NAND String Source Voltage Adjustment for Resistance Compensation
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Solution Overview
Problem
Non-volatile memory systems face failures during sensing operations, particularly when the selected memory cell is further from the source end of the NAND string, due to resistance variations along the NAND string, leading to issues like E-to-A failures, which worsen with erase/program cycles.
Innovation Solution
The voltage applied to the source end of a NAND string is adjusted based on the location of the selected memory cell without body-biasing, ensuring that the voltage magnitude depends on the cell's position, thereby compensating for source side resistance and reducing failure rates.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed voltage is applied to the source end of the NAND string, then the circuit design is simple, but sensing failures occur when the selected memory cell is further from the source end due to resistance variations
Solution Approach 1:
The patent applies dynamics by making the source end voltage adjustable rather than fixed. The voltage applied to the source end is dynamically changed based on the location of the selected memory cell, allowing the system to adapt to varying resistance conditions along the NAND string and improve sensing reliability without excessive complexity
Solution Approach 2:
The patent changes the voltage parameter at the source end based on the selected word line location. By adjusting the voltage magnitude according to the distance from the source end, the system compensates for resistance variations and maintains reliable sensing operations across different cell positions
2Reliability
If body-biasing is used to compensate for resistance variations, then sensing reliability improves, but the device complexity and process difficulty increase
Solution Approach 1:
The patent extracts the body-biasing function and replaces it with source end voltage adjustment. Instead of using complex body-biasing circuitry that requires additional transistors and control logic, the invention simplifies the approach by directly adjusting the source end voltage, thereby maintaining reliability while reducing manufacturing complexity
Solution Approach 2:
The patent introduces an intermediary mechanism where the source end voltage acts as a mediator to compensate for resistance variations. This intermediate voltage adjustment provides a simpler alternative to body-biasing, achieving the same reliability improvement without the associated manufacturing complexity
3Measurement precision
If higher voltage is applied to compensate for resistance at distant cells, then sensing accuracy improves, but power consumption increases
Solution Approach 1:
The patent applies local quality by providing different voltage levels at the source end depending on which specific memory cell is being sensed. Instead of uniformly applying high voltage to all cells, the system locally adjusts the voltage based on the selected cell's position, improving sensing accuracy only where needed and minimizing overall power consumption
Data Source
AI summary
A method and non-volatile storage system are provided in which the voltage applied to the source end of a NAND string depends on the location of the non-volatile storage element that is selected for sensing. This may be done without body-biasing the NAND string. Having the magnitude of the voltage applied to the source end of a NAND string depend on the location of the selected memory cell (without any body biasing) helps to mitigate failures that are dependent on which word line is selected during a sensing operation of one embodiment. Additionally, the magnitude of a read pass voltage may depend on either the source line voltage or the location of the selected memory cell.