L. J. Varnerin

Stored Charge Method of Transistor Base Transit Analysis

A base layer transit time analysis has been made for high-frequency transistor base donor distributions. Transit time is defined as stored charge per unit emitter current. The emphasis on the stored charge/current ratio is particularly pertinent to high-frequency performance and facilitates qualitative analyses. The analysis applies to a p-n-p transistor in which the base donor density at the emitter (which specifies emitter breakdown voltage and emitter capacity for an alloyed emitter) and total number of donors per unit area of the base (which determines base resistance and emitter to collector punch-through voltage) are specified. It is shown that shorter transit times result with retarding fields since smaller base thicknesses are possible. It is thus shown that a built-in field is of lesser importance in determining transit time than is base thickness.

Trapping of Helium Ions and the Re‐Emission of Trapped Atoms from Molybdenum

The electrical cleanup of helium on molybdenum surfaces has been investigated. In this case, the phenomenon can be described by a trapping of ions upon impact with the surface. Measurements of the trapping efficiency η (atoms removed/ions collected) have been made over a range of ion energies from 150 to 2600 ev. The re‐emission of trapped helium atoms was investigated in detail. The contribution of re‐emission to the pumping process is described by a phenomenological theory. The results indicate that the trapping efficiency is lowered by a short time re‐emission of trapped atoms. Through the long‐time re‐emission of atoms, the theory accounts quantitatively for the observed saturation of the cleanup process.

Approaches for making bubble-domain materials

The garnet materials system has provided the basis for a rapid fundamental transformation of cylindrical magnetic bubble-domain materials technology from one based on bulk single crystals to one based on epitaxy. Recent developments are reviewed in an effort to provide some perspective on the nature of this transformation and its promise for exploitation. The intrinsic adaptability of the garnet system has permitted high degrees of substrate-epitaxial film lattice matching along with structural and chemical compatibility. As a result, it has been possible to grow liquid-phase hetero-epitaxial films with the ease and simplicity usually associated with homoepitaxy, while yet retaining the flexibilities of heteroepitaxial systems. These films thus exhibit only a few defects per square centimeter and have been used with 10 000-step shift registers. The rare-earth gallium garnet substrate growth capabilities are also described as well as chemical-vapor deposition epitaxial technology and its comparison with liquid-phase epitaxy.

A perspective on magnetic materials for bubble mass memories

Recent advances in the liquid phase epitaxial growth of rare earth magnetic garnet films have enhanced prospects for a bubble mass memory. It is the purpose of this paper to review the status of materials in order to achieve some perspective. Principal problems are those of uniformity, reproducibility, and defect control. Good uniformity of LPE films has been achieved. Recent phase diagram data based on the garnet oxides in PbO-B 2 O 3 fluxes show that high orders of compositional and growth temperature control are required for reproducibility but are within the state of the art. Defect control, which is closely related to dislocation formation, seems not to be a limiting problem, attributable largely to the high energy of formation of dislocations in the garnets. Thus, even interfacial or mismatch dislocations do not form in these heteroepitaxial structures.

Operation of a Microwave Garnet Limiter

It is now possible to design a class of low level, milliwatt range ferrimagnetic microwave limiters which exhibit distinctive characteristics and important advantages over previously reported ferrimagnetic limiters. The limiter characteristically consists of a microwave transmission cavity containing as a nonlinear element a large single crystal spherical sample of yttrium iron garnet (YIG) biased to the subsidiary absorption by a dc magnetic field perpendicular to the rf magnetic field. Garnet losses increase with power above the subsidiary absorption threshold and result in a nonlinear decline in cavity Q which limits the output power. Large filling factors are needed for a significant limiting range and the large YIG single crystals now available make this limiter practical. At a given frequency the limiting threshold can be varied with the bias magnetic field, in contrast to gyromagnetic coupler limiters.