Non-volatile semiconductor memory and method for reading a memory cell
View Patent ↗A method for reading a memory cell, wherein the memory cell comprises two source/drain regions and a gate, wherein the source/drain regions are each connected to a respective local bitline, and, wherein one of the source/drain regions of a neighboring memory cell is connected to one of the local bitlines, the other source/drain region of the neighboring memory cell being connected to another local bitline, comprising the steps of connecting the local bitline that connects the source/drain region of the memory cell and the source/drain region of the neighboring memory cell to a first global bitline, connecting the local bitline that connects the other source/drain region of the memory cell to a second global bitline, connecting the local bitline that connects the other source/drain region of the neighboring memory cell to one of a plurality of local power rails, applying a gate potential to the gate of the memory cell, applying a potential to the first global bitline and applying another potential to the second global bitline, and measuring the current flowing through the first global bitline.
1. A method for reading a memory cell, wherein the memory cell comprises two source/drain regions and a gate, wherein the source/drain regions are each connected to a respective local bitline, and, wherein one of the source/drain regions of a neighboring memory cell is connected to one of the local bitlines, the other source/drain region of the neighboring memory cell is connected to another local bitline, the method comprising:
connecting the local bitline that connects the source/drain region of the memory cell and the source/drain region of the neighboring memory cell to a first global bitline;
connecting the local bitline that connects the other source/drain region of the memory cell to a second global bitline;
connecting the local bitline that connects the other source/drain region of the neighboring memory cell to one of a plurality of local power rails;
applying a gate potential to the gate of the memory cell;
applying a potential to the first global bitline and applying another potential to the second global bitline; and
measuring the current flowing through the first global bitline.
2. The method according to claim 1 , wherein the potential of the local power rail is kept at a fixed level.
3. The method according to claim 2 , wherein the potential of the local power rail is based on the potential applied to the first global bitline.
4. The method according to claim 1 , wherein further memory cells and further local bitlines are connected to the memory cell and the neighboring memory cell to form a virtual ground array, wherein the further memory cell that has one of its source/drain regions connected to the same local bitline as the memory cell has its other local bitline that connects its other source/drain region connected to a local power rail.
5. The method according to claim 1 , wherein all the local bitlines except for the local bitlines that are connected to the first global bitline and the second global bitline are connected to one of the plurality of local power rails.
6. A non-volatile semiconductor memory comprising:
a plurality of memory cells connected to a plurality of local bitlines to form a virtual ground array;
a plurality of global bitlines;
a plurality of first switching elements for connecting each of the local bitlines to one of the global bitlines;
a plurality of local power rails; and
a plurality of second switching elements for connecting the local bitlines to one of the local power rails.
7. The semiconductor memory according to claim 6 , further comprising a control unit for controlling the first switching elements and the second switching elements.
8. The semiconductor memory according to claim 7 , wherein the first switching elements and the second switching elements operate independently from each other.
9. The semiconductor memory according to claim 8 , wherein the control unit operates the first switching elements and the second switching elements so that each of the local bitlines is either connected to one of the global bitlines or to one of the local power rails or is neither connected to a global bitline nor a local power rail.
10. The semiconductor memory according to claim 9 , wherein the control unit operates the first switching elements so that the local bitlines connecting a memory cell that is to be read are connected to two respective global bitlines.
11. The semiconductor memory according to claim 10 , wherein the control unit operates the second switching elements so that the local bitlines not connecting the memory cell that is to be read are connected to one of the local power rails.
12. The semiconductor memory according to claim 6 , wherein the local power rails are connected to a fixed potential.
13. The semiconductor memory according to claim 12 , wherein the fixed potential is related to a potential that is applied to one of the global bitlines connected by the first switching elements while reading a memory cell.
14. The semiconductor memory according to claim 13 , wherein the fixed potential is based on the potential of the global bitline through which a current that is measured to determine the state stored in the memory cell is flowing.
15. The semiconductor memory according to claim 12 , wherein the local power rails are formed in a metallization layer that is the same metallization layer as the local bitlines or wordlines.
16. The semiconductor memory according to claim 12 , wherein the local power rails are connected to a wordline decoder.
17. The semiconductor memory according to claim 12 , wherein each local power rail comprises a plurality of power rails that are connected in parallel.
18. The semiconductor memory according to claim 6 , wherein the local power rails are connected by bitlines that are formed in the same layer as the global bitlines.
19. The semiconductor memory according to claim 18 , wherein each local power rail comprises a plurality of power rails that are connected in parallel by the bitline connecting the local power rails.
20. The semiconductor memory according to claim 18 , wherein the bitlines connecting the local power rails are connected to sense amplifiers.
21. The semiconductor memory according to claim 18 , wherein the bitlines connecting the local power rails are connected to a bitline decoder.
22. The semiconductor memory according to claim 6 , wherein the local power rails are connected to a fixed potential and wherein the value of the fixed potential depends on whether memory cells are to be read, written or erased.
23. The semiconductor memory according to claim 6 , wherein the memory cells comprise nitride read only memory cells.
24. A non-volatile semiconductor memory comprising:
a plurality of memory cells connected to a plurality of local bitlines to form a virtual ground array;
a plurality of global bitlines;
a plurality of first switching elements for connecting each of the local bitlines to one of the global bitlines;
a plurality of local power rails;
a plurality of second switching elements for connecting the local bitlines to one of the local power rails; and
means for controlling the first switching elements and the second switching elements.