Negative Voltage Wordline via Capacitive Coupling
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Solution Overview
Problem
Flash memory devices face challenges in achieving effective data retention and threshold voltage margin without the need for negative wordline voltage generator circuitry, which is costly and complex to implement.
Innovation Solution
The method involves capacitive coupling between adjacent wordlines to drive a selected wordline to a negative voltage without using negative voltage generator circuitry, by boosting non-selected wordlines to a positive voltage and allowing the selected wordline to float, thereby accelerating charge loss in defective memory cells during a soft erase operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If negative wordline voltage generator circuitry is used to drive selected wordline to negative voltage, then short-term data retention and threshold voltage margin are improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent uses capacitive coupling between adjacent wordlines as an intermediary mechanism to transfer voltage from non-selected wordlines to the selected wordline. By coupling the selected wordline to non-selected wordlines through capacitance, negative voltage is generated on the selected wordline without requiring dedicated negative voltage generator circuitry, thus improving reliability while reducing device complexity
Solution Approach 2:
The patent enables the wordline structure itself to generate the required negative voltage through its own capacitive properties. The capacitive coupling between adjacent wordlines allows the system to self-generate negative voltage during erase operations without external assistance from complex voltage generator circuits, reducing both device complexity and manufacturing cost
2Manufacturing precision
If negative wordline voltage generator circuitry is implemented, then threshold voltage margin is improved, but manufacturing cost increases
Solution Approach 1:
Capacitive coupling serves as an intermediary that leverages existing wordline structures to achieve the desired threshold voltage margin. By using the inherent capacitance between adjacent wordlines, the system can apply negative voltage to improve threshold voltage margin without adding expensive negative voltage generator circuitry, thus improving manufacturing precision while maintaining ease of manufacture
Solution Approach 2:
The patent uses the existing wordline structure and its capacitive properties to replicate the function of negative voltage generation. Instead of building complex negative voltage generator circuits, the system copies the voltage transfer mechanism from conventional wordline operations and applies it through capacitive coupling to achieve the same threshold voltage margin improvement at lower manufacturing cost
3Device complexity
If capacitive coupling is used to generate negative voltage on selected wordline, then device complexity is reduced, but voltage control precision may be affected
Solution Approach 1:
The patent controls the voltage on non-selected wordlines to specific parameters (e.g., boosting to positive voltage then driving to lower voltage) to precisely control the capacitive coupling effect. By carefully managing the voltage parameters on adjacent wordlines, the system achieves accurate negative voltage generation on the selected wordline without complex circuitry, maintaining voltage control precision while reducing device complexity
4Device complexity
If non-selected wordlines are boosted to positive voltage and then driven down, then negative voltage is generated on selected wordline through capacitance, but energy consumption increases
Solution Approach 1:
The patent applies periodic voltage boosting and driving down to non-selected wordlines during erase operations. By using pulsed or periodic voltage sequences rather than continuous voltage application, the system generates the necessary negative voltage on the selected wordline through capacitive coupling while minimizing overall energy consumption, thus reducing device complexity without excessive energy cost
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
This approach improves short-term data retention and threshold voltage margin without the cost and complexity of negative wordline voltage generator circuitry, ensuring proper erase operations and reducing the risk of overerasing in NAND flash memory devices.
Implementation Method 1
the selected wordline being adjacent the non-selected wordline and being capacitively coupled to the non-selected wordline, driving the non-selected wordline to a lower voltage to shift the selected wordline to less than zero volts due to capacitance effects
Data Source
AI summary
A methodology and structure for driving a selected wordline to a negative voltage without the need for a negative wordline voltage generator. The methodology includes the step of boosting a non-selected wordline to a first positive voltage. The methodology proceeds with holding a selected wordline, which is adjacent to and capacitively coupled with the non-selected wordline, at zero voltage. The methodology continues with floating the selected wordline. The methodology proceeds with driving the non-selected wordline to a lower voltage to shift the selected wordline to less than zero volts due to capacitance effects. The methodology continues with the step of accelerating charge loss in a defective memory cell connected to the selected wordline while at a negative voltage during a soft erase operation.