KR100965076B1 - Programming method for non volatile memory device - Google Patents

Abstract

A program method of a nonvolatile memory device of the present invention includes checking state information of program target cells according to an input of a program command, and performing a program operation based on a first start voltage when the program target cells are slow cells as a result of the check. Performing a program operation based on a second start voltage lower than the first start voltage when the program target cells are fast cells; and performing a program operation based on the first start voltage. Determining a program speed of the corresponding program target cells based on an amount of change in threshold voltages of the program target cells due to the corresponding program operation; Updating.

Program speed, number of program / erase operations

Description

Programming method for non volatile memory device

The present invention relates to a program method of a nonvolatile memory device.

Recently, there is an increasing demand for a nonvolatile memory device that can be electrically programmed and erased and that does not require a refresh function to rewrite data at regular intervals.

The nonvolatile memory cell is an electric program / eraseable device that performs program and erase operations by changing a threshold voltage of a cell while electrons are moved by a strong electric field applied to a thin oxide film.

A nonvolatile memory device typically includes a memory cell array in which cells in which data is stored is formed in a matrix form, and a page buffer for writing a memory to a specific cell of the memory cell array or reading a memory stored in the specific cell. The page buffer may include a pair of bit lines connected to a specific memory cell, a register for temporarily storing data to be written to the memory cell array, or a register for reading and temporarily storing data of a specific cell from the memory cell array, a voltage of a specific bit line or a specific register. It includes a sensing node for sensing a level, a bit line selection unit for controlling whether the specific bit line and the sensing node is connected.

Such a nonvolatile memory device is known to increase program speed as the number of program / erase operations increases. This is because as the number of program / erase operations increases, the charge trapped by the floating gate of each memory cell increases, and the threshold voltage of each cell increases. Therefore, even if a relatively small program pulse according to the ISPP (Incremental step pulse program) program method is applied, it is programmed above a target threshold voltage.

In consideration of such characteristics, a method of applying and setting a program start voltage low in the ISPP program method may be considered. Even when the number of program / erase operations is low, this method increases the program time. That is, as the program start voltage decreases, more pulses need to be applied.

The problem to be solved by the present invention in accordance with the above-described problem is to provide a program method of a nonvolatile memory device that can set the program start voltage variably in accordance with the change of the program speed by the increase in the number of program / erase operations.

According to an aspect of the present invention, there is provided a method of a nonvolatile memory device, which includes checking a state information of program target cells according to an input of a program command, and when the program target cells are slow cells, a first start. Performing a program operation based on a voltage; and performing a program operation based on a second start voltage lower than the first start voltage when the program target cells are fast cells as a result of the check; When the program operation is performed, determining the program speed of the program target cells based on the amount of change of the threshold voltage of the program target cells by the program operation, and if the program speed of the program target cells is faster than the reference value Status information of the cells to be programmed Updating.

In addition, the program method of the nonvolatile memory device of the present invention includes the step of checking the state information of the program target cells according to the input of a program command, and if the program target cells are a slow cell as a result of the check the program operation by the first start voltage Performing a program operation; performing a program operation according to a second start voltage lower than the first start voltage when the program target cells are fast cells; and threshold voltages of program target cells according to each program operation. Determining the program speed of the corresponding program target cells based on the amount of change; and updating the state information of the program target cells when the program speed of the program target cells is different from the program speed included in the state information. Include.

According to the above-mentioned problem solving means of the present invention, the program start voltage can be variably set according to the above-mentioned problem solving means of the present invention. In particular, in an initial operation having a small number of program / erase operations, a relatively large program start voltage may be set to compensate for a cell having a slow program speed. In addition, in a late operation having a large number of program / erase operations, a program start voltage may be set relatively small to compensate for characteristics of a cell having a high program speed. Accordingly, the time required for the overall program operation can be reduced.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, only these embodiments are intended to complete the disclosure of the present invention, and to those skilled in the art to fully understand the scope of the invention. It is provided to inform you. Like numbers refer to like elements in the figures.

1 is a view showing the overall configuration of a nonvolatile memory device to which the present invention is applied.

The nonvolatile memory device 100 includes a memory cell array 102, a page buffer 108, an X / Y-decoder 104 and 106, a high voltage generator 110, a command interface logic unit 112, and a command register ( 114, an address register / counter 116, a data register 118, and an IO buffer unit 120. An operation of the nonvolatile memory device will be described.

First, when the chip enable signal / CE is disabled and the write enable signal / WE is toggled with respect to the command interface logic unit 112, in response thereto, the command interface logic unit 112 The command signal received through the IO buffer unit 110 and the command register 114 is received, and a program command, an erase command, or a read command is generated according to the command. In this case, the command signal includes a page program setup code for determining an operation mode of the nonvolatile memory device. Meanwhile, the operation state signal / R / B output from the command interface logic unit 112 is disabled for a predetermined time, and an external memory controller (not shown) transmits the operation state signal / R / B. Receives and recognizes that the nonvolatile memory device is in an operating state such as program / erase / read. That is, during the time when the operation state signal / R / B is disabled, the program / erase / read of one page of the memory cell array is executed.

In addition, the address register / counter 116 receives an address signal received through the IO buffer unit 120 and generates a row address signal and a column address signal. The address signal corresponds to one of pages included in one of the memory cells. The data register 118 temporarily stores various data received through the IO buffer unit 120 and transfers the data to the Y-decoder 106.

The high voltage generator 110 generates bias voltages in response to the program command, erase command or read command and supplies them to the page buffer 108, the X-decoder 104, and the like.

The X-decoder 104 supplies the bias voltages supplied from the high voltage generator 110 to the memory cell array 102 in one of the blocks of the memory cell array in response to the row address signal. The Y-decoder 106 supplies a data signal to bit lines (not shown) shared by the blocks of the memory cell array through the page buffer in response to the column address signal.

The page buffer 108 latches a data signal received through the IO buffer unit 110 and the Y-decoder 106 to bit lines (not shown) shared by the blocks of the memory cell array. Output

FIG. 2 is a graph illustrating a threshold voltage change characteristic according to an increase in the number of program / erase operations of a conventional nonvolatile memory device.

As illustrated, as the number of program / erase operations increases, the threshold voltage of the program state and the threshold voltage of the erase state increase. This occurs because as the number of program / erase operations increases, the threshold voltage increases even in the erased state as the charge trapped by the floating gate of the nonvolatile memory cell increases. As a result, the amount of change in the threshold voltage according to the application of the same program pulse becomes larger. The amount of change in the threshold voltage is defined as a program speed. In other words, if the threshold voltage change is larger when the same program pulse is applied, the program speed is considered larger.

As shown, when the number of program / erase operations is 10, the threshold voltage of the program state is greater when the number of program / erase operations is 10K than the threshold voltage of the program state. The same is true in the erased state. As the program speed changes according to the number of program / erase operations as described above, a program method for compensating for such a change amount is used.

FIG. 3 is a diagram for describing a concept of a program method of a nonvolatile memory device.

As shown, a program operation is performed according to an incremental step pulse program (ISPP) program method. That is, the verification operation is performed after the program pulse is applied, and the program operation is repeated by increasing the program voltage by the step voltage Vstep for each repetition operation. At this time, considering the fact that the program speed is different according to the number of program / erase operations, a section to which a dummy program pulse is applied is added.

When the number of program / erase operations is one time, the ISPP program operation is performed based on the first start voltage Vstart1. However, when the number of program / erase operations is 10K, since the program speed is high, it is necessary to perform the ISPP program operation based on the second start voltage Vstart2 smaller than the first start voltage Vstart1. Therefore, the ISPP program operation is performed based on the second start voltage Vstart2 from the first start of the program / erase operation. Since the program start voltage is low, the program effect may not actually appear when the number of program / erase operations is 1 to 10K. Therefore, when the number of program / erase operations is 1 to 10K, the program pulses applied from the time when the second start voltage Vstart2 is applied until immediately before the first start voltage Vstart1 are applied are dummy program pulses. Can be. For the case where the number of program / erase operations is 10K or more, a dummy program pulse is applied, but the total program time becomes long until the number of program / erase operations is 10K.

4 is a flowchart illustrating a program method of a nonvolatile memory device according to an exemplary embodiment of the present invention.

First, a program command is input (step 410).

Next, the cell state information of the program target cells is checked (step 420).

The cell state information includes information about program rates of memory cells.

In this case, the cell state information is classified as a fast cell due to a fast program speed of cells to be programmed, or classified as a slow cell due to a slow program speed and stored in a separate storage. The classification of the slow cell and the fast cell is determined by the operator. That is, based on the optimized value through repeated experiments, if the program speed is faster than the reference value, it is classified as a fast cell, and if it is slower than that, it is classified as a slow cell.

 The cell state information may be stored in a spare cell, a cam cell, or the like of a register or a nonvolatile memory cell included in a control unit of the nonvolatile memory device. When stored in the register, when a power supply voltage is supplied to a nonvolatile memory device, the cell state information is set to an initial value by a power-up reset signal. Preferably, the initial value of the cell state information is set to a value indicating that the program target cells are slow cells.

For the spare cells, the program rate of each cell may be stored for each memory cell block that is a unit of an erase operation or for each page that is a unit of a program operation. State information of the program target cells may be stored for each page, or state information of the program target cells may be stored for each memory cell block.

That is, the state information of the program target cells in the same page is set to the same, or the state information of the program target cells in the same memory cell block is set to the same. However, since the same memory cell block has the same number of erase operations, it may be efficient to set the state information to be stored for each memory cell block. If the cell state information is the same, the same program start voltage is applied.

If cell state information is separately stored for each page, the program start voltage may be set differently for each page.

As a result of checking the cell state information, when the program target cell is a slow cell, a program operation is performed according to the first start voltage (steps 430 and 450).

As described with reference to FIG. 3, the first start voltage Vstart1 is a voltage applied during an initial operation having a low number of program / erase operations.

Next, the program speed of the program target cells is determined (step 460).

In the state where the first start voltage Vstart1 is applied once, the program speed is determined by measuring the threshold voltage change of each cell.

As a result of the determination, when the program target cells are fast cells, the stored cell state information is updated (steps 470 and 480).

That is, since the program target cells are stored in the cell state information stored in the register and the like, the information is modified to store the information called the fast cell. In the embodiment in which the cell state information is stored in the register, since the stored information is initialized whenever the power supply is cut off, the correct cell state information can be confirmed by such an operation.

Thereafter, the program operation and the verify operation are repeatedly performed while increasing the program voltage according to the ISPP program method (step 490).

On the other hand, in the case of the slow cells of the program target cells as a result of the determination, the stored cell state information is maintained, and the program operation and the verify operation are repeatedly performed to complete the program operation (steps 470 and 490).

On the other hand, when the cell state information is checked in step 430, when the program target cell is a fast cell, a program operation is performed according to a second start voltage (steps 430 and 440).

As described above with reference to FIG. 3, the second start voltage Vstart2 is a voltage applied in a high number of program / erase operations, and is smaller than the first start voltage Vstart1.

That is, when it is confirmed that the program target cells are the fast cells, the ISPP program operation is performed according to the reduced program start voltage (step 490).

In summary, each time a program operation is performed, the program start voltage is set by checking information about program rates of the corresponding cells in advance. According to an exemplary embodiment, program start voltages are set differently by checking cell state information separately stored for each page or for each memory cell block. That is, the program start voltage is set low for fast cells having a high program speed, and the program start voltage is set high for slow cells with a slow program speed.

5 is a flowchart illustrating a program method of a nonvolatile memory device according to another exemplary embodiment of the present invention.

The overall operation is almost the same as in FIG.

However, when the program target cells are fast cells as a result of checking the state information, there is a slight difference in the procedure to be performed later.

As a result of checking the program state information, when it is confirmed that the program target cells are fast cells, a program operation is performed according to the second program start voltage (step 540), and the program speeds of the program target cells are also determined in response to the program operation (step 540). Step 560).

That is, the program speed is determined by measuring the variation in threshold voltages of the cells in the state in which the second start voltage Vstart2 is applied once.

If the speed of the program target cells is changed from the value of the previously stored state information, the stored cell state information is updated (steps 570 and 580).

That is, when the program operation is performed according to the first program start voltage, information that the program target cells are slow cells is stored. When the program operation is performed according to the second program start voltage, the program target cells are called fast cells. The information is stored.

However, as a result of the actual determination, unlike the program state information, if the program speed is faster than the reference value or slower than the reference value, the cell state information is updated (step 580).

Preferably, when the program operation is performed according to the first program start voltage, when it is determined that the fast cell is a fast cell, state information of the fast cell is stored. In addition, when the program operation is performed according to the second program start voltage, when the determination result is the slow cell, state information of the slow cell is stored.

According to this embodiment, even when the state information of the fast cell is stored in the initial register, the program start voltage may be adjusted again according to the cell state.

In summary, each time a program operation is performed, the program start voltage is set by checking information about program rates of the corresponding cells in advance. According to an exemplary embodiment, program start voltages are set differently by checking cell state information separately stored for each page or for each memory cell block. That is, the program start voltage is set low for fast cells having a high program speed, and the program start voltage is set high for slow cells with a slow program speed.

1 is a view showing the overall configuration of a nonvolatile memory device to which the present invention is applied.

FIG. 2 is a graph illustrating a threshold voltage change characteristic according to an increase in the number of program / erase operations of a conventional nonvolatile memory device.

FIG. 3 is a diagram for describing a concept of a program method of a nonvolatile memory device.

4 is a flowchart illustrating a program method of a nonvolatile memory device according to an exemplary embodiment of the present invention.

5 is a flowchart illustrating a program method of a nonvolatile memory device according to another exemplary embodiment of the present invention.

Claims (10)

Checking state information of cells to be programmed according to an input of a program command; Performing a program operation based on a first start voltage when the target cells are slow cells as a result of the check; Performing a program operation based on a second start voltage lower than the first start voltage when the target cells are the fast cells as a result of the check; When the program operation is performed according to the first start voltage, measuring a change in threshold voltages of the program target cells according to the program operation and determining program rates of the corresponding program target cells according to the measured threshold voltage change; And updating the state information of the program target cells when the program speed of the program target cells is faster than a reference value. The method of claim 1, wherein checking the state information of the program target cells according to the input of the program command comprises: And reading state information previously stored in a state information store of the nonvolatile memory device. The method of claim 1, wherein the updating of the state information of the program target cells when the program speed of the program target cells is faster than a reference value according to the determination result And storing information indicating that the program target cells are fast cells as the state information. The method of claim 1, further comprising repeating the program operation and the verify operation while increasing the program voltage according to an incremental step pulse program (ISPP) program method after performing the program operation according to the second start voltage. Program method of a nonvolatile memory device, characterized in that. The method of claim 1, further comprising repeating the program operation and the verify operation while increasing the program voltage according to the ISPP program method when the program speed of the program target cells is slower than the reference value. Program method of volatile memory device. The method of claim 1, further comprising repeating the program operation and the verify operation while increasing the program voltage according to the ISPP program method after performing the step of updating the state information of the program target cells. Program method of a nonvolatile memory device. Checking state information of cells to be programmed according to an input of a program command; Performing a program operation based on a first start voltage when the target cells are slow cells as a result of the check; Performing a program operation based on a second start voltage lower than the first start voltage when the target cells are the fast cells as a result of the check; Measuring a threshold voltage change amount of the program target cells according to each program operation and determining a program speed of the corresponding program target cell according to the measured threshold voltage change amount; And updating the state information of the program target cells when the program speed of the program target cells is different from the program speed included in the state information. The method of claim 7, wherein the determining of the state information of the program target cells when the program speed of the program target cells is different from the program speed included in the state information Performing a program operation according to the first program start voltage and storing state information of a fast cell when the determination result is a fast cell; And performing a program operation according to the second program start voltage and storing state information of a slow cell when the determination result is a slow cell. The method of claim 7, further comprising repeating the program operation and the verify operation while increasing the program voltage according to the ISPP program method when the program speed of the program target cells is the same as the program speed included in the state information. Program method for a nonvolatile memory device comprising a. The method of claim 7, further comprising repeating the program operation and the verify operation while increasing the program voltage according to the ISPP program method after performing the step of updating the state information of the program target cells. Program method of a nonvolatile memory device.

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