Sandisk Technologies Inc.

Chun-Hung Lai

Deepanshu Dutta

Shih-Chung Lee

Shinji Sato

Masaaki Higashitani

Gerrit Jan Hemink

Ken Oowada

Ching-Huang Lu

Rajdeep Gautam

Fumiko Yano

Cheng-Kuan Yin

Noriyuki Mitsuhira

Apparatuses and techniques are described for reducing charge loss in a select gate transistor in a memory device. In one aspect, a dummy memory cell adjacent to a select gate transistor is weakly programmed during an erase operation by applying a program pulse to the dummy memory cell. The program pulse can be applied after an erase bias is applied to the memory cells and before an erase-verify test is performed, in one approach. The program pulse can be applied during the setup of the voltages for the erase-verify test. The magnitude of the program pulse can be increased in successive erase loops of an erase operation as the magnitude of a substrate voltage is also increased. The magnitude of the program pulse can also be set as an increasing function of a number of program-erase (P-E) cycles.

Programming dummy memory cells in erase operation to reduce threshold voltage downshift for select gate transistors

Systems and methods for reducing trapped electrons within a NAND string are described. During a sensing operation, one or more control circuits may discharge or initiate discharge of control gates corresponding with contiguous memory cell transistors of a NAND string from a read pass voltage (e.g., 10V) to a second voltage less than the pass voltage (e.g., 2V) in an order starting from a first set of the contiguous memory cell transistors closest to the first end of the NAND string and ending with a second set of the contiguous memory cell transistors closest to the second end of the NAND string. Subsequently, the one or more control circuits may either concurrently or simultaneously discharge the control gates corresponding with the contiguous memory cell transistors from the second voltage to a third voltage less than the intermediate voltage (e.g., from 2V to 0V).

Sequential deselection of word lines for suppressing first read issue

A non-volatile memory system utilizes partial block erasing during program operations to mitigate the effects of programming pass voltage disturbances. A programming request is received that is associated with a group of word lines from a block, such as all or a portion of the word lines. The system erases and soft programs the block prior to beginning programming. The system programs a subset of the word lines of the block for the programming request. After programming the subset of word lines, the system pauses the programming operation and performs an erase operation for the unprogrammed word lines of the block. The already programmed word lines and one or more optional buffer word lines may be inhibited from erasing during the erase operation. After erasing the unprogrammed word lines, the system completes the programming request by programming the remaining user data in the unprogrammed region of the block.

Partial block erase for block programming in non-volatile memory

Methods and devices for operating non-volatile storage are disclosed. One or more programming conditions depend on the location of the word line that is selected for programming, which may reduce or eliminate program disturb. The voltage applied to the gate of a select transistor of a NAND string may depend on the location of the selected word line. This could be either a source side or drain side select transistor. This may prevent or reduce program disturb that could result due to DIBL. This may also prevent or reduce program disturb that could result due to GIDL. A negative bias may be applied to the gate of a source side select transistor when programming at least some of the word lines. In one embodiment, progressively lower voltages are used for the gate of the drain side select transistor when programming progressively higher word lines.

Selected word line dependent select gate voltage during program

Reducing peak current and/or power consumption during verify of a non-volatile memory is disclosed. During a program verify, only memory cells in a first physical segment of the selected word line are verified during an initial program loop; memory cells in a different physical segment of the word line are locked out and not verified. The locked out memory cells may be slower to program. During a later program loop, memory cells in all physical segments are program verified. Locked out strings do not conduct a significant current during verify, thus reducing current/power consumption.

Reduced current program verify in non-volatile memory

Improving endurance for non-volatile memory by dynamic erase depth is disclosed. A group of memory cells are erased. Then, at least some of the erased memory cells are programmed. Programming the memory cells typically impacts the erase threshold distribution of those memory cells that were intended to stay erased. The erase depth of the next erase can be adjusted based on how the program operation affects the erase threshold distribution. As one example, the upper tail of the erase distribution is measured after programming. The higher the upper tail, the shallower the next erase, in one embodiment. This helps to improve endurance. In one embodiment, the erase depth is adjusted by determining a suitable erase verify level. Rather than (or in addition to) adjusting the erase verify level, the number of erase pulses that are performed after erase verify passes can be adjusted to adjust the erase depth.

Dynamic erase depth for improved endurance of non-volatile memory

Techniques disclosed herein may prevent program disturb by preventing a select transistor of an unselected NAND string from unintentionally turning on. The Vgs of a select transistor of a NAND string may be lowered from one programming pulse to the next programming pulse multiple times. The select transistor may be a drain side select transistor or a source side select transistor. Progressively lowering the Vgs of the select transistor of an unselected NAND string as programming progresses may prevent the select transistor from unintentionally turning on. Therefore, program disturb is prevented or reduced. Vgs may be lowered by applying a lower voltage to a select line associated with the select transistor. Vgs may be lowered by applying a higher voltage to bit lines associated with the unselected NAND strings as programming progresses. Vgs may be lowered by applying a higher voltage to a common source line as programming progresses.

Select gate bias during program of non-volatile storage

A set of memory cells can be erased by individually erasing portions of the set in order to normalize the erase behavior of each memory cell and provide more consistent erase rates. An erase voltage pulse can be applied to the set of memory cells with a first group of cells biased for erase and a second group biased to inhibit erase. The erase depth is made shallower as the device is cycled more.

Partitioned erase and erase verification in non-volatile memory

Methods and devices for operating non-volatile storage are disclosed. One or more programming conditions depend on the location of the word line that is selected for programming. Applying a selected word line dependent program condition may reduce or eliminate program disturb. The voltage applied to a common source line may depend on the location of the word line that is selected for programming. This may prevent or reduce punch-through conduction, which may prevent or reduce program disturb. The voltage applied to bit lines of unselected NAND strings may depend on the location of the word line that is selected for programming. This may prevent or reduce punch-through conduction.

Growing community of inventors

Kamakura, Japan

Chun-Hung Lai