# Patent

## Title
Tracking erase pulses for non-volatile memory

## Abstract

A data storage device includes a memory and a controller and may perform a method that includes comparing, in the controller, a count of erase pulses to an erase pulse threshold. The count of erase pulses corresponds to a particular region of the non-volatile memory. The method includes, in response to the count of erase pulse satisfying the erase pulse threshold, initiating a remedial action with respect to the particular region of the non-volatile memory.

## Background
FIELD OF THE DISCLOSURE
The present disclosure is generally related to erase operations in non-volatile memory.
BACKGROUND
Non-volatile data storage devices, such as universal serial bus (USB) flash memory devices or removable storage cards, have allowed for increased portability of data and software applications. Flash memory devices can enhance data storage density by storing multiple bits in each flash memory cell. For example, Multi-Level Cell (MLC) flash memory devices provide increased storage density by storing 3 bits per cell, 4 bits per cell, or more. Although increasing the number of bits per cell and reducing device feature dimensions may increase a storage density of a memory device, a bit error rate of data stored at the memory device may also increase.
Error correction coding (ECC) is often used to correct errors that occur in data read from a memory device. Prior to storage, data may be encoded by an ECC encoder to generate redundant information (e.g. “parity bits”) that may be stored with the data as an ECC codeword. As more parity bits are used, an error correction capacity of the ECC increases and a number of bits required to store the encoded data also increases.
One source of errors that occur in data stored in a memory device is a result of repeated write/erase (W/E) cycles to the memory device. Erasing a block of flash memory conventionally includes performing an “erase loop” that includes applying an erase pulse (e.g., applying an erase voltage to the erase block and removing the erase voltage), and reading the storage elements of the block. The erase loop may be repeated until all storage elements of the block have transitioned to an erased state. A number of erase pulses that are applied during each erase operation may depend of various factors, such as a physical condition of storage elements of the block and/or characteristics of data that is stored in the block. Cell threshold voltage distributions (CVDs) may shift and broaden with increasing numbers of W/E cycles, resulting in an increasing number of data errors as the memory device ages. Wear leveling techniques may be used to distribute W/E operations so that all regions of the memory are subjected to approximately an equal number of W/E cycles. As a result, wear leveling may extend a useful life of the memory device that may otherwise be limited by a portion of the memory that experiences accelerated wearing due to more frequent erase operations as compared to other portions of the memory.
However, tracking W/E cycles may provide incomplete information regarding the condition of individual erase blocks. For example, some blocks having a relatively high W/E count may reliably store data due to a low amount of wear, while some blocks having a relatively low W/E count may have reduced reliability, such as when a grown defect occurs. Managing a data storage device based on incomplete information provided by tracking W/E cycles may reduce performance and/or a useful life of the data storage device as compared to managing the data storage device based on more complete information.
SUMMARY
Counts of erase pulses applied to regions of a data storage device are tracked by a controller of the data storage device. When a number of erase pulses applied to a particular region exceeds a threshold amount, a remedial action is initiated to the particular region at least partially based on the corresponding count of erase pulses. For example, an erase block in the particular region may be scheduled for non-use based on a relatively high count of erase pulses or may be flagged for enhanced reliability techniques, such as data-parity interleaving or adaptive reading.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a particular illustrative embodiment of a system including a data storage device configured to track erase operations and erase pulses applied to multiple regions of memory and to initiate a remedial action;
FIG. 2 is a block diagram illustrating a particular embodiment of components that may be incorporated in the data storage device of FIG. 1;
FIG. 3 is a flow chart of a particular illustrative embodiment of a method of tracking erase operations and erase pulses applied to regions of a non-volatile memory; and
FIG. 4 is a flow chart of a particular illustrative embodiment of a method of tracking erase pulses applied to regions of a non-volatile memory.



DETAILED DESCRIPTION
Referring to FIG. 1, a particular embodiment of a system 100 includes a data storage device 102 coupled to a host device 130. The data storage device 102 is configured to track erase operations and erase pulses applied to multiple regions of a non-volatile memory 104 and to initiate a remedial action based on the tracked erase operations and erase pulses.
The host device 130 may be configured to provide data, such as user data 132, to be stored at the non-volatile memory 104 or to request data to be read from the non-volatile memory 104. For example, the host device 130 may include a mobile telephone, a music or video player, a gaming console, an electronic book reader, a personal digital assistant (PDA), a computer, such as a laptop computer, a notebook computer, or a tablet, solid state storage drive, any other electronic device, or any combination thereof.
The data storage device 102 includes the non-volatile memory 104 coupled to a controller 120. The non-volatile memory 104 may be a flash memory, such as a NAND flash memory. For example, the data storage device 102 may be a memory card, such as a Secure Digital SD® card, a microSD® card, a miniSDTM card (trademarks of SD-3C LLC, Wilmington, Del.), a MultiMediaCardTM (MMCTM) card (trademark of JEDEC Solid State Technology Association, Arlington, Va.), or a CompactFlash® (CF) card (trademark of SanDisk Corporation, Milpitas, Calif.). As another example, the data storage device 102 may be configured to be coupled to the host device 130 as embedded memory, such as eMMC® (trademark of JEDEC Solid State Technology Association, Arlington, Va.) and eSD, as illustrative examples.
The non-volatile memory 104 includes multiple groups of storage elements, such as word lines of a multi-level cell (MLC) flash memory that include multiple MLC flash cells. The non-volatile memory 104 may also include multiple blocks of storage elements, such as erase blocks of a flash memory that include multiple word lines in each erase block. The non-volatile memory 104 is logically partitioned into multiple regions including a first region (region 1) 110 and an Nth region (region N) 112, where N is an integer greater than one. For example, in some implementations the non-volatile memory 104 may be partitioned into two regions (i.e., N equals 2). In other implementations, the non-volatile memory 104 may be partitioned into more than two regions, including the first region 110, one or more other regions (not shown), and the Nth region 112 (i.e., N is greater than 2). Each region 110-112 can include one or more word lines, blocks, or other portions of the non-volatile memory 104. To illustrate, in an implementation where the non-volatile memory 104 includes multiple arrays, multiple planes, multiple dies, or any combination thereof, each region may include multiple word lines or blocks within a single array, plane, or die. As another example, a single region (e.g., the first region 110) may span multiple arrays, planes, or dies, or any combination thereof. To illustrate, the first region 110 may include storage elements within a first die and storage elements within a second die.
The controller 120 is configured to receive data and instructions from and to send data to the host device 130 while the data storage device 102 is operatively coupled to the host device 130. The controller 120 is further configured to send data and commands to the non-volatile memory 104 and to receive data from the non-volatile memory 104. For example, the controller 120 is configured to send data and a write command to instruct the non-volatile memory 104 to store the data to a specified address. As another example, the controller 120 is configured to send a read command to read data from a specified address of the non-volatile memory 104.
The controller 120 may include an ECC engine (not shown) that is configured to receive data to be stored to the non-volatile memory 104 and to generate a codeword. For example, the ECC engine may include an encoder configured to encode data using an ECC encoding scheme, such as a Reed Solomon encoder, a Bose-Chaudhuri-Hocquenghem (BCH) encoder, a low-density parity check (LDPC) encoder, a Turbo Code encoder, an encoder configured to encode data according to one or more other ECC encoding schemes, or any combination thereof. The ECC engine may include a decoder configured to decode data read from the non-volatile memory 104 to detect and correct, up to an error correction capability of the ECC scheme, bit errors that may be present in the data.
The controller 120 includes a set of counters 122 that are configured to track erase operations performed to the regions 110-112 of the non-volatile memory 104 and to track erase pulses performed to the regions 110-112. The set of counters 122 includes multiple counters, including a first write/erase (W/E) counter (W/E counter 1) 140 and an Nth W/E counter (W/E counter N) 142. The first W/E counter 140 has a first W/E counter value (W/E value 1) 160 that is updatable by the controller 120 to track memory accesses to the first region 110. The Nth W/E counter 142 has an Nth W/E value 162 that is also updatable by the controller 120 to track memory accesses to the Nth region 112. The set of counters 122 also includes a first erase pulse counter (erase pulse counter 1) 170 and an Nth erase pulse counter (erase pulse counter N) 172. The first erase pulse counter 170 has a first erase pulse counter value 190 that is updatable by the controller 120 to track erase pulses applied to the first region 110. The Nth erase pulse counter 172 has an Nth erase pulse value 192 that is also updatable by the controller 120 to track erase pulses applied to the Nth region 112. In an implementation where the non-volatile memory 104 is partitioned into two regions (i.e., N=2), the set of counters 122 may include a first group of the first W/E counter 140 and the first erase pulse counter 170 for the first region 110 and a second group of the Nth (second) W/E counter 142 and the Nth (second) erase pulse counter 172 for the Nth (second) region 112. In implementations where the non-volatile memory 104 is partitioned into more than two regions (i.e., N>2), the set of counters 122 may include more than two groups of W/E counters and erase pulse counters (i.e., the first W/E counter 140 and the first erase pulse counter 170, one or more additional W/E counters and erase pulse counters (not shown), and the Nth W/E counter 142 and the Nth erase pulse counter 172). The counters of the set of counters 122 may be implemented as data values stored in a random access memory (RAM) that is accessible to the firmware executing controller 120, as an illustrative example.
The controller 120 includes a memory management engine 124. The memory management engine 124 is configured to schedule erase operations of erase blocks that may be identified by an erase block address 152. For example, the erase block address 152 may correspond to a physical address (e.g., an index or other identifier) of an erase block in the non-volatile memory 104. To illustrate, the memory management engine 124 may perform a “garbage collection” operation in which valid data on an erase block is copied to another block, the erase block is erased, and the erased block is added to a list of available blocks to receive new data. The memory management engine 124 is configured to generate an erase command 150 to perform an erase operation at the erase block address 152 of the non-volatile memory 104. In addition, the memory management engine 124 is configured to provide the erase block address 152 to the set of erase counters 122.
In response to determining the erase block address 152 corresponding to a physical address of a block to be erased, the controller 120 may select a particular W/E counter of the set of counters 122 corresponding to a region of the non-volatile memory 104 that is tracked by the particular W/E counter. For example, when the erase block address 152 corresponds to the first region 110, the controller 120 may determine that the first W/E counter 140 maintains a count of erase operations to the first region 110, and as a result the first W/E value 160 may be updated by the first W/E counter 140. As another example, when the erase block address 152 corresponds to a block in the Nth region 112, which is tracked by the Nth W/E counter 142, the Nth W/E value 162 of the Nth W/E counter 142 may be updated to indicate the erase operation.
In response to the erase command 150, the memory 104 may perform one or more erase pulses to the erase block corresponding to the erase block address 152 and may send a count of erase pulses 151 to the controller 120. The controller 122 may be configured to update a value of a corresponding erase pulse counter 170-172 based on the count of erase pulses 151. In an implementation where each region 110-112 corresponds to a single erase block, each erase pulse counter 170-172 may store a total number of erase pulses that have been performed on the corresponding block. In implementations where the first region 110 includes multiple blocks, the first erase pulse value 190 may correspond to a total count of all erase pulses that have been performed in the first region 110 (i.e., a sum of erase pulses that have been applied to a first block in the first region 110, erase pulses that have been applied to a second block in the first region 110, etc.). As another example, the first erase pulse value 190 may correspond to a highest number of erase pulses that have been performed to an erase block in the first region 110. To illustrate, a count of erase pulses may be maintained for each block in the first region 110 and the first erase pulse value 190 may store a largest of the counts.
The controller 130 may be configured to compare the count of erase pulses 151 to an erase pulse threshold to identify regions and/or blocks that may have reduced reliability. For example, a “fresh” block having a relatively small count of W/E cycles may be erasable using a relatively small number of erase pulses (e.g., three). After experiencing a relatively large number of W/E cycles, the same block may not be fully erased until a relatively large number of erase pulses (e.g., twenty) have been applied. A large number of erase pulses being applied to erase a fresh block may indicate an abnormality with the block, such as a grown defect, and may signal that remedial action is to be taken. The controller 120 may be configured to compare the count of erase pulses 151, or a corresponding erase pulse counter value 190-192, to a threshold and may generate a flag 154 in response to the value satisfying the threshold. The threshold may be fixed (e.g., fifteen) or may be determined by the controller 120. For example, the controller 120 may determine the threshold based on the corresponding W/E value 160-162, such as by retrieving a stored value (e.g., accessing a lookup table indexed by W/E cycle count) or by computing the threshold using the corresponding W/E value. In response to the flag 154, the memory management engine 124 may initiate a remedial action 126 with respect to the corresponding region or block of the non-volatile memory 104.
The count of erase pulses 151 may be used to identify blocks that have a relatively high W/E count but that show reduced wear or increased wear as compared to other blocks having the same W/E count. For example, each of the W/E values 160-162 that corresponds to counts of erase operations to the particular regions tracked by the corresponding counters 140-142 may be compared to a threshold 170. In response to determining that one or more of the W/E values 160-162 satisfies the threshold 170, a flag 154 may be generated and provided to the memory management engine 124. In some embodiments, such as when the W/E counters 140-142 count up from an initial value, a value satisfies the threshold 170 when the value exceeds the threshold 170. In other embodiments, a value satisfies the threshold 170 when the value is greater than or equal to the threshold 170. Alternatively, in some embodiments, such as when the W/E counters 140-142 count down from an initial value, a value satisfies the threshold 170 when the value is less than the threshold 170. In other embodiments, a value satisfies the threshold 170 when the value is less than or equal to the threshold 170. The memory management engine 124 may receive the flag 154 and based on the count of erase pulses for the corresponding region, may select and initiate a remedial action 126 to the corresponding region of the non-volatile memory 104.
For example, when the first W/E value 160 indicates that a count of erase operations to the first region 110 satisfies the threshold 170, the controller 120 may be configured to initiate the remedial action 126 to the first region 110. The remedial action 126 may be selected as a function of the first W/E value 160 and the first erase pulse count 190. For example, because blocks having the same number of W/E cycles with a lower erase pulse count may have less wear than blocks with a higher erase pulse count, an “effective” count of W/E cycles may be determined as a more accurate indication of block wear than may be provided by the W/E value 160. As an example, the effective count of W/E cycles may be based on a multiplicative product of the first W/E value 160 and the first erase pulse value 190. As another example, the effective count of W/E cycles may be based on a ratio of the first erase pulse value 190 as compared to the first W/E value 160.
The remedial action 126 may include scheduling one or more erase blocks in the first region 110 to be unused after performing a data move operation that causes data in the one or more erase blocks to be moved to a different memory location of the non-volatile memory 104. As another example, the remedial action 126 may include flagging one or more erase blocks for enhanced reliability techniques. Enhanced reliability techniques may include using a more robust ECC scheme for data to be stored in the one or more erase blocks, such as by increasing a proportion of parity bits to data bits. As another example, the one or more erase blocks may be flagged for interleaving of data and parity across multiple logical pages of a word line. Because different logical pages of a word line may have different reliability, interleaving data and parity across multiple logical pages distributes errors from each logical page across multiple ECC codewords and reduces a probability that an uncorrectable number of errors will be introduced into any single ECC codeword. As another example, the one or more erase blocks may be flagged for dynamic reading that includes reading data by performing multiple sensing operations using multiple read voltages to identify a set of read voltages that corresponds to a fewest number of errors in the data. Potential corruption of data in the non-volatile memory 104 caused by W/E cycling effects or due to other mechanisms, such as grown defects or word line to word line short, may be anticipated based on such effective W/E cycle counts of erase operations to each of the regions 110-112 or based on the counts of erase pulses (or changes in the counts of erase pulses). The remedial action 126 may be performed for one or more of the regions 110-112 to avoid unrecoverable corruption of data resulting from accumulated W/E cycling effects or in response to detecting other conditions that may be indicated according to an amount of erase pulses.
In some implementations, the W/E counters 140-142 may count upward from a reset value (e.g., a 0 value) with each erase operation to the region tracked by the particular W/E counter 140-142. The W/E value 160-162 of each W/E counter 140-142 may be compared against the threshold 170 (e.g., each time the W/E value 160-162 is updated) to determine when a number of erase operations to a corresponding region 110-112 of the non-volatile memory 104 satisfies the threshold 170. However, in other implementations, other configurations of the W/E counters 140-142 may be applied. For example, the W/E counters 140-142 may be initially set to a value corresponding to a W/E cycle limit, and the W/E counters 140-142 may decrement the corresponding W/E value 160-162 with each erase operation. When one of the W/E values 160-162 reaches a zero value, the flag 154 may be provided to the memory management engine 124.
Because each region 110-112 may be determined according to W/E endurance characteristics, different thresholds may be used for different groups, as described with respect to FIG. 2. In other implementations, the single threshold 170 may be used for all of the regions 110-112 and an initial counter value of each of the groups may be adjusted according to characteristics of the groups. As a result, a group of erase blocks with higher W/E endurance may start with a lower initial counter value and may reach the threshold 170 after a greater number of W/E cycles than a group with lower W/E endurance that starts with a higher initial counter value.
The controller 120 may be configured to store counter values 180 to specific or dedicated portions of the non-volatile memory 104 for storage during power off conditions. For example, the controller 120 may be configured to store counter values 180 of the set of counters 122 to the non-volatile memory 104 during a session shutdown operation of the data storage device 102. The controller 120 may further be configured to retrieve the stored counter values 180 from the non-volatile memory 104 and to initialize the W/E counters 140-142 and the erase pulse counters 170-172 of the set of counters 122 according to the stored counter values 180 during a session initialization operation of the data storage device 102. To illustrate, the counter values 180 may include a table or other data structure that indicates a number of the regions 110-112 (e.g., N regions). For each region, the counter values 180 may include values of a corresponding pair of counters (e.g., the first W/E value 160 and the first erase pulse value 190 for the first region 110, an address range corresponding to the particular region (e.g., addresses of a first and last erase block within the first region 110), and a value of the threshold 170 corresponding to the particular region. For example, a number and arrangement of the regions 110-112 may be modified over the life of the data storage device 102. In addition, different regions may correspond to different thresholds.
During operation, the memory management engine 124 may identify an erase block to be erased and may provide the erase block address 152 to the set of erase counters 122. In addition, the controller 120 may issue the erase command 150 to the non-volatile memory 104, such as concurrently with providing the erase block address 152 to the set of erase counters 122.
The controller 120 may determine a particular counter of the set of counters 122 that tracks the region of the non-volatile memory 104 corresponding to the erase block address 152. For example, the erase block address 152 may correspond to an erase block in the first region 110, which may be tracked by the first W/E counter 140. In response to receiving the erase block address 152, a determination may be made that the erase block address 152 corresponds to the first W/E counter 140, and the first W/E counter 140 may update the first W/E value 160 to indicate an additional erase operation has been or is being performed within the first region 110. In addition, the first erase pulse value 190 may be updated based on the count of erase pulses 151 that is received from the memory 104.
In response to the count of erase pulses 151 or the first erase pulse value 190 satisfying an erase pulse threshold for the region or block, a corresponding flag 154 may be provided to the memory management engine 124. Alternatively or in addition, in response to the first W/E value 160 (upon being updated by the first W/E counter 140) satisfying the threshold 170, a corresponding flag 154 may be provided to the memory management engine 124. In response to receiving the flag 154, the memory management engine 124 may retrieve the first erase pulse value 190 and determine the remedial action 126 based on an effective count of W/E cycles to the first region 110. The memory management engine 124 may initiate the remedial action 126, such as by scheduling one or more erase blocks to be unused or to be used in conjunction with one or more higher reliability techniques, such as described in further detail with respect to FIG. 2.
By tracking counts of erase pulses and by selecting and initiating the remedial action 126 based on a count of erase pulses corresponding to the particular region 110-112, data loss due to mechanisms, such as grown defects, or cumulative effects of W/E cycling occurring in the particular region 110-112 may be more accurately predicted and remedied as compared to implementations that do not track erase pulses. As a result, a number of errors occurring in the stored data due to W/E cycling may be maintained at a correctable level for longer periods and a useful life of the data storage 102 may be extended. The set of counters 122 and corresponding logic to map the set of counters 122 to individual regions of the non-volatile memory 104 may be implemented in dedicated circuitry to reduce latency and processing impact on the controller 120 during the erase operation, as described in further detail with respect to FIG. 2. Alternatively, the set of erase counters 122 may be implemented via one or more software processes executed by a processer within the controller 120, or by a combination of software executed by a processor and dedicated circuitry.
Referring to FIG. 2, a particular embodiment of the data storage device 102 of FIG. 1 is illustrated and generally designated 200. The non-volatile memory 104 is illustrated as a NAND flash memory that includes multiple erase blocks, including block 0 220, block 1 222, block 2 224, block 3 226, and additional blocks up to an Mth block (block M) 228. The NAND flash memory 104 is logically partitioned into multiple erase tracking regions, illustrated as a first erase tracking region 210, a second erase tracking region 212, and additional regions up to an N−1st erase tracking region 214 and an Nth erase tracking region 216. The controller 120 includes the set of counters 122 including the first W/E counter 140 and the first erase pulse (EP) counter 170, a second W/E counter 141 and a second erase pulse counter 171, and one or more other counters including the Nth W/E counter 142 and the Nth erase pulse counter 172. The controller 120 includes address comparison circuitry 240 that is coupled to receive the erase block address 152 from the flash management engine 124 and the count of erase pulses 151 applied to the erase block address 152 and generate signals to a pair of counters that track a region 210-216 of the NAND flash memory 104 corresponding to the erase block address 152. The controller 120 further includes one or more interleaved data and parity flags 244, one or more adaptive read flags 246, and a bad block list 242.
The controller 120 is configured to provide the erase block address 152 from the flash management engine 124 to the address comparison circuitry 240. The address comparison circuitry 240 may be programmable to route particular erase block addresses 152 to particular counters of the set of counters 122. For example, the address comparison circuitry 240 may determine whether the erase block address 152 is within a first address range corresponding to the first erase tracking region 210, a second address range corresponding to the second erase tracking region 212, etc., and may generate an output signal to a corresponding one of the W/E counters 140-142 to cause the W/E counter to update its counter value. In addition, the controller 120 is configured to generate a control signal to cause a corresponding one of the erase pulse counters 170-172 to update its counter value based on the count of erase pulses 151 received from the NAND flash memory 104.
Each of the W/E counters 140-142 may be responsive to a corresponding threshold, illustrated as threshold 1, threshold 2, . . . threshold N. For example, each W/E counter 140-142 may be configured to perform comparisons of the counter's value to its corresponding threshold and to generate a flag signal in response to the value satisfying the threshold. To illustrate, when the first W/E counter 140 updates its counter value to an amount that matches the first threshold (threshold 1), the first W/E counter 140 may generate a first flag indication (Flag 1) that may be provided to the flash management engine 124 as the flag 154. Each of the W/E counters 140-142 may have a programmable threshold value such that each of the thresholds may have a distinct value, or one or more (or all) of the W/E counters 140-142 may use a same threshold value.
Each of the W/E counters 140-142 may provide a distinct flag signal to the flash management engine 124. For example, the flag indicator 154 may be a multi-bit signal, such as an interrupt signal with each bit of the interrupt signal corresponding to a distinct counter of the set of counters 122. A value of the corresponding erase pulse counter 170-172 may also be provided with the interrupt signal to the flash management engine 124. In this manner, the flash management engine 124 may determine a particular erase tracking region 210-216 that has a count of erase operations satisfying its corresponding threshold and may determine an effective count of W/E cycles based on the count of erase operations and the count of erase pulses. In response, the flash management engine 124 may select and perform the remedial action 126 of FIG. 1 to the blocks of the first erase tracking region 210.
Each of the erase pulse counters 170-172 may be configured to provide a distinct flag signal to the flash management engine 124. A value of the corresponding erase pulse counter 170-172 may be provided with an interrupt signal to the flash management engine 124. In this manner, the flash management engine 124 may determine a particular erase tracking region 210-216 that has a count of erase pulses satisfying its corresponding threshold (e.g., a first erase pulse threshold, such as a static threshold or a threshold determined based on the corresponding count of W/E cycles). In response, the flash management engine 124 may select and perform the remedial action 126 of FIG. 1 with respect to the blocks of the first erase tracking region 210.
In response to a relatively high effective count of W/E cycles (e.g., when an effective count of W/E cycles is greater than or equal to a first threshold) and/or in response to a relatively high count of erase pulses (e.g., the count of erase pulses satisfies a second erase pulse threshold), the flash management engine 124 may be configured to add addresses of the blocks of the corresponding region, such as blocks 0-3 220-226 of the first erase tracking region 210, to the bad block list 242. The flash management engine 124 may be configured to perform data move operations to transfer data from blocks scheduled to be added to the bad block list 242, such as by copying the data to one or more spare block that may be available in the non-volatile memory 104. The flash management engine 124 may be configured to prevent usage of erase blocks that have been added to the bad block list 242.
In response to a relatively low effective count of W/E cycles (e.g., when the effective count of W/E cycles is less than or equal to a second threshold) and/or in response to a count of erase pulses that indicates abnormal operation but that does not satisfy a criteria for bad block status (e.g., the count of erase pulses satisfies the first erase pulse threshold but does not satisfy the second erase pulse threshold), the flash management engine 124 may be configured to set one or more of the interleaved data and parity flags 244 to indicate that one or more erase blocks store data according to an interleaved configuration. To illustrate, because reading a single logical page of a physical page requires fewer sense operations than reading all logical pages of the physical page, ECC codewords may be stored on individual logical pages to be readable using a reduced number of sense operations. However, different logical pages of a single physical page may have different reliability. As a result, as an erase block is subjected to a number of W/E cycles approaching its threshold, an ECC codeword stored on a less reliable logical page is more likely to encounter an uncorrectable number of errors than an ECC codeword stored on a more reliable logical page. By interleaving multiple ECC codewords across multiple logical pages, errors occurring on the less-reliable logical page as well as errors occurring on the more-reliable logical page are shared among multiple ECC codewords, reducing the probability that any of the ECC codewords encounters an uncorrectable number of errors. The interleaved data and parity flags 244 may include a flag for each region 210-216 or for each erase block 220-228 in the non-volatile memory 104 and a value of each flag may be set to indicate whether the associated region or block uses a page-by-page data and parity configuration or an interleaved data and parity configuration.
In response to an intermediate effective count of W/E cycles (e.g., when the effective count of W/E cycles is between the first threshold and the second threshold), and/or in response to a count of erase pulses that indicates abnormal operation but that does not satisfy a criteria for bad block status (e.g., the count of erase pulses satisfies a third erase pulse threshold that is greater than the first erase pulse threshold but does not satisfy the second erase pulse threshold), the flash management engine 124 may be configured to set one or more of the adaptive read flags 246 to indicate that one or more erase blocks are to be read using an adaptive read technique instead of, or in addition to, using, interleaved configuration. To illustrate, a set of read voltages may correspond to boundaries between states of storage elements and may be used during sensing operations to determine a state of storage elements of a word line in an erase block. However, as W/E cycling increases, shifting of threshold voltages of storage elements may cause the boundaries between the states to shift from the read voltages. Adaptive read techniques may include performing multiple reads of an ECC codeword from an erase block and varying one or more of the read voltages. Data resulting from each read may be provided to an ECC decoder to identify a corresponding number of errors detected in the data to identify values of the read voltages that result in a reduced number of errors. A set of read voltages that is identified as resulting in reduced errors may be selected for reading the data, resulting in a more accurate representation of the data as compared to using default values of the read voltages.
A mapping of regions to counters and a logical partitioning of the non-volatile memory 104 into the regions 110-112 may be stored as an initial configuration of the memory device 102 of FIG. 1 and may be set according to an initial set of programmable values, such as determined by a manufacturer of the data storage device 102. Although FIGS. 1 and 2 illustrate multiple regions having substantially equal size and that are substantially evenly distributed throughout the non-volatile memory 104, it should be understood that in other implementations one or more of the memory regions may have a size differing from others of the memory regions. As an example, effects of W/E cycling on stored data in the non-volatile memory 104 may be dependent on one or more factors such as a location in a memory array (e.g., at an edge of the array as compared to at an interior of the array), a particular plane of multi-plane memory, a particular die of a multi-die memory, one or more other factors such as a type of data stored, a ratio of ‘0’ values to ‘1’ values in stored data at the non-volatile memory 104, or other factors. Sizes of memory regions and groups of blocks in each region may be determined according to one or more such factors.
Because partitioning of the non-volatile memory 104 into multiple regions and a mapping of regions to counters may be programmable, the data storage device 102 may be configured to accommodate various factors and various differences in effects of W/E cycling on various portions of the non-volatile memory 104. For example, an initial logical partitioning and mapping of regions to the counters 140-142 and 170-172 may be set by a manufacturer of the data storage device 102 of FIG. 1. To illustrate, regions 110-112 of the non-volatile memory 104 may be set based on results of testing portions of the non-volatile memory 104 for susceptibility to W/E cycling effects, based on types of data stored to regions of the non-volatile memory 104, such as file management data or pre-loaded content, based on one or more other criteria, or any combination thereof. The memory management engine 124 may be configured to update the logical partitioning of the non-volatile memory 104 and a corresponding mapping of regions to counters according to one or more criteria, such as according to a history of erase operations to different portions of the non-volatile memory 104.
Referring to FIG. 3, a particular embodiment of a method 300 is depicted. The method 300 may be performed in a data storage device that includes a controller and a non-volatile memory, such as a flash memory. For example, the method 300 may be performed by the data storage device 102 of FIG. 1.
The method includes updating, in a controller of the data storage device, a value of a particular write/erase (W/E) counter of a set of counters and a value of a particular erase pulse counter in response to an erase operation to a particular region of the non-volatile memory that is tracked by the particular W/E counter and the particular erase pulse counter, at 302. Erase operations to a first region of the non-volatile memory are tracked by a first W/E counter and a first erase pulse counter of the set of counters, and erase operations to a second region of the non-volatile memory are tracked by a second W/E counter and a second erase pulse counter of the set of counters. For example, erase operations to the first region 110 of FIG. 1 may be tracked by the first W/E counter 140, and the first erase pulse counter 170 and erase operations to the Nth region 112 of FIG. 1 may be tracked by the Nth W/E counter 142 and the Nth erase pulse counter 172.
In response to the value of the particular counter indicating that a count of erase operations to the particular region satisfies a first threshold, a remedial action to the particular region of the non-volatile memory is initiated, at 304. For example, the remedial action may be the remedial action 126 initiated by the memory management engine 124 of FIG. 1 and may include scheduling one or more erase blocks for non-use, flagging one or more erase blocks for data and parity interleaving, and/or flagging one or more erase blocks for adaptive read at least partially based on the value of the particular erase pulse counter.
The remedial action may be selected based on an effective count of W/E cycles. For example, the remedial action may be selected based on a product of the value of the particular W/E counter and the value of the particular erase pulse counter. As another example, the remedial action may be selected based on a ratio the value of the particular erase pulse counter as compared to the value of the particular W/E counter.
The method 300 may also include, during a session shut-down operation of the data storage device, storing values of the set of counters to the non-volatile memory. During a session initialization operation of the data storage device, stored counter values may be retrieved from the non-volatile memory and counters of the set of counters may be initialized according to the stored counter values. For example, the controller 120 may store the counter values 180 of FIG. 1 to the non-volatile memory 104 prior to powering down and may retrieve the counter values 180 from the non-volatile memory 104 during an initialization/powering up event.
Initiating the remedial action may include scheduling an erase block associated with the particular W/E counter to be unused, such as by scheduling the erase block to be added to the bad block list 242 of FIG. 2 after copying data from the erase block to another block of the memory 104. Alternatively or in addition, initiating the remedial action may include setting a flag to indicate data and parity interleaving is to be applied to the particular region (e.g., the interleaved data and parity flags 244 of FIG. 2). Alternatively or in addition, initiating the remedial action may include setting a flag to indicate adaptive reading is to be applied to the particular region (e.g., the adaptive read flags 246 of FIG. 2).
The first region may correspond to a first set of erase blocks of the non-volatile memory, and the second region may correspond to a second set of erase blocks of the non-volatile memory. As one example, the first set of erase blocks may include a single erase block and the second set of erase blocks may include another single erase block. As a second example, the first set of erase blocks may include a contiguous group of erase blocks, such as the first erase tracking region 210 of FIG. 2 that includes a contiguous group of four erase blocks 220-226. As a third example, the first set of erase blocks may include a non-contiguous group of erase blocks. To illustrate, the first set of erase blocks may include blocks that have similar physical characteristics but that may not be adjacent to each other. For example, block 0 220 and block M 228 of FIG. 2 may have common physical characteristics due to being at edges of the NAND flash memory 104. The non-volatile memory may be logically partitioned into a programmable number of regions, and a count of erase operations to each of the multiple regions may tracked by a respective counter of the set of counters.
Referring to FIG. 4, a particular embodiment of a method 400 is depicted. The method 400 may be performed in a data storage device that includes a controller and a non-volatile memory, such as a flash memory. For example, the method 400 may be performed by the data storage device 102 of FIG. 1.
A count of erase pulses may be compared to an erase pulse threshold, at 402. The count of erase pulses corresponds to a particular region of the non-volatile memory. For example, the count of erase pulses may correspond to the count of erase pulses 151 of FIG. 1.
In response to the count of erase pulses satisfying the erase pulse threshold, a remedial action may be initiated with respect to the particular region of the non-volatile memory, at 404. For example, the erase pulse threshold may be static or may be based on a count of write/erase cycles corresponding to the particular region.
Initiating the remedial action may include scheduling an erase block to be unused. Alternatively, initiating the remedial action may include setting a flag to indicate that data and parity interleaving is to be applied to the particular region. Alternatively, or in addition, initiating the remedial action may include setting a flag to indicate that adaptive reading is to be applied to the particular region. By initiating the remedial action based on the count of erase pulses, potential data loss due to abnormal conditions in the non-volatile memory, such as grown defects, may be avoided.
Although various components depicted herein are illustrated as block components and described in general terms, such components may include one or more microprocessors, state machines, or other circuits configured to enable the controller 120 of FIG. 1 to select and initiate the remedial action based on comparisons of the W/E counter values 160-162 to one or more threshold(s) 170 and further based on erase pulse counter values. For example, the controller 120 may represent physical components, such as hardware controllers, state machines, logic circuits, or other structures, to enable the controller 120 of FIG. 1 to track erase operations to individual regions 110-112 and to select and initiate one or more remedial actions to individual regions 110-112.
The controller 120 may be implemented using a microprocessor or microcontroller programmed to update counters in response to erase operations to corresponding regions of the non-volatile memory 104, and upon determining that a counter value indicates that a number of erase operations to a particular region satisfies a threshold amount, to select a remedial action at least partially based on corresponding erase pulse count, such as by scheduling one or more erase blocks for non-use or setting one or more of the interleaved data and parity flags 244 and/or the adaptive read flags 246. In a particular embodiment, the controller 120 includes a processor executing instructions that are stored at the non-volatile memory 104. Alternatively, or in addition, executable instructions that are executed by the processor may be stored at a separate memory location that is not part of the non-volatile memory 104, such as at a read-only memory (ROM).
In a particular embodiment, the data storage device 102 may be implemented in a portable device configured to be selectively coupled to one or more external devices. However, in other embodiments, the data storage device 102 may be attached or embedded within one or more host devices, such as within a housing of a host communication device. For example, the data storage device 102 may be within a packaged apparatus such as a wireless telephone, a personal digital assistant (PDA), a gaming device or console, a portable navigation device, or other device that uses internal non-volatile memory. In a particular embodiment, the data storage device 102 may be coupled to a non-volatile memory, such as a three-dimensional (3D) memory, a flash memory (e.g., NAND, NOR, Multi-Level Cell (MLC), a Divided bit-line NOR (DINOR) memory, an AND memory, a high capacitive coupling ratio (HiCR), asymmetrical contactless transistor (ACT), or other flash memories), an erasable programmable read-only memory (EPROM), an electrically-erasable programmable read-only memory (EEPROM), a read-only memory (ROM), a one-time programmable memory (OTP), or any other type of memory.
The illustrations of the embodiments described herein are intended to provide a general understanding of the various embodiments. Other embodiments may be utilized and derived from the disclosure, such that structural and logical substitutions and changes may be made without departing from the scope of the disclosure. This disclosure is intended to cover any and all subsequent adaptations or variations of various embodiments.
The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the scope of the present disclosure. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

## Claims

1. A method comprising:
in a data storage device that includes a controller and a non-volatile memory, performing:
storing, by the controller, a count of erase pulses corresponding to a particular region of the non-volatile memory and storing a write/erase (W/E) counter value associated with the particular region of the non-volatile memory;
calculating an effective count based on one of a product of the stored count of erase pulses and the stored W/E counter value or a ratio of the stored count of erase pulses to the stored W/E counter value; and
in response to the effective count satisfying a threshold, initiating a remedial action with respect to the particular region of the non-volatile memory.

2. The method of claim 1, wherein the effective count comprises the product of the stored count of erase pulses and the stored W/E counter value.

3. The method of claim 1, wherein initiating the remedial action includes scheduling an erase block to be unused.

4. The method of claim 1, wherein initiating the remedial action includes setting a flag to indicate that data and parity interleaving is to be applied to the particular region.

5. The method of claim 1, wherein initiating the remedial action includes setting a flag to indicate that adaptive reading is to be applied to the particular region.

6. A data storage device comprising:
a non-volatile memory; and
a controller, wherein the controller is configured to:
store a count of erase pulses, wherein the count of erase pulses corresponds to a particular region of the non-volatile memory;
store a write/erase (W/E) counter value associated with the particular region of the non-volatile memory;
calculate an effective count based on one of a product of the stored count of erase pulses and the stored W/E counter value or a ratio of the stored count of erase pulses to the stored W/E counter value; and
in response to the effective count satisfying a threshold, initiate a remedial action with respect to the particular region of the non-volatile memory.

7. The data storage device of claim 6, wherein the effective count comprises the product of the stored count of erase pulses and the stored W/E counter value.

8. The data storage device of claim 6, wherein the controller is configured to initiate the remedial action by scheduling an erase block to be unused.

9. The data storage device of claim 6, wherein the controller is configured to initiate the remedial action by setting a flag to indicate that data and parity interleaving is to be applied to the particular region.

10. The data storage device of claim 6, wherein the controller is configured to initiate the remedial action by setting a flag to indicate that adaptive reading is to be applied to the particular region.

11. A method comprising:
in a data storage device that includes a controller and a non-volatile memory, performing:
updating, in the controller, a value of a particular write/erase (W/E) counter and a value of a particular erase pulse counter in response to an erase operation to a particular region of the non-volatile memory that is tracked by the particular W/E counter and the particular erase pulse counter; and
in response to the value of one of a product of the value of the particular erase pulse counter and the value of the particular W/E counter or a ratio of the value of the particular erase pulse counter to the value of the particular W/E counter satisfying a threshold, initiating a remedial action with respect to the particular region of the non-volatile memory.

12. The method of claim 11, wherein erase operations to a first region of the non-volatile memory are tracked by a first W/E counter and a first erase pulse counter of a set of counters, wherein erase operations to a second region of the non-volatile memory are tracked by a second W/E counter and a second erase pulse counter of the set of counters, wherein the first region corresponds to a first set of erase blocks of the non-volatile memory, and wherein the second region corresponds to a second set of erase blocks of the non-volatile memory.

13. The method of claim 12, wherein the first set of erase blocks comprises a single erase block and wherein the second set of erase blocks comprises another single erase block.

14. The method of claim 12, wherein the first set of erase blocks includes a contiguous group of erase blocks.

15. The method of claim 12, wherein the first set of erase blocks includes a non-contiguous group of erase blocks.

16. The method of claim 11, wherein the remedial action is selected based on the product of the value of the particular W/E counter and the value of the particular erase pulse counter.

17. The method of claim 11, wherein the remedial action is selected based on the ratio of the value of the particular erase pulse counter and the value of the particular W/E counter.

18. The method of claim 11, wherein initiating the remedial action includes scheduling an erase block associated with the particular W/E counter to be unused.

19. The method of claim 11, wherein initiating the remedial action includes setting a flag to indicate that data and parity interleaving is to be applied to the particular region.

20. The method of claim 11, wherein initiating the remedial action includes setting a flag to indicate that adaptive reading is to be applied to the particular region.

21. The method of claim 11, further comprising:
during a session shut-down operation of the data storage device, storing values of the particular W/E counter and the particular erase pulse counter to the non-volatile memory; and
during a session initialization operation of the data storage device, retrieving the stored counter values from the non-volatile memory and initializing the particular W/E counter and the particular erase pulse counter according to the stored counter values.

22. The method of claim 11, wherein the non-volatile memory includes a flash memory.

23. A data storage device comprising:
a non-volatile memory; and
a controller including a particular write/erase (W/E) counter and a particular erase pulse counter, wherein the controller is configured to update a value of the particular write/erase (W/E) counter and a value of the particular erase pulse counter in response to an erase operation to a particular region of the non-volatile memory that is tracked by the particular W/E counter and the particular erase pulse counter, and
wherein, in response to the value of one of a product of the value of the particular erase pulse counter and the particular W/E counter value or a ratio of the value of the particular erase pulse counter to the value of the particular W/E counter indicating the particular region satisfies a threshold, the controller is configured to initiate a remedial action with respect to the particular region of the non-volatile memory.

24. The data storage device of claim 23, wherein erase operations to a first region of the non-volatile memory are tracked by a first W/E counter and a first erase pulse counter of a set of counters, wherein erase operations to a second region of the non-volatile memory are tracked by a second W/E counter and a second erase pulse counter of the set of counters, wherein the first region corresponds to a first set of erase blocks of the non-volatile memory, and wherein the second region corresponds to a second set of erase blocks of the non-volatile memory.

25. The data storage device of claim 24, wherein the first set of erase blocks comprises a single erase block and wherein the second set of erase blocks comprises another single erase block.

26. The data storage device of claim 24, wherein the first set of erase blocks includes a contiguous group of erase blocks.

27. The data storage device of claim 24, wherein the first set of erase blocks includes a non-contiguous group of erase blocks.

28. The data storage device of claim 23, wherein the remedial action is selected based on the product of the value of the particular W/E counter and the value of the particular erase pulse counter.

29. The data storage device of claim 23, wherein the remedial action is selected based on the ratio of the value of the particular erase pulse counter and the value of the particular W/E counter.

30. The data storage device of claim 23, wherein the controller is configured to initiate the remedial action by scheduling an erase block associated with the particular W/E counter to be unused.

31. The data storage device of claim 23, wherein the controller is configured to initiate the remedial action by setting a flag to indicate that data and parity interleaving is to be applied to the particular region.

32. The data storage device of claim 23, wherein the controller is configured to initiate the remedial action by setting a flag to indicate that adaptive reading is to be applied to the particular region.

33. The data storage device of claim 23, wherein the controller is configured to store values of the particular W/E counter and of the particular erase pulse counter to the non-volatile memory during a session shut-down operation and to retrieve the stored counter values from the non-volatile memory and initialize the particular W/E counter and of the particular erase pulse counter according to the stored counter values during a session initialization operation.

34. The data storage device of claim 23, wherein the non-volatile memory includes a flash memory.