IEC 60749-41 pdf free download
IEC 60749-41 pdf free download.Semiconductor devices – Mechanical and climatic test methods – Part 41: Standard reliability testing methods of non-volatile memory devices.
5.2.2 Data cycling
5.2.2.1 Program and erase verification
Program and erase operations during the endurance test shall be verified to have been properly executed in accordance with the device specification or the supplier’s internal stress test specification (see Clause 7).
5.2.2.2 Data patterns during cycling
The data pattern used for endurance cycling shall be agreed upon between supplier and user, and the rationale documented. It is important to cycle enough sectors of blocks during the cycling period taking into account for the target application models. See Note 1 to Entry 3.4 for a discussion of the trade-offs involved in the selection of data pattern for cycling.
The purpose of many qualifications is to test the device for the broadest possible range of failure mechanisms. The broadest possible range of failure mechanisms can be detected when the data pattern includes the full range of logic levels and adjacency conditions that would occur in actual use. For example, this full range can be achieved if the following three conditions are met. First, the data in the memory cells is cycled between all available logic states in equal measure. For example, in an SBC memory half the cells would be programmed and half left erased in any one cycle, whereas in a 4-level cell memory one-quarter of the cells would be written to each of the four available levels in any given cycle. Second, the positions of Is and Os are non-uniform, ideally quasi-random, so that all possible adjacency configurations are represented. For example, a data pattern consisting of a mix of bytes with data patterns OOH (zero zero hexadecimal), 55H, AAH, 33H, CCH, and FFH would create a wide range of adjacency patterns. Third, the data pattern in successive cycles is not the same, but rather follows a sequence. Best practice is to ensure, in this sequence, that some cells are written to all available logic states while other cells are re-written to the same logic state in every cycle. For example, in an SBC memory, a byte that was cycled to AAH in even- numbered cycles and 5AH in odd-numbered cycles would have four cells that would be written to Os and Is in alternating cycles, two cells that are re-written to 0 in every cycle, and two cells that are re-written to I in every cycle.
In some knowledge-based qualifications, endurance tests can be defined for specific failure mechanisms. Such tests can use different data patterns from that described above, optimized to increase the sensitivity to the targeted mechanisms. Examples of acceptable data patterns for such purposes include a solid programmed pattern, checkerboard/inverse-checkerboard sequence, and checkerboard with subsequent filling-in of the pattern.
Some flash EEPROM devices employ a built-in scrambling mechanism. When testing endurance of such devices, the scrambling mechanism should be enabled; disabling the scrambler for endurance cycling can stress the product beyond the stress a user can experience. A quasi-random pattern is best for testing endurance when employing scrambling.
5.2.2.3 Fraction of cells to be cycled
Qualification specifications, whether from JESD47 or developed using knowledge-based methods (JESD94) will generally require that some fraction of the memory to be cycled to the maximum number of program/erase cycles specified in the device specification and other fractions to be cycled to lesser amounts. In large memories, it can take a prohibitively long time to cycle all cells to the maximum specification, and in knowledge-based qualifications it is possible that application use conditions do not require all cells to be so cycled. The actual fraction of cells cycled to 100 % of the maximum specification, and the fraction cycled to other percentages of the specification, shall be agreed upon between supplier and user and documented, along with the rationale for the chosen fractions.IEC 60749-41 pdf download.
