Forward-Looking Read Voltage Determination Using Pattern Cells
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Solution Overview
Problem
Memory devices face challenges in efficiently determining the initial read voltage for memory cells due to resistance drift and non-uniform electrical characteristics, leading to increased read time and potential errors in data retrieval.
Innovation Solution
The use of multiple groups of pattern cells programmed to a single logic state allows for the application of higher voltages to quickly determine the threshold voltage distribution, enabling the selection of an appropriate initial read voltage for data cells, thereby reducing the time required for read operations and improving accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional voltage determination methods are used for memory cells, then read operations can be performed, but the read time is increased and accuracy is reduced due to resistance drift and non-uniform electrical characteristics
Solution Approach 1:
The patent applies preliminary action by determining the initial read voltage in advance using a lookup table that stores pre-calculated voltage values based on program verify read results. This pre-determination eliminates the need for time-consuming voltage search during actual read operations, thereby reducing read time while maintaining accuracy. The initial read voltage is calculated before the read operation based on the program verify read result, which provides advance information about the memory cell state.
Solution Approach 2:
The patent replaces the traditional iterative voltage search method (mechanical process) with a lookup table-based voltage determination method (information processing). Instead of physically searching for the correct voltage through multiple read attempts, the system uses pre-stored voltage values in a lookup table that can be quickly retrieved based on program verify read results, significantly reducing the time required for voltage determination.
2Measurement precision
If multiple voltage steps are used to determine the initial read voltage, then accuracy is improved, but the number of voltage steps and time required increases
Solution Approach 1:
The patent performs the complex voltage determination process in advance by calculating initial read voltages based on program verify read results and storing them in a lookup table. This preliminary calculation eliminates the need for multiple voltage steps during actual read operations, as the appropriate voltage is already determined and stored for quick retrieval.
Solution Approach 2:
The patent creates a copy of the voltage determination information by storing pre-calculated initial read voltage values in a lookup table. Instead of performing the actual voltage search process during read operations, the system uses these stored copies of voltage information, which can be quickly accessed without repeating the time-consuming measurement and adjustment process.
3Reliability
If resistance drift and non-uniform electrical characteristics are not accounted for, then read operations are faster, but errors in data retrieval increase
Solution Approach 1:
The patent replaces the traditional method of accounting for resistance drift through iterative voltage searching with a lookup table-based system. The lookup table stores pre-determined voltage values that compensate for resistance drift and non-uniform characteristics, allowing the system to achieve high reliability without the time penalty of iterative searches.
Solution Approach 2:
The patent uses program verify read results as feedback to determine the appropriate initial read voltage. The program verify read provides information about the actual state of memory cells, including effects of resistance drift, and this feedback is used to select or calculate the correct voltage from the lookup table, ensuring accurate data retrieval while minimizing time loss.
Data Source
AI summary
Systems, methods, and apparatus for a memory device that uses multiple groups of pattern cells to select a voltage for reading memory cells. In one approach, a controller applies different magnitude levels of voltages to each of the groups of pattern cells. The controller determines which of the groups have pattern cells that first switch (e.g., switch at the lowest magnitude of applied voltage). Based on identifying the first group to switch, the controller selects a read voltage. The selected read voltage is used to read data cells (e.g., corresponding to a codeword).