Adaptive half-round select gate biasing

Abstract

A memory device and method of operation are provided. The device includes memory cells connected to word lines and arranged in strings. Each of the strings has a drain side select gate transistor on a drain side connected to one of a plurality of bit lines. A control component is coupled to the word lines and the plurality of bit lines and the drain side select gate transistors. The control component determines a unique select gate voltage for each of a plurality of groups of the memory cells, the unique select gate voltage individually applicable to each of the plurality of groups. The control component then applies the unique select gate voltage to the drain side select gate transistor of a selected string of the strings of each of the plurality of groups of the memory cells to turn on the drain side select gate transistor of the selected string of the strings during a memory operation.

Description

Technical Field

[0001] This application relates to the operation of non-volatile memory devices. Background Technology

[0002] This section provides background information related to the technology associated with this disclosure, and is not necessarily prior art.

[0003] Semicircular drain-side selected gate (“SC-SGD”) memory technology offers several advantages, including reduced die size. To produce SC-SGDs, etching techniques are used to cut memory holes, giving them a semicircular shape and dividing blocks or rows into strings. Depending on the process used to form the SC-SGD, some inefficiencies may occur. For example, cutting the memory holes removes at least some portions of the SC-SGD, such as metal layers, otherwise their shielding channels, and / or charge trapping layers. Therefore, the SC-SGD may be affected by “adjacent” electric fields, and charge migration may occur. Furthermore, due to etching variations, some dies may be cut into SGD layers, while others may be cut into layers forming dummy word lines. Therefore, due to charge migration, it may be difficult to select the bias applied to the drain-side selected gate. Therefore, improved non-volatile memory devices and operating methods are needed. Summary of the Invention

[0004] This section provides a general overview of the disclosure and is not a full disclosure of its entire scope or all its features and advantages.

[0005] The purpose of this disclosure is to provide a memory device and a method for operating the memory device that solves and overcomes the above-mentioned disadvantages.

[0006] Therefore, one aspect of this disclosure is to provide a memory device comprising memory cells connected to one of a plurality of word lines and arranged in strings, and configured to maintain a threshold voltage. Each string has at least one drain-side selected-gate transistor on the drain side of the string connected to one of the plurality of bit lines and coupled to a memory cell of the string. A control unit is coupled to the plurality of word lines, the plurality of bit lines, and the at least one drain-side selected-gate transistor. The control unit is configured to determine a unique selected-gate voltage for each of a plurality of groups of memory cells. The unique selected-gate voltage is applied individually to each of the plurality of groups of memory cells. The control unit is also configured to apply the unique selected-gate voltage to at least one drain-side selected-gate transistor of a selected string in each of the plurality of groups of memory cells to turn on at least one drain-side selected-gate transistor of the selected string during memory operation.

[0007] According to another aspect of this disclosure, a controller for communicating with a memory device is also provided, the memory device comprising memory cells connected to one of a plurality of word lines. The memory cells are arranged in strings and configured to maintain a threshold voltage. Each string has at least one drain-side selected-gate transistor on the drain side of that string, connected to one of the plurality of bit lines and coupled to the memory cells of that string. The controller is configured to determine a unique selected-gate voltage for each of a plurality of groups of memory cells. This unique selected-gate voltage is applied individually to each of the plurality of groups of memory cells. The controller is further configured to instruct the memory device to apply the unique selected-gate voltage to at least one drain-side selected-gate transistor of a selected string in each of the plurality of groups of memory cells to turn on at least one drain-side selected-gate transistor of the selected string during memory operation.

[0008] According to an additional aspect of this disclosure, a method of operating a memory device is provided. A memory device comprising memory cells connected to one of a plurality of word lines is also provided. The memory cells are arranged in strings and configured to maintain a threshold voltage. Each string has at least one drain-side selected-gate transistor, the at least one drain-side selected-gate transistor being coupled to the memory cells of that string on the drain side of the string connected to one of the plurality of bit lines. The method includes the step of determining a unique selected-gate voltage for each of a plurality of groups of memory cells. The unique selected-gate voltage is applied individually to each of the plurality of groups of memory cells. The method further includes the step of applying the unique selected-gate voltage to at least one drain-side selected-gate transistor of a selected string in each of the plurality of groups of memory cells to turn on at least one drain-side selected-gate transistor of the selected string during memory operation.

[0009] Further applicable fields will become apparent from the description provided herein. The descriptions and specific examples in this invention are intended for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0010] The accompanying drawings described herein are for illustrative purposes only, and not for all possible specific implementations, and are not intended to limit the scope of this disclosure.

[0011] Figure 1A A block diagram of an exemplary memory device according to various aspects of this disclosure;

[0012] Figure 1B A block diagram of an example control circuit including a programming circuit, a counting circuit, and a determining circuit according to various aspects of this disclosure;

[0013] Figure 2 Schematic diagrams are shown of three types of memory architectures utilizing interleaved memory strings according to various aspects of this disclosure;

[0014] Figure 3A A cross-sectional view of an exemplary floating-gate memory cell in a NAND string according to various aspects of this disclosure is shown;

[0015] Figure 3B The following are shown along the aspects according to this disclosure. Figure 3A A cross-sectional view of the contact line shown;

[0016] Figure 4A and Figure 4B A non-volatile memory according to various aspects of this disclosure is shown, wherein the charge trapping memory cell uses a non-conductive dielectric material instead of a conductive floating gate to store charge in a non-volatile manner;

[0017] Figure 5 An exemplary block diagram of the sensing block of FIG1 is shown according to various aspects of the present disclosure;

[0018] Figure 6A It is a perspective view of a set of blocks in an exemplary three-dimensional configuration of a memory array according to various aspects of this disclosure;

[0019] Figure 6B The various aspects shown in this disclosure are as follows Figure 6A An exemplary cross-sectional view of a portion of a block;

[0020] Figure 6C The various aspects shown in this disclosure are as follows Figure 6B A graph showing the diameter of memory holes in a stack;

[0021] Figure 6D The various aspects shown in this disclosure are as follows Figure 6B A close-up view of the stacked area;

[0022] Figure 7A A schematic plan view of a memory array having multiple memory holes according to various aspects of the present disclosure is shown;

[0023] Figure 7B A cross-sectional view of a memory array according to various aspects of this disclosure is shown;

[0024] Figure 8A and Figure 8B An alternative memory structure without dummy holes is shown according to various aspects of this disclosure;

[0025] Figure 9The diagram shows a top sectional view and a corresponding vertical section of two semi-circular memory holes partially cut by SHE cutting according to various aspects of this disclosure, illustrating the redistribution of electrons due to read stress and subsequent relaxation, and the threshold voltage distribution of the drain-side selected gate switch due to redistribution and relaxation.

[0026] Figure 10 Experimental results of reading stress are shown according to various aspects of this disclosure;

[0027] Figure 11 A graph showing the threshold distribution after 100,000 block read stresses according to various aspects of this disclosure is presented.

[0028] Figure 12 Threshold voltage distributions of multiple exemplary memory cell groups using different processes employing different selected gate voltages are shown according to various aspects of this disclosure;

[0029] Figure 13 Threshold voltage plots for three memory dies according to various aspects of this disclosure are shown.

[0030] Figures 14A to 14D The threshold voltage distribution of drain-side selected gate transistors according to various aspects of this disclosure and exemplary detection threshold voltages, as well as the drain-side selected gate amount of the drain-side selected gate transistors in the string of each of the corresponding plurality of groups having a transistor threshold voltage higher than the detection threshold voltage.

[0031] Figure 15 Multiple memory cell blocks according to various aspects of this disclosure are shown, wherein the disclosed adaptive select gate bias search method or technique has been used to determine the select gate voltage of each block in the block and the threshold voltage distribution of the drain-side select gate transistor of each block.

[0032] Figures 16A to 16B The diagram shows the threshold voltage distribution of the drain-side selected gate transistor in the top block, middle block and bottom block of the semicircular memory hole for two different memory dies according to various aspects of the present disclosure.

[0033] Figure 17 Multiple memory dies of memory cells according to various aspects of this disclosure are shown, wherein the disclosed adaptive select gate bias search method or technique has been used to determine the select gate voltage of each memory die and the threshold voltage distribution of the drain-side select gate transistor of each memory die.

[0034] Figures 18A to 18BThe diagram illustrates the threshold voltage distribution of the drain-side selected gate transistors in the top block, middle block, and bottom block of a semi-circular memory hole for two different memory dies, according to various aspects of this disclosure; and

[0035] Figure 19 and Figure 20 The steps of a method for operating a memory device are shown.

[0036] For ease of understanding, the same reference numerals are used where possible to denote the same elements common in the accompanying drawings. It is conceivable that elements disclosed in one embodiment may be advantageously used in other embodiments without specific description. Detailed Implementation

[0037] In the following description, details are set forth to provide an understanding of this disclosure. In some instances, certain circuits, structures, and techniques have not been described or shown in detail so as not to obscure this disclosure.

[0038] Generally, this disclosure relates to a type of nonvolatile memory device that is well-suited to many applications. The nonvolatile memory device and associated methods of operation of this disclosure will be described in conjunction with one or more exemplary embodiments. However, the specific exemplary embodiments disclosed are merely for the purpose of clearly describing the concepts, features, advantages, and objects of the invention to allow those skilled in the art to understand and practice this disclosure. Specifically, exemplary embodiments are provided so that this disclosure will be comprehensive and will fully convey the scope to those skilled in the art. Numerous specific details, such as examples of specific components, apparatus, and methods, are set forth to provide a thorough understanding of embodiments of this disclosure. It will be apparent to those skilled in the art that specific details are not required, exemplary embodiments may be embodied in many different forms, and none should be construed as limiting the scope of this disclosure. In some exemplary embodiments, well-known processes, well-known apparatus structures, and well-known techniques are not described in detail.

[0039] In some memory devices or apparatuses, memory cells are joined together, such as in NAND strings within a block or sub-block. Each NAND string comprises a plurality of memory cells connected in series between one or more drain-side selected-gate SG transistors (SGD transistors) located on the drain side of the NAND string connected to a bit line and one or more source-side selected-gate SG transistors (SGS transistors) located on the source side of the NAND string connected to a source line. Furthermore, the memory cells may be arranged with a common control gate line (e.g., a word line) serving as a control gate. A set of word lines extends from the source side of the block to the drain side of the block. Memory cells may be connected in other types of string connections and in other ways.

[0040] In a 3D memory architecture, memory cells can be arranged in a stacked vertical string, wherein the stack includes alternating conductive and dielectric layers. The conductive layers serve as word lines connecting to the memory cells. Memory cells may include data memory cells eligible to store user data, as well as dummy memory cells or non-data memory cells not eligible to store user data.

[0041] Before programming certain non-volatile memory devices, memory cells are typically erased. For some devices, the erase operation removes electrons from the floating gate of the erased memory cell. Alternatively, the erase operation removes electrons from the charge trapping layer.

[0042] Each memory cell can be associated with a data state based on the data written in the program commands. Based on the data state of that memory cell, the memory cell will remain in an erase state or be programmed into a programmed data state. For example, in a three-bit memory device, there are eight data states, including erase and programmed states.

[0043] During the programming operation, memory cells are programmed according to the word line programming sequence. For example, programming can begin with a word line on the source side of the block and proceed to a word line on the drain side of the block. In one approach, programming of each word line is completed before programming the next word line. For example, the first word line WL0 is programmed using one or more programming pulses until programming is complete. Next, the second word line WL1 is programmed using one or more programming pulses until programming is complete, and so on. The programming pulses may include a set of increasing programming voltages, which are applied to the word line in the corresponding programming cycle or program-verify iteration. A verification operation or stage can be performed after each programming voltage to determine whether the memory cell has been programmed. When programming of a memory cell is complete, further programming of that memory cell can be prevented, while programming of other memory cells continues in subsequent programming cycles.

[0044] When creating rows and strings for memory structures, dicing operations (e.g., shallow hole etching or SHE) can be used. This SHE dicing divides a block (in memory) into multiple strings within the block. While SHE can form / define strings, SHE dicing can further separate strings, i.e., cut edge memory holes in a string in half (or approximately two equal halves). In this respect, both the SGD and the channel are separated. However, because the cells are diced, the polysilicon channel is exposed to the electric field of the adjacent SGD. During memory operations (i.e., NAND operations), channel regions close to adjacent SGDs can easily become conductive, potentially leading to "SGD downshifting," especially after intense read stress. Specifically, semi-circular SGDs (SC-SGD) exhibit a lower threshold voltage Vt compared to full-circular SGDs (FC-SGD), resulting in a wider SGD threshold voltage Vt distribution. Because cutting memory vias removes at least some portion of the SC-SGD, such as metal layers that would otherwise shield against electric fields from the channel and / or charge trapping layer, the SC-SGD may be affected by "adjacent" electric fields and charge migration. From the perspective of moving the top-pitch SGD down, using the lowest possible select gate bias is preferred. However, reducing the select gate bias can lead to other problems, such as low select gate voltage (VSG) that does not turn on the SGD cell.

[0045] Several aspects of this disclosure may be embodied in the form of an apparatus, system, method, or computer program process. Therefore, aspects of this disclosure may be entirely in the form of a hardware implementation or a software implementation (including, but not limited to, firmware, resident software, microcode, etc.), or may be a combination of hardware and software components, which are generally referred to collectively as a “circuit,” “module,” “apparatus,” or “system.” Additionally, aspects of this disclosure may be, for example, in the form of a computer program process embodied in one or more non-transitory computer-readable storage media storing computer-readable program code and / or computer-executable program code.

[0046] Additionally, various terms are used herein to refer to specific system components. Different companies may use different names to refer to the same or similar components, and this document is not intended to distinguish components with different names rather than different functions. With regard to the various functional units described in the following disclosure being referred to as “modules,” this designation is intended not to unduly limit the scope of possible implementation mechanisms. For example, a “module” may be implemented as hardware circuitry comprising custom-designed very large-scale integration (VLSI) circuitry or gate arrays, or as off-the-shelf semiconductors comprising logic chips, transistors, or other discrete components. In another example, modules may also be implemented in programmable hardware devices such as field-programmable gate arrays (FPGAs), programmable array logic units, programmable logic devices, etc. Furthermore, modules may also be implemented, at least in part, by software executed by various types of processors. For example, a module may include executable code segments that constitute one or more physical or logical blocks of computer instructions that translate into objects, procedures, or functions. Furthermore, it is not required that the executable portions of such modules be physically located together, but rather that they may include different instructions stored in different locations, and when executed together, constitute the identified module and achieve the stated purpose of the module. Executable code may include a single instruction or a collection of instructions, and may be distributed across different code segments, different programs, or multiple memory devices. In specific implementations of software or portions of software modules, the software portions may be stored on one or more computer-readable and / or executable storage media, including but not limited to electronic, magnetic, optical, electromagnetic, infrared, or semiconductor-based systems, apparatuses, or devices, or any suitable combination thereof. Generally, for the purposes of this disclosure, computer-readable and / or executable storage media may include any tangible and / or non-transitory medium capable of containing and / or storing programs for use by or in connection with an instruction execution system, apparatus, processor, or device.

[0047] Similarly, for the purposes of this disclosure, the term "component" can refer to any tangible, physical, and non-transient device. For example, a component can be in the form of hardware logic circuitry composed of custom VLSI circuitry, gate arrays, or other integrated circuits, or of off-the-shelf semiconductors including logic chips, transistors, or other discrete components, or any other suitable mechanical and / or electronic equipment. Furthermore, components can also be implemented in programmable hardware devices such as field-programmable gate arrays (FPGAs), programmable array logic components, programmable logic devices, etc. Additionally, a component can be composed of one or more silicon-based integrated circuit devices (such as chips, dies, die planes, and packages) or other discrete electrical devices, which are electrically connected to one or more other components via electrical conductors such as printed circuit boards (PCBs). Therefore, modules as defined above can be embodied or implemented as components in some embodiments, and in some cases, the terms module and component are used interchangeably.

[0048] As used herein, the term "circuit" includes one or more electrical and / or electronic components that form one or more conductive paths allowing current to flow. A circuit can be in the form of a closed-loop configuration or an open-loop configuration. In a closed-loop configuration, the circuit components may provide a return path for current. In contrast, in an open-loop configuration, the circuit components may be considered to form a circuit, although a return path for current is not included. For example, an integrated circuit is referred to as a circuit regardless of whether it is grounded (as a return path for current). In some exemplary embodiments, a circuit may include a set of integrated circuits, a single integrated circuit, or a portion of an integrated circuit. For example, a circuit may include custom VLSI circuitry, gate arrays, logic circuitry, and / or other forms of integrated circuits, and may include off-the-shelf semiconductors such as logic chips, transistors, or other discrete devices. In another example, a circuit may include one or more silicon-based integrated circuit devices (such as chips, dies, die planes, and packages) or other discrete electrical devices that are electrically connected to one or more other components via electrical conductors, such as a printed circuit board (PCB). A circuit may also be implemented as a composite circuit relative to programmable hardware devices such as field-programmable gate arrays (FPGAs), programmable array logic components, and / or programmable logic devices. In other exemplary embodiments, the circuit may include a network of non-integrated electrical and / or electronic components (with or without integrated circuit devices). Therefore, in some embodiments, modules as defined above may be embodied or implemented as circuits.

[0049] It should be understood that the exemplary embodiments disclosed herein may include one or more microprocessors and specifically stored computer program instructions that control one or more microprocessors to implement some, most, or all of the functions disclosed herein in conjunction with certain non-processor circuitry and other elements. Alternatively, some or all of the functions may be implemented by a state machine without stored program instructions or in one or more application-specific integrated circuits (ASICs) or field-programmable gate arrays (FPGAs), wherein each function or some combinations of certain functions is implemented as custom logic. Combinations of these methods may also be used. Furthermore, the reference to “controller” below should be defined as including individual circuit components, application-specific integrated circuits (ASICs), microcontrollers with control software, digital signal processors (DSPs), field-programmable gate arrays (FPGAs) and / or processors with control software, or combinations thereof.

[0050] Furthermore, as may be used herein, the terms “program,” “software,” “software application,” etc., refer to a sequence of instructions designed to be executed on a computer-implemented system. Therefore, “program,” “software,” “application,” “computer program,” or “software application” can include subroutines, functions, procedures, object methods, object implementations, executable applications, applets, service applets, source code, object code, shared libraries / dynamically loaded libraries, and / or other sequences of specific instructions designed to be executed on a computer system.

[0051] Additionally, as may be used herein, the terms “coupled,” “coupled,” or “connected” are intended to indicate a direct or indirect connection. Thus, if a first device is coupled to or is coupled to a second device, the connection may be made either directly or indirectly via another device (or component) and connection.

[0052] Regarding the use of terms such as “implementation,” “one implementation,” “exemplary implementation,” “specific implementation,” or other similar terms herein, these terms are intended to indicate that a specific feature, structure, function, operation, or characteristic described in connection with that implementation exists in at least one embodiment of this disclosure. Therefore, the appearance of phrases such as “in one implementation,” “in an implementation,” “in a particular implementation,” etc., may, but not necessarily, refer to the same implementation, but rather to “one or more, but not all, implementations,” unless expressly stated otherwise. Furthermore, the terms “comprising,” “having,” “including,” and variations thereof are used in an open-ended manner and should therefore be construed as meaning “including, but not limited to…,” unless expressly stated otherwise. Additionally, an element preceded by “comprising…” does not exclude the presence of additional identical elements in the subject matter process, method, system, article, or apparatus that includes that element, unless further limited.

[0053] The terms “a,” “an,” and “the” also mean “one or more” unless otherwise expressly stated. Furthermore, the phrase “at least one of A and B” (where A and B are variables indicating a particular object or property) used herein and / or in the appended claims indicates a choice of A or B, or a choice of both A and B, similar to the phrase “and / or.” Where more than two variables are present in such a phrase, the phrase is thereby defined as including only one of the variables, any of the variables, any combination (or subcombination) of any of the variables, and all of the variables.

[0054] Furthermore, as used herein, the terms “about” or “approximately” apply to all numerical values, whether explicitly stated or not. These terms generally refer to a range of numerical values ​​that a person skilled in the art would consider equivalent to (e.g., having the same function or result) the value referenced. In some cases, these terms may include numerical values ​​rounded to the nearest significant figure.

[0055] Furthermore, any enumerated list of items presented herein does not imply that any or all of the listed items are mutually exclusive and / or mutually inclusive, unless otherwise expressly stated. Additionally, as used herein, the term “group” should be interpreted as “one or more” according to the established theory, and in the case of “multiple groups”, it should be interpreted as a plural (multiple) of “one or more” and / or “many or more”, unless otherwise expressly stated.

[0056] In the following detailed description, reference is made to the accompanying drawings, which form a part thereof. It will be appreciated that the foregoing summary is merely exemplary and not intended to be limiting in any way. In addition to the illustrative aspects, exemplary embodiments, and features described above, further aspects, exemplary embodiments, and features will become apparent from the accompanying drawings and the following detailed description. The description of elements in each figure may refer to elements in the preceding figures. Similar reference numerals may refer to similar elements in the drawings, including alternative exemplary embodiments of similar elements.

[0057] Figure 1AThis is a block diagram of an exemplary memory device. Memory device 100 may include one or more memory dies 108. Memory die 108 includes a memory structure 126 having memory cells, such as an array of memory cells, control circuitry 110, and read / write circuitry 128. Memory structure 126 is addressable via word lines via row decoder 124 and via bit lines via column decoder 132. Read / write circuitry 128 includes a plurality of sensing blocks SB1, SB2, ..., SBp (sensing circuitry system) and allows for parallel reading or programming of pages of memory cells. Typically, controller 122 is included in the same memory device 100 (e.g., a removable memory card) as the one or more memory dies 108. Commands and data are transmitted between host 140 and controller 122 via data bus 120 and between controller and one or more memory dies 108 via line 118.

[0058] Memory structure 126 can be two-dimensional or three-dimensional. Memory structure 126 may include an array of one or more memory cells, including a three-dimensional array. Memory structure 126 may include a monolithic three-dimensional memory structure in which multiple memory levels are formed on (but not in) a single substrate such as a wafer, without an intervening substrate. Memory structure 126 may include any type of non-volatile memory integrally formed in an array of memory cells having one or more physical levels having active regions disposed on a silicon substrate. Memory structure 126 may be in a non-volatile memory device having circuitry associated with the operation of memory cells, whether the associated circuitry is on or within the substrate.

[0059] Control circuitry 110 cooperates with read / write circuitry 128 to perform memory operations on memory structure 126, and includes state machine 112, on-chip address decoder 114, and power control module 116. State machine 112 provides chip-level control of memory operations.

[0060] Storage area 113 may be provided, for example, for programming parameters. Programming parameters may include programming voltage, programming voltage bias, location parameters indicating the location of memory cells, contact connector thickness parameters, verification voltage, etc. Location parameters may indicate the location of the memory cell within the entire NAND string array, the location of the memory cell within a specific NAND string group, the location of the memory cell on a specific plane, etc. Contact connector thickness parameters may indicate the thickness of the contact connector, the substrate or material constituting the contact connector, etc.

[0061] On-chip address decoder 114 provides an address interface between the hardware addresses used by the host or memory controller and the hardware addresses used by decoders 124 and 132. Power control module 116 controls the power and voltage supplied to word lines and bit lines during memory operation. This power control module may include drivers for word lines, SGS transistors, and SGD transistors with source lines. In one approach, a sensing block may include bit line drivers. The SGS transistor is a select-gate transistor at the source terminal of the NAND string, and the SGD transistor is a select-gate transistor at the drain terminal of the NAND string.

[0062] In some embodiments, some of the components may be combined. In various designs, one or more components (alone or in combination) other than memory structure 126 may be considered as at least one control circuit configured to perform the actions described herein. For example, the control circuit may include any or a combination of control circuit 110, state machine 112, decoder 114 / 132, power control module 116, sensing blocks SBb, SB2, ..., SBp, read / write circuit 128, controller 122, etc.

[0063] The control circuitry may include programming circuitry configured to perform programming and verification operations on a set of memory cells, wherein the set of memory cells includes memory cells allocated to represent one of a plurality of data states, and memory cells allocated to represent another of the plurality of data states; the programming and verification operations include multiple programming and verification iterations; and in each programming and verification iteration, the programming circuitry performs programming on a word line, after which the programming circuitry applies a verification signal to a word line. The control circuitry may also include a counting circuit configured to obtain a count of memory cells that pass a verification test for one data state. The control circuitry may further include a determining circuit configured to determine a specific programming and verification iteration among the plurality of programming and verification iterations based on an amount by which the count exceeds a threshold, in which a verification test is performed on the memory cells allocated to represent the other data state.

[0064] For example, Figure 1B This is a block diagram of an exemplary control circuit 150 including a programming circuit 151, a counting circuit 152, and a determining circuit 153.

[0065] The off-chip controller 122 may include a processor 122c, storage devices (memory) such as ROM 122a and RAM 122b, and an error correction code (ECC) engine 245. The ECC engine can correct multiple read errors caused when the upper tail of the Vth distribution becomes too high. However, in some cases, uncorrectable errors may exist. The techniques provided herein reduce the likelihood of uncorrectable errors.

[0066] Memory devices 122a and 122b include code, such as an instruction set, and processor 122c is operable to execute the instruction set to provide the functionality described herein. Alternatively or otherwise, processor 122c may access code from storage device 126a of memory structure 126, such as reserved areas of memory cells in one or more word lines. For example, controller 122 may use code to access memory structure 126, such as for programming operations, read operations, and erase operations. The code may include boot code and control code (e.g., a set of instructions). Boot code is software that initializes controller 122 during boot or startup and enables controller 122 to access memory structure 126. Controller 122 may use code to control one or more memory structures 126. Upon power-up, processor 122c fetches boot code from ROM 122a or storage device 126a for execution, and the boot code initializes system components and loads control code into RAM 122b. Once the control code is loaded into RAM 122b, it is executed by processor 122c. The control code includes drivers that perform basic tasks such as controlling and allocating memory, prioritizing instruction processing, and controlling input and output ports.

[0067] Generally speaking, control code may include instructions to perform the functions described herein, including the steps of the flowcharts discussed further below, and provide voltage waveforms, including those discussed further below.

[0068] In one embodiment, the host is a computing device (e.g., a laptop computer, desktop computer, smartphone, tablet computer, digital camera) that includes one or more processors and one or more processor-readable storage devices (RAM, ROM, flash memory, hard disk drive, solid-state memory) storing processor-readable code (e.g., software) for programming the one or more processors to perform the methods described herein. The host may also include additional system memory, one or more input / output interfaces, and / or one or more input / output devices that communicate with the one or more processors.

[0069] In addition to NAND flash memory, other types of non-volatile memory can also be used.

[0070] Semiconductor memory devices include volatile memory devices, such as dynamic random access memory (“DRAM”) or static random access memory (“SRAM”) devices; non-volatile memory devices, such as resistive random access memory (“ReRAM”), electrically erasable programmable read-only memory (“EEPROM”), flash memory (which can also be considered a subset of EEPROM), ferroelectric random access memory (“FRAM”), and magnetoresistive random access memory (“MRAM”); and other semiconductor elements capable of storing information. Each type of memory device can have different configurations. For example, flash memory devices can be configured in either a NAND or NOR configuration.

[0071] The memory device can be formed from passive and / or active components in any combination. By way of non-limiting example, passive semiconductor memory elements include ReRAM device elements, which in some embodiments include resistivity-switching storage elements, such as antifuse or phase-change materials, and optional steering elements, such as diodes or transistors. Furthermore, by way of non-limiting example, active semiconductor memory elements include EEPROM and flash memory device elements, which in some embodiments include elements comprising charge storage regions, such as floating gates, conductive nanoparticles, or charge storage dielectric materials.

[0072] Multiple memory elements can be configured such that they are connected in series or that each element can be accessed individually. By way of non-limiting example, a flash memory device (NAND memory) in a NAND configuration typically contains memory elements connected in series. A NAND string is an example of a group of transistors connected in series, comprising memory cells and SG transistors.

[0073] NAND memory arrays can be configured such that the array consists of multiple memory strings, where a string consists of multiple memory elements that share a single bit line and are accessed as a group. Alternatively, memory elements can be configured such that each element can be accessed individually, such as in a NOR memory array. NAND and NOR memory configurations are examples, and memory elements can be configured in other ways. Semiconductor memory elements located within and / or on the substrate can be arranged in two or three dimensions, such as two-dimensional or three-dimensional memory structures.

[0074] In a two-dimensional memory structure, semiconductor memory elements are arranged in a single plane or a single memory device level. Typically, in a two-dimensional memory structure, the memory elements are arranged in a plane (e.g., in an xy-direction plane) that extends substantially parallel to the main surface of the substrate supporting the memory elements. The substrate may be a wafer on which layers of the memory elements are formed, or it may be a carrier substrate attached to the memory elements after they are formed. As a non-limiting example, the substrate may include a semiconductor, such as silicon.

[0075] Memory elements can be arranged in a single memory device level in an ordered array (such as in multiple rows and / or columns). However, memory elements can be arranged in unconventional or non-orthogonal configurations. Each memory element may have two or more electrodes or contact lines, such as bit lines and word lines.

[0076] A three-dimensional memory array is arranged such that the memory elements occupy multiple planes or multiple memory device levels, thereby forming a three-dimensional structure (i.e., in the x, y, and z directions, where the z direction is substantially perpendicular and the x and y directions are substantially parallel to the main surface of the substrate).

[0077] As a non-limiting example, a three-dimensional memory structure can be vertically arranged as a stack of multiple two-dimensional memory device levels. As another non-limiting example, a three-dimensional memory array can be arranged as multiple vertical columns (e.g., columns extending substantially perpendicular to the main surface of the substrate, i.e., along the y-direction), each column having multiple memory cells. The columns can be arranged in a two-dimensional configuration, for example, in the xy-plane, resulting in a three-dimensional arrangement of memory elements, wherein the elements are located on multiple vertically stacked memory planes. Other configurations of the three-dimensional memory elements can also constitute a three-dimensional memory array.

[0078] By way of non-limiting example, in a three-dimensional array of NAND strings, memory elements can be coupled together to form NAND strings within a single horizontal (e.g., xy) memory device level. Alternatively, memory elements can be coupled together to form vertical NAND strings spanning multiple horizontal memory device levels. Other three-dimensional configurations are conceivable, where some NAND strings contain memory elements within a single memory level, while others contain memory elements spanning multiple memory levels. The three-dimensional memory array can also be designed in NOR and ReRAM configurations.

[0079] Typically, in a monolithic three-dimensional memory array, one or more memory device classes are formed over a single substrate. Optionally, the monolithic three-dimensional memory array may also have one or more memory layers at least partially within the single substrate. As a non-limiting example, the substrate may include a semiconductor, such as silicon. In a monolithic three-dimensional array, the layer constituting each memory device class of the array is typically formed on the layer of the underlying memory device class of the array. However, the layers of adjacent memory device classes in a monolithic three-dimensional memory array may be shared or may have intervening layers between memory device classes.

[0080] Two-dimensional arrays can then be formed individually and then packaged together to form a non-monolithic memory device with multiple memory layers. For example, a non-monolithic stacked memory can be constructed by forming memory stages on separate substrates and then stacking the memory stages on top of each other. The substrates can be thinned or removed from the memory device stages before stacking, but since the memory device stages are initially formed on separate substrates, the resulting memory array is not a monolithic three-dimensional memory array. Furthermore, multiple two-dimensional or three-dimensional memory arrays (monolithic or non-monolithic) can be formed on separate chips and then packaged together to form a stacked chip memory device.

[0081] Figure 2 Schematic diagrams of three types of memory architectures utilizing interleaved memory strings are shown. For example, reference numeral 201 shows a schematic diagram of a first exemplary memory architecture, reference numeral 203 shows a schematic diagram of a second exemplary memory architecture, and reference numeral 205 shows a schematic diagram of a third exemplary memory architecture. In some embodiments, as shown, the memory architecture may include an array of interleaved NAND strings.

[0082] Figure 2 Blocks 200 and 210 of memory cells in an exemplary two-dimensional configuration of the memory array of Figure 1 are shown. The memory array may include a plurality of such memory blocks 200 and 210. Each exemplary block 200, 210 includes multiple NAND strings and corresponding bit lines, such as BL0, BL1, ... shared between blocks. Each NAND string is connected at one end to a drain-side selected gate (SGD), and the control gate of the drain-side selected gate is connected via a common SGD line. The NAND string is connected at its other end to a source-side selected gate (SGS), which is then connected to a common source line 220. Sixteen word lines, such as WL0-WL15, extend between the SGD and SGS. In some cases, dummy word lines that do not contain user data may also be used in memory arrays adjacent to selected gate transistors. Such dummy word lines can shield edge data word lines from certain edge effects.

[0083] One type of non-volatile memory that can be provided in a memory array is a floating-gate memory, such as... Figure 3A and Figure 3B The floating-gate memory shown is of this type. However, other types of non-volatile memory can also be used. As discussed in further detail below, Figure 4A and Figure 4B In another example shown, the charge-trapping memory cell uses a non-conductive dielectric material instead of a conductive floating gate to store charge in a non-volatile manner. A three-layer dielectric formed of silicon oxide, silicon nitride, and silicon oxide (“ONO”) is sandwiched between the surface of a conductive control gate and a semi-conductive substrate above the memory cell channel. The cell is programmed by injecting electrons from the cell channel into the nitride, where electrons are trapped and stored in a limited area. The stored charge then detectably alters the threshold voltage of a portion of the cell channel. The cell is erased by injecting hot holes into the nitride. A similar cell can be provided with a split-gate configuration, where a doped polysilicon gate extends above a portion of the memory cell channel to form a separate selection transistor.

[0084] In another approach, NROM cells are used. For example, two bits are stored in each NROM cell, where an ONO dielectric layer extends over a channel between the source and drain diffusion regions. The charge for one data bit is located in the dielectric layer adjacent to the drain, and the charge for the other data bit is located in the dielectric layer adjacent to the source. Multi-state data storage is obtained by reading the binary states of the spatially separated charge storage regions within the dielectric, respectively. Other types of non-volatile memories are also known.

[0085] Figure 3A Cross-sectional views of exemplary floating-gate memory cells 300, 310, and 320 in a NAND string are shown. In this figure, bit lines or NAND string directions enter the page, and word lines are oriented from left to right. For example, word line 324 extends across a NAND string that includes corresponding channel regions 306, 316, and 326. Memory cell 300 includes a control gate 302, a floating gate 304, a tunnel oxide layer 305, and a channel region 306. Memory cell 310 includes a control gate 312, a floating gate 314, a tunnel oxide layer 315, and a channel region 316. Memory cell 320 includes a control gate 322, a floating gate 321, a tunnel oxide layer 325, and a channel region 326. Each of memory cells 300, 310, and 320 is located in a different corresponding NAND string. A polysilicon interlayer dielectric (IPD) layer 328 is also shown. Control gates 302, 312, and 322 are part of the word line. Figure 3B A cross-sectional view along the contact line connector 329 is provided.

[0086] Control gates 302, 312, and 322 are wound around floating gates 304, 314, and 321, thereby increasing the surface contact area between control gates 302, 312, and 322 and floating gates 304, 314, and 321. This results in higher IPD capacitance, which in turn results in a higher coupling ratio, making programming and erasing easier. However, as NAND memory devices are scaled down, the spacing between adjacent cells 300, 310, and 320 becomes smaller, so there is almost no space between two adjacent floating gates 302, 312, and 322 for control gates 302, 312, and 322 and the IPD layer 328.

[0087] As an alternative, such as Figure 4A and Figure 4B As shown, planar or flat memory cells 400, 410, and 420 have been developed in which the control gates 402, 412, and 422 are flat or planar; that is, the control gate is not wrapped around the floating gate, and the only contact between the control gate and the charge storage layer is from above it. In this case, there is no advantage to having a tall floating gate. Instead, the floating gate is fabricated to be thinner. Furthermore, the floating gate can be used to store charge, or a thin charge trapping layer can be used to trap charge. This method avoids the ballistic electron transport problem, where electrons can travel through the floating gate after tunneling through the tunnel oxide during programming.

[0088] Figure 4A A cross-sectional view of exemplary charge-trapping memory cells 400, 410, and 420 in a NAND string is shown. This view is taken in the word line direction of the memory cells 400, 410, and 420, including planar control gates and charge-trapping regions, as a two-dimensional example of memory cells 400, 410, and 420 in the memory cell array of FIG. 1. Charge-trapping memory can be used in NOR and NAND flash memory devices. This technology uses an insulator such as a SiN film to store electrons, compared to floating-gate MOSFET technology which uses conductors such as doped polysilicon to store electrons. For example, word line 424 extends across a NAND string including corresponding channel regions 406, 416, and 426. A portion of the word line provides control gates 402, 412, and 422. IPD layer 428, charge-trapping layers 404, 414, and 421, polysilicon layers 405, 415, and 425, and tunnel layers 409, 407, and 408 are located below the word line. Each charge trapping layer 404, 414, 421 extends continuously within its respective NAND string. The flat configuration of the control gates allows for a thinner fabrication compared to floating gates. Furthermore, memory cells can be placed closer together.

[0089] Figure 4B The contact line connector 429 is shown. Figure 4AA cross-sectional view of the structure. The NAND string 430 includes an SGS transistor 431, exemplary memory cells 400, 433, ... 435, and an SGD transistor 436. Passages in the IPD layer 428 of the SGS transistor 431 and SGD transistor 436 allow communication between the control gate layer 402 and the floating gate layer. For example, the control gate layer 402 and the floating gate layer may be polysilicon, and the tunnel oxide layer may be silicon oxide. The IPD layer 428 may be a stack of nitride (N) and oxide (O), such as in a NONON configuration.

[0090] NAND strings can be formed on a substrate including a p-type substrate region 455, an n-type well 456, and a p-type well 457. N-type source / drain diffusion regions sd1, sd2, sd3, sd4, sd5, sd6, and sd7 are formed in the p-type well. A channel voltage Vch can be directly applied to the channel region of the substrate.

[0091] Figure 5 An exemplary block diagram of the sensing block SB1 of Figure 1 is shown. In one approach, the sensing block includes multiple sensing circuits. Each sensing circuit is associated with a data latch. For example, exemplary sensing circuits 550a, 551a, 552a, and 553a are associated with data latches 550b, 551b, 552b, and 553b, respectively. In one approach, different corresponding sensing blocks can be used to sense different subsets of bit lines. This allows the processing load associated with the sensing circuits to be partitioned and processed by a corresponding processor in each sensing block. For example, a sensing circuit controller 560 in SB1 can communicate with this group of sensing circuits and latches. The sensing circuit controller 560 may include a precharge circuit 561 that provides a voltage to each sensing circuit for setting a precharge voltage. In one possible approach, the voltage may be provided to each sensing circuit independently, for example, via a data bus and a local bus. In another possible approach, a common voltage may be provided to each sensing circuit simultaneously. The sensing circuit controller 560 may also include the precharge circuit 561, a memory 562, and a processor 563. Memory 562 may store code that can be executed by a processor to perform the functions described herein. These functions may include reading latches 550b, 551b, 552b, and 553b associated with sensing circuits 550a, 551a, 552a, and 553a, setting bit values ​​in the latches, and providing voltages for setting pre-charge levels in the sensing nodes of sensing circuits 550a, 551a, 552a, and 553a. Further exemplary details of the sensing circuit controller 560 and the sensing circuits 550a, 551a, 552a, and 553a are provided below.

[0092] In some embodiments, a memory cell may include a tag register comprising a set of latches storing tag bits. In some embodiments, the number of tag registers may correspond to the number of data states. In some embodiments, one or more tag registers may be used to control the type of verification technique used when verifying a memory cell. In some embodiments, the output of the tag bits may modify associated logic of the device, such as address decoding circuitry, to select a specified cell block. Body operations (e.g., erase operations, etc.) may be performed using tags set in the tag register, or a combination of tag registers and address registers, as in implicit addressing, or alternatively by direct addressing using only address registers.

[0093] Figure 6A This is a perspective view of a set of blocks 600 in an exemplary three-dimensional configuration of the memory array of FIG1. ​​On the substrate are exemplary blocks BLK0, BLK1, BLK2, and BLK3 of memory cells (memory elements), and a peripheral region 604 having circuitry used by blocks BLK0, BLK1, BLK2, and BLK3. For example, the circuitry may include voltage drivers 605 connectable to the control gate layers of blocks BLK0, BLK1, BLK2, and BLK3. In one approach, the control gate layers at a common height in blocks BLK0, BLK1, BLK2, and BLK3 are commonly driven. The substrate 601 may also carry circuitry beneath blocks BLK0, BLK1, BLK2, and BLK3, along with one or more lower metal layers patterned in conductive paths to carry signals from the circuitry. Blocks BLK0, BLK1, BLK2, and BLK3 are formed in a central region 602 of the memory device. In the upper region 603 of the memory device, one or more upper metal layers are patterned in conductive paths to carry circuit signals. Each block BLK0, BLK1, BLK2, BLK3 includes a stacked region of memory cells, where alternating levels of the stack represent word lines. In one possible approach, each block BLK0, BLK1, BLK2, BLK3 has opposing layered sides from which vertical contacts extend upwards to the upper metal layer to form connections with the conductive paths. Although four blocks BLK0, BLK1, BLK2, BLK3 are shown as an example, two or more blocks extending in the x and / or y directions can be used.

[0094] In one possible approach, the length of the plane in the x-direction represents the direction in which the signal path to the word line extends through one or more upper metal layers (word line or SGD line direction), and the width of the plane in the y-direction represents the direction in which the signal path to the bit line extends through one or more upper metal layers (bit line direction). The z-direction represents the height of the memory device.

[0095] Figure 6B It shows Figure 6A An exemplary cross-sectional view of a portion of one of blocks BLK0, BLK1, BLK2, and BLK3. The block comprises a stack 610 of alternating conductive and dielectric layers. In this example, in addition to data word line layers (word lines) WLL0 to WLL10, the conductive layers include two SGD layers, two SGS layers, and four dummy word line layers DWLD0, DWLD1, DWLS0, and DWLS1. The dielectric layers are labeled DL0 to DL19. Furthermore, a region of the stack 610 including NAND strings NS1 and NS2 is shown. Each NAND string contains memory vias 618 and 619 filled with material forming memory cells adjacent to the word lines. Region 622 of the stack 610 is shown in… Figure 6D This is shown in more detail below, and discussed further in detail below.

[0096] Stack 610 includes a substrate 611, an insulating film 612 located on the substrate 611, and a portion of a source line SL. NS1 has a source terminal 613 at the bottom 614 of the stack and a drain terminal 615 at the top 616 of the stack 610. Contact line connectors (e.g., slots, such as metal-filled slots) 617, 620 may be provided periodically across the stack 610 as interconnects extending through the stack 610, such as to connect source lines to specific contact lines above the stack 610. Contact line connectors 617, 620 may be used during word line formation and subsequently metal-filled. A portion of a bit line BL0 is also shown. A conductive via 621 connects the drain terminal 615 to BL0.

[0097] Figure 6C It shows Figure 6B A graph showing the diameter of memory apertures in a stack. The vertical axis is... Figure 6B The stack alignment is shown, and the width (wMH) of memory holes 618 and 619, such as the diameter, is shown. Figure 6A Word line layers WLL0-WLL10 are repeated as an example, and are located at corresponding heights z0-z10 in the stack. In such memory devices, the memory vias etched through the stack have very high aspect ratios. For example, a depth-to-diameter ratio of approximately 25 to 30 is common. The memory vias may have a circular cross-section. Due to the etching process, the width of the memory via can vary along the length of the via. Typically, the diameter of the memory via gradually decreases from its top to its bottom. That is, the memory via is tapered, narrowing at the bottom of the stack. In some cases, a slight narrowing occurs at the top of the via near the select gate, causing the diameter of the memory via to slightly widen before gradually decreasing from its top to its bottom.

[0098] Due to the non-uniformity of memory via width, the programming speed, including the programming slope and erase speed of the memory cell, can vary based on the location of the memory cell along the memory via (e.g., based on the height of the memory cell in the stack). For smaller diameter memory vias, the electric field across the tunnel oxide is relatively strong, resulting in relatively high programming and erase speeds. One approach is to define a group of adjacent word lines with a diameter similar to the memory via (e.g., within a defined diameter range) and apply an optimized verification scheme to each word line in the group. Different groups can have different optimized verification schemes.

[0099] Figure 6D It shows Figure 6B A close-up view of region 622 of the stack 610. Memory cells are formed at different levels of the stack at the intersection of word line layers and memory vias. In this example, SGD transistors 680, 681 are disposed above dummy memory cells 682, 683 and data memory cell MC. Multiple layers may be deposited, for example, along the sidewalls (SW) of the memory via 630 and / or within each word line layer using atomic layer deposition. For example, each column (e.g., a pillar formed by material within the memory via 630) may include a charge trapping layer or film 663 (such as SiN or other nitrides), a tunnel layer 664, a polysilicon body or channel 665, and a dielectric core 666. The word line layers may include a blocking oxide / bulk high-k material 660, a metal blocking layer 661, and a conductive metal 662 (such as tungsten) as control gates. For example, control gates 690, 691, 692, 693, and 694 are provided. In this example, all layers except the metal are provided within the memory via 630. In other methods, some layers within the layer can be in the control gate layer. Additional pillars are similarly formed in different memory vias. These pillars can form pillared active regions (AA) of the NAND string.

[0100] When a data memory cell MC is programmed, electrons are stored in a portion of the charge trapping layer 663 associated with the memory cell MC. These electrons are attracted from the channel 665 into the charge trapping layer 663 and pass through the tunnel layer 664. The Vth of the memory cell MC increases proportionally to the amount of stored charge. During an erase operation, the electrons return to the channel 665.

[0101] Each memory via 630 may be filled with multiple annular layers, including a barrier oxide layer, a charge trapping layer 663, a tunnel layer 664, and a channel layer 665. The core region of each memory via 630 is filled with the host material, and the multiple annular layers are located between the core region and the word line in each memory via 630.

[0102] NAND strings can be considered to have floating channels 665 because the length of the channels 665 is not formed on the substrate. In addition, NAND strings are provided by multiple word line layers stacked one on top of the other and separated from each other by dielectric layers.

[0103] Figure 7A A schematic plan view of a memory array 700 with multiple memory vias 722 and multiple dummy vias 705 is shown. These multiple memory vias can be vertical chains of memory cells as described herein, and the multiple dummy vias do not require a complete memory structure. Shallow trench etch or shallow etched feature (SHE) 710 extends through multiple word lines (e.g., five), but not completely through the chip, to electrically isolate adjacent strings from each other. The SHE extends directly through a set of aligned dummy vias 705, thereby preventing those dummy vias 705 from storing data or otherwise becoming functional memory cells.

[0104] Now for reference Figure 8A and 8B There are no fictitious holes. (And) Figure 7A and 7B Unlike the memory structure 700, SHE 810 is located in the gap between two adjacent rows of memory cells and overlaps with memory vias 825 to form a working chain. This working chain has a trench etched into at least one side of the SGD switch at the top of the working memory chain, shown here as memory via 825. This configuration significantly improves yield and memory density because all memory vias 822, 825 are functional, i.e., fewer memory vias are wasted.

[0105] Unlike the fully circular memory hole 822, the memory hole 825 and SGD switch, which are partially cut by the SHE 810, have a semi-circular shape, which can be a semi-circle or larger or smaller than a semi-circle. In some cases, the memory hole 825 and SGD switch can be smaller than a semi-circle on one side of the SHE 810 and larger than a semi-circle on the other side of the SHE 810.

[0106] Memory holes 822, 825 and multiple bit lines 830 (labeled as) Figure 8A Bit lines 0-7 are connected. For ease of illustration, only eight bit lines 830 are shown. Bit lines 830 extend above the memory holes and are connected to select the memory holes via connection points. The memory holes in each string region are also connected at one end to the SGD switch or the drain-side select gate SGD transistor and at the other end to the SGS switch. The SHE trench 810 can be etched into a portion of the SGD switch.

[0107] As mentioned above, it may be difficult to select the bias applied to the drain-side select gate SGD. Figure 9This is a top sectional view of two semi-circular memory holes partially cut using SHE 810. Figure 9 The leftmost part) and the corresponding vertical section ( Figure 9 The middle section shows a graph illustrating the threshold voltage distribution of the SGD switch due to read stress and subsequent electron redistribution, as well as the redistribution and relaxation. Figure 9 (The rightmost part). As shown in the figure, the redistribution caused by read stress may result in a temporary downward shift in the threshold voltage Vt of the SGD switch or transistor. Figure 10 The experimental results illustrating read stress are shown. For this experiment, the selected string exhibits charge redistribution within the charge trapping layer (CTL) (small select gate voltage VSG) and charge loss through the oxide block (large select gate voltage VSG), while the unselected string exhibits lateral charge migration induced by the selected string's select gate voltage VSG. Therefore, as shown, different select gate voltages VSG are applied to the drain-side select gate SGD transistors on multiple strings, and 10,000 block read stress and power cycles are repeated. Figure 11 A graph showing the threshold distribution after 100,000 block read stresses is presented. Therefore, a downward shift exists in the semi-circular drain-side selected gate (SC-SGD) after read interference. This interference occurs in the selected string and its SHE-adjacent strings ( Figure 9 Additionally, at approximately 3.8 au of the select-gate voltage VSG, the drain-side select-gate SGD shift and injection interference are significantly reduced. Finally, the drain-side select-gate SGD threshold voltage Vt distribution recovers after relaxation.

[0108] Figure 12 The threshold voltage Vt distributions of multiple exemplary memory cell groups using different selection gate voltages VSGs with different processes (e.g., no OPS (upper spacing SGD), OPS (case 1), OPS (case 2), and OPS (case 3)) are shown. Figure 13 The threshold voltage Vt plots for three memory dies (e.g., memory die 108) are shown. As illustrated, different dies are turned on, and the process responds differently to the select gate voltage or bias VSG. Generally, whenever possible, it is preferable to use the lowest possible select gate voltage VSG to mitigate the risk of drain-side select gate SGD downshift. However, due to variations in the manufacturing process, different dies can have different threshold voltages Vt for the drain-side select gate SGD transistor. For example, in Figure 13 In this configuration, die 1 has the perfect threshold voltage Vt of the drain-side selected-gate SGD transistor, so all bits are below 3a.u. In this case, an overdrive voltage Vt can be applied to the minimum selected-gate voltage VSG of 3a.u. OVERDRIVEThe drain-side selected-gate SGD transistor is turned on when (e.g., 0.5au) = 3.5au. Other dies (die 2) have a wider threshold voltage Vt for the drain-side selected-gate SGD transistor, so all bits are below 3.2au. In this case, an overdrive voltage V can be applied to the minimum selected-gate voltage VSG of 3.2au. OVERDRIVE These drain-side selected-gate SGD transistors are turned on at a threshold voltage of 3.7au (e.g., 0.5au). Some dies (die 3) have a higher threshold voltage Vt for the drain-side selected-gate SGD transistors, so all bits are below 3.8au. In this case, it is possible to turn on the minimum selected-gate voltage Vt at VSG = 3.8au by adding the overdrive voltage Vt. OVERDRIVE These drain-side select-gate (SGD) transistors are turned on when (e.g., 0.5au) = 4.3au. Therefore, it is desirable to allow different dies to have different select-gate voltage (VSG) biases.

[0109] Therefore, this paper describes a memory device (e.g., Figure 1A Memory device 100), which includes a word line connected to a plurality of word lines (e.g., Figure 6B Data word line layer (word line) WLL0-WLL10 or Figure 6D The memory cells of WLL10 (e.g., Figure 6D The data storage unit MC and virtual memory units 682, 683). The memory units are arranged in a string (e.g., Figure 6B The NAND strings NS1 and NS2 are configured to hold a threshold voltage Vt or Vth. Similarly, each string has at least one drain-side selected-gate SGD transistor on the drain side of that string, connected to one of the multiple bit lines and coupled to a memory cell of the string. The device also includes control circuitry or components (e.g., Figure 1A The control circuit 110, decoder 114 / 132, power control module 116, sensing blocks SB1, SB2, ..., SBp, read / write circuit 128, controller 122, Figure 1B Control circuit 150 and / or Figure 5The control unit (such as a sensing circuit controller 560, or any combination thereof) is coupled to a plurality of word lines and a plurality of bit lines and a plurality of drain-side selected-gate SGD transistors. The control unit is configured to determine a unique selected-gate voltage (VSG) for each of a plurality of groups of memory cells. This unique selected-gate voltage (VSG) is applied individually to each of the plurality of groups of memory cells. The control unit is also configured to apply the unique selected-gate voltage (VSG) to at least one drain-side selected-gate SGD transistor of a selected string in each of the plurality of groups of memory cells to turn on at least one drain-side selected-gate SGD transistor of the selected string during memory operation.

[0110] According to one aspect, at least one drain-side selected-gate (SGD) transistor is configured to maintain a transistor threshold voltage. The control unit is further configured to adaptively adjust the unique selected-gate voltage VSG based on the transistor threshold voltage of at least one SGD transistor in each of a plurality of groups of memory cells. More specifically, the control unit is further configured to, in response to receiving a selected-gate bias search command, detect the threshold voltage VSG. DETECT Initialize to a predetermined detection threshold voltage. Next, set the select gate voltage VSG of at least one drain-side select-gate SGD transistor in the string of each of the multiple groups of memory cells to the detection threshold voltage V. DETECT Then, the control unit selects at least one drain-side gate SGD transistor with a voltage higher than the detection threshold V for each of the multiple groups of memory cells. DETECT The drain-side selected gate quantity of the transistor threshold voltage is counted. The control unit is configured to determine whether the drain-side selected gate quantity is greater than a drain-side selected gate quantity detection threshold. In response to the drain-side selected gate quantity not being greater than the drain-side selected gate quantity detection threshold, the control unit decrements the detection threshold voltage V by Δ (e.g., 0.4au). DETECT And return the select gate voltage VSG of at least one drain-side select-gate SGD transistor of the string of multiple packets applied to the memory cell as the detection threshold voltage V. DETECT .

[0111] Figures 14A to 14D The threshold voltage Vt distribution and exemplary detection threshold voltage V of a drain-side selected gate SGD transistor are shown. DETECT And the drain-side selected-gate SGD transistors in each of the corresponding multiple groups have a voltage higher than the detection threshold V. DETECT The gate quantity is selected on the drain side of the transistor threshold voltage. Therefore, as shown in the figure, the threshold voltage V is detected. DETECTThe voltage is set to 4.6au, and the control unit selects at least one drain-side gate SGD transistor with a voltage higher than the detection threshold V for each of the multiple groups of memory cells. DETECT The drain-side selected gate quantity of the transistor threshold voltage is counted, and there is no count bit (i.e., the drain-side selected gate quantity is zero). The control unit determines that the drain-side selected gate quantity is not greater than the drain-side selected gate quantity detection threshold, and since the drain-side selected gate quantity is not greater than the drain-side selected gate quantity detection threshold, the threshold voltage V is detected by Δ. DETECT Decreasing detection threshold voltage V DETECT And return the select gate voltage VSG of at least one drain-side select-gate SGD transistor of the string of multiple packets applied to the memory cell as the detection threshold voltage V. DETECT Therefore, the control unit repeats this decrementing and counting process. Figures 14B to 14D The control unit continues this process until it determines that the drain-side selected gate amount is greater than the drain-side selected gate amount detection threshold. The control unit is also configured to set the unique selected gate voltage VSG to be equal to the detection threshold voltage V in response to the drain-side selected gate amount being greater than the drain-side selected gate amount detection threshold. DETECT Plus the predetermined fixed overdrive voltage V OVERDRIVE The adaptive selection gate voltage (VSG) is then used. The control unit then completes the gate bias selection search.

[0112] According to one aspect, the control unit is further configured to periodically determine the unique selected gate voltage (VSG) for each of a plurality of groups of memory cells. According to another aspect, the control unit is further configured to count a loop as equal to the number of times memory operations have been performed on memory cells for one or more of the plurality of groups of memory cells. The control unit is also configured to determine whether the loop count exceeds a predetermined loop count threshold. Then, in response to the loop count exceeding the predetermined loop count threshold, the control unit determines the unique selected gate voltage for each of the plurality of groups of memory cells. In other words, a selected gate bias search can be performed after a plurality of loops exceeding the predetermined loop count threshold.

[0113] Figure 15 Multiple memory cell blocks are illustrated, wherein the disclosed adaptive select-gate bias search method or technique has been used to determine the select-gate voltage VSG of each block and the threshold voltage Vt distribution of the drain-side select-gate SGD transistor of each block. According to one aspect, multiple groups of memory cells comprise multiple blocks (e.g., Figure 15 (blocks x and block y), each block includes multiple memory units. Figures 16A to 16BThe diagram shows the threshold voltage Vt distribution of the drain-side select-gate SGD transistors in the top, middle, and bottom blocks of a full-circular memory via, a semi-circular memory via, and a semi-circular memory via, for two different memory dies. Therefore, an adaptive select-gate bias or voltage VSG can be applied to different blocks (e.g., different blocks (regions) may have different SHE etch conditions, and thus their vulnerability may differ), depending on the block (region) level drain-side select-gate SGD threshold voltage Vt. By doing so, each block (region) is guaranteed to obtain its own "minimum VSG bias" to minimize the risk of read stress-induced SGD downshift. Due to manufacturing process variations, some regions of the die have poorer SGD upper tail threshold voltages Vt, and therefore require higher select-gate voltages VSG. Other regions of the die have smaller SGD upper tails, and therefore require smaller select-gate voltages VSG.

[0114] Figure 17 Multiple memory dies of memory cells are shown, wherein the disclosed adaptive select-gate bias search method or technique has been used to determine the select-gate voltage VSG of each memory die and the threshold voltage Vt distribution of the drain-side select-gate SGD transistor of each memory die. According to one aspect, the memory component may further include multiple memory dies NAND die 0, NAND die 1, NAND die 2, NAND die 3, NAND die 4, NAND die 5, NAND die 6, and NAND die 7 (e.g., memory die 108), each memory die comprising a memory cell. Thus, multiple groups of memory cells may include the multiple memory dies NAND die 0, NAND die 1, NAND die 2, NAND die 3, NAND die 4, NAND die 5, NAND die 6, and NAND die 7, each physically separated from the others. Figures 18A to 18B The diagram shows the threshold voltage Vt distribution of the drain-side select-gate SGD transistor in the top block, middle block, and bottom block of a semi-circular memory via for two different memory dies. Therefore, an adaptive select-gate bias or voltage can be applied to different dies based on their own drain-side select-gate SGD threshold voltage Vt. By doing so, each die can be guaranteed to minimize the risk of read stress-induced SGD downshift using its own “minimum VSG bias.” Due to manufacturing process variations, some dies have a poorer SGD upper tail threshold voltage Vt, thus requiring a higher select-gate voltage VSG. Some other dies have a smaller SGD upper tail, thus requiring a smaller select-gate voltage VSG.

[0115] Figure 19and Figure 20 The steps of a method for operating a memory device are illustrated. As described above, a memory device (e.g., Figure 1A The memory device 100) includes a word line connected to a plurality of word lines (e.g., Figure 6B Data word line layer (word line) WLL0-WLL10 or Figure 6D The memory cells of WLL10 (e.g., Figure 6D The data storage unit MC and virtual memory units 682, 683). The memory units are arranged in a string (e.g., Figure 6B The NAND strings NS1 and NS2 are configured to hold a threshold voltage Vt or Vth. Generally, each string has at least one drain-side selected gate transistor on the drain side of one string connected to one of a plurality of bit lines and coupled to a memory cell of the string. (See first for reference.) Figure 19 The method includes step 1000 of determining a unique select gate voltage (VSG) for each of a plurality of groups of memory cells. The unique select gate voltage (VSG) is applied individually to each of the plurality of groups of memory cells. A next step of the method is 1002, which involves applying the unique select gate voltage (VSG) to at least one drain-side select gate (SGD) transistor of a selected string in each of the plurality of groups of memory cells to turn on at least one drain-side select gate (SGD) transistor of the selected string during memory operation.

[0116] As described above, according to one aspect, the plurality of groups of memory cells includes a plurality of blocks, each comprising a plurality of memory cells. According to another aspect, the memory device further includes a plurality of memory dies 108, the plurality of memory dies comprising memory cells, and wherein the plurality of groups of memory cells includes a plurality of memory dies 108 that are physically separated from each other.

[0117] Now for reference Figure 20 The method further includes step 1004: adaptively adjusting the unique select-gate voltage VSG based on the transistor threshold voltage of at least one drain-side select-gate SGD transistor in each of a plurality of groups of memory cells. Similarly, at least one drain-side select-gate SGD transistor is configured to maintain the transistor threshold voltage. Therefore, the method further includes step 1006: initiating an adaptive select-gate bias search or a select-gate bias search, and step 1008: in response to receiving a select-gate bias search command, detecting the threshold voltage VSG. DETECTInitialize to a predetermined detection threshold voltage. The next step of the method is 1010: set the select gate voltage VSG of at least one drain-side select-gate SGD transistor of each of the multiple groups of memory cells to the detection threshold voltage V. DETECT The next step of the method is 1012: for each of the multiple groups of memory cells, at least one drain-side selected gate SGD transistor in the string has a voltage higher than the detection threshold V. DETECT The method counts the drain-side selected gate amount of the transistor threshold voltage. The method proceeds to step 1014: determining whether the drain-side selected gate amount is greater than a drain-side selected gate amount detection threshold. Then the method includes step 1016: in response to the drain-side selected gate amount not being greater than the drain-side selected gate amount detection threshold, decrementing the detection threshold voltage V by Δ detection threshold voltage (e.g., 0.4au). DETECT And return the select gate voltage VSG of at least one drain-side select-gate SGD transistor of the string of multiple packets applied to the memory cell as the detection threshold voltage V. DETECT The method further includes step 1018: in response to the drain-side selected gate amount being greater than the drain-side selected gate amount detection threshold, setting the unique selected gate voltage VSG to be equal to the detection threshold voltage V. DETECT Plus the predetermined fixed overdrive voltage V OVERDRIVE The method also includes step 1020: completing the gate bias search.

[0118] According to one aspect, a select-gate voltage (VSG) or bias search can be performed periodically. Therefore, the method includes the step of periodically determining a unique select-gate voltage (VSG) for each of a plurality of groups of memory cells. According to another aspect, a search can be triggered based on the loop result. Therefore, the method includes the step of counting a loop count equal to the number of times memory operations have been performed on memory cells for one or more of the plurality of groups of memory cells. Next, it is determined whether the loop count exceeds a predetermined loop count threshold. The method continues with the following step: in response to the loop count exceeding the predetermined loop count threshold, determining a unique select-gate voltage (VSG) for each of the plurality of groups of memory cells.

[0119] The advantages of the memory devices and methods disclosed herein include minimizing the half-circular drain-side select gate (SGD) downshift without the risk of cutting off the NAND string due to a low select gate voltage (VSG). Furthermore, because the memory devices and methods disclosed herein can perform an adaptive select gate bias search for each block and / or each memory die, each die or block can achieve its own “minimum VSG” bias.

[0120] Obviously, changes may be made to what is described and shown herein without departing from the scope defined in the appended claims. The foregoing description of embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or limiting of this disclosure. Various elements or features of a particular embodiment are generally not limited to that particular embodiment, but are interchangeable where applicable and can be used in selected embodiments, even if not specifically shown or described. The same applies to many other aspects. Such variations should not be considered as departing from this disclosure, and all such modifications are intended to be included within the scope of this disclosure.

Claims

1. A memory device, the memory device comprising: A memory cell, the memory cell being connected to one of a plurality of word lines and being arranged in series and configured to hold a threshold voltage; Each of the strings has at least one drain-side selected gate transistor, the at least one drain-side selected gate transistor being located on the drain side of the string connected to one of the multiple bit lines and coupled to the memory cell of the string. and A control unit, coupled to the plurality of word lines and the plurality of bit lines and the at least one drain-side selected gate transistor, and configured to: A uniquely selected gate voltage is determined for each of a plurality of groups of the memory cells, the uniquely selected gate voltage being applied individually to each of the plurality of groups of the memory cells, such that a different uniquely selected gate voltage is determined for each of the plurality of groups, and The corresponding uniquely selected gate voltage is applied to at least one drain-side selected gate transistor of a selected string in each of the plurality of groups of the memory cell to turn on at least one drain-side selected gate transistor of the selected string during memory operation. Determining the corresponding unique select gate voltage includes: for each of a plurality of groups of the memory cells, (i) setting the select gate voltage to a detection threshold voltage, and (ii) selectively adjusting the detection threshold voltage and setting the select gate voltage to the adjusted detection threshold voltage; (iii) Setting the corresponding unique selection gate voltage in response to the adjustment of the detection threshold voltage.

2. The memory device of claim 1, wherein the plurality of groups of the memory cells comprises a plurality of blocks, each comprising a plurality of the memory cells.

3. The memory device of claim 1, further comprising a plurality of memory dies, the plurality of memory dies including the memory cells, and wherein the plurality of groups of the memory cells includes the plurality of memory dies each physically separated from each other.

4. The memory device of claim 1, wherein the control unit is further configured to adaptively adjust the corresponding unique select gate voltage based on the transistor threshold voltage of the at least one drain-side select gate transistor of each of the plurality of groups of the memory cells.

5. The memory device of claim 1, wherein the at least one drain-side selected gate transistor is configured to maintain a transistor threshold voltage, and the control element is further configured to: In response to receiving a select gate bias search command, the detection threshold voltage is initialized to a predetermined detection threshold voltage; The select gate voltage of at least one drain-side select gate transistor of the string of each of the plurality of packets applied to the memory cell is set as the detection threshold voltage; The number of drain-side selected gates having a transistor threshold voltage higher than the detection threshold voltage in at least one drain-side selected gate transistor of each of the plurality of groups of the memory cells is counted. Determine whether the drain-side selected gate amount is greater than the drain-side selected gate amount detection threshold; In response to the drain-side selected gate amount not being greater than the drain-side selected gate amount detection threshold, the detection threshold voltage is decremented by Δ detection threshold voltage and the selected gate voltage of at least one drain-side selected gate transistor of the string of each of the plurality of groups of the memory cell is set to the detection threshold voltage. In response to the drain-side selected gate amount being greater than the drain-side selected gate amount detection threshold, the corresponding unique selected gate voltage is set to an adaptive selected gate voltage equal to the detection threshold voltage plus a predetermined fixed overdrive voltage. and Complete the gate bias selection search.

6. The memory device of claim 1, wherein the control unit is further configured to periodically determine the uniquely selected gate voltage for each of the plurality of groups of the memory cell.

7. The memory device of claim 1, wherein the control unit is further configured to: The loop count is set to the number of times the memory operation has been performed on one or more of the plurality of groups of the memory cell; Determine whether the loop count exceeds a predetermined loop count threshold; and In response to the cycle count exceeding the predetermined cycle count threshold, the corresponding unique selected gate voltage for each of the plurality of groups of the memory cell is determined.

8. A controller for communicating with a memory device, the memory device comprising memory cells connected to one of a plurality of word lines and arranged in strings and configured to hold a threshold voltage, each of the strings having at least one drain-side selected-gate transistor, the at least one drain-side selected-gate transistor being coupled to the memory cells of the string on the drain side of the string connected to one of the plurality of bit lines, the controller being configured to: A uniquely selected gate voltage is determined for each of a plurality of groups of the memory cells, the uniquely selected gate voltage being applied individually to each of the plurality of groups of the memory cells, such that a different uniquely selected gate voltage is determined for each of the plurality of groups, and The memory device is instructed to apply the corresponding unique select gate voltage to at least one drain-side select gate transistor of a selected string in each of the plurality of groups of the memory cell, so as to turn on at least one drain-side select gate transistor of the selected string during memory operation. Determining the corresponding unique gate voltage includes: For each of the multiple groups of the memory cells, (i) a selected gate voltage is set to a detection threshold voltage, and (ii) the detection threshold voltage is selectively adjusted and the selected gate voltage is set to the adjusted detection threshold voltage. (iii) Setting the corresponding unique selection gate voltage in response to the adjustment of the detection threshold voltage.

9. The controller of claim 8, wherein the plurality of groups of the memory cells comprises a plurality of blocks, each comprising a plurality of the memory cells.

10. The controller of claim 8, wherein the memory device further comprises a plurality of memory dies, the plurality of memory dies comprising the memory cells, and wherein the plurality of groups of the memory cells comprises the plurality of memory dies each physically separated from each other.

11. The controller of claim 8, wherein the controller is further configured to instruct the memory device to adaptively adjust the corresponding unique select gate voltage based on the transistor threshold voltage of the at least one drain-side select gate transistor of each of the plurality of groups of the memory cells.

12. The controller of claim 8, wherein the at least one drain-side selected gate transistor is configured to maintain a transistor threshold voltage, and the controller is further configured to: In response to receiving a select gate bias search command, the detection threshold voltage is initialized to a predetermined detection threshold voltage; The memory device is instructed to set the select gate voltage of at least one drain-side select gate transistor of the string of each of the plurality of packets of the memory cell to the detection threshold voltage; The memory device is instructed to count the number of drain-side selected gates in at least one drain-side selected gate transistor of each of the plurality of groups of the memory cells, which have a transistor threshold voltage higher than the detection threshold voltage. Determine whether the drain-side selected gate amount is greater than the drain-side selected gate amount detection threshold; In response to the drain-side selected gate amount not being greater than the drain-side selected gate amount detection threshold, the memory device is instructed to decrement the detection threshold voltage by Δ detection threshold voltage and return to instructing the memory device to set the selected gate voltage of at least one drain-side selected gate transistor of the string of each of the plurality of groups of the memory cell to the detection threshold voltage; In response to the drain-side selected gate amount being greater than the drain-side selected gate amount detection threshold, the memory device is instructed to set the corresponding unique selected gate voltage to an adaptive selected gate voltage equal to the detection threshold voltage plus a predetermined fixed overdrive voltage. and Complete the gate bias selection search.

13. The controller of claim 8, wherein the controller is further configured to periodically determine the uniquely selected gate voltage for each of the plurality of groups of the memory cells.

14. A method of operating a memory device, the memory device comprising memory cells connected to one of a plurality of word lines and arranged in strings and configured to maintain a threshold voltage, each of the strings having at least one drain-side selected gate transistor, the at least one drain-side selected gate transistor being coupled to the memory cells of the string on the drain side of the string connected to one of the plurality of bit lines, the method comprising the steps of: A uniquely selected gate voltage is determined for each of a plurality of groups of the memory cells, the uniquely selected gate voltage being applied individually to each of the plurality of groups of the memory cells, such that a different uniquely selected gate voltage is determined for each of the plurality of groups, and The corresponding uniquely selected gate voltage is applied to at least one drain-side selected gate transistor of a selected string in each of the plurality of groups of the memory cell to turn on at least one drain-side selected gate transistor of the selected string during memory operation. Determining the corresponding unique select gate voltage includes: for each of a plurality of groups of the memory cells, (i) setting the select gate voltage to a detection threshold voltage, (ii) selectively adjusting the detection threshold voltage and setting the select gate voltage to the adjusted detection threshold voltage; and (iii) setting the corresponding unique select gate voltage in response to the adjustment of the detection threshold voltage.

15. The method of claim 14, wherein the plurality of groups of the memory cells comprises a plurality of blocks, each comprising a plurality of the memory cells.

16. The method of claim 14, wherein the memory device further comprises a plurality of memory dies, the plurality of memory dies comprising the memory cells, and wherein the plurality of groups of memory cells comprises the plurality of memory dies each physically separated from each other.

17. The method of claim 14, further comprising the step of: The corresponding unique gate voltage is adaptively adjusted based on the transistor threshold voltage of at least one drain-side selected gate transistor in each of the plurality of groups of the memory cells.

18. The method of claim 14, wherein the at least one drain-side selected gate transistor is configured to maintain a transistor threshold voltage, the method further comprising the step of: In response to receiving a select gate bias search command, the detection threshold voltage is initialized to a predetermined detection threshold voltage; The select gate voltage of at least one drain-side select gate transistor of the string of each of the plurality of packets applied to the memory cell is set as the detection threshold voltage; The number of drain-side selected gates having a transistor threshold voltage higher than the detection threshold voltage in at least one drain-side selected gate transistor of each of the plurality of groups of the memory cells is counted. Determine whether the drain-side selected gate amount is greater than the drain-side selected gate amount detection threshold; In response to the drain-side selected gate amount not being greater than the drain-side selected gate amount detection threshold, the detection threshold voltage is decremented by Δ detection threshold voltage and the selected gate voltage of at least one drain-side selected gate transistor of the string of each of the plurality of groups of the memory cell is set to the detection threshold voltage. In response to the drain-side selected gate amount being greater than the drain-side selected gate amount detection threshold, the corresponding unique selected gate voltage is set to an adaptive selected gate voltage equal to the detection threshold voltage plus a predetermined fixed overdrive voltage. and Complete the gate bias selection search.

19. The method of claim 14, further comprising the step of periodically determining the uniquely selected gate voltage for each of the plurality of groups of the memory cell.

20. The method of claim 14, further comprising the step of: The loop count is set to the number of times the memory operation has been performed on one or more of the plurality of groups of the memory cell; Determine whether the loop count exceeds a predetermined loop count threshold; and In response to the cycle count exceeding the predetermined cycle count threshold, the corresponding unique selected gate voltage for each of the plurality of groups of the memory cell is determined.

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