Use of tests at elevated temperatures to accelerate the life of an m.o.s. integrated circuit

Assurances of a long service life will often be demanded of m.o.s. integrated circuits used in telecommunication equipment. An attempt has accordingly been made to identify failure risks and devise life-prediction procedures by accelerated testing, ambient temperature being the primary stress variable. The test vehicle, manufactured on a volume production line, had a simple circuit configuration permitting direct access to its constituent transistors and allowing each of them to be operated under different electrical conditions. The parameters monitored included threshold voltages, both of the transistors and of a spurious device, gain factors, transistor resistances (in the conduction mode), leakage currents and protective-diode breakdown voltage. The most significant response was obtained from the transistor threshold voltages, which change substantially but in a manner consistent both with the electrical operating conditions and with known physical theories of charge instability in the m.o.s. system. It is suggested that at least the drift of transistor threshold voltage is amenable to a life-prediction procedure, and it is shown how the results could be exploited for procurement-specification purposes.