Nonvolatile semiconductor memory device
View Patent ↗A nonvolatile semiconductor memory device comprises a memory cell array which includes memory cells and reference cells, the reference cells including a first reference cell and a second reference cell. A data judging control unit generates an average reference current based on a first reference current from the first reference cell and a second reference current from the second reference cell, and determines data of each of the memory cells by comparison of a read-out current of each memory cell with the average reference current. A control unit performs a program verification operation to each memory cell. A compensation current supplying unit supplies a compensation current to a bit line of a target memory cell when a leak current of a neighboring memory cell adjacent to the target memory cell exceeds a predetermined reference value during the program verification operation.
1. A nonvolatile semiconductor memory device comprising:
a memory cell array including memory cells and reference cells, the reference cells including a first reference cell and a second reference cell;
a data judging control unit generating an average reference current based on a first reference current supplied from the first reference cell and a second reference current supplied from the second reference cell, the data judging control unit determining data of each of the memory cells by comparison of a read-out voltage of each of the memory cells with the average reference current;
a control unit performing a program verification operation to each memory cell of the memory cell array; and
a compensation current supplying unit supplying a compensation current to a bit line of a target memory cell of the memory cell array when a leak current of a neighboring memory cell adjacent to the target memory cell exceeds a predetermined reference value during the program verification operation of the control unit to the target memory cell, said compensation current compensating the leak current of the neighboring memory cell.
2. The nonvolatile semiconductor memory device according to claim 1 wherein the control unit includes a first control unit that performs a program operation to the target memory cell of the memory cell array until a first reference voltage that is lower than a target reference voltage is obtained.
3. The nonvolatile semiconductor memory device according to claim 2 wherein the control unit includes a second control unit that detects the leak current of the neighboring memory cell adjacent to the target memory cell during the program verification operation being performed to the target memory cell, and determines whether the detected leak current exceeds the predetermined reference value.
4. The nonvolatile semiconductor memory device according to claim 1 wherein the compensation current supplying unit includes a transistor connected to the bit line of the target memory cell and a current supply circuit connected to the transistor.
5. The nonvolatile semiconductor memory device according to claim 1 wherein the data judging control unit includes a program-verification reference cell that has a predetermined threshold value.
6. The nonvolatile semiconductor memory device according to claim 1 wherein the data judging control unit comprises:
a first program-verification reference cell having a first threshold value used to set the first reference current;
a second program-verification reference cell having a second threshold value used to set a target reference current; and
a third reference cell having a threshold value used to detect the leak current of the neighboring memory cell.
7. The nonvolatile semiconductor memory device according to claim 6 wherein the first reference current set by the first program-verification reference cell is lower than the target reference current set by the second program-verification reference cell.
8. The nonvolatile semiconductor memory device according to claim 1 wherein each of the memory cells of the memory cell array is configured to store 2 bits of information by trapping charge in a charge-trap layer of a silicon nitride film.