Memory device and method of operating the same

1. A memory device comprising:

a memory block including a plurality of pages;

a voltage generator configured to generate a program voltage or a verify voltage applied to a selected page among the plurality of pages;

a page buffer connected to the selected page through bit lines and configured to perform a precharge operation, an evaluation operation, and a sensing operation on the bit lines during a verify operation; and

a control circuit configured to store page addresses of slow pages of which a program operation speed for each is slower than an average program speed of the plurality of pages, and adjust an evaluation time of the evaluation operation according to the page addresses.

2. The memory device of claim 1 , wherein the control circuit comprises:

an address decoder configured to decode an address and output a row address and a column address;

an address register configured to store the page addresses;

a page buffer controller configured to output page buffer control signals for controlling the page buffer in response to a page buffer control code;

a voltage generator controller configured to output an operation code for controlling the voltage generator in response to a voltage generator control code; and

an operation controller configured to execute an algorithm for a program operation in response to a command, compare a page address in the row address with the page addresses stored in the address register, and output the page buffer control code and the voltage generator control code so that the evaluation time is adjusted according to a comparison result.

3. The memory device of claim 2 , wherein the voltage generator sets a level of the verify voltage according to the operation code, and adjusts a time when the verify voltage is output.

4. The memory device of claim 2 , wherein the page buffer controls the precharge operation, the evaluation operation, and the sensing operation according to the page buffer control signals.

5. The memory device of claim 4 , wherein the page buffer precharges the bit lines to a positive voltage during the precharge operation, performs the evaluation operation during a first evaluation time or a second evaluation time shorter than the first evaluation time so that a threshold voltage of memory cells in the selected page is reflected on the bit lines, and performs the sensing operation of sensing a voltage or a current of a bit line on which the evaluation operation is performed and storing data corresponding to the sensing result in a latch.

6. The memory device of claim 5 , wherein, when an address identical to a page address in the row address is not present among the page addresses stored in the address register, the operation controller outputs the page buffer control code and the voltage generator control code so that the evaluation operation is performed during the first evaluation time.

7. The memory device of claim 5 , wherein, when an address identical to a page address in the row address is present among the page addresses stored in the address register, the operation controller outputs the page buffer control code and the voltage generator control code so that the evaluation operation is performed during the second evaluation time.

8. The memory device of claim 5 , wherein the operation controller outputs the page buffer control code and the voltage generator control code so that the evaluation operation is performed during the second evaluation time and the evaluation operation is performed until a program operation of a slow page is completed.

9. The memory device of claim 5 , wherein the operation controller outputs the page buffer control code and the voltage generator control code so that the evaluation operation is performed during the first evaluation time being from a start of a program operation of a slow page to a reference time point, and outputs the page buffer control code and the voltage generator control code so that the evaluation operation is performed during the second evaluation time being from the reference time point to an end of the program operation.

10. A method of operating a memory device, the method comprising:

classifying each of a plurality of pages as a fast page or a slow page according to a program operation speed; and

performing a verify operation for a program operation such that an evaluation operation is performed during a first evaluation time when a selected page is the fast page, and performing the verify operation such that the evaluation operation is performed during a second evaluation time shorter than the first evaluation time when the selected page is the slow page,

wherein the program operation ends when the verify operation has passed, and classifying and performing are repeated until the verify operation passes when the verify operation has failed.

11. The method of claim 10 , wherein the classifying of each of the plurality of pages as the fast page or the slow page comprises:

performing a test program operation on the plurality of pages;

classifying a page of which a program speed is slower than a reference speed as the slow page, and classifying a page of which the program speed is faster than the reference speed as the fast page, as a result of the test program operation; and

storing a page address of each of the slow pages in an address register.

12. The method of claim 11 , wherein the performing of the verify operation comprises:

precharging bit lines connected to the selected page among the plurality of pages to a positive voltage;

applying a verify voltage to a word line connected to the selected page, and performing the evaluation operation during the first or second evaluation time; and

performing a sensing operation of sensing data according to a voltage or a current of the bit lines and storing the sensed data in latches.

13. The method of claim 12 , wherein, when the verify operation of all memory cells in the selected page has passed, the program operation ends, and

when cells of which the verify operation has not passed are present among memory cells in the selected page, it is determined that the verify operation has failed.

14. A method of operating a memory device, the method comprising:

classifying each of a plurality of pages as a fast page or a slow page according to a program operation speed; and

performing a verify operation for a program operation such that an evaluation operation is performed during a first evaluation time when a selected page is the fast page, performing the verify operation such that the evaluation operation is performed based on the first evaluation time when the selected page is the slow page, and performing the verify operation such that the evaluation operation is performed during a second evaluation time shorter than the first evaluation time when a reference time point is reached during a program operation of the slow page,

wherein the program operation ends when the verify operation has passed, and classifying and performing are repeated until the verify operation passes when the verify operation has failed.

15. The method of claim 14 , wherein the classifying of each of the plurality of pages into the fast page or the slow page comprises:

performing a test program operation on the plurality of pages;

classifying a page of which a program speed is slower than a reference speed as the slow page, and classifying a page of which the program speed is faster than the reference speed as the fast page, as a result of the test program operation; and

storing a page address of each of the slow pages in an address register.

16. The method of claim 15 , wherein the performing of the verify operation of the slow page comprises:

precharging bit lines connected to the selected page among the plurality of pages to a positive voltage;

applying a verify voltage to a word line connected to the selected page, performing the evaluation operation during the first evaluation time from a start of the program operation to the reference time point, and performing the evaluation operation during the second evaluation time after the reference time point; and

performing a sensing operation of sensing data according to a voltage or a current of the bit lines and storing the sensed data in latches.

17. The method of claim 14 , wherein the reference time point is set according to the number of program pulses applied to the slow page.

18. The method of claim 14 , wherein the reference time point is set to a time point at which cells of which a threshold voltage is increased to a target voltage among memory cells in the slow page are detected.

19. The method of claim 18 , further comprising:

when the cells of which the threshold voltage is increased to the target voltage are detected, performing a verify operation using a sub target voltage lower than the target voltage before performing a verify operation using the target voltage of a next loop.