Staggered 3D NAND Read Recovery for Read Window Budget Loss
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
3D NAND flash memory devices face read window budget (RWB) degradation due to threshold voltage (Vt) shift and cell-to-cell variation, exacerbated by temperature changes and random telegraph noise, which traditional methods struggle to address effectively.
Innovation Solution
Implementing a staggered read recovery process where wordlines in a 3D NAND array are transitioned to ground sequentially after a read operation, providing a grounding path for charge dissipation and reducing trapped charges at grain boundaries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If all wordlines are transitioned to ground simultaneously after a read operation, then the read operation is simple and fast, but charge traps at grain boundaries cause RWB degradation due to incomplete charge discharge
Solution Approach 1:
The patent segments the wordline grounding process into multiple stages. Instead of grounding all wordlines simultaneously, the controller grounds wordlines in sequential groups (e.g., first group of wordlines, then second group of wordlines). This segmentation allows charges to discharge more completely from charge traps at grain boundaries while maintaining reasonable read operation speed.
Solution Approach 2:
The patent applies a preliminary action by introducing a delay period between the read operation and the grounding of wordlines. The controller waits for a predetermined time after the read operation before initiating the grounding sequence. This preliminary delay allows charges to begin discharging from charge traps before the wordlines are fully grounded, improving RWB without significantly impacting read speed.
2Reliability
If smaller program steps are used to compensate for RWB loss, then RWB degradation is reduced, but programming time increases
Solution Approach 1:
The patent applies preliminary action by grounding wordlines before the programming operation is complete. The controller grounds wordlines in a predetermined sequence after the read operation, which prepares the charge distribution in advance for subsequent programming operations. This reduces the need for smaller program steps and decreases overall programming time while maintaining RWB.
3Reliability
If operating temperature range is limited to reduce RWB loss, then temperature-induced Vt shift is reduced, but use cases and deployment are significantly limited
Solution Approach 1:
The patent segments the charge discharge process by grounding wordlines in multiple sequential groups rather than simultaneously. This segmentation allows charges to discharge gradually from charge traps at grain boundaries, reducing temperature-induced Vt shift effects. The controller can maintain a wider operating temperature range while preserving RWB through this segmented grounding approach.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enhances read noise reduction and temperature sensitivity, improving 3D NAND performance and enabling continued scaling by minimizing RWB degradation.
Implementation Method 1
transitioning the wordlines to ground in a staggered manner provides a grounding path for charge dissipation
Data Source
AI summary
After reading a 3D (three dimensional) NAND array, the wordlines of the 3D NAND array can be transitioned to ground in a staggered manner. The 3D NAND array includes a 3D stack with multiple wordlines vertically stacked, including a bottom-most wordline, a top-most wordline, and middle wordlines between the bottom-most wordline and the top-most wordline. A controller that controls the reading can set the multiple wordlines to a read voltage for reading operations and then transition a selected wordline of the multiple wordlines from the read voltage to ground prior to transitioning the other wordlines to ground. Thus, the controller will transition the other wordlines from the read voltage to ground after a delay.