Patent Publication Number: US-2015085563-A1

Title: Memory and memory system including the same

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority of Korean Patent Application No. 10-2013-0113880, filed on Sep. 25, 2013, which is incorporated herein by reference in its entirety. 
     TECHNICAL FIELD 
     This patent document relates to a memory and a memory system including the same. 
     BACKGROUND 
     A memory cell of a memory device is formed of a capacitor for storing a charge, which is a data and a transistor for switching the capacitor. The logic level of the data, which is high (logic level 1) or low (logic level 0), depends on accumulation of a charge in the capacitor, meaning that the logic level of the data depends on the voltage of the capacitor. 
     Since the data is stored in the form of accumulated charges in the capacitor, theoretically there is no consumption of power. However, since the accumulated charges in the capacitor are discharged and thus the amount of the accumulated charges decreases due to current leakage caused by a PN bond of the transistor, the data may be lost without power supply. To prevent the data loss, the capacitor of the memory cell should be recharged repeatedly before the data stored in the capacitor is lost in order to retain the amount of charges. This process of repeatedly recharging the memory cell is referred to as a refresh operation. 
     The refresh operation is performed in the memory device in response to a refresh command applied from a memory controller. The memory controller applies the refresh command to the memory device repeatedly within a predetermined period in consideration of a data retention time of the memory device. For example, when the data retention time of the memory device is approximately 64 ms, the entire memory cells in the memory device may be refreshed according to about 8000 times of inputs of the refresh command, the memory controller applies the refresh command to the memory device approximately 8000 times for approximately 64 ms to perform the refresh operation. 
     As the integration degree of the memory device is increased, the gap between multiple word lines included in the memory device is decreased and the coupling effect between the neighboring word lines is raised. For this reason, when a particular word line of the memory device is frequently activated, compared with the neighboring word lines during the refresh operation, the data of the memory cells coupled with a plurality of word lines adjacent to the particular word line may be damaged. This phenomenon is referred to as word line disturbance. 
     SUMMARY 
     Various embodiments according to the present invention having a memory, which may normally operate even when data of memory cells are likely to be degraded due to word line disturbance and a memory system including the same. 
     In an embodiment, a memory may include a plurality of word lines each coupled to one or more memory cells; an address storage unit suitable for storing an address of a word line selected for access by a control unit among the plurality of word lines at a first time point; and the control unit suitable for sequentially refreshing the plurality of word lines in response to application of a refresh command, refreshing one or more adjacent word lines adjacent to a word line corresponding to the address stored in the address storage unit in response to every Nth application of the refresh command where N is a natural number and selecting one or more of the plurality of word lines for access, wherein the first time point is included in time section other than a refresh section in which the control unit refreshes one or more word lines in response to application of the refresh command. 
     In an embodiment, a memory may include a plurality of word lines each coupled to one or more memory cells; an address input unit suitable for receiving an address from outside; an address counting unit suitable for performing a counting operation when a refresh command is applied and generating a counting address using the counting result; an address storage unit suitable for storing an address of a word line selected for activation by a control unit among the plurality of word lines at a first time point; and the control unit suitable for activating a word line corresponding to the address received by the address input unit in response to application of an active command and refreshing a word line corresponding to the counting address in response to application of the refresh command and one or more adjacent word lines adjacent to a word line corresponding to the address stored in the address storage unit in response to every Nth application of the refresh command where N is a natural number, wherein the first time point is included in time section other than refresh section in which the control unit refreshes one or more word lines in response to application of the refresh command. 
     In an embodiment, a memory system may include a memory having a plurality of word lines each coupled to one or more memory cells and suitable for sequentially refreshing the plurality of word lines in response to application of a refresh command, selecting one or more of the plurality of word lines for access, storing an address of the selected word line among the plurality of word lines at a first time point, and refreshing one or more adjacent word lines adjacent to a word line corresponding to the stored address in response to every Nth application of the refresh command; and a memory controller suitable for periodically applying the refresh command to the memory, wherein the first time point is included in time section other than refresh section in which one or more word lines are refreshed in response to application of the refresh command. 
     In an embodiment, a memory may include a plurality of cell arrays each having a plurality of word lines coupled to one or more memory cells; an address storage unit suitable for storing an address of a word line selected for access by each of a plurality of word line control units among the plurality of word lines in each of the cell arrays at a first time point; a refresh control unit suitable for activating a plurality of refresh active signals one or more times in response to application of a refresh command and a target active signal in response to every Nth application of the refresh command where N is a natural number; and the plurality of word line control units each suitable for sequentially refreshing the plurality of word lines of a corresponding cell array in response to application of a corresponding refresh active signal among the plurality of refresh active signals, refreshing one or more adjacent word lines adjacent to a word line corresponding to the address stored in the address storage unit in the corresponding cell array in response to every Nth application of the corresponding refresh active signal among the plurality of refresh active signals when the target active signal is activated, and selecting one or more of the plurality of word lines for access, wherein the time point is included in time section other than refresh section in which the plurality of word line control units refresh one or more word lines in response to application of the refresh command. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a circuit diagram illustrating a part of a cell array included in a memory; 
         FIG. 2  is a block diagram illustrating a memory in accordance with an embodiment of the present invention; 
         FIG. 3  is a block diagram illustrating a word line control unit of the memory shown in  FIG. 2 ; 
         FIGS. 4A to 4D  are block diagrams illustrating an address storage unit of the memory shown in  FIG. 2 ; 
         FIG. 5  is a timing diagram illustrating an exemplary operation of the memory of the memory shown in  FIG. 2 ; 
         FIG. 6  is a block diagram illustrating a memory in accordance with another embodiment of the present invention; 
         FIG. 7  is a block diagram illustrating a Kth word line control unit of the memory shown in  FIG. 6 ; 
         FIG. 8  is a block diagram illustrating an address storage unit of the memory shown in  FIG. 6 ; 
         FIG. 9  is a timing diagram illustrating an exemplary operation of the memory of the memory shown in  FIG. 6 ; and 
         FIG. 10  is a block diagram illustrating a memory system in accordance with another embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various examples and implementations of the disclosed technology will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the present invention to those skilled in the art. Throughout the disclosure, like reference numerals refer to like parts throughout the various figures and embodiments of the present invention. 
     The drawings are not necessarily to scale and in some instances, proportions may have been exaggerated in order to clearly illustrate features of the embodiments. When a first layer is referred to as being “on” a second layer or “on” a substrate, it not only refers to a case where the first layer is formed directly on the second layer or the substrate but also a case where a third layer exists between the first layer and the second layer or the substrate. It is also noted that in this specification, “connected/coupled” refers to one component not only directly coupling another component but also indirectly coupling another component through an intermediate component. In addition, a singular form may include a plural form as long as it is not specifically mentioned in a sentence. 
     When a word line is activated, precharged or refreshed, a memory cell coupled to the word line is refreshed. 
     In the description, an adjacent word line refers to a word line, which is disposed adjacent to a specific word line such that data of memory cells coupled to the adjacent word line may be influenced by an active operation of the specific word line. 
       FIG. 1  is a circuit diagram Illustrating a portion of a cell array of a memory device. 
       FIG. 1  shows a plurality of word lines WLK−1, WLK and WLK+1 disposed in parallel to each other in a cell array. The Kth word line WLK marked with ‘HIGH_ACT’ is a word line that is frequently activated, compared with the (K−1)th word line WLK−1 and the (K+1)th word line WLK+1. The (K−1)th word line WLK−1 and the (K+1)th word line WLK+1 are neighboring word lines disposed adjacent to the Kth word line WLK. The word lines WLK−1, WLK and WLK+1 are coupled with memory cells CELL_K−1, CELL_K and CELL_K+1, respectively. The memory cells CELL_K−1, CELL_K and CELL_K+1 also coupled to bit lines BL include cell transistors TR_K−1, TR_K and TR_K+1 and cell capacitors CAP_K−1, CAP_K and CAP_K+1, respectively. 
     When the Kth word line WLK is activated or deactivated (precharged), the word line disturbance may occur and the voltages of the neighboring word lines WLK−1 and WLK+1 are raised or dropped due to the coupling effect occurring between the Kth word line WLK and the neighboring word lines WLK−1 and WLK+1, which may affect the amount of charges stored in the cell capacitors CAP_K−1 and CAP_K+1 of the neighboring word lines WLK−1 and WLK+1. Therefore, as the Kth word line WLK is activated and pre-charged frequently, the Kth word line WLK frequently toggles between the active state and the pre-charge state, the amount of charges stored in the cell capacitors CAP_K−1 and CAP_K+1 or the data stored in the memory cells CELL_K−1 and CELL_K+1 of the neighboring word lines WLK−1 and WLK+1 may be damaged. 
     Additionally, since the electromagnetic wave generated as the Kth word line WLK toggles between the active state and the pre-charge state causes electrons to go in and out of the cell capacitors of the neighboring word lines, the data of the memory cells coupled with the neighboring word lines may be damaged. 
       FIG. 2  is a block diagram illustrating a memory in accordance with an embodiment of the present invention. 
     Referring to  FIG. 2 , the memory may include a command input unit  210 , an address input unit  220 , a command decoder  230 , a control unit  240 , an address counting unit  250 , an address storage unit  260  and a cell array  270 . The cell array  270  may include a plurality of word lines WL0 to WLM respectively coupled to one or more memory cells. 
     The command input unit  210  may receive commands CMDs applied from a memory controller and the address input unit  220  may receive addresses ADDs applied from the memory controller. The commands CMDs and the addresses ADDs may be multi-bit signals. 
     The command decoder  230  may decode the command CMDs inputted through the command input unit  210  and generate an active command ACT and a refresh command REF. When a combination of the input command signals CMDs corresponds to the active command ACT, the command decoder  230  may activate the active command ACT and when a combination of the input command signals CMDs corresponds to the refresh command REF, the command decoder  230  may activate the refresh command REF. 
     The address counting unit  250  may perform counting one or more times when the refresh command REF is applied and generate a counting address CNT_ADD, which indicates one of the multiple word lines WL0 to WLN, using the counting result. The address counting unit  250  may increases a value of the counting address CNT_ADD by one whenever a refresh active signal REF_ACT is activated. For example, the value of the counting address CNT_ADD may be changed in such a manner that the next value of the counting address CNT_ADD indicates the (K+1)th word line when the current value of the counting address CNT_ADD indicates the Kth word line. 
     The address counting unit  250  may not perform the counting operation when a target active signal TAR_ACT is activated. The refresh active signal REF_ACT and the target active signal TAR_ACT will be described below. 
     The address storage unit  260  may store an address of a word line selected by the word line control unit  242  included in the control unit  240  among the plurality of word line WL0 to WLM at a non-refreshing time point. The non-refreshing time point may be included between two sequential refresh sections. That is, at the non-refreshing time point, the memory may perform an operation other than the refresh operation. A reason that the address storage unit  260  stores the address of the selected word line among the plurality of word lines WL0 to WLM at the non-refreshing time point may be described as follows. 
     The memory during an active operation may select a word line among the plurality of word lines WL0 to WLM and activate the selected word line when an active command is applied. The memory during an access operation may access an activated word line and precharge the accessed active word line. Accessing the activated word line may mean writing data to or reading data from one or more memory cells coupled to the activated word line. The memory during a refresh operation may select a word line corresponding to a counting address among the plurality of word lines WL0 to WLM and sequentially refresh one or more of the multiple word lines WL0 to WLM using the counting address whenever the refresh command REF is applied one time. 
     The memory may access the selected word line among the plurality of word lines during time section other than a refresh section, during which the refresh operation may be performed. That is, the word line selected during time section other than the refresh section may be the one activated for access. As described above, word line disturbance may occur when a specific word line is activated at a high frequency. Thus, the currently-activated word line is highly likely to cause word line disturbance than other word lines. 
     Thus, the address storage unit  260  may store as a stored address STO_ADD the address of the currently selected word line or the currently-activated word line among the plurality of word lines WL0 to WLM at the non-refreshing time point during time section other than the refresh section or between two sequential refresh sections. Furthermore, the address storage unit  260  may output the stored address STO_ADD stored at the non-refreshing time point when the refresh active signal REF_ACT and the target active signal TAR_ACT are activated. The address storage unit  260  will be described below in detail with reference to  FIG. 4 . 
     The control unit  240  during an active operation selects a word line corresponding to an input address IN_ADD inputted through the address input unit  220  among the plurality of word lines WL0 to WLM and activates the selected word line when the active command ACT is applied. The control unit  240  during an access operation may access an activated word line and precharge the accessed active word line. Accessing the activated word line may mean writing data to or reading data from one or more memory cells MC coupled to the activated word line. 
     The control unit  240  during a normal refresh operation selects a word line corresponding to the counting address CNT_ADD among the plurality of word lines WL0 to WLM and refreshes the selected word line when the refresh command REF is applied. The control unit  240  may sequentially refresh one or more of the multiple word lines WL0 to WLM using the counting address CNT_ADD whenever the refresh command REF is applied one time. 
     The control unit  240  during a target refresh operation selects one or more word lines adjacent to a word line corresponding to the stored address STO_ADD stored in the address storage unit  260  and refreshes the selected word lines in response to Nth application of the refresh command REF where N is a natural number. 
     The normal refresh operation and the target refresh operation may be performed during the refresh section. The refresh section may be set from when a refresh command is applied to when a refresh operation for one or more word lines in response to the applied refresh command is completed. 
     The control unit  240  may refresh sequentially one or more word lines corresponding to the counting address CNT_ADD in response to every application of the refresh command REF during the normal refresh operation and refresh one or more word lines adjacent to the word line corresponding to the stored address STO_ADD in response to Nth application of the refresh command REF during the target refresh operation. The control unit  240  may refresh one or more adjacent word lines selected by the stored address STO_ADD as well as the word line selected by the counting address CNT_ADD in response to Nth application of the refresh command REF during the target refresh operation. Further, the control unit  240  may refresh only one or more adjacent word lines selected by the stored address STO_ADD in response to Nth application of the refresh command REF during the target refresh operation. 
     The value of N may be changed depending on design. In the following descriptions, as an example, N is set to four (N=4) and the control unit  240  may refresh one word line corresponding to the counting address CNT_ADD when the refresh command REF is applied during the normal refresh operation and refresh two word lines adjacent to the word line according to the stored address STO_ADD whenever the refresh command REF is applied four times during the target refresh operation. When the word line corresponding to the stored address STO_ADD is the word line WLK, the two adjacent word line may be a first adjacent word line WLK−1 and a second adjacent word line WLK+1. The first and second adjacent word lines may be selected in a different order depending on design. 
     The control unit  240  may include a refresh control unit  241  and a word line control unit  242 . 
     The refresh control unit  241  activates the refresh active signal REF_ACT and the target active signal TAR_ACT in response to the refresh command REF applied from the command input unit  210  through the command decoder  230 . The refresh control unit  241  may refresh active signal REF_ACT one or more times in response to every application of the refresh command REF and activate the target active signal TAR_ACT in response to every Nth application of the refresh command REF. The target active signal TAR_ACT may indicate the target refresh operation that is performed during a target refresh operation section. The refresh control unit  241  may count a number of applications of the refresh command REF. When the number of applications of the refresh command REF reaches the number N, the refresh control unit  241  may activate the target active signal TAR_ACT and then count the number of applications of the refresh command REF from the beginning. 
     For example, the refresh control unit  241  may activate the refresh active signal REF_ACT in response to every application of the refresh command REF. Then, when the number of applications of the refresh command REF reaches four (N=4), the refresh control unit  241  may activate the target active signal TAR_ACT and activate the refresh active signal REF_ACT two times for refreshing the first and second adjacent word lines WKL−1 and WLK+1. 
     The word line control unit  242  selects and activates a word line corresponding to the input address IN_ADD when the active command ACT is applied and selects and activates a word line corresponding to the counting address CNT_ADD when the refresh active signal REF_ACT is activated. When the target active signal TAR_ACT is activated, the word line control unit  242  sequentially selects and refreshes the first and second adjacent word lines WKL−1 and WLK+1 adjacent to the word line WLK corresponding to the stored address STO_ADD. 
     In the above-described example, when the refresh command REF is applied for the Nth time, the stored address STO_ADD may be used to select a word line for the target refresh operation. The address counting unit  250  may not perform the counting operation when the target active signal TAR_ACT is activated. Therefore, all of the word lines may be refreshed through the normal refresh operation. 
     The memory in accordance with the embodiment of the present invention may sequentially refresh a plurality of word lines WL0 to WLM during the normal refresh operation and additionally refresh one or more word lines adjacent to a word line corresponding to the stored word line at a non-refreshing time point through the target refresh operation whenever the refresh command is applied N times. Thus, it is possible to prevent a data loss of word lines adjacent to a word line, which is activated at a high frequency. 
       FIG. 3  is a block diagram illustrating a word line control unit  242  of the memory shown in  FIG. 2 . 
     Referring to  FIG. 3 , the word line control unit  242  may include an address generator  310 , an address transmitter  320  and a word line driver  330 . 
     The address generator  310  sequentially generates a first adjacent address corresponding to the first adjacent word line and a second adjacent address corresponding to the second adjacent word line using the stored address STO_ADD outputted from the address storage unit  260  and outputs each of the generated addresses as a target address TAR_ADD when the target active signal TAR_ACT is activated. For example, when the target active signal TAR_ACT is activated, the address generator  310  may generate the first adjacent address that may be lesser by 1 than the stored address STO_ADD and output the generated first adjacent address as the target address TAR_ADD in response to a first activation of the refresh active signal REF_ACT during activation of the target active signal TAR_ACT and generate the second adjacent address that may be greater by 1 than the stored address STO_ADD and output the generated second adjacent address as the target address TAR_ADD in response to a second activation of the refresh active signal REF_ACT during activation of the target active signal TAR_ACT. The first and second adjacent addresses may be outputted in a different order depending on design. 
     The address transmitter  320  transmits one of the input address IN_ADD, the counting address CNT_ADD and the target address TAR_ADD as an address signal ATR_ADD. The address transmitter  320  may transmit as the address signal ATR_ADD the input address IN_ADD when the active command ACT is applied, the counting address CNT_ADD when the refresh active signal REF_ACT is activated and the target address TAR_ADD when the refresh active signal REF_ACT and the target active signal TAR_ACT are activated. 
     The word line driver  330  activates a word line corresponding to the address signal ATR_ADD among the plurality of word lines WL0 to WLM when one of the active command ACT and the refresh active signal REF_ACT is activated. The word line driver  330  may drive the word line corresponding to the address signal ATR_ADD to a voltage corresponding to the activation level. 
       FIGS. 4A to 4D  are block diagrams illustrating an address storage unit  260  of the memory shown in  FIG. 2 . 
     Referring to  FIGS. 4A to 4D , the address storage unit  260  may include a storage  420  and one of signal generators  410 A,  410 B,  410 C and  410 D. 
     The address storage unit  260  may be implemented in various ways to store an address of a word line selected by the control unit  240  among the plurality of word lines WL0 to WLM at the non-refreshing time point. Hereafter, four implementations will be described. 
       FIG. 4A  is a block diagram illustrating the address storage unit  260  as an implementation of the embodiment of the present invention. 
     Referring to  FIG. 4A , the signal generator  410 A generates a latch signal LAT_SIG, which is periodically activated within a preset period, and the storage  420  stores the address signal ATR_ADD when the latch signal LAT_SIG is activated. 
     The memory in accordance with the embodiment of the present invention may periodically perform the refresh operation during the refresh section in response to the periodical refresh command REF. The signal generator  410 A may activate the latch signal LAT_SIG at the preset period such that the latch signal LAT_SIG may be activated during time section other than the refresh section. 
     The preset period may differ depending on design. Thus, a number of addresses to be stored as the stored address STO_ADD in the address storage unit  260  per N applications of the refresh command REF may depend on the preset period the latch signal LAT_SIG. As the preset period becomes shorter, the addresses to be stored in the storage  420  per N applications of the refresh command REF may increase and as the set period becomes longer, the addresses to be stored in the storage  420  per N applications of the refresh command REF may decrease. 
     The storage  420  may store the address signal ATR_ADD as the stored address STO_ADD when the latch signal LAT_SIG is activated. The address signal ATR_ADD may indicate a word line currently selected by the control unit  240 , regardless of a currently performed operation including the active operation, the write operation and the read operation. The storage  420  may store the address of the currently-selected word line as the address signal ATR_ADD when the latch signal LAT_SIG is activated. The storage  420  may output the stored address STO_ADD when the refresh active signal REF_ACT and the target active signal TAR_ACT are activated. 
       FIG. 4B  is a block diagram illustrating the address storage unit  260  as another implementation of the embodiment of the present invention. 
     The address storage unit  260  may include a signal generator  410 B and the storage  420 . The storage  420  shown in  FIG. 4B  may be the same as the one shown in  FIG. 4A . The signal generator  410 B counts a number of applications of the active command ACT and generates a latch signal LAT_SIG, which is activated in response to Mth (M is a natural number) application of the active command ACT, and the storage  420  stores the address signal ATR_ADD when the latch signal LAT_SIG is activated. 
     The memory in accordance with the embodiment of the present invention may activate a word line when the active command ACT is applied and perform an access operation such as a write or read operation on the activated word line. The signal generator  410 B may activate the latch signal LAT_SIG in response to Mth application of the activate command ACT, such that the latch signal LAT_SIG may be activated during time section other than the refresh section. The signal generator  410 B may count a number of applications of one of a precharge command PRE, a write command and a read command instead of the activate command ACT to generate the latch signal LAT_SIG. 
     The number M of applications of the active command ACT as a threshold to activate the latch signal LAT_SIG may differ depending on design. Thus, a number of addresses to be stored as the stored address STO_ADD in the storage  420  per N applications of the refresh command REF may depend on the number M of applications of the activate command ACT. As the number M becomes greater, the addresses to be stored in the storage  420  per N applications of the refresh command REF may decrease and as the number M becomes lesser, the addresses to be stored in the storage  420  per N applications of the refresh command REF may increase. 
       FIG. 4C  is a block diagram illustrating the address storage unit  260  as yet another implementation of the embodiment of the present invention. 
     The address storage unit  260  may include a signal generator  410 C and the storage  420 . The storage  420  shown in  FIG. 4C  may be the same as the one shown in  FIG. 4A . The signal generator  410 C generates a latch signal LAT_SIG, which is activated a preset time after Qth (Q is a natural number) application of the refresh command REF and the storage  420 C stores the address signal ATR_ADD when the latch signal LAT_SIG is activated. 
     Since the refresh section is predetermined, the signal generator  410 C may activate the latch signal LAT_SIG the preset time after Mth application of the refresh command REF such that the latch signal LAT_SIG may be activated during time section other than the refresh section. 
     The number Q of applications of the refresh command REF as a threshold to activate the latch signal LAT_SIG may differ depending on design. Thus, a number of addresses to be stored as the stored address STO_ADD in the storage  420  per N applications of the refresh command REF may depend on the number Q of applications of the refresh command REF. As the number Q becomes greater, the addresses to be stored in the storage  420  per N applications of the refresh command REF may decrease and as the number Q becomes lesser, the addresses to be stored in the storage  420  per N applications of the refresh command REF may increase. 
       FIG. 4D  is a block diagram illustrating the address storage unit  260  as another implementation of the embodiment of the present invention. 
     The address storage unit  260  may include a signal generator  410 D and the storage  420 . The storage  420  shown in  FIG. 4D  may be the same as the one shown in  FIG. 4A . The signal generator  410 D generates a latch signal LAT_SIG, which is activated in response to Mth (M is a natural number) application of the active command ACT after Qth (Q is a natural number) application of the refresh command REF and the storage  420 D stores the address signal ATR_ADD when the latch signal LAT_SIG is activated. 
     Since the refresh section is predetermined and the memory in accordance with the embodiment of the present invention may activate a word line when the active command ACT is applied and perform an access operation such as a write or read operation on the activated word line, the signal generator  410 D may activate the latch signal LAT_SIG in response to Mth application of the active command ACT after Qth application of the refresh command REF such that the latch signal LAT_SIG may be activated during time section other than the refresh section. 
     The number Q of applications of the refresh command REF and the number M of applications of the active command ACT as a threshold to activate the latch signal LAT_SIG may differ depending on design. Thus, a number of addresses to be stored as the stored address STO_ADD in the storage  420  per N applications of the refresh command REF may depend on the number Q of applications of the refresh command REF and the number M of applications of the active command ACT. As the number Q or M becomes greater, the addresses to be stored in the storage  420  per N applications of the refresh command REF may decrease and as the number Q or M becomes lesser, the addresses to be stored in the storage  420  per N applications of the refresh command REF may increase. 
     In addition to the embodiments according to the present inventions described above, the address storage unit  260  may be Implemented in various ways to store an address of a word line selected by the control unit  240  among the plurality of word lines WL0 to WLM at the non-refreshing time point. 
     The memory in accordance with the embodiment of the present invention may store an address of a word line, which is performing an active operation, and refresh the word line corresponding to the stored address during the refresh operation, thereby reducing the possibility that word line disturbance occurs. Furthermore, since the memory in accordance with the embodiment of the present invention does not need a component for detecting a word line that may cause word line disturbance, that is, a word line that is activated at a high frequency, the area of the circuit may be reduced. 
       FIG. 5  is a timing diagram illustrating an exemplary operation of the memory of the memory shown in  FIG. 2 . 
       FIG. 5  illustrates an exemplary case where one word line is refreshed per one application of the refresh command REF and two adjacent word lines, or the first and second adjacent word lines, according to the stored address STO_ADD are refreshed per four applications of the refresh command REF. The refresh command REF may be repeatedly applied to the memory with a preset interval and the active command ACT may be repeatedly applied to the memory between periodical applications of the refresh command REF. 
     Referring to  FIGS. 2 to 5 , the operation of the memory will be described. 
     When the refresh command REF is applied for the first time, the refresh active signal REF_ACT may be activated. At this time, the counting address CNT_ADD may have a value corresponding to a word line, for example WL0, and thus the word line WL0 may be refreshed. When the refresh command REF is applied for the second and third times, the counting address CNT_ADD may sequentially have values for the word lines WL1 and WL2, and the word lines WL1 and WL2 may be sequentially refreshed. The respective refresh operations may be performed during preset refresh sections REF_SEC 1  to REF_SEC 3  shown in  FIG. 5 . 
     When the active command ACT is applied between applications of the refresh command REF, a word line corresponding to the input address IN_ADD may be activated. The address storage unit  260  may store the address signal ATR_ADD at the non-refreshing time point NRTP.  FIG. 5  shows as an example, the non-refreshing time point NRTP between the second and third refresh sections REF_SEC 2  and REF_SEC 3 . 
     When the refresh command REF is applied for the fourth time, the target active signal TAR_ACT may be activated. When the refresh active signal REF_ACT is activated for the first time during activation of the target active signal TAR_ACT, the first adjacent word line WLK−1, which corresponds to the target address TAR_ADD according to the stored address STO_ADD, may be refreshed regardless of the ongoing normal refresh operation. Then, when the refresh active signal REF_ACT is activated for the second time during the activation of the target active signal TAR_ACT, the second adjacent word line WLK+1, which corresponds to the target address TAR_ADD according to the stored address STO_ADD, may be refreshed. 
     After fourth application of the refresh command REF, the plurality of word lines WL0 to WLN may be refreshed according to the counting address CNT_ADD in response to application of the refresh command REF. At every fourth application of the refresh command REF, the memory may generate the target address TAR_ADD based on the stored address STO_ADD stored at a non-refreshing time point and refresh one or more adjacent word lines corresponding to the target address TAR_ADD. 
     The memory in accordance with the embodiment of the present invention may activate one or more word lines per every application of the refresh command REF and refresh one or more adjacent word lines corresponding to the target address TAR_ADD per predetermined number, which may be greater than 2 such as 4 described above, applications of the refresh command REF. The memory in accordance with the embodiment of the present invention may refresh a word line corresponding to the counting address CNT_ADD as well as adjacent word lines corresponding to the target address TAR_ADD per predetermined number of applications of the refresh command REF. 
       FIG. 6  is a block diagram illustrating a memory in accordance with another embodiment of the present invention. 
     Referring to  FIG. 6 , the memory may include a command input unit  610 , an address input unit  620 , a command decoder  630 , a refresh control unit  640 , a plurality of word line control units  650 _ 1  to  650 _ 4 , an address counting unit  660 , an address storage unit  670 , a plurality of cell arrays  680 _ 1  to  680 _ 4  and a cell array selection unit  690 .  FIG. 6  shows four cell arrays  680 _ 1  to  680 _ 4 , which may vary according to circuit design. 
     The command input unit  610 , the address input unit  620  and the command decoder  630  are the same as the command input unit  210 , the address input unit  220  and the command decoder  230  of  FIG. 2 , respectively. In accordance with the embodiment of the present invention, an input address IN_ADD received through the address input unit  620  may include a cell array address SA_ADD for selecting one of the plurality of cell arrays  680 _ 1  to  680 _ 4 . 
     The cell array selection unit  690  generates a plurality of active signals ACT 1  to ACT 4  corresponding to the cell arrays  680 - 1  to  680 - 4  respectively. When an active command ACT is applied with the input address IN_ADD including the cell array address SA_ADD indicating one of the plurality of cell arrays  680 _ 1  to  680 _ 4 , the cell array selection unit  690  may activate one of the plurality of active signals ACT 1  to ACT 4  corresponding to the cell array address SA_ADD. For example, the cell array selection unit  690  may activate the first active signal ACT 1  when the active command ACT is applied and the cell array address SA_ADD indicates the first cell array  680 _ 1 . 
     The refresh control unit  640  controls a refresh operation of the memory in response to every application of the refresh command REF. The refresh control unit  640  may sequentially activate refresh active signals REF_ACT 1  to REF_ACT 4  respectively corresponding to the cell arrays  680 _ 1  to  680 _ 4  in response to every application of the refresh command REF. Furthermore, the refresh control unit  640  may activate a target active signal TAR_ACT and sequentially activate the refresh active signals REF_ACT 1  to REF_ACT 4  one or more times in response to every Nth application of the refresh command REF. 
     In the following descriptions, the refresh control unit  640  sequentially activates the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  one time per every application of the refresh command REF and two times per every Nth application of the refresh command REF. There is time gap between activations of each of the refresh active signals REF_ACT 1  to REF_ACT 4  for reducing a peak current caused by the refresh operation. All of the refresh active signals REF_ACT 1  to REF_ACT 4  may be activated within a refresh section, that is, a refresh cycle tREF. 
     Each of the plurality of word line control units  650 _ 1  to  650 _ 4  activates a word line corresponding to the input address IN_ADD when a corresponding one of the plurality of active signals ACT 1  to ACT 4  is activated. Furthermore, when each of the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  is activated, the corresponding one of the plurality of the word line control units  650 _ 1  to  650 _ 4  may activate a word line corresponding to the counting address CNT_ADD. When the target active signal TAR_ACT is activated, each of the word line control units  650 _ 1  to  650 _ 4  may activate adjacent word lines respectively selected through stored addresses STO_ADD 1  to STO_ADD 4  stored in the address storage unit  670 . Each of the word line control units  650 _ 1  to  650 _ 4  may be the same as the word line control unit  250  shown in  FIG. 2 . The word line control units  650 _ 1  to  650 _ 4  will be described below in detail with reference to  FIG. 7 . 
     The address counting unit  660  performs counting one or more times when the refresh command REF is applied and generates the counting address CNT_ADD, which indicates one of the multiple word lines WL0 to WLN included in each of the plurality of cell arrays  680 _ 1  to  680 _ 4 , using the counting result. The address counting unit  660  may increase a value of the counting address CNT_ADD by one whenever one of the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  is activated.  FIG. 6  illustrates an example that the address counting unit  660  performs counting in response to the refresh active signal REF_ACT 4 . For example, the value of the counting address CNT_ADD may be changed in such a manner that the next value of the counting address CNT_ADD indicates the (K+1)th word line when the current value of the counting address CNT_ADD indicates the Kth word line. The plurality of word lines WL0 to WLM of the cell arrays  680 _ 1  to  680 _ 4  may be sequentially refreshed according to the counting address CNT_ADD. 
     The address storage unit  670  stores addresses of word lines selected by each of the word line control units  650 _ 1  to  650 _ 4  among the plurality of word lines WL0 to WLM of each of the plurality of cell arrays  680 _ 1  to  680 _ 4  at a non-refreshing time point. The non-refreshing time point may be included between two sequential refresh sections. That is, at the non-refreshing time point, the memory may perform an operation other than the refresh operation. A reason why the address storage unit  670  stores the addresses of the selected word lines of the plurality of cell arrays  680 _ 1  to  680 _ 4  at the non-refreshing time point is the same as described above with reference to  FIG. 2 . 
     The address storage unit  670  may store as one of stored addresses STO_ADD 1  to STO_ADD 4  the address of the currently selected word line or the currently-activated word line among the plurality of word lines WL0 to WLM of one of the plurality of cell arrays  680 _ 1  to  680 _ 4  selected by the cell array selection unit  690  at the non-refreshing time point during time section other than the refresh section or between two sequential refresh sections. Furthermore, the address storage unit  670  may output one of the stored addresses STO_ADD 1  to STO_ADD 4  stored at the non-refreshing time point when corresponding one of the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  and the target active signal TAR_ACT are activated. For example, the address storage unit  670  may output the stored address STO_ADD 1  corresponding to the first cell array  680 _ 1  among the stored addresses STO_ADD 1  to STO_ADD 4  when the target active signal TAR_ACT and the first refresh active signal REF_ACT 1  are activated. The plurality of word line control units  650 _ 1  to  650 _ 4  may refresh first and second adjacent word lines adjacent to a word line corresponding to each of the stored addresses STO_ADD 1  to STO_ADD 4  in the corresponding cell arrays according to the addresses STO_ADD 1  to STO_ADD 4  outputted from the address storage unit  640 . The address storage unit  670  will be described below in detail with reference to  FIG. 7 . 
     During the normal refresh operation, the memory in accordance with the embodiment of the present invention may sequentially refresh the plurality of word lines in the plurality of cell arrays. Whenever the refresh command is applied N times, the memory may additionally refresh one or more adjacent word lines adjacent to each of the word lines corresponding to the stored addresses in the plurality of cell arrays at a non-refreshing time point through the target refresh operation. Thus, the memory in accordance with the embodiment of the present invention may prevent a data loss of word lines adjacent to a word line, which is activated at a high frequency. 
       FIG. 7  is a block diagram illustrating the Kth word line control unit  650 _K of the memory shown in  FIG. 6 . 
     Referring to  FIG. 7 , the word line control unit  650 _K may include an address generator  710 , an address transmitter  720  and a word line driver  730 . 
     The address generator  710  sequentially generates a first adjacent address corresponding to the first adjacent word line and an second adjacent address corresponding to the second adjacent word line using the stored address STO_ADDK outputted from the address storage unit  760  and outputs each of the generated addresses as the target address TAR_ADDK when the target active signal TAR_ACT is activated. For example, when the target active signal TAR_ACT is activated, the address generator  710  may generate the first adjacent address that may be lesser by 1 than the address STO_ADDK and output the generated first address as the target address TAR_ADD in response to a first activation of the refresh active signal REF_ACTK during activation of the target active signal TAR_ACT. Furthermore, the address generator  710  may generate the second adjacent address that may be greater by 1 than the address STO_ADDK and output the generated second adjacent address as the target address TAR_ADD in response to a second activation of the refresh active signal REF_ACTK during activation of the target active signal TAR_ACT. The first and second adjacent addresses may be outputted in a different order depending on design. 
     The address transmitter  720  transmits one of the input address IN_ADD, the counting address CNT_ADD and the target address TAR_ADDK as the address signal ATR_ADDK. The address transmitter  720  may transmit as the address signal ATR_ADDK the input address IN_ADD when the Kth active signal ACTK is activated, the counting address CNT_ADD when the Kth refresh active signal REF_ACTK is activated, and the target address TAR_ADD when the target active signal TAR_ACT and the Kth refresh active signal REF_ACTK are activated. 
     The word line driver  730  activates a word line corresponding to the address signal ATR_ADDK among the plurality of word lines WL0 to WLM of the corresponding cell array  680 _K when one of the Kth active signal ACTK and the Kth refresh active signal REF_ACK is activated. For reference, K is a natural number ranging from 1 to 4. 
       FIG. 8  is a block diagram illustrating the address storage unit  670  of the memory shown in  FIG. 6 . 
     Referring to  FIG. 8 , the address storage unit  670  may include a signal generator  810  and a plurality of storages  820 _ 1  to  820 _ 4 . 
     The signal generator  810  generates a plurality of latch signals LAT_SIG 1  to LAT_SIG 4 . As described above with reference to  FIG. 4 , the address storage unit  670  may be implemented in various ways to store the stored addresses STO_ADD 1  to STO_ADD 4  or to activate the latch signals LAT_SIG 1  to LAT_SIG 4  at the non-refreshing time point. The plurality of latch signals LAT_SIG 1  to LAT_SIG 4  may correspond to the plurality of cell arrays  680 _ 1  to  680 _ 4  and the plurality of storages  820 _ 1  to  820 _ 4 , respectively. Hereafter, when the plurality of latch signals LAT_SIG 1  to LAT_SIG 4  are activated at a preset period, will be described. 
     An enable signal LAT_EN may be periodically activated during time section other than the refresh section. When the enable signal LAT_EN and one of the first to fourth active signals ACT 1  to ACT 4  are activated, the signal generator  810  may activate one of the plurality of latch signals LAT_SIG 1  to LAT_SIG 4  corresponding to the activated one of the first to fourth active signals ACT 1  to ACT 4 . For example, when the first active signal ACT 1  and the enable signal LAT_EN are activated, the signal generator  810  may activate the first latch signal LAT_SIG 1  corresponding to the first active signal ACT 1 . 
     Each of the storages  820 _ 1  to  820 _ 4  stores corresponding one of the address signals ATR_ADD 1  to ATR_ADD 4  as the stored addresses STO_ADD 1  to STO_ADD 4  when corresponding one of the first to fourth latch signals LAT_SIG 1  to LAT_SIG 4  is activated. Each of the address signals ATR_ADD 1  to ATR_ADD 4  may indicate a word line currently selected by corresponding one of the plurality of word line control units  650 _ 1  to  650 _ 4 , regardless of currently performed operation including the active operation, the write operation and the read operation. When the target active signal TAR_ACT is activated, each of the storages  820 _ 1  to  820 _ 4  may output corresponding one of the stored addresses STO_ADD 1  to STO_ADD 4  in response to activation of corresponding one of the refresh active signals REF_ACT 1  to REF_ACT 4 . For example, the first storage  820 _ 1  may store the first address signal ATR_ADDR 1  as the stored address STO_ADD 1  when the first latch signal LAT_SIG 1  is activated and output the stored address STO_ADD 1  when the target active signal TAR_ACT and the first refresh active signal REF_ACT 1  are activated. 
       FIG. 9  is a timing diagram illustrating an exemplary operation of the memory of the memory shown in  FIG. 6 . 
       FIG. 9  illustrates an exemplary case where the word lines in the plurality of cell arrays  680 _ 1  to  680 _ 4  are sequentially refreshed per one application of the refresh command REF. Two adjacent word lines, or the first and second adjacent word lines adjacent to each of word lines in the plurality of cell arrays  680 _ 1  to  680 _ 4  corresponding to the stored addresses STO_ADD 1  to STO_ADD 4  are refreshed per four applications of the refresh command REF. The refresh command REF may be repeatedly applied to the memory within a preset interval and the active command ACT may be repeatedly applied to the memory between periodic applications of the refresh command REF. As an example, the normal refresh operation is started from the word line WL0 and word lines corresponding to the stored addresses STO_ADD 1  to STO_ADD 4  in the respective cell arrays at a non-refreshing time point are represented by WLX, WLY, WLZ and WLU, respectively, where X, Y, Z and U are natural numbers ranging from 1 to M. 
     Referring to  FIGS. 6 to 8 , the operation of the memory will be described. 
     When the refresh command REF is applied for the first time, the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  may be sequentially activated and the word line corresponding to the counting address CNT_ADD in each of the cell arrays  680 _ 1  to  680 _ 4  may be refreshed. The counting address CNT_ADD may have a value corresponding to the word line WL0. When the refresh command REF is applied for the second and third times, the counting address CNT_ADD may sequentially have values for the word lines WL1 and WL2 and the word lines WL1 and WL2 corresponding to the counting address CNT_ADD in each of the cell arrays  680 _ 1  to  680 _ 4  may be sequentially refreshed. The respective refresh operations may be performed during preset refresh sections REF_SEC 1  to REF_SEC 3  shown in  FIG. 9 . 
     When the active command ACT is applied between applications of the refresh command REF, a word line corresponding to the input address IN_ADD may be activated in the cell array selected by the cell array address SA_ADD. The address storage unit  670  may store the address signals ATR_ADD 1  to ATR_ADD 4  of the selected cell array at non-refreshing time points NRTP 1  to NRTP 4 , respectively.  FIG. 9  shows as an example the non-refreshing time points NRTP 1  to NRTP 4  between the third and fourth refresh sections REF_SEC 3  and REF_SEC 4 . Each of the first to fourth active signals ACT 1  to ACT 4  may be activated when the active command ACT is applied and a corresponding cell array is selected. 
     When the refresh command REF is applied for the fourth time, the target active signal TAR_ACT may be activated. When the plurality of refresh active signal REF_ACT 1  to REF_ACT 4  are sequentially activated for the first time during activation of the target active signal TAR_ACT, the first adjacent word lines WLX−1, WLY−1, WLY−1 and WLU−1, which respectively correspond to the target addresses TAR_ADD 1  to TAR_ADD 4  according to the stored addresses STO_ADD 1  to STO_ADD 4 , may be refreshed regardless of the ongoing normal refresh operation. Then, when the plurality of refresh active signals REF_ACT 1  to REF_ACT 4  are activated for the second time during activation of the target active signal TAR_ACT, the second adjacent word lines WLX+1, WLY+1, WLY+1 and WLU+1, which respectively correspond to the target addresses TAR_ADD 1  to TAR_ADD 4  according to the stored addresses STO_ADD 1  to STO_ADD 4 , are refreshed. 
     After fourth application of the refresh command REF, the plurality of word lines WL0 to WLN in each of the cell arrays  680 _ 1  to  680 _ 4  may be refreshed according to the counting address CNT_ADD in response to application of the refresh command REF. At every fourth application of the refresh command REF, the memory may generate the target addresses TAR_ADD 1  to TAR_ADD 4  based on the stored addresses STO_ADD 1  to STO_ADD 4  stored at a non-refreshing time point and refresh one or more adjacent word lines corresponding to the target addresses TAR_ADD 1  to TAR_ADD 4 . 
       FIG. 10  is a block diagram illustrating a memory system in accordance with another embodiment of the present invention. 
     Referring to  FIG. 10 , the memory system includes a memory  1010  and a memory controller  1020 . 
     The memory controller  1020  controls the operation of the memory  1010  by applying commands CMDs and addresses ADDs to the memory  1010  and exchanges data DATA with the memory  1010  during a read or write operation. The memory controller  1020  may transmit the commands CMDs to input a refresh command REF, an active command ACT, or a precharge command PRE to the memory  1010 . When the active command ACT is inputted, the memory controller  1020  may transmit the addresses ADDs to the memory controller  1020  so as to select a cell array and a word line to activate. When the refresh command REF is inputted, an address CNT_ADD generated inside the memory  1010  or an address STO_ADD stored in the memory  1010  are used. Thus, the memory controller  1020  does not need to transmit the addresses ADDs to the memory  1010 . 
     The memory  1010  of  FIG. 9  receives the commands CMDs and the addresses ADDs and performs an active operation when the active command ACT is inputted or performs a refresh operation when the refresh command REF is inputted. At this time, the memory  1010  performs the active operation or the refresh operation in the same manner as described above with reference to  FIGS. 2 to 9 . Furthermore, when a read or write command is applied from the memory controller  1020 , the memory  1010  exchanges data DATA with the memory controller  1020 . 
     For reference, bit lines BL are not Illustrated in the cell arrays  270  and  680 _ 1  to  680 _ 4  of  FIGS. 2 and 6 . 
     In accordance with embodiments according to the present invention, since an additional refresh operation is periodically performed on memory cells in which data may be degraded due to word line disturbance, the memory and the memory system may operate normally. 
     The first time point is included in a time section other than the refresh section. The first time point may be a ‘random time point’ that is decided randomly regardless of the influence of other elements of the memory, or it may be a ‘predetermined/set time point that satisfies a predetermined/set condition. 
     While this specification contains many exemplary embodiments according to the present invention, these should not be construed as limitations on the scope of any invention or of what may be claimed, but rather as descriptions of features that may be specific to particular embodiments of particular inventions. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable subcombination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination and the claimed combination may be directed to a subcombination or variation of a subcombination. 
     Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. Moreover, any separation of various system components in the embodiments described herein, should not be understood as requiring such separation in all embodiments. 
     In the drawings and specification, there have been disclosed typical exemplary embodiments of the invention, and although specific terms are employed, they are used in a generic and descriptive sense only and not for purposes of limitation. As for the scope of the invention, it is set forth in the following claims. Therefore, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.