Non-volatile memory with word line ramp sensing for memory cell tracking
AssigneeSanDisk Technologies LLC
InventorsAlbert Chen, Eric Fu, Jiahui Yuan, Anirudh Amarnath, Xiang Yang
Life of this patent
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Abstract
A non-volatile storage apparatus stores data in the non-volatile memory cells by programming the non-volatile memory cells to a set of data states and reads data stored in the non-volatile memory cells by sensing for a set of read reference levels for the data states. To address data retention issues, including memory cells having the threshold voltages drift over time, one or more of the set of read reference levels are shifted based on sensing the non-volatile memory cells for two different conditions during a single ramping up of a voltage signal applied to the non-volatile memory cells.
Claims20
A non-volatile storage apparatus, comprising:
- non-volatile memory cells;
- and
- a control circuit connected to the non-volatile memory cells, the control circuit is configured to store data in the non-volatile memory cells by programming the non-volatile memory cells to a set of data states, the control circuit is configured to read data stored in the non-volatile memory cells by sensing for a set of read reference levels for the data states, the control circuit is further configured to shift one or more of the read reference levels based on sensing the non-volatile memory cells for two different conditions during a single ramping up of a voltage signal applied to the non-volatile memory cells.
A method, comprising:
- ramping up of a voltage signal applied to a set of non-volatile memory cells storing data in a set of data states defined by threshold voltage distributions;
- sensing the non-volatile memory cells for a first threshold voltage in response to the voltage signal during the ramping up;
- sensing the non-volatile memory cells for a second threshold voltage in response to the voltage signal during the ramping up;
- shifting one or more read reference voltages based on the sensing the non-volatile memory cells for the first threshold voltage and the sensing the non-volatile memory cells for the second threshold voltage;
- and
- performing a read process for the non-volatile memory cells using the shifted one or more read reference voltages.
A non-volatile storage apparatus, comprising:
- non-volatile memory cells;
- a first word line connected to the non-volatile memory cells;
- and
- a control circuit connected to the non-volatile memory cells and the first word line, the control circuit is configured to store data in the non-volatile memory cells by programming the non-volatile memory cells to a set of data states defined by threshold voltage distributions, the control circuit is configured to read data stored in the non-volatile memory cells by sensing the non-volatile memory cells in response to a set of read reference voltages, the control circuit is further configured to:
- ramp up of a word line voltage applied to the first word line from a first voltage level to a test target voltage level,
- sense the non-volatile memory cells for a first threshold voltage in response to the word line voltage during the ramp up,
- sense the non-volatile memory cells for a second threshold voltage in response to the word line voltage during the ramp up,
- determine a number of the memory cells having a threshold voltage greater than the first threshold voltage and less than or equal to the second threshold voltage based on the sensing of the non-volatile memory cells for the first threshold voltage and the sensing of the non-volatile memory cells for the second threshold voltage, and
- shift the one or more of the read reference voltages based on the number of the memory cells having a threshold voltage greater than the first threshold voltage and less than or equal to the second threshold voltage.
Dependencies are inferred from the claim text.