Abstract: Techniques are provided for programming and reading memory cells in a 3D stacked non-volatile memory device by compensating for variations in a memory hole diameter. The memory hole diameter is smaller at the bottom of the stack, resulting in more severe read disturb. To compensate, programming of memory cells at the lower word line layers is modified. In one approach, threshold voltage (Vth) distributions of one or more data states are narrowed during programming so that a lower read pass voltage can be used in a subsequent sensing operation. A sufficient spacing is maintained between the read pass voltage and the upper tail of the highest data state. The Vth distributions can be downshifted as well. In another approach, the read pass voltage is not lowered, but the lowest programmed state is upshifted to provide spacing from the upper tail of the erased state.

Abstract: A number (Nwl) of programmed word lines in a block of NAND strings is determined by measuring a reference combined current (Iref) in the block when all of the memory cells are in a conductive state. Subsequently, to determine if a word line is a programmed word line, an additional combined current (Iadd) in the block is measured with a demarcation voltage applied to the selected word line. The selected word line is determined to be programmed word lines if Idd is less than Iref by at least a margin. Nwl can be used to adjust an erase-verify test of an erase operation by making the erase-verify test relatively hard to pass when the number is relatively small and relatively easy to pass when the number is relatively large. Or, Nwl can be used to identify a next word line to program in the block.

Abstract: An erase operation for a 3D stacked memory device assigns storage elements to groups according to an expected erase speed. The storage elements are then erased according to their group to provide a more uniform erase depth and a tighter erase distribution. In one approach, the control gate voltages are set differently for the different groups to slow down the storage elements which are expected to have a faster programming speed. An erase or inhibit status can be set for all groups together. In another approach, the control gate voltages are common for the different groups but an erase or inhibit status is set for each group separately.

Abstract: A program operation for a set of non-volatile storage elements. A count is maintained of a number of program pulses which are applied to an individual storage element in a slow programming mode, and an associated bit line voltage is adjusted based on the count. Different bit line voltages can be used, having a common step size or different steps sizes. As a result, the change in threshold voltage of the storage element within the slow programming mode, with each program pulse can be made uniform, resulting in improved programming accuracy. Latches maintain the count of program pulses experienced by the associated storage element, while in the slow programming mode. The storage element is in a fast programming mode when its threshold voltage is below a lower verify level, and in the slow programming mode when its threshold voltage is between the lower verify level and a higher verify level.

Abstract: Upon selecting non-volatile storage elements to be sensed, the system obtains information about the position of these non-volatile storage elements, determines sensing parameters based at least in part on this information, pre-charges a charge storage device and, while maintaining the voltage level of the bit lines of these memory cells at a constant value, applies a reference signal to these non-volatile storage elements for a certain duration of time, afterwards determining whether, for the certain duration of time, the current conducted by these non-volatile storage elements exceeds a predetermined value.

Abstract: A number (Nwl) of programmed word lines in a block of NAND strings is determined by measuring a reference combined current (Iref) in the block when all of the memory cells are in a conductive state. Subsequently, to determine if a word line is a programmed word line, an additional combined current (Iadd) in the block is measured with a demarcation voltage applied to the selected word line. The selected word line is determined to be programmed word lines if Idd is less than Iref by at least a margin. Nwl can be used to adjust an erase-verify test of an erase operation by making the erase-verify test relatively hard to pass when the number is relatively small and relatively easy to pass when the number is relatively large. Or, Nwl can be used to identify a next word line to program in the block.

Abstract: Techniques are provided for programming and reading memory cells in a 3D stacked non-volatile memory device by compensating for variations in a memory hole diameter. The memory hole diameter is smaller at the bottom of the stack, resulting in more severe read disturb. To compensate, programming of memory cells at the lower word line layers is modified. In one approach, threshold voltage (Vth) distributions of one or more data states are narrowed during programming so that a lower read pass voltage can be used in a subsequent sensing operation. A sufficient spacing is maintained between the read pass voltage and the upper tail of the highest data state. The Vth distributions can be downshifted as well. In another approach, the read pass voltage is not lowered, but the lowest programmed state is upshifted to provide spacing from the upper tail of the erased state.

Abstract: A structure and fabrication process are provided for a 3D stacked non-volatile memory device which compensates for variations in a memory hole diameter. The memory hole diameter is smaller at the bottom of the stack, resulting in more severe read disturb. To compensate, the word line layers are thicker at the bottom of the stack and can increase gradually from the bottom to the top of the stack. As a result, the length of the control gates of the memory cells is greater at the bottom of the stack. The capacitance between the control gate and a charge trapping layer increased in proportion to the length of the control gates. During programming, a narrower threshold voltage (Vth) distribution is achieved for these memory cells. The Vth distributions can be placed closer together and downshifted to allow lowering of a read pass voltage in a subsequent sensing operation, reducing read disturb.

Abstract: A structure and fabrication process are provided for a 3D stacked non-volatile memory device which compensates for variations in a memory hole diameter. The memory hole diameter is smaller at the bottom of the stack, resulting in more severe read disturb. To compensate, the word line layers are thicker at the bottom of the stack and can increase gradually from the bottom to the top of the stack. As a result, the length of the control gates of the memory cells is greater at the bottom of the stack. The capacitance between the control gate and a charge trapping layer increased in proportion to the length of the control gates. During programming, a narrower threshold voltage (Vth) distribution is achieved for these memory cells. The Vth distributions can be placed closer together and downshifted to allow lowering of a read pass voltage in a subsequent sensing operation, reducing read disturb.

Abstract: An erase operation for a 3D stacked memory device adjusts a start time of an erase period and/or a duration of the erase period for each storage element based on a position of the storage element. A voltage is applied to one or both drive ends of a NAND string to pre-charge a channel to a level which is sufficient to create gate-induced drain leakage at the select gate transistors. With timing based on a storage element's distance from the driven end, the control gate voltage is lowered to encourage tunneling of holes into a charge trapping layer in the erase period. The lowered control gate voltage results in a channel-to-control gate voltage which is sufficiently high to encourage tunneling. The duration of the erase period is also increased when the distance from the driven end is greater. As a result, a narrow erase distribution can be achieved.

Abstract: Techniques are provided for erasing memory cells in a 3D stacked non-volatile memory device in a way which avoids prolonging erase time as the erase speed deceases due to the accumulation of program-erase cycles. In particular, a step size for erase pulses can be set which is a function of the number of program-erase cycles, e.g., as indicated by a count of program-erase cycles, a loop count during programming which is a function of programming speed, or an initial program voltage which is a function of programming speed. Further, the erase operation can account for different erase speeds of memory cells in different word line layers.

Abstract: Upon selecting non-volatile storage elements to be sensed, the system obtains information about the position of these non-volatile storage elements, determines sensing parameters based at least in part on this information, pre-charges a charge storage device and, while maintaining the voltage level of the bit lines of these memory cells at a constant value, applies a reference signal to these non-volatile storage elements for a certain duration of time, afterwards determining whether, for the certain duration of time, the current conducted by these non-volatile storage elements exceeds a predetermined value.

Abstract: An erase operation for a 3D stacked memory device selectively inhibits subsets of memory cells which meet a verify condition as the erase operation progresses. As a result, the faster-erasing memory cells are less likely to be over-erased and degradation is reduced. Each subset of memory cells can be independently erased by controlling a select gate, drain (SGD) transistor line, a bit line or a word line, according to the type of subset. For a SGD line subset or a bit line subset, the SGD line or bit line, respectively, is set at a level which inhibits erase. For a word line subset, the word line voltage is floated to inhibit erase. An inhibit or uninhibit status can be maintained for each subset, and each type of subset can have a different maximum allowable number of fail bits.

Abstract: Techniques are provided for erasing memory cells in a 3D stacked non-volatile memory device in a way which avoids prolonging erase time as the erase speed deceases due to the accumulation of program-erase cycles. In particular, a step size for erase pulses can be set which is a function of the number of program-erase cycles, e.g., as indicated by a count of program-erase cycles, a loop count during programming which is a function of programming speed, or an initial program voltage which is a function of programming speed. Further, the erase operation can account for different erase speeds of memory cells in different word line layers.

Abstract: In a 3D stacked non-volatile memory device, the threshold voltages are evaluated and adjusted for select gate, drain (SGD) transistors at drain ends of strings of series-connected memory cells. To optimize and tighten the threshold voltage distribution, the SGD transistors are read at lower and upper levels of an acceptable range. SGD transistors having a low threshold voltage are subject to programming, and SGD transistors having a high threshold voltage are subject to erasing, to bring the threshold voltage into the acceptable range. The evaluation and adjustment can be repeated such as after a specified number of program-erase cycles of an associated sub-block. The condition for repeating the evaluation and adjustment can be customized for different groups of SGD transistors. Aspects include programming SGD transistors with verify and inhibit, erasing SGD transistors with verify and inhibit, and both of the above.

Abstract: An erase operation for a 3D stacked memory device adjusts a start time of an erase period and/or a duration of the erase period for each storage element based on a position of the storage element. A voltage is applied to one or both drive ends of a NAND string to pre-charge a channel to a level which is sufficient to create gate-induced drain leakage at the select gate transistors. With timing based on a storage element's distance from the driven end, the control gate voltage is lowered to encourage tunneling of holes into a charge trapping layer in the erase period. The lowered control gate voltage results in a channel-to-control gate voltage which is sufficiently high to encourage tunneling. The duration of the erase period is also increased when the distance from the driven end is greater. As a result, a narrow erase distribution can be achieved.

Abstract: Upon selecting non-volatile storage elements to be sensed, the system obtains information about the position of these non-volatile storage elements, determines sensing parameters based at least in part on this information, pre-charges a charge storage device and, while maintaining the voltage level of the bit lines of these memory cells at a constant value, applies a reference signal to these non-volatile storage elements for a certain duration of time, afterwards determining whether, for the certain duration of time, the current conducted by these non-volatile storage elements exceeds a predetermined value.

Abstract: An erase operation for a 3D stacked memory device selectively inhibits subsets of memory cells which meet a verify condition as the erase operation progresses. As a result, the faster-erasing memory cells are less likely to be over-erased and degradation is reduced. Each subset of memory cells can be independently erased by controlling a select gate, drain (SGD) transistor line, a bit line or a word line, according to the type of subset. For a SGD line subset or a bit line subset, the SGD line or bit line, respectively, is set at a level which inhibits erase. For a word line subset, the word line voltage is floated to inhibit erase. An inhibit or uninhibit status can be maintained for each subset, and each type of subset can have a different maximum allowable number of fail bits.

Abstract: Techniques for sensing the threshold voltage of a memory cell during reading and verify operations by compensating for changes, including temperature-based changes, in the resistance of a bit line or other control line. A memory cell being sensed is in a block in a memory array and the block is in a group of blocks. A portion of the bit line extends between the group of blocks and a sense component and has a resistance which is based on the length/distance and the temperature. Various parameters can be varied with temperature and the group of blocks to provide the compensation, including bit line voltage, selected word line voltage, source line voltage, sense time and/or sense current or voltage.

Abstract: A read process for a 3D stacked memory device provides an optimum level of channel boosting for unselected memory strings, to repress both normal and weak-erase types of read disturbs. The channel is boosted by controlling of voltages of bit lines (Vbl), drain-side select gates (Vsgd_unsel), source-side select gates (Vsgs_unsel), a selected level (word line layer) of the memory device (Vcg_sel), and unselected levels of the memory device (Vcg_unsel). A channel can be boosted by initially making the drain-side and source-side select gates non-conductive, to allow capacitive coupling from an increasing Vcg_unsel. The drain-side and/or source-side select gates are then made conductive by raising Vsgd_unsel and/or Vsgs_unsel, interrupting the boosting. Additionally boosting can occur by making the drain-side and/or source-side select gates non-conductive again while Vcg_unsel is still increasing. Or, the channel can be driven at Vbl.