3D NAND Flash Memory Failure Detection and Localization
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
3D NAND Flash memory devices face failures that cause unselected strings to conduct, leading to excessive bit-line current leakage, which can impact entire memory planes or dies, especially due to local defects causing source-select or drain-select line discontinuity, known as 'Hi-Z failures, and existing technologies lack effective methods to detect and localize these failures.
Innovation Solution
A method and apparatus that utilize control circuitry to sense current flowing through memory strings during erase-verification and re-read operations, comparing currents to detect failures, and initiate corrective actions such as programming memory cells to a positive threshold voltage to reduce leakage, thereby localizing the failure to a specific memory block or sub-block.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If unselected strings are allowed to conduct during erase operations, then erase speed is improved, but bit-line current leakage increases and affects entire memory planes
Solution Approach 1:
The memory device is divided into multiple independently detectable blocks, allowing failure localization to specific blocks rather than entire planes. The control circuitry segments the detection process by individually sensing current in each block during erase operations, enabling targeted corrective actions without affecting other blocks.
Solution Approach 2:
The control circuitry performs preliminary detection during the erase operation by sensing current flow through select transistors before the failure can propagate. Erase-verification operations are conducted as a preliminary check to identify Hi-Z failures early, allowing corrective programming to be applied preventively to affected blocks.
2Reliability
If current sensing and failure detection circuits are added, then failure detection capability is improved, but device complexity increases
Solution Approach 1:
The control circuitry is designed to perform multiple functions: it controls erase operations, senses current flow during erase, detects Hi-Z failures, and initiates corrective programming. By making the control circuitry multi-functional rather than adding separate dedicated circuits, the patent improves failure detection capability while minimizing the increase in device complexity.
Solution Approach 2:
The memory device performs self-diagnosis and self-correction through the control circuitry that automatically detects failures during normal erase operations and initiates corrective programming without external intervention. The system uses its existing operational infrastructure for detection and correction, reducing the need for additional complex external monitoring equipment.
3Reliability
If corrective programming is applied to all blocks, then reliability is improved, but processing time increases
Solution Approach 1:
Corrective programming is applied selectively only to blocks where Hi-Z failures are detected, rather than uniformly to all blocks. The control circuitry localizes the quality change (programming to positive threshold voltage) to specific affected blocks, reducing unnecessary processing time for healthy blocks while maintaining reliability in problematic areas.
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
Effectively detects and mitigates Hi-Z failures by reducing bit-line current leakage, preventing the failure from affecting other blocks, and maintaining functionality of the remaining memory blocks, thus enhancing the reliability of 3D NAND Flash memory devices.
Implementation Method 1
sensing a current flowing through the string
Data Source
AI summary
A method includes, in a memory block, which includes at least a string of memory cells that is selectable using at least a select transistor, sensing a current flowing through the string. A failure in the memory block, which causes the string to conduct even when unselected using the select transistor, is detected based on the sensed current. A corrective action is initiated in response to the identified failure.