Suggested Single Event Upset Figure of Merit

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Abstract
This paper examines a number of concepts that are connected, directly or indirectly, with the problem of assigning a single event upset figure of merit to a specific oevice. Single event rates depend both on device and circuitry, through the critical charge requisite for upset, and upon the device geometry and technology, which determine the target size and charge collection capability. Each of these factors must be taken into account when determining device susceptibility. Upset rates in space additionally depend on the environment. Device response in trapped proton belts and in the cosmic ray environment is sufficiently oifferent that a single susceptibility measure is inadequate. We conclude that devices should be characterizea by a proton susceptibility, and by an upset rate in a reference cosmic ray environment. We present a simple expression, based on laboratory measurement, that approximates the cosmic ray upset rate ano propose it as a figure of merit. Calculated and measured values for upset rates are sensitive to several factors. The field funneling effect is known to increase both the magnitude of collected charge and the effective sensitive circuit volume during single events relative to the static parameters. Thus, experimental sensitive area measurements obtained from single event data exceed values predicted from inspection of static circuit layout configurations. Also, more charge is collected from any specific event than is predicted by using depletion region extent to determine charge collection volumes. This effect must be included when critical upset charge values are determined from experimental upset thresholds.

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