Reference Cell Adjustment Circuit for Non-Volatile Memory Read Margin Stability
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Solution Overview
Problem
Non-volatile memory devices face the challenge of charge gain or soft programming, which causes a shift in reference levels during read cycles, degrading the read margin and potentially increasing chip area, especially when using multiple reference cells for every read cycle.
Innovation Solution
A semiconductor device and method that employs a first reference cell and a second reference cell with an adjustment circuit, including a comparator and trimming circuit, to compare and adjust the first reference level based on the second reference level, thereby maintaining the initial current level and preventing charge gain without increasing chip area.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple reference cells are used for every read cycle to prevent charge gain, then reliability is improved, but device complexity and chip area increase
Solution Approach 1:
The reference cell functionality is segmented into two distinct cells: a first reference cell used during read operations and a second reference cell used for adjustment operations. This segmentation allows each cell to perform a specific function, preventing charge gain accumulation while maintaining read margin stability without requiring multiple reference cells for every read cycle
Solution Approach 2:
The adjustment circuit performs preliminary adjustment of the first reference cell's reference level using the second reference cell before read operations. By pre-adjusting the reference level to compensate for charge gain, the system maintains reliability without needing multiple reference cells during actual read cycles
2Reliability
If multiple reference cells are used for every read cycle to prevent charge gain, then reliability is improved, but chip area increases
Solution Approach 1:
The reference cell functionality is segmented into two distinct cells: a first reference cell used during read operations and a second reference cell used for adjustment operations. This segmentation allows each cell to perform a specific function, preventing charge gain accumulation while maintaining read margin stability without requiring multiple reference cells for every read cycle
Solution Approach 2:
The second reference cell serves as a reference copy that provides a stable reference level for adjusting the first reference cell. By using this copy to periodically adjust the first reference cell, the system maintains reliability with minimal chip area, avoiding the need to store multiple active reference cells
3Reliability
If reference cell levels are adjusted frequently to prevent charge gain, then reliability is improved, but productivity decreases
Solution Approach 1:
The adjustment circuit operates periodically rather than continuously, adjusting the first reference cell's reference level at predetermined intervals using the second reference cell. This periodic adjustment maintains reference level stability and reliability while minimizing interference with read operation speed and productivity
Data Source
AI summary
A semiconductor device includes a first reference cell used for programming or reading non-volatile memory cells, and an adjustment circuit adjusting a first reference level of the first reference cell when the first reference level is changed.