Alpha-particle-induced soft errors in MOS RAMS

Carter, Paul Michael (1987) Alpha-particle-induced soft errors in MOS RAMS. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The continuing trend in the area of semiconductor memories towards higher levels of integration and the demand for product with lower power consumption has resulted in a decrease in the amount of charge needed to record information on memory storage sites. In the case of MOS technology, stored charges have become so low that the charge collected from an alpha particle passing through a sensitive part of the device surface can be enough to alter the data stored on the memory, causing an alpha-particle-induced `soft error'. The alpha-particle-induced soft error rate behaviour of a number of manufacturer's MOS 64K DRAMs was studied and characterized against parameters such as cycle time and supply voltage. From these results the conclusion was reached that the error rates were dominated by hits on the bit lines (which carry data from the cell to the sense amplifier) rather than the cells themselves. It was also found that many manufacturer's devices suffered from sensing imbalances causing an unnecessarily high susceptibility to soft errors. Studies of the sensitivity of different areas of the chip surface were also performed. Certain MOS resistive load SRAMs were found to be susceptible to alpha particles and characterizations of these devices similar to those of the DRAMs are presented. Computer simulation of an SRAM cell showed how the alpha particle sensitivity of the cell is affected by various design parameters and a simple mechanism which reduced the cell's sensitivity is presented and discussed. To study the charge collection properties of MOS DRAM bit lines, a test chip was built, consisting of a number of differently designed bit line structures laid out across it surface. The results of collected charge measurements taken from these bit lines while under alpha particle bombardment are given and interpreted. (D75970/87)

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