Surfaces

Experiments on electroforming of Metal-Oxide-Metal thin film sandwiches which have been electroformed to exhibit voltage-controlled negative resistance are summarized and an outline of recent evidence in favour of localized or filamentary conduction is given.A similar review is given of the experiments on oxide sandwich structures which have been formed to exhibit current-controlled negative resistance or threshold switching and memory switching. Current theories are reviewed briefly. Finally oxide memory devices are compared with those based upon the chalcogenide glasses.

D. P. Oxley

Electroforming, Switching and Memory Effects in Oxide Thin Films

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Active and Passive Electronic Components provides a forum for the science and technology of all types of electronic components, and publishes experimental and theoretical papers on topics such as transistors, hybrid circuits and sensors.

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Active and Passive Electronic Components

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