阅读说明：本技术 对存储器件进行编程的方法及相关存储器件 (Method of programming a memory device and related memory device ) 是由 崔莹 贾建权 游开开 于 2019-10-12 设计创作，主要内容包括：当对包括耦合到多个字线和多个位线的多个存储单元的存储器件进行编程时,对多个字线中的两个相邻的第一和第二字线执行粗略编程。接下来,在对第一字线和第二字线执行粗略编程之后的第一时段期间,对多个位线中的未选择的位线进行预充电。另外,在第一时段的开始时导通未选择的位线和第二字线之间的沟道,并且在第一时段的结束之前关断该沟道。然后,在第一时段之后的第二时段期间,对第一字线执行精细编程。(When programming a memory device including a plurality of memory cells coupled to a plurality of word lines and a plurality of bit lines, coarse programming is performed on two adjacent first and second word lines of the plurality of word lines. Next, unselected bit lines of the plurality of bit lines are precharged during a first period after performing the coarse programming on the first word line and the second word line. In addition, a channel between the unselected bit line and the second word line is turned on at the beginning of the first period, and is turned off before the end of the first period. Then, during a second period after the first period, fine programming is performed on the first word line.)

1. A method of programming a NAND memory device comprising a plurality of memory cells coupled to a plurality of word lines and a plurality of bit lines, the method comprising:

performing coarse programming on a first word line of the plurality of word lines;

performing the coarse programming on a second word line of the plurality of word lines;

precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line;

turning on a channel between the unselected bit line and the first word line by applying a positive turn-on voltage to the second word line at the beginning of the first period, and turning off the channel between the unselected bit line and the first word line before the end of the first period, wherein the first word line and the second word line are adjacent; and

performing fine programming on the first word line during a second period after the first period.

2. The method of claim 1, further comprising:

precharging the unselected bit lines by applying a first pre-pulse voltage having a first width to the unselected bit lines during the first period; and

turning on and off the channel between the unselected bit line and the first word line by applying a second pre-pulse voltage having a second width to the unselected word line, wherein the second width is less than the first width.

3. The method of claim 2, wherein a rising edge of the first pre-pulse voltage is aligned with a rising edge of the second pre-pulse voltage.

4. The method of claim 1, further comprising:

performing the coarse programming on the first word line by ramping up the first word line to a first voltage; and

performing the fine programming on the first word line by ramping up the first word line to a second voltage, wherein the second voltage is greater than the first voltage.

5. A method of programming a NAND memory device comprising a plurality of memory cells coupled to a plurality of word lines and a plurality of bit lines, the method comprising:

performing coarse programming on a first word line of the plurality of word lines;

performing the coarse programming on a second word line of the plurality of word lines;

precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line;

reducing a channel voltage of the first word line during the first period; and

performing fine programming on the first word line during a second period after the first period.

6. The method of claim 5, further comprising:

precharging the unselected bit lines by applying a positive pre-pulse voltage to the unselected bit lines during the first period; and

reducing the channel voltage of the first word line by applying a negative pre-pulse voltage to the first word line during the first period.

7. The method of claim 5, further comprising:

performing the coarse programming on the first word line by ramping up the first word line to a first voltage; and

performing the fine programming on the first word line by ramping up the first word line to a second voltage, wherein the second voltage is greater than the first voltage.

8. A NAND memory device comprising:

a plurality of word lines;

a plurality of bit lines;

a plurality of memory cells coupled to the plurality of word lines and the plurality of bit lines; and

a control unit configured to:

performing coarse programming on a first word line of the plurality of word lines;

performing the coarse programming on a second word line of the plurality of word lines;

precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line;

turning on a channel between the unselected bit line and the first word line at the beginning of the first period by applying a positive turn-on voltage to the second word line, and turning off the channel between the unselected bit line and the first word line before the end of the first period, wherein the first word line and the second word line are adjacent; and

performing fine programming on the first word line during a second period after the first period.

9. The NAND memory device of claim 8, wherein the control unit is further configured to:

precharging the unselected bit lines by applying a first pre-pulse voltage having a first width to the unselected bit lines during the first period; and

turning on and off the channel between the unselected bit line and the first word line by applying a second pre-pulse voltage having a second width to the unselected word line, wherein the second width is less than the first width.

10. The NAND memory device of claim 9, wherein a rising edge of the first pre-pulse voltage is aligned with a rising edge of the second pre-pulse voltage.

11. The NAND memory device of claim 8, wherein the control unit is further configured to:

performing the coarse programming on the first word line by ramping up the first word line to a first voltage; and

performing the fine programming on the first word line by ramping up the first word line to a second voltage, wherein the second voltage is greater than the first voltage.

12. The NAND memory device of claim 8, wherein the plurality of memory cells are arranged in a three-dimensional four-level cell (3D QLC) structure.

13. A NAND memory device comprising:

a plurality of word lines;

a plurality of bit lines;

a plurality of memory cells coupled to the plurality of word lines and the plurality of bit lines; and

a control unit configured to:

performing coarse programming on a first word line of the plurality of word lines;

performing the coarse programming on a second word line of the plurality of word lines;

precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line;

reducing a channel voltage of the first word line during the first period; and

performing fine programming on the first word line during a second period after the first period.

14. The NAND memory device of claim 13, wherein the control unit is further configured to:

precharging the unselected bit lines by applying a positive pre-pulse voltage to the unselected bit lines during the first period; and

reducing the channel voltage of the first word line by applying a negative pre-pulse voltage to the first word line during the first period.

15. The NAND memory device of claim 13, wherein the control unit is further configured to:

performing the coarse programming on the first word line by ramping up the first word line to a first voltage; and

performing the fine programming on the first word line by ramping up the first word line to a second voltage, wherein the second voltage is greater than the first voltage.

16. The NAND memory device of claim 13, wherein the plurality of memory cells are arranged in a three-dimensional four-level cell (3D QLC) structure.

Technical Field

The present invention relates to a method of programming a memory device and a related memory device, and more particularly, to a method of programming a memory device having a 3D QLC structure and a related memory device.

Background

Semiconductor memories have become increasingly popular for use in various electronic devices. For example, non-volatile semiconductor memory is used in cellular phones, digital cameras, personal digital assistants, mobile computing devices, non-mobile computing devices, and other devices. Recently, ultra-high density storage devices using a three-dimensional (3D) stacked memory structure (sometimes referred to as a Bit Cost Scalable (BiCS) architecture) have been proposed. For example, a 3D NAND stack flash memory device may be formed from an array of alternating conductive and dielectric layers. Storage holes are drilled in the layers to define a number of storage layers simultaneously. The NAND string is then formed by filling the storage hole with an appropriate material. The control gate of the memory cell is provided by a conductive layer.

Single Level Cell (SLC) nonvolatile memory can store only one bit per storage element, while multi-level cell (MLC) nonvolatile memory can store more than one bit per cell. For example, a NAND memory having 16 voltage levels per cell may be referred to as a four-level cell (QLC) memory, and may represent 4 bits of data per cell.

Each planar NAND memory consists of an array of memory cells connected by a plurality of word lines and bit lines. Data is programmed into or read from the planar NAND memory page by page. To mitigate the effects of floating gate-to-floating gate coupling, 3D QLC NAND memory can be programmed by coarse and fine programming to improve overall programming speed. In the related art programming method, a first word line is programmed to a first voltage V by coarse programming_PGM1Programming the second word line to the first voltage V by coarse programming_PGM1Programming the first word line to a second voltage V by fine coarse programming_PGM2Programming the second word line to a second voltage V by fine coarse programming_PGM2In which V is_PGM2>V_PGM1。

During fine programming of the first word line, when the selected bit line is precharged, a signal path between the first and second word lines is cut off, and residual electrons generated when the first word line is coarsely programmed cannot be discharged. Thus, the prior art programming method tends to cause program disturb.

Disclosure of Invention

A method of programming a memory device includes a plurality of memory cells coupled to a plurality of word lines and a plurality of bit lines. The method comprises the following steps: performing coarse programming on a first word line of the plurality of word lines; performing the coarse programming on a second word line of the plurality of word lines; precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line; turning on a channel between the unselected bit line and the second word line at the beginning of the first period and turning off the channel between the unselected bit line and the second word line before the end of the first period; and performing fine programming on the first word line during a second period after the first period.

The present invention also provides a method of programming a memory device including a plurality of memory cells coupled to a plurality of word lines and a plurality of bit lines. The method comprises the following steps: performing coarse programming on a first word line of the plurality of word lines; performing the coarse programming on a second word line of the plurality of word lines; precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line; reducing a channel voltage of the first word line during the first period; and performing fine programming on the first word line during a second period after the first period.

The present invention also provides a memory device, comprising: a plurality of word lines; a plurality of bit lines; a plurality of memory cells coupled to the plurality of word lines and the plurality of bit lines; and a control unit. The control unit is configured to: performing coarse programming on a first word line of the plurality of word lines; performing the coarse programming on a second word line of the plurality of word lines; precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line; turning on a channel between the unselected bit line and the second word line at the beginning of the first period and turning off the channel between the unselected bit line and the second word line before the end of the first period; and performing fine programming on the first word line during a second period after the first period.

The present invention also provides a memory device, comprising: a plurality of word lines; a plurality of bit lines; a plurality of memory cells coupled to the plurality of word lines and the plurality of bit lines; and a control unit. The control unit is configured to: performing coarse programming on a first word line of the plurality of word lines; performing the coarse programming on a second word line of the plurality of word lines; precharging unselected bit lines of the plurality of bit lines during a first period after performing the coarse programming on the first word line and the second word line; reducing a channel voltage of the first word line during the first period; and performing fine programming on the first word line during a second period after the first period.

These and other objects of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiments which are illustrated in the various figures and drawings.

Drawings

FIG. 1 is a top view showing a NAND string according to an embodiment of the invention.

FIG. 2 is a diagram illustrating an equivalent circuit of a NAND string according to an embodiment of the present invention.

Fig. 3 is a diagram illustrating a memory device 100 having read/write circuits for reading and programming memory cells according to an embodiment of the present invention.

Fig. 4 is a diagram illustrating an exemplary structure of an array of memory cells according to an embodiment of the present invention.

FIG. 5 is a flow chart illustrating a method of programming an array of memory cells in a memory device according to an embodiment of the present invention.

Fig. 6 is a diagram illustrating an embodiment of performing the method depicted in fig. 5.

Fig. 7 is a flowchart illustrating a method of programming an array of memory cells in a memory device according to another embodiment of the present invention.

Fig. 8 is a diagram illustrating an embodiment of performing the method depicted in fig. 7.

Detailed Description

FIG. 1 is a top view showing a NAND string according to an embodiment of the invention. Fig. 2 is a diagram showing an equivalent circuit thereof. In a flash memory system using a NAND structure, a plurality of transistors are arranged in series and sandwiched between two select gates, which is referred to as a NAND string. The NAND string depicted in FIGS. 1 and 2 includes four transistors 101-104 coupled in series and sandwiched between a top select gate SG _ T (on the drain side) and a bottom select gate SG _ B (on the source side). The top select gate SG _ T is arranged to connect the NAND string to a bit line via a bit line contact, and may be controlled by applying an appropriate voltage to the select gate line SGTL. The bottom select gate SG _ B is arranged to connect the NAND string to a source line, and may be controlled by applying an appropriate voltage to the select gate line SGBL. Each of the transistors 101 to 104 includes a control gate and a floating gate. For example, transistor 101 includes control gate CG1 and floating gate FG1, transistor 102 includes control gate CG2 and floating gate FG2, transistor 103 includes control gate CG3 and floating gate FG3, and transistor 104 includes control gate CG4 and floating gate FG 4. Control gate CG1 is connected to word line WL1, control gate CG2 is connected to word line WL2, control gate CG3 is connected to word line WL3, and control gate CG4 is connected to word line WL 4.

For purposes of illustration, FIGS. 1 and 2 show four memory cells in a NAND string. In other embodiments, a NAND string may include 8 memory cells, 16 memory cells, 32 memory cells, 64 memory cells, 128 memory cells, and so on. However, the number of memory cells in a NAND string does not limit the scope of the present invention.

A typical architecture for a flash memory system using a NAND structure includes several NAND strings. Each NAND string is connected to the source line by its bottom select gate SG _ B, controlled by select line SGBL, and connected to its associated bit line by its top select gate SG _ T, controlled by select line SGTL. Each bit line and the corresponding NAND string(s) connected to the bit line via bit line contacts comprise a column of the array of memory cells. The bit line is shared by multiple NAND strings. Typically, bit lines run on top of the NAND strings in a direction perpendicular to the word lines and are connected to one or more sense amplifiers.

FIG. 3 is a diagram illustrating a memory device 100 having read/write circuits for reading and programming a page of memory cells (or other cells) in parallel, according to an embodiment of the invention. The memory device 100 includes an array (two-dimensional or three-dimensional) of memory cells 10, a control circuit 20, read/write circuits 30A and 30B, row decoders 40A and 40B, column decoders 50A and 50B, and a controller 60. In one embodiment, access to the memory array 10 by the various peripheral circuits is implemented in a symmetric fashion, on opposite sides of the array, so that the densities of access lines and circuitry on each side are reduced by half. The read/write circuits 30A and 30B include multiple sense blocks SB that allow a page of memory cells to be read or programmed in parallel. The array of memory cells 10 is addressable by word lines via row decoders 40A and 40B and by bit lines via column decoders 50A and 50B. In a typical embodiment, the memory cells 10, control circuit 20, read/write circuits 30A and 30B, row decoders 40A and 40B, and column decoders 50A and 50B may be fabricated on a memory chip 70. Commands and data are transferred between the host and the controller 60 via signal lines 82 and between the controller 60 and the memory chip 70 via signal lines 84. A plurality of dummy cells, dummy word lines, and dummy bit lines (not shown) may be arranged in dummy storage areas DMX and DMY, which are typically disposed along the sides of the memory array 10 for read/write testing after the memory device 100 is completed.

The control circuit 20 is configured to cooperate with the read/write circuits 30A and 30B to perform memory operations on the array of memory cells 10. The control circuit 20 includes a state machine 22, an on-chip address decoder 24, and a power control module 26. The state machine 22 is configured to provide chip-level control of memory operations. The on-chip address decoder 24 is configured to provide an address interface between that used by the host or a memory controller to the hardware address used by the row decoders 40A, 40B and the column decoders 50A, 50B. Power control module 26 is configured to control the power and voltages supplied to the word lines and bit lines during each memory operation.

Fig. 4 is a diagram illustrating an exemplary structure of an array of memory cells 10 according to an embodiment of the present invention. The array of memory cells 10 is divided into BLOCKs₁～BLOCK_IA number of blocks of memory cells are represented, where I is a positive integer and typically equals a larger number. The block contains a set of NAND strings that are passed through the bit line BL₁-BL_MAnd a group of common word lines WL₁～WL_NAccess, where M and N are integers greater than 1. One terminal of the NAND string is connected to a corresponding bit line via a top select gate (connected to select gate line SGTL), and another terminal is connected to the source line via a bottom select gate (connected to select gate line SGBL). Each block is typically divided into a plurality of pages. In one embodiment, the block is the unit of conventional erase, while the page is the unit of conventional program. However, other units of erase/programming may be used.

In an embodiment, the array of memory cells 10 includes a triple well including a p-type substrate, an n-well within the p-type substrate, and a p-well within the n-well. The channel, source and drain regions are typically located in a p-well. The p-well and n-well are considered part of a p-type substrate with the entire array of memory cells 10 within one p-well, with trenches in the p-well providing electrical isolation between the NAND strings. In another embodiment, the array of memory cells 10 includes a triple well comprising an n-type substrate, a p-well within the n-type substrate, and an n-well within the p-well. The p-well and n-well are considered part of an n-type substrate, with the channel, source and drain regions typically being located in the n-well. However, the implementation of memory cells in NAND strings does not limit the scope of the present invention.

In the present invention, the memory device 100 may be a NAND memory device in which an array of memory cells 10 is arranged in a 3D QLC structure. However, the type of memory device 100 does not limit the scope of the present invention.

Fig. 5 is a flow chart illustrating a method of programming an array of memory cells 10 in the memory device 100 according to an embodiment of the present invention. For illustrative purposes, the bit line BL is composed of a plurality of bit lines₁-BL_MBit line BL in_mAnd the group of common word lines WL₁～WL_NTwo adjacent word lines WL in_nAnd WL_n+1The controlled memory cells are addressed, where M is a positive integer less than M and N is a positive integer less than N. The flow chart in fig. 5 comprises the following steps:

step 510: word line WL_nCoarse programming is performed.

Step 520: word line WL_n+1Coarse programming is performed.

Step 530: for unselected bit lines BL during the first period_mA pre-charge is performed.

Step 540: turning on unselected bit lines BL at the beginning of the first period_mWith unselected word lines WL_n+1And turn off the unselected bit lines BL before the end of the first period of time_mWith unselected word lines WL_n+1The channel in between.

Step 550: during a second period after the first period, for the selected word line WL_nFine programming is performed.

In one embodiment, one or any combination of control circuitry 20, read/write circuits 30A and 30B, row decoders 40A and 40B, column decoders 50A and 50B, and/or controller 60 may be referred to as a control unit capable of performing a programming process as depicted in FIG. 5.

In step 510, the word line WL can be replaced by a new word line WL_nRamping up to a first voltage V_PGM1To word line WL_nCoarse programming is performed. If it is to be paired with word line WL_nMore than one page is programmed, then the process proceeds to the next word line WL_n+1Previously, all pages to be programmed were coarse programmed.

In step 520, the word line WL can be replaced by a new word line WL_n+1Ramping up to a first voltage V_PGM1To word line WL_n+1A coarse programming is performed. If it is to be paired with word line WL_n+1More than one page is programmed, then all pages to be programmed are coarsely programmed before proceeding to the next word line.

Fig. 6 is a diagram illustrating an embodiment of performing steps 530 and 540 in the method depicted in fig. 5. Fig. 6 depicts the levels of the relevant signal lines, which will be explained together with the flow chart in fig. 5.

In step 530, the bit line BL may be selected by switching to the unselected bit line BL during the first period_mApplying a pre-pulse voltage V having a first width W1_PP1To unselected bit lines BL_mA pre-charge is performed. In step 540, unselected bit lines BL_mAnd unselected word lines WL_n+1The channel therebetween can pass to the unselected word line WL at the beginning of the first period_n+1Applying a second pre-pulse voltage V having a second width W2_PP2And on, wherein the second width W2 is less than the first width W1. Also, the prepulse voltage V_PP1And V_PP2So that the unselected bit lines BL are aligned_mAnd unselected word lines WL_n+1The channel in between may be turned off before the end of the first period. Therefore, it is possible to pass through the unselected bit lines BL_mWith unselected word lines WL_n+1The channel therebetween drains the selected word line WL generated in step 510_nResidual electrons on the substrate.

In the present invention, the method of programming the array of memory cells 10 in the memory device 100 may further include programming the memory cells by performing a first programming operation during a first period of timeDuring which a pre-pulse voltage V is applied_CCAnd biasing the dummy storage region DMY to the pre-pulse voltage V_PP1And will divide word line WL_n+1All word lines except for the unselected select gate lines SGTL and SGBL are biased at ground voltage to precharge the unselected select gate lines SGTL and SGBL.

In step 550, the unselected bit lines BL may be selected by applying a voltage to the unselected bit lines BL during the second period_mAnd unselected select gate lines SGTL and SGBL biased at ground, ramping up dummy storage area DMY to pass voltage V_PASSWord line WL to be selected_nRamping up to a pass voltage V_PASSAnd then to be greater than the first voltage V_PGM1And a passing voltage V_PASSSecond voltage V_PGM2And a word line WL to be removed_nAll but the word lines are ramped up to the pass voltage V_PASSTo the selected word line WL during the second period_nFine programming is performed. If it is to be paired with word line WL_nMore than one page is programmed, then the process proceeds to the next word line WL_n+1Previously, all pages to be programmed were fine programmed.

Fig. 7 is a flowchart illustrating a method of programming an array of memory cells 10 in the memory device 100 according to another embodiment of the present invention. For illustrative purposes, the bit line BL is composed of a plurality of bit lines₁-BL_MBit line BL in_mAnd the group of common word lines WL₁～WL_NTwo adjacent word lines WL in_nAnd WL_n+1The controlled memory cells are addressed, where M is a positive integer less than M and N is a positive integer less than N. The flow chart in fig. 7 comprises the following steps:

step 710: word line WL_nCoarse programming is performed.

Step 720: word line WL_n+1Coarse programming is performed.

Step 730: for unselected bit lines BL during the first period_mA pre-charge is performed.

Step 740: lowering the selected word line WL during a first period_nThe channel voltage of (1).

Step 750: at a second time after the first time periodDuring a period, for the selected word line WL_nFine programming is performed.

The implementation of steps 710, 730, and 750 is similar to the implementation of steps 510, 530, and 550 described above.

Fig. 8 is a diagram illustrating an embodiment of performing steps 730 and 740 in the method depicted in fig. 7. Fig. 8 depicts the level of the relevant signal line, which level will be explained together with the flow chart in fig. 7.

In step 740, the word line WL may be selected by turning to the selected word line WL during the first period_nApplying a negative pre-pulse voltage V_PP3To lower the selected word line WL_nThe channel voltage of (1). Thus, the selected word line WL generated in step 710_nThe residual electrons on can be selected from the selected word line WL_nAnd (4) discharging.

In the present invention, coarse and fine programming can be employed to improve overall programming speed. After the selected word line is coarsely programmed and before the selected word line is finely programmed, a channel between the corresponding unselected bit line and the adjacent unselected word line may be turned on to drain residual electrons generated during coarse programming on the selected word line. Alternatively, the channel voltage of the selected word line may be lowered in order to drain residual electrons generated during the coarse programming on the selected word line. Thus, the method can reduce program disturb when programming memory cells in a memory device.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.