Semiconductor device and reading method

1. A reading method of a NAND flash memory, comprising:

a first step, pre-charging a sensing node by a voltage from a voltage-supply node;

a second step, discharging a voltage of the sensing node to the voltage-supply node to perform a prescribed operation;

a third step, after the prescribed operation, recharging the sensing node by the voltage from the voltage-supply node; and

a fourth step, after the third step, discharging a NAND string and performing sensing of a memory cell,

wherein the prescribed operation comprises resetting a latch circuit of a page buffer/sensing circuit or making a selected bit line to be in a floating state during a period until an unselected bit line finishes discharging.

2. The reading method according to claim 1 , wherein

a driving capability of the voltage-supply node in the third step is equal to or greater than a driving capability of the voltage-supply node in the first step.

3. The reading method according to claim 1 , wherein

in the third step, a driving capability of the voltage-supply node changes in stages.

4. The reading method according to claim 1 , further comprising a fifth step of connecting electrically a selected bit line to the sensing node after the sensing node is recharged.

5. A semiconductor device, comprising:

a NAND memory cell array;

a reading member, reading data from a selected page of the memory cell array; and

an output member, outputting the data read by the reading member to an outside, wherein

the reading member comprises a page buffer/sensing circuit connected to the memory cell array via a bit line,

after pre-charging a sensing node by a voltage from a voltage-supply node, the reading member discharges a voltage of the sensing node to the voltage-supply node before discharging a NAND string to perform a prescribed operation, and recharges the sensing node by the voltage from the voltage-supply node after the prescribed operation.

6. The semiconductor device according to claim 5 , wherein

the prescribed operation comprises resetting a latch circuit of the page buffer/sensing circuit or making a selected bit line to be in a floating state during a period until an unselected bit line finishes discharging.

7. The semiconductor device according to claim 5 , wherein

the reading member comprises a bit-line selection circuit connected to the page buffer/sensing circuit, and the bit-line selection circuit comprises an even-numbered selection transistor for selecting an even-numbered bit line and an odd-numbered selection transistor for selecting an odd-numbered bit line,

the prescribed operation makes the even-numbered selection transistor or the odd-numbered selection transistor non-conducting, and makes the selected even-numbered bit line or the selected odd-numbered bit line to be in a floating state.

8. The semiconductor device according to claim 5 , wherein

the reading member comprises a driving circuit for driving the voltage-supply node, and the driving circuit recharges the sensing node with a driving capability equal to or greater than a driving capability when the bit line is pre-charged.

9. The semiconductor device according to claim 8 , wherein

the driving circuit responds to a switching control signal and supplies a supply voltage or a reference potential to the voltage-supply node, and the driving circuit responds to a plurality of drive signals and changes a driving capability of the supply voltage of the voltage-supply node.

10. The semiconductor device according to claim 6 , wherein

the page buffer/sensing circuit comprises: the voltage-supply node, the sensing node, the latch circuit, a first selection transistor connected between the voltage-supply node and the sensing node, a second selection transistor connected between the sensing node and the bit line, and a third selection transistor connected between the sensing node and the latch circuit, and

the reading member makes the first selection transistor and the third selection transistor conducting, makes the second selection transistor non-conducting, and connects the latch circuit electrically to a reference potential of the voltage-supply node to reset the latch circuit.

11. The semiconductor device according to claim 6 , wherein

the page buffer/sensing circuit comprises: the voltage-supply node, the sensing node, the latch circuit, a first selection transistor connected between the voltage-supply node and the sensing node, a second selection transistor connected between the sensing node and the bit line, and a third selection transistor connected between the sensing node and the latch circuit, and

the reading member makes the first selection transistor conducting, makes the second selection transistor and the third selection transistor non-conducting, and connects the sensing node electrically to a reference potential of the voltage-supply node, and makes the selected bit line to be in a floating state.

12. The semiconductor device according to claim 10 , wherein

the page buffer/sensing circuit further comprises other latch circuits that receive data held in the latch circuit, and

when the reading member performs continuous reading, the latch circuit holds data read from a next selected page of the memory cell array during a period in which data of the other latch circuits is output.