Redundancy circuits for semiconductor memory
View Patent ↗A semiconductor random access memory device has an array of normal memory and an array of dummy memory cells. The array of the dummy memory cells are controlled in order to form a redundant twin-cell structure that includes at least one of the dummy memory cells.
1. A memory system comprising:
an array of normal memory cells;
an array of dummy memory cells having less capacitance than the normal memory cells; and
means for controlling the array of the dummy memory cells in order to form a redundant twin-cell structure comprising at least one of the dummy memory cells.
2. The memory system of claim 1 , wherein the array of normal memory cells are tested to detect a defective normal memory cell, and wherein the redundant twin-cell structure is used in place of the defective normal memory cell.
3. The memory system of claim 2 further comprising a plurality of world lines providing access to a plurality of the array of normal memory cells, at least one redundancy word line providing access to a plurality of the array of dummy memory cells, and a decoder circuit coupled to the world lines and redundancy word line.
4. The memory system of claim 3 , wherein the redundant twin-cell structure comprises one dummy word cell and one normal memory cell combined as twin-cell used for single-bit storage.
5. The memory system of claim 3 , wherein the redundant twin-cell structure comprises two dummy word cells combined as twin-cell used for single-bit storage.
6. A memory system comprising:
a row interface circuit;
a decoder circuit coupled to the row interface circuit; and
a plurality of memory arrays, each of the plurality of memory arrays coupled to the decoder circuit and each further comprising:
a plurality of world lines coupling a plurality of normal memory cells;
at least one redundancy word line coupling a plurality of dummy memory cells,
having less storage capacitance than normal cells; and
a plurality of bit lines coupling the plurality of normal memory cells and dummy memory cells;
wherein the row interface circuit controls the decoder circuit such that the decoder circuit accesses the at least one redundancy word line to form a redundant twin-cell structure.
7. The memory system of claim 6 , wherein the plurality of normal memory cells are tested to detect a defective normal memory cell, and wherein the redundant twin-cell structure is used in place of the defective normal memory cell.
8. The memory system of claim 7 , wherein the redundant twin-cell structure comprises one dummy memory cell and one normal memory cell combined as twin-cell used for single-bit storage.
9. The memory system of claim 7 , wherein the redundant twin-cell structure comprises two dummy memory cells combined as twin-cell used for single-bit storage.
10. A memory system comprising:
a decoder circuit coupled to a row interface circuit; and
a memory array coupled to the decoder circuit, the memory array further comprising:
a plurality of world lines coupling a plurality of normal memory cells; and
a redundancy word line coupling a plurality of dummy memory cells having less
storage capacitance than normal memory cells;
wherein the decoder circuit accesses the redundancy word line to form a redundant twin-cell structure using two dummy memory cells.
11. The memory system of claim 10 , wherein the redundancy word line comprises two dummy word lines tied together to provide access to the plurality of dummy memory cells.
12. The memory system of claim 10 further comprising a plurality of bit lines coupling the plurality of normal memory cells and dummy memory cells in order to selectively access the contents of the normal and dummy memory cells.
13. A memory system comprising:
a decoder circuit coupled to a row interface circuit; and
a memory array coupled to the decoder circuit, the memory array further comprising:
a plurality of world lines coupling a plurality of normal memory cells; and
at least one redundancy word line coupling a plurality of dummy memory cells,
which have less storage capacitance than normal memory cells;
wherein the decoder circuit accesses the redundancy word line to form at least one redundant twin-cell structure using one dummy memory cell and one normal memory cell.
14. The memory system of claim 13 , wherein the redundancy word line comprises two dummy word lines tied together to provide access to the plurality of dummy memory cells.
15. The memory system of claim 13 further comprising a plurality of bit lines coupling the plurality of normal memory cells and dummy memory cells in order to selectively access the contents of the normal and dummy memory cells, and wherein the dummy memory cells are formed at the edges of the memory array and are influenced by a proximity effect to cause there shape to dictate less storage capacitance that normal memory cells.
16. A method of storing information in a semiconductor memory device having a memory array with normal memory cells and with dummy memory cells, the method comprising:
running a test on the normal memory cells within the memory array in order to detect a defective normal memory cell;
identifying a word line associated with the defective normal memory cell;
disabling the word line associated with the defective normal memory cell; and
enabling dummy memory cells configured as twin-cells in place of the defective normal cell, wherein the dummy memory cells are formed in such a way that they have less storage capacitance than do normal memory cells.
17. The method of claim 16 , further comprising using the dummy memory cells configured as twin-cells for single-bit storage.
18. A method of storing information in a semiconductor memory device having a memory array with normal memory cells and with dummy memory cells, the method comprising:
running a test on the normal memory cells within the memory array in order to detect a defective normal memory cell;
identifying a word line associated with the defective normal memory cell; and
coupling the word line associated with the defective normal memory cells with a redundancy word line associated with dummy memory cells having less storage capacitance than normal memory cells such that twin-cells are configured comprising at least one normal memory cell and one dummy memory cell.
19. The method of claim 18 , further comprising using at least one normal memory cell and one dummy memory cell configured as twin-cells for single-bit storage.
20. A memory cell array comprising:
a plurality of word lines and a plurality of bit lines;
at least one redundancy word line;
at least some of the plurality of word lines and at least some of the plurality of bit lines intersecting at a plurality of normal memory cells, thereby providing access to the plurality of normal memory cells via at least some of the plurality of word lines and at least some of the plurality of bit lines; and
the at least one redundancy word line and at least some of the plurality of bit lines intersecting at a plurality of dummy memory cells having less storage capacitance than normal memory cells, thereby providing access to the plurality of dummy memory cells via the at least one redundancy word line and at least some of the plurality of bit lines;
wherein at least one dummy memory cell is combined with another memory cell to form a twin-cell structure for single-bit storage.
21. The memory cell array of claim 20 , wherein the twin-cell structure for single-bit storage comprises one dummy memory cell and one normal memory cell combined together.
22. The memory cell array of claim 20 , wherein the twin-cell structure for single-bit storage comprises two dummy memory cells combined together.