The Effects of Extended Temperatures on Flash Endurance and Data Retention
August 10, 2020 | BY: Aaron FrankDownload PDF
The electrical charge stored in a flash memory cell degrades over time, and will degrade much faster at extended temperatures. This degradation has been modelled to follow the Arrhenius Equation, degrading exponentially as temperature rises.
JEDEC Solid State Technology Association, an independent semiconductor engineering trade organization and standardization body, defines two specifications applicable to SSD endurance. The JEDEC specification for commercial flash SSD devices call for a client class SSD device to maintain a bit error rate (BER) of 10-15 or less, and retain data for minimum of one year at 30°C. The JEDEC spec also defines the data retention at elevated temperatures, but the retention time is quite alarming. Per JESD218, a client class SSD must maintain its data integrity at the defined BER for only 500 hours at 52°C (less than 21 days) or 96 hours at 66°C (only four days).
Figure 1: Example Graph Showing Temperature Effects and P/E Cycling on Flash Data Retention
Flash SSD devices which are specifically designed for high-temperature operation must support reliable data retention at operational temperatures exceeding 85°C, and at storage temperatures often quoted up to 125°C. Rarely however, will a flash vendor guarantee data retention at these high temperatures because the length of storage time at extreme temperatures is frighteningly low. Take, for example, the chart in Figure 1 (above) where the device is rated for 10-year data retention at 40°C. Interpreting the graph for a 100,000 P/E cycled cell at a storage temperature of 115°C returns an unacceptably low data retention time of about one day. Luckily, the same uncycled cell stored at 115°C has a retention time close to a year.
Download our white paper, Flash Memory Lifespan and Reliability: Examining the Long-Term Impacts of Reads, Temperature, and Other Factors, to learn more about how factors such as extended temperatures, reads, and Program/Erase (P/E) cycles impact the long-term reliability of flash memory devices.