MRAM design with local write conductors of reduced cross-sectional area
Embodiments of the present invention disclose an MRAM device having a plurality of magnetic memory cells grouped into words, and write conductors for carrying write currents to write to the memory cells, wherein at least some of the write conductors have a reduced cross-sectional area in the vicinity of a group of memory cells.
1. A magnetic memory device, comprising:
a plurality of magnetic memory cells arranged to form rows; and
first write conductors to energize the cells during write operations, each write conductor having at least some portion of increased cross-sectional area and a portion of reduced cross-sectional area; wherein the portions of reduced cross-sectional area are of a material having a higher electro-migration limit than the portions of increased cross-sectional area.
2. The magnetic memory device of claim 1 , wherein the first write conductors each comprise a common global write line corresponding to a first portion of increased cross-sectional area, a local write line that branches from a common global write line, the local write line corresponding to the portion of reduced cross-sectional area.
3. The magnetic memory device of claim 2 , wherein the common global write line feeds several local write lines.
4. The magnetic memory device of claim 3 , wherein each of the several local write lines spans a group of magnetic memory cells in a row defining a word.
5. The magnetic memory device of claim 4 , wherein the word comprises one of 8 or 16 bits.
6. The magnetic memory device of claim 4 , wherein each local write line extends longitudinally along a row.
7. The magnetic memory device of claim 1 , wherein a ratio of the portions of reduced cross-sectional area to the portions of increased cross-sectional area is 1:4.
8. The magnetic memory device of claim 1 , wherein the portions of reduced cross-sectional area have a smaller thickness than the portions of increase cross-sectional area.
9. The magnetic memory device of claim 1 , wherein the portions of reduced cross-sectional area have a smaller width than the portions of increase cross-sectional area.
10. The magnetic memory device of claim 4 , further comprising a word selection device to select a particular group of memory cells defining a word to be written to during a write operation.
11. The magnetic memory device of claim 10 , wherein the word selection device comprises a write transistor to connect each local write line to a ground potential.
12. The magnetic memory device of claim 11 , wherein the write transistor is controlled by read common global line.
13. The magnetic memory device of claim 4 , further comprising second write conductors, each associated with a memory cell and extending in a direction transverse to the first write conductors.
14. The magnetic memory device of claim 13 , wherein each second write conductor is connected to ground potential through a dedicated read access transistor.
15. The magnetic memory device of claim 14 , further comprising a single line to control the read access transistors associated with each group.