Sense Amplifier Back-Gate Voltage Control for Threshold Variation
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Solution Overview
Problem
NAND type flash memory semiconductor devices face reliability issues that need to be improved.
Innovation Solution
A semiconductor memory device configuration including a memory cell, a bit line connected to the memory cell, and a sense amplifier connected through the bit line, featuring a sense node, a capacitive element, and a static latch circuit to enhance data retention and sensing capabilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sense amplifier is used to sense data from memory cells, then data reading capability is improved, but threshold voltage variations in the sense transistor cause erroneous data determination
Solution Approach 1:
The patent applies parameter changes by dynamically adjusting the threshold voltage of the sense transistor using a back-gate voltage. During the sensing operation, a first back-gate voltage is applied to achieve optimal sensing performance, and during the post-sensing operation, a second back-gate voltage is applied to correct threshold voltage shifts. This dynamic parameter adjustment resolves the contradiction by maintaining both high sensing accuracy and reliable data determination despite threshold voltage variations.
Solution Approach 2:
The patent implements a feedback mechanism where the back-gate voltage is adjusted based on the operating phase (sensing vs. post-sensing). The control circuit monitors the operation stage and automatically switches between different back-gate voltages to compensate for threshold voltage drift, ensuring accurate data determination while maintaining reliable sensing performance throughout the operation cycle.
2Productivity
If the sense transistor operates during sensing, then data sensing is enabled, but threshold voltage shift occurs leading to data determination errors
Solution Approach 1:
The patent applies preliminary action by pre-adjusting the back-gate voltage before the sensing operation begins. The control circuit is configured to switch to the first back-gate voltage in advance of the sensing phase, ensuring the sense transistor is properly biased for high-performance sensing while preventing threshold voltage shifts that would occur during the operation.
Solution Approach 2:
The patent implements periodic action by alternating between two distinct back-gate voltage levels corresponding to different operational phases. During sensing operations, the first back-gate voltage is applied periodically, and during post-sensing operations, the second back-gate voltage is applied periodically. This periodic switching maintains both high productivity during sensing and high reliability during data retention.
Data Source
AI summary
A semiconductor memory device includes a memory cell, a bit line connected to the memory cell, a sense amplifier connected to the memory cell through the bit line, and a control circuit. The sense amplifier includes a sense node connected to the bit line, a first capacitive element connected to the sense node and a sense transistor having a gate connected to the sense node. The control circuit is configured to adjust a voltage applied to a back gate of the sense transistor or a source of the sense transistor to correct a variation of a threshold voltage of the sense transistor.