Abstract
Heavy charged particle induced soft errors in semiconductor memory devices have been a field failure problem for the manufacturers and the users of microelectronic systems in recent years, but these did not become significant until the introduction of 16k and 64k dynamic Random Access Memories (dRAMs). Soft errors, sometimes referred to as "single event upsets" (SEUs), can deposit sufficient electrical charge on integrated circuit nodes to initiate logic state reversal without causing any permanent changes in the device. Therefore, correctable errors may be introduced randomly in space and time that are distinguishable from intended states only by their information content. In terms of memory circuits, dRAMs turn out to be the most susceptible to such errors because they contain relatively the smallest individual elements and are operated on the smallest amounts of charge. A hardware system has being designed and constructed with a view to using it in the detection of neutrons. A feasibility study was initially carried out to demonstrate that dRAMs may be used as heavy charged particle detectors and furthermore can be sensitive to neutrons. The addition of a thermal neutron to charged particle converter which makes use of the (n,a) reaction maximizes detection efficiency of the incident neutrons. A model has been developed to examine the use of possible converters with respect to soft error generation including those factors that determine the optimum thickness and the efficiency of such a detector. The construction of a detector that is also position sensitive has many attractions, therefore experiments were carried out to investigate the relative sensitivity of specific elements within the dRAM chips to cycle time. Any area of the device with an electric field has the potential to separate charge and acts as a collector. A heavy charged particle can, therefore, discharge a storage capacitor either by disturbing the bit lines or by causing the information to be inverted during the sensing of the sense amplifiers. Hence, the variation of the memory cycle time allowed to determine from the dependence of soft error, whether the impact of charged particles was in the region of memory cells or of the bit lines and sense amplifiers which has left the bit line-sense amplifier contribution to soft error rate as the dominant one. The findings from this research highlight the usefulness of such a device as a radiation sensor and, in particular, as a position sensitive one.