Memory Cell Reading via Segmented Threshold Voltage Groups
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Solution Overview
Problem
Conventional flash memory requires a high reference voltage and numerous program shots to properly read data, as the distribution of high-threshold-voltage and low-threshold-voltage states are not effectively distinguishable, leading to inefficient programming and reading operations.
Innovation Solution
The proposed method involves a memory system with a memory array and operation circuits that program and read two bits of data using a lower reference voltage, employing a sense amplifier and control unit to determine digital states by comparing cell currents, allowing for effective reading even when threshold voltage distributions overlap.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a high reference voltage is used to distinguish high-threshold-voltage and low-threshold-voltage states, then reading accuracy is improved, but program shots and program time increase significantly
Solution Approach 1:
The patent segments the threshold voltage distribution into distinct groups (first group with lower threshold voltages and second group with higher threshold voltages) and applies different reference voltages for reading each group. This allows accurate reading without requiring excessively high reference voltages, thereby reducing program shots and program time while maintaining reading accuracy.
Solution Approach 2:
The patent changes the reference voltage parameter dynamically based on the threshold voltage group being read. By adjusting the reference voltage to match the specific group's characteristics rather than using a uniformly high reference voltage, the system achieves accurate reading with lower voltage stress, reducing the number of program shots required.
2Reliability
If a high reference voltage is applied as a judging criterion, then data reading reliability is improved, but the voltage level and program shots required increase
Solution Approach 1:
The patent divides the memory cells into multiple groups based on their threshold voltage characteristics and assigns different reference voltages to each group. This segmentation allows reliable reading at lower voltage levels for each specific group, avoiding the need for high voltage stress while maintaining reading reliability.
Solution Approach 2:
The patent applies the principle of local quality by tailoring the reference voltage to the specific characteristics of each threshold voltage group. Instead of using a uniformly high reference voltage across all cells, each group receives a reference voltage optimized for its local characteristics, achieving reliable reading with reduced voltage stress.
3Quantity of substance
If the distribution of high-threshold-voltage and low-threshold-voltage states are allowed to overlap, then memory cell density is improved, but reading capability deteriorates in conventional methods
Solution Approach 1:
The patent segments the overlapping threshold voltage distributions into distinct readable groups by applying different reference voltages. By reading different groups with different reference voltages, the system can distinguish between overlapping distributions, maintaining reading capability while enabling higher memory cell density through overlapping voltage states.
Solution Approach 2:
The patent introduces an additional dimension for reading by using multiple reference voltages corresponding to different threshold voltage groups. This multi-dimensional reading approach allows the system to distinguish between overlapping distributions that would be indistinguishable with a single reference voltage, thereby maintaining reading capability while increasing density.
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 reduces the number of program shots and shortens program time by accurately reading data stored in memory cells with overlapping high- and low-threshold-voltage states, using a lower reference voltage and comparing cell currents to determine digital states.
Implementation Method 1
The sense amplifier senses a first cell current and a second cell current corresponding to the first and the second bits, respectively, by applying a voltage on the memory cell
Data Source
AI summary
A memory comprises a memory cell, a sense amplifier, and a control unit. The memory cell stores a first bit and a second bit. The sense amplifier senses a first cell current and a second cell current corresponding to the first and the second bits respectively with a voltage applying on the memory cell. The control unit determines a digital state of the first bit by comparing a first reference current with the first cell current or by comparing a reference data with a first delta current between the first cell current and the second cell current.