Test method


The switching test method makes use of applying sequenced high dose rate and low dose rate exposure on a set of units of a specific part type. Hereby the term unit refers to one package and all devices that are assembled therein. First, all the units of a specific part type are grouped into five exposure series, five units each. Then all of these exposure series (except the first one) are irradiated at a high dose rate to different dose levels, the so called dose switches. After the high dose rate step a low dose rate exposure is concatenated, irradiating all exposure series in parallel. The goal of the high dose rate exposure is to achieve certain degradation levels, different for each exposure series.

The idea behind the switching test method is based on the observation that the device degradation rate during the low dose rate exposure is independent from the previous high dose rate step. As a consequence the low dose rate degradation curve recorded after a high dose rate step is parallel to the one of a pure low dose rate exposure, but shifted. I.e. this means that also only segments of the low dose rate characteristics can be measured. A low dose rate characteristic representative for the entire investigated dose regime can be constructed from several segments obtained from various exposure series, by shifting them to the left (see Figure).

The time benefit of the switching test method is due to irradiating several exposure series in parallel, thus measuring different segments of the degradation curve in parallel. With the parallelisation the overall time of the low dose rate exposure can be reduced by a factor corresponding to the number of dose steps. The trade-off is a considerably larger sample size.

Figure 1: Schematic illustration of the switching test method. The low dose rate degradation curve has a steeper degradation curve than the high dose rate degradation curve. The entire low dose rate degradation curve can be composed from shifting the LDR segments obtained from each switch [BOC05].