Flash Memory Status Flag Read Reliability
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In complementary read flash memory, the read result after erasing a status flag stored in a twin cell is undefined, leading to a possibility of reading a false status flag value due to the maintained threshold voltage relationship between memory cells.
Innovation Solution
A storage device is designed with a data memory unit that uses complementary read mode for data storage and a status memory unit that uses reference read mode for storing a status flag, ensuring a uniquely defined value after erasure by comparing currents through flash memory cells with a reference current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If complementary read mode is used for storing status flag in twin cell, then data storage capability is improved, but read result after erasure becomes undefined
Solution Approach 1:
The memory system is divided into two distinct segments: data memory units that use complementary read mode for general data storage, and status memory units that use reference read mode for status flag storage. This segmentation allows each segment to be optimized for its specific function, resolving the contradiction between data storage capability and read result definition.
Solution Approach 2:
Different read modes are applied to different locations within the memory system. Complementary read mode is applied to data memory units where undefined read results after erasure are acceptable, while reference read mode is applied to status memory units where defined read results are critical. This local differentiation of quality resolves the contradiction.
2Measurement precision
If reference read mode is used for status flag storage, then read result after erasure is uniquely defined, but voltage difference required for reading increases
Solution Approach 1:
The memory system is divided into two distinct segments: data memory units that use complementary read mode for general data storage, and status memory units that use reference read mode for status flag storage. This segmentation allows each segment to be optimized for its specific function, resolving the contradiction between data storage capability and read result definition.
Solution Approach 2:
Different read modes are applied to different locations within the memory system. Complementary read mode is applied to data memory units where undefined read results after erasure are acceptable, while reference read mode is applied to status memory units where defined read results are critical. This local differentiation of quality resolves the contradiction.
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 allows for accurate and defined reading of the status flag after erasure, improving data retention properties and preventing false value readings, while reducing the voltage difference required for reading, thus enhancing the reliability and efficiency of data storage.
Implementation Method 1
The cells that constitute the twin cell can be in either a low threshold voltage state or a high threshold voltage state. The low threshold voltage state is a state where a threshold voltage (Vth) of a transistor that forms a cell is lower than a specified reference value. The high threshold voltage state is a state where a threshold voltage (Vth) of a transistor that forms a cell is equal to or higher than the specified reference value.
Implementation Method 2
the first total current of the twin cells forced to flow into the first input terminal of the sense circuit commonly is compared with the reference signal on the second input terminal, whereby whether the twin cells have been written or blank can be detected at a high speed
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A storage device includes a data memory unit and a status memory unit. The data memory unit includes a pair of flash memory cells to be read by a complementary read mode, and 1-bit data is stored therein by the pair of flash memory cells. The status memory unit includes a flash memory cell to be read by a reference read mode, and a status flag is stored therein by the flash memory cell.