1. Franklin Duan, etc, AMD IRW2006 1 Impact of Monitoring Voltage on the Lifetime Extrapolation During the Accelerated Degradation Tests Franklin Duan, Stephen Cooper, Amit Marathe, John Zhang, Sankaran Kartik Jayanarayanan, AMD, One AMD place, PO Box 3453, M/S 143, Sunnyvale, CA 94088 Contact email: franklin.duan@amd.com, Tel: (408) 749-4795

2. Franklin Duan, etc, AMD IRW2006 2 Motivation Purpose: to compare or benchmark the reliability of different technology generations. Problem statement: it is found that not only the stress voltage affects your lifetime extraction, but also the monitoring voltage will play a considerable role. Lifetime extrapolation must consider this impact. People who are interested: mostly industry people, who need to compare and evaluate the reliability of each technology; or the people who want to study the lifetime in a quantitative way rather than qualitatively.

3. Franklin Duan, etc, AMD IRW2006 3 How to get the lifetime Lifetime is usually too long to get in the use conditions. Suppose a CPU chip has 10 years lifetime and there is no way to test for 10 years. Accelerated tests under higher voltages are usually used to extrapolate the lifetime at use conditions. This is the method generally used in industry to obtain and evaluate the lifetime using reasonable short test time.

4. Franklin Duan, etc, AMD IRW2006 4 How the lifetime be extrapolated Device are stressed at higher voltages and lifetimes these voltages are obtained. The test time to obtain these lifetimes is reasonably shorter since the voltages used are higher. Lifetime at use voltage is then extrapolated by the above lifetimes.

5. Franklin Duan, etc, AMD IRW2006 5 How the device be stressed Device is degraded after stressed at a certain stress voltage (left chart). The percentage of degradation (right chart) is recorded after a certain stress time period. Lifetime is obtained when a certain amount of degradation is reached. The way the data recorded is to apply a certain voltage (e.g., VG=VD=1V in the left chart) and measure the current at each time interval. The way to choose these monitor voltages will also play a big role and cannot be ignored. This is the focus of this paper.

6. Franklin Duan, etc, AMD IRW2006 6 Impact of monitor voltage on lifetime We have found that: lifetime is different when the monitor voltage is different, even stressed at the same stress voltage. This is usually ignored in most of the literatures and lifetime studies. In general, the less the monitor voltage, the lower lifetime, at the same stress voltage.

7. Franklin Duan, etc, AMD IRW2006 7 Why consider this impact (of monitor voltage) Suppose there are two technologies which may use different monitor voltages in the reliability testing and the data is as shown above. Now the question is: Is the lifetime difference is due to the different technologies, or due the use of different monitor voltage during the stress test? It is definitely confusing if we don’t consider the impact of the monitor voltage when doing these tests.

8. Franklin Duan, etc, AMD IRW2006 8 How to consider monitor voltage impact The good news is: degradation vs. monitor voltage follows an good exponential model. Lifetime as a function of monitor voltage can then be derived from the above model. Using this model, one can evaluate the lifetime at any given monitor voltage. Therefore, even though we use different monitor voltage for different technology, one can still compare their lifetime accurately. VM is the monitoring voltage V0 is the coefficient

9. Franklin Duan, etc, AMD IRW2006 9 Model does not depend on stress voltage used within the same technology As shown is the degradation vs. monitor voltage tested in the device from the same technology, but with two different stress voltages. The slope of the fitting line is the same for different stress voltages for the device under the same technology. Hence model is independent on the stress voltage used.

10. Franklin Duan, etc, AMD IRW2006 10 But, model is dependent on different technology As shown are the degradation vs. monitor voltage at different stress time for SOI and BULK technologies. Both technologies follow good exponential model. But the slope rate is different. One has to obtain the model separately for each technology.

11. Franklin Duan, etc, AMD IRW2006 11 In summary It is generally understood that the lifetime will depend on the stress voltages used in the accelerated test. The monitoring voltage is usually ignored. We found that the monitoring voltage has a considerable impact on the lifetime in the accelerated test: –Even using the same stressing voltage, the lifetime can be different if the monitoring voltage is different. –A good model is established to estimate the impact of the monitor voltage on lifetime It is important and also doable to consider this impact in the lifetime evaluation, esp. to compare the reliability in different technologies or foundries.

12. Franklin Duan, etc, AMD IRW2006 12 Acknowledgement The authors would like to thank Kurt Taylor and Steve Clark for management support for this project and technical discussions. The authors also thank Rick Francis and Tesfay Stifanos, Martin Trench and Rolf Geilenkeuser for providing some testing and the samples.