Static memory long write test

• US 5,577,051 A
• Filed: 12/22/1993
• Issued: 11/19/1996
• Est. Priority Date: 12/22/1993
• Status: Expired due to Term

• Current Assignee: Micron Technology, Inc.
• Original Assignee: SGS Thomson Microelectronics Inc (STMicroelectronics NV)
• Inventors: McClure, David C.
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): CHUNG, PHUNG M
• Application Number:
  US08/173,197
• Time in Patent Office: 1,063 Days
• Field of Search: 371/21.4, 371/21.1, 371/15.1, 371/21.3, 365/201, 365/154, 365/49, 324/210
• US Class Current: 714/721
• CPC Class Codes: G11C 11/41 forming static cells with positive feedback, i.e. cells not needing refreshing or charge regeneration, e.g. bistable multivibrator or Schmitt trigger
• CPC Class Codes: G11C 29/02 Detection or location of defective auxiliary circuits, e.g. defective refresh counters
• CPC Class Codes: G11C 29/025 in signal lines
• CPC Class Codes: G11C 29/50 Marginal testing, e.g. race, voltage or current testing

Abstract

According to the present invention, after a test data pattern has been written to selected static memory cells, the wordlines of the memory cells are turned off and the bitline true and bitline complement of the memory cells are simultaneously pulled to a predetermined logic level for the duration of the long write test so that the memory cells are disturbed. After the long write test, the contents of the memory cells are read to determine which memory cells contain corrupted data and therefore have bitline to memory cell leakage problems.

Claims

1. A method for performing a long write test on a static memory, comprising the steps of:

writing a test data pattern to a plurality of memory cells, having a data contents, of a static memory, wherein each memory cell, having at least one wordline, is connected to a bitline true and a bitline complement;

turning off the wordline of each .memory cell of the plurality of memory cells during the long write test;

pulling both the bitline true and bitline complement connected to each memory cell of the plurality of memory cells down to a low logic level during the long write test;

exiting the long write test; and

reading the data contents of the plurality of memory cells to determine which of the plurality of memory cells contain corrupted data.

2. The method of claim 1, wherein the static memory is a static random access memory (SRAM).

3. The method of claim 1, wherein the static memory is a First In First Out (FIFO) memory.

4. The method of claim 1, wherein the bitline true is connected to a bitline true load and the bitline complement is connected to a bitline complement load, and the bitline true load and the bitline complement load are turned off when the bitline true and the bitline complement are pulled down to a low logic level during the long write test.

5. The method of claim 4, wherein the bitline true load and the bitline complement load are turned off for the duration of the long write test by forcing a bus connected to the bitline true load, the bitline complement load, a first pull-down transistor gate, and a second pull-down transistor gate to a predetermined logic level, and wherein the first pull-down transistor gate is connected to the bitline true load and the second pull-down transistor gate is connected to the bitline complement load.

6. The method of claim 5, wherein the bitline true load is a first transistor gate and the bitline complement load is a second transistor gate.

7. The method of claim 6, wherein the bitline true load is a first p-channel transistor gate, the bitline complement load is a second p-channel transistor gate, the first pull-down transistor gate is a first n-channel pull-down transistor, and the second pull-down transistor gate is a second n-channel pull-down transistor, such that when the bus is forced to the predetermined logic level, the first p-channel transistor gate and the second p-channel transistor gate are turned off, the first n-channel pull-down transistor and the second n-channel pull-down transistor are turned on, and the bitline true and bitline complement are pulled to a logic low level.

8. The method of claim 5, wherein the predetermined logic level is a high logic level.

9. The method of claim 1, wherein each of the memory cells is a Poly-R Load memory cell.

10. The method of claim 1, wherein each of the memory cells is a 6 Transistor memory cell.

11. The method of claim 1, wherein the low logic level is equal to ground potential.

12. The method of claim 1, wherein the bitline true is connected to a first passgate, the bitline complement is connected to a second passgate, a column decode signal is connected to both the first passgate and the second passgate, a first write driver having a first data input signal is connected to the first passgate, and a second write driver having a second data input signal is connected to the second passgate, and wherein the bitline true and the bitline complement are pulled to a low logic level by setting the column decode signal to a predetermined logic level, thus turning on a column of the static memory such that the first write driver and the second write driver force the bitline true and the bitline complement to the low logic level.

13. The method of claim 12, wherein the first passgate is a first n-channel transistor and the second passgate is a second n-channel transistor, the column decode signal is connected to the gate of the first n-channel transistor and the gate of the second n-channel transistor, and a source/drain of the first passgate is connected to the first write driver and a source/drain of the second passgate is connected to the second write driver.

14. The method of claim 12, wherein a plurality of columns, having column addresses, of the static memory are turned on by setting the column decode signal to the predetermined logic level, thus overriding the column addresses.

15. The method of claim 12, further comprising a bitline true load connected to the bitline true, a bitline complement load connected to the bitline complement, and a bus connected to the bitline true load and the bitline complement load, wherein the bitline true load and the bitline complement load are turned off for the duration of the long write test by forcing the bus to the predetermined logic level.

16. The method of claim 15, wherein the bitline true load and the bitline complement load are a first p-channel transistor gate and a second p-channel transistor gate, respectively.

17. The method of claim 12, wherein the predetermined logic level is equal to a logic high level.

18. A memory structure which provides improved long write testing of a static memory, comprising:

at least one wordline of a memory cell;

a bitline true of the memory cell which is connected to a true bitline load element and a first pull-down transistor;

a bitline complement of the memory cell which is connected to a complement bitline load element and a second pull-down transistor;

a bus connected to the bitline true load element, the first pull-down transistor, the bitline complement load element, and the second pull-down transistor, wherein after data of a test data pattern has been written to the memory cell, the wordline is turned off during a long write test, and the bitline true and bitline complement are pulled down to a low logic level by forcing the bus to a predetermined logic level such that the bitline true load and the bitline complement load are turned off during the long write test.

19. The memory structure of claim 18, wherein the bitline load is a first transistor gate and the bitline complement load is a second transistor gate.

20. The memory structure of claim 19, wherein the bitline true load is a first p-channel transistor gate, the bitline complement load is a second p-channel transistor gate, the first pull-down transistor gate is a first n-channel pull-down transistor, and the second pull-down transistor gate is a second n-channel pull-down transistor, such that when the bus is forced to the predetermined logic level, the first p-channel transistor gate and the second p-channel transistor gate are turned off, the first n-channel pull-down transistor and the second n-channel pull-down transistor are turned on, and the bitline true and bitline complement are pulled to a logic low level.

21. The memory structure of claim 18, wherein the predetermined logic level is a high logic level.

22. The memory structure of claim 18, wherein the memory cell is a Poly-R Load memory cell.

23. The memory structure of claim 18, wherein the memory cell is a 6 Transistor memory cell.

24. The memory structure of claim 18, wherein the low logic level is equal to ground potential.

25. The memory structure of claim 18, wherein the static memory is a static random access memory (SRAM).

26. The memory structure of claim 18, wherein the static memory is a First In First Out (FIFO) memory.

27. A memory structure which provides improved long write testing of a static memory, comprising:

a bitline true connected to a first transistor of a memory cell;

a bitline complement connected to a second transistor of the memory cell;

a first passgate connected to the bitline true;

a second passgate connected to the bitline complement;

a column decode signal connected to the first passgate and the second passgate;

a first write driver, having a first data input signal, which is connected to the first passgate;

a second write driver, having a second data input signal, which is connected to the second passgate; and

a wordline connected to the first transistor and the second transistor of the memory cell, wherein after data of a test data pattern has been written to the memory cell, the wordline is turned off during a long write test, and the bitline true and the bitline complement are pulled to a logic low level by setting the column decode signal to a predetermined logic level, thus turning on a column of the static memory such that the first write driver and the second write driver force the bitline true and the bitline complement to the logic low level.

28. The memory structure of claim 27, wherein the first passgate is a first n-channel transistor and the second passgate is a second n-channel transistor, the column decode signal is connected to a gate of the first n-channel transistor and a gate of the second n-channel transistor, and a source/drain of the first passgate is connected to the first write driver and a source/drain of the second passgate is connected to the second write driver.

29. The memory structure of claim 27, wherein a plurality of columns, having column addresses, of the static memory are turned on by setting the column decode signal to the predetermined logic level, thus overriding the column addresses.

30. The memory structure of claim 27, further comprising a bitline true load connected to the bitline true, a bitline complement load connected to the bitline complement, and a bus connected to the bitline true load and the bitline complement load, wherein the bitline true load and the bitline complement load are turned off for the duration of the long write test by forcing the bus to the predetermined logic level.

31. The memory structure of claim 30, wherein the bitline true load and the bitline complement load are a first p-channel transistor gate and a second p-channel transistor gate, respectively.

32. The memory structure of claim 27, wherein the predetermined logic level is equal to a logic high level.

33. The memory structure of claim 27, wherein the static memory is a static random access memory (SRAM).

34. The memory structure of claim 27, wherein the static memory is a First In First Out (FIFO) memory.