Phase change memory device and related programming method

• US 20080074918A1
• Filed: 04/23/2007
• Published: 03/27/2008
• Est. Priority Date: 09/27/2006
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Cho, Woo-Yeong, Kang, Sang-Beom, Ro, Yu-Hwan, Lee, Kwang-Jin
• Granted Patent: US 7,522,449 B2
• Time in Patent Office: Days
• US Class Current: 365/163
• CPC Class Codes: G11C 11/5678 using amorphous/crystalline phase transition storage elements
• CPC Class Codes: G11C 13/0004 comprising amorphous/crystalline phase transition cells
• CPC Class Codes: G11C 13/0064 Verifying circuits or methods
• CPC Class Codes: G11C 13/0069 Writing or programming circuits or methods
• 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
• CPC Class Codes: G11C 2013/0076 Write operation performed depending on read result

Abstract

In various methods of performing program operations in phase change memory devices, selected memory cells are repeatedly programmed to obtain resistance distributions having desired characteristics such as adequate sensing margins.

Claims

1. A method of performing a program operation in a phase change memory device comprising a plurality of phase change memory cells, the method comprising:

(a) selecting multiple memory cells among the plurality of phase change memory cells;

(b) programming a bit of program data to each of the selected memory cells, wherein each bit of program data comprises a bit of set data or a bit of reset data;

(c) performing a verification read operation on the selected memory cells, the verification read operation comprising comparing a bit of read data stored in each of the selected memory cells with a corresponding bit among the program data;

(d) identifying any failed cells, for which the read data is detected to be different from the corresponding program data, among the selected memory cells by determining whether each bit of read data stored in the selected memory cells is the same as the corresponding bit among the program data;

(e) upon identifying at least one failed cell among the selected memory cells, determining whether a corresponding bit of program data for any of the failed cells comprises a bit of set data, and determining whether a corresponding bit of program data for any of the failed cells comprises a bit of reset data;

(f) upon determining that a corresponding bit of program data for any of the failed cells comprises a bit of set data, re-programming all of the selected memory cells for which the corresponding bit of program data comprises a bit of set data; and

(g) upon determining that a corresponding bit of program data for any of the failed cells comprises a bit of reset data, re-programming each of the failed cells for which the corresponding bit of program data comprises a bit of reset data, and not re-programming selected memory cells that have been successfully programmed with a bit of reset data.

2. The method of claim 1, further comprising:

(h) upon determining, in the verification read operation, that each bit of read data stored in the selected memory cells is identical to a corresponding bit among the program data, terminating the program operation.

3. The method of claim 2, further comprising:

repeating (c), (d), (e), and (f) until each bit of read data stored in the selected memory cells is the same as a corresponding bit among the program data.

4. The method of claim 1, further comprising:

(h) upon determining, in the verification read operation, that each bit of read data stored in the selected memory cells is the same as a corresponding bit among the program data, determining whether each of the selected memory cells for which the corresponding bit of program data comprises a bit of reset data has been successfully programmed twice in succession; and

(i) upon determining that at least one of the selected memory cells for which the corresponding bit of program data comprises a bit of reset data has not been successfully programmed twice in succession, repeating (b), (c), (d), (e), (f) and (g) until each of the selected memory cells for which the corresponding bit of program data comprises a bit of reset data has been successfully programmed twice in succession.

5. The method of claim 1, further comprising:

(h) upon determining, in the verification read operation, that each bit of read data stored in the selected memory cells is the same as a corresponding bit among the program data, determining whether each of the selected memory cells has been successfully programmed twice in succession; and

(i) upon determining that at least one of the selected memory cells has not been successfully programmed twice in succession, repeating (b), (c), (d), (e), (f) and (g) until each of the selected memory cells has been successfully programmed twice in succession.

6. The method of claim 1, wherein each of the plurality of phase change memory cells comprises a phase change material and a diode.

7. The method of claim 1, wherein programming the bit of program data to each of the selected memory cells comprises:

applying respective program currents or program voltages to the selected memory cells to heat respective phase change materials within the selected memory cells.

8. A method of performing a program operation in a phase change memory device comprising a plurality of phase change memory cells, the method comprising:

(a) selecting multiple memory cells among the plurality of phase change memory cells;

(b) programming a bit of program data to each of the selected memory cells, wherein each bit of program data comprises a bit of set data or a bit of reset data;

(c) performing a verification read operation on the selected memory cells, the verification read operation comprising comparing a bit of read data stored in each of the selected memory cells with a corresponding bit among the program data;

(d) identifying any failed cells, for which the read data is detected to be different from the corresponding program data, among the selected memory cells by determining whether each bit of read data stored in the selected memory cells is the same as the corresponding bit among the program data; and

(e) upon identifying at least one failed cell among the selected memory cells, re-programming all of the selected memory cells.

9. The method of claim 8, further comprising:

(f) upon determining, in the verification read operation, that each bit of read data stored in the selected memory cells is identical to a corresponding bit among the program data, terminating the program operation.

10. The method of claim 8, further comprising:

repeating (c), (d), and (e) until each of the selected memory cells has been successfully programmed.

11. The method of claim 8, further comprising:

upon identifying at least one failed cell among the selected memory cells, generating a fail indication; and

re-programming all of the selected memory cells in response to the fail indication.

12. The method of claim 8, wherein each of the plurality of phase change memory cells comprises a phase change material and a diode.

13. The method of claim 8, wherein programming the bit of program data to each of the selected memory cells comprises:

applying respective program currents or program voltages to the selected memory cells to heat respective phase change materials within the selected memory cells.

14. A method of performing a program operation in a phase change memory device comprising a plurality of phase change memory cells, the method comprising:

(a) selecting multiple memory cells among the plurality of phase change memory cells;

(b) programming a bit of program data to each of the selected memory cells, wherein each bit of program data comprises a bit of set data or a bit of reset data;

(c) performing a verification read operation on the selected memory cells, the verification read operation comprising comparing a bit of read data stored in each of the selected memory cells with a corresponding bit among the program data;

(d) identifying any failed cells, for which the read data is detected to be different from the corresponding program data, among the selected memory cells by determining whether each bit of read data stored in the selected memory cells is the same as the corresponding bit among the program data; and

(e) upon identifying at least one failed cell among the selected memory cells, re-programming all failed cells among the selected memory cells.

15. The method of claim 14, further comprising:

(f) upon determining, in the verification read operation, that each bit of read data stored in the selected memory cells is identical to a corresponding bit among the program data, terminating the program operation.

16. The method of claim 14, further comprising:

repeating (c), (d), and (e) until each of the selected memory cells has been successfully programmed.

17. The method of claim 14, further comprising:

upon identifying at least one failed cell among the selected memory cells, generating a fail indication; and

re-programming all failed cells among the selected memory cells in response to the fail indication.

18. The method of claim 14, wherein each of the plurality of phase change memory cells comprises a phase change material and a diode.

19. The method of claim 14, wherein each of the plurality of phase change memory cells comprises a phase change material and an access transistor.

20. The method of claim 14, wherein programming the bit of program data to each of the selected memory cells comprises:

applying respective program currents or program voltages to the selected memory cells to heat respective phase change materials within the selected memory cells.