R. R. O'Brien

Analysis of the impurity atom distribution near the diffusion mask for a planar p-n junction

Presented here are the results from a mathematical investigation of the impurity atom distribution within a planar p-n junction. Two fundamentally different diffusion processes are considered: In the first, a constant impurity atom concentration is maintained at the semiconductor surface; in the second, a fixed quantity of impurity atoms is involved in the entire diffusion process. The results of this investigation show than a one-dimensional approximation inadequately characterizes the impurity atom distribution within a planar junction, and that in theory, the planar junction is not at a constant distance from its impurity atom source. Instead, the junction is closer to its source at the semiconductor surface than deep within the bulk material. Further, it is shown that when diffusion takes place from a source of constant concentration density, the junction impurity atom gradient is maximum at the semiconductor surface. In contrast, this junction impurity atom gradient is shown to exhibit a minimum at the semiconductor surface when the total number of impurity atoms is time invariant throughout the entire semiconductor material.

Dynamics of Charge Collection from Alpha-Particle Tracks in Integrated Circuits

We studied the transient characteristics of charge collection from alpha-particle tracks in silicon devices. We have run computer calculations using the finite element method, in parallel with experimental work. When an alpha particle penetrates a pn-junction, the generated carriers drastically distort the junction field. After alpha particle penetration, the field, which was originally limited to the depletion region, extends far down into the bulk silicon along the length of the alpha-particle track and funnels a large number of carriers into the struck junction. After less than one nanosecond, the field recovers to its position in the normal depletion layer, and, if the track is long enough, a residue of carriers is left to be transported by diffusion. The extent of this field funneling is a function of substrate concentration, bias voltage, and the alpha-particle energy.

A statistical approach to the design of diffused junction transistors

Monte Carlo methods of statistical analysis are applied to the problems of transistor design and optimization. The experimental tolerances associated with any diffusion process are shown to represent an important factor in the initial design of diffused junction transistors. Many transistor parameters exhibit a substantial degree of sensitivity to small variations in the diffusion process. This is confirmed by a comparison between the theoretical and experimental open-base breakdown voltage, and current gain, for a large number of devices. It is therefore proposed that the design of a transistor be based upon attaining a specified set of electrical characteristics when the device is assumed to be fabricated by a non-ideal diffusion process. An electronic computer has been used in an investigation of the foregoing problem. The investigation shows further that a margin-of-safety must be designed into each electrical parameter of a transistor to assure that the resulting device satisfies a given set of design specifications, even though this margin-of-safety may differ for each parameter. In this paper examples are presented to illustrate the theoretical trade-off between several opposing transistor parameters that exhibit a substantial degree of variability due to a non-ideal diffusion process.

Depletion Layer Properties in Double Diffused Transistors

ABSTRACT For the double diffused transistor, Poissons equation is solved in one dimension; this solution is used to determine depletion layer properties of its collector and emitter junctions. Assuming an impurity atom distribution characterized by the summation of complementary error functions, depletion layer widths are established far the equilibrium emitter junction and for the reverse biased collector junction. Applications of this analysis are presented throughout a wide range of physical and geometrical parameters; graphical illustrations are given for the electrical base width, the collector ‘ punch-through ’ voltage, and others.

Open-base Breakdown in Diffused N-P-N Junction Transistors†

ABSTRACT A one-dimensional analysis is presented on the open-base breakdown characteristics of diffused n-p-n transistors. From breakdown voltage measurements upon selected devices—in conjunction with breakdown voltage calculations—‘ effective ’ values are established for the ionization rate of electrons in germanium and silicon p-n junctions, when biased substantially below avalanche breakdown. These ‘ effective ’ electron ionization rates are used to calculate the open-base breakdown voltage for transistors exhibiting a large collector punch-through voltage ; such calculations are graphically illustrated throughout iv range of parameters applicable to many practical situations. A discussion is also presented on the influence of an abrupt conductivity increase within the collector junction space-charge layer, of the typo encountered in an idealized epitaxial structure.