Memory device

A memory device may include a plurality of memory cells; and an error detection unit suitable for latching first read data of one or more memory cells selected from the plurality of memory cells after refreshing the selected memory cells, in a first phase, and suitable for detecting errors of the selected memory cells before refreshing the selected memory cells, in a second phase.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority of Korean Patent Application No. 10-2015-0127457, filed on Sep. 9, 2015, which is incorporated herein by reference in its entirety.

BACKGROUND

Exemplary embodiments of the present invention relate to a memory device.

2. Description of the Related Art

Memory devices may include a plurality of memory cells, each of which includes a cell transistor serving as a switch and a cell capacitor for storing a charge (data). Data of a memory cell may be determined as ‘high’ (logic 1) or ‘low’ (logic 0) depending on the charge stored in the cell capacitor of the memory cell, that is, whether a terminal voltage of the cell capacitor is high or low.

In principle, maintaining data stored in a memory cell as an accumulated charge in a cell capacitor, requires no power consumption. However, in practice, an initial charge stored in a cell capacitor may degrade overtime due to a leakage current caused, for example, near a PN junction of a MOS transistor, which in turn may cause a data loss. Furthermore, as the degree of integration of memory devices continues to increase and the width of line patterns (or critical dimension) decreases, the capacitance of a cell capacitor is reduced as compared with the capacitance of a bit line capacitor, so that a voltage difference for distinguishing data stored in the memory cell becomes smaller. As a result, there is an increased likelihood that a 1-bit failure occurs. Such 1-bit failure is commonly referred to as an intermittent tWR failure (hereinafter, also referred to as an intermittent failure).

An intermittent failure does not occur continuously in a specific cell but may occur rather irregularly, hence addressing such a failure may be problematic.

For example, a memory device such as a DRAM may perform a typical refresh operation on a constant cycle. Since an intermittent failure may occur during a refresh operation, it is difficult to prevent an intermittent failure through a typical refresh operation. Furthermore, even though a failed cell detected through a test in a production stage of a memory device may be repaired with a redundancy cell, it may be difficult to prevent an intermittent failure through conventional test and repair since an intermittent failure may also occur in a memory cell which is not detected as a failed cell.

SUMMARY

Various embodiments are directed to a memory device which detects and corrects intermittent failure of memory cells during own operation.

In an embodiment a memory device may include a plurality of memory cells; and an error detection unit suitable for latching first read data of one or more memory cells selected from the plurality of memory cells after refreshing the selected memory cells, in a first phase, and suitable for detecting errors of the selected memory cells before refreshing the selected memory cells, in a second phase.

In another embodiment, a memory device may include: a plurality of memory cells; a refresh counter suitable for generating a refresh address; a detection counter suitable for generating row and column detection addresses; a period signal generation unit suitable for sequentially activating first and second period signals in a period when the refresh address and the row detection address are substantially equal to each other; and an error detection unit suitable for latching first read data of first memory cells corresponding to the row and column detection addresses among the plurality of memory cells in response to a refresh command when the second period signal is activated in a first phase, and suitable for detecting errors of the first memory cells in response to the refresh command using second read data of the first memory cells when the first period signal is activated in a second phase.

In accordance with the present technology, intermittent fail of a memory cell is detected during an operation of a memory device and is corrected, so that it is possible to allow the memory device to normally operate even though the intermittent fail occurs.

DETAILED DESCRIPTION

A detection operation may include detecting an intermittent failure of a memory device. A detection operation may include correcting an intermittent failure of a memory device.

In an embodiment, a detection operation may include first and second sub-operations. A first sub-operation may include a first reading of data of one or more selected memory cells from a plurality of memory cells and latching the first read data. The second sub-operation may include a second reading of the data of the same one or more selected memory cells, and comparing the second read data from the second sub-operation with the latched data form the first sub-operation for detecting an intermittent failure. The second sub-operation may further include correcting the one or more memory cells for which an intermittent failure has been detected.

FIG. 1is a configuration diagram of a memory device, according to with an embodiment of the present invention.

Referring toFIG. 1, the memory device may include a cell array110, a refresh counter120, a detection counter130, a flag signal generation unit140, a period signal generation unit150, an error detection unit160, a refresh control unit170, a row circuit180, and a column circuit190.

The cell array110may include a plurality of rows WL0to WL1023(word lines), a plurality of columns BL0to BL127(bit lines), and a plurality of memory cells MC coupled between the word lines and the bit lines. The number of rows, columns, and memory cells may vary.

The refresh counter120may perform a counting operation to whenever a refresh signal REFA is activated. For example, the refresh counter120may generate counting addresses CNT_ADD<0:9> and may increase the counting addresses CNT_ADD<0:9> by 1 whenever the refresh signal REFA is activated. Increasing the counting addresses CNT_ADD<0:9> by 1 means that if, for example, a Kthword line is selected this time, the counting addresses CNT_ADD<0:9> are changed so that a K+1thword line will be selected next time. However, in a period in which the counting addresses CNT_ADD<0:9> and row detection addresses DET_RADD<0:9> are substantially equal, a first period signal SEC1is activated and the refresh counter120may perform no counting in response to the first period signal SEC1, even though the refresh signal REFA is activated. That is, when the first period signal SEC1has been activated, the refresh counter120may skip the counting.

The detection counter130may generate row and column detection addresses DET_RADD<0:9>, DET_CADD<0:4> for selecting memory cells for performing a detection operation, from the plurality of memory cells MC of the cell array110. Whenever a detection operation is completed, the detection counter130may increase the row detection addresses DET_RADD<0:9> or the column detection addresses DET_CADD<0:4>. When the row detection addresses DET_RADD<0:9> or the column detection addresses DET_CADD<0:4> reach an end value, the detection counter130may repeat the counting from an initial value. The completion of a detection operation may represent that first and second sub-operations have been sequentially completed once with respect to selected memory cells.

In an embodiment, whenever a detection operation is completed, the detection counter130may increase the column detection addresses DET_CADD<0:4>. When the detection operation is completed at the end value of the column detection addresses DET_CADD<0:4> (for example, a maximum value), the detection counter130may change the value of the column detection addresses DET_CADD<0:4> to an initial value (for example, a minimum value) and increase the column detection addresses DET_RADD<0:9>.

In another embodiment, whenever a detection operation is completed, the detection counter130may increase the row detection addresses DET_RADD<0:9>. For example, when the detection operation is completed at the end value of the row detection addresses DET_RADD<0:9> (for example, a maximum value), the detection counter130may change the value of the row detection addresses DET_RADD<0:9> to an initial value (for example, a minimum value) and increase the row detection addresses DET_CADD<0:4>.

The flag signal generation unit140may toggle to a logic value of a flag signal FLAG in response to a refresh signal REFA in a detection period in which a detection operation is performed. When a detection period signal DET_OP indicating the detection period is activated, the flag signal generation unit140may toggle to the logic value of the flag signal FLAG in response to the refresh signal REFA. For example, when the flag signal FLAG has a first logic value (for example, low), the flag signal generation unit140may change the flag signal FLAG from the first logic value to a second logic value (for example, high) in response to the refresh signal REFA in the detection period. Furthermore, when the flag signal FLAG has the second logic value, the flag signal generation unit140may change the flag signal FLAG from the second logic value to the first logic value in response to the refresh signal REFA in the detection period. When the flag signal FLAG has the first logic value, the activation period of the detection period signal DET_OP may be substantially equal to the activation period of a second period signal SEC2. When the flag signal FLAG has the second logic value, the activation period of the detection period signal DET_OP may be substantially equal to the activation period of the first period signal SEC1.

The flag signal FLAG may have the first logic value to represent a first phase of the detection period in which a first sub-operation is performed in response to the activation of the refresh signal REFA. The flag signal FLAG may have the second logic value to represent a second phase of the detection period in which a second sub-operation is performed in response to the activation of the refresh signal REFA.

The period signal generation unit150may generate the first period signal SEC1, the second period signal SEC2, and/or the detection period signal DET_OP. The period signal generation unit150may sequentially activate the first period signal SEC1and the second period signal SEC2in the period in which the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> may be substantially equal. When the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are substantially equal, the period signal generation unit150may activate the first period signal SEC1. In a state in which the first period signal SEC1has been activated, the period signal generation unit150may deactivate the first period signal SEC1and activate the second period signal SEC2in response to the refresh signal REFA. In a state in which the second period signal SEC2has been activated, the period signal generation unit150may deactivate the second period signal SEC2in response to the refresh signal REFA. The period signal generation unit150may transfer the second period signal SEC2as the detection period signal DET_OP in the first sub-operation and may transfer the first period signal SEC1as the detection period signal DET_OP in the second sub-operation.

The error detection unit160may detect and correct errors of selected memory cells correspond ng to the row detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4> among the plurality of memory cells MC of the cell array110. The error detection unit160may latch data, which has been read from the selected memory cells, in response to the refresh signal REFA in the first phase of the detection period (the first logic value of FLAG and the activation of DET_OP). Furthermore, the error detection unit160may compare the data, which has been read from the selected memory cells, with the latched data and detect errors in response to the refresh signal REFA in the second phase of the detection period (the second logic value of FLAG and the activation of DET_OP).

When the read data and the latched data are substantially equal to each other, the error detection unit160may determine the states of the selected memory cells to be pass (no fail). When the read data and the latched data are different from each other, the error detection unit160may determine the states of the selected memory cells to be fail (failed). When the states of the selected memory cells are determined to be fail, the error detection unit160may control the column circuit190and the like such that the latched data may be written in the selected memory cells (a write-back operation). When no error is detected, the error detection unit160may deactivate (for example, low) a detection signal DET. When an error is detected, the error detection unit160may activate (for example, high) the detection signal DET.

The refresh control unit170may activate the refresh signal REFA whenever a refresh command REF is received.

The row circuit180may be a circuit for controlling active and precharge operations of word lines selected by row addresses RADD<0:9>, the counting addresses CNT_ADD<0:9>, or the row detection addresses DET_RADD<0:9>. The row circuit180may activate word lines corresponding to the row addresses RADD<0:9> in response to an active signal ACT activated when an active command is inputted, and may precharge the activated word lines in response to a precharge signal PRE activated when a precharge command is inputted. In the case in which the detection period signal DET_OP has been deactivated, the row circuit180may activate/precharge word lines corresponding to the counting addresses CNT_ADD<0:9> as the refresh signal REFA is activated. In the case in which the detection period signal DET_OP has been activated, the row circuit180may activate/precharge word lines corresponding to the row detection addresses DET_RADD<0:9> as the refresh signal REFA is activated.

The column circuit190may read data DATA from memory cells MC coupled to bit lines selected by column addresses CADD<0:4> in response to a read signal RD activated when a read command is inputted, and may write the data DATA to the memory cells MC in response to a write signal WT activated when a write command is inputted. The data DATA may be inputted/outputted to/from the cell array110through the column circuit190.

When the flag signal FLAG has the first logic value and the detection period signal DET_OP has been activated, the column circuit190may transmit data of the memory cells corresponding to the row detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4> to the error detection unit160in response to the refresh signal REFA. When the flag signal FLAG has the second logic value and the detection period signal DET_OP has been activated, the column circuit190may transmit the data of the memory cells corresponding to the row detection addresses DET_RADD<0:9 and the column detection addresses DET_CADD<0:4> to the error detection unit160in response to the REFA, and write data transmitted from the error detection unit160in the memory cells corresponding to the row detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4> in response to the detection signal DET.

A reference numeral101indicates a plurality of lines for transferring various signals between the error detection unit160and the column circuit190. In the embodiment ofFIG. 1, four bit lines may correspond to respective values of the column addresses CADD<0:4> or the column detection addresses DET_CADD<0:4>.

When the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are substantially equal, the memory device may perform a detection operation with respect to memory cells corresponding to the root detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4>. Furthermore, the memory device may refresh word lines corresponding to the counting addresses CNT_ADD<0:9>. Accordingly, in a period in which the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are substantially equal, detection and refresh operations are performed with respect to the memory cells corresponding to the row detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4>.

At this time, the memory device may refresh word lines corresponding to the counting addresses CNT_ADD<0:9> and then perform the first sub-operation of the detection operation. The memory device may perform the second sub-operation of the detection operation and then refresh word lines corresponding to the counting addresses CNT_ADD<0:9>. Hence, the detection operation may be performed between consecutive refresh operations, that is, in a period from the time when a previous refresh operation has been completed to the time when a next refresh operation starts. Consequently, a refresh influence to the detection operation may be excluded, so that it is possible to enhance the accuracy of the detection operation.

FIG. 2is a configuration diagram of an example of a detection counter130, that may be employed with a memory device according to an embodiment of the present invention.

Referring toFIG. 2the detection counter130may include a first counting unit210and a second counting unit220.

The first counting unit210may count the column detection addresses DET_CADD<0:4> (for example, increase the column detection addresses DET_CADD<0:4> by 1) whenever the detection operation is completed. When the detection operation is completed at the end value of the column detection addresses DET_CADD<0:4> (for example, 11111), the first counting unit210may initialize the column detection addresses DET_CADD<0:4> to an initial value (for example, 00000) and activate a row counting signal RCNT. To this end, in a state in which the flag signal FLAG has the second logic value and the detection period signal DET_OP has been activated, the first counting unit210may count the column detection addresses DET_CADD<0:4> as the refresh signal REFA is activated. Furthermore, in a state in which the flag signal FLAG has the second logic value, and the detection period signal DET_OP has been activated at the end value of the column detection addresses DET_CADD<0:4>, the first counting unit210may initialize the column detection addresses DET_CADD<0:4> to an initial value as the refresh signal REFA is activated. In addition, when a first external counting signal ECNT1is activated, the first counting unit210may count the column detection addresses DET_CADD<0:4>. The first external counting signal ECNT1may be a signal used for counting the column detection addresses DET_CADD<0:4> regardless of the completion of the detection operation.

The second counting unit220may count the row detection addresses DET_RADD<0:9> (for example, increase the row detection addresses DET_RADD<0:9> by 1) whenever the row counting signal RCNT is activated. When the row counting signal RCNT is activated at the end value of the row detection addresses DET_RADD<0:9> (for example, 1111111111), the second counting unit220may initialize the row detection addresses DET_RADD<0:9> to an initial value (for example, 0000000000). In addition, when a second external counting signal ECNT2is activated, the second counting unit220may count the row detection addresses DET_RADD<0:9>. The second external counting signal ECNT2may be a signal which is used when counting the row detection addresses DET_RADD<0:9> regardless of the initialization of the column detection addresses DET_CADD<0:4>.

FIG. 3is a configuration diagram of the detection counter130according to another embodiment of the present invention.

Referring toFIG. 3, the detection counter130may include a first counting unit310and a second counting unit320.

The first counting unit310may count the row detection addresses DET_RADD<0:9> (for example, increase the row detection addresses DET_RADD<0:9> by 1) when the detection operation is completed. For example, when the detection operation is completed at the end value of the row detection addresses DET_RADD<0:9> (for example, 1111111111), the first counting unit310may initialize the row detection addresses DET_RADD<0:9> to an initial value (for example, 0000000000) and activate a column counting signal YCNT. To this end, in a state in which the flag signal FLAG has the second logic value and the detection period signal DET_OP has been activated, the first counting unit310may count the row detection addresses DET_RADD<0:9> as the refresh signal REFA is activated. Furthermore, in a state in which the flag signal FLAG has the second logic value, and the detection period signal DET_OP has been activated at the end value of the row detection addresses DET_RADD<0:9>, the first counting unit310may initialize the row detection signal DET_RADD<0:9> to an initial value as the refresh signal REFA is activated. In addition, when a first external counting signal ECNT1is activated, the first counting unit310may count the row detection addresses DET_RADD<0:9>. The first external counting signal ECNT1may be a signal used for counting the row detection addresses DET_RADD<0:9> regardless of the completion of the detection operation.

The second counting unit320may count the column detection addresses DET_CADD<0:4> (for example, increase the column detection addresses DET_CADD<0:4> by 1) whenever the column counting signal YCNT is activated. When the column counting signal YCNT is activated at the end value of the column detection addresses DET_CADD<0:4> (for example, 11111), the second counting unit320may initialize the column detection, addresses DET_CADD<0:4> to an initial value (for example, 00000). In addition, when a second external counting signal ECNT2is activated, the second counting unit320may count the column detection addresses DET_CADD<0:4>. The second external counting signal ECNT2may be a signal used for counting the column detection addresses DET_CADD<0:4> regardless of the initialization of the row detection addresses DET_RADD<0:9>.

FIG. 4is a configuration diagram of an example of a flag signal generation unit140that may be employed with a memory device, according to an embodiment of the present invention.

Referring toFIG. 4, the flag signal generation unit140may include a D flip-flop410.

The D flip-flop410may output the flag signal FLAG to be low in an initial state. The flag signal FLAG outputted from the D flip-flop410may be inverted and may be inputted to the D flip-flop410again.

In the state in which the detection period signal DET_OP has been activated, the D flip-flop410may latch an inputted signal and output the flag signal FLAG as the refresh signal REFA is activated. Accordingly, when the detection period signal DET_OP and the refresh signal REFA are activated in the state in which the flag signal FLAG is low, the flag signal FLAG may be changed to high. When the detection period signal DET_OP and the refresh signal REFA are activated in the state in which the flag signal FLAG is high, the FLAG may be changed to low.

FIG. 5is a configuration diagram of an example of a period signal generation unit150that may be employed with a memory device, according to an embodiment of the present invention.

Referring toFIG. 5, the period signal generation unit150may include a first period signal generation section510, a second period signal generation section520, and/or a detection period signal generation section530.

The first period signal generation section510may include a comparison part511and a signal generation part512. The comparison part511may compare the counting addresses CNT_ADD<0:9> with the row detection addresses DET_RADD<0:9>, deactivate (for example, low) a comparison signal CMP when the addresses are not substantially equal. The comparison part511may compare the counting addresses CNT_ADD<0:9> with the row detection addresses DET_RADD<0:9> and activate (for example, high) the comparison signal CMP when the addresses are substantially equal. The signal generation part512may activate the first period signal SEC1when the comparison signal CMP is activated, and may deactivate the first period signal SEC1in response to the refresh signal REFA in a state in which the comparison signal CMP has been activated.

The second period signal generation section520may latch and store the first period signal SEC1when the refresh signal REFA is activated. The second period signal generation section520may output the latched value as the second period signal SEC2when the refresh signal REFA is deactivated. Accordingly, in a state in which the first period signal SEC1has been activated, the value of the SEC1may be latched when the refresh signal REFA is activated. When the refresh signal REFA is deactivated, the latched value may be outputted and the second period signal SEC2may be activated. In a state in which the first period signal SEC1has been deactivated, the value of the SEC1may be latched when the refresh signal REFA may be activated. When the refresh signal REFA is deactivated, the latched value may be outputted and the second period signal SEC2may be deactivated. The second period signal generation section520may deactivate the second period signal SEC2in an initialized state.

The detection period signal generation section530may include a selection signal generation part531and a selection part532. The selection signal generation part531may generate a selection signal SEL which may change whenever the second period signal SEC2has been activated and is deactivated (for example, at a falling edge). The selection signal generation part531may output an initial value 0 as a logic level of the selection signal SEL, and may change the logic value of the selection signal SEL from 0/1 to 1/0 at the falling edge of the second period signal SEC2. The selection part532may select the second period signal SEC2and output the detection period signal DET_OP when the selection signal SEL is 0, and may select the first period signal SEC1and output the detection period signal DET_OP when the selection signal SEL is 1.

FIG. 6is a diagram illustrating an operation of period signal generation unit150, according to an embodiment of the present invention.

Referring toFIG. 6, when the counting addresses CNT_ADD<0:9> and the row detection addresses DETRADD<0:9> are different from each other, the comparison signal CMP may be substantially maintained to be low. When the counting addresses CNT_ADD<0:9> and the row detection addresses DETRADD<0:9> are substantially equal, the comparison signal CMP may be activated, and the first period signal SEC1may be activated in response to the comparison signal CMP. In a state in which the comparison signal CMP has been activated, the first period signal SEC1may be deactivated in response to the refresh signal REFA and the second period signal SEC2may be activated. In a state in which the first period signal SEC1has been deactivated, the second period signal SEC2may be deactivated in response to the refresh signal REFA.

The selection signal SEL may toggle between 0 and 1 in response to the second period signal SEC2. When the selection signal SEL is 0, the second period signal SEC2may be transferred as the detection period signal DET_OP. When the selection signal SEL is 1, the first period signal SEC1may be transferred as the detection period signal DET_OP.

FIG. 7is a configuration diagram of error detection unit160, according to an embodiment of the present invention.

Referring toFIG. 7, the error detection unit160may include a plurality of data latch sections710_0to710_3, a plurality of data comparison sections720_0to720_3, a detection signal generation section730, and a plurality of data transmission sections740_0to740_3. Reference numerals IN0to IN3denote input lines through which data is transferred to be inputted to the error detection unit160, and reference numerals OUT0to OUT3denote output lines through which data is transferred to be outputted from the error detection unit160. The lines101ofFIG. 1may include the input lines IN0to IN3and the output lines OUT0to OUT3.

The plurality of data latch sections710_0to710_3respectively correspond to the input lines IN0to IN3, and may latch data transferred to the respective input lines IN0to In3when the flag signal FLAG has the first logic value and the detection period signal DET_OP and the refresh signal REFA have been activated. Data of the input lines IN0to IN3may be data firstly read from selected memory cells MC. The plurality of data latch sections710_0to710_3may output the latched data (LD0to LD3).

The plurality of data comparison sections720_0to720_3may output results DC0to DC3, which have been obtained by comparing the latched data LD0to LD3outputted from the respective data latch sections710_0to710_3with data transferred to the respective input lines INC to IN3when the flag signal FLAG has the second logic value and the detection period signal DET_OP and the refresh signal REFA have been activated. The data comparison sections720_0to720_3may deactivate the results DC0to DC3(for example, low) when the latched data LD0to LD3are substantially equal to data of the input lines IN0to IN3. The data comparison sections720_0to720_3may activate the results DC0to DC3(for example, high) when the latched data LD0to LD3are different from the data of the input lines IN0to IN3.

The detection signal generation section730may deactivate the detection signal DET when all the results DC0to the DC3are deactivated, that is, when the first read data (the latched data LD0to LD3) is substantially equal to the second read data (the data of the input lines IN0to IN3) in the case in which the flag signal FLAG has the second logic value and the detection period signal DET_OP and the refresh signal REFA have been activated. Furthermore, in the case in which the flag signal FLAG has the second logic value and the detection period signal DET_OP and the refresh signal REFA have been activated, the detection signal generation section730may activate the detection signal DET when one or more signals of the results DC0to the DC3are activated, that is, when the first read data is different from the secondly read data.

The plurality of data transmission sections740_0to740_3may respectively transfer the data LD0to LD3, which have been outputted from the data latch sections710_0to710_3respectively, to the output lines OUT0to OUT3when the detection signal DET is activated in the case in which the flag signal FLAG has the second logic value and the detection period signal DET_OP has been activated. The data transferred to the output lines OUT0to OUT3may be written in the selected memory cells MC via the column circuit190. At this time, a write-back operation may be performed after a pass/fail determination of the selected memory cells is completed.

FIG. 8is a timing diagram illustrating an operation of the memory device ofFIG. 1, according to an embodiment of the present invention.FIG. 8is a diagram illustrating the operation of the memory device when the detection counter130according to the embodiment ofFIG. 2is used. Hereinafter, the counting addresses CNT_ADD<0:9>, the row detection addresses DET_RADD<0:9> and the column detection addresses DET_CADD<0:4> are expressed by decimal numbers.

Referring toFIG. 8, in the memory device, all the counting addresses CNT_ADD<0:9>, the row detection addresses DET_RADD<0:9>, and the column detection addresses DET_CADD<0:4> are 0 in an initial state. The flag signal FLAG is low in an initial state.

In a period in which the flag signal FLAG is low and the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are 0, a refresh operation of a word line corresponding to the counting addresses CNT_ADD<0:9>=0 may be performed in response to the refresh signal REFA. At this time, the counting addresses CNT_ADD<0:9> are not increased. The detection period signal DET_OP may be activated at the falling edge of the refresh signal REFA. And then, the first-sub operations may be performed for memory cells corresponding to the row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0:4>=0 in response to the refresh signal REFA. At this time, the counting addresses CNT_ADD<0:9> may be increased from 0 to 1.

Since the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are different in a period of the counting addresses CNT_ADD<0:9> from 1 to 1023, no detection operation is performed. When the counting addresses CNT_ADD<0:9> are counted from 1023 to 0 and are substantially equal to the row detection addresses DET_RADD<0:9> again, the detection period signal DET_OP is activated and the second-sub operations are performed for the memory cells corresponding to the to row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0:4>=0 in response to the refresh signal REFA. When the second-sub operations are completed, the column detection addresses DET_CADD<0:4> are counted from 0 to 1. At this time, the counting addresses CNT_ADD<0:9> are not increased. Then, a refresh operation of a word line is performed in response to the refresh signal REFA, and the counting addresses CNT_ADD<0:9> may be increased from 0 to 1.

After the detection operations of memory cells corresponding to the row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0:4>=1 to 31 are sequentially performed, the row detection addresses DET_RADD<0:9> may be increased from 0 to 1. The detection operations of memory cells coupled to word lines corresponding to the row detection addresses DET_RADD<0:9>=1 to 1023 may be performed according to processes which are similar to the processes described above. When the detection operations of memory cells corresponding to the row and column detection addresses DET_RADD<0:9>=1023, DET_CADD<0:4=31 are completed detection operations may be repeated from the memory cells corresponding to the row and column detection addresses DET_RADD<0:9>=0, DET_CADD<0:4>=0.

FIG. 9is a diagram illustrating the operation of a memory device employing a detection counter130according to the embodiment ofFIG. 3is used. Hereinafter, the counting addresses CNT_ADD<0:9>, the row detection addresses DET_RADD<0:9>, and the column detection addresses DET_CADD<0:4> are expressed by decimal numbers.

Referring toFIG. 9, in the memory device, all the counting addresses CNT_ADD<0:9> the row detection addresses DET_RADD<0:9>, and the column detection addresses DET_CADD 0:4> are 0 in an initial, state. The flag signal FLAG is low in an initial state.

In a period in which the flag signal FLAG is low and the counting addresses CNT_ADD<0:9 > and the row detection addresses DET_RADD<0:9> are 0, a refresh operation of a word line corresponding to the counting addresses CNT_ADD<0:9>=0 may be performed in response to the refresh signal REFA. At this time, the counting addresses CNT_ADD<0:9> are not counted, i.e., they are not increased. The detection period signal DET_OP may be activated at the falling edge of the refresh signal REFA. And then, the first-sub operations may be performed for memory cells corresponding to the row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0.4>=0 in response to the refresh signal REFA. At this time, the counting addresses CNT_ADD<0:9> may be counted, i.e. increased from 0 to 1.

Since the counting addresses CNT_ADD<0:9> and the row detection addresses DET_RADD<0:9> are different in a period of the counting addresses CNT_ADD<0:9> from 1 to 1023, no detection operation is performed. When the counting addresses CNT_ADD<0:9> are counted from 1023 to 0 and are substantially equal to the row detection addresses DET_RADD<0:9> again, the detection period signal DET_OP is activated and the second-sub operations are performed for the memory cells corresponding to the row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0:4>=0 in response to the refresh signal REFA. When the second-sub operations are completed, the row detection addresses DET_RADD<0:9> are counted from 0 to 1 At this time, the counting addresses CNT_ADD<0:9> are not counted. Then, a refresh operation of a word line is performed in response to the refresh signal REFA, and the counting addresses CNT_ADD<0:9> is counted from 0 to 1.

After the detection operations of memory cells corresponding to the row detection addresses DET_RADD<0:9>=1 to 1023 and the column detection addresses DET_CADD<0:4>=0 are sequentially performed, the column detection addresses DET_CADD<0:4> may be counted from 0 to 1. The detection operations of memory cells coupled to word lines corresponding to the column detection addresses DET_CADD<0:4>=1 to 31 are performed in processes similar to the above. When the detection operations of memory cells corresponding to the row detection addresses DET_RADD<0:9>=1023 and the column detection addresses DET_CADD<0:4>=31 are completed, detection operations may be repeated from the memory cells corresponding to the row detection addresses DET_RADD<0:9>=0 and the column detection addresses DET_CADD<0:4>=0.

Although various embodiments have been described for illustrative purposes, it will be apparent to those skilled in the art that various may change and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.