EEPROM Application Review and Recommendations

1. EEPROM Application Review and Recommendations Yuan Chen JPL For use only by JPL, NASA, and companies under contract to JPL or NASA. Not for external release.

2. Lessons Learned • Parts level - potential early failures resulting from extrinsic memory cell defects; • Examples • MER pre-launch page failure • Genesis single bit failures • System/design level – timing or usage outside specifications. • Examples • DI and MER single bit failures on board, but could not be confirmed at parts level • ST-5 single bit failure resulting from controlling FPGA causing the write timing to be non-compliant with the parts datasheet • Key Point: Risk mitigation should be at both parts level and system/design level. For use only by JPL, NASA, and companies under contract to JPL or NASA.

3. Both endurance and data retention are defined against 1% cumulative failure percentage in datasheet. 0.1% or even 0.01% should be used for space applications. The EEPROM has 10-year data retention at 0.01% cumulative failure rate at and below 70ºC. The 10-year data retention is for “intrinsic or healthy cells”, not for weak cells. “Extrinsic or weak cells” can fail any time before 10-yeardata retention life. Weak cells may have several order of magnitude lower data retention or endurance lifetime, much higher failure rate and much lower activation energy. Weak cells can be induced by random process defects and/or programming and weak cell failures are randomly distributed. Weak bit failure statistics can be described by Poisson distribution. The probability of having x number of bit failures is EEPROM weak bit failure rates can be estimated based on total bit failures and total bit time. Intrinsic Cells versus Weak Cells • Key points: • Weak cells determine the EEPROM reliability. • Weak cell failure rate needs to be estimated for each mission For use only by JPL, NASA, and companies under contract to JPL or NASA.

4. Recommendations – Parts Level • Parts level: • Use the parts per the specification on operating voltage and timing • Make sure the parts have gone through pre-screening. If you are not sure, the parts should be written all “0” and then read a couple of thousand times for detecting possible weak cells. • The operating temperature (or ambient temperature, back of die temperature) cannot be over 70ºC. • If the mission life is over 10 years, additional analysis is needed. • Keep a record of number of writes to the EEPROM. For use only by JPL, NASA, and companies under contract to JPL or NASA.

5. Recommendations – System/Design Level • System and design level: • Use EDAC code. • Use redundancy in image/code. • Assuming 90% reliability for one image • Design in bit and page redundancy to allow for programming around failed bit or pages. • Perform worst case timing analysis in board level to make sure that the timing meets the manufacturer's specification with necessary margin. • Minimize crosstalk and signal/Vdd noise. • Minimize the number of write/erase cycles during ground and pre-launch testing. • Understand the system EEPROM configuration and estimate the weak cell failure rate for each mission. For use only by JPL, NASA, and companies under contract to JPL or NASA.