Patent Application
20210391016
Embodiments of the disclosure relate generally to memory sub-systems, and more specifically, relate to a modified seeding scheme during a program operation in a memory sub-system.
A memory sub-system can include one or more memory devices that store data. The memory devices can be, for example, non-volatile memory devices and volatile memory devices. In general, a host system can utilize a memory sub-system to store data at the memory devices and to retrieve data from the memory devices.
The present disclosure will be understood more fully from the detailed description given below and from the accompanying drawings of various embodiments of the disclosure.
Aspects of the present disclosure are directed to a modified seeding scheme during a program operation in a memory sub-system. A memory sub-system can be a storage device, a memory module, or a hybrid of a storage device and memory module. Examples of storage devices and memory modules are described below in conjunction with
A memory sub-system can include high density non-volatile memory devices where retention of data is desired when no power is supplied to the memory device. For example, NAND memory, such as 3D flash NAND memory, offers storage in the form of compact, high density configurations. A non-volatile memory device is a package of one or more die, each including one or more planes. For some types of non-volatile memory devices (e.g., NAND memory), each plane includes of a set of physical blocks. Each block includes of a set of pages. Each page includes of a set of memory cells (“cells”). A cell is an electronic circuit that stores information. A data block hereinafter refers to a unit of the memory device used to store data and can include a group of memory cells, a word line group, a word line, or individual memory cells. Each data block can include a number of sub-blocks, where each sub-block is defined by a set of associated pillars (e.g., a vertical conductive trace) extending from a shared bit line. Memory pages (also referred to herein as “pages”) store one or more bits of binary data corresponding to data received from the host system. To achieve high density, a string of memory cells in a non-volatile memory device can be constructed to include a number of memory cells at least partially surrounding a pillar of channel material. The memory cells can be coupled to access lines, which are commonly referred to as “word lines,” often fabricated in common with the memory cells, so as to form an array of strings in a block of memory. The compact nature of certain non-volatile memory devices, such as 3D flash NAND memory, means word lines are common to many memory cells within a block of memory.
During a programming operation, a selected memory cell(s) can be programmed with the application of a programming voltage to a selected word line. Due to the word line being common to multiple memory cells, unselected memory cells can be subject to the same programming voltage as the selected memory cell(s). If not otherwise preconditioned, the unselected memory cells can experience effects from the programming voltage on the common word line. These programming voltage effects can include the condition of charge being stored in the unselected memory cells which are expected to maintain stored data. This programming voltage effect is termed a “programming disturbance” or “program disturb” effect. The program disturb effect can render the charge stored in the unselected memory cells unreadable altogether or, although still apparently readable, the contents of the memory cell can be read as a data value different than the intended data value stored before application of the programming voltage.
The presence of residue electrons, such as electrons trapped or otherwise remaining inside the poly-silicon channel of a charge storage structure after an earlier operation (e.g., a previous program operation), can contribute to the program disturb effect. At the end of a program verify operation, for example, a pass voltage (Vpass) applied to the word lines that are not being programmed ramps down and word lines on the source side having a high threshold voltage will cut off prior to word lines with a lower threshold voltage. Therefore, electrons will be trapped inside the poly-silicon channel at the word lines with the lower threshold voltage (i.e., between the cut off word lines) and become residue electrons. Since the poly-silicon channel (i.e., the pillar channel region) in some non-volatile memory devices is a floating channel that may not be connected to a bulk grounded body, there is generally no path for residual electrons in the channel region to discharge other than through towards the source of the memory string. A programming operation generally includes a seeding phase where a seeding voltage (e.g., 2 volts) is applied on the string and a ground voltage (e.g., 0 volts) is applied to all of the word lines intersecting the string, including the selected word line. Using a ground voltage during the seeding phase causes the source side word lines to remain off and the residue electrons remain trapped on the source side of the selected word line at the end of the seeding phase. These residue electrons can contribute to program disturb in a number of ways. For example, when the pass voltage or a program voltage is ramped up in a subsequent program operation, the selected word line can suffer from hot-electron (“hot-e”) disturb where a large voltage differential between the gate and source causes the residue electrons to be injected from a drain depletion region into the floating gate. In addition, this voltage differential can initiate an electrostatic field of sufficient magnitude to change the charge on the selected word line and cause the contents of the memory cell to be programmed inadvertently or read incorrectly. Furthermore, the electrostatic field can cause local electron-hole pair generation in the channel region, leading to even more electrons that can be injected into the selected word line.
Aspects of the present disclosure address the above and other deficiencies by implementing a modified seeding scheme during a program operation in a memory sub-system. In one embodiment, the memory sub-system initiates a program operation on a memory device, causes a seeding voltage to be applied to a string of memory cells in a data block of the memory device during a seeding phase of the program operation, and causes a positive voltage to be applied to a first plurality of word lines of the data block during the seeding phase. Each of the first plurality of word lines is coupled to a corresponding memory cell of a first plurality of memory cells in the string, and the first plurality of word lines comprises a selected word line associated with the program operation. This positive voltage can reduce electron barriers at those memory cells coupled to the corresponding word lines, allowing any residue electrons trapped on the source side to flow past the barriers and to the drain side of the string. In addition, the memory sub-system can cause at least one of a negative voltage or a ground voltage to be applied to other word lines of the string during the seeding phase, to actively push the residue electrons from the source side to the drain side. As a result, most, if not all, of the residue electrons can be purged from channel of the string during the seeding phase, such that when a high program voltage is subsequently applied to the selected word line, the residue electrons are not present and are not injected into the selected word line. Accordingly, program disturb effects can be significantly reduced, resulting in improved program performance in the memory sub-system.
A memory sub-system 110 can be a storage device, a memory module, or a hybrid of a storage device and memory module. Examples of a storage device include a solid-state drive (SSD), a flash drive, a universal serial bus (USB) flash drive, an embedded Multi-Media Controller (eMMC) drive, a Universal Flash Storage (UFS) drive, a secure digital (SD) card, and a hard disk drive (HDD). Examples of memory modules include a dual in-line memory module (DIMM), a small outline DIMM (SO-DIMM), and various types of non-volatile dual in-line memory modules (NVDIMMs).
The computing system 100 can be a computing device such as a desktop computer, laptop computer, network server, mobile device, a vehicle (e.g., airplane, drone, train, automobile, or other conveyance), Internet of Things (IoT) enabled device, embedded computer (e.g., one included in a vehicle, industrial equipment, or a networked commercial device), or such computing device that includes memory and a processing device.
The computing system 100 can include a host system 120 that is coupled to one or more memory sub-systems 110. In some embodiments, the host system 120 is coupled to different types of memory sub-system 110.
The host system 120 can include a processor chipset and a software stack executed by the processor chipset. The processor chipset can include one or more cores, one or more caches, a memory controller (e.g., NVDIMM controller), and a storage protocol controller (e.g., PCIe controller, SATA controller). The host system 120 uses the memory sub-system 110, for example, to write data to the memory sub-system 110 and read data from the memory sub-system 110.
The host system 120 can be coupled to the memory sub-system 110 via a physical host interface. Examples of a physical host interface include, but are not limited to, a serial advanced technology attachment (SATA) interface, a peripheral component interconnect express (PCIe) interface, universal serial bus (USB) interface, Fibre Channel, Serial Attached SCSI (SAS), a double data rate (DDR) memory bus, Small Computer System Interface (SCSI), a dual in-line memory module (DIMM) interface (e.g., DIMM socket interface that supports Double Data Rate (DDR)), etc. The physical host interface can be used to transmit data between the host system 120 and the memory sub-system 110. The host system 120 can further utilize an NVM Express (NVMe) interface to access the memory components (e.g., memory devices 130) when the memory sub-system 110 is coupled with the host system 120 by the PCIe interface. The physical host interface can provide an interface for passing control, address, data, and other signals between the memory sub-system 110 and the host system 120.
The memory devices 130, 140 can include any combination of the different types of non-volatile memory devices and/or volatile memory devices. The volatile memory devices (e.g., memory device 140) can be, but are not limited to, random access memory (RAM), such as dynamic random access memory (DRAM) and synchronous dynamic random access memory (SDRAM).
Some examples of non-volatile memory devices (e.g., memory device 130) include negative- and (NAND) type flash memory and write-in-place memory, such as three-dimensional cross-point (“3D cross-point”) memory. A cross-point array of non-volatile memory can perform bit storage based on a change of bulk resistance, in conjunction with a stackable cross-gridded data access array. Additionally, in contrast to many flash-based memories, cross-point non-volatile memory can perform a write in-place operation, where a non-volatile memory cell can be programmed without the non-volatile memory cell being previously erased. NAND type flash memory includes, for example, two-dimensional NAND (2D NAND) and three-dimensional NAND (3D NAND).
Each of the memory devices 130 can include one or more arrays of memory cells. One type of memory cell, for example, single level cells (SLC) can store one bit per cell. Other types of memory cells, such as multi-level cells (MLCs), triple level cells (TLCs), and quad-level cells (QLCs), can store multiple bits per cell. In some embodiments, each of the memory devices 130 can include one or more arrays of memory cells such as SLCs, MLCs, TLCs, QLCs, or any combination of such. In some embodiments, a particular memory device can include an SLC portion, and an MLC portion, a TLC portion, or a QLC portion of memory cells. The memory cells of the memory devices 130 can be grouped as pages that can refer to a logical unit of the memory device used to store data. With some types of memory (e.g., NAND), pages can be grouped to form blocks.
Although non-volatile memory components such as a 3D cross-point array of non-volatile memory cells and NAND type flash memory (e.g., 2D NAND, 3D NAND) are described, the memory device 130 can be based on any other type of non-volatile memory, such as read-only memory (ROM), phase change memory (PCM), self-selecting memory, other chalcogenide based memories, ferroelectric transistor random-access memory (FeTRAM), ferroelectric random access memory (FeRAM), magneto random access memory (MRAM), Spin Transfer Torque (STT)-MRAM, conductive bridging RAM (CBRAM), resistive random access memory (RRAM), oxide based RRAM (OxRAM), negative- or (NOR) flash memory, electrically erasable programmable read-only memory (EEPROM).
A memory sub-system controller 115 (or controller 115 for simplicity) can communicate with the memory devices 130 to perform operations such as reading data, writing data, or erasing data at the memory devices 130 and other such operations. The memory sub-system controller 115 can include hardware such as one or more integrated circuits and/or discrete components, a buffer memory, or a combination thereof. The hardware can include a digital circuitry with dedicated (i.e., hard-coded) logic to perform the operations described herein. The memory sub-system controller 115 can be a microcontroller, special purpose logic circuitry (e.g., a field programmable gate array (FPGA), an application specific integrated circuit (ASIC), etc.), or other suitable processor.
The memory sub-system controller 115 can include a processor 117 (e.g., a processing device) configured to execute instructions stored in a local memory 119. In the illustrated example, the local memory 119 of the memory sub-system controller 115 includes an embedded memory configured to store instructions for performing various processes, operations, logic flows, and routines that control operation of the memory sub-system 110, including handling communications between the memory sub-system 110 and the host system 120.
In some embodiments, the local memory 119 can include memory registers storing memory pointers, fetched data, etc. The local memory 119 can also include read-only memory (ROM) for storing micro-code. While the example memory sub-system 110 in
In general, the memory sub-system controller 115 can receive commands or operations from the host system 120 and can convert the commands or operations into instructions or appropriate commands to achieve the desired access to the memory devices 130. The memory sub-system controller 115 can be responsible for other operations such as wear leveling operations, garbage collection operations, error detection and error-correcting code (ECC) operations, encryption operations, caching operations, and address translations between a logical address (e.g., logical block address (LBA), namespace) and a physical address (e.g., physical block address) that are associated with the memory devices 130. The memory sub-system controller 115 can further include host interface circuitry to communicate with the host system 120 via the physical host interface. The host interface circuitry can convert the commands received from the host system into command instructions to access the memory devices 130 as well as convert responses associated with the memory devices 130 into information for the host system 120.
The memory sub-system 110 can also include additional circuitry or components that are not illustrated. In some embodiments, the memory sub-system 110 can include a cache or buffer (e.g., DRAM) and address circuitry (e.g., a row decoder and a column decoder) that can receive an address from the memory sub-system controller 115 and decode the address to access the memory devices 130.
In some embodiments, the memory devices 130 include local media controllers 135 that operate in conjunction with memory sub-system controller 115 to execute operations on one or more memory cells of the memory devices 130. An external controller (e.g., memory sub-system controller 115) can externally manage the memory device 130 (e.g., perform media management operations on the memory device 130). In some embodiments, memory sub-system 110 is a managed memory device, which includes a raw memory device 130 having control logic (e.g., local controller 135) on the die and a controller (e.g., memory sub-system controller 115) for media management within the same memory device package. An example of a managed memory device is a managed NAND (MNAND) device. Memory device 130, for example, can represent a single die having some control logic (e.g., local media controller 135) embodied thereon. In some embodiments, one or more components of memory sub-system 110 can be omitted.
In one embodiment, memory device 130 includes a memory device program management component 113 that can oversee, control, and/or manage data access operations, such as program operations, performed on a non-volatile memory device, such as memory device 130, of memory sub-system 110. A program operation, for example, can include a number of phases, such as a seeding phase, a pass voltage ramp up phase, a program voltage ramp up phase, and a program recovery phase. Program management component 113 is responsible for causing certain voltages to be applied (or indicating which voltages to apply) to memory device 130 during the program operation. The seeding phase generally includes global boosting of channel voltages of inhibited strings (i.e., strings on which a memory cell is not being programmed) in the memory device 130 in an attempt to counter-act program disturb resulting from the use of high voltage program pulses. A seeding voltage applied to the string (e.g., on the bit line) causes the source, drain and channel of the string to couple at higher voltage levels, thus better inhibiting program disturb. Since relatively high voltages are applied during the program voltage ramp up phase, the program recovery phase allows the device to recover from the high voltage modes. In general, during the program recovery phase all signals are ramped down to some lower voltage level. In one embodiment, program management component 113 causes a word line driver to apply a seeding voltage to a string of memory cells in a data block of the memory device 130 during the seeding phase of the program operation, and causes a positive voltage to be applied to a first plurality of word lines of the data block during the seeding phase. Each of the first plurality of word lines is coupled to a corresponding memory cell of a first plurality of memory cells in the string, and the first plurality of word lines comprises a selected word line associated with the program operation. This positive voltage can reduce electron barriers at those memory cells coupled to the correspond word lines, allowing any residue electrons trapped on the source side to flow past the barriers and to the drain side of the string. In addition, the program management component 113 can cause at least one of a negative voltage or a ground voltage to be applied to other word lines of the string during the seeding phase, to actively push the residue electrons from the source side to the drain side. Further details with regards to the operations of the program management component 113 are described below.
In some embodiments, the memory sub-system controller 115 includes at least a portion of program management component 113. For example, the memory sub-system controller 115 can include a processor 117 (e.g., a processing device) configured to execute instructions stored in local memory 119 for performing the operations described herein. In some embodiments, program management component 113 is part of the host system 110, an application, or an operating system. In other embodiment, local media controller 135 includes at least a portion of program management component 113 and is configured to perform the functionality described herein. In such an embodiment, program management component 113 can be implemented using hardware or as firmware, stored on memory device 130, executed by the control logic (e.g., program management component 113) to perform the operations related to the modified seeding scheme described herein.
Each memory cell 212 may include, for example, a floating gate transistor or a charge trap transistor and may comprise a single level memory cell or a multilevel memory cell. The floating gate may be referred to as a charge storage structure 235. The memory cells 212, the source select gate 220, the drain select gate 230, and the GIDL generator 240 can be controlled by signals on their respective control gates 250.
The control signals can be applied by program management component 113, or at the direction of program management component 113, to select lines (not shown) to select strings, or to access lines (not shown) to select memory cells 212, for example. In some cases, the control gates can form a portion of the select lines (for select devices) or access lines (for cells). The drain select gate 230 receives a voltage that can cause the drain select gate 230 to select or deselect the string 200. In one embodiment, each respective control gate 250 is connected to a separate word line (i.e., access line), such that each device or memory cell can be separately controlled. The string 200 can be one of multiple strings of memory cells in a block of memory cells in memory device 130. For example, when multiple strings of memory cells are present, each memory cell 212 in string 200 may be connected to a corresponding shared word line, to which a corresponding memory cell in each of the multiple strings is also connected. As such, if a selected memory cell in one of those multiple strings is being programmed, a corresponding unselected memory cell 212 in string 200 which is connected to the same word line as the selected cell can be subjected to the same programming voltage, potentially leading to program disturb effects. Accordingly, in one embodiment, program management component 113 causes a word line driver to apply a seeding voltage to the bit line 234 during a seeding phase of the program operation, and causes a positive voltage to be applied to certain control gates 250 of the devices and/or cells 212 in string 200 during the seeding phase. In addition, the memory sub-system can cause at least one of a negative voltage or a ground voltage to be applied to other control gates 250 of the devices and/or cells 212 in string 200 during the seeding phase, to actively push the residue electrons from the source side to the drain side. As a result, most, if not all, of the residue electrons can be purged from channel of the string during the seeding phase, such that when a high program voltage is subsequently applied to the selected word line, the residue electrons are not present and are not injected be injected into the selected word line.
Timing diagram 300 illustrates the various phases of a program operation 300, according to one embodiment. In this embodiment, different signals are applied to various devices in memory device 130 in each of the illustrated phases. During the seeding phase 310, program management component 113 causes a signal 301 having a seeding voltage (e.g., 3 volts) to be applied to the bit line 234 of the string 200. In one embodiment, program management component 113 sends a signal to the word line driver (or some other component) instructing that driver to apply signal 301 to the bit line 234. Signal 301 can remain at the seeding voltage throughout the pass voltage ramp up phase 320 and the program voltage ramp up phase 330. During the program recovery phase 340, signal 301 returns to a ground voltage (e.g., 0V). During the seeding phase 310, program management component 113 further causes signal 302 to be applied to the drain select gate 230. Signal 302 (e.g., 7V) activates the drain select gate 230 (e.g., turns it “on”) thereby allowing the seeding voltage to flow from bit line 234 through the drain select gate 230 to the various data word lines connected to string 200. In one embodiment, the data word lines include one or more word lines connected to the remaining memory cell(s) 212 of string 200. These cells 212 are generally used for storing data, such as data from host system 120. Signal 302 returns to a ground voltage during pass voltage ramp up phase 320, program voltage ramp up phase 330, and program recovery phase 340.
In one embodiment, program management component 113 can cause a positive voltage to be applied to certain word lines of the string 200 during the seeding phase 310, where the positive voltage can be seen at the control gates 250 of the corresponding memory cells 212. The positive voltage can reduce electron barriers at those certain word lines, allowing any residue electrons trapped on the source side to flow past the barriers and to the drain (i.e., bit line 234). In addition, program management component 113 can cause a negative voltage to be applied to other word lines of the string 200 during the seeding phase 310, to actively push the residue electrons from the source side to the drain side.
As illustrated in timing diagram 300, program management component 113 can cause a signal 303 with positive voltage (e.g., 1V) to be applied to a selected word line (i.e., the word line being programmed (WLn)) and any word lines above the selected word line in the string (i.e., those word lines located between WLn and the drain select gate 230. This positive voltage ensures that the channel potential is mainly determined by the seeding voltage (e.g., 3V). This higher channel potential leads to a larger drain induced barrier lowering (DIBL) effect on the adjacent source side word lines (i.e., the next word lines lower down the string (WLn−1 and WLn−2)), allowing more residue electrons to flow to the drain side. During the pass voltage ramp up phase 320, the signal 303 is increased to a higher voltage (e.g., 10V) and during the program voltage ramp up phase 330, the signal 303 is increased to an even higher voltage (e.g., 20V). Signal 303 returns to a ground voltage during program recovery phase 340. In addition, program management component 113 can cause a signal 304 with a positive voltage (e.g., 2V) to be applied to the adjacent source side word lines (i.e., WLn−1 and WLn−2). This positive voltage can also reduce the electron barriers in these word lines. During the pass voltage ramp up phase 320 and the program voltage ramp up phase 330, the signal 304 is increased to a higher voltage (e.g., 10V). Signal 304 returns to a ground voltage during program recovery phase 340. In one embodiment, program management component 113 can cause different voltages to be applied to WLn−1 and WLn−2. For example, a higher voltage can be applied on WLn−1 and a lower voltage can be applied on WLn−2 since WLn−1 receives more threshold voltage reduction due to the DIBL effect than WLn−2. In another embodiment, the same voltage could be applied to WLn−1, WLn−2, and WLn−3, as well.
In one embodiment, program management component 113 can cause a signal 305 with negative voltage (e.g., −1V) to be applied to the remaining data word lines (i.e., WLn−3 and below). The negative voltage leads to an even lower channel potential for these word lines which can actively push the residue electrons trapped there towards the drain. During the pass voltage ramp up phase 320 and the program voltage ramp up phase 330, the signal 305 is increased to a higher voltage (e.g., 10V). Signal 305 returns to a ground voltage during program recovery phase 340. In one embodiment, program management component 113 causes a signal 306 with a ground voltage (i.e., 0V) to be applied to the source select gate 220 throughout seeding phase 310, pass voltage ramp up phase 320, program voltage ramp up phase 330, and program recovery phase 340. It should be understood that the specific voltage levels described herein are merely examples, and that in other embodiments, different voltage levels can be used.
Timing diagram 400 illustrates the various phases of a program operation 400, according to one embodiment. In this embodiment, different signals are applied to various devices in memory device 130 in each of the illustrated phases. During the seeding phase 410, program management component 113 causes a signal 401 having a seeding voltage (e.g., 3 volts) to be applied to the bit line 234 of the string 200. Signal 401 can remain at the seeding voltage throughout the pass voltage ramp up phase 420 and the program voltage ramp up phase 430. During the program recovery phase 440, signal 401 returns to a ground voltage (e.g., 0V). During the seeding phase 410, program management component 113 further causes signal 402 to be applied to the drain select gate 230. Signal 402 (e.g., 7V) activates the drain select gate 230 (e.g., turns it “on”) thereby allowing the seeding voltage to flow from bit line 234 through the drain select gate 230 to the various data word lines connected to string 200. In one embodiment, the data word lines include one or more word lines connected to the remaining memory cell(s) 212 of string 200. These cells 212 are generally used for storing data, such as data from host system 120. Signal 402 returns to a ground voltage during pass voltage ramp up phase 420, program voltage ramp up phase 430, and program recovery phase 440.
In one embodiment, program management component 113 can cause a positive voltage to be applied to certain word lines of the string 200 during the seeding phase 410, where the positive voltage can be seen at the control gates 250 of the corresponding memory cells 212. The positive voltage can reduce electron barriers at those certain word lines, allowing any residue electrons trapped on the source side to flow past the barriers and to the drain (i.e., bit line 234). In addition, program management component 113 can cause a negative voltage to be applied to other word lines of the string 200 during the seeding phase 410, to actively push the residue electrons from the source side to the drain side.
As illustrated in timing diagram 400, program management component 113 can cause a signal 403 with positive voltage (e.g., 1V) to be applied to a selected word line (i.e., the word line being programmed (WLn)) and any word lines above the selected word line in the string (i.e., those word lines located between WLn and the drain select gate 230. This positive voltage ensures that the channel potential is mainly determined by the seeding voltage (e.g., 3V). This higher channel potential leads to a larger drain induced barrier lowering (DIBL) effect on the adjacent source side word lines (i.e., the next word lines lower down the string (WLn−1 and WLn−2)), allowing more residue electrons to flow to the drain side. During the pass voltage ramp up phase 420, the signal 403 is increased to a higher voltage (e.g., 10V) and during the program voltage ramp up phase 430, the signal 403 is increased to an even higher voltage (e.g., 20V). Signal 403 returns to a ground voltage during program recovery phase 440. In addition, program management component 113 can cause a signal 404 with a positive voltage (e.g., 5V) to be applied to the adjacent source side word lines (i.e., WLn−1 and WLn−2). This positive voltage ensures that the memory cells 212 to which these word lines are attached, are fully activated, allowing the seeding voltage applied to the bit line to pass WLn−1 and WLn−2 through to the source side. During the pass voltage ramp up phase 420 and the program voltage ramp up phase 430, the signal 404 is increased to a higher voltage (e.g., 10V). Signal 404 returns to a ground voltage during program recovery phase 440. Furthermore, program management component 113 can cause a signal 405 with a positive voltage (e.g., 2V) to be applied to the next source side word line (i.e., WLn−3). This positive voltage can avoids a sharp change in channel potential between WLn−2 and WLn−4 Such a sharp change would create a large electric field, leading to increased local electron generation, which would exacerbate the program disturb problem for the selected word line WLn. The intermediate voltage of signal 405 results in a more gradual change in channel potential. During the pass voltage ramp up phase 420 and the program voltage ramp up phase 430, the signal 404 is increased to a higher voltage (e.g., 10V). Signal 404 returns to a ground voltage during program recovery phase 440. In one embodiment, program management component 113 can cause different voltages to be applied to WLn−1 and WLn−2. For example, a higher voltage can be applied on WLn−1 and a lower voltage can be applied on WLn−2 since WLn−1 receives more threshold voltage reduction due to the DIBL effect than WLn−2. In another embodiment, the same voltage could be applied to WLn−1, WLn−2, and WLn−3, as well.
In one embodiment, program management component 113 can cause a signal 406 with ground voltage (e.g., 0V) to be applied to the remaining data word lines (i.e., WLn−4 and below). The ground voltage leads to a low channel potential for these word lines which can actively push the residue electrons trapped there towards the drain. During the pass voltage ramp up phase 420 and the program voltage ramp up phase 430, the signal 406 is increased to a higher voltage (e.g., 10V). Signal 406 returns to a ground voltage during program recovery phase 440. In one embodiment, program management component 113 causes a signal 407 with a ground voltage (i.e., 0V) to be applied to the source select gate 220 throughout seeding phase 410, pass voltage ramp up phase 420, program voltage ramp up phase 430, and program recovery phase 440.
In one embodiment, each of the devices in string 200 has an associated threshold voltage (Vt) which represents a voltage at which each device switches from an “off” state to an “on” state, or vice versa. For example, the memory cells connected to the WLn+1 and the selected word line WLn can have a threshold voltage of −2V, the memory cell connected to WLn−1 and WLn−2 can have a threshold voltage of 5V, the memory cells connected to WLn−3 through WLn−15 can have a threshold voltage of −1V, and the memory cells connected to WLn−16 and WLn−17 can have a threshold voltage of 5V. In one embodiment, the channel potential 500 of the string 200 represents a difference between a voltage applied at the control gate of each device (i.e., a gate voltage (Vg)) and a representative threshold voltage. In one embodiment, there is a first representative threshold voltage on the drain-side of the selected word line (WLn) and a second representative threshold voltage on the source-side of the selected word line (WLn). Each representative threshold voltage can be the highest threshold voltage on the drain-side and the source-side, respectively. Thus, in the illustrated embodiment, the first representative threshold voltage on the drain-side can be the −2V associated with memory devices connected to WLn+1 and WLn and the second representative threshold voltage on the source-side can be the 5V associated with the memory devices connected to WLn−1, WLn−2, WLn−16 and WLn−17. Since WLn−1 has the highest threshold voltage on the source-side of the selected word line, the highest number of source-side residue electrons are trapped there. This represents the worst case scenario in terms of program disturb effect, so the corresponding threshold voltage can be used as the representative threshold voltage.
As described above with respect to
As a result, the channel potential 500 on the drain-side of the selected word line (WLn) is 3V (i.e., a gate voltage of 1V minus the first representative threshold voltage of −2V) and the channel potential 500 on the source side of the selected word line (WLn) is −6V (i.e., a gate voltage of −1V minus the second representative threshold voltage of 5V). Thus, the differential in the channel potential 500 from the drain side to the source side is −9V. Note that if a ground voltage (0V) were applied on the word lines, the drain-side channel potential would be 2V, the source-side channel potential would be −5V and the differential would be only −7V. Thus, applying the positive voltage to certain word lines and the negative voltage to other word lines increases the potential gradient between the drain-side and the source-side of the selected word line (WLn). Since the source side of the selected word line (WLn) has a lower channel potential, the residue electrons 520 trapped on the source side tend to flow toward the drain side during the seeding phase, and past the lowered barrier at WLn−1 and WLn−2, where they can be purged via the bit line 234. Under the worst case pattern, the electron barrier on WLn−1 and WLn−2 seen by residue electrons 520 is 5V in a seeding scheme and can be reduced to less than 2V using the techniques described herein. This indicates that more than 60% of residue electrons can be purged during the seeding phase, and thus, that the program disturb from hot-electron injection during the program voltage ramp up phase can also be expected to reduce by approximately 60%.
In one embodiment, each of the devices in string 200 has an associated threshold voltage (Vt) which represents a voltage at which each device switches from an “off” state to an “on” state, or vice versa. For example, the memory cells connected to the WLn+1 and the selected word line WLn can have a threshold voltage of −2V, the memory cell connected to WLn−1 and WLn−2 can have a threshold voltage of 5V, the memory cells connected to WLn−3 through WLn−15 can have a threshold voltage of −1V, and the memory cells connected to WLn−16 and WLn−17 can have a threshold voltage of 5V. In one embodiment, the channel potential 600 of the string 200 represents a difference between a voltage applied at the control gate of each device (i.e., a gate voltage (Vg)) and a representative threshold voltage. In one embodiment, there is a first representative threshold voltage on the drain-side of the selected word line (WLn) and a second representative threshold voltage on the source-side of the selected word line (WLn). Each representative threshold voltage can be the highest threshold voltage on the drain-side and the source-side, respectively. Thus, in the illustrated embodiment, the first representative threshold voltage on the drain-side can be the −2V associated with memory devices connected to WLn+1 and WLn and the second representative threshold voltage on the source-side can be the 5V associated with the memory devices connected to WLn−1, WLn−2, WLn−16 and WLn−17.
As described above with respect to
As a result, the channel potential 600 on the drain-side of the selected word line (WLn) is 3V (i.e., a gate voltage of 1V minus the first representative threshold voltage of −2V) and the channel potential 600 on the source side of the selected word line (WLn) is −5V (i.e., a gate voltage of 0V minus the second representative threshold voltage of 5V). Thus, the differential in the channel potential 600 from the drain side to the source side is −8V. Applying the positive voltage to certain word lines and the ground voltage to other word lines increases the potential gradient between the drain-side and the source-side of the selected word line (WLn). Since the source side of the selected word line (WLn) has a lower channel potential, the residue electrons 620 trapped on the source side tend to flow toward the drain side during the seeding phase, and past the lowered barrier at WLn−1 and WLn−2, where they can be purged via the bit line 234.
At operation 705, a program operation is initiated. For example, the processing logic (e.g. processor 117 or local media controller 135) can initiate a program operation on a memory device (e.g., memory device 130). In one embodiment, the program operation includes a seeding phase, a pass voltage ramp up phase, a program voltage ramp up phase, and a program recovery phase. In certain embodiments, each of these phases can be repeated numerous times in a cycle during a single programming operation. The seeding phase generally includes global boosting of channel voltages of inhibited strings in the memory device 130 in an attempt to counter-act program disturb resulting from the use of high voltage program pulses. During the pass voltage ramp up phase, a pass voltage (Vpass) is applied to word lines of the memory device 130 in order to boost the channel voltage of the associated channel. During the program voltage ramp up phase, a program voltage is applied to selected word lines (e.g., WLn) of the memory device 130, in order to program a certain level of charge to the selected memory cells on the word lines representative of a desired value. Since relatively high voltages are applied during the program voltage ramp up phase 330, the program recovery phase allows the device to recover from the high voltage modes.
At operation 710, a seeding voltage is applied to a string of memory cells. For example, the processing logic can cause a seeding voltage to be applied to a string of memory cells in a data block of the memory device during the seeding phase of the program operation. During the seeding phase 310/410, program management component 113 causes a signal 301/401 having a seeding voltage (e.g., 3 volts) to be applied to the bit line 234 of the string 200. Signal 301/401 can remain at the seeding voltage throughout the pass voltage ramp up phase 320/420 and the program voltage ramp up phase 330/430. In one embodiment, the seeding voltage is higher than that used in the seeding phases of program operations in order to increase the channel potential of the string 200.
At operation 715, a positive voltage is applied to certain word lines. For example, the processing logic can cause a positive voltage to be applied to a first plurality of word lines of the data block during the seeding phase, wherein each of the first plurality of word lines is coupled to a corresponding memory cell of a first plurality of memory cells in the string, the first plurality of word lines comprising a selected word line associated with the program operation. In one embodiment, program management component 113 can cause a positive voltage to be applied to certain word lines of the string 200 during the seeding phase 310/410, where the positive voltage can be seen at the control gates 250 of the corresponding memory cells 212. The positive voltage can reduce electron barriers at those certain word lines, allowing any residue electrons trapped on the source side to flow past the barriers and to the drain (i.e., bit line 234).
In one embodiment, program management component 113 can cause a first positive voltage (e.g., 1V) to be applied to the selected word line (i.e., WLn) and can cause a second positive voltage to be applied to one or more first word lines (e.g., WLn−1 and WLn−2) adjacent to the selected word line (i.e., WLn), wherein the one or more first word lines adjacent to the selected word line are coupled to one or more of the first plurality of memory cells on a source-side of the first memory cell in the string of memory cells. In general, the second positive voltage is greater than the first positive voltage. For example, in the embodiment illustrated in timing diagram 300, the second positive voltage is 2V, and in the embodiment illustrated in timing diagram 400, the second positive voltage is 5V. Program management component 113 can optionally cause a third positive voltage to be applied to one or more second word lines (e.g., WLn−3) adjacent to the one or more first word lines (e.g., WLn−1 and WLn−2), wherein the one or more second word lines adjacent to the one or more first word lines are coupled to one or more of the first plurality of memory cells on a source-side of the memory cells coupled to the one or more first word lines. In general, the third positive voltage is greater than the first positive voltage and less than the second positive voltage. For example, in the embodiment illustrated in timing diagram 400, the third positive voltage is 2V.
At operation 720, a negative voltage or a ground voltage is applied to other word lines. For example, the processing logic can cause at least one of a negative voltage or a ground voltage to be applied to a second plurality of word lines of the data block during the seeding phase, wherein each of the second plurality of word lines is coupled to a corresponding memory cell of a second plurality of memory cells in the string, wherein the second plurality of memory cells are adjacent to the first plurality of memory cells on a source side of the string of memory cells. For example, in the embodiment illustrated in timing diagram 300, program management component 113 causes a negative voltage (e.g., −1V) to be applied to WLn−3 through WLn−17, and in the embodiment illustrated in timing diagram 400, program management component 113 causes a ground voltage (i.e., 0V) to be applied to WLn−4 through WLn−17. This negative voltage can actively push the residue electrons from the source side to the drain side.
In one embodiment, program management component 113 can cause the positive and/or negative voltages to be applied to the word lines of the data block only during certain seeding phases of the program operation. For example, the program operation might include a plurality of seeding phases, a plurality of pass voltage ramp up phases, and plurality of a program voltage ramp up phases, which are repeated in sequence. In one embodiment, the positive and/or negative voltages are applied to the first plurality of word lines only during a subset of the plurality of seeding phases occurring after a threshold number of the plurality of program voltage ramp up phases have occurred. For example, if the threshold value was four, the positive and/or negative voltages would not be applied during the first four seeding phases, but would be applied in any seeding phases after that. In another embodiment, if the total number of seeding phases to be performed is known in advance, program management component 113 might cause the positive and/or negative voltages to be applied only during the law few seeding phases (e.g., during the last five seeding phases). In the first number of seeding phases, a ground voltage can be applied instead of the positive and/or negative voltages.
The machine can be a personal computer (PC), a tablet PC, a set-top box (STB), a Personal Digital Assistant (PDA), a cellular telephone, a web appliance, a server, a network router, a switch or bridge, or any machine capable of executing a set of instructions (sequential or otherwise) that specify actions to be taken by that machine. Further, while a single machine is illustrated, the term “machine” shall also be taken to include any collection of machines that individually or jointly execute a set (or multiple sets) of instructions to perform any one or more of the methodologies discussed herein.
The example computer system 800 includes a processing device 802, a main memory 804 (e.g., read-only memory (ROM), flash memory, dynamic random access memory (DRAM) such as synchronous DRAM (SDRAM) or Rambus DRAM (RDRAM), etc.), a static memory 806 (e.g., flash memory, static random access memory (SRAM), etc.), and a data storage system 818, which communicate with each other via a bus 830.
Processing device 802 represents one or more general-purpose processing devices such as a microprocessor, a central processing unit, or the like. More particularly, the processing device can be a complex instruction set computing (CISC) microprocessor, reduced instruction set computing (RISC) microprocessor, very long instruction word (VLIW) microprocessor, or a processor implementing other instruction sets, or processors implementing a combination of instruction sets. Processing device 802 can also be one or more special-purpose processing devices such as an application specific integrated circuit (ASIC), a field programmable gate array (FPGA), a digital signal processor (DSP), network processor, or the like. The processing device 802 is configured to execute instructions 826 for performing the operations and steps discussed herein. The computer system 800 can further include a network interface device 808 to communicate over the network 820.
The data storage system 818 can include a machine-readable storage medium 824 (also known as a computer-readable medium, such as a non-transitory computer-readable medium) on which is stored one or more sets of instructions 826 or software embodying any one or more of the methodologies or functions described herein. The instructions 826 can also reside, completely or at least partially, within the main memory 804 and/or within the processing device 802 during execution thereof by the computer system 800, the main memory 804 and the processing device 802 also constituting machine-readable storage media. The machine-readable storage medium 824, data storage system 818, and/or main memory 804 can correspond to the memory sub-system 110 of
In one embodiment, the instructions 826 include instructions to implement functionality corresponding to the program management component 113 of
Some portions of the preceding detailed descriptions have been presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the ways used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of operations leading to a desired result. The operations are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
It should be borne in mind, however, that all of these and similar terms are to be associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. The present disclosure can refer to the action and processes of a computer system, or similar electronic computing device, that manipulates and transforms data represented as physical (electronic) quantities within the computer system's registers and memories into other data similarly represented as physical quantities within the computer system memories or registers or other such information storage systems.
The present disclosure also relates to an apparatus for performing the operations herein. This apparatus can be specially constructed for the intended purposes, or it can include a general purpose computer selectively activated or reconfigured by a computer program stored in the computer. Such a computer program can be stored in a computer readable storage medium, such as, but not limited to, any type of disk including floppy disks, optical disks, CD-ROMs, and magnetic-optical disks, read-only memories (ROMs), random access memories (RAMs), EPROMs, EEPROMs, magnetic or optical cards, or any type of media suitable for storing electronic instructions, each coupled to a computer system bus.
The algorithms and displays presented herein are not inherently related to any particular computer or other apparatus. Various general purpose systems can be used with programs in accordance with the teachings herein, or it can prove convenient to construct a more specialized apparatus to perform the method. The structure for a variety of these systems will appear as set forth in the description below. In addition, the present disclosure is not described with reference to any particular programming language. It will be appreciated that a variety of programming languages can be used to implement the teachings of the disclosure as described herein.
The present disclosure can be provided as a computer program product, or software, that can include a machine-readable medium having stored thereon instructions, which can be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form readable by a machine (e.g., a computer). In some embodiments, a machine-readable (e.g., computer-readable) medium includes a machine (e.g., a computer) readable storage medium such as a read only memory (“ROM”), random access memory (“RAM”), magnetic disk storage media, optical storage media, flash memory components, etc.
In the foregoing specification, embodiments of the disclosure have been described with reference to specific example embodiments thereof. It will be evident that various modifications can be made thereto without departing from the broader spirit and scope of embodiments of the disclosure as set forth in the following claims. The specification and drawings are, accordingly, to be regarded in an illustrative sense rather than a restrictive sense.
