Nonvolatile semiconductor memory device and method of operating the same which stably perform erase operation

1. A nonvolatile semiconductor memory device comprising:

a memory array configured to include a plurality of nonvolatile memory cells arranged in a matrix form and a plurality of word lines; and

an X-decode section configured to select a selected word line selected from said plurality of word lines, supply a negative voltage to said selected word line, and supply a positive voltage to unselected word lines which are not said selected word line, at the time of an erase operation,

wherein said X-decode section includes:

a plurality of output drivers configured to be provided corresponding to said plurality of word lines, each of said plurality of output drivers outputs at least one of said negative voltage and said positive voltage,

a negative voltage decoder configured to supply said negative voltage to said plurality of output drivers, and

a positive voltage decoder configured to supply said positive voltage to said plurality of output drivers,

wherein each of said plurality of output drivers, based on a word line selection signal for selecting one of said plurality of word lines and a voltage selection signal for selecting one of said negative voltage and said positive voltage, supplies voltage corresponding to said voltage selection signal to corresponding one of said plurality of word lines,

wherein said voltage selection signal includes a negative-voltage selection signal for selecting said negative voltage and a positive-voltage selection signal for selecting said positive voltage,

wherein said each of the plurality of output drivers includes:

a first transistor configured to receive said word line selection signal at a gate, be connected to a first node at one terminal and a second node at another terminal, and be a first conductive type,

a second transistor configured to receive said positive-voltage selection signal at a gate, be connected to said first node at one terminal and said second node at another terminal, and be said first conductive type,

a third transistor configured to receive said word line selection signal at a gate, be connected to said second node at one terminal and a third node at another terminal, and be a second conductive type, and

a fourth transistor configured to receive said negative-voltage selection signal at a gate, be connected to said second node at one terminal and said third node at another terminal, and be said second conductive type,

wherein said first node receives said positive voltage,

said third node receives said negative voltage, and

said second node is connected to corresponding one of said plurality of word lines.

2. The nonvolatile semiconductor memory device according to claim 1 , further comprising:

a X-predecoder configured to output said word line selection signal based on a first address signal,

wherein said negative voltage decoder outputs said negative-voltage selection signal based on a second address signal and

said positive voltage decoder outputs said positive-voltage selection signal based on said second address signal.

3. The nonvolatile semiconductor memory device according to claim 2 , wherein said X-decode section further includes:

a negative-voltage level shifter configured to supply said negative voltage to said negative voltage decoder, and

a positive-voltage level shifter configured to supply said positive voltage to said positive voltage decoder.

4. The nonvolatile semiconductor memory device according to claim 3 , wherein said plurality of nonvolatile memory cells is separated to a plurality of sectors, and

said negative-voltage level shifter and said positive-voltage level shifter are provided every one of plurality of sectors.

5. The nonvolatile semiconductor memory device according to claim 3 , wherein said plurality of nonvolatile memory cells is separated to a plurality of cell groups, and

said negative voltage decoder and said positive voltage decoder are provided every one of plurality of cell groups.

6. A method of operating the nonvolatile semiconductor memory device, comprising:

(a) selecting a selected word line from a plurality of word lines, at the time of an erase operation in a memory array including said plurality of nonvolatile memory cells arranged in a matrix form and a plurality of word lines; and

(b) supplying a negative voltage to said selected word line, and supplying a positive voltage to unselected word lines which are not said selected word line,

wherein said step (a) includes:

(a1) selecting said selected word line, based on a word line selection signal for selecting one of said plurality of word lines,

wherein said step (b) includes:

(b1) supplying said negative voltage to said selected word line based on a negative-voltage selection signal for selecting said negative voltage, and supplying said positive voltage to said unselected word lines based on a positive-voltage selection signal for selecting said positive voltage,

wherein said step (a1) includes:

(a11) supplying said word line selection signal to gates of a first transistor with a first conductive type and a third transistor with a second conductive type,

wherein said step (b1) includes:

(b11) supplying said positive-voltage selection signal to a gate of a second transistor with said first conductive type, and supplying said negative-voltage selection signal to a gate of a fourth transistor with said second conductive type,

wherein said first transistor is connected to a first node at one terminal and a second node at another terminal,

said second transistor is connected to said first node at one terminal and said second node at another terminal,

said third transistor is connected to said second node at one terminal and a third node at another terminal, and

said fourth transistor is connected to said second node at one terminal and said third node at another terminal,

wherein said first node receives said positive voltage,

said third node receives said negative voltage, and

said second node is connected to said selected word lines.

7. The method of operating the nonvolatile semiconductor memory device according to claim 6 , wherein said step (a11) includes:

(a111) outputting said word line selection signal based on a first address signal,

wherein said step (b11) includes:

(b111) outputting said negative-voltage selection signal based on a second address signal, and outputting said positive-voltage selection signal based on said second address signal.

8. The method of operating the nonvolatile semiconductor memory device according to claim 6 , wherein said step (b1) includes:

(b12) supplying said negative voltage from a negative-voltage level shifter to said third node, and

(b13) supplying said positive voltage from a positive-voltage level shifter to said first node.