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Investigations of gold surface-state energy levels in gold-doped MOS transistors
World Abstracts on Microelectronics and Reliability
377
(September 1979). The electrical properties of transistors and quartz crystal oscillators whose packages were tin-plated after assembly of the components show unstable behaviour when exposed to elevated temperatures during storage. Mass spectrometric investigations have shown that water vapor inside the package is the cause. Several possibilities of water vapor formation during temperature storage are described in this paper. The increase of collector leakage current of transistors as well as the decrease of the resonant frequency and the increase of the series resistance of quartz crystal oscillators are also explained. Possibilities for the prevention of the action of water vapor in packages now in use are discussed. A new type of package is described which prevents the formation of water vapor within it.
Investigations of guld surface-stute energy levels in gold-doped MOS transistors. G. R. MOGHAL. Int. J. Electron. 47, (2) 107 (1979). Measurements of threshold voltage for conduction of both p- and n-channel gold-doped and non-gold-doped MOS (111) transistors with variation in temperature from 300 K to 80 K reveal two blocks of gold acceptor s?,lrface states. One is at 0.12eV from the conduction band edge and the other at 0.1 eV from the valence band edge and a further rise in surface state charge close to the valence band edge, suggests another gold energy level near the band edge. Hall-effect measurements also confirm these gold energy levels near the band edge.
Aging of solder connection to Ti-Pd-Au films. PETER M. HALL and LLOYD W. CONDRA. IEEE Trans. Components, Hybrids, Mfg Technol. Chmt-2, (3) 279 (September 1979). Soldered connections to TiPdAu film composites show enhanced resistance changes (up to 0.02 ohms) during elevated temperature aging. This is attributed to solid-state dissolution by solder of Au from under the fillet edge, forming a AuSn intermetallic phase. The pull strength of soldered external leads decreases by as much as 40 percent during aging, probably by solid-state dissolution of Pd, forming PdSn4. Neither of these effects is expected to be troublesome at normal operating temperatures.
Analysis of the effects of mechanical stress on the properties of p-channel MOS structures. Part I. Choice of the theoretical model The effect of stress on the valence hand structure in silicon. BOGDAN MOESCHKE. Electron Technol. 12, (1) 29. The effect of mechanical stress on the properties of silicon P/MOS structure is analyzed theoretically and experimentally from the viewpoint of possible application of this structure as a direct pressure transducer. The choice of the theoretical model of the investigated structure is given. The effect of stress on the valence band structure in silicon is considered. Further theoretical and experimental results will be presented in Part II of the paper.
3. C I R C U I T
AND
SYSTEMS
RELIABILITY,
MAINTENANCE
AND
REDUNDANCY
Optimal number of minimal repairs before replacement. KYUNG S. PARK. IEEE Trans. Reliab. R-28, (2) 137 (June 1979). This paper presents a model for determining the optimal number of minimal repairs before replacement. The basic concept parallels the periodic replacement model with minimal repair at failure introduced by Barlow & Hunter, the only difference being the replacement is signaled by the number of previous minimal repairs performed on the unit. In the case of Weibull distribution, which is widely used for failures, the optimal solution is simple and more cost effective compared to Barlow & Hunter's Policy II.
Evaluation of equipment reliability. S. HOWARD. Proc. Internepcon, Brighton, U.K., October 1978, p. 74. Equipment reliability is becoming increasingly important in many fields of industrial application, particularly when the equipment is used to control high risk processing plants such as those containing associated hazards to the public and personnel also plants where unnecessary shutdowns would be prohibitively costly. Where these conditions present themselves it becomes necessary to quantify equipment reliability. This usually takes the form of equipment failure rates for the various modes of failure.
Vibration, shock and intense noise testing for reliability. WAYNE TUSTIN. IEEE Trans. Reliab. R-28, (2) 129 (June 1979). Avionic units (particularly those used aboard highperformance aircraft and missiles) should be tested with vibration, shock, and intense noise. The goal of such laboratory-testing is to identify weaknesses so that corrective steps toward high reliability can be taken. Test equipments and their applications to simulating potentially damaging environments are considered. These subjects are noteworthy because of the 1977 revision of MIL-STD-781C.
Parameter estimation with noncontinuous inspection. D. N. P. MURTHY. IEEE Trans. Reliab. R-28, (2) 148 (June 1979). The maximum likelihood and moments methods are discussed for estimating the parameters of reliability models with intermittent inspection. In such a formulation, the actual failure time is not known, because failure is detected only at the first inspection time after the failure. For the exponential distribution, both methods yield the same result.
The interpretation of failure data using Weiholl plots. M. BEASLEY. Proc. Internepcon, Brighton, U.K., October 1978, p. 148. Life testing of components of equipment is always expensive and often yields only a sparse amount of data. It is thus vitally important that the most accurate predictions about the total population should be drawn from the sample data. It is usual to plot times-to-failure in a cumulative distribution. It is suggested that the use of median ranking gives optimum results in the long run and a simple method of calculating ranks is given. Ranking methods may be used in plotting any type of cumulative distribution but they are especially useful in connection with the Weibull distribution. The effects of infant failures and wear-out are shown by plotting artificial data. A practical example of real data is given and some conclusions are drawn from it. M.R. 20/3A---N
Improvement of supervision schedules for protective systems. TOSHIYUKI INAGAKI, KOICHI INOUE and HAJIME AKASHI. IEEE Trans. Reliab. R-28, (2) 141 (June 1979). Improvement of supervision schedule is considered for protective-systems of multiple components. Each component is periodically supervised. Our improvement procedure consists of two steps. (1) Determine the time length of supervision and duration of successive supervisions which maximize the minimum point availability for simultaneous supervision schedule where all components are supervised simultaneously. (2) Improve the supervision schedule of Step 1 by constructing a staggered supervision schedule. In this schedule components are divided into subgroups, and supervisions of subgroups are staggered while components in the same subgroup are supervised simultaneously. A systematic method is given to optimize allocating components into subgroups for a specified number of subgroups and staggering of supervisions. An example illustrates the method.
377
(September 1979). The electrical properties of transistors and quartz crystal oscillators whose packages were tin-plated after assembly of the components show unstable behaviour when exposed to elevated temperatures during storage. Mass spectrometric investigations have shown that water vapor inside the package is the cause. Several possibilities of water vapor formation during temperature storage are described in this paper. The increase of collector leakage current of transistors as well as the decrease of the resonant frequency and the increase of the series resistance of quartz crystal oscillators are also explained. Possibilities for the prevention of the action of water vapor in packages now in use are discussed. A new type of package is described which prevents the formation of water vapor within it.
Investigations of guld surface-stute energy levels in gold-doped MOS transistors. G. R. MOGHAL. Int. J. Electron. 47, (2) 107 (1979). Measurements of threshold voltage for conduction of both p- and n-channel gold-doped and non-gold-doped MOS (111) transistors with variation in temperature from 300 K to 80 K reveal two blocks of gold acceptor s?,lrface states. One is at 0.12eV from the conduction band edge and the other at 0.1 eV from the valence band edge and a further rise in surface state charge close to the valence band edge, suggests another gold energy level near the band edge. Hall-effect measurements also confirm these gold energy levels near the band edge.
Aging of solder connection to Ti-Pd-Au films. PETER M. HALL and LLOYD W. CONDRA. IEEE Trans. Components, Hybrids, Mfg Technol. Chmt-2, (3) 279 (September 1979). Soldered connections to TiPdAu film composites show enhanced resistance changes (up to 0.02 ohms) during elevated temperature aging. This is attributed to solid-state dissolution by solder of Au from under the fillet edge, forming a AuSn intermetallic phase. The pull strength of soldered external leads decreases by as much as 40 percent during aging, probably by solid-state dissolution of Pd, forming PdSn4. Neither of these effects is expected to be troublesome at normal operating temperatures.
Analysis of the effects of mechanical stress on the properties of p-channel MOS structures. Part I. Choice of the theoretical model The effect of stress on the valence hand structure in silicon. BOGDAN MOESCHKE. Electron Technol. 12, (1) 29. The effect of mechanical stress on the properties of silicon P/MOS structure is analyzed theoretically and experimentally from the viewpoint of possible application of this structure as a direct pressure transducer. The choice of the theoretical model of the investigated structure is given. The effect of stress on the valence band structure in silicon is considered. Further theoretical and experimental results will be presented in Part II of the paper.
3. C I R C U I T
AND
SYSTEMS
RELIABILITY,
MAINTENANCE
AND
REDUNDANCY
Optimal number of minimal repairs before replacement. KYUNG S. PARK. IEEE Trans. Reliab. R-28, (2) 137 (June 1979). This paper presents a model for determining the optimal number of minimal repairs before replacement. The basic concept parallels the periodic replacement model with minimal repair at failure introduced by Barlow & Hunter, the only difference being the replacement is signaled by the number of previous minimal repairs performed on the unit. In the case of Weibull distribution, which is widely used for failures, the optimal solution is simple and more cost effective compared to Barlow & Hunter's Policy II.
Evaluation of equipment reliability. S. HOWARD. Proc. Internepcon, Brighton, U.K., October 1978, p. 74. Equipment reliability is becoming increasingly important in many fields of industrial application, particularly when the equipment is used to control high risk processing plants such as those containing associated hazards to the public and personnel also plants where unnecessary shutdowns would be prohibitively costly. Where these conditions present themselves it becomes necessary to quantify equipment reliability. This usually takes the form of equipment failure rates for the various modes of failure.
Vibration, shock and intense noise testing for reliability. WAYNE TUSTIN. IEEE Trans. Reliab. R-28, (2) 129 (June 1979). Avionic units (particularly those used aboard highperformance aircraft and missiles) should be tested with vibration, shock, and intense noise. The goal of such laboratory-testing is to identify weaknesses so that corrective steps toward high reliability can be taken. Test equipments and their applications to simulating potentially damaging environments are considered. These subjects are noteworthy because of the 1977 revision of MIL-STD-781C.
Parameter estimation with noncontinuous inspection. D. N. P. MURTHY. IEEE Trans. Reliab. R-28, (2) 148 (June 1979). The maximum likelihood and moments methods are discussed for estimating the parameters of reliability models with intermittent inspection. In such a formulation, the actual failure time is not known, because failure is detected only at the first inspection time after the failure. For the exponential distribution, both methods yield the same result.
The interpretation of failure data using Weiholl plots. M. BEASLEY. Proc. Internepcon, Brighton, U.K., October 1978, p. 148. Life testing of components of equipment is always expensive and often yields only a sparse amount of data. It is thus vitally important that the most accurate predictions about the total population should be drawn from the sample data. It is usual to plot times-to-failure in a cumulative distribution. It is suggested that the use of median ranking gives optimum results in the long run and a simple method of calculating ranks is given. Ranking methods may be used in plotting any type of cumulative distribution but they are especially useful in connection with the Weibull distribution. The effects of infant failures and wear-out are shown by plotting artificial data. A practical example of real data is given and some conclusions are drawn from it. M.R. 20/3A---N
Improvement of supervision schedules for protective systems. TOSHIYUKI INAGAKI, KOICHI INOUE and HAJIME AKASHI. IEEE Trans. Reliab. R-28, (2) 141 (June 1979). Improvement of supervision schedule is considered for protective-systems of multiple components. Each component is periodically supervised. Our improvement procedure consists of two steps. (1) Determine the time length of supervision and duration of successive supervisions which maximize the minimum point availability for simultaneous supervision schedule where all components are supervised simultaneously. (2) Improve the supervision schedule of Step 1 by constructing a staggered supervision schedule. In this schedule components are divided into subgroups, and supervisions of subgroups are staggered while components in the same subgroup are supervised simultaneously. A systematic method is given to optimize allocating components into subgroups for a specified number of subgroups and staggering of supervisions. An example illustrates the method.