High temperature methods for enhancing retention characteristics of memory devices
First Claim
1. A method for improving retention characteristics of a memory device including a plurality of memory cells, comprising:
- baking the plurality of memory cells at a temperature level for a sufficient duration to cause shallow trapped charges to be expelled from the plurality of memory cells;
after the baking step, verifying the plurality of memory cells to determine if written data in memory cells are unchanged from before the baking step;
if the plurality of memory cells fail the verify step, reprogramming failing memory cells to the high threshold voltage state again; and
after the reprogramming step, determining that the number of times that the memory cells have been reprogrammed is equal to or less than N number of times and returning to the baking step.
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Abstract
Methods are described for improving the retention of a memory device by execution of a retention improvement procedure. The retention improvement procedure comprises a baking process of the memory device in a high temperature environment, a verifying process of the memory device that checks the logic state of memory cells, and a reprogramming process to program the memory device once again by programming memory cells in a 0-state to a high-Vt state. The baking step of placing the memory device in a high temperature environment causes a charge loss by expelling shallow trapped charges, resulting in the improvement of retention reliability.
12 Citations
9 Claims
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1. A method for improving retention characteristics of a memory device including a plurality of memory cells, comprising:
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baking the plurality of memory cells at a temperature level for a sufficient duration to cause shallow trapped charges to be expelled from the plurality of memory cells; after the baking step, verifying the plurality of memory cells to determine if written data in memory cells are unchanged from before the baking step; if the plurality of memory cells fail the verify step, reprogramming failing memory cells to the high threshold voltage state again; and after the reprogramming step, determining that the number of times that the memory cells have been reprogrammed is equal to or less than N number of times and returning to the baking step. - View Dependent Claims (2, 3, 4, 5)
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6. A method for improving retention characteristics of a memory device including a plurality of memory cells, comprising:
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programming and erasing the plurality of memory cells; excluding one or more memory cells in the plurality of memory cells that do not pass the programming and erasing steps; baking the memory cells at a temperature level for a sufficient duration to cause shallow trapped charges to be expelled from the memory cells; after the baking step, verifying the plurality of memory cells to determine if written data in the memory cells are unchanged from before the baking step; if the memory cells fail the verify step, reprogramming failed memory cells to the high threshold voltage state; and after the reprogramming step, determining that the number of times that the memory cells have been reprogrammed is equal to or less than N number of times and returning to the baking step. - View Dependent Claims (7, 8, 9)
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Specification