Enhanced Low Dose Rate Sensitivity (ELDRS) remains one of the trickiest problems in TID testing. MIL-STD-883 TM1019.9 gives us a framework, but the practical decisions around dose rate selection are still debated.
The basic issue: some bipolar devices show significantly worse degradation at low dose rates (10-50 mrad(Si)/s) than at the standard high dose rate (50-300 rad(Si)/s). TM1019 allows high dose rate testing with a 1.5× overtest factor, but this rebound-based approach doesn’t catch all ELDRS-susceptible parts. True low dose rate testing at 10 mrad/s to reach 100 krad takes about 115 days; a serious schedule impact.
Some questions that come up regularly in practice:
Is 10 mrad/s low enough? Most ELDRS characterization has been done at 10 mrad/s, but some devices show additional degradation at even lower rates. The “true” space dose rate for many missions is 0.1-1 mrad/s. How confident are we that 10 mrad/s captures the worst case?
Elevated temperature testing as an accelerator. There’s research showing that irradiation at elevated temperature (100°C) and moderate dose rate can approximate low dose rate response. This is based on the premise that ELDRS is driven by space charge buildup and hydrogen transport, both of which are temperature-activated. But the correlation isn’t perfect for all device types. Who’s using this approach in production, and what confidence level do you assign to it?
The 1.5× overtest — is it enough? TM1019 allows high dose rate testing at 1.5× the requirement if the part passes. This was meant to be conservative, but there are documented cases of parts that pass at 1.5× HDR and fail at true LDR. Is 2× more appropriate? Should the factor depend on the technology type?
Which technologies are we still worried about? Classic ELDRS parts are bipolar linears such as voltage regulators, op-amps, comparators. But what about BiCMOS mixed-signal devices? And modern CMOS technologies showing dose rate effects?
Interested to hear what RHA test strategies people are using and how they justify them to their review boards.