Non-volatile semiconductor memory device and readout method thereof

1. A non-volatile semiconductor device comprising:

a plurality of memory strings formed by series connection of a plurality of memory cells respectively connected to word lines, wherein each of the memory strings is connected between a bit line via a first select gate transistor and a source line via a second select gate transistor; and

a control circuit controlling the first and second select gate transistors, such that when the voltage of the word line is raised to a predetermined value for data readout from the memory cell, a first status where the first select gate transistor is turned on and the second select gate transistor is turned off and second status where the first select gate transistor is turned off and the second select gate transistor is turned on are generated alternately.

2. The non-volatile semiconductor device as claimed in claim 1 , wherein the control circuit controls the first and second select gate transistors, such that the first status and the second status are generated alternately after a high level voltage is applied to gates of the first and second select gate transistors to turn on both of the first and second select gate transistors.

3. The non-volatile semiconductor device as claimed in claim 1 , wherein the control circuit controls the first and second select gate transistors, such that a high level voltage is applied to gates of the first and second select gate transistors to turn on both of the first and second select gate transistors, and then the first select gate transistor is turned on and the second select gate transistor is turned off, and then the first status and the second status are generated alternately.

4. The non-volatile semiconductor device as claimed in claim 1 , wherein the first select gate transistor is a select gate transistor connected to a select gate line SGD of the drain side, and the second select gate transistor is a select gate transistor connected to a select gate line SGS of the source side.

5. The non-volatile semiconductor device as claimed in claim 1 , wherein the first select gate transistor is a select gate transistor connected to a select gate line SGS of the source side, and the second select gate transistor is a select gate transistor connected to a select gate line SGD of the drain side.

6. The non-volatile semiconductor device as claimed in claim 1 , wherein the control circuit controls the first and second select gate transistors, such that when the first status and the second status are generated alternately, at least one period when both of the first and second select gate transistors are turned off exists.

7. The non-volatile semiconductor device as claimed in claim 1 , wherein the control circuit controls the first and second select gate transistors, such that the first status and the second status are generated alternately and repeatedly.

8. A readout method of a non-volatile semiconductor device, wherein the non-volatile semiconductor device comprises a plurality of memory strings formed by series connection of a plurality of memory cells respectively connected to word lines, wherein each of the memory strings is connected between a bit line via a first select gate transistor and a source line via a second select gate transistor, and

wherein the readout method comprises

controlling the first and second select gate transistors, such that when the voltage of the word line is raised to a predetermined value for data readout from the memory cell, a first status where the first select gate transistor is turned on and the second select gate transistor is turned off and second status where the first select gate transistor is turned off and the second select gate transistor is turned on are generated alternately.

9. The readout method as claimed in claim 8 , wherein the first and second select gate transistors are controlled, such that the first status and the second status are generated alternately after a high level voltage is applied to gates of the first and second select gate transistors to turn on both of the first and second select gate transistors.

10. The readout method as claimed in claim 8 , wherein the first and second select gate transistors are controlled, such that a high level voltage is applied to gates of the first and second select gate transistors to turn on both of the first and second select gate transistors, and then the first select gate transistor is turned on and the second select gate transistor is turned off, and then the first status and the second status are generated alternately.

11. The readout method as claimed in claim 8 , wherein the first select gate transistor is a select gate transistor connected to a select gate line SGD of the drain side, and the second select gate transistor is a select gate transistor connected to a select gate line SGS of the source side.

12. The readout method as claimed in claim 8 , wherein the first select gate transistor is a select gate transistor connected to a select gate line SGS of the source side, and the second select gate transistor is a select gate transistor connected to a select gate line SGD of the drain side.

13. The readout method as claimed in claim 8 , wherein the first and second select gate transistors are controlled, such that when the first status and the second status are generated alternately, at least one period when both of the first and second select gate transistors are turned off exists.

14. The readout method as claimed in claim 8 , wherein the first and second select gate transistors are controlled, such that the first status and the second status are generated alternately and repeatedly.