Non-volatile Memory Program Algorithm Device And Method

• US 20140269058A1
• Filed: 03/14/2014
• Published: 09/18/2014
• Est. Priority Date: 03/14/2013
• Status: Active Grant

• Current Assignee: Silicon Storage Technology Incorporated (Microchip Technology Incorporated)
• Original Assignee: Silicon Storage Technology Incorporated (Microchip Technology Incorporated)
• Inventors: Liu, Xian, Kotov, Alexander, Yoo, Jong-Won, Cheng, James, Bavinov, Dmitry
• Granted Patent: US 9,431,126 B2
• Time in Patent Office: Days
• US Class Current: 365/185.03
• CPC Class Codes: G11C 11/5628 Programming or writing circuits; Data input circuits
• CPC Class Codes: G11C 11/5642 Sensing or reading circuits; Data output circuits
• CPC Class Codes: G11C 16/0441 comprising cells containing multiple floating gate devices, e.g. separate read-and-write FAMOS transistors with connected floating gates
• CPC Class Codes: G11C 16/10 Programming or data input circuits
• CPC Class Codes: G11C 16/12 Programming voltage switching circuits
• CPC Class Codes: G11C 16/3459 Circuits or methods to verify correct programming of nonvolatile memory cells
• CPC Class Codes: G11C 16/3486 Circuits or methods to prevent overprogramming of nonvolatile memory cells, e.g. by detecting onset or cessation of current flow in cells and using the detector output to terminate programming

Abstract

A non-volatile memory device and method for programming cells using repeated pulses of program voltages, with interleaved read operations to determine the level of read current, until the desired programming state is achieved. Each successive program pulse has one or more program voltages increased by a step value relative to the previous pulse. For a single level cell type, each cell is individually removed from the programming pulses after reaching a first read current threshold, and the step value is increased for one or more kicker pulses thereafter. For a multi-level cell type, the step value drops after one of the cells reaches a first read current threshold, some cells are individually removed from the programming pulses after reaching a second read current threshold while others are individually removed from the programming pulses after reaching a third read current threshold.

Claims

1. A method of programming a memory device having memory cells each including source and drain regions in a semiconductor substrate with a channel region therebetween, a floating gate disposed over and affecting a conductivity of at least a portion of the channel region, and one or more additional conductive gates insulated from the floating gate and the substrate, wherein each memory cell is programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region, the method comprising:

1) applying a pulse of programming voltages to the source regions and the one or more conductive gates for a plurality of the memory cells,

2) reading program states of the plurality of memory cells, and

3) repeating steps 1 and 2 until at least one of the plurality of memory cells exhibits a read current in step 2 which reaches a first threshold value, wherein the repeating of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated;

after the first threshold value has been reached, for each of a first subset of the plurality of memory cells;

4) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

5) reading a program state of the memory cell, and

6) repeating steps 4 and 5 until the memory cell exhibits a read current in step 5 which reaches a second threshold value different from the first threshold value, wherein the repeating of steps 4 and 5 includes increasing at least one of the programming voltages of step 4 by a second step value each time step 4 is repeated, wherein the second step value is less than the first step value; and

after the first threshold value has been reached, for each of a second subset of the plurality of memory cells;

7) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

8) reading a program state of the memory cell, and

9) repeating steps 7 and 8 until the memory cell exhibits a read current in step 8 which reaches a third threshold value different from the first and second threshold values, wherein the repeating of steps 7 and 8 includes increasing at least one of the programming voltages of step 7 by a third step value each time step 7 is repeated, wherein the third step value is less than the first step value.

2. The method of claim 1, wherein the second and third step values are equal to each other.

3. The method of claim 1, wherein the first and third step values are greater than the second step value.

4. The method of claim 1, wherein the first threshold value is greater than the second threshold value, and the second threshold value is greater than the third threshold value.

5. The method of claim 1, wherein the one or more additional conductive gates for each memory cell includes a control gate disposed over and affecting the conductivity of a second portion of the channel region.

6. The method of claim 1, wherein after the second threshold value has been reached for the first subset of the plurality of memory cells, and after the third threshold value has been reached for the second subset of the plurality of memory cells, for each of a third subset of the plurality of memory cells the method further comprising:

10) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

11) reading a program state of the memory cell, and

12) repeating steps 10 and 11 until the memory cell exhibits a read current in step 11 which reaches a fourth threshold value different from the first and second and third threshold values, wherein the repeating of steps 10 and 11 includes increasing at least one of the programming voltages of step 10 by a fourth step value each time step 10 is repeated, wherein the fourth step value is greater than the second and third step values.

7. The method of claim 6, wherein the fourth step value is equal to the first step value.

8. The method of claim 6, further comprising:

after the fourth threshold value is reached for all the third subset of the plurality of memory cells, applying a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all of the third subset of the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a fifth step value relative to the programming voltages applied in steps 10-12.

9. The method of claim 8, wherein the fifth step value is greater than the fourth step value.

10. A method of programming a memory device having memory cells each including source and drain regions in a semiconductor substrate with a channel region therebetween, a floating gate disposed over and affecting a conductivity of at least a portion of the channel region, and one or more additional conductive gates insulated from the floating gate and the substrate, wherein each memory cell is programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region, the method comprising:

for each of a first subset of a plurality of the memory cells;

1) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

2) reading a program state of the memory cell, and

3) repeating steps 1 and 2 until the memory cell exhibits a read current in step 2 which reaches a first threshold value, wherein the repeating of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated; and

for each of a second subset of the plurality of memory cells;

4) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

5) reading a program state of the memory cell, and

6) repeating steps 4 and 5 until the memory cell exhibits a read current in step 5 which reaches a second threshold value different from the first threshold value, wherein the repeating of steps 4 and 5 includes increasing at least one of the programming voltages of step 4 by a second step value each time step 4 is repeated.

11. The method of claim 10, wherein the first and second step values are equal to each other.

12. The method of claim 10, wherein the second step value is greater than the first step value.

13. The method of claim 10, wherein the first threshold value is greater than the second threshold value.

14. The method of claim 10, wherein the one or more additional conductive gates for each memory cell includes a control gate disposed over and affecting the conductivity of a second portion of the channel region.

15. The method of claim 10, wherein after the first threshold value has been reached for the first subset of the plurality of memory cells, and after the second threshold value has been reached for the second subset of the plurality of memory cells, for each of a third subset of the plurality of memory cells the method further comprising:

7) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

8) reading a program state of the memory cell, and

9) repeating steps 7 and 8 until the memory cell exhibits a read current in step 8 which reaches a third threshold value different from the first and second threshold values, wherein the repeating of steps 7 and 8 includes increasing at least one of the programming voltages of step 7 by a third step value each time step 7 is repeated, wherein the third step value is greater than the first and second step values.

16. The method of claim 16, further comprising:

after the third threshold value is reached for all the third subset of the plurality of memory cells, applying a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all of the third subset of the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a fourth step value relative to the programming voltages applied in steps 7-9.

17. The method of claim 16, wherein the fourth step value is greater than the third step value.

18. A method of programming a memory device having memory cells each including source and drain regions in a semiconductor substrate with a channel region therebetween, a floating gate disposed over and affecting a conductivity of at least a portion of the channel region, and one or more additional conductive gates insulated from the floating gate and the substrate, wherein each memory cell is programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region, the method comprising:

for each of a plurality of the memory cells;

1) applying a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

2) reading a program state of the memory cell, and

3) repeating steps 1 and 2 until the memory cell exhibits a read current in step 2 which reaches a first threshold value, wherein the repeating of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated; and

after the first threshold value is reached for all the plurality of memory cells, applying a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a second step value relative to the programming voltages applied in steps 1-3.

19. The method of claim 18, wherein the second step value is greater than the first step value.

20. A memory device, comprising:

memory cells each including;

source and drain regions in a semiconductor substrate with a channel region therebetween,

a floating gate disposed over and affecting a conductivity of at least a portion of the channel region,

one or more additional conductive gates insulated from the floating gate and the substrate,

wherein each memory cell is configured to be programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region;

control circuitry configured to;

1) apply a pulse of programming voltages to the source regions and the one or more conductive gates for a plurality of the memory cells,

2) read program states of the plurality of memory cells, and

3) repeat steps 1 and 2 until at least one of the plurality of memory cells exhibits a read current in step 2 which reaches a first threshold value, wherein the repeat of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated;

after the first threshold value has been reached, for each of a first subset of the plurality of memory cells;

4) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

5) read a program state of the memory cell, and

6) repeat steps 4 and 5 until the memory cell exhibits a read current in step 5 which reaches a second threshold value different from the first threshold value, wherein the repeat of steps 4 and 5 includes increasing at least one of the programming voltages of step 4 by a second step value each time step 4 is repeated, wherein the second step value is less than the first step value; and

after the first threshold value has been reached, for each of a second subset of the plurality of memory cells;

7) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

8) read a program state of the memory cell, and

9) repeat steps 7 and 8 until the memory cell exhibits a read current in step 8 which reaches a third threshold value different from the first and second threshold values, wherein the repeat of steps 7 and 8 includes increasing at least one of the programming voltages of step 7 by a third step value each time step 7 is repeated, wherein the third step value is less than the first step value.

21. The memory device of claim 20, wherein the second and third step values are equal to each other.

22. The memory device of claim 20, wherein the first and third step values are greater than the second step value.

23. The memory device of claim 20, wherein the first threshold value is greater than the second threshold value, and the second threshold value is greater than the third threshold value.

24. The memory device of claim 20, wherein the one or more additional conductive gates for each memory cell includes a control gate disposed over and affecting the conductivity of a second portion of the channel region.

25. The memory device of claim 20, wherein after the second threshold value has been reached for the first subset of the plurality of memory cells, and after the third threshold value has been reached for the second subset of the plurality of memory cells, for each of a third subset of the plurality of memory cells the controller is configured to:

10) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

11) read a program state of the memory cell, and

12) repeat steps 10 and 11 until the memory cell exhibits a read current in step 11 which reaches a fourth threshold value different from the first and second and third threshold values, wherein the repeat of steps 10 and 11 includes increasing at least one of the programming voltages of step 10 by a fourth step value each time step 10 is repeated, wherein the fourth step value is greater than the second and third step values.

26. The memory device of claim 25, wherein the fourth step value is equal to the first step value.

27. The memory device of claim 25, further comprising:

after the fourth threshold value is reached for all the third subset of the plurality of memory cells, the controller configured to apply a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all of the third subset of the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a fifth step value relative to the programming voltages applied in steps 10-12.

28. The memory device of claim 27, wherein the fifth step value is greater than the fourth step value.

29. A memory device comprising:

memory cells each including;

source and drain regions in a semiconductor substrate with a channel region therebetween,

a floating gate disposed over and affecting a conductivity of at least a portion of the channel region,

one or more additional conductive gates insulated from the floating gate and the substrate,

wherein each memory cell is configured to be programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region;

control circuitry configured to;

for each of a first subset of a plurality of the memory cells;

1) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

2) read a program state of the memory cell, and

3) repeat steps 1 and 2 until the memory cell exhibits a read current in step 2 which reaches a first threshold value, wherein the repeat of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated; and

for each of a second subset of the plurality of memory cells;

4) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

5) read a program state of the memory cell, and

6) repeat steps 4 and 5 until the memory cell exhibits a read current in step 5 which reaches a second threshold value different from the first threshold value, wherein the repeat of steps 4 and 5 includes increasing at least one of the programming voltages of step 4 by a second step value each time step 4 is repeated.

30. The memory device of claim 29, wherein the first and second step values are equal to each other.

31. The memory device of claim 29, wherein the second step value is greater than the first step value.

32. The memory device of claim 29, wherein the first threshold value is greater than the second threshold value.

33. The memory device of claim 29, wherein the one or more additional conductive gates for each memory cell includes a control gate disposed over and affecting the conductivity of a second portion of the channel region.

34. The memory device of claim 29, wherein after the first threshold value has been reached for the first subset of the plurality of memory cells, and after the second threshold value has been reached for the second subset of the plurality of memory cells, for each of a third subset of the plurality of memory cells the control circuit is configured to:

7) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

8) read a program state of the memory cell, and

9) repeat steps 7 and 8 until the memory cell exhibits a read current in step 8 which reaches a third threshold value different from the first and second threshold values, wherein the repeat of steps 7 and 8 includes increasing at least one of the programming voltages of step 7 by a third step value each time step 7 is repeated, wherein the third step value is greater than the first and second step values.

35. The memory device of claim 34, further comprising:

after the third threshold value is reached for all the third subset of the plurality of memory cells, the control circuitry configured to apply a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all of the third subset of the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a fourth step value relative to the programming voltages applied in steps 7-9.

36. The memory device of claim 35, wherein the fourth step value is greater than the third step value.

37. A memory device comprising:

memory cells each including;

source and drain regions in a semiconductor substrate with a channel region therebetween,

a floating gate disposed over and affecting a conductivity of at least a portion of the channel region,

one or more additional conductive gates insulated from the floating gate and the substrate,

wherein each memory cell is configured to be programmable by applying programming voltages to the source region and the one or more additional conductive gates to cause electrons originating from the drain region to be injected onto the floating gate, and wherein a program state of each memory cell is readable by applying a voltage differential between the source and the drain regions and measuring a read current in the channel region;

control circuitry configured to;

for each of a plurality of the memory cells;

1) apply a pulse of programming voltages to the source region and the one or more conductive gates of the memory cell,

2) read a program state of the memory cell, and

3) repeat steps 1 and 2 until the memory cell exhibits a read current in step 2 which reaches a first threshold value, wherein the repeat of steps 1 and 2 includes increasing at least one of the programming voltages of step 1 by a first step value each time step 1 is repeated; and

after the first threshold value is reached for all the plurality of memory cells, apply a kicker pulse of programming voltages to the source regions and the one or more conductive gates for all the plurality of the memory cells, wherein the applying of the kicker pulse includes increasing at least one of the programming voltages by a second step value relative to the programming voltages applied in steps 1-3.

38. The memory device of claim 37, wherein the second step value is greater than the first step value.