MICROBEAM MAPPING OF SINGLE EVENT LATCHUPS AND SINGLE EVENT UPSETS INCMOS SRAMS

The first simultaneous microbeam mapping of single event upset (SEU) a nd latchup (SEL) in the CMOS RAM HM65162. is presented. We found that the shapes of the sensitive areas depend on V-DD, on the ions being us ed and on the site on the chip being hit by the ion. In particular, we found SEL sensitive sites close to the main power supply lines betwee n the memory-bit-arrays by detecting the accompanying current surge. A ll these SELs were also accompanied by bit-flips elsewhere in the memo ry (which we call 'indirect' SEUs in contrast to the well known SEUs i nduced in the hit memory cell only). When identical SEL sensitive site s were hit farther away from the supply lines only indirect SEL sensit ive sites could be detected. We interpret these events as 'latent' lat chups in contrast to the 'classical' ones detected by their induced cu rrent surge. These latent SELs were probably decoupled from the main s upply lines by the high resistivity of the local supply lines.