High Permittivity Materials Research Articles

Use of high-relative-permittivity materials in high-delay coaxial lines

The delay characteristics of a common type of electromagnetic delay line are considered as both an unshielded line and a shielded line filled with materials of high relative permittivity.

Suppression of travelling high-field-domain mode oscillations in GaAs by dielectric surface loading

It is shown that travelling high-field-domain-mode oscillations in GaAs, with n0l > 1012cm-2, can be suppressed by attaching a dielectric material of high permittivity (BaTiO3) to the surfaces of the GaAs. Experimental results observed with a sampling oscilloscope are given.

Dielectric Relaxation in Strontium Titanate Solid Solutions Containing Lanthania

The dielectric properties of solid solutions in the system SrTiO3-La2/3TiO3 were measured in a frequency range from 200 to 105 Hz and at temperatures from -190 to 400°C. The relative permittivity of the solid solutions is lower that of pure SrTiO3 and pronounced dielectric nonlinearity was not observed. Two separate groups of dielectric relaxation peaks were observed, a low temperature relaxation which occured in a temperature region below room temperature and a higher temperature process which occured at about 200°C. The experimental results were analyzed in the light of current theories for relaxation in high permittivity materials. It is suggested that the higher temperature relaxation is associated with a Maxwell-Wagner phenomenon due to the different properties of grain and grain boundaries in the ceramic specimen. For the lower temperature process the evidence is compatible with an ionic model of the Debye type. It is suggested that the existence of the A site vacancy in the perovskite ABO3 lattice introduced by the lanthanum substitution distorts the oxygen octahedron, producing more than one possible “non central” sites for the Ti4+ ion. The relaxation arises from the thermal motion over potential barriers separating these alternative sites.

Microminiaturization by thin film and solid circuit techniques

Surface problems in substrates for microcircuits, including methods of measuring substrate cleanliness by radioactive tracer techniques, are discussed. The growth of nuclei in thin films is described and illustrated and deposition techniques for nickel-chromium alloys to form resistors are described in detail, including recently developed stainless-steel resistors. Dielectric films have been studied and nucleation mechanisms for some types of dielectric are outlined. Problems of stress and strain in thin films are also investigated. Reactive sputtering techniques for films of higher permittivity materials are described and details of capacitors given. Practical details of packing density, etc., using microcircuits prepared by these processes are described, and layouts and possible construction methods are suggested. Multiple layer thin film constructions are also described. On semiconductor solid circuits, unijunction transistors have been fabricated in many ways and diffusion, masking, etc., techniques are described for resistors and capacitors. U.S.A. work on computer elements, including the combination of solid circuit elements into complete circuit functions, is described. The hybrid concept of microminiaturization is given and it is concluded that increased reliability can be obtained by the use of solid circuit microminiature techniques combined with the intelligent use of redundancy.

An improved resonant-cavity method of measuring high-frequency losses in materials

The measurement of h.f. losses in a sample of material is often made by observing the reduction in the Q-factor of a resonant cavity when the sample is introduced into it. Unfortunately, materials of high permittivity and large losses tend seriously to disturb the distribution of the field in the cavity and thus to make precise measurements difficult. In the present proposal an attempt is made to avoid that problem by placing the sample not in the cavity itself but in a short length of evanescent guide coupled to it. The case is discussed of a cavity resonant in the H01 mode and coupled through the end wall to a corresponding evanescent guide into which the sample can be introduced, and it is shown that this arrangement should be capable of yielding accurate values of loss tangent for such materials as semiconductors, which present difficulties in conventional equipment.

A junction ceramic capacitor

A new type of ceramic capacitor is described. A novel construction enables thin insulating layers of a high-permittivity material to be formed in such a manner that they are mechanically strong. The thickness of the layers is controllable, so that capacitances ranging from 0.5μF at 3 V to 0.05μF at 200 V are possible. The units have the form of discs of 1 cm2 area per side and a thickness of 0.1 cm. The junction ceramic capacitor is suitable for coupling and by-passing applications, particularly in transistor circuits, where it should be an inexpensive replacement for more conventional types. The construction and electrical characteristics of the new capacitor are given.

Resonance and supergain effects in small ferromagnetically or dielectrically loaded biconical antennas

The input impedance and the radiation pattern of thin biconical antennas which contain materials of high dielectric permittivity <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\epsilon</tex> and high magnetic permeability <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu</tex> can be evaluated by methods due to Schelkunoff and Tai. Examination of numerical results shows that resonances of the input impedance are obtainable for antenna lengths much shorter than that of the ordinary half-wave dipole. It becomes also apparent, however, that the impedance bandwidth at these resonances is narrow and decreases with increasing <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\epsilon</tex> and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\mu</tex> . Analysis of the pertinent equations leads to the following conclusions concerning radiation patterns: 1) The pattern of an antenna which is small in terms of free-space wavelengths <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda</tex> and is also small in terms of material wavelengths, <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\lambda/\sqrt{\mu\epsilon}</tex> , is essentially that of a small current element in air; 2) If the biconical antenna is small in terms of free-space wavelengths, but is large in terms of material wavelengths the radiation pattern is also that of a small current element, except in certain well defined and very narrow frequency bands where multilobe or narrow lobe patterns appear. A similar "supergain" effect has been noted by Knudsen [33] in his discussion of small loops which carry currents of varying phase.

The measurement of the dielectric properties of high-permittivity materials at centimetre wavelengths

The measurement of the dielectric properties of high-permittivity materials at centimetre wavelengths

The measurement of the dielectric properties of high-permittivity materials at centimetre wavelengths

The measurement of the dielectric properties of high-permittivity materials at centimetre wavelengths

The measurement of the dielectric properties of high-permittivity materials at centimetre wavelengths

The paper gives the results of room-temperature measurements on ceramic (polycrystalline) specimens of magnesium, calcium, strontium and barium titanates at frequencies of 1.5 and 9450 Mc/s (3.18 cm), and on barium titanate at 24000 Mc/s (1.25 cm). It is found that the latter material is unique among this series in showing a considerable fall in permittivity, and a large increase in the loss tangent, at the higher frequencies, compared with the behaviour at 1.5 Mc/s. Variable temperature measurements on barium titanate show that the crystallo-graphic change which is known to occur around 120°C, the Curie point of the material, affects the permittivity at 9450 and 1.5 Mc/s in an analogous manner. Room-temperature measurements at the same frequencies on a range of barium-strontium titanate compositions are also described, and attention is drawn to the composition 56% BaTiO3: 44% SrTiO3, having a permittivity of 760 and loss tangent of 0.02 at 9450 Mc/s and 20°C, as likely to be of value in microwave work. The difficulties associated with the measurement of high-permittivity values at centimetre wavelengths are discussed, and a full description is given of the three methods developed for different parts of the investigation.