DOE OSTI2014
We are using the DoD MIL-STD as our guide for microelectronics aging (MIL-STD 883J, Method 1016.2: Life/Reliability Characterization Tests). In that document they recommend aging at 3 temperatures between 200-300C, separated by at least 25C, with the supply voltage at the maximum recommended voltage for the devices at 125C (3.6V in our case). If that voltage causes excessive current or power then it can be reduced and the duration of the tests extended. The MIL-STD also recommends current limiting resistors in series with the supply. Since we don’t have much time and we may not have enough ovens and other equipment, two temperatures separated by at least 50C would be an acceptable backup plan. To ensure a safe range of conditions is used, we are executing 24-hour step tests. For these, we will apply the stress for 24 hours and then measure the device to make sure it wasn’t damaged. During the stress the PUFs should be exercised, but we don’t need to measure their response. Rather, at set intervals our devices should be returned to nominal temperature (under bias), and then measured. The MIL-STD puts these intervals at 4, 8, 16, 32, 64, 128, 256, 512 and 1000 hours, although the test can be stopped early if 75% of the devices have failed. A final recommendation per the MIL-STD is that at least 40 devices should be measured under each condition. Since we only have 25 parts, we will place 10 devices in each of two stress conditions.