Method and memory used for reducing program disturbance by adjusting voltage of dummy word line

1. A method for operating a memory, the memory comprising an upper deck and a lower deck, the upper deck being formed above the lower deck, the upper deck comprising a first upper dummy word line close to the lower deck, the lower deck comprising a first lower dummy word line close to the upper deck, the method comprising:

applying a first upper bias voltage to the first upper dummy word line, wherein the first upper bias voltage is different from a first upper threshold voltage of a first upper dummy cell corresponding to the first upper dummy word line; and

applying a first lower bias voltage to the first lower dummy word line, wherein the first lower bias voltage is different from a first lower threshold voltage of a first lower dummy cell corresponding to the first lower dummy word line.

2. The method of claim 1 , wherein:

a first difference between the first upper bias voltage and the first upper threshold voltage is lower than a first threshold; and

a second difference between the first lower bias voltage and the first lower threshold voltage is lower than the first threshold.

3. The method of claim 2 , wherein:

the first difference is higher than the second difference.

4. The method of claim 1 , wherein the lower deck further comprises a second lower dummy word line farther to the upper deck than the first lower dummy word line, the method further comprising:

applying a second lower bias voltage to the second lower dummy word line, wherein the second lower bias voltage is different from a second lower threshold voltage of a second lower dummy cell corresponding to the second lower dummy word line.

5. The method of claim 4 , wherein:

a first difference between the first upper bias voltage and the first upper threshold voltage is higher than a first threshold;

a second difference between the first lower bias voltage and the first lower threshold voltage is lower than the first threshold; and

a third difference between the second lower bias voltage and the second lower threshold voltage is lower than the first threshold.

6. The method of claim 5 , wherein a difference between the first difference and the second difference is within a predetermined range, and another difference between the first difference and the third difference is within the predetermined range.

7. The method of claim 1 , wherein the upper deck further comprises a second upper dummy word line farther to the lower deck than the first upper dummy word line, the method further comprising:

applying a second upper bias voltage to the second upper dummy word line, wherein the second upper bias voltage is different from a second upper threshold voltage of a second upper dummy cell corresponding to the second upper dummy word line.

8. The method of claim 7 , wherein:

a first difference between the first upper bias voltage and the first upper threshold voltage is lower than a first threshold;

a second difference between the first lower bias voltage and the first lower threshold voltage is lower than the first threshold; and

a fourth difference between the second upper bias voltage and the second upper threshold voltage is higher than the first threshold.

9. The method of claim 8 , wherein a difference between the fourth difference and the first difference is within a predetermined range, and another difference between the fourth difference and the second difference is within the predetermined range.

10. The method of claim 1 , wherein the upper deck further comprises a second upper dummy word line farther to the lower deck than the first upper dummy word line, the lower deck further comprises a second lower dummy word line farther to the upper deck than the first lower dummy word line, the method further comprising:

applying a second lower bias voltage to the second lower dummy word line, wherein the second lower bias voltage is different from a second lower threshold voltage of a second lower dummy cell corresponding to the second lower dummy word line; and

applying a second upper bias voltage to the second upper dummy word line, wherein the second upper bias voltage is different from a second upper threshold voltage of a second upper dummy cell corresponding to the second upper dummy word line.

11. The method of claim 10 , wherein:

a first difference between the first upper bias voltage and the first upper threshold voltage is lower than a first threshold;

a second difference between the first lower bias voltage and the first lower threshold voltage is lower than a second threshold;

a third difference between the second lower bias voltage and the second lower threshold voltage is lower than the first threshold; and

a fourth difference between the second upper bias voltage and the second upper threshold voltage is higher than the second threshold.

12. The method of claim 11 , wherein a difference between the fourth difference and the first difference is within a predetermined range, and another difference between the fourth difference and the second difference is within the predetermined range.

13. The method of claim 11 , wherein a difference between the fourth difference and the second difference is within a predetermined range, and another difference between the fourth difference and the third difference is within the predetermined range.

14. The method of claim 1 , further comprising:

adjusting the first upper threshold voltage of the first upper dummy cell corresponding to the first upper dummy word line such that the first upper bias voltage is different from the first upper threshold voltage; and

adjusting the first lower threshold voltage of the first lower dummy cell corresponding to the first lower dummy word line such that the first lower bias voltage is different from the first upper threshold voltage,

wherein the first upper bias voltage is the same as the first lower bias voltage, and first upper threshold voltage is different from the first lower threshold voltage.

15. The method of claim 1 , wherein the first upper threshold voltage of the first upper dummy cell corresponding to the first upper dummy word line and the first lower threshold voltage of the first lower dummy cell corresponding to the first lower dummy word line are unadjusted.

16. A memory device, comprising:

an upper deck comprising a first upper dummy word line;

a lower deck comprising a first lower dummy word line, wherein the upper deck is above the lower deck; and

a driving circuit configured to:

apply a first upper bias voltage to the first upper dummy word line, wherein the first upper bias voltage is different from a first upper threshold voltage of a first upper dummy cell corresponding to the first upper dummy word line; and

apply a first lower bias voltage to the first lower dummy word line, wherein the first lower bias voltage is different from a first lower threshold voltage of a first lower dummy cell corresponding to the first lower dummy word line.

17. The memory device of claim 16 , wherein the lower deck further comprises a second lower dummy word line farther to the upper deck than the first lower dummy word line, and the driving circuit is further configured to:

apply a second lower bias voltage to the second lower dummy word line, wherein the second lower bias voltage is different from a second lower threshold voltage of a second lower dummy cell corresponding to the second lower dummy word line,

wherein a first difference between the first upper bias voltage and the first upper threshold voltage is higher than a second difference between the first lower bias voltage and the first lower threshold voltage; and

the first difference is higher than a third difference between the second lower bias voltage and the second lower threshold voltage.

18. The memory device of claim 16 , wherein the upper deck further comprises a second upper dummy word line farther to the lower deck than the first upper dummy word line, and the driving circuit is further configured to:

apply a second upper bias voltage to the second upper dummy word line, wherein the second upper bias voltage is different from a second upper threshold voltage of a second upper dummy cell corresponding to the second upper dummy word line, wherein:

a fourth difference between the second upper bias voltage and the second upper threshold voltage is higher than a first difference between the first upper bias voltage and the first upper threshold voltage; and

the fourth difference is higher than a second difference between the first lower bias voltage and the first lower threshold voltage.

19. The memory device of claim 16 , wherein the upper deck further comprises a second upper dummy word line farther to the lower deck than the first upper dummy word line, the lower deck further comprises a second lower dummy word line farther to the upper deck than the first lower dummy word line, and the driving circuit is further configured to:

apply a second lower bias voltage to the second lower dummy word line, wherein the second lower bias voltage is different from a second lower threshold voltage of a second lower dummy cell corresponding to the second lower dummy word line; and

apply a second upper bias voltage to the second upper dummy word line, wherein the second upper bias voltage is different from a second upper threshold voltage of a second upper dummy cell corresponding to the second upper dummy word line,

wherein a first difference between the first upper bias voltage and the first upper threshold voltage is lower than a first threshold;

a second difference between the first lower bias voltage and the first lower threshold voltage is lower than a second threshold;

a third difference between the second lower bias voltage and the second lower threshold voltage is lower than the first threshold; and

a fourth difference between the second upper bias voltage and the second upper threshold voltage is higher than the second threshold.

20. The memory device of claim 16 , further comprising a joint oxide layer formed between the upper deck and the lower deck.