Nonvolatile Memory Read Voltage Determination via Valley Cell Counts
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Solution Overview
Problem
Nonvolatile memory devices face challenges in accurately determining read voltage levels for different states due to threshold voltage distribution shifts and overlaps, leading to inefficiencies in data reading operations.
Innovation Solution
A method and device that perform valley cell count operations and determine read voltage levels based on cell counts and reference parameters for each state, allowing for precise sensing operations by optimizing read voltage levels for each state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed read voltage level is used for all memory cells, then the device complexity is reduced, but the measurement precision of threshold voltage distributions deteriorates due to shifts and overlaps
Solution Approach 1:
The patent performs preliminary valley cell count operations to determine the distribution characteristics of threshold voltages before conducting the actual read operation. By pre-determining the valley point and distribution shape through counting cells at different voltage levels, the system prepares accurate read voltage level information in advance, enabling precise reading without requiring complex real-time adjustments during the read operation itself.
Solution Approach 2:
The patent dynamically adjusts the read voltage level parameter based on the determined threshold voltage distribution characteristics. Instead of using a fixed read voltage, the system changes the read voltage parameter to match the actual distribution state, optimizing the read operation for the current conditions while maintaining manageable device complexity through algorithmic adaptation.
2Measurement precision
If valley cell count operations are performed to accurately determine read voltage levels, then the measurement precision improves, but the productivity decreases due to additional operation steps
Solution Approach 1:
The valley cell count operations are performed as a preliminary step to establish accurate read voltage levels, which then enable faster subsequent read operations. The initial investment in time for valley determination improves the efficiency of all following read operations by eliminating the need for repeated voltage adjustments or trial-and-error reading attempts.
Solution Approach 2:
The patent maintains continuous useful action by using the determined valley information and distribution characteristics to guide subsequent read operations. The accurately determined read voltage levels ensure that following read operations proceed efficiently without interruptions or retries, maintaining high productivity while benefiting from the initial precision measurements.
Data Source
AI summary
In a method of reading data in a nonvolatile memory device including a plurality of memory cells having a plurality of states including a first state and a second state, a first read operation for the first state is performed, and a second read operation for the second state is performed. To perform the first read operation, cell counts for a valley of the first state are obtained by performing a valley cell count operation for the first state, a first read voltage level for the first state is determined based on the cell counts and at least one first reference parameter for the first state, and a first sensing operation for the first state is performed by using the first read voltage level. To perform the second read operation, a second read voltage level for the second state is determined based on the cell counts and at least one second reference parameter for the second state, and a second sensing operation for the second state is performed by using the second read voltage level.