KR100443792B1 - Circuit for programming a flash EEPROM and method of programming a flash EEPROM using the same - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a program circuit of a flash ypyrom and a program method using the same. In the process of raising a threshold voltage of a memory cell by executing a program, the reference voltages of the memory cell are continuously compared with a threshold voltage of the memory cell. When the threshold voltage rises to the level, the program operation is completed, thereby preventing excessive programming and at the same time, the program circuit of the flash memory cell capable of confirming the maximum and minimum values of the threshold voltage without performing a separate verification step after the program completion; A program method using the same is disclosed.

Description

Program circuit for Flash EPIROM and method of programming using the same {Circuit for programming a flash EEPROM and method of programming a flash EEPROM using the same}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a program circuit of a flash memory cell and a program method using the same, and more particularly, to a program circuit of a flash memory cell capable of identifying a threshold voltage of a flash memory cell without performing a step of checking a threshold voltage which is generally performed after a program. It relates to a program method using the same.

The flash memory cell is largely composed of a floating gate, a control gate, and a source / drain, and a program is applied by applying a predetermined program voltage to the control gate and the drain, respectively.

The conventional program circuit performs a program so that the threshold voltage of the memory cell is equal to or higher than the target voltage, and then checks whether the threshold voltage of the memory cell has risen to the target voltage through a predetermined verification step for the cells in which the program is completed.

The program circuit checks whether the threshold voltage of the memory cell is higher than the target threshold voltage in the verifying step after the program operation is completed. That is, since the threshold voltage of the memory cell is checked using the target threshold voltage as the minimum voltage, it is not possible to confirm whether the memory cell is over programmed, and thus the reliability of the threshold voltage distribution is degraded. Therefore, in order to implement a multi level memory cell, an ISPP (Increasement Step Pulse Program) should be used.

Accordingly, in order to solve the above problem, the present invention implements a program to raise the threshold voltage of the memory cell to a target voltage, but generates various levels of reference voltages and compares the reference voltages with the threshold voltages of the memory cells. The purpose of the present invention is to provide a program circuit of a flash memory cell capable of confirming the maximum value and the minimum value of a threshold voltage by comparing a plurality of reference voltages and threshold voltages at the same time that the program is completed, and a program method using the same.

1 is a program circuit diagram of a flash memory cell in accordance with the present invention.

2 is a program circuit diagram of a flash memory cell according to another embodiment of the present invention.

3 is a voltage distribution diagram illustrating a threshold voltage level of a memory cell after a program operation.

<Explanation of symbols for the main parts of the drawings>

11, 21: memory cells 12, 22: program time determination circuit

13, 23: registers 14, 24: program unit

15: reference voltage generator 16, 26: comparison unit

161 to 163, 261 to 263: comparison means

251 to 253: current setting means 27: voltage supply means

A program circuit of a flash Y pyrom according to a first embodiment of the present invention is a program circuit of a flash memory cell that raises a threshold voltage of a memory cell to a target voltage through a program operation, and generates a reference voltage of different levels. And a voltage generator and a comparator for comparing the threshold voltages of the memory cells with reference voltages having different levels, respectively.

The program circuit of the flash Y pyrom according to the second embodiment of the present invention includes a program time determining circuit that determines a time required for programming a memory cell according to a target threshold voltage, and data on a program time required by the program time determining circuit. A register for storing a memory, a program unit for programming a memory cell for a predetermined time according to the data stored in the register, a reference voltage generator for generating reference voltages of various levels, and a threshold level different from a threshold voltage of the memory cell. And a comparison unit for comparing the reference voltages, respectively.

A program circuit of a flash Y pyrom according to a third embodiment of the present invention is a program circuit of a flash memory cell that raises a threshold voltage of a memory cell to a target voltage through a program operation. And a comparator for comparing the current setting means of and the amount of current flowing through each of the current setting means and the amount of current flowing in the memory cell, respectively.

The program circuit of the flash Y pyrom according to the fourth embodiment of the present invention includes a program time determining circuit that determines a time required for programming a memory cell according to a target threshold voltage, and data on a program time required by the program time determining circuit. And a program unit for programming a memory cell for a predetermined time according to the data stored in the register, a plurality of current setting means designed to flow a different amount of current, a current amount flowing through each current setting means, And a comparison unit for comparing the amounts of current flowing through the memory cells, respectively.

In addition, the programming method of the flash Y pyrom according to the present invention, while programming the memory cell using the circuit described in the first embodiment or the second embodiment of the present invention and at the same time using the comparison unit Comparing the reference voltages and stopping the program when the threshold voltage of the memory cell rises to the target level voltage.

Program method of flash Y pyrom according to another embodiment of the present invention

The memory cells are programmed using the circuits described in the third or fourth embodiment described above, and at the same time, the threshold voltage and the different amounts of currents of the memory cells are compared using the comparison unit, and the amount of current flowing through the memory cells is the target current amount. If it decreases, the program is stopped.

In the above, the first and second embodiments of the present invention relate to a program circuit of a flash memory cell capable of checking a threshold voltage distribution of a memory cell by simultaneously programming a memory cell and comparing a threshold voltage and a reference voltage of the memory cell. .

In the third and fourth embodiments of the present invention, a flash memory capable of checking a threshold voltage distribution of a memory cell by programming a memory cell and simultaneously comparing the amount of current flowing through the memory cell with the amount of current flowing by the plurality of current setting means, respectively. It relates to the program circuit of the cell.

Hereinafter, with reference to the accompanying drawings will be described an embodiment of the present invention in more detail.

1 is a program circuit diagram of a flash Y pyrom comparing a threshold voltage and a reference voltage of a memory cell.

Referring to FIG. 1, a program circuit of a flash Y pyrom is generated by a program time determining circuit 12 and a program time determining circuit 12 that determine a time required for programming the memory cell 11 according to a target threshold voltage. The memory cell 11 is programmed for a predetermined time in accordance with the register 13 storing data for program required time and the data stored in the register 13 to raise the threshold voltage of the memory cell 11 to the target threshold voltage. It consists of a program unit 14, a reference voltage generator 15 for generating reference voltages of various levels, and a plurality of comparison means, and a threshold voltage of a memory cell is commonly applied to the first input terminal of the plurality of comparison means. Each of the second input terminals is provided with different reference voltages, and includes a comparator 16 determining the level of the threshold voltage of the memory cell.

The reference voltage generator 15 is composed of a plurality of resistors R11 to R14 connected in series between the power supply voltage terminal and the ground voltage terminal, and the power supply voltage drops by a predetermined voltage by the plurality of resistors R11 to R14. To generate various levels of reference voltages Va, Vb, and Vc. That is, a voltage dropped by the first resistor R11 is generated as the first reference voltage Va at the first node N11 between the first and second resistors R11 and R12, and the first and second voltages. The voltage dropped by the resistors R11 and R12 is generated as the second reference voltage Vb at the second node N12 between the second and third resistors R12 and R13. In addition, a voltage dropped by the first to third resistors R11 to R13 is generated as the third reference voltage Vc at the third node N13 between the third and fourth resistors R13 and R14.

Hereinafter, the operation of the program circuit will be described.

First, the program time determining circuit 12 determines a necessary program time for raising the threshold voltage of the memory cell to the target threshold voltage, and then stores the generated signal in the register 13.

The signal stored in the register 13 is applied to the program unit 14, and according to the signal of the register 13, the program unit 14 programs the memory cell 11 for a predetermined time. The program unit 14 generates a voltage required for executing the program, that is, a high voltage and a drain voltage to be applied to the control gate of the memory cell 11, and includes a time calculating device so that the corresponding time is determined according to the data stored in the register 13. Only the high voltage and the drain voltage are applied to the memory cell to program the memory cell 11.

At this time, the threshold voltage Vt of the memory cell is commonly applied to the first input terminal of the first to third comparison means 161 to 163 of the comparator 13, and is generated by the reference voltage generator 15. The first to third reference voltages Va, Vb, and Vc are applied to the second input terminals of the first to third comparison means 161 to 163, respectively, to change the threshold voltage Vt of the memory cell while executing a program. Monitor continuously.

When the program operation of the memory cell 11 is completed after a predetermined time has elapsed, the output voltage of the first to third comparison means 161 to 163 of the comparator 16 is measured, and the threshold voltage of the memory cell is at a certain level. It can be determined whether it is distributed at.

Referring to Figure 3 in more detail as follows.

For example, assuming that the first to third reference voltages are 3 V, 2 V, and 1 V, respectively, the output voltage V ₁₁ of the first comparing means 161 is at a low level, and the second and third comparing means are at a low level. If the output voltages V ₁₂ and V ₁₃ of 162 and 163 are at a high level, this means that the threshold voltage of the memory cell is raised to a voltage corresponding to a second level higher than 2V and lower than 3V by a program operation.

In the above, three reference voltages are generated and the change of the threshold voltage is sensed through three comparison means. However, the voltage difference with respect to each reference voltage is further subdivided by increasing the number of resistors of the reference voltage generator 15. Accordingly, the number of the comparison means of the comparator 16 is also increased accordingly, so that the level of the threshold voltage can be measured more accurately.

Thus, in the related art, the threshold voltage distribution of the cell can be confirmed only by performing a separate verification step after the program operation of the memory cell is performed. However, in the present invention, the reference voltages Va, Vb and Since the program is executed while comparing Vc) with the threshold voltage of the memory cell, the amount of change in the threshold voltage of the memory cell can be immediately confirmed without a separate checking step after the program operation is completed.

In addition, in the related art, it is only possible to confirm whether the threshold voltage of the memory cell is higher than the target voltage through the verifying step, and it is not possible to determine how much the threshold voltage is increased. However, the present invention is a minimum voltage and a maximum voltage of the threshold voltage. Can predict the threshold voltage distribution as well as whether or not a transient program is generated for the memory cell.

On the other hand, although not shown in the drawing, a signal obtained by logically combining the output signals of the first to third comparison means 161 to 163 is used as the enable signal of the program unit 14, whereby the threshold voltage of the memory cell is increased. Over-programming can also be prevented by stopping the program operation when the target level is reached.

Hereinafter, an operation of a program circuit of a flash memory cell that compares the amount of current flowing through the memory cell with different amounts of current flowing by the plurality of current setting means will be described with reference to FIG. 2.

As shown in FIG. 2, a program circuit of a flash memory cell according to another embodiment of the present invention includes a program time determination circuit 22 that determines a time required for programming the memory cell 21 according to a target threshold voltage; The memory cell 21 is programmed by programming the memory cell 21 for a predetermined time according to the register 13 for storing data on the program time required by the program time determining circuit 22 and the data stored in the register 23. A program unit 24 for raising a threshold voltage of the target voltage to a target threshold voltage, a plurality of current setting means 251 to 253 designed to flow different amounts of current, a current amount flowing through each current setting means, and a memory cell. Comparing section 26 for comparing the amount of current flowing through each.

Each current setting means 251 to 253 is composed of transistors N21 to N23 having different resistance values, and a predetermined voltage is applied to the gate electrodes of the transistors N21 to N23 by the voltage supply means 27. do. At this time, the voltage supply means 27 has a structure in which a transistor N24 connected to a gate and a drain is connected in series from the current source C21, and the predetermined voltage to be applied to the gates of the transistors N21 to N23 by supplying current to the drain. To generate a voltage. When a predetermined voltage is applied to the gate electrodes of the transistors N21 to N23, different amounts of current flow through the transistors having different on-resistance.

The comparator 26 senses the amount of current flowing through the memory cell through one terminal, and senses and compares different amounts of current flowing through the current setting means 251 through 253 through the other terminal, respectively. Comparison means 261 to 263.

Hereinafter, the operation of the program circuit will be described.

First, the program time determination circuit 22 determines a necessary program time for raising the threshold voltage of the memory cell 21 to the target threshold voltage, and then stores the generated signal in the register 23.

The signal stored in the register 23 is applied to the program unit 24, and the program unit 24 programs the memory cell 21 for a predetermined time in accordance with the signal of the register 23. The program unit 24 generates a voltage required for executing a program, that is, a high voltage and a drain voltage to be applied to the control gate of the memory cell 21, and includes a time calculating device so as to correspond to the data stored in the register 23 for a corresponding time. Only the high voltage and the drain voltage are applied to the memory cell to program the memory cell 21.

When the program operation of the memory cell 21 is completed, a predetermined voltage is applied to the control gate and the drain of the memory cell 21, and then the memory cell is provided through the first input terminal of the first to third comparison means 261 to 263. The current flowing in 21 is sensed. Different amounts of current are sensed by the first to third current setting means 251 to 253 at the second input terminals of the first to third comparison means 261 to 263. The first to third comparison means 261 to 263 compare the amount of current flowing through the memory cell 21 with the amount of first to third current flowing through the current setting means 251 to 253, respectively, and output a result value. .

Thus, as described with reference to FIG. 1, after the program operation is completed, the threshold voltage threshold voltage change amount of the memory cell 21 is immediately identified through the output signal of the first to third comparison means 261 to 263 without a separate checking step. The minimum and maximum voltages for the threshold voltages can be predicted to more clearly determine the threshold voltage distribution as well as whether a transient program is generated for the memory cell.

Referring to Figure 3 in more detail as follows.

For example, if the output voltage V ₂₁ of the first comparing means 261 is low level, and the output voltages V ₂₂ and V _{23 of} the second and third comparing means 262 and 263 are high level, The amount of current flowing through the memory cell is greater than the second current and less than the first current by the program operation, thereby increasing the threshold voltage of the memory cell to a voltage corresponding to the second level.

In addition, although the change of the threshold voltage is sensed through the three current setting means 251 to 253 and the three comparison means 261 to 263, the current amount of the memory cell is increased when the number of the current setting means and the comparison means is increased. The change in can be sensed more precisely, so that the level of the threshold voltage can be measured more accurately.

In the above, after the program operation is completed, the amount of current flowing through the memory cell is sensed through a read operation to measure a change in threshold voltage of the memory cell. However, when the memory cell 21 is programmed, the current flowing through the memory cell 21 gradually decreases while the threshold voltage of the memory cell 21 increases, so that the change in the amount of current flowing through the memory cell while sensing the memory cell is simultaneously sensed. The threshold voltage change amount of the memory cell may be measured.

Hereinafter, a method of measuring a threshold voltage change of a memory cell by simultaneously measuring a change in the amount of current flowing through the memory cell while programming the memory cell will be described.

While programming the memory cell 21, the amount of current flowing through the memory cell 21 using the first to third comparison means 261 to 263 and the first to third current setting means 251 to 253. Compare the amounts of the first through third currents flowing respectively. The program operation is stopped when the threshold voltage of the memory cell 21 satisfies the target voltage value while continuously monitoring the output signals V ₂₁ to V _{23 of} the first to third comparison means 261 to 263. As a result, the program operation is completed without a separate checking step and the distribution of threshold voltages can be checked.

Like the program circuit shown in FIG. 1, the program circuit may predict a minimum voltage and a maximum voltage with respect to a threshold voltage, and logically combine the output signals of the first to third comparison means 261 to 263. The signal may be used as an enable signal of the program unit 24 to prevent excessive programming by stopping the program operation when the threshold voltage of the memory cell reaches the target level.

As described above, the present invention implements a program while sensing a change in the threshold voltage, and stops the program when the threshold voltage reaches a target level, thereby preventing excessive programming, and without the need for a separate confirmation step The lowest and highest values for the voltage can be checked simultaneously, improving the reliability of the circuit's operation.

Claims (10)

A program unit for raising a threshold voltage of the memory cell; A reference voltage generator for generating reference voltages of different levels; And a comparison unit comparing the threshold voltages of the memory cells with reference voltages of different levels, and stopping the operation of the program unit when the threshold voltages of the memory cells rise to a target period. A program time determining circuit for determining a time required for programming a memory cell according to a target threshold voltage; A register for storing data on a program required time generated in the program time determining circuit; A program unit for programming a memory cell for a predetermined time according to the data stored in the register; A reference voltage generator for generating reference voltages of different levels; And a comparison unit comparing the threshold voltage of the memory cell with reference voltages of different levels, and stopping the operation of the program unit when the threshold voltage of the memory cell rises to a target period. The method according to claim 1 or 2, And the reference voltage generator comprises a plurality of resistors connected in series between a power supply voltage terminal and a ground power supply terminal. The method according to claim 1 or 2, The comparator comprises a plurality of comparison means to which the threshold voltage of the memory cell is commonly applied to the first input terminal, and the different reference voltages are respectively applied to the second input terminal. . A program unit for raising a threshold voltage of the memory cell; A plurality of current setting means for generating different amounts of reference current, And comparing a current amount of the reference currents generated from the current setting means with an amount of current flowing through the memory cell, and stopping the operation of the program unit when the threshold voltage of the memory cell rises to a target period. Program circuit of flash memory cell. A program time determining circuit for determining a time required for programming a memory cell according to a target threshold voltage; A register for storing data on a program required time generated in the program time determining circuit; A program unit for programming a memory cell for a predetermined time according to the data stored in the register; A plurality of current setting means for generating different amounts of reference current, And comparing a current amount of the reference currents generated from the current setting means with an amount of current flowing through the memory cell, and stopping the operation of the program unit when the threshold voltage of the memory cell rises to a target period. Program circuit of flash memory cell. The method according to claim 5 or 6, Wherein each current setting means comprises a transistor connected between one input terminal of each comparison means and ground and having a predetermined resistance value. The method according to claim 5 or 6, The comparator comprises a plurality of comparison means for sensing the amount of current flowing through the memory cell through one terminal, and for sensing and comparing the reference current amount of each current setting means through the other terminal, respectively. Program circuit of memory cells. The memory cell is programmed using the circuit according to any one of claims 1 and 2, and the threshold of the memory cell and the reference voltages of the different levels are compared using the comparator, respectively, and the threshold of the memory cell is used. Stopping the program when the voltage rises to the target level. A memory cell is programmed using the circuit according to any one of claims 5 and 6, and at the same time, the amount of current flowing through the memory cell and the amount of current flowing through the memory cell are compared using the comparison unit, respectively. The program method of a flash memory cell, characterized in that the program is stopped when the target current amount decreases.