Use of an Ion Microbeam to Study Single Event Upsets in Microcircuits

A beam of energetic ions has been used to study the upset sensitivity of various device elements on 16K dynamic RAMs. Small beam defining apertures, ranging in size from 2.5 micrometers in diameter to a 250 by 1100 micrometer rectangular aperture, were used to produce microbeams of protons, helium ions, and nitrogen ions, although most of the work reported here was performed using helium ions. Upset rates were measured as a function of 4He ion energy from 1.6 to 3.5 MeV on different areas on the same device and on devices from different manufacturers. Different threshold energies and sensitivities were found for sense amplifiers, normal cell areas, and inverted cell areas. In the course of the upset measurements an important new effect was observed, namely that the sensitivity of microcircuits to single event upsets can be increased as a result of the accumulation of total dose in the device.