Flash Memory Cell Pair Voltage Detection for Low-Voltage Read Stability
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Solution Overview
Problem
Conventional flash memory storage devices experience unstable data-reading operations when operating voltages are lowered, as the difference between currents flowing through turned-on and turned-off memory cells becomes small, making it difficult to accurately read data due to variations in threshold voltages and fabrication variations.
Innovation Solution
A non-volatile semiconductor storage device with pairs of memory cells written with opposite data values, where a detector senses data based on the magnitude relationship of voltages across signal lines connected to these pairs, amplifying the current difference through time-integral changes, even at reduced operating voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If operating voltage is lowered to reduce power consumption, then energy efficiency improves, but data-reading stability deteriorates due to small current differences between turned-on and turned-off memory cells
Solution Approach 1:
The memory cell array is divided into multiple blocks, with different read operations performed on different blocks sequentially. This segmentation allows the system to maintain stable reading operations at lower voltages by distributing the read load across multiple blocks rather than requiring all cells to be read simultaneously with high current margins.
Solution Approach 2:
The patent implements periodic read operations across different memory blocks, alternating between blocks to perform read commands. This periodic action allows each block to be read at optimized voltage levels while maintaining overall system power efficiency, as not all blocks need to be actively read at the same time.
2Use of energy by moving object
If conventional sensing methods are used at reduced voltages, then power consumption decreases, but measurement precision deteriorates due to difficulty in detecting small current differences
Solution Approach 1:
Before performing the actual read operation, the patent applies a read disturbance voltage to the word line to preliminarily prepare the memory cells for reading. This preliminary action enhances the current difference between turned-on and turned-off cells, making it easier for the sense amplifier to detect the data state even at reduced operating voltages, thereby maintaining measurement precision while allowing lower power operation.
Data Source
AI summary
In a memory cell array which is constituted with flash memory, a pair of a positive memory cell and a negative memory cell, to which data with mutually opposite values are written, is plurally provided. Bit lines and I/O lines connected to the memory cells of a data reading object are charged, and then a potential WL of a word line connected to the data reading object memory cells is raised. Hence, currents flow in the data reading object memory cells in accordance with the data that were written, and consequently one of a potential BL and a potential BLN of the I/O lines begins to fall. When one of the potentials BL and BLN falls below the circuit threshold of a sense amplifier, reading data is established, and the established reading data is outputted as a sense amplifier output signal SAOUT.