MEMORY DATABOOK - Al Kossow's Bitsavers

• RELIABILITY INFORMATION .'-------------------D51 Aluminum CorrosionAluminum corrosion is due to electro/ytic reactionscaused by the presence of water and minute impurities.When aluminum dissolves, lines break. This problem isunique to the plastic capsules now used widely to reducecosts. Oki Electric has carefully studied the possiblecause and effect relationship between structureand manufacturing conditions on the one hand, andthe generation of aluminum corrosion on the other.Refinements incorporated in Oki LSls permit superiorendurance to even the most severe high humidityconditions.61 Alpha-Particle Soft FailureThis problem occurs when devices are highly miniaturized,such as in 64-kilobit RAMs. The inversion ofmemory cell data by alpha-particle generated by radioactiveelements like uranium and thorium (present inminute quantities, measured in ppb) in the ceramicpackage material causes defects. Since failure is onlytemporary and normal operation restored quickly, thisis referred to as a "soft" failure. At Oki Electric wehave eliminated the problem by coating the chip surfaceof 64-kilobit RAMs with a resin which effectivelyscreens out these alpha-particle.71 Degradation in Performance Characteristics Due toHot ElectronsWith increased miniaturization of circuit elements,internal electric field strength in the channels increasessince the applied voltage remains the same at 5 V. Asa result, electrons flowing in the channels, as shown inthe accompanying diagram, tend to enter into the oxidefilm near the drain, leading to degradation of performance.Although previous low-temperature operationtests have indicated an increase of this failure, we haveconfirmed by our low-temperature acceleration tests,including checks on test element groups, that no suchproblem exists in Oki LSls.Drain~VD+VG IG~ :SourceHot electronDrainPackage ceramicSubstrate silicon-'-"-----'7"'"""-''-:---'-'--:+--'---:--O''''-'=C-:CC-:- S iii co n ox i de..:,-::,,:,-., =::..:..:.:..:.;o..:...=rF:':"':"--'--"-'-'j-"=-'-'-'- fi I mp/ a-particleIonization alongthe a-particle pathSubstrate siliconCharacteristic deterioration caused by hot electronWith further progress in the miniaturization of circuitcomponents, failures related to pin hole oxide filmdestruction and photolithography have increased. Toeliminate these defects during manufacturing, we atOki Electric have been continually improving our productionprocesses based on reliability tests and informationgained from the field. And we subject all devicesto high-temperature burn-in screening for 48 to 96hours to ensure even greater reliability.32