Summary

Endurance is the cumulative number of erase/program cycles before the device fails a data sheet parameter. Reprogrammable nonvolatile memories, such as flash EEPROMs, have a failure rate associated with endurance that is best represented by the classical “bathtub curve”. There are the “infant mortality”, “useful life”, and “wearout” regions. When attempting to describe the endurance of a device, manufacturers typically claim some number of cycles. In terms of the classical “bathtub” curve, this level is the cumulative number of cycles through the “useful life” region where the cumulative failures are less than a guaranteed value, e.g., 1% for 10,000 cycles. The number of cycles is supposed to be less than the value at the knee of the curve separating the “useful life” region from the “wearout” region. In practice, the stated level should be significantly less than the actual value at the onset of wearout. During the “useful life” region, there will be a small, but constant failure rate. The issue facing manufacturers is to assure each device has been screened to eliminate “infant mortality”, has an endurance value greater than the stated level, and the failure rate in the “useful life” region meets industry standards, reference IEEE Std 1005-1998 “Definition and Characterization of Floating Gate Semiconductor Arrays” and JEDEC Test Method A117 for additional information.