Microelectronics in airborne equipment

WORLD

ABSTRACTS

ON MICROELECTRONICS

Microeleetronics in airborne e q u i p m e n t . B. MITCHELL, Electron. Engng. June (1970), p. 67. Over the past seven years, significant advances have been made in the design of airborne electronic equipment. These advances have been brought about by the use of integrated and hybrid circuits, and by the ingenuity displayed in applying and improving these techniques. In this article, the experiences of one company are used to illustrate how microelectronic technology has been applied in the design and development of interrogators, transponders, a.u.h.f./v.h.f, transceiver and integrated data systems. A 12 bit m o n o l i t h i c IC D to A c o n v e r t e r . V. O'DoNoGHUE, Microelectronics, July (1970), p. 19. Digital to Analogue converters translate a coded digital

7. S E M I C O N D U C T O R

INTEGRATED

T h e i n f l u e n c e o f d o n o r - a c c e p t o r pair f o r m a t i o n a n d s p a c e c h a r g e o n the f a b r i c a t i o n of p-n j u n c tions by diffusion. A. V. SHELLEYand R. H. Tm~DGOLO. Solid-St. Electron., Vol. 13 (1970), p. 1219. The combined effects of donor-acceptor pair formation and space charge on the fabrication of p - n junctions by diffusion are considered. Pair formation is described by a non-equilibrium second-order, rate equation and the space charge field by Zaromb's approximation. It is shown that the diffusion of a singularly ionized impurity of one type, into a semiconductor uniforrrdy doped with an impurity of the opposite type can, as the result of pair formation, produce relatively sharp, asymmetric junction profiles at considerable junction depths. T h e o r e t i c a l p h o n o n l i m i t e d e l e c t r o n m o b i l i t y in silicon. H. I. RALPH, Solid St. Commun. 8 (1970), p. 1095. The phonon limited electron mobility in silicon has been calculated from knowledge of the pseudopotential form factors. Account has been taken of the ion polarization in the presence of a phonon and agreement with experiment has been obtained within a factor of 2. Some sources of error which might lead to this disagreement have been pointed out. Carrier transport a c r o s s m e t a l - s e m i c o n d u c t o r barriers. C. Y. CHANG and S. M. SZE, Solid-St. Electron. 13 (1970), p. 727. Carrier transport across metal-semiconductor barriers has been studied theoretically and experimentally to give a generalized and quantitative presentation. The thermionic and tunneling processes have been analyzed in terms of accurate quantum transmission coefficients. The effects of image-force lowering, temperature, and two-dimensional variation of impurity concentration have also been incorporated in the theory. Theoretical results give a description of the current transport, due to combined effect of tunneling and thermionic emission over a temperature range from essentially absolute zero to the highest practical temperatures, and over doping densities

AND RELIABILITY

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signal into equivalent analogue voltages or currents for the purposes of controlling an instrument system or process in response to a flow of digitally coded commands. Originally developed for use in scientific computing applications, digital to analogue converters are used in hybrid computers and simulators as elements which perform the digital control of fixed or quasi-fixed functions such as potentiometer setting and initial condition setting. Because a D to A converter is the smallest conceptual function block in conversion systems - - a n d by this we mean the most general purpose circuit - - t h e areas of application are constantly widening. This is brought about principally by two factors. T h e first being the availability of D to A building blocks at very low cost and the need for higher operating speeds in general electronic systems and equipments.

CIRCUITS, DEVICES AND MATERIALS from 1014 cm -a to complete degeneracy. An interesting result of the analysis is the existence of a minimum in the saturation current density ffs near 10 te cm-a; the current density rises slightly at lower dopings because of enhanced transmission coefficient for thermionic emission and increases drastically at higher dopings because of tunneling. For example, for PtSi-Si system at 300°K with a barrier height of 0"85 eV, .78 is 80 nA/cm 2 at 1014 cm -a, reaches a minimum of 60 nA/cm ~at 10 TMcm -3, then rapidly increases to 10 a A/cm 2 at 10 ~° cm -a. In the high doping range the average saturation current density is considerably increased by the effect of twodimensional impurity variation. The room-temperature transition doping for breakdown in metal-silicon systems occurs at 8 × 1017 cm-a; for lower dopings the breakdown is due to avalanche multiplication, and for higher dopings it is due to tunneling of carriers from the metal Fermi level to semiconductor bands. The metal-silicon diodes were fabricated by planar technology with guardring structures to eliminate edge effects. Extensive experimental studies, including current-voltage, capacitance-voltage, and photoelectric measurements covering the doping range from 1014 to 1020 cm -2 and the temperature range from 77 to 373°K, gave good agreement with theoretical predictions.

Q u a n t u m m e c h a n i c a l c a l c u l a t i o n o f the c a r r i e r distribution a n d the t h i c k n e s s o f the i n v e r s i o n l a y e r o f a M O S field-effect transistor. A. P. GNADINGER and H. E. TALLEY, Solid-St. Electron. 13 (1970), p. 13001. The carrier distribution in the inversion layer of a MOS-structure at room temperature was calculated assuming a quantization of the allowed energy elevels at the surface and a linear electrostatic potential. It was found that for strong inversion the carrier distribution deviates considerably from the one found by using classical statistics but approaches the classical limit for weak inversion when many electric subbands are occupied. A new definition for the channel thickness was introduced based on the integrated