Sandisk Technologies Inc.

Vinh Diep

Ching-Huang Lu

Yingda Dong

Ashish Kumar Baraskar

Zhengyi Zhang

Liang Pang

Changyuan Chen

Henry Chin

Wei Zhao

Xuehong Yu

Han-Ping Chen

Ching Huang Lu

Techniques are provided to reduce neighbor word line interference and charge loss in a multi-pass program operation. In one implementation, the first pass of a multi-pass program operation uses one or more program pulses without performing associated verify tests. The memory cells may be programmed to different intermediate threshold voltage (Vth) distributions in the first program pass. Different bit line voltages can be used to obtain the different intermediate Vth distributions when the single program pulse is applied. In other cases, multiple program pulses are applied without performing verify tests. The intermediate Vth distributions can be provided for the memory cells assigned to the higher data states but not the lower data states, or for memory cells assigned to both the higher and lower data states.

Multi-pass programming process for memory device which omits verify test in first program pass

Techniques are provided for optimizing a program operation in a memory device to compensate for program speed variations due to block oxide thinning. In one approach, during a program operation, a program voltage which indicates program speed is acquired from sub-blocks with the highest and lowest program speeds. An initial program voltage for intermediate sub-blocks can be determined based on the acquired program voltages and the positions of the intermediate sub-blocks. The technique can accommodate a loss of one or both acquired program voltages if the programming is interrupted. In another approach, a program voltage which indicates program speed is acquired from one sub-block, and for a later-programmed sub-block, an appropriate offset is located from a table and summed with the acquired program voltage to determine an optimum initial program voltage.

Memory device with compensation for program speed variations due to block oxide thinning

Techniques are provided for optimizing an erase operation in a memory device to compensate for erase speed variations due to blocking oxide thinning In an erase operation for a block, the channels of NAND strings in different sub-blocks can be charged up by different amounts. One approach adjusts the control gate voltage of a first select gate transistor in a NAND string. This adjusts the amount of holes generated in the channel due to gate-induced drain leakage. Another approach adjusts the control gate voltage of additional select gate transistors in the NAND string to adjust the conductivity of the adjacent channel regions. Another approach applies different bit line voltages to different rows of NAND strings in each sub-block.

Memory device with compensation for erase speed variations due to blocking oxide layer thinning

Techniques are described for programming memory cells with reduced widening of the threshold voltage distributions. Bit line voltages are adjusted during verify tests for memory cells assigned to the upper data state in a pair of adjacent data states which are concurrently verified. An elevated bit line voltage is applied and then stepped up in successive program loops. A lower, fixed bit line voltage is used for verifying the lower data state in the pair of adjacent data states. In one option, the step size increases progressively over the program loops. In another option, the minimum level of the elevated bit line voltage is lower for higher data states. In another option, the minimum level of the elevated bit line voltage is set as a function of data states, program-erase cycles and/or temperature.

Multi-state programming in memory device with loop-dependent bit line voltage during verify

Techniques are described for reducing program disturb including neighbor word interference in a memory device. Voltages applied to the word lines adjacent to the selected word line WLn during program and read operations are adjusted. The adjacent word lines include WLn&#x2212;1, a source-side adjacent word line of WLn, and WLn+1, a drain side adjacent word line of WLn. In one aspect, VWLn&#x2212;1&#x3c;VWLn+1 during the verify tests of the program operation for the data states above the lowest programmed data state and VWLn&#x2212;1=VWLn+1 during the verify test for the lowest programmed data state. Also, VWLn&#x2212;1&#x3c;VWLn+1 during a read operation which distinguishes between the programmed data states and VWLn&#x2212;1=VWLn+1 during a read operation which distinguishes between erased state and the lowest programmed data state.

Memory device with reduced neighbor word line interference using adjustable voltage on source-side unselected word line

Systems, methods, and devices of the various embodiments provide both 'string-sharing' drain select gate electrodes and 'string-selective' drain select gate electrodes in vertical NAND strings. Various embodiments may provide two or more vertical NAND strings sharing a common drain select gate electrode while also having separate additional drain select gate electrodes not electrically connected across the two or more vertical NAND strings.

Three dimensional NAND memory device with drain select gate electrode shared between multiple strings

Apparatuses and techniques are described for programming memory cells with a narrow threshold voltage (Vth) distribution in a memory device. In a first program pass of a multi-pass program operation, pass voltages of the word lines adjacent to a selected word line are adjusted to increase electron injection in a portion of a charge-trapping layer between the selected word line and an adjacent source side unselected word line. In a second, final program pass of the multi-pass program operation, the pass voltages are adjusted to reduce electron injection in the portion of the charge-trapping layer between the selected word line and the adjacent source side unselected word line.

Multi-pass programming with modified pass voltages to tighten threshold voltage distributions

Apparatuses and techniques are described for reducing charge loss in a select gate transistor in a memory device. In one aspect, a refresh operation is performed repeatedly to couple up data word line voltages but not dummy word line voltages. The refresh operation can involve applying a voltage pulse to the data word lines of a block when the block is not being used for a storage operation such as a program, read or erase operation. When the voltage pulse is applied to the data word lines, the dummy word lines can be set to a low level such as 0 V. This low level prevents or limits coupling up of the dummy memory cells to avoid creating an electric field which can cause holes to move from the dummy memory cells to adjacent select gate transistors.

Preventing refresh of voltages of dummy memory cells to reduce threshold voltage downshift for select gate transistors

Apparatuses and techniques are described for programming memory cells with a narrow threshold voltage (Vth) distribution in a memory device. In one approach, the final pass of a multi-pass program operation on a word line WLn includes applying a variable voltage to WLn+1 during verify tests on WLn. The variable voltage (Vread) can be an increasing function of the verify voltage on WLn, and thus a function of the data state for which the verify test is performed. In one approach, Vread on WLn+1 is stepped up with each increase in the verify voltage on WLn. The step size in Vread can be the same as, or different than, the step size in the verify voltage. Vread can be different for each different verify voltage, or multiple verify voltages can be grouped for use with a common Vread.

Adjusting voltage on adjacent word line during verify of memory cells on selected word line in multi-pass programming

Techniques for reducing a downshift in the threshold voltage of a select gate transistor of a memory device. Due to an electric field in a NAND string, holes can move in a charge-trapping layer from a dummy memory cell to a select gate transistor and combine with electrons in the transistor, reducing the threshold voltage. In one approach, the electric field is reduced at the end of a sensing operation by ramping down the voltage of the dummy memory cells before ramping down the voltage of the select gate transistors. The ramp down of the voltage of the selected memory cells can occur after ramping down the voltage of the dummy memory cells and before ramping down of the voltage of the select gate transistors. A further option involves elevating the voltage of the select gate transistors before it is ramped down.

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Vinh Diep