Multi-Voltage Read Circuit for NAND Flash Memory Error Reduction
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Solution Overview
Problem
In semiconductor storage apparatuses, the variation in charge amounts within memory cells over time leads to data value errors, as the threshold voltage changes, making it challenging to accurately read data values without introducing errors.
Innovation Solution
A semiconductor storage apparatus with a memory cell array and a read circuit that applies multiple reading voltages to determine data values by sensing the ON or OFF state of memory cells, using boundary voltages to minimize errors through estimation processes like lower, middle, and upper estimation processes to adjust and optimize the reading voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a single reading voltage is used to read data values from memory cells, then the reading operation is simple and fast, but data value errors increase due to threshold voltage variations over time
Solution Approach 1:
The patent segments the reading operation into multiple stages by dividing the voltage range into multiple regions (first voltage region, second voltage region, etc.). Instead of using a single reading voltage, the system applies different reading voltages corresponding to different regions, allowing accurate determination of data values even when threshold voltages vary over time. This segmentation resolves the contradiction by maintaining reading speed while improving accuracy through multi-level voltage regions.
Solution Approach 2:
The patent implements dynamic reading voltage adjustment based on the determined data value. After reading a first data value using a first reading voltage, the system determines a second reading voltage based on the first data value and uses it to read a second data value. This dynamic adjustment allows the reading operation to adapt to threshold voltage variations, resolving the contradiction between simple fixed-voltage reading and accurate variable-voltage reading.
2Reliability
If multiple reading voltages are applied to determine data values, then data value accuracy improves, but the complexity of the reading operation increases
Solution Approach 1:
The patent performs preliminary actions by first reading a first data value using a first reading voltage, then determining a second reading voltage based on the first data value before reading the second data value. This sequential approach with preliminary voltage determination simplifies the overall complexity by using the result of one reading operation to guide the next, rather than requiring complex parallel voltage application circuits.
Solution Approach 2:
The patent employs feedback mechanisms where the first data value read is used to determine the second reading voltage. This feedback loop allows the system to adapt the reading voltage based on previous readings, reducing the need for complex multi-voltage application circuits while maintaining high accuracy. The feedback-based voltage adjustment simplifies the device architecture compared to simultaneous multi-voltage application systems.
3Reliability
If reading voltages are adjusted to compensate for threshold voltage variations, then data value errors decrease, but the time required for reading operations increases
Solution Approach 1:
The patent implements periodic reading operations with periodic voltage adjustments. The system reads a first data value, determines a second reading voltage based on the first data value, and then reads a second data value using the second reading voltage. This periodic adjustment pattern allows the system to compensate for threshold voltage variations without requiring continuous complex voltage modulation, thereby reducing the time overhead compared to continuous adaptive voltage adjustment.
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 effectively reduces the number of data value errors by accurately determining the optimal boundary voltages, ensuring reliable data retrieval and storage in NAND type flash memory systems.
Implementation Method 1
memory cells that hold amounts of charges corresponding to data values
Implementation Method 2
senses ON or OFF of the memory cell for each reading voltage
Data Source
AI summary
According to one embodiment, a semiconductor storage apparatus includes a memory cell array and a read circuit. The memory cell array includes a memory cell which is connected to a word line. A threshold voltage of the memory cell corresponds to a data value of multiple bits. The read circuit receives designation of one bit among the multiple bits, applies a first reading voltage and a second reading voltage corresponding to the designated bit to the word line, senses ON or OFF of the memory cell for each reading voltage, and outputs a first sensed value and a second sensed value after performing the sensing for each reading voltage. The first sensed value is a sensing result in a case where the first reading voltage is applied. The second sensed value is a sensing result in a case where the second reading voltage is applied.