Semiconductor Memory Device Current Measurement Voltage Adjustment
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Solution Overview
Problem
Semiconductor memory devices, such as NAND flash memory, face errors in read data due to the discharge of electrons from floating gates over time, leading to shifts in threshold voltage, which can result in incorrect data retrieval.
Innovation Solution
A semiconductor memory device and method that includes a current measurement circuit to detect changes in current flowing through bit lines and a logic group to adjust read, verification, or pass voltages based on measured current, ensuring accurate data retrieval by compensating for the retention characteristic of memory cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed read voltage is used for data retrieval, then the device structure remains simple, but threshold voltage shifts due to electron discharge cause read errors over time
Solution Approach 1:
The patent implements a feedback mechanism where the measured current magnitude is fed back to the logic group, which then adjusts the read voltage or pass voltage accordingly. This closed-loop feedback system continuously compensates for threshold voltage shifts, maintaining accurate data retrieval despite retention characteristic degradation over time.
Solution Approach 2:
The system performs self-adjustment by automatically measuring the current magnitude and modifying its own read voltage or pass voltage based on the measured values. This self-service mechanism eliminates the need for external calibration or manual intervention, allowing the device to autonomously compensate for threshold voltage shifts.
2Reliability
If the read voltage is dynamically adjusted based on current measurement, then read accuracy improves, but the operation time increases due to additional measurement and adjustment steps
Solution Approach 1:
The patent performs preliminary current measurement and threshold voltage shift detection before the actual data read operation. By anticipating the required voltage adjustment in advance, the system minimizes the time penalty during the critical data retrieval phase, as the voltage is already optimized when reading begins.
3Reliability
If current measurement and voltage adjustment circuits are added, then retention characteristic compensation is achieved, but manufacturing complexity increases
Solution Approach 1:
The logic group serves multiple functions: it controls the word line voltages, measures current magnitude, determines threshold voltage shifts, and adjusts read/pass voltages based on measurements. This multi-functionality reduces the need for separate dedicated circuits, simplifying the overall device structure and easing manufacturing despite the enhanced compensation capability.
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
The solution effectively prevents errors in read data by dynamically adjusting voltages in response to shifts in threshold voltage due to retention characteristics, thereby improving the reliability of data read operations.
Implementation Method 1
a current measurement circuit configured to measure a current flowing through a selected bit line
Implementation Method 2
a program operation and an erase operation may be performed through F-N tunneling. Electrons are accumulated in the floating gate by the program operation
Data Source
AI summary
A semiconductor memory device includes a memory block comprising cell strings each of which includes a plurality of memory cells, a current measurement circuit measure a current flowing through a selected bit line coupled to a selected cell string when a data read operation or a program verification operation is performed, and a logic group configured to change a read voltage, a program verification voltage, or a pass voltage in response to the measured current.