Flash Memory Device for Variably Controlling Program Voltage and Method of Programming the Same

• US 20090207664A1
• Filed: 07/11/2008
• Published: 08/20/2009
• Est. Priority Date: 02/20/2008
• Status: Active Grant

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Kim, Moo-Sung, Lee, Sung-Soo
• Granted Patent: US 7,688,631 B2
• Time in Patent Office: Days
• US Class Current: 365/185.190
• CPC Class Codes: G11C 16/12 Programming voltage switching circuits

Abstract

Provided is a method of programming the flash memory device including setting increments of program voltages according to data states expressed as threshold voltage distributions of multi-level memory cells. An Increment Step Pulse Programming (ISPP) clock signal corresponds to a loop clock signal and the increments of the program voltages and is generated in response to program pass/fail information. A default level enable signal is generated by performing a counting operation until reaching the increments of the program voltages, in response to the loop clock signal. An additional level enable signal is generated by performing a counting operation until reaching the increments of the program voltages, in response to the ISPP clock signal. The program voltage is increased by 1 increment, in response to the default level enable signal. The program voltage is increased by 2 increments, in response to the additional level enable signal.

Claims

1. A method of programming a flash memory device, the method comprising:

setting increments of program voltages according to one or more data states expressed as one or more threshold voltage distributions of multi-level memory cells;

generating an Increment Step Pulse Programming (ISPP) clock signal in response to program pass/fail information, the ISPP clock signal corresponding to a loop clock signal and to the increments of the program voltages;

generating a default level enable signal by performing a first counting operation that counts up to the increments of the program voltages, in response to the loop clock signal;

generating an additional level enable signal by performing a second counting operation that counts up to the increments of the program voltages, in response to the ISPP clock signal;

increasing the program voltage by 1 increment, in response to the default level enable signal; and

increasing the program voltage by 2 increments, in response to the additional level enable signal.

2. The method of claim 1, wherein each data state is obtained as a result of testing the flash memory device having the multi-level memory cells.

3. The method of claim 1, wherein each of the 2 increments that the program voltage is increased by, in response to the additional level enable signal, is less than the 1 increment.

4. The method of claim 1, further comprising:

distributing the program voltages;

comparing the distributed program voltages with a reference voltage and generating a pumping clock signal according to the result of the comparison; and

generating the program voltages in response to the pumping clock signal.

5. A flash memory device comprising:

a program control logic unit generating a loop clock signal and an Increment Step Pulse Programming (ISPP) information signal, in response to program pass/fail information;

an ISPP control logic unit generating a default level enable signal and an additional level enable signal, in response to the loop clock signal and the ISPP information signal;

a program voltage regulator variably increasing a program voltage, distributing the program voltage and comparing it to a reference voltage, and generating a pumping clock signal according to the result of the comparison, in response to the default level enable signal and the additional level enable signal; and

a charge pump unit generating the program voltage, in response to the pumping clock signal.

6. The flash memory device of claim 5, wherein the ISPP information signal includes information pertaining to increments of the program voltage for each data state determined from threshold voltage distributions of multi-level memory cells in each of a plurality of data states obtained as a result of testing the flash memory device.

7. The flash memory device of claim 5, wherein the ISPP control logic unit comprises:

a clock generator receiving the loop clock signal and the ISPP information signal and generates an ISPP clock signal;

a first counter performing a counting operation and generating a corresponding default level enable signal when output values of the first counter reach target increments of the program voltage, in response to the loop clock signal; and

a second counter performing a counting operation and generating a corresponding additional level enable signal when output values of the second counter reach target increments of the program voltages, in response to the ISPP clock signal.

8. The flash memory device of claim 5, wherein the program voltage regulator comprises:

a plurality of first and second resistors connected between the generated program voltage and the distributed program voltage, in series;

a first level control unit selectively short-circuiting the first resistors, in response to the default level enable signal;

a second level control unit selectively short-circuiting the second resistors, in response to the additional level enable signal; and

a level detection and pumping clock control unit receiving an oscillation signal, comparing the distributed program voltage and the reference voltage, and generating the oscillation signal as the pumping clock signal according to the result of the comparison.

9. The flash memory device of claim 8, wherein the first level control unit comprises:

a plurality of switches transmitting a high voltage in response to the default level enable signal; and

a plurality of high voltage NMOS transistors selectively short-circuiting the first resistors, in response to outputs of the switches.

10. The flash memory device of claim 8, wherein the second level control unit comprises:

a plurality of switches transmitting a high voltage in response to the additional level enable signal; and

a plurality of high voltage NMOS transistors selectively short-circuiting the second resistors, in response to outputs of the switches.

11. The flash memory device of claim 8, wherein the level detection and pumping clock control unit comprises:

a comparator comparing the distributed program voltage with the reference voltage;

a NAND gate receiving the oscillation signal and an output of the comparator; and

an inverter receiving an output of the NAND gate and outputting the pumping clock signal based on the received output of the NAND gate.

12. A flash memory device comprising:

a program control logic unit generating a loop clock signal, an Increment Step Pulse Programming (ISPP) information signal, a discharge enable signal, and a regulator enable signal, in response to program pass/fail information;

an ISPP control logic unit generating a default level enable signal and an additional level enable signal, in response to the loop clock signal and the ISPP information signal;

a program voltage regulator variably increasing a program voltage, distributing the program voltage, generating a first voltage by distributing the program voltage, comparing the first voltage with a reference voltage, and generating a pumping clock signal, in response to the discharge enable signal, the default level enable signal, the additional level enable signal, and the regulator enable signal; and

a charge pump unit generating the program voltage, in response to the pumping clock signal.

13. The flash memory device of claim 12, wherein the ISPP information signal includes information pertaining to increments of the program voltages in each of a plurality of data states determined from threshold voltage distributions of multi-level memory cells at each of the plurality of data states obtained as a result of testing the flash memory device.

14. The flash memory device of claim 12, wherein the ISPP control logic unit comprises:

a clock generator receiving the loop clock signal and the ISPP information signal and generating an ISPP clock signal;

a first counter performing a counting operation and generating a corresponding default level enable signal when output values of the first counter reach target increments of the program voltages, in response to the loop clock signal; and

a second counter performing a counting operation and generating a corresponding additional level enable signal when output values of the second counter reach target increments of the program voltages, in response to the ISPP clock signal.

15. The flash memory device of claim 12, wherein the program voltage regulator comprises:

a discharge circuit unit discharging the program voltage to a power voltage, in response to the discharge enable signal;

a first level control unit comprising a plurality of first resistors connected between the program voltage and a second voltage in series and selectively short-circuiting the first resistors, in response to the default level enable signal;

a second level control unit comprising a plurality of second resistors connected between the second voltage and the first voltage in series and selectively short-circuiting the second resistors, in response to the additional level enable signal; and

a level detection and pumping clock control unit receiving an oscillation signal, comparing the first voltage with the reference voltage, and generating the oscillation signal as a pumping clock signal according to the result of the comparison.

16. The flash memory device of claim 15, wherein the discharge circuit unit comprises a PMOS transistor connected in series between the power voltage and the program voltage and a NMOS transistor of a high voltage depletion type, wherein a gate of the PMOS transistor is connected to the discharge enable signal and a gate of the high voltage depletion type NMOS transistor is connected to the power voltage.

17. The flash memory device of claim 15, wherein the first level control unit comprises:

the first resistors;

a plurality of switches transmitting high voltage in response to the default level enable signal; and

a plurality of high voltage NMOS transistors selectively short-circuiting the first resistors, in response to outputs of the switches.

18. The flash memory device of claim 15, wherein the second level control unit comprises:

the second resistors;

a plurality of switches transmitting a high voltage in response to the additional level enable signal; and

a plurality of high voltage NMOS transistors selectively short-circuiting the second resistors, in response to outputs of the switches.

19. The flash memory device of claim 15, wherein the regulator enable circuit unit comprises a resistor and a NMOS transistor connected in series between the first voltage and a ground voltage, wherein a gate of the NMOS transistor is connected to the regulator enable signal.

20. The flash memory device of claim 15, wherein the level detection and pumping clock control unit comprises:

a comparator which compares the first voltage and the reference voltage;

a NAND gate which receives an output of the comparator and the oscillation signal; and

an inverter which receives an output of the NAND gate and outputs the pumping clock signal based on the received output of the NAND gate.