Semiconductor Device Soft Erase Threshold Voltage Distribution
Solution Overview
Problem
The reliability of semiconductor devices is reduced due to the wide threshold voltage distribution of memory cells, which can lead to data misreading as the distribution overlaps with other states, especially in multi-level and triple-level cell systems.
Innovation Solution
A method and semiconductor device that perform a soft erase operation on memory cells with threshold voltages higher than a reference voltage to reduce the threshold voltage distribution width, using a circuit group and control circuit to selectively apply voltages and perform channel boosting to decrease the threshold voltages of over-programmed cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If memory cells are programmed into one of a plurality of program states to increase storage capacity, then the storage density is improved, but the threshold voltage distribution width increases causing overlap between different program states which reduces reliability
Solution Approach 1:
The patent segments the memory cell array into multiple blocks and implements independent soft erase operations on specific blocks containing over-programmed cells. This allows selective threshold voltage adjustment without affecting other memory regions, maintaining storage capacity while improving reliability through localized correction.
Solution Approach 2:
The patent changes the threshold voltage parameter of over-programmed memory cells by applying soft erase operations that reduce the threshold voltage of cells exceeding the reference voltage. This parameter adjustment narrows the threshold voltage distribution width and prevents overlap between different program states, thereby improving data reading accuracy while preserving multi-level cell storage capacity.
2Reliability
If the threshold voltage distribution width is increased to improve reliability, then the margin between program states is improved, but the threshold voltage distribution overlaps with other states causing data misreading
Solution Approach 1:
The patent implements a feedback mechanism where the controller monitors threshold voltages of programmed memory cells and identifies those exceeding a reference voltage. Based on this feedback, the controller selectively applies soft erase operations to over-programmed cells, adjusting their threshold voltages back to acceptable ranges. This closed-loop control prevents threshold voltage distribution overlap and eliminates data misreading while maintaining reliable program state distinction.
Solution Approach 2:
The patent dynamically adjusts the threshold voltage parameter of memory cells through soft erase operations. By reducing the threshold voltage of over-programmed cells that exceed the reference voltage, the patent narrows the threshold voltage distribution width and eliminates overlap between different program states, thereby preventing data misreading while maintaining reliable state distinction.
3Reliability
If a full erase operation is performed on memory blocks, then the threshold voltage distribution is reset, but the productivity is reduced due to the time-consuming nature of complete erasure
Solution Approach 1:
The patent extracts and targets only the specific memory blocks containing over-programmed cells for soft erase operations, rather than erasing entire memory blocks or arrays. This selective approach removes only the problematic cells that need threshold voltage adjustment, maintaining reliability by correcting over-programmed cells while preserving productivity through reduced operation time compared to full block erasure.
Solution Approach 2:
The patent applies partial erase action by performing soft erase operations only on memory blocks identified as containing over-programmed cells, rather than conducting full block erasure. This partial action is sufficient to correct the threshold voltage distribution issues in affected blocks while minimizing the impact on overall system productivity and operation speed.
4Reliability
If soft erase operation is selectively performed on memory cells with threshold voltages greater than reference voltage, then the threshold voltage distribution width is reduced, but the device complexity increases due to additional control circuits and operations
Solution Approach 1:
The patent implements a controller that performs multiple functions: normal programming operations, reading operations, and soft erase operations for threshold voltage correction. By integrating these diverse functions into a single controller, the patent manages the complexity of selective soft erase operations while maintaining reliable threshold voltage distribution control through a unified control architecture.
Solution Approach 2:
The patent uses parameter-based control where the controller compares threshold voltages against a reference voltage parameter to identify over-programmed cells. This parameter-driven approach enables selective soft erase operations that narrow the threshold voltage distribution width and improve reliability, while the parameter-based control mechanism manages device complexity through straightforward voltage comparison and decision logic.
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
The method effectively reduces the threshold voltage distribution width, enhancing the reliability of semiconductor devices by ensuring a margin between voltage distributions and preventing data misreading.
Implementation Method 1
selectively increasing potential differences between the channels and the selected memory cells to reduce threshold voltages of memory cells, which have a higher level than a reference level, among programmed memory cells
Data Source
AI summary
A method of operating a semiconductor device includes performing a program operation on selected memory cells of a selected page, and selectively performing a soft erase operation on memory cells having threshold voltages greater than a reference voltage, among the selected memory cells, to reduce a width of a threshold voltage distribution of the selected memory cells.