Nonvolatile Memory Voltage Generator for Threshold Compensation
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Solution Overview
Problem
Nonvolatile memory devices face reliability issues due to threshold voltage degradation caused by electron leakage from floating gates or charge trap layers, leading to read errors, especially in multi-level cells where small changes in threshold voltage can result in significant errors.
Innovation Solution
A nonvolatile memory device and method that involve a voltage generator to supply select and unselect read voltages to word lines during read operations, with the ability to adjust these voltages based on adjacent word lines to compensate for threshold voltage changes, and a read method that includes error detection and voltage adjustment to ensure accurate data retrieval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional read operation is performed with fixed read voltages, then the read operation is simple and fast, but read errors occur due to threshold voltage degradation from electron leakage
Solution Approach 1:
The patent applies dynamics by making the read voltage adjustable rather than fixed. The voltage generator dynamically changes the read voltage applied to unselected word lines based on detected read errors. When read errors occur, the system increases the read voltage to compensate for threshold voltage degradation caused by electron leakage, thereby maintaining read accuracy without requiring complete redesign of the memory structure.
Solution Approach 2:
The patent implements feedback by monitoring read operations and using the detected errors to adjust subsequent read voltages. The controller detects read errors and feeds this information back to the voltage generator, which then modifies the read voltage for unselected word lines. This closed-loop feedback mechanism ensures that the read voltage adapts to the actual state of the memory cells, compensating for threshold voltage shifts without requiring complex structural changes.
2Reliability
If the insulating layer thickness is increased to prevent electron leakage, then reliability improves, but manufacturing precision requirements increase and device complexity increases
Solution Approach 1:
Instead of changing the physical parameter of insulating layer thickness, the patent changes the electrical parameter of read voltage. By adjusting the read voltage magnitude, the system compensates for electron leakage effects without requiring modifications to the insulating layer structure. This approach avoids the manufacturing precision challenges associated with controlling thin film thickness while maintaining reliability through electrical parameter adjustment.
3Reliability
If read voltage is increased to compensate for threshold voltage degradation, then read accuracy improves, but power consumption increases
Solution Approach 1:
The patent applies local quality by selectively applying different voltages to different word lines during read operations. Only unselected word lines receive the adjusted (higher) read voltage, while selected word lines maintain their normal operating voltage. This localized voltage adjustment compensates for threshold voltage degradation in specific regions without unnecessarily increasing power consumption across the entire memory array, thereby improving read accuracy with minimal additional power cost.
Data Source
AI summary
An object of the present inventive concept is providing a nonvolatile memory device having improved reliability by compensating a threshold voltage of a flash memory cell.A nonvolatile memory device according to the present inventive concept includes a memory cell array connected to a plurality of word lines; and a voltage generator for supplying a select read voltage to a select word line and an unselect read voltage to an unselect word line among the plurality of word lines when a read operation is performed. The voltage generator generates the unselect read voltage having a different level according to whether the unselect word line is adjacent to the select word line or not.A nonvolatile memory device according to the present inventive concept compensates a threshold voltage increased or decreased due to various causes. According to the present inventive concept, reliability of a nonvolatile memory device is improved.