Reliability

When extrapolating TDDB test results to operating voltage, there is the E model, which expresses lifetime as an exponential of field, and the 1/E model, which uses the reciprocal of field. Which statement about their difference is correct?

  1. AThe 1/E model always gives the shorter lifetime
  2. BExtrapolated to low fields, their predicted lifetimes differ greatly, and the E model generally gives shorter (more conservative) estimates
  3. CThe two models always predict the same lifetime
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Answer: B. Extrapolated to low fields, their predicted lifetimes differ greatly, and the E model generally gives shorter (more conservative) estimates

Depending on how high-field test results are extrapolated to actual operating fields, predicted lifetimes can differ by orders of magnitude. Generally, the E model predicts shorter lifetimes at low field and the 1/E model longer ones, so the E model is often used for conservative evaluation. Which is appropriate has been debated depending on film type and field range.

  • A. Generally the E model gives the shorter lifetime.
  • B. Correct. They diverge at low field, with the E model being conservative.
  • C. Predictions change greatly with the extrapolation method.
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More Reliability questions

  1. Which correctly lists the three periods that make up the bathtub curve, showing how failure rate changes over time?
  2. Which correctly describes electromigration?
  3. Which correctly describes MTBF (mean time between failures)?
  4. In accelerated tests that raise temperature to shorten life test time, which model is often used to express the relationship between temperature and lifetime?
  5. Which correctly describes TDDB (time-dependent dielectric breakdown)?