Patent Publication Number: US-2023152982-A1

Title: Memory device for individually applying voltages to word lines adjacent to selected word line, and operating method thereof

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0159134, filed on Nov. 18, 2021, and Korean Patent Application No. 10-2022-0056275, filed on May 6, 2022, in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     BACKGROUND 
     1. Field 
     Example embodiments of the present disclosure relate to a memory device, and more particularly, to a memory device individually applying word lines adjacent to a selected word line. 
     2. Description of Related Art 
     A semiconductor memory device may be classified as a volatile memory device, in which stored data disappear when a power supply is turned off, such as a static random access memory (SRAM) or a dynamic random access memory (DRAM), or a nonvolatile memory device, in which stored data are retained even when a power supply is turned off, such as a flash memory device, a phase-change RAM (PRAM), a magnetic RAM (MRAM), a resistive RAM (RRAM), or a ferroelectric RAM (FRAM). 
     A three-dimensional semiconductor memory device may include a cell string that is implemented by stacking memory cells in a direction perpendicular to a substrate for the purpose of improving the degree of integration. However, as the degree of integration of the three-dimensional semiconductor memory device is improved, the number of word lines connected with one memory block is increasing. There is a need to decrease program operation speed without the reduction of reliability during a program operation. 
     SUMMARY 
     Provided are a memory device individually applying word lines adjacent to a selected word line, and an operating method thereof. 
     Additional aspects will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the presented embodiments. 
     According to an aspect of an example embodiment, a memory device may include a memory block including a first adjacent word line, a selected word line, and a second adjacent word line provided in a direction perpendicular to a substrate and an address decoding circuit. In a first setup period in which the selected word line is set up, the address decoding circuit may be configured to apply a first pre-setup voltage to the first adjacent word line, apply a first setup voltage that is higher than the first pre-setup voltage to the first adjacent word line, apply a second pre-setup voltage to the second adjacent word line, and apply a second setup voltage that is higher than the second pre-setup voltage to the second adjacent word line. The first pre-setup voltage may be higher than the second pre-setup voltage. 
     According to an aspect of an example embodiment, a method of operating a memory device that includes a first adjacent word line, a selected word line, and a second adjacent word line provided in a direction perpendicular to a substrate, may include applying a first pre-setup voltage to the first adjacent word line in a first setup period in which the selected word line is set up, applying a second pre-setup voltage to the second adjacent word line in the first setup period, applying a first setup voltage that is higher than the first pre-setup voltage to the first adjacent word line in the first setup period, and applying a second setup voltage that is higher than the second pre-setup voltage to the second adjacent word line in the first setup period. The first pre-setup voltage may be higher than the second pre-setup voltage. 
     According to an aspect of an example embodiment, a memory device may include a memory block including a first adjacent word line, a selected word line, and a second adjacent word line provided in a direction perpendicular to a substrate, and an address decoding circuit configured to set up the selected word line in a first period between a start time point and an end time point, apply a first pre-setup voltage to the first adjacent word line in a second period between the start time point and a first time point, apply a first setup voltage that is higher than the first pre-setup voltage to the first adjacent word line in a third period between the first time point and the end time point, apply a second pre-setup voltage to the second adjacent word line in a fourth period between the start time point and a second time point, and apply a second setup voltage that is higher than the second pre-setup voltage to the second adjacent word line in a fifth period between the second time point and the end time point. The first pre-setup voltage may be higher than the second pre-setup voltage. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The above and other aspects, features, and advantages of certain example embodiments of the present disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which. 
         FIG.  1    is a block diagram of a memory device according to an example embodiment; 
         FIG.  2    is a diagram illustrating a first memory block of a plurality of memory blocks included in a memory cell array in  FIG.  1    according to an example embodiment; 
         FIG.  3    is a graph of voltages applied to a selected word line, an upper adjacent word line, and a lower adjacent word line, according to an example embodiment; 
         FIG.  4    is a diagram illustrating threshold voltage distributions of memory cells of  FIG.  2    according to an example embodiment; 
         FIG.  5    is a graph of voltages applied to an upper adjacent word line, according to an example embodiment; 
         FIG.  6 A  is a graph of points in time when voltages are applied to an upper adjacent word line, according to an example embodiment; 
         FIG.  6 B  is a graph of points in time when voltages are applied to a lower adjacent word line, according to an example embodiment; 
         FIG.  7 A  is a graph of voltages applied to an upper adjacent word line, according to an example embodiment; 
         FIG.  7 B  is a graph of voltages applied to a lower adjacent word line, according to an example embodiment; and 
         FIG.  8    is a flowchart of an method of a memory device according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example embodiments of the present disclosure will be described in detail and clearly to such an extent that one skilled in the art easily carries out the present disclosure. With regard to the description of the present disclosure, to make the overall understanding easy, like components will be marked by like reference signs/numerals in drawings, and thus, additional description will be omitted to avoid redundancy. 
     In a conventional memory device, a memory cell of an erase state, which is connected with a selected word line, may be programmed due to hot electron injection (HCI) that occurs due to a voltage difference of upper and lower adjacent word lines located above and below the selected word line. 
     In example embodiments, a first pre-setup voltage higher than a read voltage of a seventh program state (or last program state, highest program state, nth program state of n program states, etc.) of memory cells connected with the selected word line may be applied to the upper adjacent word line, and thus, a channel-off period may not occur in a channel corresponding to memory cells connected with the upper adjacent word line. Thus, the HCI may be prevented. 
     Furthermore, times at which a first setup voltage and a second setup voltage are applied may be adjusted, and thus, program operation speed of the selected word line may be improved. Additionally, the program operation speed of the selected word line may be improved by making a level difference of the first pre-setup voltage and the first setup voltage great. 
       FIG.  1    is a block diagram of a memory device according to an example embodiment. In some embodiments, a memory device  100  may be a nonvolatile memory device that is based on a NAND flash memory. However, the present disclosure is not limited thereto. For example, the memory device  100  may be one of various types of memory devices such as a dynamic random access memory (DRAM), a static RAM (SRAM), a phase-change RAM (PRAM), a magnetoresistive RAM (MRAM), a resistive RAM (RRAM), and a ferroelectric RAM (FRAM). 
     Referring to  FIG.  1   , the memory device  100  may include a memory cell array  110 , an address decoding circuit  120 , a voltage generation circuit  130 , a page buffer circuit  140 , an input/output circuit  150 , and a control logic circuit  160 . 
     The memory cell array  110  may include a plurality of memory blocks. Each of the plurality of memory blocks may include a plurality of cell strings. Each of the plurality of cell strings may include a plurality of cell transistors connected in series between a bit lines BL and a common source line. The plurality of cell transistors may be connected with string selection lines SSL, word lines WL, and ground selection lines GSL. A structure of the plurality of memory blocks will be described in detail with reference to  FIG.  2   . 
     The address decoding circuit  120  may be connected with the memory cell array  110  through the string selection lines SSL, the word lines WL, and the ground selection lines GSL. The address decoding circuit  120  may receive an address ADDR from an external device (e.g., a memory controller) and may decode the received address ADDR. The address decoding circuit  120  may control voltages of the string selection lines SSL, the word lines WL, and the ground selection lines GSL based on a decoding result. 
     In detail, during a setup period (i.e., in a setup period, within a setup period, throughout a setup period, etc.) of a selected word line of the word lines WL, the address decoding circuit  120  may apply a first pre-setup voltage to an upper adjacent word line and may then apply a first setup voltage higher than the first pre-setup voltage to the upper adjacent word line. 
     During the setup period of the selected word line of the word lines WL, the address decoding circuit  120  may apply a second pre-setup voltage to a lower adjacent word line and may then apply a second setup voltage higher than the second pre-setup voltage to the lower adjacent word line. This will be described in more detail with reference to  FIG.  3   . 
     The selected word line may refer to a word line targeted for a program operation of a memory device. The upper adjacent word line and the lower adjacent word line may refer to word lines adjacent to the selected word line. The upper adjacent word line may refer to a word line located on an upper side of the selected word line (or above the selected word line). The lower adjacent word line may refer to a word line located on a lower side of the selected word line (or below the selected word line). 
     The setup period of the selected word line may refer to a period in which a voltage necessary to perform the program operation is applied to a selected word line (e.g., WL 2 ) before the program operation is performed on the selected word line (e.g., WL 2 ). 
     The voltage generation circuit  130  may generate various voltages necessary for the memory device  100  to operate. For example, the voltage generation circuit  130  may generate various voltages based on a power supply voltage VCC, such as a plurality of program voltages, a plurality of pass voltages, a plurality of verify voltages, a plurality of selection read voltages, a plurality of non-selection read voltages, a plurality of erase voltages, and a plurality of erase verify voltages. In some embodiments, the voltage generation circuit  130  may generate the first pre-setup voltage, the first setup voltage, the second pre-setup voltage, and the second setup voltage. 
     The page buffer circuit  140  may be connected with the memory cell array  110  through bit lines BL. The page buffer circuit  140  may read data stored in the memory cell array  110  by sensing voltage changes of the bit lines BL and may temporarily store the read data. The page buffer circuit  140  may receive data from the input/output circuit  150  and may store the received data in the memory cell array  110  by controlling the bit lines BL based on the received data. 
     The input/output circuit  150  may exchange data “DATA” with the external device (e.g., a memory controller). For example, the input/output circuit  150  may receive the data “DATA” from the external device and may provide the received data “DATA” to the page buffer circuit  140 . The input/output circuit  150  may receive the data “DATA” from the page buffer circuit  140  and may output the received data “DATA” to the external device. 
     The control logic circuit  160  may control an overall operation of the memory device  100 . For example, the control logic circuit  160  may receive a command CMD and a control signal CTRL from the external device (e.g., a memory controller) and may control various operations (e.g., a program operation, a read operation, and an erase operation) of the memory device  100  based on the received signals. 
     Below, to describe embodiments of the present disclosure, the embodiments of the present disclosure will be described based on the read operation of the memory device  100 . However, the present disclosure is not limited thereto. For example, it may be understood that the embodiments of the present disclosure may be applied to a word line setup operation or various operations (e.g., a program operation, a verify operation, and an erase operation) of the memory device  100 , in which any other operation voltages are generated. 
       FIG.  2    is a diagram illustrating a first memory block of a plurality of memory blocks included in a memory cell array in  FIG.  1    according to an example embodiment. In some embodiments, the memory device  100  of  FIG.  1    may be a flash memory device that includes a plurality of memory blocks. 
     A memory block of a three-dimensional structure will be described with reference to  FIG.  2   , but the present disclosure is not limited thereto. The memory block according to the present disclosure may have a two-dimensional memory block structure. A first memory block BLK 1  will be described with reference to  FIG.  2   , but the present disclosure is not limited thereto. The remaining memory blocks may be similar in structure to the first memory block BLK 1 . 
     In some embodiments, the first memory block BLK 1  may correspond to a physical erase unit of the memory device  100 . However, the present disclosure is not limited thereto. For example, the erase unit may be changed to a page unit, a word line unit, a sub-block unit, etc. 
     The first memory block BLK 1  may include a plurality of cell strings CS 11 , CS 12 , CS 21 , and CS 22 . The plurality of cell strings CS 11 , CS 12 , CS 21 , and CS 22  may be arranged in a row direction and a column direction to form rows and columns. 
     Each of the plurality of cell strings CS 11 , CS 12 , CS 21 , and CS 22  includes a plurality of cell transistors. For example, each of the plurality of cell strings CS 11 , CS 12 , CS 21 , and CS 22  may include string selection transistors SSTa and SSTb, a plurality of memory cells MC 1  to MC 9 , ground selection transistors GSTa and GSTb, and dummy memory cells DMC 1  and DMC 2 . In an embodiment, each of a plurality of cell transistors included in the cell strings CS 11 , CS 12 , CS 21 , and CS 22  may be a charge trap flash (CTF) memory cell. 
     In each cell string, the plurality of memory cells MC 1  to MC 9  are serially connected and are stacked in a direction perpendicular to a plane defined by the row direction and the column direction, that is, in a height direction. The string selection transistors SSTa and SSTb are serially connected, and the serially-connected string selection transistors SSTa and SSTb are interposed between a bit line BL 1  or BL 2  and the plurality of memory cells MC 1  to MC 9 . The ground selection transistors GSTa and GSTb may be serially connected with each other, and the serially-connected ground selection transistors GSTa and GSTb may be interposed between the plurality of memory cells MC 1  to MC 9  and a common source line CSL. 
     In some embodiments, the first dummy memory cell DMC 1  may be interposed between the plurality of memory cells MC 1  to MC 9  and the ground selection transistors GSTa and GSTb. In some embodiments, the second dummy memory cell DMC 2  may be interposed between the plurality of memory cells MC 1  to MC 9  and the string selection transistors SSTa and SSTb. 
     The ground selection transistors GSTa and GSTb of the cell strings CS 11 , CS 12 , CS 21 , and CS 22  may be connected in common with a ground selection line GSL. In some embodiments, ground selection transistors in the same row may be connected with the same ground selection line, and ground selection transistors in different rows may be connected with different ground selection lines. For example, the first ground selection transistors GSTa of the cell strings CS 11  and CS 12  in the first row may be connected with a first ground selection line, and the first ground selection transistors GSTa of the cell strings CS 21  and CS 22  in the second row may be connected with a second ground selection line. 
     In some embodiments, ground selection transistors provided at the same height from a substrate may be connected with the same ground selection line, and ground selection transistors provided at different heights therefrom may be connected with different ground selection lines. 
     Memory cells of the same height from the substrate or the ground selection transistors GSTa and GSTb are connected in common with the same word line, and memory cells of different heights therefrom are connected with different word lines. For example, the plurality of memory cells MC 1  to MC 9  of the cell strings CS 11 , CS 12 , CS 21 , and CS 22  may be connected with a plurality of word lines WL 1  to WL 9 . 
     String selection transistors, which belong to the same row, from among the first string selection transistors SSTa of the same height are connected with the same string selection line, and string selection transistors belonging to different rows are connected with different string selection lines. For example, the first string selection transistors SSTa of the cell strings CS 11  and CS 12  in the first row may be connected in common to a string selection line SSL 1   a,  and the first string selection transistors SSTa of the cell strings CS 21  and CS 22  in the second row may be connected in common to a string selection line SSL 2   a.    
     Likewise, second string selection transistors, which belong to the same row, from among the second string selection transistors SSTb at the same height are connected with the same string selection line, and second string selection transistors in different rows are connected with different string selection lines. For example, the second string selection transistors SSTb of the cell strings CS 11  and CS 12  in the first row are connected in common with a string selection line SSL 1   b,  and the second string selection transistors SSTb of the cell strings CS 21  and CS 22  in the second row may be connected in common with a string selection line SSL 2   b.    
     In some embodiments, dummy memory cells at the same height may be connected with the same dummy word line, and dummy memory cells at different heights may be connected with different dummy word lines. For example, the first dummy memory cells DMC 1  may be connected with a first dummy word line DWL 1 , and the second dummy memory cells DMC 2  may be connected with a second dummy word line DWL 2 . 
     In some embodiments, the first memory block BLK 1  illustrated in  FIG.  2    is only an example. The number of cell strings may increase or decrease, and the number of rows of cell strings and the number of columns of cell strings may increase or decrease depending on the number of cell strings. Also, the number of cell transistors (i.e., GST, MC, DMC, and SST) of the first memory block BLK 1  may increase or decrease, and the height of the first memory block BLK 1  may increase or decrease depending on the number of cell transistors. In addition, the number of lines (i.e., GSL, WL, DWL, and SSL) connected with cell transistors may increase or decrease depending on the number of cell transistors. 
     As a memory cell distant from the substrate is first programmed, a channel of a cell string may be separated and boosted when a memory cell close to the substrate is programmed. As such, a potential difference may occur between the boosted channels, and the HCI may occur due to the potential difference of the boosted channels. The HCI may be prevented in the program operation of a selected word line by adjusting voltages respectively applied to word lines adjacent to the selected word line. This will be described in more detail with reference to  FIG.  3   . 
       FIG.  3    is a graph of voltages applied to a selected word line, an upper adjacent word line, and a lower adjacent word line, according to an example embodiment. Referring to  FIG.  3   , different voltages are respectively applied to a selected word line WL 2 , an upper adjacent word line WL 3 , and a lower adjacent word line WL 1 . In  FIG.  3   , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     Referring to  FIG.  2   , the selected word line WL 2  may be the second word line WL 2 . The upper adjacent word line WL 3  may be the third word line WL 3  upwardly adjacent to the second word line WL 2 . The lower adjacent word line WL 1  may be the first word line WL 1  downwardly adjacent to the second word line WL 2 . The lower adjacent word line WL 1  may be closer to the substrate than the upper adjacent word line WL 3 . In some embodiments, the upper adjacent word line WL 3  may be in a state where the program operation is completed, and the lower adjacent word line WL 1  may be in an erase state. 
     An address decoding circuit may perform the setup operation for the program operation of the selected word line WL 2  during a word line setup period between a start time point Ts and an end time point Te. The setup operation may refer to an operation of applying a voltage necessary to perform the program operation to the selected word line WL 2  before the program operation of the selected word line WL 2  is performed. 
     The address decoding circuit may apply a boosting voltage VB to the selected word line WL 2  during a period from the start time point Ts to time point T 0 . The boosting voltage VB may be a voltage that is higher than a voltage applied to the selected word line WL 2  before the setup period. 
     The address decoding circuit may apply a write voltage VT for the program operation to the selected word line WL 2  at the time point T 0 . The write voltage VT may have a target voltage level of the selected word line WL 2  to be applied for programming. The write voltage VT may be higher than the boosting voltage VB. A voltage level of the selected word line WL 3  may reach a level of the write voltage VT at time point tc. 
     During the setup period (or word line setup period), the address decoding circuit may apply a voltage to each of the upper adjacent word line WL 3  and the lower adjacent word line WL 1  in two steps. In detail, during a first pre-setup period PR 1  between the start time point Ts and a first time point T 1 , the address decoding circuit may apply a first pre-setup voltage PV 1  to the upper adjacent word line WL 3 . A voltage level of the upper adjacent word line WL 3  may reach a level of the first pre-setup voltage PV 1  at time point to between the start time point Ts and the first time point T 1 . In some embodiments, the first pre-setup voltage PV 1  may be higher than a read voltage corresponding to a seventh program state of memory cells connected with the upper adjacent word line WL 3 . 
     In a conventional memory device, when the program operation is performed with respect to the selected word line WL 2 , a channel corresponding to a memory cell connected with an upper word line of the selected word line WL 2  may be shut off; in this case, a voltage of the channel corresponding to the memory cell connected with the upper word line may be negative. 
     Also, when the program operation is performed with respect to the selected word line WL 2 , a channel corresponding to a memory cell connected with a lower word line of the selected word line WL 2  may be supplied with a boosting voltage for assisting the program operation of the selected word line WL 2 ; in this case, a voltage of the channel corresponding to the memory cell connected with the lower word line may be positive. 
     In the case where a voltage difference between the negative voltage of the channel corresponding to the memory cell connected with the upper word line and the positive voltage of the channel corresponding to the memory cell connected with the lower word line is great, a memory cell of an erase state, which is connected with the selected word line WL 2 , may be programmed by the HCI. 
     In contrast, a memory device according to the present disclosure may supply the upper adjacent word line WL 3  with the first pre-setup voltage PV 1  higher than the read voltage of the seventh program state of memory cells connected with the upper adjacent word line WL 3 , and thus, a channel-off period may not occur in the channel corresponding to memory cells connected with the upper adjacent word line WL 3 . Accordingly, the HCI may be prevented. 
     During a first setup period ST 1  between the first time point T 1  and the end time point Te, the address decoding circuit may apply a first setup voltage SV 1  to the upper adjacent word line WL 3 . A voltage of the upper adjacent word line WL 3  may reach the first setup voltage SV 1  at time point tb. The first setup voltage SV 1  may be higher than the first pre-setup voltage PV 1 . 
     In some embodiments, in the case where the HCI degradation characteristic of the selected word line WL 2  is good, as a magnitude difference of the first pre-setup voltage PV 1  and the first setup voltage SV 1  becomes greater, the program operation speed of the selected word line WL 2  may become better. 
     During a second pre-setup period PR 2  between the start time point Ts and a second time point T 2 , the address decoding circuit may apply a second pre-setup voltage PV 2  to the lower adjacent word line WL 1 . A voltage of the lower adjacent word line WL 1  may reach the second pre-setup voltage PV 2  at time point td. The second pre-setup voltage PV 2  may be lower than the first pre-setup voltage PV 1 . 
     During a second setup period ST 2  between the second time point T 2  and the end time point Te, the address decoding circuit may apply a second setup voltage SV 2  to the lower adjacent word line WL 1 . A voltage of the lower adjacent word line WL 1  may reach the second setup voltage SV 2  at time point te. The second setup voltage SV 2  may be higher than the second pre-setup voltage PV 2 . For example, the second pre-setup voltage PV 2  may be between 0 V and 10 V, and the second setup voltage SV 2  may be between 7 V and 10 V. 
     As the second pre-setup voltage PV 2  is applied to the lower adjacent word line WL 1  during the setup period of the selected word line WL 2 , the coupling-up effect may be maximized. As such, a speed at which the selected word line WL 2  is set up may be improved. Also, as there is improved the speed at which the selected word line WL 2  is set up, a time taken to perform the program operation may decrease. 
     That is, as the first pre-setup voltage PV 1  is applied to the upper adjacent word line WL 3  during the first pre-setup period PR 1 , the first setup voltage SV 1  is applied to the upper adjacent word line WL 3  during the first setup period ST 1 , the second pre-setup voltage PV 2  is applied to the lower adjacent word line WL 1  during the second pre-setup period PR 2 , and the second setup voltage SV 2  is applied to the lower adjacent word line WL 1  during the second setup period ST 2 , the hot electron injection (HCI) of the selected word line WL 2  may be blocked, and the program operation speed may be improved. 
       FIG.  4    is a diagram illustrating threshold voltage distributions of memory cells of  FIG.  2    according to an example embodiment. Below, to describe embodiments of the present disclosure easily, it is assumed that each of the memory cells of the memory device  100  is a triple level cell (TLC) configured to store 3-bit data. However, the present disclosure is not limited thereto. For example, each memory cell may be a single level cell (SLC) storing 1-bit data, or a multi-level cell (MLC), a TLC, or a quad level cell (QLC) storing n-bit data (n being a natural number more than 1). 
     Referring to  FIGS.  2  and  4   , each memory cell may be programmed to have one of an erase state “E” and first to seventh program states P 1  to P 7 . To read data programmed in the memory cells, the memory device  100  may use a plurality of read voltages VRD 1  to VRD 7 . For example, to read data programmed in memory cells connected with a word line, the memory device  100  may sequentially apply the plurality of read voltages VRD 1  to VRD 7  to the word line. In some embodiments, the plurality of selection read voltages VRD 1  to VRD 7  may have voltage levels for distinguishing the erase state “E” and the first to seventh program states P 1  to P 7 . 
     In an embodiment, the first pre-setup voltage PV 1  that is applied to the upper adjacent word line WL 3  may be higher than the seventh read voltage VRD 7  of the upper adjacent word line WL 3 . The second pre-setup voltage PV 2  that is applied to the lower adjacent word line WL 1  may be lower than the first read voltage VRD 1  of the selected word line WL 2 . 
     As the first setup voltage SV 1  of the upper adjacent word line WL 3  becomes smaller, the program operation speed of the selected word line WL 2  may decrease. To prevent the above issue, the first setup voltage SV 1  of the upper adjacent word line WL 3  may be set to be higher than the first pre-setup voltage PV 1 . 
     As the first setup voltage SV 1  of the upper adjacent word line WL 3  becomes greater, a threshold voltage distribution of memory cells connected with the selected word line WL 2  may become wider. In this case, a distance between threshold voltage distributions may decrease. This may mean that the probability that a program fail occurs increases. To prevent the above issue, the first setup voltage SV 1  of the upper adjacent word line WL 3  may be set to be lower than a first reference voltage. For example, the first reference voltage may be 10 V. 
     Also, as the second setup voltage SV 2  of the lower adjacent word line WL 1  becomes smaller, the program operation speed of the selected word line WL 2  may decrease. To prevent the above issue, the second setup voltage SV 2  of the lower adjacent word line WL 1  may be set to be higher than the second pre-setup voltage PV 2 . 
     As the second setup voltage SV 2  of the lower adjacent word line WL 1  becomes greater, a threshold voltage distribution of memory cells connected with the selected word line WL 2  may become wider. In this case, a distance between threshold voltage distributions may decrease. This may mean that the probability that a program fail occurs increases. To prevent the above issue, the second setup voltage SV 2  of the lower adjacent word line WL 1  may be set to be lower than a second reference voltage. For example, the second reference voltage may be 10 V. 
       FIG.  5    is a graph of voltages applied to an upper adjacent word line, according to an example embodiment. Voltages that are applied to an upper adjacent word line depending on the seventh read voltage VRD 7  of the upper adjacent word line are illustrated in  FIG.  5   . In  FIG.  5   , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     Referring to Case A in which the seventh read voltage VRD 7  of the upper adjacent word line is a first voltage Va, during a first pre-setup period PR 1   a,  the address decoding circuit may apply a first pre-setup voltage PV 1   a  higher than the first voltage Va to the upper adjacent word line. During a first setup period ST 1   a,  the address decoding circuit may apply a first setup voltage SV 1   a  to the upper adjacent word line. The first pre-setup voltage PV 1   a  and the first setup voltage SV 1   a  may respectively correspond to the first pre-setup voltage PV 1  and the first setup voltage SV 1  of  FIG.  3   . 
     Referring to Case B in which the seventh read voltage VRD 7  of the upper adjacent word line is a second voltage Vb, during a first pre-setup period PR 1   b,  the address decoding circuit may apply a first pre-setup voltage PV 1   b  higher than the second voltage Vb to the upper adjacent word line. During a first setup period ST 1   b,  the address decoding circuit may apply a first setup voltage SV 1   b  to the upper adjacent word line. The first pre-setup voltage PV 1   b  and the first setup voltage SV 1   b  may respectively correspond to the first pre-setup voltage PV 1  and the first setup voltage SV 1  of  FIG.  3   . 
     As described above, magnitudes of the first pre-setup voltage and the first setup voltage may change depending on a magnitude of the seventh read voltage VRD 7 . As the magnitude of the seventh read voltage VRD 7  increases, the magnitude of the first pre-setup voltage may increase. Also, because the first setup voltage is higher than the first pre-setup voltage, as the magnitude of the first pre-setup voltage increases, the magnitude of the first setup voltage may increase. 
     That is, in the case where a magnitude of the seventh read voltage VRD 7  changes depending on a word line, magnitudes of the first pre-setup voltage and the first setup voltage may be differently set for each word line. For example, referring to  FIG.  2   , the magnitude of the first pre-setup voltage when the upper adjacent word line is the third word line WL 3  may be different from the magnitude of the first pre-setup voltage when the upper adjacent word line is the fifth word line WL 5 . 
       FIG.  6 A  is a graph of points in time when voltages are applied to an upper adjacent word line, according to an example embodiment. Start time points of the first setup period are illustrated in  FIG.  6 A . In  FIG.  6 A , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     The case where the seventh read voltage VRD 7  of the upper adjacent word line is the first voltage Va may correspond to the case (refer to  FIG.  5   ) where the seventh read voltage VRD 7  of the upper adjacent word line is the first voltage Va, and the case where the seventh read voltage VRD 7  of the upper adjacent word line is the second voltage Vb may correspond to the case (refer to  FIG.  5   ) where the seventh read voltage VRD 7  of the upper adjacent word line is the second voltage Vb. 
     As the first pre-setup voltage becomes smaller, a time at which the address decoding circuit applies the first setup voltage may become later. Referring to the case where the seventh read voltage VRD 7  of the upper adjacent word line is the first voltage Va, at a first pre point T 1   a,  the address decoding circuit may apply the first setup voltage SV 1   a  to the upper adjacent word line. 
     Referring to the case where the seventh read voltage VRD 7  of the upper adjacent word line is the second voltage Vb, in a first time point T 1   b,  the address decoding circuit may apply the first pre-setup voltage SV 1   b  to the upper adjacent word line. 
     When the first pre-setup voltage PV 1   a  is smaller than the first pre-setup voltage PV 1   b,  a time at which the first setup voltage SV 1   a  is applied may be later than a time at which the first setup voltage SV 1   b  is applied. That is, a length of the first pre-setup period PR 1   a  may be longer than a length of the first pre-setup period PR 1   b.    
     In some embodiments, in the case where the HCI degradation characteristic of the selected word line WL 2  is good, as a length of a period in which the first pre-setup voltage is applied increases, the program operation speed of the selected word line WL 2  may become better. 
       FIG.  6 B  is a graph of points in time when voltages are applied to a lower adjacent word line, according to an example embodiment. Start time points of the second setup period are illustrated in  FIG.  6 B . In  FIG.  6 B , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     Each of a second pre-setup voltage PV 2   a  and a second pre-setup voltage PV 2   b  may correspond to the second pre-setup voltage PV 2  of  FIG.  3   , and each of a second setup voltage SV 2   a  and a second setup voltage SV 2   b  may correspond to the second setup voltage SV 2  of  FIG.  3   . 
     Referring to the case where a time at which the second setup voltage SV 2   a  is applied is a second time point T 2   a,  the address decoding circuit may apply the second pre-setup voltage PV 2   a  to the lower adjacent word line during a second pre-setup period PR 2   a  between the start time point Ts and the second time point T 2   a  and may apply the second setup voltage SV 2   a  to the lower adjacent word line during a second setup period ST 2   a  between the second time point T 2   a  and the end time point Te. 
     Referring to the case where a time at which the second setup voltage SV 2   b  is applied is a second time point T 2   b,  the address decoding circuit may apply the second pre-setup voltage PV 2   b  to the lower adjacent word line during a second pre-setup period PR 2   b  between the start time point Ts and the second time point T 2   b  and may apply the second setup voltage SV 2   b  to the lower adjacent word line during a second setup period ST 2   b  between the second time point T 2   b  and the end time point Te. 
     In some embodiments, in the case where the HCI degradation characteristic of the selected word line WL 2  is good, the program operation speed of the selected word line WL 2  in the case where the time at which the second setup voltage SV 2   a  is applied is the second time point T 2   a  may be faster than the program operation speed of the selected word line WL 2  in the case where the time at which the second setup voltage SV 2   b  is applied is the second time point T 2   b.    
     That is, in the case where the HCI degradation characteristic of the selected word line WL 2  is good, as a length of a period in which the second pre-setup voltage is applied increases, the program operation speed of the selected word line WL 2  may become better. 
       FIG.  7 A  is a graph of voltages applied to an upper adjacent word line, according to an example embodiment. Voltages that are applied to the upper adjacent word line as a program loop is repeated are illustrated in  FIG.  7 A . In  FIG.  7 A , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     Each of a first upper pre-setup voltage PV 11 , a second upper pre-setup voltage PV 12 , and an N-th upper pre-setup voltage PV 1 N may correspond to the first pre-setup voltage PV 1  of  FIG.  3   , and each of a first upper setup voltage SV 11 , a second upper setup voltage SV 12 , and an N-th upper setup voltage SV 1 N may correspond to the first setup voltage SV 1  of  FIG.  3   . 
     A memory device may perform a program operation in an incremental pulse programming (ISPP) manner such that threshold voltages of memory cells connected with a selection word line have a given value. As the program loop is repeated, the threshold voltages of the memory cells connected with the selection word line may gradually increase. The program loop may be repeated until levels of the threshold voltages of all the memory cells connected with the selected word line reach a verify voltage. 
     The memory device may apply a voltage to the upper adjacent word line in two steps every program loop. In detail, during a first program loop, the memory device may apply the first upper pre-setup voltage PV 11  to the upper adjacent word line and may then apply the first upper setup voltage SV 11  to the upper adjacent word line. The first upper setup voltage SV 11  may be higher than the first upper pre-setup voltage PV 11 . 
     When it is determined that the threshold voltages of the memory cells connected with the selected word line are not higher than the verify voltage, the memory device may perform a second program loop. During the second program loop, the memory device may apply the second upper pre-setup voltage PV 12  to the upper adjacent word line and may then apply the second upper setup voltage SV 12  to the upper adjacent word line. The second upper pre-setup voltage PV 12  may be higher than the first upper pre-setup voltage PV 11 . The second upper setup voltage SV 12  may be higher than the second upper pre-setup voltage PV 12 . 
     When it is determined that the threshold voltages of the memory cells connected with the selected word line are not higher than the verify voltage, the memory device may perform a third program loop. During the third program loop, the memory device may apply the third upper pre-setup voltage to the upper adjacent word line and may then apply the third upper setup voltage to the upper adjacent word line. The third upper pre-setup voltage may be higher than the second upper pre-setup voltage PV 12 . The third upper setup voltage may be higher than the third upper pre-setup voltage. 
     During the N-th program loop, the memory device may apply the N-th upper pre-setup voltage PV 1 N to the upper adjacent word line and may then apply the N-th upper setup voltage SV 1 N to the upper adjacent word line. In an embodiment, during the N-th program loop, the memory device may apply the N-th upper pre-setup voltage PV 1 N higher than the seventh read voltage VRD 7  of the upper adjacent word line to the upper adjacent word line and may then apply the N-th upper setup voltage SV 1 N to the upper adjacent word line. The N-th program loop may correspond to a program period where the memory cells connected with the selected word line are completely programmed. The N-th upper pre-setup voltage PV 1 N may be higher than the (N−1)-th upper pre-setup voltage. The N-th upper setup voltage SV 1 N may be higher than the N-th upper pre-setup voltage PV 1 N. 
     That is, as the program loop is repeated, a magnitude of an upper pre-setup voltage that is applied to the upper adjacent word line may increase until the levels of the threshold voltages of all the memory cells connected with the selected word line reach the verify voltage. 
     However, the magnitudes of the first to (N−1)-th upper pre-setup voltages applied in the first to (N−1)-th program loops may be smaller than the seventh read voltage VRD 7  of the memory cells connected with the upper adjacent word line. While the program operation is performed based on the ISPP manner, as the address decoding circuit applies a voltage to the upper adjacent word line in two steps every program loop, the number of program loops to be performed may decrease. As the number of program loops to be performed decreases, a time during which the memory device performs the program operation on the selected word line may decrease. 
       FIG.  7 B  is a graph of voltages applied to a lower adjacent word line, according to an example embodiment. Voltages that are applied to the lower adjacent word line as a program loop is repeated are illustrated in  FIG.  7 B . In  FIG.  7 B , a horizontal axis denotes a time, and a vertical axis denotes a magnitude of a voltage. 
     Each of a first lower pre-setup voltage PV 21 , a second lower pre-setup voltage PV 22 , and an N-th lower pre-setup voltage PV 2 N may correspond to the second pre-setup voltage PV 2  of  FIG.  3   , and each of a first lower setup voltage SV 21 , a second lower setup voltage SV 22 , and an N-th lower setup voltage SV 2 N may correspond to the second setup voltage SV 2  of  FIG.  3   . 
     The memory device may apply a voltage to the lower adjacent word line in two steps every program loop. In detail, during the first program loop, the memory device may apply the first lower pre-setup voltage PV 21  to the lower adjacent word line and may then apply the first lower setup voltage SV 21  to the lower adjacent word line. 
     The first lower pre-setup voltage PV 21  may be lower than the first read voltage VRD 1  of memory cells connected with a selected word line. The first lower setup voltage SV 21  may be higher than the first lower pre-setup voltage PV 21 . When it is determined that the threshold voltages of the memory cells connected with the selected word line are not higher than the verify voltage, the memory device may perform the second program loop. 
     During the second program loop, the memory device may apply the second lower pre-setup voltage PV 22  to the lower adjacent word line and may then apply the second lower setup voltage SV 22  to the lower adjacent word line. A magnitude of the second lower pre-setup voltage PV 22  may be equal to a magnitude of the first lower pre-setup voltage PV 21 . The second lower setup voltage SV 22  may be higher than the first lower setup voltage SV 21 . 
     When it is determined that the threshold voltages of the memory cells connected with the selected word line are not higher than the verify voltage, the memory device may perform the third program loop. 
     During the N-th program loop, the memory device may apply the N-th lower pre-setup voltage PV 2 N to the lower adjacent word line and may then apply the N-th lower setup voltage SV 2 N to the lower adjacent word line. Herein, “N” may be a natural number of 3 or more. A magnitude of the N-th lower pre-setup voltage PV 2 N may be equal to the magnitude of the first lower pre-setup voltage PV 21 . A magnitude of the N-th lower setup voltage SV 2 N may be greater than a magnitude of the (N−1)-th lower setup voltage. 
     While the program operation is performed on the selected word line in the ISPP manner, as the address decoding circuit applies a voltage to the lower adjacent word line in two steps every program loop, the number of program loops to be performed may decrease. That is, a time during which the program operation is performed on the selected word line may decrease. 
       FIG.  8    is a flowchart of an method of a memory device according to an example embodiment. An operating method of a memory device according to some embodiments of the present disclosure will be described with reference to  FIG.  8   . The memory device may correspond to the memory device  100  of  FIG.  1   . 
     In operation S 110 , during the setup period in which a selected word line is set up, the memory device may apply a first pre-setup voltage to an upper adjacent word line and may apply a second pre-setup voltage to a lower adjacent word line. The first pre-setup voltage may be higher than a read voltage corresponding to a seventh program state of memory cells connected with the upper adjacent word line. The second pre-setup voltage may be lower than a read voltage corresponding to a first program state of the memory cells connected with the selected word line. The first pre-setup voltage may be higher than the second pre-setup voltage. 
     In operation S 120 , the memory device may apply a first setup voltage higher than the first pre-setup voltage to the upper adjacent word line. That is, the memory device may apply a voltage to the upper adjacent word line in two steps during the setup period. 
     In operation S 130 , the memory device may apply a second setup voltage higher than the second pre-setup voltage to the lower adjacent word line. The first pre-setup voltage may be higher than the second pre-setup voltage. That is, the memory device may apply a voltage to the lower adjacent word line in two steps during the setup period. 
     According to embodiments of the present disclosure, a memory device that individually applies voltages to word lines adjacent to a selected word line and an operating method thereof are provided. 
     According to some embodiments of the present disclosure, as a voltage is applied to each of upper and lower adjacent word lines adjacent to a selected word line in two steps, the HCI may be suppressed; as the upper and lower adjacent word lines are individually controlled, a setup period of the selected word line may be shortened. 
     While the present disclosure has been described with reference to example embodiments thereof, it will be apparent to those of ordinary skill in the art that various changes and modifications may be made thereto without departing from the spirit and scope of the present disclosure as set forth in the following claims.