FAST – Reliability Assessment using „Faster-than-at-Speed Test“
since 02.2017, DFG-Project: WU 245/19-1
State-of-the-art nanoscale technologies allow for the integration of billions of transistors with feature sizes of 14 nm or below into a single chip. This enables innovative approaches and solutions in many application domains, but it also comes along with fundamental challenges. Early life failures are particularly critical, as they can cause product recalls associated with a loss of billions of dollars. A major cause of early life failures are "weak" devices that operate correctly during manufacturing test, but cannot stand operational stress in the field. While other failure mechanisms, such as aging or external disturbances, to some extent, may be compensated by a robust design, potential early life failures must be detected by tests, and the respective systems have to be sorted out. This requires specific approaches far beyond today’s state-of-the-art.
As they work properly in the beginning, weak structures must be identified by analyzing the non-functional circuit behavior with the help of appropriate observables. Besides power consumption, the circuit timing is one of the most important reliability indicators. In particular, small delay faults may indicate marginal hardware that can degrade further under stress. However, they can be “hidden” at nominal frequency and only be detected at higher frequencies (“faster-than-at-speed test” / FAST). Therefore, conventional approaches for testing reach their limitations, and
new methods must be investigated and developed in the following three domains:
- Specific techniques for „design for test“ (DFT) must be developed to deal with the challenges of testing beyond nominal frequency.
- Strategies for test scheduling must ensure that a maximum fault coverage is achieved with a minimum number of test frequencies and a short test time.
- Appropriate metrics are needed to quantify the coverage of weak devices. Here it is particularly challenging to distinguish the behavior of week devices from variations due to nanoscale integration.
Since FAST imposes extreme requirements on the automatic test equipment (ATE), it is very important to support an efficient implementation as a built-in self-test (BIST).
Within the framework of the project, strategies and solutions will be developed for the problems mentioned above. This way, the enormous cost of a traditional „burn-in“ test can be reduced, thus enabling the introduction of nanoscale technology to new application domains.