# Patent

## Title
Method of initializing 3D non-volatile memory device

## Abstract

A 3D non-volatile memory device may include a dummy string selection line, string selection lines, wordlines, bitlines, a ground selection line, and memory layers. Each of the memory layers comprising channel lines respectively coupled to the bitlines via first ends and coupled to a common source line of the memory layer via second ends. The dummy string selection line, the string selection lines, the wordlines, and the ground selection line intersect with the channel lines, and each of the channel lines defines a memory string. Initializing the 3D non-volatile memory device may include programming string selection transistors coupled with the string selection lines to have one or more threshold values, and programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the string selection transistors function as string selection transistors.

## Background
CROSS-REFERENCES TO RELATED APPLICATION
The present application claims the benefit of Korean application number 10-2015-0160049, filed on Nov. 14, 2015, which is herein incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
1. Field
Embodiments of the present disclosure relate to a semiconductor memory technique, and more particularly, to a method of initializing a 3D non-volatile memory device.
2. Description of the Related Art
Due to increasing demands for portable application devices, such as digital cameras, smart phones, and tablet PCs, and replacement of conventional hard disk drives with solid-state drives (SSDs), markets for non-volatile memory devices are rapidly growing. Among these non-volatile memory devices, NAND flash memory devices are popular due to low manufacturing cost for high degree of integration.
Recently, downscaling the NAND flash memory device with a conventional two-dimensional (2D) memory cell array architecture has become more difficult as 20 nm or smaller photolithography techniques have reached their limits. In addition, design issues, which are related to reduction of a sensing margin in accordance with reduction of a number of electrons stored in a data storage film (e.g., a floating gate), and related to disturbances between memory cells, have become barriers against the downscaling of the conventional 2D memory cell array architecture.
To address the issues for downscaling a NAND flash memory device, various 3D NAND flash array structures have been suggested. For example, the Korean Patent Laid-Open Gazette No. 10-2011-011166 discloses a “layer selection by erase operation (LASER)” structure having a channel-stacked array structure, the entire disclosure thereof is incorporated herein in its entirety by reference. Unlike conventional 2D flat-panel type memory arrays, the 3D LASER structure requires a memory layer selection with respect to stacked memory layers for a read operation, a write operation, or an erase operation, where the memory layer selection is performed based on combinations of string selection transistors with one another. As another example for the 3D NAND flash memory device having memory layer selecting mechanism based on a “layer selection by multi-level operation (LSM)” using multi-level string selection transistors has been suggested.
To select a memory layer in the various 3D NAND flash memory devices, such as based on the LASER structure and the LSM structure, it is desirable to program or initialize string selection transistors to cause them to have certain threshold values. It is required to obtain a sharp distribution of threshold values of programmed string selection transistors, and further desirable to program the string selection transistors without an interlayer disturbance between memory arrays. In addition, while a programming bias is applied to a selected wordline coupled with a selected memory cell to program the selected memory cell, for a reliable program operation on the selected memory cell, it is preferable not to cause any disturbance to other memory cells sharing the selected wordline.
In order to program or initialize the string selection transistors, it is generally required to incorporate and utilize a dummy string selection transistor into a memory string. As the dummy string selection transistor may be a redundancy, it may become an obstacle to be overcome for downscaling 3D non-volatile memory devices.
SUMMARY OF THE INVENTION
Embodiments of the present disclosure provide a method of initializing a 3D non-volatile memory device for multi-level programming string selection transistors, such that the string selection transistors have threshold values exhibiting a sharp distribution without a complicated peripheral circuit, and utilizing redundancy of a dummy string selection transistor to increase integration degree of the 3D non-volatile memory device.
According to an aspect of the present disclosure, there is provided a method of initializing a 3D non-volatile memory device, which includes dummy string selection line, a plurality of string selection lines, a plurality of wordlines, a ground selection line, and a plurality of memory layers, each of the memory layers comprising a plurality of channel lines respectively coupled to a plurality of bitlines via first ends of the plurality of channel lines and coupled to a common source line of the memory layer via second ends of the plurality of channel lines, wherein the at least one dummy string selection line, the plurality of string selection lines, the plurality of wordlines, and the ground selection line intersect with the plurality of channel lines, and each of the plurality of channel lines defines a memory string.
In accordance with an embodiment, the method may include programming a plurality of string selection transistors coupled with the plurality of string selection lines to have at least one or more threshold values; and programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors. In accordance with an embodiment, programming a plurality of string selection transistors may be performed by using the dummy string selection line.
The programming a plurality of string selection transistors may include applying a first program voltage to a selected string selection line coupled to a selected memory layer among the plurality of memory layers, the selected string selection line being coupled to a plurality of string selection transistors; verifying whether threshold voltages of the plurality of string selection transistors reach a target value to determine the plurality of string selection transistors as programmed string selection transistors or unprogrammed string selection transistors; programming memory cell transistors of one or more of memory strings coupled with the programmed string selection transistors to have a predetermined threshold voltage, by applying a second program voltage to a selected wordline among the plurality of wordlines, the predetermined threshold voltage being suitable to make each of the programmed memory cell transistors function as a screening transistor; and program-inhibiting channel lines of the programmed string selection transistors using the programmed memory cell transistors as screening transistors and applying a third program voltage to the selected string selection line to selectively program the unprogrammed string selection transistors.
The applying the first program voltage, the verifying whether the threshold voltages of the plurality of string selection transistors reach the target value, and the applying the third program voltage may respectively include performing an incremental step pulse programming (ISPP) technique. In an embodiment, the plurality of selection transistors coupled with the selected string selection line may be a first plurality of string selection transistors. The method may further include, before the applying the first program voltage is performed, erasing a second plurality of string selection transistors coupled with the plurality of string selection lines and a plurality of memory cell transistors coupled with the plurality of wordlines, the second plurality of string selection transistors including the first plurality of string selection transistors. The verifying whether the threshold voltages of the plurality of string selection transistors reach the target value may include applying a sensing voltage to the plurality of bitlines; and applying a voltage substantially equal to the sensing voltage to common source lines of unselected memory layers among the plurality of memory layers.
The programming the memory cell transistors of the one or more of memory strings coupled with the programmed string selection transistors may include program-inhibiting a memory cell transistor of a memory string coupled with a corresponding one of the unprogrammed string selection transistors. Furthermore, the programming the memory cell transistors may further include applying a voltage equal to or higher than a common collector voltage to a bitline coupled with the corresponding one of the unprogrammed string selection transistors to induce channel potential boosting at the memory string coupled with the corresponding unprogrammed string selection transistor.
The program-inhibiting channel lines of the programmed string selection transistors may include applying a ground voltage to a common source line of the selected memory layer; and applying a common collector voltage to common source lines of unselected memory layers among the plurality of memory layers and to the plurality of bitlines to float channel lines of memory strings of the unselected memory layers.
The program-inhibiting the channel lines of the programmed string selection transistors may include applying a voltage smaller than the threshold voltages of the programmed memory cell transistors to the selected wordline coupled with the programmed memory cell transistors; and applying the third program voltage to the selected string selection line to selectively program the unprogrammed string selection transistors.
Programming a dummy string selection transistor may include initially levelling the dummy string selection transistor by programming threshold values of the dummy string selection transistor to have a determined first target value; and programming the initially levelled dummy string selection transistor to have a second target value by applying an erase voltage signal to the common source line of the selected memory layer, such that the programmed dummy string selection transistor functions as string selection transistors.
The erase voltage signal may be an erase voltage signal having a time varying section, and the dummy string selection transistors may be programmed to the second target value by grounding or floating the dummy string selection line in the time varying section of the erase voltage signal. The time varying section may include an increasing ramp section or a decreasing ramp section.
The time varying erase voltage signal may be applied to a first common source line coupled to the selected first memory layer. In addition, the method may further include applying a voltage signal for erase inhibition to one or more of common source lines other than the first common source line, the one or more common source lines being coupled to one or more of unselected memory layers among the plurality of memory layers when the time varying erase voltage signal is applied and the threshold values of the first plurality of string selection transistors in the first memory layer are set. The method may include causing the plurality of bitlines to float when the first time varying erase voltage signal is applied.
In accordance with an embodiment, the plurality of channel lines of the 3D non-volatile memory device may have a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, a pipe-shaped BiCs structure, or a combination thereof. In addition, the 3D non-volatile memory device may be a NAND flash memory device.
According to another aspect of the present disclosure, a method of initializing a 3D non-volatile memory device, may include programming string selection transistors coupled with the plurality of string selection lines to have determined threshold values based on an incremental step pulse programming (ISPP) mode with regard to a memory layer selected among the plurality of memory layers; and programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors. The method may further include, before programming string selection transistors, erasing the plurality of string selection transistors.
The plurality of channel lines of the 3D non-volatile memory device may have a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, a pipe-shaped BiCs structure, or a combination thereof. Furthermore, the 3D non-volatile memory device is a NAND flash memory device.
According to an aspect of the present disclosure, a method of initializing a 3D non-volatile memory device may include applying a first program voltage to a selected string selection line coupled to a selected memory layer among the plurality of memory layers, the selected string selection line being coupled to a plurality of string selection transistors; verifying whether threshold voltages of the plurality of string selection transistors reach a target value to determine the plurality of string selection transistors as programmed string selection transistor or unprogrammed string selection transistor; applying a voltage equal to or higher than a common collector voltage to a first bitline coupled to a first memory string including the unprogrammed string selection transistor, applying a ground signal to a second bitline coupled to a second memory string including programmed string selection transistor, and applying a program voltage to the dummy ground line, thereby inducing channel potential boost at the first memory string such that dummy ground transistors in the second memory string are programmed to have a predetermined threshold value to function as a screening transistor and dummy ground transistors in the first memory strings are not programmed; selectively programming the unprogrammed string selection transistor by turning the programmed dummy ground transistors off and applying a third program voltage to the selected string selection line; and programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors.
In accordance with an embodiment, applying the first program voltage, verifying whether the threshold voltages of the plurality of string selection transistors reach the target value, and applying the third program voltage respectively may include performing an incremental step pulse programming (ISPP) technique. Furthermore, the plurality of selection transistors coupled with the selected string selection line may be a first plurality of string selection transistors, and the method may further include, before applying the first program voltage is performed, erasing a second plurality of string selection transistors coupled with the plurality of string selection lines and a plurality of memory cell transistors coupled with the plurality of wordlines, the second plurality of string selection transistors including the first plurality of string selection transistors.



BRIEF DESCRIPTION OF THE DRAWINGS
Hereinafter, embodiments of the present disclosure will be described in greater detail with reference to the accompanying drawings.
FIG. 1 is a block diagram showing a 3D non-volatile memory device according to an embodiment of the present disclosure;
FIGS. 2A and 2B are perspective views showing 3D non-volatile memory devices including memory cell arrays according to various embodiments of the present disclosure;
FIG. 3 is a flowchart showing a process of initializing string selection transistors of a 3D non-volatile memory device according to an embodiment the present disclosure;
FIGS. 4A to 4I are circuit diagrams sequentially showing a process of initializing string selection transistors of a 3D non-volatile memory device according to an embodiment of the present disclosure;
FIG. 5A is a diagram showing a distribution of threshold values of string selection transistors, which is measured in a first operation step of FIG. 3 according to embodiments of the present disclosure, FIG. 5B is a timing diagram showing states of biases applied to a 3D non-volatile memory device in second and third operation steps, FIG. 5C is a timing diagram showing states of biases applied to a 3D non-volatile memory device in a fourth operation step, and 5D through 5F are diagrams showing various profiles of an erase voltage for initializing the dummy string selection transistor;
FIG. 6A is circuit diagram illustrating a process for programming a selected memory cell of a 3D non-volatile memory device that is initialized by a process of initializing string selection transistors according to an embodiment of the present disclosure, FIG. 6B is a graph showing measured transfer characteristics of string selection transistors initialized to multi levels according to an embodiment of the present disclosure, and FIG. 6C is a graph showing measured transfer characteristics of a programmed memory cell and an unselected and inhibited memory cell in the selected memory layer, and an unselected and inhibited memory cell and erased memory cell in an unselected memory layer;
FIG. 7 is a block diagram showing a memory system according to an embodiment of the present disclosure;
FIG. 8 is a block diagram showing a storage device including a solid state disk (SSD) according to an embodiment of the present disclosure;
FIG. 9 is a block diagram showing a memory system according to an embodiment of the present disclosure;
FIG. 10 is a block diagram showing a data storage device according to an embodiment of the present disclosure; and
FIG. 11 is a block diagram showing a flash memory device and a computing system including the same, according to an embodiment of the present disclosure.



DETAILED DESCRIPTION OF THE INVENTION
The present disclosure will now be described more fully with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as being 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 concept of the invention to those skilled in the art.
Like numbers refer to like elements throughout. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
It will be understood that when an element or layer is referred to as being “on” another element or layer, the element or layer can be directly on another element or layer or intervening elements or layers. In contrast, when an element is referred to as being “directly on” another element or layer, there are no intervening elements or layers present. Furthermore, a structure or a form shape “adjacent to” other shape may overlap the adjacent shape or be arranged below the adjacent shape.
The relative terms including “below,” “above,” “upper,” “lower,” “horizontal,” and “vertical” may be used to describe a relationship between an element, a layer, or a region and another element, another layer, or another region as shown in the drawings. It should be understood that the terms are not limited to the orientations shown in the drawings.
FIG. 1 is a block diagram showing a 3D non-volatile memory device 100 in accordance with an embodiment of the present disclosure.
Referring to FIG. 1, the 3D non-volatile memory device 100 may include a memory cell array 110 having a plurality of memory cells, a row decoder 120, a read/write circuit 130, and a column decoder 140. The memory cell array 110 may be connected to the row decoder 120 via wordlines WL1 to WLn, string selection lines SSL, a dummy string selection line DSSL, and a ground selection line GSL. Furthermore, the memory cell array 110 may be connected to the read/write circuit 130 via bitlines BL1 to BLm.
A dummy string selection line DSSL may be used for bit selection in order to initialize string selection transistors coupled to string selection lines SSL. When the initialization of the string selection transistors is completed, the dummy string selection line DSSL may be also initialized to have a certain threshold value, and then, function as a string selection transistor for selecting a memory layer.
If the 3D non-volatile memory device 100 is a NAND flash memory device, the memory cell array 110 may include memory cell strings (not shown) in which a plurality of memory cells are electrically connected in series. A dummy string selection transistor DSST for interconnecting a bitline and a memory cell string and at least two or more string selection transistors connected in series to the dummy string selection transistor DSST may be arranged at first ends of the memory cell strings. Second ends of the memory cell strings may be connected to a common source line, and a ground selection transistor GST (e.g., an NMOS selection transistor) to be connected to the common source line CSL may be provided at the second ends of the memory cell strings.
The wordlines WL1 to WLn may be connected to control gates of memory cells arranged in a column-wise direction, respectively. The bitlines BL1 to BLm may be connected to the first ends of the string selection transistors, respectively.
A plurality of memory cells having control gate electrode coupled with the respective wordlines WL1 to WLn, in a row-wise direction may constitute a logical page, where a number of logical pages may be determined by a storage capacity of the memory cells. For example, according to a level of the storage capacity, one or more of a single level cell (SLC) memory device, in which each memory cell stores 1 bit, a multi level cell (MLC) memory device, in which each memory cell stores 2 bits, an eight level cell (8LC) memory device, in which each memory cell stores 3 bits, and a sixteen level cell (16LC) memory device, in which each memory cell stores 4 bits may be provided.
Memory cells of the memory cell array 110 may be arranged in a 2D array structure that is disposed substantially parallel to the main surface of a semiconductor substrate or a 3D array structure having a channel perpendicular to a main surface of a semiconductor substrate or one or more memory layers stacked in a vertical direction of the main surface of the semiconductor substrate. For example, the 3D array structure in accordance with an embodiment of the present disclosure may be a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, or a pipe-shaped BiCs structure, where various layer selection methods described below may be applied to the structure. However, the above-described structures are merely examples, and embodiments of the present disclosure are not limited thereto.
The memory cells constituting a page may be programmed in a same program cycle. For example, memory cells connected to a wordline WL1 may be programmed to have an identical program state (or have a target value) in the same program cycle. Alternatively, the memory cells connected to the wordline WL1 may be programmed to have different program states, for example, in a single program cycle, a first memory cell may be programmed to have a first program state P1, a second memory cell adjacent to the first memory cell may be programmed to have a second program state P2, and other memory cells may be programmed to have a third program state P3. However, embodiments of the present disclosure are not limited thereto. In accordance with another embodiment, SLC device has an interleaved architecture, and even-numbered cells and odd-numbered cells may constitute two pages different from each other. For example, a 4 kb SLC device may include wordlines for 65,536 memory cells. Furthermore, in case of an MLC device, since each cell stores one least significant bit (LSB) and one most significant bit (MSB), the MLC device has four pages. For example, in the MLC device, MSB pages and LSB pages on even-numbered bitlines and MSB pages and LSB pages on odd-numbered bitlines may be provided.
The row decoder 120 performs initialization of string selection transistors of a memory layer by controlling the plurality of string selection lines SSL and the dummy string selection line DSSL as described above. In accordance with an embodiment, the row decoder 120 may select a plurality of string selection lines SSL or may drive corresponding string selection transistors by applying a voltage or a current thereto.
Furthermore, the row decoder 120 may select any one of wordlines of a memory block. The row decoder 120 may apply a wordline voltage generated by a voltage generator (not shown) to the selected wordline of the selected memory block. During a programming operation based on an incremental step pulse programming (ISPP) technique, the row decoder 120 may apply a program voltage Vpgm and a verification voltage Vvfy to a selected wordline and apply a pass voltage Vpass to an unselected wordline.
The memory cell array 110 may be addressed by the bitlines BL1 to BLm via the column decoder 140. The read/write circuit 130 may receive data from an external circuit via the column decoder 140, or may transmit data to the external circuit via the column decoder 140.
The read/write circuit 130 may include a page buffer (not shown) and may operate as a sense amplifier or a write driver according to operation modes. However, in the present disclosure, “read/write circuit” and “page buffer” may be used as equivalent terms and shall be understood as interchangeable terms. During a program operation, the read/write circuit 130 receives data to a selected bitline of the cell array 110. During a read operation, the read/write circuit 130 may read out data stored in a selected memory cell via a selected bitline, latch the read out data, and output the latched data to the external circuit.
The read/write circuit 130 may perform a verification operation associated with a program operation on a selected memory cell in response to a transmission signal received from a control logic 180 and, in response to the transmission signal, may output a result of the verification operation as page buffer signals over a plurality of number of times. In accordance with an embodiment, the read operation of the read/write circuit 130 may be performed based on charge integration using a bitline parasitic capacitor.
The read/write circuit 130 may include a page buffer and may operate as a detection amplifier or a write driver according to operation modes. However, in the present specification, a read/write circuit and a page buffer may be used as equivalent terms and shall be understood as inter-compatible terms. During a program operation, the read/write circuit 130 receives data from an external circuit and transmits a bitline voltage corresponding to data to be programmed to a bitline of the cell array 110. During a read operation, the read/write circuit 130 may read out data stored in a selected memory cell via a bitline, latch the read out data, and output the latched data to the external circuit.
The read/write circuit 130 may perform a verification operation associated with a program operation regarding a memory cell in response to a transmission signal transmitted from a control logic 180 and, in response to the transmission signal, may output a result of the verification operation as page buffer signals over a plurality of number of times. In accordance with an embodiment, the read operation of the read/write circuit 130 may utilize charge integration using a bitline parasitic capacitor. Furthermore, the read/write circuit 130 may measure a string current or voltage output to a bitline for programming verification during a program operation for initializing string selection transistors based on the ISPP technique. A verification technique may be performed by a current sensing circuit coupled with the bitline. In accordance with an embodiment, the current sensing circuit may be provided in the read/write circuit 130.
In an embodiment of the present disclosure, memory cells may be programmed page by page using the ISPP technique on the basis of a verification process for checking whether a threshold voltage of a corresponding memory cell reaches a level of a target voltage. The ISPP technique may be performed by a current sensing circuit (not shown) coupled with the bitlines BL1 to BLm.
The control logic 180 may execute program-verify loops based on the ISPP technique, thereby programming selected memory cells and/or string selection transistors. The pass/fail verification circuit 150 verifies whether a programmed memory cell and/or string selection transistors are at a desired level ever time when a program loop count increases. If the programmed memory cell and/or string selection transistors have a desired target level (a threshold value or a target value), it may be determined as a program pass, and the program operation and verification operation on the programmed memory cell and/or string selection transistors are terminated. However, if the programmed memory cell and/or string selection transistors do not reach the target value, it may be determined as a program fail, and the pass/fail verification circuit 150 may generate a count signal (not shown). The pass/fail verification circuit 150 may determine a fail of the program operation, and then transmit the determined result to the control logic 180.
In response to a command CMD, the control logic 180 may control one or more of the row decoder 120, the read/write circuit 130, the column decoder 140, the pass/fail verification circuit 150, the program loop turn detector 160, and the comparator 170 to perform a pulsed program operation and a verification operation based on the ISPP technique. The program loop turn detector 160 and the comparator 170 may be circuits for determining whether a memory cell to be programmed, a string selection transistor, or both are abnormally slow cells or abnormally fast cells. In other embodiments, the program loop turn detector 160 and the comparator 170 may be omitted.
The control logic 180 may determine whether to terminate or continue a program operation according to the pass/fail result transmitted from the pass/fail verification circuit 150. When the fail result is received from the pass/fail verification circuit 150, the control logic 180 may cause a voltage generator (not shown) to generate a program voltage Vpgm increased by ΔVISPP and a verification voltage Vvfy and a page buffer 130 to proceed a follow-up program loop. On the contrary, when the control logic 180 receives the pass result, a program operation on selected memory cells will be terminated.
In various designs, the control logic 180 may be integrated on the same chip with the memory cell array 110. However, embodiments of the present disclosure are not limited thereto. In an embodiment, the control logic 180 may be implemented in a different chip from the memory cell array 110. For example, as in a solid state drive (SSD), the control logic 180 may be provided at a flash translation layer (FTL), which is an independent chip separated from the memory cell array 110.
Furthermore, although the pass/fail verification circuit 150, the program loop turn detector 160, and the comparator 170 are configured to be separate elements from the control logic 180 as shown in FIG. 1, the present disclosure is not limited thereto. For example, at least one of the pass/fail verification circuit 150, the program loop turn detector 160, and the comparator 170 may be implemented as software or hardware in the control logic 180. Furthermore, at least one of the pass/fail verification circuit 150, the program loop turn detector 160, and the comparator 170 may be omitted or another circuit component may be added.
FIGS. 2A and 2B are perspective views showing 3D non-volatile memory devices 100A and 100B respectively including memory cell arrays (e.g., the memory cell array 110 of FIG. 1) in accordance with various embodiments of the present disclosure.
Referring to FIG. 2A, the 3D non-volatile memory device 100A may include memory cells that are arranged by being aligned in a first direction (e.g., x-axis direction), a second direction (e.g., y-axis direction), and in a third direction (e.g., z-axis direction). Both of the first and second directions are parallel to a main surface Sa of a substrate SS, and the third direction is perpendicular to the main surface Sa of the substrate SS. The substrate SS may be one of a semiconductor substrate, such as a Si monocrystalline substrate, a compound semiconductor substrate, a SOI substrate, and a strained substrate, but embodiments are not limited thereto. The substrate SS may also be a ceramic substrate, a polymer substrate or a fabric layer for implementing a flexible device.
The first direction and the second direction may be orthogonal to each other. To form the above-described memory cells, a plurality of memory layers L1 to Ln are stacked by interposing interlayer insulation layers IL therebetween. Each of the plurality of memory layers L1 to Ln may include a plurality of channel lines that respectively extend in the x-axis direction and adjacent channel line are separated from each other at a predetermined distance in the y-axis direction. In accordance with an embodiment, the plurality of channel lines may be semiconductor material layers, each having a line shape. In the semiconductor material layers, suitable impurity regions may be formed to provide source/drain regions of one or more dummy string selection transistor, string selection transistors, memory cell transistors, or ground selection transistors which will be described below. However, embodiments of the present disclosure are not limited thereto. For example, the memory cell transistors may be junctionless or junction-free memory cell transistors. In this case, impurity regions for forming junctions between memory cells adjacent to each other may be omitted.
The semiconductor material layer may contain a suitable n-type polysilicon, a polysilicon, or a p-type polysilicon according to a memory cell arrays architecture, such as a bit cost scalable (BiCs) structure, a vertical-recess-array-transistor (VRAT) structure, or a terabit cell array transistor (TCAT) structure. In accordance with another embodiment, the channel lines may be formed of a monocrystalline silicon, a compound semiconductor, a carbon-based material, a polymer material, or any of various other suitable channel materials other than conventional semiconductor materials.
Bitlines BL may be coupled with first ends of the plurality of channel lines, respectively. One bitline may be coupled with first ends of corresponding channel lines of the memory layers L1 to Ln, and the corresponding channel lines are arranged in the z-axis direction to share the coupled bitline, and the sharing of the bitline by the channel lines can be secured via an interlayer conductive member, such as a via plug CP.
Common source lines CSL may be respectively connected to second ends of the plurality of channel lines. The common source lines CSL electrically connected to the second ends of the plurality of channel lines may be patterned to have a shape including steps, and a predetermined bias may be independently applied to a selected semiconductor layer by forming contact plugs (not shown) that contact respective steps of the common source lines CSL.
A plurality of wordlines WL may each extend in the y-axis direction and the z-axis direction, and adjacent wordlines WL are separated with each other at a predetermined distance in the x-axis direction. The plurality of wordlines WL may intersect with the plurality of channel lines in respective memory layers L1 to Ln to be shared by memory cells in the y-axis direction in the respective memory layers L1 to Ln. In this case, conductive layers constituting the plurality of wordlines WL may intersect with the plurality of channel lines, and data storage layers for storing data may be interposed between the conductive layers and the plurality of channel lines. The conductive layers may have a gate all around structure for surrounding the data storage layers, or a double gate structure for passing over the data storage layers.
In accordance with an embodiment, each of the plurality of memory cells may include a charge storage layer, such as a floating gate or a charge trapping layer which may be insulated from a corresponding channel line and a corresponding wordline respectively via a tunnel insulation layer and a blocking insulation layer. The charge storage layer may function as a data storage layer. For example, each of the plurality of memory cells having the charge trapping layer may have any one of a polysilicon-silicon dioxide-silicon nitride-silicon dioxide-silicon (SONOS) structure, a polysilicon-alumina-silicon nitride-silicon dioxide-silicon (SANOS) structure, a tantalum or titanium nitride-alumina-silicon nitride-silicon dioxide-silicon (TANOS), a metal-alumina-silicon nitride-silicon dioxide-silicon (MANOS) structure, or a metal-alumina-silicon nitride-band engineered oxide-silicon (Be-MANOS) structure, and each of the plurality of memory cells may be stacked in an order of a gate electrode, a blocking insulation layer, a charge trapping layer, a tunnel insulation layer, and a substrate. However, they are merely examples, and the charge trapping layer is not limited to a silicon nitride layer and may be formed of various other suitable candidate materials, for example, oxides of other transition metals or composite structures including structures having dispersed therein nano-crystals.
The conductive layers constituting the wordlines WL may extend onto the blocking insulation layer formed on the charge trapping layer. The plurality of memory cells may be electrically connected in series, and constitute memory strings. Although the 3D non-volatile memory devices 100A of FIG. 2A includes 10 wordlines WL1 to WL10, it is merely an example, and a number of the wordlines WL may be the same as a number of memory cells included in a single string, e.g., 32 or 64.
In accordance with an embodiment, the 3D non-volatile memory device 100A may include two or more string selection transistors formed at each of the channel lines. In accordance with an embodiment, the string selection transistors may be multi-level transistors that have a plurality of programmable states respectively corresponding to a plurality of threshold values (or threshold voltages). In accordance with an embodiment, the string selection transistors may be formed of the same material, and also may have substantially the same structure as that of the memory cells.
FIG. 2A shows that three string selection transistors are provided for each single channel line and four string selection lines SSL1, SSL2, and SSL3 each extend in the y-axis and z-axis directions and adjacent string selection lines are separated from each other at a predetermined distance. As a result, each of the string selection lines SSL1, SSL2, and SSL3 may be coupled with a corresponding plurality of string selection transistors that are arranged in a y-z plane. Similarly to the wordlines WL, the string selection lines SSL1, SSL2, and SSL3 may have a structure surrounding data storage layers or extending over the data storage layers for controlling threshold values of the string selection transistors formed on the plurality of channel lines.
Although the three string selection lines SSL1, SSL2, and SSL3 are shown in FIG. 2A, the number of string selection lines SSL is not limited thereto. The number of string selection lines SSL may be determined to allow independent selection of each of the memory layers L1 to Ln according to any combination of the number of the memory layers L1 to Ln and threshold values of the string selection transistors coupled with string selection lines SSL. Detailed descriptions thereof will be given below.
The string selection lines SSL1, SSL2, and SSL3 may pass across a plurality of memory layers L1 to Ln, where each of the string selection lines SSL1, SSL2, and SSL3 may be coupled in common with string selection transistors which are stacked in the z-axis direction and arranged in the y-axis direction (or are arranged in y-z planes), and control the string selection transistors to program or erase selected string selection transistors. In addition, after the string selection transistors are completely initialized, the string selection lines SSL1, SSL2, and SSL3 may be driven to select memory layers L1 to Ln by turning on or off the string selection transistors arranged in the first direction (the x-axis direction) during the operations on the memory cells. In an embodiment, the string selection lines SSL1, SSL2, and SSL3 may be arranged between first ends of memory strings coupled with the bitlines BL and the first wordline WL1.
One or more dummy string selection lines DSSL may be provided between the first string selection line SSL1 and the bitline BL. The dummy string selection line DSSL may be coupled with a gate electrode of a dummy string selection transistor DSST arranged at the channel line. The dummy string selection line DSSL may be provided for bit selection during a programming operation for initializing the string selection transistors. After the string selection transistors are completely initialized, the dummy string selection transistor DSST may be programmed to function as another string selection transistor. Detailed descriptions thereof will be given below.
A ground selection line GSL may be disposed between the wordlines WL and the common source lines CSL. The ground selection line GSL passes across the plurality of memory layers L1 to Ln, where the ground selection line GSL may be coupled in common with ground select transistors stacked in the z-axis direction and arranged in the y-axis direction (or in y-z planes), to turn on or off the ground select transistors.
Referring to FIG. 2B, in accordance with an embodiment, the 3D non-volatile memory device 100B may include memory cells that are arranged in a first direction (e.g., an x-axis direction) and a second direction (e.g., a y-axis direction), and in a third direction (e.g., z-axis direction). Both of the x-axis direction and the y-axis direction are parallel to a main surface Sa of a substrate SS, and the z-axis direction is perpendicular to the main surface Sa of the substrate SS. The above descriptions on the string selection lines SSL, dummy string selection lines DSSL, wordlines WL, and ground selection lines GSL of the 3D non-volatile memory device 100A of FIG. 2A may be similar to those of the 3D non-volatile memory device 100B as long as there is no contradiction therebetween.
The 3D non-volatile memory device 100B may include one or more dummy string selection lines DSSL, a plurality of string selection lines SSL, a plurality of wordlines, and a ground selection line GSL, which intersect with a plurality of channel lines from first ends to second ends of the plurality of channel lines.
In the 3D non-volatile memory device 100B, a semiconductor body SB may be coupled with a common source line CSL. Although, in the embodiment of FIG. 2B, the ground selection line GSL, the common source line CSL, and the semiconductor body SB are sequentially arranged in the x-direction, it is merely an example, and, in another embodiment, the ground selection line GSL, the semiconductor body SB, and the common source line CSL are sequentially arranged in the x-direction. The common source lines CSL may be also patterned to have a stair shape including steps, and contact plugs (not shown) contacting the respective steps are formed as described in FIG. 2A to apply a bias independently to a selected memory layer.
FIG. 3 is a flowchart 300 showing a method of initializing string selection transistors of a 3D non-volatile memory device in accordance with an embodiment the present disclosure, and FIGS. 4A to 4I are circuit diagrams sequentially showing a process of initializing string selection transistors SST and a dummy string selection transistor DSST of a 3D non-volatile memory device 100 in accordance with an embodiment of the present disclosure. FIG. 5A illustrates a distribution of threshold values of string selection transistors determined in operation S20 in accordance with embodiments of the present disclosure, FIG. 5B is a timing diagram showing states of biases applied to a 3D non-volatile memory device in operations S40a and S40b, FIG. 5C is a timing diagram showing states of biases applied to a 3D non-volatile memory device in an operation S50, and FIGS. 5D through 5F are diagrams showing various profiles of an erase voltage for initializing the dummy string selection transistor DSST.
Referring to FIGS. 3 and 4A, an erase operation may be performed with respect to all of memory layers L1, L2, and L3 or any one selected memory layer (operation S10). FIG. 4A shows an example in which an erase operation is performed with respect to a selected memory layer L1. In an example, to select memory layer L1, an erase voltage signal Vers may be applied to channel lines of the memory layer L1 via a common wire line, e.g., a common source line CSL1, and all bitlines BL1, BL2, and BL3 may be floated. In this case, all of wordlines WL1 to Wln may be floated or grounded. A dummy string selection line DSSL may also be floated. In accordance with an embodiment, if the wordlines WL1 to WLn are grounded, string selection lines SSL1, SSL, and SSL3 and all memory cells may be erased. The erasing of the memory cells may replace an erase operation required during an operation for programming screen transistors described below.
Because the string selection lines SSL1, SSL2, and SSL3 are grounded, an erase operation on the plurality of string selection transistors SST may be performed. In an embodiment, the erase operation on the string selection transistors SST may be performed using an incremental step pulse erase (ISPE) scheme by applying voltage signals Vers in the form of serially incremental erase pulses and then performing an verification operation for determining whether the erase operation on the string selection transistors SST has been properly performed after application of each erase pulse, such that threshold values (or threshold voltages) of the string selection transistors SST have an predetermined erase distribution. If the erase operation is successfully completed, the threshold values of the string selection transistors SST may be smaller than or equal to 0 V.
In an embodiment, the erase operation may be performed using a program before erase (PBE) technique. When the PBE technique is activated, the 3D non-volatile memory device 100 may program all the string selection transistors SST coupled with the string selection lines SSL1, SSL2, and SSL3 and included in the memory layer L1 to have the same state. Specifically, the string selection transistors SST coupled with the string selection lines SSL1, SSL2, and SSL3 in the memory layer L1 may have substantially the same threshold voltage. Dummy string selection transistors DSST coupled with the dummy string selection line (DSSL) may not be programmed. Next, an erase operation as described above may be initiated with respect to the programmed string selection transistors SST. Furthermore, if desirable, to further sharpen an erase distribution of the string selection transistors SST, a soft program may be additionally performed on the strongly-erased string selection transistors SST.
Next, referring to FIG. 3, at S20 (referred to hereinafter as a first programming operation), string selection transistors coupled with a selected string selection line of a selected memory layer are programmed to have one or more target states Vthr by applying a program voltage thereto. FIG. 4B shows an example in which the selected memory layer is the first memory layer L1, a first string selection line SSL1 is selected, and string selection transistors SST1L of the selected memory layer L1 that are coupled with the selected string selection line SSL1 and arranged in a second direction (e.g., a y-axis direction) are programmed by applying a program voltage Vpgm to the string selection line SSL1.
In this case, a first program pulse of an initial program loop, e.g., a voltage pulse having a level in a range from about 10 V to about 14 V, may be applied to the string selection line SSL1, and then a second program loop may be performed by applying a second program voltage Vpgm increased by a predetermined value ΔVISPP, e.g., in a range from about 0.2 V to about 1 V, to the string selection line SSL1. In subsequent program loops, the program voltage Vpgm pulse is continuously increased by the predetermined value ΔVISPP as a number of the program loops increases, the increased voltage pulse will be repeatedly applied to the selected string selection line SSL1.
Referring back to FIG. 3, at S30, in the program loops, a verification operation for determining whether threshold values of the programmed string selection transistors SST1L reach a target value (or a target threshold voltage) Vthr by applying a verification voltage (e.g., the verification voltage Vvfy of FIG. 4C) to the string selection line SSL1 after the first program operation is performed. By performing the verification operation S30, programmed string selection transistors and unprogrammed string selection transistors may be detected. The verification operation S30 may be performed in combination with a coarse-fine sensing scheme or a fine-sensing scheme. However, embodiments of the present disclosure are not limited thereto.
If it is determined in the verification operation S30 that the programmed string selection transistor SST1L coupled with the string selection line SSL1 have reached the target threshold voltage Vthr, a program inhibition may be performed on the string selection transistor SST1L determined as having reached the target threshold voltage, and the determined string selection transistor may be excluded in a subsequent program loop. If not, a next program loop may be performed by applying a program voltage increased by the predetermined value ΔVISPP to the string selection transistor SST1L determined as not having reached the target voltage.
In an embodiment, a sensing circuit (not shown) of the page buffer (e.g., the page buffer 130 of FIG. 1) may detect an ON/OFF state of a selected string selection transistor SST1L via a bitline of the string selection transistor SST1L and provide a detected result to the pass/fail verification circuit 150 of FIG., and thus the verification operation S30 may be performed.
FIG. 4C illustrates performing the verification operation S30 of FIG. 3 on the string selection transistors arranged in a second direction (e.g., the y-axis direction) of the selected memory layer L1. A sensing voltage Va, e.g., 0.7 V, is applied to the bitlines BL1 to BL3 to pre-charge channel lines. The sensing voltage Va may be used for pre-charging capacitive components (e.g., parasitic capacitance) of the bitlines BL.
A pass voltage Vpass, for example, a power voltage Vdd may be applied to the dummy string selection transistors DSST via the dummy string selection line DSSL, such that the dummy string selection transistors DSST function as pass transistors. A suitable pass voltage Vpass may be applied to the other unselected string selection lines SSL2 and SSL3 and the wordlines WL1 to WLn. The pass voltage Vpass may be applied to the ground source line GSL to turn on a ground select transistor GST.
In an embodiment, to perform the verification operation S30 of FIG. 3 on the selected memory layer L1, a voltage having a level substantially equal to the sensing voltage Va may be applied to common source lines CSL2 and CSL3 of the unselected memory layers L2 and L3, thereby preventing a current from flowing through the channel lines in the unselected memory layer L2 and L3. The common source line CSL1 of the selected memory layer L1 may be grounded.
In the operation S30, in the selected memory layer L1, a first plurality of string selection transistors that have been programmed to reach a target state (corresponding to a target threshold voltage) and a second plurality of string selection transistors that have not reached the target state may be determined. For example, in a subsequent process, an electric potential of a bitline coupled with a programmed string selection transistor may become 0 V, whereas an electric potential of a bitline coupled with an unprogrammed string selection transistor may become an operation voltage Vcc. As a result, a screening transistor may be programmed by using different electric potentials as will be described below.
FIG. 5A shows a distribution K of threshold values Vthr of the string selection transistors coupled with the selected string selection line SSL1. A first portion of the distribution related to unprogrammed string selection transistors UPSST of FIG. 4C having a threshold value Vthr smaller than the verification voltage Vvfy may be shown in the left region A. A second portion of the distribution related to programmed string selection transistors PSST of FIG. 4C having a threshold value Vthr greater than the verification voltage Vvfy may be shown in the right region B.
The programmed string selection transistors PSST of FIG. 4C distributed in the right region B of FIG. 5A may be excluded in a next program loop using the ISPP technique as described above. Instead, the next program loop may be performed on the unprogrammed string selection transistors UPSST of FIG. 4C, such that a program voltage increased by a predetermined value ΔVISPP may be applied to the unprogrammed string selection transistors UPSST.
Referring to FIG. 4D, the unprogrammed string selection transistor UPSST, which has been determined as such by the operation S30 and is coupled with the string selection line SSL1, is indicated by a dotted line circle, whereas the programmed string selection transistors PSST are indicated by solid line circles. A ground voltage or a voltage higher than the ground voltage, e.g., a common collector voltage Vcc, may be applied to the common source lines CSL1, CSL2, and CSL3 of the memory layers L1, L2, and L3, a voltage equal to or higher than the common collector voltage Vcc may be applied to the bitline BL1 coupled with the unprogrammed string selection transistor UPSST, and the common collector voltage Vcc may be applied to the dummy string selection line DSSL, thereby inducing a channel potential boost for program inhibition at a memory string STR′ coupled with the unprogrammed string selection transistor UPSST. The ground voltage may be applied to bitlines BL2 and BL3 coupled with the programmed string selection transistors PSST, and thus corresponding channel lines are grounded. The common ground line GSL may be grounded to turn off common ground transistors GST.
Next, a program voltage Vpgm is applied to a wordline WLx selected from among the wordlines WL1 to WLn. The pass voltage Vpass may be applied to the string selection lines SSL1, SSL2, and SSL3 and the other wordlines WL1 to WLx−1 and WLx+1 to WLn, such that the string selection transistors SST and the memory cells MCT coupled to the other wordlines WL1 to WLx−1 and WLx+1 to WLn function as pass transistors. At S40a of FIG. 3, memory cells PMCT of FIG. 4D coupled with memory strings, which include the programmed string selection transistors PSST and grounded channel lines, may be selectively programmed by a program voltage Vpgm to have a predetermined threshold value. In a next program loop, the programmed memory cells PMCT may function as screening switches (or screening transistors) to exclude the already programmed string selection transistors PSST from the next program loop. In this regard, the threshold value of the programed memory cells PMCT may be any value suitable for the programmed memory cells PMCT to function as ON/OFF switches. In the present disclosure, the operation for programming the memory cells PMCT is referred to as an operation for programming screening transistors.
In contrast, at S40b of FIG. 3, the common collector voltage Vcc is applied to the string STR′, and thus a dummy string selection transistor DSST coupled to the string STR′ is turned off, and a corresponding channel line becomes floated. An electric potential of the channel line of the memory string STR′, which is capacitively coupled with a gate voltage applied to the wordline WLx, may be automatically boosted from a level corresponding to a difference between the common collector voltage Vcc and a threshold voltage Vth of a string selection transistor to a boosting voltage in a range from about 7 V to about 10 V, and thus programming of one or more of memory cells IMCT coupled to the string STR′ may be inhibited at S40b of FIG. 3. A hatched region BS indicates that a corresponding channel line has a boosted electric potential. Each of the memory cells IMCT indicated by a dotted line circle corresponds to a program-inhibited memory cell.
FIG. 4D shows an example that the memory cell transistors PMCT coupled with any one of the wordlines, e.g., a wordline WLx are used as screening transistors. Thus, a degree of integration of a 3D non-volatile memory device 100 may be increased compared to a non-volatile memory device including additional transistors that function as the screening transistors.
According to an embodiment shown in FIG. 4E, an uppermost wordline WLn that is adjacent to the common ground line GSL may be coupled to memory cell transistors PMCT that functions as the screening transistors.
In another embodiment also shown in FIG. 4E, a 3D non-volatile memory device 100′ may include a plurality of wordlines WL1 to WLn−1 and a dummy ground line DMGL disposed between an uppermost wordline WLn−1 and a common ground line GSL, and utilize a dummy transistor coupled with the dummy ground line DMGL as the screening transistor. In this case, the dummy transistor may be programmed by applying a program voltage Vpgm to the dummy ground line DMGL.
Referring to FIG. 5B, waveforms of signals for selectively programming one or more of screening transistors of a 3D non-volatile memory device are illustrated. The reference character BL1 denotes a bitline to which a common source voltage Vcc is applied for program inhibition, and the reference characters BL2 and BL3 denote bitlines to which a ground voltage GROUND is applied for programming the one or more screening transistors. In the embodiment shown in FIG. 5B, transistors coupled with a wordline WLx may be programmed to function as screening transistors. However, embodiments of the present disclosure are not limited thereto. As described above, transistors that are coupled with a dummy ground line (e.g., the dummy ground line DMGL of FIG. 4E), instead of the wordline WLx, may be programmed to function as screening transistors. In this case, a program voltage Vpgm may be applied to the dummy ground line DMGL, thereby programming the screening transistors.
Next, referring back to FIG. 4F, to select the first memory layer L1 including the unprogrammed string selection transistors UPSST, the common source line CSL1 of the selected memory layer L1 is grounded, a common collector voltage Vcc is applied to other common source lines CSL2 and CSL3 of the unselected memory layers L2 and L3, a power voltage (e.g., the common collector voltage Vcc) is applied to the common ground line GSL, and the common collector voltage Vcc, for example, is applied to the bitlines BL1, BL2, and BL3, thereby electrically floating memory strings of the unselected memory layers L2 and L3.
Next, a voltage (e.g., a read-out voltage Vread or the common collector voltage Vcc) smaller than a threshold voltage Vth of a programmed memory cell transistor PMCT (that is, a screening transistor), is applied to the wordline WLx, thereby turning the programmed memory cell transistors PMCT off and turning unprogrammed screening transistors IMCT on. Here, at S50 of FIG. 3, when a program voltage Vpgm, e.g., a program pulse increased by ΔVISPP using the ISPP technique, is applied to the string selection line SSL1, channel lines of memory strings STR′ coupled with the unprogrammed string selection transistors UPSST are grounded, and thus the unprogrammed string selection transistors UPSST are programmed to a target value.
On the other hand, the programmed memory cell transistors PMCT are turned off and channel lines of corresponding memory strings other than the memory string STR′ are electrically floated. Thus, electrical potentials at these channel lines are boosted, and the programmed string selection transistors PSST are program-inhibited. Furthermore, memory strings of the unselected memory layers L2 and L3 are program-inhibited due to the common collector voltage Vcc applied to the common ground lines CSL2 and CSL3, regardless of whether memory cells coupled with the wordline WLx are turned on or off.
Waveforms of signals shown in FIG. 5C may correspond to the above-described bias states. Any bias voltage may be applied to the bitlines BL1, BL2, and BL3. As described above, if the dummy ground line DMGL (e.g., the dummy ground line DMGL of FIG. 4E) is provided, the common collector voltage Vcc may be applied to the dummy ground line DMGL. Therefore, as shown in FIG. 4E, the programmed string selection transistors PSST of the selected memory layer L1 may be program-inhibited due to the bias voltages applied to the common source lines CSL1, CSL2, and CSL3.
Referring back to FIG. 3, according to the above-described embodiments, the programming operation S20, the verification operation S30, the operations S40a and S40b for selectively programming memory cells to make the programmed memory cells function as screening memory cells, and the operation S50 for programming unprogrammed string selection transistors by using the screening memory cells, are performed on string selection transistors coupled with the selected string selection line (or a first string selection line) SSL1 of the selected memory layer (or a first memory layer) L1 using the ISPP technique. Thus, initialization of the string selection transistors coupled with the selected string selection line SSL1 and included in the selected memory layer L1 may be completed.
In the above-described embodiment, like memory cells constituting a page, string selection transistors arranged in a second direction (e.g., the y-axis direction of FIG. 4F) have the same program state corresponding to a target value (or a target threshold voltage) in the same program cycle, but embodiments of the present disclosure are not limited thereto. For example, in a single program cycle, a plurality of string selection transistors may be programmed to have different states, for example, a first program state, a second program state, and a third program state. Furthermore, according to another embodiment, having single level select transistors having an interleaved architecture, even-numbered cells and odd-numbered cells may constitute two pages different from each other. In an embodiment having multi-level transistors, since each transistor stores one least significant bit (LSB) and one most significant bit (MSB) like a memory cell, the MLC transistor has four pages. For example, in such an embodiment, MSB pages and LSB pages may be provided on even-numbered bitlines and odd-numbered bitlines, respectively.
As described above, when initialization of string selection transistors coupled with the selected string selection line SSL1 of the selected memory layer L1 is completed, string selection transistors coupled with a second string selection line SSL2 adjacent to the first string selection line SSL1 may be sequentially performed. When initialization of all of the selection transistors included in the selected memory layer L1 is completed, initialization of the dummy string selection transistor DSST of the selected memory layer L1 may be performed according to the method of initializing the dummy string selection transistors DSST as described below.
When initialization of the dummy string selection transistor DSST included in the first memory layer L1 is completed, a processes for initializing the string selection transistors SST and the dummy string selection transistor DSST included in a second and third memory layers L2 and L3 may be sequentially performed in the same way of the initialization process on selected first memory layer L1 as described above. Thus, the initialization of the string selection transistors SST and the dummy string selection transistors DSST of the 3D non-volatile memory device 100 may be completed.
In another embodiment, the initialization of the dummy string selection transistor DSST may be separately performed after the initialization of the string selection transistors SST of all of the memory layers L1, L2, and L3 is completed. In this case, the initialization of dummy string selection transistors DSST of the respective memory layers L1, L2, and L3 may be implemented by selecting a memory layer among the memory layers L1, L2 and L3, and then, programming dummy string selection transistors DSST in the selected memory layer to have a target value.
As described above, when threshold values of all of the string selection transistors SST and the dummy string selection transistors DSST of the memory layers L1, L2, and L3 has been set to have predetermined target values, the combination of the programmed dummy string selection transistors DSST and the string selection transistors SST may be utilized to enable selection of a memory layer among the memory layers L1, L2, and L3 without incurring a disturbance of the other unselected memory layers according to a LSM technique. In this case, a program operation, a read operation, or an erase operation may be performed on a selected memory cell in the selected memory layer by using an addressing method identical with or similar to a 2-dimensional memory cell array in the related art.
Hereinafter, a method of programming dummy string selection transistors DSST, that is performed after threshold values of string selection transistors SST have been set, will be described.
Referring back to FIG. 3, when programming of the string selection transistors SST has been completed, an initial levelling operation S60 for programming threshold values of the dummy string selection transistors DSST to a predetermined target level may be performed. In an embodiment, the initial levelling operation may be simultaneously performed with regard to the plurality of memory layers L1, L2, and L3. Referring to FIG. 4G, a bias state for simultaneously performing initial levelling operations with regard to the dummy string selection transistors DSST of all of the memory layers L1, L2, and L3 is described.
In an embodiment, a programming operation of the dummy string selection transistors DSST may be performed by using the Fowler-Nordheim tunnelling technique with respect to charge trap layers of the dummy string selection transistors DSST. In this way, the dummy string selection transistors DSST may be programmed, such that the threshold values of the dummy string selection transistors DSST have a predetermined target level.
In an embodiment, the initial levelling operation for programming the dummy string selection transistors DSST to a predetermined target level may be performed by grounding all of the bitlines BL1, BL2, and BL3, applying a high program voltage Vpgm, e.g., from about 20 V to about 25 V, to the dummy string selection line DSSL, and grounding the ground selection line GSL. The common source lines CSL1, CSL2, and CSL3 may be grounded. During the initial levelling operation, weak pass voltages Vpass (e.g., from about 8 V to about 10 V) may be applied to string selection lines SSL1, SSL2, and SSL3 and wordlines WL1 to WLn, such that the string selection transistors SST and memory cell transistors MCT disposed in the channel lines become pass transistors.
After the initial levelling operation, the dummy string selection transistor DSST may be set to have a predetermined threshold value by applying an erase voltage signal to the common source line of a memory layer selected from among initially-levelled memory layers. FIG. 4H shows that an erase voltage signal Vers is applied to the common source line CSL1 of the first memory layer L1. As shown in FIG. 4H, a suitable voltage signal for preventing erase inhibition or programming disturbance may be applied to the common source lines CSL2 and CSL3 of the unselected memory layers L2 and L3. In other embodiment, the common source lines CSL2 and CSL3 of the unselected memory layers L2 and L3 may be grounded.
In an embodiment, the erase voltage signal Vers may be an erase voltage signal having a level suitably selected based on a target threshold value for the dummy string selection transistor DSST to function as an additional string selection transistor together with the string selection transistors SST. FIG. 5D illustrates erase voltage signals Vers1, Vers2, Vers3, and Vers4, each having four different levels. While the erase voltage signal Vers is being applied, the bitlines BL1, BL2, and BL3 may be electrically floated and the dummy string selection line DSSL may be grounded, as shown in FIG. 4H.
Wordlines WL1 to WLn coupled with the respective memory cell transistors MCT may be grounded or electrically floated. When the wordlines WL are grounded, erase operations may occur at the respective memory cell transistors MCT. When the wordlines WL1 to WLn are floated, potentials of the floated wordlines WL1 to WLn may increase due to capacitive coupling between the floated wordlines WL1 to WLn and corresponding channel lines, and thus erase inhibition may be induced to the coupled memory cell transistors MCT. Furthermore, while a time varying erase voltage signal Vers is being applied, the ground selection line GSL may be floated.
Since the dummy string selection line DSSL is shared by a plurality of the memory layers L1, L2 and L3, an unwanted programming operation, i.e., a programming disturbance may occur at another already-initialized dummy string selection transistor at an unselected memory layer due to potential of the dummy string selection line DSSL. To address the programming disturbance, a voltage signal Vinhibit for erase inhibition, e.g., a voltage of about 10 V that is smaller than the maximum value of the erase voltage signal, may be applied to the respective common source lines CSL2 and CSL3 of the unselected memory layers L2 and L3.
Since the voltage signal for erase inhibition may induce a gate-induced-drain-leakage (GIDL) at the common source lines CSL2 and CSL3 of an unselected memory layer L2 and L3, the programming disturbance may be more suppressed as an erase inhibition voltage increases. However, excessive channel potential may induce soft erase of the string selection transistors SST of the unselected layers L2 and L3. Therefore, a suitable voltage signal Vinhibit for erase inhibition may be determined by considering the channel potential of channel lines of the unselected layers L2 and L3.
In another embodiment, as shown in FIGS. 5E and 5F, the erase voltage signal Vers (hereinafter referred to as a time varying erased voltage signal) may be a voltage signal having a time varying section. The time varying erase voltage signal Vers may be a first ramping erase voltage signal RVS1 having an increasing ramp section as shown in FIG. 5E, or a second ramping erase voltage signal RVS2 having a decreasing ramp section as shown in FIG. 5F. While the time varying erased voltage signal Vers is being applied, a row decoder (e.g., the row decoder 120 of FIG. 1) may control a dummy string selection line DSSL of a selected memory layer in order to change states of the dummy string selection transistors DSST coupled with the dummy string selection line DSSL during a time interval of the time varying section, that is, to set threshold voltages of the dummy string selection transistors DSST.
The controlling of the dummy string selection line DSSL includes controlling erase state of the dummy string selection transistors DSST, such that each of the dummy string selection transistors DSST may have a suitable threshold value. For example, referring to FIGS. 4H and 5E, when a ramping erase voltage signal Vers having a time varying section in an increasing mode is applied to the common source line CSL1 of the selected memory layer L1, and for example, the initially-grounded dummy string selection line DSSL is floated at any time point T, e.g., time points T1, T2, T3, and T4 within the time varying section of the ramping erase voltage signal Vers, operation for erasing the dummy string selection transistors DSST that are coupled in the y-axis direction by the dummy string selection line DSSL may be terminated at the corresponding floating time point T. As a result, threshold values (or threshold voltages) Vth of the dummy string selection transistors DSST may be set to a predetermined value. For example, when the dummy string selection line DSSL is floated at any one of the time points T1, T2, T3, and T4, the dummy string selection transistors DSST may be sequentially set to any of threshold values including 3 V, 1 V, −1 V, and −3 V according to the erased degree based on the time points.
Although the time varying section of the ramping erase voltage signal RVS1 of FIG. 5E shows profiles of increasing linearly with time, the present disclosure is not limited thereto. For example, the time varying section may have a signal profile having one or more steps that discretely increase, a curved (e.g., non-linear) profile that continuously increases, or a combination thereof.
In another embodiment, referring to FIGS. 4H and 5F, when a erase voltage signal RVS2 having an decreasing ramp section is applied to the common source line CSL1 of the selected memory layer L1, and, for example, the initially-floated dummy string selection line DSSL may be grounded at any time point, for example, time points T1, T2, T3, and T4, within the time varying section, an operation for erasing the dummy string selection transistors DSST coupled in the y-axis direction with the dummy string selection line DSSL are initiated at the time point. As a result, threshold values (or threshold voltages) Vth of the dummy string selection transistors DSST may be set to any of threshold values, for example, −3 V, −1 V, 1 V, and 3 V.
Although the time varying section of the ramping erase voltage signal RVS2 of FIG. 5F shows profiles of decreasing linearly with time, the present disclosure is not limited thereto. For example, the time varying section may have a signal profile having one or more steps that discretely decrease, a curved (e.g., non-linear) profile that continuously decreases, or a combination thereof. For example, the time varying section may have a signal profile in which a linearly increasing or decreasing profile and discretely increasing or decreasing step profile successively appear may be applied.
Although the time varying erase voltage signal Vers having a time varying section in an increasing mode or a decreasing mode as shown in FIGS. 5E and 5F have four time points, there are merely examples. A suitable floating time point or a suitable grounding time point may be selected based on a threshold value required for a dummy string selection transistor of each of memory layers for selecting a memory layer. As described above, when the erase voltage signal Vers is applied via the common source line CSL1, erase degree of the dummy string selection transistors DSST having an initially-set program levels may be controlled by controlling the dummy string selection line DSSL in the time varying section, thereby setting the dummy string selection transistors DSST arranged in the y-direction within a selected memory layer to have a predetermined threshold value.
After setting the states (that is, threshold values) of the dummy string selection transistors DSST included in the memory layer L1 have been set, dummy string selection transistors DSST of the other memory layers L2 and L3 may be set in the same way to the memory layer L1, and therefore the 3D non-volatile memory device 100 may be completely initialized. FIG. 4I illustrates a bias state for setting states of dummy string selection transistors of the memory layer L2, wherein the dummy string selection line DSSL is grounded at the beginning of a time varying section of the erase voltage signal Vers applied to the common source line CSL2 and the dummy string selection line DSSL is floated at a time T during the time varying section of the erase voltage signal Vers, the time T being selected according to a desired threshold value.
As described above, when all of threshold values of string selection transistors SST and the dummy string selection transistors DSST of the memory layers L1, L2, and L3 are set to target threshold values, a memory layer may be selected, and a program operation, a read operation, or an erase operation may be performed to an addressed memory cell of the selected memory layer without an disturbance of the other unselected layers by using a method identical or similar to a 2D memory cell addressing method in the related art.
FIG. 6A is a circuit diagram illustrating a non-volatile memory device 200 including string selection transistors and dummy selection transistors initialized in accordance with an embodiment of the present disclosure, FIG. 6B is a graph showing measured transfer characteristics of dummy string selection transistors and string selection transistors initialized to multi levels in accordance with an embodiment of the present disclosure, and FIG. 6C is a graph showing measured transfer characteristics of a programmed memory cell C1 of a selected memory layer, an unselected and inhibited memory cell C2 of the selected memory layer, unselected and inhibited memory cells C3 of an unselected memory layer and erased memory cell C4 of an unselected memory layer.
Each of first and second memory layers L1 and L2 of the non-volatile memory device 200 of FIG. 6A in accordance with an embodiment may be selected by a multi-level operation scheme. Specifically, a layer selection by multilevel scheme (LSM) is performed such that a memory layer in which all the string selection transistors are turned on may be selected, whereas another memory layer in which even one of string selection transistors is turned off may be unselected. Referring to FIG. 6A, numbers 1, 2, 3, and 4 allocated to each of the dummy string selection transistor DSST and the three string selection transistor SST indicate states corresponding to respective threshold values of the dummy string selection transistor DSST and the three string selection transistor SST. For example, states of the dummy string selection transistors DSST and three string selection transistors SST indicated by the numbers 1, 2, 3, and 4 may respectively correspond to −1 V, 1 V, 3 V, and 5 V of the threshold values Vth as shown in Table 1. Voltages V2, V3, V1, and V4 shown in FIG. 6B respectively allocated to the dummy string selection line DSSL, and string selection lines SSL1, SSL2, and SSL3 of FIG. 6A, indicate values of voltages applied to the dummy string selection line DSSL and respective string selection lines SSL1, SSL2, and SSL3 for selecting a memory layer L2. The Curves CE, P1, P2 and P3 of the measured transfer characterstics of dummy selection transistor DSST and string select transistors SST correspond to states 4, 1, 2 and 3, respectively. Table 1 exemplifies a case where the voltages V2, V3, V1, and V4 are applied to the string selection lines DSSL, SSL1, SSL2, and SSL3. Here, the values of the voltages V1, V2, V3 and V4 are indicated by arrows a1, a2, a3, and a4 shown in FIG. 6B, respectively.














TABLE 1







SST
Vth of DSST







Status
or SSTs
DSSL
SSL1
SSL2
SSL3









1
−1 V 
V2
V3
V1
V4



2
1 V
V2
V3
V1
V4



3
3 V
V2
V3
V1
V4



4
5 V
V2
V3
V1
V4










Referring back to FIG. 6A, as shown in Table 1, when states of a dummy string selection transistor and respective string selection transistors are set and corresponding voltages are respectively applied to the dummy string selection transistors and the string selection transistors, a plurality of string selection transistors each indicated by a dotted line circle P among the dummy string selection transistors DSST and string selection transistors SST are turned off, and the other string selection transistors are turned on. Because the turned off string selection transistors are disposed in the first memory layer L1, the second memory layer L2 may be selected.
Although the above-stated embodiment exemplifies four string selection lines including one dummy string selection line, the number of string selection lines may be reduced for increasing integration density of the memory device 300. According to an embodiment, since each of dummy selection transistors and string selection transistors has two or more multi-level threshold values, a layer may be selected based on the LSM scheme.
For example, a plurality of string selection transistors arranged in the y-axis direction and stacked in the z-axis direction (or in an y-z plane) for sharing respective selection lines may be initialized such that threshold values of the plurality of string selection transistors gradually increase or decrease in the z-axis direction. In this case, if a number of the shared string selection lines is r, a number of accessible memory layers may be 2r when the r is an even number or may be 2r-1 when the r is an odd number. Table 2 below shows values of bias voltages to be applied to respective string selection lines for selecting each memory layer with 4 string lines when a 3D stacked non-volatile memory device in accordance with an embodiment includes 16 memory layers. In accordance with an embodiment of the present disclosure, the number of string selection transistors for selecting memory layers may be exponentially reduced in the LSM scheme, and string selection transistors having multi-level states may be initialized with a single signal having one time varying section.








TABLE 2







Threshold Value









Memory
SSL Bias















Layer
1st SST
2nd SST
3rd SST
4th SST
1st SSL
2nd SSL
3rd SSL
4th SSL


























1st Layer
3
V
−1
V
3
V
−1
V
3.5
V
0
V
3.5
V
0
V


2nd Layer
3
V
−1
V
2
V
1
V
3.5
V
0
V
2.5
V
1.5
V


3rd Layer
3
V
−1
V
1
V
2
V
3.5
V
0
V
1.5
V
2.5
V


4th Layer
3
V
−1
V
−1
V
3
V
3.5
V
0
V
0
V
3.5
V


5th Layer
2
V
1
V
3
V
−1
V
2.5
V
1.5
V
3.5
V
0
V


6th Layer
2
V
1
V
2
V
1
V
2.5
V
1.5
V
2.5
V
1.5
V


7th Layer
2
V
1
V
1
V
2
V
2.5
V
1.5
V
1.5
V
2.5
V


8th Layer
2
V
1
V
−1
V
3
V
2.5
V
1.5
V
0
V
3.5
V


9th Layer
1
V
2
V
3
V
−1
V
1.5
V
2.5
V
3.5
V
0
V


10th Layer
1
V
2
V
2
V
1
V
1.5
V
2.5
V
2.5
V
1.5
V


11th Layer
1
V
2
V
1
V
2
V
1.5
V
2.5
V
1.5
V
2.5
V


12th Layer
1
V
2
V
−1
V
3
V
1.5
V
2.5
V
0
V
3.5
V


13th Layer
−1
V
3
V
3
V
−1
V
0
V
3.5
V
3.5
V
0
V


14th Layer
−1
V
3
V
2
V
1
V
0
V
3.5
V
2.5
V
1.5
V


15th Layer
−1
V
3
V
1
V
2
V
0
V
3.5
V
1.5
V
2.5
V


16th Layer
−1
V
3
V
−1
V
3
V
0
V
3.5
V
0
V
3.5
V









In accordance with an embodiment of the present disclosure, since memory cells in an yz plane are arranged in a matrix-like shape, the memory cells coupled commonly with a selection line WLi, which is selected for programming a selected memory cell S, may be biased with a high programming voltage Vpgm. In this case, while the selected memory cell S is being programmed, an unwanted program or a disturbance may occur at unselected memory cells NS coupled to the selection line WLi. Therefore, it is desirable for an operation for programming the selected memory cell S to have bit selectivity. In an embodiment, a bitline program voltage, e.g., 0 V, may be applied to a second bitline BL2 connected to a memory string STR2_2 including the memory cell S to be programmed, whereas a higher voltage for example, a common collector voltage (or a power voltage) Vcc, e.g., about 2.3 V, may be applied to first and third bitlines BL1 and BL3 that are respectively connected to the other memory strings STR2_1 and STR2_3. At least one or more string selection transistors of the other memory strings STR2_1 and STR2_3 are turned off by the higher voltage (i.e., the common collector voltage) Vcc, and thus the unselected memory strings STR2_1 and STR2_3 may be biased to a high channel potential, e.g., 8 V, reducing a voltage drop via a tunnelling insulation layer of a memory cell in the unselected memory strings STR2_1 and STR2_3. As a result, a self-boosted program inhibition (SBPI) scheme (or SBPI mode) for preventing electrons from tunnelling from a channel to a data storage layer may be performed. Another SBPI scheme in which the program operation has bit selectivity may be performed. A hatched region indicated by the reference character BS denotes a channel with a boosted potential. Due to the program inhibition, the other memory cells NS coupled with the wordline WLi are not programmed.
According to another embodiment, although a pass voltage Vpass is applied to the remaining wordlines WL1 to WLi−1 and WLi+1 to WLn coupled with the unselected memory cells in the embodiment shown in FIG. 6A, embodiments of the present disclosure are not limited thereto. For example, a program voltage Vpgm may be applied to the wordline WLi of the selected memory cell S, two wordlines WLi−1 and WLi+1 coupled with two unselected memory cells adjacent to the selected memory cell S in a same string may be grounded, and the pass voltage Vpass may be applied to the remaining wordlines WL1 to WLi−2 and WLi+2 to WLn.
In another embodiment, during a program operation, to suppress a program disturbance like a soft erase, a pass disturbance, or an edge disturbance, the program operation may be performed in accordance with a local SBPI scheme or an asymmetric SBPI scheme. Technical configurations known in the art may be referred to for the local SBPI scheme or the asymmetric SBPI scheme.
FIG. 6C shows a first response C1 of a selected memory string of a selected memory layer that is programmed, a second response C2 of an unselected memory string of the selected memory layer, and a third response C3 of the remaining memory strings of an unselected memory layer that are program-inhibited, and thus a reliable program operation suppressing the program disturbance may be performed.
The program operation may be performed by using the ISPP technique for controlling a threshold value Vth programmed based on a bit-by-bit program-verification algorithm as described above. Furthermore, although the above embodiments have been described in relation to program operations, a memory layer may also be selected by an LSM scheme in accordance with an embodiment of the present disclosure to perform a read operation and an erase operation. The read operation or the erase operation may be performed by applying a read voltage Vread (e.g., 0 V) or an erase voltage Vers (e.g., a negative voltage or a ground voltage) to a selected wordline in a selected memory layer and applying a pass voltage Vpass (e.g., from 4 V to 5 V) to unselected wordlines in the selected memory layer.
FIG. 7 is a block diagram showing a memory system 500 in accordance with an embodiment.
Referring to FIG. 7, the memory system 500 includes a memory controller 510 and a non-volatile memory device 520. The memory controller 510 may perform error correcting codes with respect to the non-volatile memory device 520. The memory controller 510 may control the non-volatile memory device 520 based on commands and addresses from an external circuit.
The memory controller 510 may perform an error correcting encoding process on a data requested to write, when the memory controller 510 receives a write request from a host. Furthermore, the memory controller 510 may control the non-volatile memory device 520 to program the encoded data at a memory region corresponding to a provided address. Furthermore, during a read operation, the memory controller 510 may perform an error correcting decoding process on a data output from the non-volatile memory device 520. Errors included in output data may be corrected by the error correcting decoding process. To detect and correct the errors, the memory controller 510 may include an error correction block 515.
The non-volatile memory device 520 may include a memory cell array 521 and a page buffer 523. The memory cell array 521 may include an array of single-level memory cells or 2 or higher bit multi-level memory cells. When the memory controller 510 receives an initialization request, the memory controller 510 may initialize string selection transistors of respective memory layers to have a predetermined state (threshold voltage) by using a programming technique or an erasing technique using time varying erase voltage signals.
FIG. 8 is a block diagram showing a storage device 1000 including a SSD in accordance with an embodiment of present disclosure.
Referring to FIG. 8, the storage device 1000 includes a host 1100 and a SSD 1200. The SSD 1200 may include a SSD controller 1210, a buffer memory 1220, and a non-volatile memory device 1230. The SSD controller 1210 provides electric and physical connections between the host 1100 and the SSD 1200. In an embodiment, the SSD controller 1210 provides an interface between the host 1100 and the SSD 1200 in correspondence to a bus format of the host 1100. Furthermore, the SSD controller 1210 may decode commands provided by the host 1100 and access the non-volatile memory device 1230 based on a result of the decoding. Unlimited examples of the bus format of the host 1100 may include USB (Universal Serial Bus), SCSI (Small Computer System Interface), PCI express, ATA (Advanced Technology Attachment), PATA (Parallel ATA), SATA (Serial ATA), and SAS (Serial Attached SCSI).
A data to be written provided by the host 1100 or a data read out from the non-volatile memory device 1230 may be temporarily stored in the buffer memory 1220. When the host 1100 sends a read request and data existing in the non-volatile memory device 1230 is cached, the buffer memory 1220 may provide a cache function for providing cached data directly to the host 1100. Generally, data transmission rate based on a bus format (e.g., SATA or SAS) of the host 1100 may be faster than data transmission speed of memory channels of the SSD 1200. In this case, the large-capacity buffer memory 1220 may be provided to minimize performance deterioration due to the speed difference. The buffer memory 1220 therefor may be a synchronous DRAM for providing sufficient buffering performance. However, the present invention is not limited thereto.
The non-volatile memory device 1230 may be provided as a storage medium of the SSD 1200. For example, the non-volatile memory device 1230 may be a NAND-type flash memory with large storage capacity. For another example, a NOR-type flash memory, a phase-change memory, a magnetic memory, a resistive memory, a ferrodielectric memory, or a memory system including a combination thereof may be applied as the non-volatile memory device 1230.
FIG. 9 is a block diagram showing a memory system 2000 in accordance with another embodiment of the present disclosure.
Referring to FIG. 9, the memory system 2000 may include a memory controller 2200 and a flash memory device 2100. The flash memory device 2100 may include the non-volatile memory devices 100, 200, and 300 as described above with reference to FIGS. 1 through 7. The flash memory device 2100 may detect memory cells with abnormal speeds during verification of target states, and thus the flash memory device 2100 may show reliable program performance.
The memory controller 2200 may be configured to control the flash memory device 2100. An SRAM 2230 may be used as an operation memory for the CPU 2210. A host interface 2220 may embody a data exchange protocol for the host to be connected to the memory system 2000. An error correction circuit 2240 equipped in the memory controller 2200 may detect and correct errors included in data read out from the flash memory device 2100. A memory interface 2250 may perform interfacing with the flash memory device 2100. A CPU 2210 may perform overall control operations for data exchange of the memory controller 2200. The memory system 2000 in accordance with the present invention may further include a ROM (not shown) that stores code data for interfacing with a host.
The flash memory device 2100 may be configured to communicate with an external circuit (e.g., a host) via one of various interface protocols, such as USB, MMC, PCI-E, SAS, SATA, PATA, SCSI, ESDI, or IDE. The memory system 2000 in accordance with the present invention may be applied to various user devices, such as a ultra mobile PC (UMPC), a workstation, a net-book, a personal digital assistant (PDA), a portable computer, a web tablet, a wireless phone, a mobile phone, a smart phone, a digital camera, a digital audio recorder, a digital audio player, a digital picture recorder, a digital picture player, a digital video recorder, a digital video player, a device capable of transmitting and receiving data wirelessly, or a home network.
FIG. 10 is a block diagram showing a data storage device 3000 in accordance with another embodiment of the present disclosure.
Referring to FIG. 10, the data storage device 3000 may include a flash memory 3100 and a flash controller 3200. The flash controller 3200 may control the flash memory 3100 based on control signals received from an external circuit connected to the data storage device 3000. A 3D memory array structure of the flash memory 3100 may be a channel stacked structure, a straight-shaped bit cost scalable structure, or a pipe-shaped BiCs structure. However, the above-stated structures are merely examples, and the present invention is not limited thereto.
The data storage device 3000 in accordance with the present invention may constitute a memory card device, a SSD device, a multimedia card device, a SD card, a memory stick device, a hard disk drive device, a hybrid drive device, or a USB flash device. For example, the data storage device 3000 in accordance with the present invention may be a memory card that satisfies a standard or a specification to be generally used in an electronic device, such as a digital camera or a personal computer.
FIG. 11 is a block diagram showing a flash memory device 4100 and a computing system 4000 including the flash memory device 4100 in accordance with an embodiment of the present disclosure.
Referring to FIG. 11, the computing system 4000 in accordance with the present disclosure may include the flash memory device 4100, a memory controller 4200, a modem 4300, such as a baseband chipset, a microprocessor 4500, and a user interface 4600 that are electrically connected to a bus 4400.
The flash memory device 4100 shown in FIG. 10 may be a non-volatile memory device as described above. The computing system 4000 in accordance with the present invention may be a mobile device. In this case, the computing system 4000 may further include a battery 4700 for supplying a power for operating the computing system 4000. Although not shown, the computing system 4000 in accordance with the present invention may further include an application chipset, a camera image processor (CIS), or a mobile DRAM. The memory controller 4200 and the flash memory device 4100 may constitute a SSD using a non-volatile memory device for storing data.
In accordance with an embodiment of the present disclosure, there may be provided a method of initializing a 3D non-volatile memory device capable of increasing integration of the 3D non-volatile memory device by increasing the number of selectable memory layers by programming a dummy string selection transistor that is used to initialize string selection transistors for selecting any one memory layer from among a plurality of memory layers constituting a 3D non-volatile memory device in order to utilize redundancy of the dummy string selection transistor as a string selection transistor. Furthermore, when the string selection transistors are initialized by using the ISPP technique, threshold values of the string selection transistors may be set to be distributed narrowly, thereby providing a more reliable method of initializing a 3D non-volatile memory device.
A non-volatile memory device and/or a memory controller in accordance with the present invention may be mounted via various types of packages. For example, a non-volatile memory device and/or a memory controller may be mounted via any of various packages including PoP (Package on Package), Ball grid arrays (BGAs), Chip scale packages (CSPs), Plastic Leaded Chip Carrier (PLCC), Plastic Dual In-Line Package (PDIP), Die in Waffle Pack, Die in Wafer Form, Chip On Board (COB), Ceramic Dual In-Line Package (CERDIP), Plastic Metric Quad Flat Pack (MQFP), Thin Quad Flatpack (TQFP), Small Outline (SOIC), Shrink Small Outline Package (SSOP), Thin Small Outline (TSOP), System In Package (SIP), Multi Chip Package (MCP), Wafer-level Fabricated Package (WFP), or Wafer-Level Processed Stack Package (WSP).
While embodiments of the present disclosure has been particularly shown and described, 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 disclosure as defined by the following claims.

## Claims

1. A method of initializing a three-dimensional (3D) non-volatile memory device, the 3D non-volatile memory device comprising a dummy string selection line, a plurality of string selection lines, a plurality of wordlines, a plurality of bitlines, a ground selection line, and a plurality of memory layers, each of the memory layers comprising a plurality of channel lines respectively coupled to the plurality of bitlines via first ends of the plurality of channel lines and coupled to a common source line of the memory layer via second ends of the plurality of channel lines, wherein the dummy string selection line, the plurality of string selection lines, the plurality of wordlines, and the ground selection line intersect with the plurality of channel lines, and each of the plurality of channel lines defines a memory string, the method comprising:
programming a plurality of string selection transistors coupled with the plurality of string selection lines to have at least one or more threshold values; and
programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors.

2. The method of claim 1, wherein programming a plurality of string selection transistors comprises:
applying a first program voltage to a selected string selection line coupled to a selected memory layer among the plurality of memory layers, the selected string selection line being coupled to a plurality of string selection transistors;
verifying whether threshold voltages of the plurality of string selection transistors reach a target value to determine the plurality of string selection transistors as programmed string selection transistors or unprogrammed string selection transistors;
programming memory cell transistors of one or more of memory strings coupled with the programmed string selection transistors to have a predetermined threshold voltage, by applying a second program voltage to a selected wordline among the plurality of wordlines, the predetermined threshold voltage being suitable to make each of the programmed memory cell transistors function as a screening transistor; and
program-inhibiting channel lines of the programmed string selection transistors using the programmed memory cell transistors as screening transistors and applying a third program voltage to the selected string selection line to selectively program the unprogrammed string selection transistors.

3. The method of claim 2, wherein applying the first program voltage, verifying whether the threshold voltages of the plurality of string selection transistors reach the target value, and applying the third program voltage respectively include performing an incremental step pulse programming (ISPP) technique.

4. The method of claim 2, wherein verifying whether the threshold voltages of the plurality of string selection transistors reach the target value includes:
applying a sensing voltage to the plurality of bitlines; and
applying a voltage substantially equal to the sensing voltage to common source lines of unselected memory layers among the plurality of memory layers.

5. The method of claim 2, wherein programming the memory cell transistors of the one or more of memory strings coupled with the programmed string selection transistors includes program-inhibiting a memory cell transistor of a memory string coupled with a corresponding one of the unprogrammed string selection transistors.

6. The method of claim 5, wherein programming the memory cell transistors further includes applying a voltage equal to or higher than a common collector voltage to a bitline coupled with the corresponding one of the unprogrammed string selection transistors to induce channel potential boosting at the memory string coupled with the corresponding unprogrammed string selection transistor.

7. The method of claim 2, wherein program-inhibiting channel lines of the programmed string selection transistors includes:
applying a ground voltage to a common source line of the selected memory layer; and
applying a common collector voltage to common source lines of unselected memory layers among the plurality of memory layers and to the plurality of bitlines to float channel lines of memory strings of the unselected memory layers.

8. The method of claim 2, wherein program-inhibiting the channel lines of the programmed string selection transistors includes:
applying a voltage smaller than the threshold voltages of the programmed memory cell transistors to the selected wordline coupled with the programmed memory cell transistors; and
applying the third program voltage to the selected string selection line to selectively program the unprogrammed string selection transistors.

9. The method of claim 1, wherein programming a plurality of string selection transistors is performed by using the dummy string selection line.

10. The method of claim 1, further comprising: before applying the first program voltage to a selected string selection line, erasing the plurality of string selection transistors coupled with the plurality of string selection lines and a plurality of memory cell transistors coupled with the plurality of wordlines.

11. The method of claim 1, wherein programming a dummy string selection transistor includes:
initially levelling the dummy string selection transistor by programming threshold values of the dummy string selection transistor to have a determined first target value; and
programming the initially levelled dummy string selection transistor to have a second target value by applying an erase voltage signal to the common source line of the selected memory layer, such that the programmed dummy string selection transistor functions as string selection transistors.

12. The method of claim 11, wherein the erase voltage signal has a level selected based on the second target value.

13. The method of claim 11, wherein the erase voltage signal is an erase voltage signal having a time varying section, and the dummy string selection transistors are programmed to the second target value by grounding or floating the dummy string selection line in the time varying section of the erase voltage signal.

14. The method of claim 11, wherein the time varying section of the time varying erase voltage signal comprises a ramping section, a step-like section, or a combination thereof.

15. The method of claim 11, wherein the time varying section comprises an increasing ramp section or a decreasing ramp section.

16. The method of claim 11, wherein the time varying erase voltage signal is applied to a first common source line coupled to the selected first memory layer, the method further comprising:
applying a voltage signal for erase inhibition to one or more of common source lines other than the first common source line, the one or more common source lines being coupled to one or more of unselected memory layers among the plurality of memory layers when the time varying erase voltage signal is applied and the threshold values of the first plurality of string selection transistors in the first memory layer are set.

17. The method of claim 11, further comprising causing the plurality of bitlines to float when the first time varying erase voltage signal is applied.

18. The method of claim 1, wherein the plurality of channel lines of the 3D non-volatile memory device have a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, a pipe-shaped BiCs structure, or a combination thereof.

19. The method of claim 1, wherein the 3D non-volatile memory device is a NAND flash memory device.

20. A method of initializing a three-dimensional (3D) non-volatile memory device, the 3D non-volatile memory device comprising a dummy string selection line, a plurality of string selection lines, a plurality of wordlines, a plurality of bitlines, a ground selection line, and a plurality of memory layers, each of the memory layers comprising a plurality of channel lines respectively coupled to the plurality of bitlines via first ends of the plurality of channel lines and coupled to a common source line of the memory layer via second ends of the plurality of channel lines, wherein the dummy string selection line, the plurality of string selection lines, the plurality of wordlines, and the ground selection line intersect with the plurality of channel lines, and each of the plurality of channel lines defines a memory string, the method comprising:
programming string selection transistors coupled with the plurality of string selection lines to have determined threshold values based on an incremental step pulse programming (ISPP) mode with regard to a memory layer selected among the plurality of memory layers; and
programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors.

21. The method of claim 20, further comprising, before programming string selection transistors, erasing the plurality of string selection transistors.

22. The method of claim 20, wherein the plurality of channel lines of the 3D non-volatile memory device have a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, a pipe-shaped BiCs structure, or a combination thereof.

23. The method of claim 20, wherein the 3D non-volatile memory device is a NAND flash memory device.

24. A method of initializing a three-dimensional (3D) non-volatile memory device, the 3D non-volatile memory device comprising a dummy string selection line, a plurality of string selection lines, a plurality of wordlines, a plurality of bitlines, a ground selection line, and a plurality of memory layers, each of the memory layers comprising a plurality of channel lines respectively coupled to the plurality of bitlines via first ends of the plurality of channel lines and coupled to a common source line of the memory layer via second ends of the plurality of channel lines, wherein the dummy string selection line, the plurality of string selection lines, the plurality of wordlines, and the ground selection line intersect with the plurality of channel lines, and each of the plurality of channel lines defines a memory string, the method comprising:
applying a first program voltage to a selected string selection line coupled to a selected memory layer among the plurality of memory layers, the selected string selection line being coupled to a plurality of string selection transistors;
verifying whether respective threshold voltages of the plurality of string selection transistors reach a target value to respectively determine the plurality of string selection transistors as programmed string selection transistors or unprogrammed string selection transistors;
applying a voltage equal to or higher than a common collector voltage to a first bitline coupled to a first memory string including an unprogrammed string selection transistor, applying a ground signal to a second bitline coupled to a second memory string including a programmed string selection transistor, and applying a second program voltage to the dummy ground line, thereby inducing channel potential boost at the first memory string such that dummy ground transistors in the second memory string are programmed to have a predetermined threshold value to function as a screening transistor and dummy ground transistors in the first memory strings are not programmed;
selectively programming the unprogrammed string selection transistor by turning the programmed dummy ground transistors off and applying a third program voltage to the selected string selection line; and
programming a dummy string selection transistor coupled with the dummy string selection line to have a predetermined threshold value, such that the dummy string selection transistor together with the plurality of string selection transistors function as string selection transistors.

25. The method of claim 24, wherein applying the first program voltage, verifying whether the threshold voltages of the plurality of string selection transistors reach the target value, and applying the third program voltage respectively include performing an incremental step pulse programming (ISPP) technique.

26. The method of claim 24, wherein the plurality of selection transistors coupled with the selected string selection line is a first plurality of string selection transistors, the method further comprising, before applying the first program voltage is performed, erasing a second plurality of string selection transistors coupled with the plurality of string selection lines and a plurality of memory cell transistors coupled with the plurality of wordlines, the second plurality of string selection transistors including the first plurality of string selection transistors.

27. The method of claim 24, wherein, verifying whether the threshold voltages of the plurality of string selection transistors reach the target value includes:
applying a sensing voltage to the plurality of bitlines; and
applying a voltage substantially equal to the sensing voltage to common source lines of unselected memory layers among the plurality of memory layers.

28. The method of claim 24, wherein, selectively programming the unprogrammed string selection transistors includes applying a ground voltage to a common source line of the selected memory layer, applying a common collector voltage to common source lines of the unselected memory layers among the plurality of memory layers and to the plurality of bitlines to float channel lines of memory strings of the unselected memory layers.

29. The method of claim 24, wherein the 3D non-volatile memory device has a channel stacked structure, a straight-shaped bit cost scalable (BiCs) structure, a pipe-shaped BiCs structure, or a combination thereof.

30. The method of claim 24, wherein the 3D non-volatile memory device is a NAND flash memory device.