Patent Application
20240347122
The present disclosure is related generally to non-volatile memory and, more particularly, to improved data recovery schemes for memory devices that are optimized to operate at very high read performance and with a very low power consumption.
Semiconductor memory is widely used in various electronic devices such as cellular telephones, digital cameras, personal digital assistants, medical electronics, mobile computing devices, servers, solid state drives, non-mobile computing devices and other devices. Semiconductor memory may be non-volatile memory or volatile memory. A non-volatile memory allows information to be stored and retained even when the non-volatile memory is not connected to a source of power (e.g., a battery).
Non-volatile memory devices include one or more memory chips having multiple arrays of memory cells. The memory arrays may have associated decoders and circuits for performing read, write, and erase operations. Memory cells within the arrays may be arranged in horizontal rows and vertical columns. Each row may be addressed by a word line, and each column may be addressed by a bit line. Data may be loaded into columns of the array using a series of data busses. Each column may hold a predefined unit of data, for instance, a word encompassing two bytes of information.
In some applications, semiconductor memory is used to store very large amounts of data that are repeatedly accessed (e.g., read) very rapidly. For example, in some machine learning applications, large language models that include a terabyte (or more) of data must be stored in memory and retrieved at a very high data rate. Accordingly, such applications require very high bandwidth and low power.
Currently, high bandwidth volatile memory devices (e.g., DRAM memory devices called “high bandwidth memory” or “HBM”) are used for such applications. Non-volatile memory (e.g., NAND) is significantly less expensive than DRAM, but the bandwidth of conventional NAND memory devices is too low, and the power consumption of conventional NAND memory devices is too high to provide a viable alternative to HBM devices. Therefore, there is a need to provide high bandwidth, low power non-volatile memory.
One aspect of the present disclosure is related to a method of operating a memory package. The method includes the step of preparing a plurality of memory dies. Each memory die has a plurality of memory blocks with arrays of memory cells. The plurality of memory dies include a plurality of user data dies that contain user data and an XOR die that contains XOR data. The method continues with the step of detecting a read error during a read operation in a failed die of the plurality of user data dies. The method proceeds with the step of reading some of the user data of the user data dies besides the failed die and reading some of the XOR data of the XOR die. The method continues with the step of performing a read recovery operation that includes an XOR operation using, as inputs, the user data of the user data dies besides the failed die and the XOR data of the XOR die.
According to another aspect of the present disclosure, the step of detecting the read error during the read operation includes a failing error correction code (ECC) operation.
According to yet another aspect of the present disclosure, the user data in the plurality of user data dies and the XOR data in the XOR die are in a single bit per memory cell (SLC) storage scheme.
According to still another aspect of the present disclosure, the SLC storage scheme of the user data is a first SLC storage scheme with a first threshold voltage Vt window, and the SLC storage scheme of the XOR data is a second SLC storage scheme that has a second threshold voltage window Vt that is greater than the first threshold voltage Vt window.
According to a further aspect of the present disclosure, the first SLC storage scheme is associated with a first read pass voltage VREAD_1, and the second SLC storage scheme is associated with a second read pass voltage VREAD_2 that is greater than the first read pass voltage VREAD_1.
According to yet a further aspect of the present disclosure, all of the memory cells programmed according to the first SLC storage scheme have threshold voltages below 2 V.
According to still a further aspect of the present disclosure, some of the memory cells programmed according to the second SLC storage scheme have threshold voltages above 2 V.
According to another aspect of the present disclosure, the plurality of memory dies are all of similar construction such that for each address of each word line in any one of the memory dies. There is a corresponding word line with the same address in every other one of the plurality of memory dies.
According to yet another aspect of the present disclosure, the step of detecting the read error during the read operation occurs when performing the read operation on a selected word line that has a selected address. The step of reading some of the user data and some of the XOR data includes reading the word lines that have the same selected address in the user data dies other than the failed die and in the XOR die.
Another aspect of the present disclosure is related to a memory package that includes a plurality of memory dies. Each of the memory dies has a plurality of memory blocks with arrays of memory cells. The plurality of memory dies includes a plurality of user data dies that contain user data and an XOR die that contains XOR data. The memory package also includes circuitry for reading the user data and the XOR data. The circuitry is configured to detect a read error during a read operation in a failed die of the plurality of user data dies and read some of the user data of the user data dies besides the failed die and reading some of the XOR data of the XOR die. The circuitry is also configured to perform a read recovery operation that includes an XOR operation using, as inputs, the user data of the user data dies besides the failed die and the XOR data of the XOR die.
According to another aspect of the present disclosure, the circuitry is configured to detect the read error during the read operation in response to an error correction code (ECC) operation failing.
According to yet another aspect of the present disclosure, the user data in the plurality of user data dies and the XOR data in the XOR die are in a single bit per memory cell (SLC) storage scheme.
According to still another aspect of the present disclosure, the SLC storage scheme of the user data is a first SLC storage scheme with a first threshold voltage Vt window, and the SLC storage scheme of the XOR data is a second SLC storage scheme that has a second threshold voltage window Vt that is greater than the first threshold voltage Vt window.
According to a further aspect of the present disclosure, the first SLC storage scheme is associated with a first read pass voltage VREAD_1 and the second SLC storage scheme is associated with a second read pass voltage VREAD_2 that is greater than the first read pass voltage VREAD_1.
According to yet a further aspect of the present disclosure, all of the memory cells programmed according to the first SLC storage scheme have threshold voltages below 2 V.
According to still a further aspect of the present disclosure, some of the memory cells programmed according to the second SLC storage scheme have threshold voltages above 2 V.
According to another aspect of the present disclosure, the plurality of memory dies are all of similar construction such that for each address of each word line in any one of the memory dies, there is a corresponding word line with the same address in every other one of the plurality of memory dies.
According to yet another aspect of the present disclosure, the circuitry is configured to detect the read error during the read operation occurs when performing the read operation on a selected word line that has a selected address. The some of the user data and some of the XOR data that the circuitry reads includes the word lines that have the same selected address in the user data dies other than the failed die and in the XOR die.
Yet another aspect of the present disclosure is related to a computing system that includes a processing unit and a plurality of non-volatile memory packages that are in electrical communication with the processing unit. At least one of the non-volatile memory packages includes a plurality of memory dies, and each memory die has a plurality of memory blocks with arrays of memory cells. The plurality of memory dies also includes a plurality of user data dies that contain user data and an XOR die that contains XOR data. The at least one non-volatile memory package also includes circuitry for reading the user data and the XOR data. The circuitry is configured to detect a read error during a read operation in a failed die of the plurality of user data dies and read some of the user data of the user data dies besides the failed die and reading some of the XOR data of the XOR die. The circuitry is also configured to perform a read recovery operation that includes an XOR operation using, as inputs, the user data of the user data dies besides the failed die and the XOR data of the XOR die.
According to another aspect of the present disclosure, the circuitry is configured to detect the read error during the read operation in response to an error correction code (ECC) operation failing.
These and other features and advantages of the subject disclosure will become more readily appreciated when considered in connection with the following description of the presently preferred embodiments, appended claims and accompanying drawings, in which:
Technology is described for improving reliability of a memory package that includes a plurality of memory dies. The plurality of memory dies includes a plurality of user data dies, which contain user data, and an XOR die, which is programmed by using an XOR operation that includes as inputs, the user data in the user data dies. In the event that a read error occurs when performing a read operation in one of the user data dies, then an XOR operation can be performed using the XOR data and the user data contained in the non-failing user data dies to recover the data of the failing die. These techniques are discussed in further detail below.
The storage system 100 is connected to a host 102, which can be a computer; server; electronic device (e.g., smart phone, tablet or other mobile device); appliance; or another apparatus that uses memory and has data processing capabilities. In some embodiments, the host 102 is separate from, but connected to, the storage system 100. In other embodiments, the storage system 100 is embedded within the host 102.
The components of the storage system 100 depicted in
The memory controller 104 includes a host interface 110 that is connected to and in communication with the host 102. In one embodiment, a host interface 110 implements an NVM Express (NVMe) over PCI Express (PCIe). Other interfaces can also be used, such as SCSI, SATA, etc. The host interface 110 also is connected to a network-on-chip (NOC) 112.
An NOC is a communication subsystem on an integrated circuit. The NOC's can span synchronous and asynchronous clock domains or use un-clocked asynchronous logic. NOC technology applies networking theory and methods to on-chip communications and brings notable improvements over conventional bus and crossbar interconnections. The NOC improves the scalability of systems on a chip (SoC) and the power efficiency of complex SoCs compared to other designs.
The wires and the links of the NOC are shared by many signals. A high level of parallelism is achieved because all links in the NOC can operate simultaneously on different data packets. Therefore, as the complexity of integrated subsystems keep growing, a NOC provides enhanced performance (such as throughput) and scalability in comparison with previous communication architectures (e.g., dedicated point-to-point signal wires, shared buses, or segmented buses with bridges). In other embodiments, the NOC 112 can be replaced by a bus.
Connected to and in communication with NOC 112 is a processor 114, an ECC engine 116, a memory interface 118, and a DRAM controller 120. The DRAM controller 120 is used to operate and communicate with local high speed volatile memory 108 (e.g., DRAM). In other embodiments, the local high speed volatile memory 108 can be SRAM or another type of volatile memory.
In operation, the processor 114 performs the various controller memory operations, such as programming, erasing, reading, and memory management processes. In one embodiment, the processor 114 is programmed by firmware. In other embodiments, the processor 114 is a custom and dedicated hardware circuit without any software. The processor 114 also implements a translation module, as a software/firmware process or as a dedicated hardware circuit.
In many systems, the non-volatile memory is addressed internally to the storage system using physical addresses associated with one or more memory dies. However, the host system will use logical addresses to address the various memory locations. This enables the host to assign data to consecutive logical addresses, while the storage system is free to store the data as it wishes among the locations of the one or more memory dies. To implement this system, the memory controller 104 (e.g., the translation module) performs address translation between the logical addresses used by the host and the physical addresses used by the memory dies.
One example implementation is to maintain tables (i.e., the L2P tables referenced above) that identify the current translation between logical addresses and physical addresses. An entry in the L2P table may include an identification of a logical address and corresponding physical address. Although logical address to physical address tables (or L2P tables) include the word “tables” they need not literally be tables. Rather, the logical address to physical address tables (or L2P tables) can be any type of data structure. In some examples, the memory space of a storage system is so large that the local memory 108 cannot hold all of the L2P tables. In such a case, the entire set of L2P tables are stored in non-volatile memory 106 and a subset of the L2P tables are cached (L2P cache) in the local high speed volatile memory 108.
The ECC engine 116 performs error correction services. For example, the ECC engine 116 performs data encoding and decoding, as per an implemented ECC technique. In one embodiment, the ECC engine 116 is an electrical circuit programmed by software. For example, the ECC engine 116 can be a processor that can be programmed. In other embodiments, the ECC engine 116 is a custom and dedicated hardware circuit without any software. In another embodiment, the function of ECC engine 116 is implemented by the processor 114.
The memory interface 118 communicates with the non-volatile memory 106. In one embodiment, the memory interface provides a Toggle Mode interface. However, other interfaces also can be used. In some example implementations, the memory interface 118 (or another portion of the controller 104) implements a scheduler and buffer for transmitting data to and receiving data from one or more memory die.
In one embodiment, the non-volatile memory 106 includes one or more memory die.
The memory die 200 includes a memory array 202 that can include non-volatile memory cells, as described in further detail below. The memory array 202 includes a plurality of layers of word lines that are organized as rows, and a plurality of layers of bit lines that are organized as columns. However, other orientations can also be implemented.
The memory die 200 also includes row control circuitry 204, whose outputs 206 are connected to respective word lines of the memory array 202. In operation, the row control circuitry 204 receives a group of M row address signals and one or more various control signals from a system control logic circuit 208 and may include such circuits as row decoders 210, array terminal drivers 212, and block select circuitry 214 for both reading and writing (programming) operations.
The row control circuitry 204 also may include read/write circuitry. The memory die 200 also includes column control circuitry 216 including sense amplifier(s) 218 whose input/outputs 220 are connected to respective bit lines of the memory array 202. Although only a single block is shown for memory array 202, the memory die 200 can include multiple arrays that can be individually accessed.
The column control circuitry 216 receives a group of N column address signals and one or more various control signals from system control logic 208. The column control circuitry 216 may also include such circuits as column decoders 222; array terminal receivers or driver circuits 224; block select circuitry 226; read/write circuitry; and I/O multiplexers.
The system control logic 208 receives data and commands from memory controller 104 (
The system control logic 208 also can include a power control module 230 that controls the power and voltages supplied to the rows and columns of memory structure 202 during memory operations and may include charge pumps and regulator circuits for creating regulating voltages. The system control logic 208 also includes storage 232 (e.g., RAM, registers, latches, etc.), which may be used to store parameters for operating memory array 202.
In operation, commands and data are transferred between the memory controller 104 and the memory die 200 via a memory controller interface 234 (also referred to as a “communication interface”). The memory controller interface 234 is an electrical interface for communicating with memory controller 104. Examples of the memory controller interface 234 include a Toggle Mode Interface and an Open NAND Flash Interface (ONFI). Other I/O interfaces can also be used in other embodiments.
In an embodiment, the system control logic 208 also includes column replacement control circuits 236, described in more detail below.
In some embodiments, all elements of the memory die 200, including the system control logic 208, can be formed as part of a single die. In other embodiments, some or all of the system control logic 208 can be formed on a different die.
In one embodiment, the memory structure 202 comprises a three-dimensional memory array of non-volatile memory cells in which multiple memory levels are formed above a single substrate, such as a wafer. The memory structure 202 may include any type of non-volatile memory that are monolithically formed in one or more physical levels of memory cells having an active area disposed above a silicon (or other type of) substrate. In one example, the non-volatile memory cells include charge-trapping layers and are arranged in a plurality of vertical NAND strings.
In another embodiment, the memory structure 202 includes a two-dimensional memory array of non-volatile memory cells. In one example, the non-volatile memory cells are NAND flash memory cells utilizing floating gates. Other types of memory cells (e.g., NOR-type flash memory) can also be used.
The exact type of memory array architecture or memory cell included in memory structure 202 is not limited to the examples above. Many different types of memory array architectures or memory technologies can be used to form memory structure 202. No particular non-volatile memory technology is required for purposes of the new claimed embodiments proposed herein. For example, suitable technologies for the memory cells of the memory structure 202 include ReRAM memories (resistive random access memories), magnetoresistive memory (e.g., MRAM, Spin Transfer Torque MRAM, Spin Orbit Torque MRAM), FeRAM, phase change memory (e.g., PCM), and the like. Examples of suitable technologies for memory cell architectures of memory structure 202 include two dimensional arrays, three dimensional arrays, cross-point arrays, stacked two dimensional arrays, vertical bit line arrays, and the like. One example of a ReRAM cross-point memory includes reversible resistance-switching elements arranged in cross-point arrays accessed by X lines and Y lines (e.g., word lines and bit lines).
In another embodiment, the memory cells may include conductive bridge memory elements. A conductive bridge memory element may also be referred to as a programmable metallization cell. A conductive bridge memory element may be used as a state change element based on the physical relocation of ions within a solid electrolyte. In some cases, a conductive bridge memory element may include two solid metal electrodes, one relatively inert (e.g., tungsten) and the other electrochemically active (e.g., silver or copper), with a thin film of the solid electrolyte between the two electrodes. As temperature increases, the mobility of the ions also increases causing the programming threshold for the conductive bridge memory cell to decrease. Thus, the conductive bridge memory element may have a wide range of programming thresholds over temperature.
Another example is magnetoresistive random access memory (MRAM) that stores data by magnetic storage elements. The elements are formed from two ferromagnetic layers, each of which can hold a magnetization, and the ferromagnetic layers are separated by a thin insulating layer. One of the two ferromagnetic layers is a permanent magnet that is set to a particular polarity, and the other ferromagnetic layer's magnetization can be changed to match that of an external field to store memory. The memory array may be built from a grid of such memory cells. In one embodiment, for programming, each memory cell lies between a pair of write lines that are arranged at right angles to each other, parallel to the cell, one above and one below the cell. When current is passed through the write lines, an induced magnetic field is created. MRAM based memory embodiments will be discussed in more detail below.
Phase change memory (PCM) exploits the unique behavior of chalcogenide glass. One embodiment uses a GeTe—Sb2Te3 super lattice to achieve non-thermal phase changes by simply changing the co-ordination state of the Germanium atoms with a laser pulse (or light pulse from another source). Therefore, the doses of programming are laser pulses. The memory cells can be inhibited by blocking the memory cells from receiving the light. In other PCM embodiments, the memory cells are programmed by current pulses. Note that the use of “pulse” in this document does not require a square pulse but includes a (continuous or non-continuous) vibration or burst of sound, current, voltage light, or another wave. These memory elements within the individual selectable memory cells, or bits, may include a further series element that is a selector, such as an ovonic threshold switch or metal insulator substrate.
The technology described herein is not limited to a single specific memory structure, memory construction or material composition, but covers many relevant memory structures within the spirit and scope of the technology as described herein and as understood by one of ordinary skill in the art.
The elements of
Another area in which the memory structure 202 and the peripheral circuitry are often at odds is in the processing involved in forming these regions, since these regions often involve differing processing technologies and the trade-off in having differing technologies on a single die. For example, when the memory structure 202 is NAND flash, this is an NMOS structure, while the peripheral circuitry is often CMOS based.
Elements such as the sense amplifier circuits, charge pumps, logic elements in a state machine, and other peripheral circuitry in the system control logic 208 often employ PMOS devices. Processing operations for manufacturing a CMOS die will differ in many aspects from the processing operations optimized for an NMOS flash NAND memory or other memory cell technologies.
To improve upon these limitations, embodiments described below can separate the elements of
For example, a NAND memory die can be optimized for an NMOS based memory array structure, without worrying about the CMOS elements that have now been moved onto a control die that can be optimized for CMOS processing. This allows more space for the peripheral elements, which can now incorporate additional capabilities that could not be readily incorporated were they restricted to the margins of the same die holding the memory cell array.
The two die can then be bonded together in a bonded multi-die memory circuit, with the array on the one die connected to the periphery elements on the other die. Although the following will focus on a bonded memory circuit of one memory die and one control die, other embodiments can use more die, such as two memory die and one control die, for example.
The integrated memory assembly 240 includes two types of semiconductor die (or more succinctly, “die”). The memory die 242 includes the memory structure 202 with the non-volatile memory cells. A control die 244 includes control circuitry 208, 216, and 204 (as described above). In some embodiments, the control die 244 is configured to connect to the memory structure 202 in the memory die 242. In some embodiments, the memory die 242 and control die 244 are bonded together.
The system control logic 208, the row control circuitry 204, and the column control circuitry 216 may be formed by a common process (e.g., CMOS process), so that adding elements and functions, such as the ECC controller, more typically found on a memory controller 104 may require few or no additional process steps, i.e., the same process steps used to fabricate controller 104 may also be used to fabricate the system control logic 208, the row control circuitry 204, and the column control circuitry 216.
Thus, while moving such circuits from a die such as the memory die 242 may reduce the number of steps needed to fabricate such a die, adding such circuits to a die such as control die 244 may not require many additional process steps. The control die 244 also could be referred to as a CMOS die, due to the use of CMOS technology to implement some or all of the control circuitry 204, 208, 216.
Electrical paths may extend from the column control circuitry 216 in the control die 244 through pads on the control die 244 that are bonded to corresponding pads of the memory die 242, which are connected to the bit lines of the memory structure 202. Each bit line of the memory structure 202 may have a corresponding one of the electrical paths 220, including a pair of bond pads, which connects to the column control circuitry 216.
Similarly, the row control circuitry 204, including the row decoder 210, the array drivers 212, and the block select 214 are coupled to the memory structure 202 through electrical paths 206. Each of the electrical paths 206 may correspond to a data containing word line, a dummy word line, or a select gate line. Additional electrical paths may also be provided between control die 244 and memory die 242.
For purposes of this document, the phrases “a control circuit,” “control circuitry,” or “one or more control circuits” can include any one of or any combination of the memory controller 104; the state machine 228; all or a portion of the system control logic 208; all or a portion of row control circuitry 204; all or a portion of column control circuitry 216; a microcontroller; a microprocessor; and/or other similar functioned circuits.
The control circuit can include hardware only or a combination of hardware and software (including firmware). For example, one or more controllers programmed by firmware to perform the functions described herein is one example of a control circuit. A control circuit can include a processor, FGA, ASIC, integrated circuit, or other type of circuit.
In some embodiments, there is more than one control die 244 and more than one memory die 242 in an integrated memory assembly 240. In some embodiments, the integrated memory assembly 240 includes a stack of multiple control dies 244 and multiple memory dies 242.
Each control die 304 is affixed (e.g., bonded) to at least one memory die 306. Some of the bond pads 308/310 are depicted, although there may be many more bond pads. A space between two die 306, 304 that are bonded together is filled with a solid layer 312, which may be formed from epoxy or other resin or polymer. This solid layer 312 protects the electrical connections between the die 306, 304 and further secures the die together. Various materials may be used as solid layer 312, but in some embodiments, it may be Hysol epoxy resin from Henkel Corp., having offices in California, USA.
Integrated memory assembly 300 may for example be stacked with a stepped offset, leaving the bond pads at each level uncovered and accessible from above. Wire bonds 314 connected to the bond pads connect control die 304 to substrate 302. A number of such wire bonds may be formed across the width of each control die 304 (i.e., into the page of
A memory die through silicon via (TSV) 316 may be used to route signals through each memory die 306. A control die TSV 318 may be used to route signals through each control die 304. The TSVs 316, 318 may be formed before, during or after formation of the integrated circuits in semiconductor die 306, 304. The TSVs may be formed by etching holes through the wafers. The holes may then be lined with a barrier against metal diffusion. The barrier layer may in turn be lined with a seed layer, and the seed layer may be plated with an electrical conductor such as copper, although other suitable materials such as aluminum, tin, nickel, gold, Solder balls 320 optionally may be affixed to contact pads 322 on a lower surface of substrate 302. Solder balls 320 may be used to couple integrated memory assembly 300 electrically and mechanically to a host device such as a printed circuit board. Solder balls 320 may be omitted where the integrated memory assembly 300 is to be used as an LGA package. Solder balls 320 may form a part of an interface between integrated memory assembly 300 and memory controller 104 (
Some of the bond pads 308, 310 are depicted, but there may be many more bond pads than are illustrated. A space between two die 306, 304 that are bonded together is filled with a solid layer 312, which may be formed from epoxy or other resin or polymer. In contrast to the example in
As has been briefly discussed above, control die 304 and memory die 306 may be bonded together. Bond pads on each control die 304 and each memory die 306 may be used to bond the two die together. In some embodiments, the bond pads are bonded directly to each other, without solder or other added material, in a so-called Cu-to-Cu bonding process.
In a Cu-to-Cu bonding process, the bond pads are controlled to be highly planar and formed in a highly controlled environment largely devoid of ambient particulates that might otherwise settle on a bond pad and prevent a close bond. Under such properly controlled conditions, the bond pads are aligned and pressed against each other to form a mutual bond based on surface tension.
As has been briefly discussed above, the control die 304 and the memory die 306 may be bonded together. Bond pads on each control die 304 and each memory die 306 may be used to bond the two die together. In some embodiments, the bond pads are bonded directly to each other, without solder or other added material, in a so-called Cu-to-Cu bonding process. In a Cu-to-Cu bonding process, the bond pads are controlled to be highly planar and formed in a highly controlled environment largely devoid of ambient particulates that might otherwise settle on a bond pad and prevent a close bond. Under such properly controlled conditions, the bond pads are aligned and pressed against each other to form a mutual bond based on surface tension. Such bonds may be formed at room temperature, though heat also may be applied. In embodiments using cu-to-cu bonding, the bond pads may be about 5 μm square and spaced from each other with a pitch of 5 μm to 5 μm. Although this process is referred to herein as cu-to-cu bonding, this term also may apply even where the bond pads are formed of materials other than copper. When the area of bond pads is small, it may be difficult to bond the semiconductor die together. The size of and pitch between bond pads may be further reduced by providing a film layer on the surfaces of the semiconductor die including the bond pads. The film layer is provided around the bond pads. When the die are brought together, the bond pads may bond to each other, and the film layers on the respective die may bond to each other. Such a bonding technique may be referred to as hybrid bonding. In embodiments using hybrid bonding, the bond pads may be about 5 μm square and spaced from each other with a pitch of 1 μm to 5 μm. Bonding techniques may be used providing bond pads with even smaller (or greater) sizes and pitches.
Some embodiments may include a film on a surface of the control die 304 and the memory die 306. Where no such film is initially provided, a space between the die may be under filled with an epoxy or other resin or polymer. The under-fill material may be applied as a liquid which then hardens into a solid layer. This under-fill step protects the electrical connections between control die 304 and memory die 306, and further secures the die together. Various materials may be used as under-fill material, such as Hysol epoxy resin from Henkel Corp., having offices in California, U.S.A.
As will be explained below, in one embodiment the alternating dielectric layers and conductive layers are divided into, for example, four or five (or a different number of) regions by isolation regions IR.
The non-volatile memory cells are arranged in memory holes, and each memory cell can store one or more bits of data, e.g., up to five bits of data per memory cell. More details of the three dimensional monolithic memory array that comprises memory structure 202 is provided below.
In one embodiment, a block of memory cells is a unit of erase. That is, all memory cells of a block are erased together. In other embodiments, the blocks can be divided into sub-blocks, each of which includes a plurality of word lines, and the sub-blocks can be the unit of erase. Memory cells also can be grouped into blocks for other reasons, such as to organize the memory structure to enable the signaling and selection circuits.
In some embodiments, a block represents groups of connected memory cells as the memory cells of a block share a common set of word lines. For example, the word lines for a block are all connected to all of the vertical NAND strings for that respective block. Although
Each block typically is divided into one or more pages, with each page being a unit of programming/writing and a unit of reading. Other units of programming also can be used. In an embodiment, one or more pages of data are typically stored in one row of memory cells. For example, one or more pages of data may be stored in memory cells connected to a common word line. In an embodiment, a page includes data stored in all memory cells connected to a common word line within the block.
The block depicted in
In one embodiment, the isolation regions only divide the layers used to implement select gates so that NAND strings in different regions can be independently selected. In one example implementation, a bit line connects to one memory hole/vertical column/NAND string in each of regions 454, 456, 458, 460, and 462. In that implementation, each block has twenty-four rows of active columns and each bit line connects to five rows in each block.
In one embodiment, all of the five memory holes/vertical columns/NAND strings connected to a common bit line are connected to the same set of word lines; therefore, the system uses the drain side selection lines to choose one (or another subset) of the five to be subjected to a memory operation (program, verify, read, and/or erase).
Although
The structure of
In one embodiment, erasing the memory cells is performed using gate induced drain leakage (GIDL), which includes generating charge carriers at the GIDL generation transistors such that the carriers get injected into the charge trapping layers of the NAND strings to change (reduce) respective threshold voltages Vt of the memory cells. In the embodiment of
Embodiments that use GIDL at both sides of the NAND string may have GIDL generation transistors at both sides. Embodiments that use GIDL at only the drain side of the NAND string may have GIDL generation transistors only at the drain side. Embodiments that use GIDL at only the source side of the NAND string may have GIDL generation transistors only at the source side.
The GIDL generation transistors have an abrupt PN junction to generate the charge carriers for GIDL and, during fabrication, a phosphorous diffusion is performed at the polysilicon channel of the GIDL generation transistors. In some cases, the GIDL generation transistor with the shallowest phosphorous diffusion is the GIDL generation transistor that generates the charge carriers during erase. However, in some embodiments charge carriers can be generated by GIDL at multiple GIDL generation transistors at a particular side of the NAND string.
The memory holes/vertical columns 428, 430 are depicted protruding through the drain side select layers, source side select layers, dummy word line layers, GIDL generation transistor layers and word line layers. In one embodiment, each memory hole/vertical column comprises a vertical NAND string. Below the memory holes/vertical columns and the layers listed below is substrate 464, an insulating film 466 on the substrate, and source line SL. The NAND string of memory hole/vertical column 428 has a source end at a bottom of the stack and a drain end at a top of the stack. As in agreement with
For ease of reference, drain side select layers, source side select layers, dummy word line layers, GIDL generation transistor layers and data word line layers collectively are referred to as conductive layers.
In one embodiment, the conductive layers are made from a combination of TiN and Tungsten. In other embodiments, other materials can be used to form the conductive layers, such as doped polysilicon, metal such as Tungsten, metal silicide, such as nickel silicide, tungsten silicide, aluminum silicide or the combination thereof.
In some embodiments, different conductive layers can be formed from different materials. Between conductive layers are dielectric layers DL. In one embodiment, the dielectric layers are made from SiO2. In other embodiments, other dielectric materials can be used to form the dielectric layers.
The non-volatile memory cells are formed along memory holes/vertical columns which extend through alternating conductive and dielectric layers in the stack. In one embodiment, the memory cells are arranged in NAND strings. The word line layers WL0-W161 connect to memory cells (also called data memory cells). The dummy word line layers connect to a plurality of dummy memory cells, which do not store data. In some embodiments, the data memory cells and the dummy memory cells may have a same structure. The drain side select layers SGD0 and SGD1 are used to electrically connect and disconnect the NAND strings to and from the bit lines. The source side select layers SGS0 and SGS1 are used to electrically connect and disconnect the NAND strings to and from the source line SL.
When a memory cell is programmed, electrons are stored in a portion of the charge trapping layer 480 which is associated with (e.g., in) the memory cell. These electrons are drawn into the charge trapping layer 480 from the channel 476, through the tunneling dielectric 478, in response to an appropriate voltage on word line region 482. The threshold voltage (Vt) of a memory cell is increased in proportion to the amount of stored charge.
In one embodiment, the programming is achieved through Fowler-Nordheim tunneling of the electrons into the charge trapping layer 480. During an erase operation, the electrons return to the channel 476 or holes are injected into the charge trapping layer 480 to recombine with electrons. In one embodiment, erasing is achieved using hole injection into the charge trapping layer 480 via a physical mechanism such as GIDL, as described above.
In one embodiment, the programming is achieved through Fowler-Nordheim tunneling of the electrons into the charge trapping layer 480. During an erase operation, the electrons return to the channel 476 or holes are injected into the charge trapping layer 480 to recombine with electrons. In one embodiment, erasing is achieved using hole injection into the charge trapping layer 480 via a physical mechanism such as GIDL, as described above.
Similarly, the drain side select line/layer SGD1 is separated by isolation regions 446, 448, 450, and 452 (illustrated in
Although the example memories of
Turning now to
All of the dies (Dies 01-15 and the XOR die) have similar constructions. In other words, all sixteen of these dies have the same number of planes, the same number of memory blocks per plane, the same number of strings per memory block, and the same number of word lines per memory block, and the same number of memory cells per word line. Thus, each memory cell in any of the dies has an address (a particular plane/block/string/word line/memory cell combination), and all of the other memory dies (including the XOR Die) have memory cells with an identical address. This will be useful in the XOR data recovery operation discussed in further detail below.
The memory cells of each of the memory blocks in any of the memory dies can be programmed to retain one or more bits of data per memory cell. A one bit per memory cell storage scheme, known as single-level cell (SLC), is depicted in
In an exemplary embodiment, the memory cells of the user data Dies 01-15 are programmed according to a first SLC storage scheme that has a relatively tight threshold voltage Vt distribution, and the memory cells of the XOR Die are programmed according to a different, second storage scheme that has a relatively wider threshold voltage Vt distribution. More specifically an example of the first SLC storage scheme is depicted in
Turning now to
One problem with data storage for read-intensive operations, such as LLM operations, is sometimes known as “read disturb.” Read disturb occurs when the elevated read pass voltage VREAD, which is applied to the unselected word lines during each read operation, inadvertently induces a weak programming effect in certain memory cells of a memory block being read. This weak programming effect can increase the threshold voltages Vt of the memory cells in the memory block, particularly the memory cells that are in the erased data state Er. Over time, if this process is repeated very frequently (as occurs in LLM processing) without any intervening erase and program cycles, the accumulated charges in the memory cells can alter their threshold voltages Vt. For example,
Turning back to
In an example, if a read failure occurs in user data Die 03 on a word line that has an address of WL0/String 0/Memory Block 0/Plane 0, then the data contained in the word lines with this same address but in user Dies 01, 02, 04-15 and the XOR Die are all read. Then, for each memory cell, the XOR operation is performed to recover the bit that should have been contained in that memory cell of the failed word line. By repeating this operation for each memory cell of the failed word line, all of the data in the failed word line can be recovered. This process works for any number of user data dies in the memory package above one, i.e., two or more user data dies plus the XOR Die.
According to an exemplary embodiment, each memory cell in the XOR die is programmed according to the following formula using, as inputs, the data programmed into the memory cells with the same address in user data Dies 01-15:
Due to the nature of the XOR (exclusive OR) operation, when a read error occurs in any of the user data Dies 01-15, for each memory cell that failed the read operation, the data in failed Die X can be recovered by inputting data from the same memory cell in the non-failing user data Dies 01-15 and the XOR Die into the formula:
This formula can work for any suitable number of user data dies in a memory package. In a simple example, suppose there are two user data dies (designated Die 01 and Die 02) and one XOR Die. If a memory cell in Die 01 that has a given address is programmed to contain the bit “0” and the same memory cell in Die 02 is programmed to contain the bit “1”, then the same memory cell in the XOR Die will be programmed to the bit “1” according to Formula 1, which is found above (XOR Die=0⊕1). If Die 01 then encounters a read failure such that the bit of this memory cell cannot be determined even by the ECC engine, then the user data from Die 02 and the XOR data from the XOR Die are input into Formula 2, i.e., Die 01=“1” (Die 02)⊕“1” (XOR Die). The result of this operation is the bit “0”, which was the original bit for this memory cell in Die 01. This is repeatable for any combination of bits in Dies 01 and 02 or for more than two dies, e.g., the fifteen memory Dies 01-15 depicted in
Turning now to
Referring still to
Because there is no particular order that they have to be read in, the XOR recovery operation does not require prioritization that would interrupt other memory operations being performed by the non-failing user data dies.
At step 1102, read operations are performed in the user data dies, e.g., Dies 01-15 in the exemplary embodiment of
At step 1104, for each read operation in any of the user data dies, an ECC operation is performed by the ECC engine to check the data for bit errors. The ECC engine has a certain threshold of bit errors that it can correct. If the number of bit errors in a word line that is read is less than or equal to the threshold, then the ECC operation will perform the correction and the read operation will pass. On the other hand, if the number of bit errors is greater than the threshold, then the ECC operation will fail.
At decision step 1106, it is determined if the ECC operation failed. If the answer at decision step 1106 is “no,” then at step 1108, the read operation is a success. At step 1110, the corrected data is sent to the user or host, e.g., the GPU 502 depicted in
If the answer at decision step 1106 is “yes,” then at step 1112, the XOR recovery operation is performed to recover the data that the ECC engine was unable to correct. As discussed above, for each memory cell at the equivalent address in the failing die, the data at the same address in the non-failing user data dies and in the XOR die is read. Using this data, an XOR operation is then performed to determine what bit the memory cell of the failing user data die should have contained. Through this process, all of the data from the failed read operation can be recovered. The process then proceeds to step 1110, and the recovered data is output to the user or host, e.g., the GPU depicted in
In some embodiments, following a read failure, the data in the memory block that experienced the read failure can either be in-place refreshed or relocated to a different memory block in the same die. This may then necessitate a reprogramming of the XOR die to adjust for the changes.
For purposes of this document, reference in the specification to “an embodiment,” “one embodiment,” “some embodiments,” or “another embodiment” may be used to describe different embodiments or the same embodiment.
For purposes of this document, a connection may be a direct connection or an indirect connection (e.g., via one or more others parts). In some cases, when an element is referred to as being connected or coupled to another element, the element may be directly connected to the other element or indirectly connected to the other element via intervening elements. When an element is referred to as being directly connected to another element, then there are no intervening elements between the element and the other element. Two devices are “in communication” if they are directly or indirectly connected so that they can communicate electronic signals between them.
For purposes of this document, the term “based on” may be read as “based at least in part on.”
For purposes of this document, without additional context, use of numerical terms such as a “first” object, a “second” object, and a “third” object may not imply an ordering of objects, but may instead be used for identification purposes to identify different objects.
For purposes of this document, the term “set” of objects may refer to a “set” of one or more of the objects.
The foregoing detailed description has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. The described embodiments were chosen in order to best explain the principles of the proposed technology and its practical application, to thereby enable others skilled in the art to best utilize it in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope be defined by the claims appended hereto.
| Number | Date | Country | |
|---|---|---|---|
| 63300630 | Jan 2022 | US |
