Semiconductor memory device controlling operation timing of the sense circuit
View Patent ↗According to one embodiment, a semiconductor memory device includes a memory cell array, a bit line, a source line, and a sense circuit. The memory cell array includes memory strings which include memory cells connected in series and stacked above a semiconductor substrate. The bit line is coupled to one of the memory strings and is capable of transferring data. The source line is coupled to one of the memory strings. When data is read, a read current flows from a bit line into the source line. The sense circuit is coupled to the bit line and senses read data. An operation timing of the sense circuit is determined on the basis of a current flowing through the source line.
1. A semiconductor memory device comprising:
a plurality of memory strings including memory cells connected in series and stacked above a semiconductor substrate;
bit lines electrically coupled to one of the memory strings;
source lines electrically coupled to one of the memory strings;
a sense circuit electrically coupled to one of the bit lines;
a generation module configured to generate a reference current based on a current flowing through the source line;
a reference sense circuit configured to sense the reference current; and
a sense control circuit configured to control an operation timing of the sense circuit based on a sense operation,
wherein the operation timing of the sense circuit is determined based on the current flowing in the source line.
2. The device according to claim 1 , wherein the plurality of memory strings include a first memory string electrically coupled to the bit lines and a first source line and a second memory string electrically coupled to the bit lines and a second source line,
the second source line is electrically isolated from the first source line, and
the operation timing of the sense circuits in reading data from the first memory string is determined based on current flowing through the second source line.
3. The device according to claim 2 , further comprises third memory strings coupled to the bit line and a third source line,
the third source line is electrically isolated from the first and second source lines, and
the operation timing of the sense circuit in reading data from the first memory string is determined based on currents flowing through the second source line and the third source line.
4. The device according to claim 1 , wherein the plurality of memory strings include a first cell group which includes first memory string and a second memory string electrically coupled to a first source line and a second cell group which includes a third memory string and a fourth memory string electrically coupled to a second source line,
the first source line is electrically coupled to the second source line,
the first and second memory strings hold complementary data to each other, and
the operation timing of the sense circuits in reading data from the first cell group is determined based on currents flowing through the first source lines and the second source line.
5. The device according to claim 4 , wherein the first cell group is used as a ROM fuse.
6. The device according to claim 1 ,
wherein the operation timing of the sense circuits is determined based on the sense operation timing of the reference current by the reference sense circuit,
the sense circuits sense data by at least two sense operations and omit a second sense operation for a column determined to be on in a first sense operation, and
a magnitude of the reference current generated by the generation module and/or or the number of reference sense circuits used are variable according to the number of memory cells to be sensed.
7. The device according to claim 6 , wherein the generation module includes:
a first transistor, a source of which is connected to the source line; and
a second transistor, a drain current of which is a drain current, and
a size of the first transistor or a size of the second transistor are variable according to the number of memory cells to be sensed.
8. The device according to claim 6 , wherein the magnitude of the reference current flowing through each of the reference sense circuits is substantially constant in the first and second sense operations.
9. The device according to claim 6 , wherein
the magnitude of the reference current flowing through each of the reference sense circuits in the second sense operation is smaller than that in the first sense operation.
10. The device according to claim 6 , wherein the memory string includes:
a pillar semiconductor layer electrically isolated from the semiconductor substrate,
a gate insulating film disposed to surround the semiconductor layer,
a charge storage layer disposed to surround the gate insulating film,
a block layer disposed to surround the charge storage layer, and
a plurality of gate electrodes disposed to surround the block layer, and
the semiconductor layer has one end electrically coupled to the bit line and the other end electrically coupled to the source line.
11. A method of reading data from a semiconductor memory device including a plurality of memory strings including memory cells connected in series and stacked above a semiconductor substrate, the method comprising:
selecting a first memory string from the memory strings and allowing a cell current to flow in a bit line electrically coupled to the first memory string;
generating a reference current based on currents flowing through source lines electrically coupled to unselected second memory strings;
sensing the reference current; and
sensing the cell current with the timing based on the result of sensing the reference current,
wherein the sensing the cell current is performed on a plurality of columns simultaneously,
second sensing is performed on a column in which a memory cell has been determined to be off after the cell current has been sensed, and
a magnitude of the reference current or a number of reference sense circuits which sense the reference current are variable according to a number of memory cells to be sensed.
12. The method according to claim 11 , wherein the first memory string is electrically coupled to a first source line, and
the second memory string is electrically coupled to a second source line electrically isolated from the first source line.
13. The method according to claim 12 , wherein the reference current is generated further based on a third source line electrically coupled to an unselected third memory string, and
the third source line is electrically isolated from the first and second source lines.
14. The method according to claim 11 , wherein the first memory string is electrically coupled to the source line and
the first memory string is used as a ROM fuse.
15. The method according to claim 11 , wherein the magnitude of the reference current flowing through each of the reference sense circuits is substantially constant in the first and second sense operations.
16. The method according to claim 11 , wherein the magnitude of the reference current flowing through each of the reference sense circuits in the second sense operation is smaller than that in the first sense operation.