Non-volatile semiconductor memory device and data programming method

• US 6,738,293 B1
• Filed: 04/15/2003
• Issued: 05/18/2004
• Est. Priority Date: 08/27/1993
• Status: Expired due to Fees

• Current Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Original Assignee: Kabushiki Kaisha Toshiba (Toshiba Corporation)
• Inventors: Iwahashi, Hiroshi
• Primary Examiner(s): LE, VU ANH
• Application Number:
  US10/413,826
• Publication Number:
  US 20040080983A1
• Time in Patent Office: 399 Days
• Field of Search: 365/185.28, 365/185.24, 365/185.3, 365/185.09
• US Class Current: 365/185.28
• CPC Class Codes: G11C 16/0483 comprising cells having several storage transistors connected in series
• CPC Class Codes: G11C 16/12 Programming voltage switching circuits
• CPC Class Codes: G11C 16/24 Bit-line control circuits
• CPC Class Codes: G11C 16/26 Sensing or reading circuits; Data output circuits

Abstract

In a non-volatile semiconductor memory, a large current can be flowed through the memory cell during reading. The number of the column lines can be reduced. The electron injection to the floating gates of the respective memory cells is averaged to reduce the dispersion of the threshold voltages thereof. The electron emission from the floating gates of the respective memory cells is also averaged to reduce the dispersion of the threshold voltages thereof. An increase in chip size due to latch circuits can be prevented. By noting that either of a plurality of “0” or “1” of the binary data are stored such in the memory cells of the memory cell bundle or block, a negative threshold voltage is allocated to the memory cells for storing the more bit side data of the binary data. A single column line is used in common for the two adjacent memory blocks. To inject electrons to the floating gates of the memory cells, voltage is increased gradually and stopped when electrons have been injected up to a predetermined injection rate. Electrons are once emitted from the floating gates, and thereafter the electrons are injected again to store one of a binary data. Further, the data latch circuits can be formed at any positions remote from the memory cell array.

Claims

1. A non-volatile semiconductor memory device, comprising:

a memory cell array including memory cells arranged in a matrix form having rows and columns, each of the memory cells having a drain, a source, a floating gate, and a control gate, and being arranged, so as to be stored data by varying a threshold voltage in dependence upon an amount of electrons injected in the floating gate;

row lines, to each of which the control gates of the memory cells in the same row are commonly connected;

column lines, to each of which the drains of the memory cells in the same column are commonly connected;

a row decoder for selecting the row line;

a column decoder for selecting the column line;

data detecting means for detecting data stored in the memory cell, which is selected by the row decoder and the column decoder;

data writing means for injecting electrons to the floating gate of the memory cell, which is selected by the row and column decoders, to set a first predetermined threshold voltage in order to write at least one of binary data items in the memory cell;

data erasing means for allowing the floating gates of the memory cells that are commonly connected to the same column line and a plurality of row lines to simultaneously discharge electrons, then injecting electrons to the floating gates of the memory cells, and setting a second predetermined threshold voltage having a positive value which is lower than that of the first predetermined threshold value in order to store at least the other of the binary data items; and

current breaking means for disconnecting a current path from the selected column line via the discharged memory cells which are connected to the row lines, to the row lines not the selected memory cell but non-selected memory cells being connected, from the floating gates of the discharged memory cells electrons being discharged by the data erasing means, when electrons are injected to the floating gate of the selected memory cell by the data erasing means, or data is read out from the selected memory cell,

electrons are injected to the floating gates of the memory cells by the data erasing means, and thereafter, electrons are selectively injected to the floating gate of the memory cell by the data writing means;

a programming voltage is applied to the control gate of the memory cell in order to inject electrons to the floating gate of the memory cell, the value of the programming voltage, to be applied to the control gate thereof, at the time of the injection of electrons performed by the data writing means being higher than the value of the programming voltage, to be applied to the control gate thereof, at the time of the injection of electrons performed by the data erasing means.

2. The non-volatile semiconductor memory device according to claim 1, wherein the data erasing means further includes stopping means for after electrons are discharged from the floating gates of the memory cells, injecting electrons to the floating gates of the memory cells a plurality of times, checking the amount of injected electrons, judging that the amount of injected electrons reaches a predetermined value, and then stopping the injection of electrons to the floating gates of the memory cells.

3. The non-volatile semiconductor memory device according to claim 1, further comprising programming voltage generating means for generating a programming voltage used when electrons are injected by the data writing means, and a programming voltage used when electrons are injected by the data erasing means.

4. The non-volatile semiconductor memory device according to claim 3, wherein the programming voltage generating means is connected to the row decoder, and applies the programming voltages, via the selected row line to the control gate of the memory cells.

5. The non-volatile semiconductor memory device according to claim 2, wherein the checking of the amount of injected electron is performed by applying a voltage to the control gate of the memory cell, which voltage is lower than a voltage applied to the control gate when the data detecting means detects data at the time of a normal readout operation.

6. The non-volatile semiconductor memory device according to claim 1, wherein the drains of the memory cells are connected to a data writing transistor, and the data writing means writes data to the memory cell and the data erasing means writes data to the memory cells by turning on the data writing transistor.

7. The non-volatile semiconductor memory device according to claim 6, wherein a current supply capacity of the data writing transistor when the data writing means writes data to the memory cell is larger than a current supply capacity of the data writing transistor when the data erasing means writes data to the memory cell.

8. The non-volatile semiconductor memory device according to claim 3, wherein the programming voltage generating means further generates a voltage to be applied to the control gate of the memory cell in order that the data detecting means detects data at the time of the normal readout operation, and a voltage to be applied to the control gate of the memory cell in order that the data detecting means detects data at the time of the of the amount of the injected electron.

9. The non-volatile semiconductor memory device according to claim 1, wherein after electrons are injected to the memory cells by the data erasing means, electrons are injected to the memory cell by the data writing means.

10. The non-volatile semiconductor memory device according to claim 9, wherein the data erasing means performs injection of electrons to all of the memory cells for storing data in the memory cell array, and then the data writing means selectively performs injection of electrons to the memory cell.

11. The non-volatile semiconductor memory device according to claim 1, wherein the memory cells are formed on a p-well, and the data erasing means allows the floating gates of the memory cells to discharge electrons by applying a high voltage the p-well.

12. A non-volatile semiconductor memory device, comprising:

a memory cell array including memory cells arranged in a matrix form having rows and columns, each of the memory cells having a drain, a source, a floating gate and a control gate, and storing at least a first data item or a second data item by varying a threshold voltage in dependence upon an amount of electrons injected in the floating gate;

row lines, to each of which the control gates of the memory cells in the same row are commonly connected;

column lines, to each of which the drains of the memory cells in the same column are commonly connected;

a row decoder for selecting the row line;

data detecting means for detecting data stored in a selected memory cell;

injecting means for applying programming voltages to the selected row line to apply the programming voltages to the control gates of the memory cells, a voltage value of one of the programming voltages used for storing the first data is being higher than a voltage value of the other of the programming voltages used for storing the second data, and for injecting electrons to the floating gate of the selected memory cell,

discharging means for allowing the floating gates of the memory cells commonly connected to the same column line and a plurality of row lines to simultaneously discharge electrons; and

current breaking means for disconnecting a current path from the selected column line via the discharged memory cells which are connected to the row lines other than the row line to which the selected memory cell is connected, wherein the discharged memory cells are the memory cells from the floating gates of which electrons are discharged by the discharging means, when electrons are injected to the floating gate of the selected memory cell in order to store the second data item, or data is read out from the selected memory cell,

wherein after discharging electrons from the floating gates of the memory cells, each of which connected to the plurality of row lines and which commonly connected to the same column line, by said discharging means, electrons are injected to the floating gates of the memory cells by said injecting means to store the second data item, thereby a threshold voltage of the memory cells is set at a positive predetermined voltage, after that electrons are injected to the floating gate of the selected memory cell to store said first data item, the threshold voltage of the memory cell which stores the first data item being higher than that of the memory cell which stores the second data item.

13. The non-volatile semiconductor memory device according to claim 12, further comprising programming voltage means for generating the programming voltages.

14. The non-volatile semiconductor memory device according to claim 13, wherein the programming voltage generating means is connected to the row decoder, and applies the each programming voltage to the control gates of the memory cells via the selected row line.

15. The non-volatile semiconductor memory device according to claim 12, wherein after the injecting means injects electrons to the floating gate, an amount of electrons injected to the floating gate is checked by the use of the data detecting means.

16. The non-volatile semiconductor memory device according to claim 15, wherein the amount of electrons injected to the floating gate of the memory cell for storing the second data item is checked by applying a predetermined voltage to the control gate of the memory cell by the use of the data detecting means.

17. The non-volatile semiconductor memory device according to claim 16, wherein the predetermined voltage is lower than a voltage applied to the control gate of the selected memory cell when the data detecting means detects data in a normal readout operation.

18. A non-volatile semiconductor memory device, comprising:

a memory cell array including memory cells arranged in a matrix form having rows and columns, each of the memory cells having a drain, a source, a floating gate, and a control gate, and being arranged, so as to be stored data by varying a threshold voltage in dependence upon an amount of electrons injected in the floating gate;

row lines, to each of which the control gates of the memory cells in the same row are commonly connected;

column lines, to each of which the drains of the memory cells in the same column are commonly connected;

a row decoder for selecting the row line;

a column decoder for selecting the column line;

means for detecting data stored in the memory cell, which is selected by the row decoder and the column decoder;

means for injecting electrons to the floating gate of the memory cell, which is selected by row and column decoders, to set a first predetermined threshold voltage in order to write at least one of binary data items in the memory cell;

means for allowing the floating gates of the memory cells that are commonly connected to the same column line and a plurality of row lines to simultaneously discharge electrons, then injecting electrons to the floating gates of the memory cells, and setting a second predetermined threshold voltage having a positive value which is lower than that of the first predetermined threshold value in order to store at least the other of the binary data items; and

means for disconnecting a current path from the selected column line via the discharged memory cells which are connected to the row lines, to the row lines not the selected memory cell but non-selected memory cells being connected, from the floating gates of the discharged memory cells electrons being discharged by the means for data erasing, when electrons are injected to the floating gate of the selected memory cell by the means for data erasing, or data is read out from the selected memory cell,

electrons are injected to the floating gates of the memory cells by the means for data erasing, and thereafter, electrons are selectively injected to the floating gate of the memory cell by the means for data writing;

a programming voltage is applied to the control gate of the memory cell in order to inject electrons to the floating gate of the memory cell, the value of the programming voltage, to be applied to the control gate thereof, at the time of the injection of electrons performed by the means for data writing being higher than the value of the programming voltage, to be applied to the control gate thereof, at the time of the injection of electrons performed by the means for data erasing.

19. A non-volatile semiconductor memory device, comprising:

a memory cell array including memory cells arranged in a matrix form having rows and columns, each of the memory cells having a drain, a source, a floating gate and a control gate, and storing at least a first data item or a second data item by varying a threshold voltage in dependence upon an amount of electrons injected in the floating gate;

row lines, to each of which the control gates of the memory cells in the same row are commonly connected;

column lines, to each of which the drains of the memory cells in the same column are commonly connected;

a row decoder for selecting the row line;

means for detecting data stored in a selected memory cell;

means for applying programming voltages to the selected row line to apply the programming voltages to the control gates of the memory cells, a voltage value of one of the programming voltages used for storing the first data is being higher than a voltage value of the other of the programming voltages used for storing the second data, and for injecting electrons to the floating gate of the selected memory cell,

means for allowing the floating gates of the memory cells commonly connected to the same column line and a plurality of row lines to simultaneously discharge electrons; and

means for disconnecting a current path from the selected column line via the discharged memory cells which are connected to the row lines other than the row line to which the selected memory cell is connected, wherein the discharged memory cells are the memory cells from the floating gates of which electrons are discharged by the means for discharging, when electrons are injected to the floating gate of the selected memory cell in order to store the second data item, or data is read out from the selected memory cell,

wherein after discharging electrons from the floating gates of the memory cells, each of which connected to the plurality of row lines and which commonly connected to the same column line, by said means for discharging, electrons are injected to the floating gates of the memory cells by said means for injecting to store the second data item, thereby a threshold voltage of the memory cells is set at a positive predetermined voltage, after than electrons are injected to the floating gate of the selected memory cell to store said first data item, the threshold voltage of the memory cell which stores the first data item being higher than that of the memory cell which stores the second data item.