Variable Depth Bragg Peak Method for Single Event Effects Testing

The Variable Depth Bragg Peak (VDBP) method for measuring the Single Event Effects (SEE) cross-section of an integrated circuit (IC) in a closed package as a function of ion linear energy transfer (LET) is described. The method uses long-range, high-energy heavy ions that can penetrate the package and deposit charge in the device's sensitive volume (SV), the depth of which is not known. A series of calibrated energy degraders is used to vary the depth of the Bragg peak relative to the device's sensitive volume. When the Bragg peak is located at the sensitive volume, the measured SEE cross-section is a maximum, as is the LET, which is calculated using a Monte Carlo-based program, TRIM that takes both straggling and spread in beam energy and angle into account. Degrader thickness is varied and the change in LET is calculated while the corresponding cross-section is measured. Good agreement was obtained between the LET-dependence of the single event upset (SEU) cross-section for a 4 Mbit memory in an unopened package using the above method and that for an identical de-lidded part previously measured.