Ion microbeam probing of sense amplifiers to analyze single event upsets in a CMOS DRAM

An ion microbeam radiation system has been used to probe the relative contribution of individual circuits and nodes of a CMOS DRAM to single event upsets (SEUs). This instrument, which uses monoenergetic collimated ions from a 3-MV tandem accelerator, can produce an ion beam with a diameter as small as 1 μm. The precise alignment capability of the system allows positioning of the beam to any location in the circuit with an accuracy of better than 1 μm. The monoenergetic beam with the device under vacuum simplifies the analysis of the experimental results. The results show that alpha-particle hits on sensitive nodes within the sense amplifiers dominate the SEU rate. This domination is due to the presence in the sense amplifiers of n-channel devices which can collect charge from the entire ion track. In contrast, the memory cells and bit lines contain only p⁺ nodes in an n-well, which shields them from charge generated in the substrate