World Abstracts on Microelectronics and Reliability
Solid-state power relays enter the IC era. ALEXANDERL1DOW and WILLIAM COLLINS. Electronics, 59 (29 December 1982). S3X technology installs an optically coupled bipolar transistor, n - M O S devices, and a thyristor in C-MOS-type n wells.
been used on 1K RAMS. The RAMs functioned reliably at a dose of 2 x 105 Rad(Si) and failed at a dose of 5 × l0 s Rad(Si). The 1K RAM is capable of operating from 7.5 to 12 volts and has an access time from address change of 160nsec at 10 volts.
A radiation hardened 256 x 4 bulk CMOS RAM. L. S. NAPOLI, R. K. SMELTZER, R. DONNELLY and J. YEH. RCA Rev. 43, 458 (1982). A radiation hardened version of the C2L process has been developed that utilizes all-low-temperature processes subsequent to channel oxidation. This process has
Multiprocessor architecture tunes in to transaction processing. KENNETH I. COHEN. Electronics, 94 (27 January 1983). Dependable, modular, instruction-set-independent system can be expanded in small increments and easily adopt higher-performance microprocessors.
7. S E M I C O N D U C T O R
Moderate inversion in MOS devices. YANNIS TSIVIDIS. SolidSt. Electron. 25 (11), 1099 (1982). The region of validity of c o m m o n approximations for weak and strong inversion is examined. It is shown that at the lower limit of what is often defined as strong inversion region, incremental quantities such as transconductance can be an order of magnitude smaller than the value predicted by using c o m m o n strong inversion approximations. It is suggested that the limits of validity of widely used approximations for various quantities in weak and strong inversion can be judged by the value of a single parameter, namely the ratio of the inversion layer capacitance to the sum of the oxide capacitance and the depletion region capacitance. It is shown that in the region where this parameter takes values above 0.1, weak inversion approximations are in serious error; similarly, in the region where this parameter takes values below 10, strong inversion approximations are in serious error. The definition of a "moderate inversion region" between the above two limit points is proposed. The width of this region is calculated for a variety of process parameters and values of the quasiFermi potential difference, and is found to exceed 0.5 V in m a n y cases. The accuracy of commonly used approximations for the extrapolated threshold voltage is examined. A re-extrapolation technique in Newton-Sor computer simulation of semiconductor devices. CHENG T. WANG. Solid-St. Electron, 25 (11), 1083 (1982). A novel extrapolation technique which learns from the failure of previous linear extrapolation result and subsequently changes the extrapolation scale accordingly is found to be very useful in dealing with the divergence problem in Newton-Successive Over Relaxation (SOR) computer simulation of semiconductor devices. The algorithm and an example are described in this paper. On the analysis of diffusion length measurements by SEM. C. DONOLATO. Solid-St. Electron. 25 (11), 1077 (1982). A simpler analysis is given of the diffusion problem related to the scanning electron microscope measurements of bulk diffusion lengths in semiconductors using scanning normal to a p-n junction or a Schottky barrier. The current profile due to a point source is obtained in form of the Fourier transform of an expression containing elementary functions only. It is shown that this form can be readily adapted to include the presence of a back ohmic contact and allows an easier discussion of the case of an extended generation. Review paper. Approximations for Fermi-Dirac integrals, especially the function ~ 1/2 01) used to describe electron density in a semiconductor. J. S. BLAKEMORE. Solid-St. Electron. 25 ill), 1067 (1982). The history of studies of the family of Fermi Dirac integrals is briefly reviewed, and the relevance of these integrals to transport properties via the Boltzmann transport equation is noted. The role of the integral (2/x/n)F1/2(~l)==-o~1;2(~)~ U in relating reduced Fermi energy r/ to electron density in a "'parabolic" band makes it especially important that this member of the family be capable of expression in approximate forms of reasonable accuracy. High precision series forms, and published tabula-
tions, for the various members of the family are noted, and the remainder of the paper deals with approximations that have been proposed for u(r/) and for r/(u). The former permits deduction of carrier density from Fermi energy, and the latter permits the inverse. Successful expressions for each purpose are described, with graphs of the error so incurred. On early stage degradation in Zn diffused GaAs LED. C. COGNETTI, M. CONTI and G. CHIARETTL Solid-St. Electron. 25 (11), 1093 (1982). Life tests performed at high temperature on zinc-diffused GaAs LED show a decrease of emitted power which is accompanied by an apparent shift of the peak emission toward shorter wavelengths. This shift is also noted in photoluminescence and photoconduction spectra. A careful analysis of these measurements reveals that the effect must be attributed to a change in absorption coefficient of the zinc-diffused front region, surface recombination velocity and electron diffusion length remaining essentially constant. Laser irradiated LEDs also show this effect; consequently it has to be attributed to a recombination activated degradation of the P region, possibly zinc precipitation.
The role of germanium in evaporated Au-Ge OHMIC contacts to GaAs. A. ILIADIS and K. E. SINGER. Solid-St. Electron. 26 (1), 7 (1983). Auger depth profiling, electron probe microanalysis, electron beam induced current and conventional scanning electron microscopy have been used to study the inhomogeneous reaction which takes place during the alloying of evaporated A u - G e films on (100), n-type GaAs. These measurements have been correlated with I V and C - V data taken for heat treatment below the A u - G e eutectic temperature (360°C) and specific contact resistance measurements above 360°C. The picture which emerges is that of the key role of the germanium in the metallurgical reaction, in addition to its accepted role as the n + dopant. A simple metallurgical model is proposed which is based on the A u - G e being the main reactive system at the interface responsible for the formation of the rectangular particles which are the pathways for the current. Minimum contact resistance correlates with the m a x i m u m growth of these particles. Deposition and properties of RF reactively sputtered SiO2 layers. J. KORTLANDTand L. OOSTING. Solid St. Technol., 153 (October 1982). Silicon dioxide layers were deposited on silicon by rf reactive sputtering using a high purity Si target in an oxygen ambient. The sputtered SiO2 was subsequently used as the dielectric in MOS capacitors with aluminium as gate material. The parameters which were varied include the oxygen pressure during sputtering, the target substrate distance and the AI evaporation method. The mobile ion density, No, is 1-2 x 1017 m -2 in MOS structures in which the AI of the gate was evaporated from a tungsten boat and less than 5 × 1014m -2 for e-gun evaporated A1. The number of interface states, Ns~, obtained from the C - V characteristics of MOS devices fabricated from "as-deposited" rf sputtered oxide is 1.7 × 1015 m - 2 . A heat treatment above 750°C prior to the AI evaporation reduces Ns., to 2.5 6 × 1014m 2 but increases N,,.